Considerations on a K20 small block endurance build - K20A.org .:. The K Series Source . Honda / Acura K20a k24a Engine Forum
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Old 07-24-2015, 08:36 AM   #1
LotusElise
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Default Considerations on a K20 small block endurance build

Hi guys,

over one year ago my K20 had an very bad overheating due to a wrenched off radiator plastic sidewall, since that time the compression of the engine is at 11,5-12,3 bar (167-178 psi). With that said a overhaul of the engine is planed (pistons, liners, gasket, ...) to get it fit for the following specification paper:
  • K20 block
  • highest peak-to-peak power band (s. explanation below)
  • maximum mean piston speed 24,2 m/s for endurance

After a short search I found some inspiration for my block calculations at Doug's threat (https://www.k20a.org/forum/showthread.php?t=114024) and at NtegraDryvr threat (https://www.k20a.org/forum/showpost.p...1&postcount=11) ...shown in the following.


Source: LotusElise calculations

I investigated three different displacements: 2.0, 2.2 and 2.4 liter with more or less common crankshafts and bore sizes. SS means short stroke, LS long stroke and * means stock block or ** means designed for same max. piston acceleration as the stock K20 has it. The 2.6 was just for comparison of a top dog drag block with a endurance racing block. The 87x99, I was not sure if possible with a K20 block, so I decided to calculate with a K24 block height of (212+19 mm), also just for comparison. Design case was to get a mean piston speed of 24,2 m/s and 19 bar IMEP, which is not too far from reality.

Considering the specification paper one can say, a high displacement doesn't automatically translate to the best peak-to-peak power band, where peak-to-peak power band means peak torque to peak power distance in terms of power height and engine speed difference (as high and broad as possible = fastest acceleration with same gear ratio ). But it's clear why K24's are so famous, they need only a small invest, but these seems to be not the best solution for a 24,2 m/s endurance racing block design.

Most surprising for me was, and this shows a further parameter is needed: 10-90 % MFB duration, that a bored block with a stock crankshaft comes out best (90x86). But take a look into my observations:
  • K20SS, 90x78.5, the best 2 liter racer, despite the higher fuel consumption due to the higher FMEP at high end, this is a real 10 krpm K-series endurance race engine block, with the very best peak-to-peak power band in the K20. It's clear why F1 had choosen even higher R/S ratio's because of the more increasing peak-to-peak power band and the increased piston remaining time, which opens the door for retarded igntion timing at MBT or for higher CR numbers or of course higher engine speeds (in a thermodynamically way too). Because of the higher stress in the crank assembly due to the higher piston acceleration (because of relatively longer TDC remain time) a high strength material is needed to get the same endurance as with the 86x86 at 24.2 m/s mean piston speed. I love that option, but needs, because of the 10 krpm engine speed range, a fully build block, oil pump, ... and head...that's purely for endurance racing applications.
  • K20, 86x86 a valuable stock block design and in terms of peak-to-peak the better endurance design compared the K24*. It is clear why the K-Series hype began, VTC lifted the peak-to-peak power band up so that even a F20C (1033 PS/min, 85814 m/s) has it hard to beat and the best bang for the buck in terms of money and k20 block design
  • K22SS, 90x86, surprise surprise...I like that 2.2 block design. A very good peak-to-peak power band and the better mechanical and thermodynamical behaviour compared to a 86.5x93 block: lower piston skirt force, longer TDC remain time and lower uncompensated 2. order mass forces! Additionally stock crank , liners need anyway an overhaul and with same valve motion the lengthes of intake and exhaust can be kept...just a increase of gas velocity which helps to increase the VE
  • K22LS, 86.5x93 seems to be in both versions, K22LS and the K22LS**, a bit of an under dog, but going through the internet shows it much more common as the K22SS version . Maybe the kit's could gain more win for the companies or there are missing points in my considerations . I was searching for kit's (crankshaft, rods, piston incl. rings, bearings and balanced): about 2700 to 3000 (ZRP, BC, InlinePRO, ERL Performance, ...).
  • K24SS, 89.7x93, an attractive peak-to-peak power band, but also possibly the highest block invest necessary. The lower R/S or higher FMEP leads a more mad fuel efficiency compared to the K24* or K24**. Anyway this design is at the upper limit in terms of displacement production of a K20 block.
  • K24*, K24**, 87x99, not the best bang for the buck in terms of a endurance racing engine but in the higher area of it . A bit lower peak-to-peak power band as the 86x86, shorter shift-to-shift times or need a lower final drive. A lot of guys compensate the lower piston acceleration with a higher mean piston speed (equal at 25.7 m/s), which could be done for save as the maximum piston acceleration is much lower compared to the 86x86 block design, because of 2nd Newton's law F ~ a. Once the block hasn't to be a K20, this is defenitly the one to go for many applications (daily driver, fast circuit tracks,...) but by far not every
  • K26, 89x106, R/S of 1.4, which is at the lower end what is possible (< 1.3 means design constraints), is only build for acceleration. Despite a 90x106, unbeatable peak-to-peak power band, enourmous stress forces in all moving components. This is the high end of the K-series, or what was kept of it , in terms of peak-to-peak power band, redline and invest! E.g. SickSilver_ep3 build threat already reached the 460 PS (roughly 420 whp) margin. So even in that engine speed area an IMEP of 19 bar is possible, just to validate my assumption above .

Out of that, the K22SS seems to be the most attractive version for me. What about your observations and experiences? Anything to add? I appreciate your meaning, guys!
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Old 07-24-2015, 10:12 AM   #2
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Default Re: Considerations on a K20 small block endurance build

Part list for K22SS. Please let me know if there are better options:

Pistons:
  • Wiseco K634M89, 89 mm bore, CR = 11.6:1, 320 g
  • Wiseco K573M89AP, 89 mm bore, CR = 12.3:1, 360 g
  • Wiseco K650M89AP, 89 mm bore, CR = 12.92:1, 355 g
  • CP SC71425X, 90 mm bore, CR = 12.5:1, .... g, +1 mm oversized valves
  • ...

Gaskets:
  • Wiseco, 89 mm bore, 0.76 mm thickness, #?
  • Golden Eagle, 90 mm bore, ... mm thickness, GEM-GHG103-90
  • recommended by Joe McCarthy: Cometic head gasket MLS, 90 mm bore, part #H1912SP1040S or the customized for 4Piston of Cometic
  • recommended by Ben: Cosworth head gasket with 90 mm bore

Liners:
  • Stock liners could have a safe bore of 87 mm (NA), citation of Blazed
  • Darton MID cylinder liners, # 400-190-P, 86-90 mm bore (Darton homepage)

Any suggestions or added info is appreciated?

Last edited by LotusElise; 09-19-2017 at 01:12 PM..
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Old 07-25-2015, 01:27 AM   #3
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Default Re: Considerations on a K20 small block endurance build

Got some minds on the list from Larry of EDYN and maxim, a K20a.org member.

The first was why going to the last oversized bore option first? So I calculated 89x86 (1038 PS/min) and 88x86 (1028 PS/min) too. Those options also comes out as a valuable bore-stroke-combination, direct ranking followers of the 90x86 version.

The second was a further and OEM-heavy bore-stroke-combination: 87x90.7 (991 PS/min). F22C crank with either OEM conrods and custom piston or custom conrods and out of the shelf 87 mm pistons - just depends on the compression height of the pistons. K20actr.J, a member from here, already run the last version of that already (InlinePro conrods, CP pistons). His build thread could be found here. From a point of view of the peak-to-peak power band it is defenitly a better combination than the K22LS, can be revved up to 8.15 krpm for the same max piston acceleration as K20 has (1008 PS/min). Definitly not for endurance use, just for comparison , revving it up to 9 krpm means 102934 m/s piston acceleration/45 m/s max piston speed/27.2 m/s mean piston speed but also 1113 PS/min...some sort of sprint racing application or high potential daily driver.

Summing up, the most attractive version for me is still the 90x86 mm version, but Larry's criticism is good, why not going to a 89x86 bore-stroke-combination, just to have the option for an overhaul.


Some notes to the bore-stroke-combinations:
As everyone knows, the 1-2-4-3 inline firing order has neither 1st order unbalanced mass forces nor 1st and 2nd order momemt of mass. But it has 2nd order of unbalanced mass forces, of an undeniably height.

With that in mind every different combination of crankshaft-conrod-piston leads to a different vibration behaviour...if you go lightweight in rods and pistons, the crankshaft counterweights should be adapted, if you go heavy weight there will be definitly a shift in the oscillating vertical forces.

A second point on that, the lower the R/S ratio, the higher the need to compensate the 2nd order mass forces (R/S goes down -> piston acceleration over crank angle got more unsymmetrical (vertical plane) -> increases 2nd order mass forces due to 2nd Newtons law, s. following picture)


Source: LotusElise calculations
Note: a = acceleration, v = velocity, s = way, SS = K20SS, LS = K24*, both at 24,2 m/s mean piston speed


Markus

Last edited by LotusElise; 07-25-2015 at 04:19 AM..
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Old 07-25-2015, 07:02 AM   #4
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Default Re: Considerations on a K20 small block endurance build

ok,i read your other thread.
Let's go to proceedings

you want quality,longevity,reliability,endurance and as far as possible use oem parts for your k20 block.
Crank:
I would say go with 90.7mm f22 crank.r/s ratio is not the best but no so bad. High r/s ratio is not always good choice if we speak about performance... Oem crank all we knows that have very very good quality.That don't mean aftermarket have issue.i dont have personally experience but 3 friends had used aftermarket with no good results.I don't know if all parts placed correct(bearings etc)
This crankshaft (f22) is a balance that reconciles the above Conditions.

You like high rev to remind honda philosophy.Believe me from personally experience you can rev all day /all night 9000 rpm and special conditions 9300. Joe mcarthy used gunningham rods and was happy at 9550rpm with cp pistons.

I would say dont go 90mm.stay 89. In future you will have the possibility to open 89.5 or 90mm.with 90mm the material between sleeves of k20 block is very thin.if ask darton they recommend for street use and too many miles 89 all motor and 88 high high boost.you can go 2157cc with stock sleeves.very very good torque & power!! (87x90.7) or 2257(89x90.7)
cams:
tray stage 3 cams.i make 310-315 at 8750rpm with toda a3 (2157)and now go with prayoonto 3.
Now my engine have 1200km with normal tune on k-pro (low vtc low advance etc..)

When i took the internals from 2.157 cc k20 block,the pistons had no any issues in skirts after 10.000km and 9300 revlimiter.(No coats at skirts.You can do this)

Pistons/rods:
It is stupid to put oem pistons & rods when you have an open bench block.
Here you must place aftermarket internals with 12.8-13 max c/r if you use 100 oct gas
Look this engine here.280whp 89x90.7 with normal gas!
https://www.k20a.org/forum/showthread.php?t=65672
Not bad at all! And this motor had to get a further power if read this thread!!

Good luck.I hope the best!!
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Old 07-25-2015, 01:11 PM   #5
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Thumbs up Re: Considerations on a K20 small block endurance build

Thanks K20actr.J, I appreciate your meaning on that.
Quote:
Originally Posted by K20actr.J View Post
Crank:
Oem crank all we knows that have very very good quality....but 3 friends had used aftermarket with no good results...crankshaft (f22) is a balance that reconciles the above Conditions.
Yes, concerning the part list as far as possible on the OEM way or parts of proven strength and endurance properties...indeed, the F22C crankshaft would be one of it! But as you already stated...
Quote:
Originally Posted by K20actr.J View Post
...90.7mm f22 crank.r/s ratio is not the best but no so bad. High r/s ratio is not always good choice if we speak about performance...
Yes Joe wrote me that too...
Quote:
Originally Posted by K20actr.J View Post
...used gunningham rods and was happy at 9550rpm with cp pistons.
...(more info to Cunningham rods here) but he also stated the need for upgrades for following parts: cam chain tensioner, oil pump and valve springs, which made the part list longer and the need for head work and more budget increases. Anyway I like your 87x90.7 suggestion as the option to go to 2.3 l with a 89x90.7 bore-stroke-combi sounds very attractive in terms of torque production, I read the thread you recommended me .
Quote:
Originally Posted by K20actr.J View Post
...stay 89. In future you will have the possibility to open 89.5 or 90mm...
I will definitly do so!
Quote:
Originally Posted by K20actr.J View Post
cams:
tray stage 3 cams.i make 310-315 at 8750rpm with toda a3 (2157)...
Wow, that's pretty well, about 17,8 bar [email protected] krpm and 100 RON is a healty setup. Would you mind to share the ignition timing value at peak power?
Quote:
Originally Posted by K20actr.J View Post
...i took the internals from 2.157 cc k20 block,the pistons had no any issues in skirts after 10.000km and 9300 revlimiter.
Sounds healty. Your driving profile is mainly sportive daily driving?
Quote:
Originally Posted by K20actr.J View Post
Pistons/rods:
...must place aftermarket internals with 12.8-13 max c/r if you use 100 oct gas
Ok thanks , I stored that in mind: 12.8:1/295 ca/100 RON (CR/IN duration/fuel quality)
Quote:
Originally Posted by K20actr.J View Post
Good luck.I hope the best!!
Thanks man, I will do a thread on that for keeping you up to date. The plan is to buy a keen engine for a refresh and engine build. This will be going to be interesting, as it will be definitly different compared to what could be found in the tuner market or in here. I am very excited

Once more, thanks for your thought's and experience!
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Old 07-26-2015, 07:49 AM   #6
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Default Re: Considerations on a K20 small block endurance build

From a technical view the following allures me, a K24 short block with a Henry Velasco (crankshaft service in Downey, CA) crankshaft. It's a 1,998 l K20SSS (super short stroke ) with an 90x78,5 bore-stroke size and a R/S ratio of 2.07, which has equal piston acceleration like the K20SS at 9.353 krpm. While the crank assembly is bored, the valetrain get's exhausted ...needs plenty of engine speed enhancer goodies.

Compared to the K20SS peak-to-peak power band increases only a few points, but some get's of interest, the longer "TDC dwell duration" of the piston. This could bring further improvements: better ignition timing vs. MBT = farer knock margin, combustion efficiency...and so on.

The high revving abillity could be used to run a higher final drive ratio to compensate partly the lesser torque (vs. e.g. a 87x99) but still having the bigger shift-to-shift engine speed band...less shifts, easier to handle at the circuit (MT and dog box too).

But it isn't a 212 mm block height...rather a money pit .

How to throttle that pit? My suggestion would be a
  • revised K20 with 87x86 (2045 cc), R/S ratio = 1.62, 24,2 m/s mean piston [email protected] krpm with the following internals
  • stock block with bored and honed stock liners, cleaned and refreshed (200-600 €)
  • stock crankshaft, depending on the wear should be honed for oversize bearings (200-300 €)
  • stock conrods, depending on the pistons/rod-bundle price, maybe aftermarket ones
  • stock valvetrain
  • stock cylinder head
  • stock cam chain tensioner (Joe used those in the Hondata Bonville engine which was redlined at 9.7 krpm)
  • stock oil pump (Joe's improved oil pump technique used in 9.7 krpm endurance engines)
  • aftermarket high CR pistons and pins (600-700 €, maybe in a bundle with rods)
  • aftermarket head gasket kit (100 €)
  • stock main bearings, new (79 €)
and set redline at 8.8 krpm, as beyond that the oil pump began to cavitate (according to DRAG). With the right externals (CAI, IM, H, E) a lift of the redline might be valuable, e.g. in a 2nd stage to 9.3 krpm. I am not sure about the right parts, but I colored those which might need an adaption.

This seems to be a good 1st stage before sleeving the block (e.g. ERL Performance, about 1500 € + 600 € core + 400 € shipping to Europe) to increase displacement to 2140 cc or 2188 cc. The for now safed money could be e.g. invested in the block refresh and the 1st stage build (about 1500 € for parts, 1000-2000 € for K20A2 long block assembly).

I would like to discuss that for further and better solutions.

Last edited by LotusElise; 07-26-2015 at 07:59 AM..
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Old 08-14-2015, 12:39 AM   #7
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Default Re: Considerations on a K20 small block endurance build

The first two questions should be: what are the rules and what is the budget. The third would be what is the objective.

If this isn't being built to fit in a racing class then the objective replaces the rules. If there are rules the objective defines the goal within those rules; for road racing a new set of tires is usually worth more than a few hp.

You may also be overthinking the rod/stroke ratio etc. There are lots of threads on lots of forums that come to the conclusion that the correct rod length is the one that connects the crank to the piston. Piston compression height and stroke being determined by other design parameters far more important.

If deck height is also a variable, it can become a function of airflow and combustion, which is fuel, combustion chamber, etc. dependent. Pro Stock and Engine Masters engines have rod/stroke ratios around 1.5. Kaase built a 404cid Boss 429 with a really small more and a really long stroke (rod/stroke ratio around 1.4) for the last competition. I don't know his considerations but they probably revolved around combustion (the small bore) and creating a lot of intake vacuum to utilize the high flowing heads (the low rod/stroke ratio).

If you are racing the rules will probably determine the displacement and possibly intake restrictions. You are interested in power under the curve for the gearing you have or can use and for the tracks you are running at. Keep in mind you may stay in a higher gear to avoid a shift and may be down in the rev range if you encounter traffic. Generally (really always), the largest displacement wins unless the rules attach a weight or other penalty. Can you think of any case where a race car is built not to have the largest allowed displacement?

Pistons shouldn't be coming from a catalog; they should be correct for your bore, ring stack, piston-to-valve clearance, and compression ratio. Some engine builders may have the right custom piston in stock because they sell the bore/cam/CR combination regularly.

Your budget will determine what can really be accomplished. There is always a tradeoff between cost, power, and reliability. Discussing crankshafts one engine builder wrote in another thread: "That $3500 [for a very high-end crank] sounds painful until you ruin a sleeved block, rod, piston, head, and the whole works...and the time to rebuild. After that the extra 2k over the cheap ones doesn't sound so bad."

Note that in road racing a bad downshift is a serious risk to the engine. And new tires can be worth more than a few extra hp.

Last edited by DavidNJ; 08-14-2015 at 12:44 AM..
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Old 08-14-2015, 05:53 AM   #8
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Default Re: Considerations on a K20 small block endurance build

Thanks DavidNJ,

interesting thoughts!

Quote:
Originally Posted by DavidNJ View Post
The first two questions should be: what are the rules and what is the budget. The third would be what is the objective.
It's different, but objective-heavy . Main objective is the validation of the suitability of my 1D-engine model under an optimum out of costs, technical allures and legal limits.

Quote:
Originally Posted by DavidNJ View Post
...that come to the conclusion that the correct rod length is the one that connects the crank to the piston....
LOL

Quote:
Originally Posted by DavidNJ View Post
Piston compression height and stroke being determined by other design parameters far more important.
Custum piston (combustion forming), the other design parameter like friction, HC production, oil deposition, topple propensity, valve clearance, squish and so on are in my focus...

Quote:
Originally Posted by DavidNJ View Post
If deck height is also a variable...
It is...

Quote:
Originally Posted by DavidNJ View Post
...Kaase built a 404cid Boss 429 with a really small more and a really long stroke (rod/stroke ratio around 1.4) for the last competition...
Interesting oberservation! What bore size on that V8?

No way for me, as IMEP increase (19+ bar) and FMEP reduction are in my objectives list.

Quote:
Originally Posted by DavidNJ View Post
...Can you think of any case where a race car is built not to have the largest allowed displacement?
I never saw or heard about a K27 successful Honda endurance racing engine...maybe because I don't live in the US ?!

Quote:
Originally Posted by DavidNJ View Post
Pistons shouldn't be coming from a catalog; they should be correct for your bore, ring stack, piston-to-valve clearance, and compression ratio.
s. above

Quote:
Originally Posted by DavidNJ View Post
...There is always a tradeoff between cost, power, and reliability. Discussing crankshafts one engine builder wrote in another thread: "That $3500 [for a very high-end crank] sounds painful until you ruin a sleeved block, rod, piston, head, and the whole works...and the time to rebuild. After that the extra 2k over the cheap ones doesn't sound so bad."
Good point ...there is a thread here about breaking bolts of KTuned PS/AC delete, a small and very good piece to get clearance for custom intake manifolds, but it seems to be it has a problem...just think of a breaking alternator bracket at 9000 rpm (crank speed), it will produce a mess at the intake side with all that stored angular momentum.

Just curious, if you have the following pool of basic parts:
  • K24 block, 231,5 mm block heigth
  • K20 block, 212 mm
  • H23 block, 219,5 mm
  • F20C crank, 84 mm stroke
  • k20 crank, 86 mm
  • F22C1 crank, 90,7 mm
  • H23 crank, 95 mm
  • K24 crank, 99 mm
what block concept you would like going to build if your main objectives are: naturally aspirated, [email protected] krpm, IMEP > 19 bar from 5 to 8.7 krpm, reliability, responsiveness and durabilty for a load profile like about 50 hill climb races before overhaul?

I appreciate your meaning to that

Markus
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Old 08-14-2015, 10:05 AM   #9
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Default Re: Considerations on a K20 small block endurance build

What you ask? hahaha
As you know k20 or k24 block.(more reliable....of course)
with k20 block you can rev 9100-9300
with k24 9600+ with no any issue.
but when speak about k24 block the devil inside tell ''go with 99mm crank.'' haha
what you love?
high rev?go with 90.7mm. is up to you
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Old 08-14-2015, 01:16 PM   #10
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Default Re: Considerations on a K20 small block endurance build

Quote:
Originally Posted by K20actr.J View Post
What you ask? hahaha
Nothing new in the K-series world...I am approximatly 10 years to late to do something innovative ...so nothing special.

Quote:
Originally Posted by K20actr.J View Post
...with k20 block you can rev 9100-9300
with k24 9600+ with no any issue. ...
That's interesting, I just calculated the tension of the rod bolts due to only axial mass force of rod, piston, rings and piston pin. It's about 390 N/mm@8.9 krpm with 7/16" bolts or more figurative 5 times of my car (3.5 tons!!!)...no shear force and so on, only by mass force...that's definitly a point to scrutinise when calculating the rod bolts.

Quote:
Originally Posted by K20actr.J View Post
...but when speak about k24 block the devil inside tell ''go with 99mm crank.'' haha what you love? high rev?go with 90.7mm. is up to you
The 87x99 has enough air demand to show the limits of the OEM head, VE declines early, even the 87x90.7 tend to show that limits when exceeding the 8.8 krpm...

...cylinder head port shaping is a topic I have no experience. At my work there being used 3D-CAD-CFD methods to calculate the right port shape to exploit it's full potential without weaken or even cutting water or oil channels...

...but even my rough 1D-calculation shows, working on those ports is sensitive to where the peak VE comes to lie down, as the air/gasoline velocity is very important for both, the combustion efficiency and the VE...think of cylinder balancing...means porting, flowing, porting flowing, porting, flowing...$$$$.

So I tend to start with an OEM or a very mild ported head at a lower displacement block: 87x86 (K20 block) or 87x90.7 (definitly K24 block)...as I don't know an expert here in Europe with working capacity (Andre Norrback, the only one I know from this forum, was told me is taking a rest) yet.

Also valve motion...BC, Skunk2, SVM, and so on...I calculated only with the high speed cam profiles of the SVM 212, that rocks ...but I also saw, port flow at low lifts is the most restricting thing as there easily is reached 0.5 Mach...you have to know beyond 0.4-0.5 Mach ports behave like bottlenecks in NA engines due to the relatively low pressure drop -> here 2nd order wave power comes to play...so low lift flow is of importance when you want to have a very broad table of torque or VE...the max lift value doesn't play that importance...more important is a steep lift curve in the beginning and at the end in the range of possible valve lift de- and accelerations...

...many questions, requirements and limitations. No single but many optima . So I believe those answers are not easy...but I will do my best to find one of those
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Old 08-27-2015, 12:58 PM   #11
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Default Re: Considerations on a K20 small block endurance build

Lots of nice numbers posted there Markus, but what's the engine going to be used for?

If it's a dyno guinea pig to validate your software then surely the cheapest option would be best?

There's also S2000 WTCC spec bottom end, still short stroke but not as much as a 90x78. (87x84) The like's of Artman Racing (Estonia) can supply. (Arrow crank/rods, Italian pistons).

P.S, you don't need to go to the states to get a block sleeved. ;)
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Old 08-27-2015, 04:28 PM   #12
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Default Re: Considerations on a K20 small block endurance build

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...what's the engine going to be used for? If it's a dyno guinea pig to validate your software then surely the cheapest option would be best?
Doug, fine to hear from you...you are back from scrambling?

From a standpoint of economical considerations YES, from a standpoint validation quality NO. The more far the thermodynamic and geometric properties differs from the calibrated reference, the more the algorithm have to show it's weakness or strength.

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...(87x84) The like's of Artman Racing (Estonia) can supply. (Arrow crank/rods, Italian pistons).
Thanks I will check this out . I already got a quotation to Cunningham rods with rod bolts of a bigger size than M10 thread (they could integrate 7/16" threads). I will do an inquire to ZRP and Arrow too.

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P.S, you don't need to go to the states to get a block sleeved. ;)
Yes, I already found a company here at my place installing sleeves. If not necessary I will stick on the stock sleeves.
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Old 09-19-2017, 01:01 PM   #13
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Default Review with a different approach

As we discussed that bore size topic in the RS machine piston threat (s. here: https://www.k20a.org/forum/showthread...=214713&page=2) I revised my approach about engine size consideration. The new approach is rated at same rod bolt tensil stress for all considered strokes below. I used a very simple linear approach for the rod weight, which depends on rod length and for the piston weight, depending on bore size and piston height to calculate peak acceleration forces in the rod bolts. That means the engine speed has to be iteratively calculated to get the one, where the rod bolt tension are reaching the aimed value. The first picture shows the displacement one get with different combinations of bore and stroke size in a K20 or for the 99 mm stroke case the K24 block.

Displacement over Cranksize and Bore.jpg

Here you can see the influence of bore and stroke size regarding the displacement of the engine. From the smallest OEM bore and stroke size (86x84) with 1952 ccm up to the biggest OEM crankshaft and custom bore size (90x99), giving one 2519 ccm.

In a second step I did calculate the rod bolt tensil stress, where the above mentioned value get reached. The rod weight was from 441 g (86x92 engine) to 542 g (87x99 engine) and the piston weight was from 320 g (86 mm bore) up to 365 g (90 mm bore). For the those who are interested in the math of the kinematic approach, I set the barycenter of the rod to 1/3 of length from big bore side. As an example, the resulted engine speed for the 86x86 engine was at 8965 rpm at that rod tensil stress and was considered as redline. The peak power engine speed was considered to be 400 rpm lower. The concluding graph shows the maximum wheel power output, assuming a drivetrain efficiency of 0.88 and a BMEP at peak power of 15 bar, which is a challenging task, e.g. the 86x86 engine would produce 252 [email protected] rpm. Not much engines reach that power level at the mentioned engine speed, most engine builders need higher engine speed for that.

Wheelpower rated at equal rod bolt tensil stress.jpg

Please consider this are power ratings for endurable applications like endurance races, this is not valid for drag race or similar as there are mean weight ranges are used (no lightweight parts) for rod and piston assembly. As a final conclusion, it doesn't matter much if you use a F22C or BC 92 mm crank, buy that you get more easy or cheap. Interestingly, to keep up with an 87x99 engine, one need to bore the 86 mm stroke engine up to 88 mm bore, which means sleeving the block or adding about 1500-2000 Euro to the build budget. Once you do the sleeving anyway, a 90x86 engine equals power-wise to an 88x99 engine. Most guys would say a 90 mm bore size want be durable, finally the K20 crank just can compete endurance- and peak power-wise with an 87x99 engine. Acceleration would be different, because of the higher torque of the 99 mm storke engine at engine speeds below peak power, leading to a power line, which don't fall as fast as the 86 mm stroke engine would have it. Another interesting graph would be the piston dome size to get equal compression ratio and combining the above with my peak-to-peak power approach...stay tuned for that .

Markus

Last edited by LotusElise; 09-25-2017 at 03:01 AM..
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Old 09-19-2017, 06:57 PM   #14
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Default Re: Considerations on a K20 small block endurance build

Great post! I'm becoming more and more interested in a 14.1:1 high compression 89x86 motor running e85. It would lack the down low torque in 1st and 2nd gear but that also is a positive (reduces drive train stress).
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Old 09-19-2017, 07:59 PM   #15
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Default Re: Considerations on a K20 small block endurance build

Helpful info.
Great!
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Old 09-19-2017, 08:07 PM   #16
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Default Re: Review with a different approach

Quote:
Originally Posted by LotusElise View Post

Interestingly, to keep up with an 87x99 engine, one need to bore the 86 mm stroke engine up to 88 mm bore, which means sleeving the block or adding about 1500-2000 Euro to the build price. Once you do the sleeving anyway, a 90x86 engine equals power-wise to an 88x99 engine.
Interesting. I would've guessed the 88x86 would still not match the 87x99 in peak power due to the overall smaller displacement. What are the theoretical rev limits for the two motors? You're prediction would suggest that bore size makes a bigger difference than stroke on the smaller motors? This seems counterintuitive.

And when you mention the f22 or BC2.2 crank, are you saying that more power would be made with an 86x92 motor compared to a 89x86? (Assuming both would have a similar displacement).
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Old 09-20-2017, 08:53 AM   #17
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Default Re: Review with a different approach

Thanks guys .

Please keep in mind, I made simplifications concerning crank assembly part weight and equalized the VE level at peak power. Both have a significant influence on the peak power result. So this is a sort of overview, for a specific engine budget, especially if it is huge, an individual look has to be taken. To give you an idea about the sensitivity of the system:
  • A -100 g piston weight (Reference: 321 g for the 86 mm bore piston) reduction means a increase of 883 rpm in redline, leading to plus of around 20 whp at equal VE or BMEP at peak power and same rod bolt tensil stress
  • A -100 g rod weight (Reference for the 86x86 engine: 460 g) reduction means a increase of 375 rpm in redline and adds about 10 whp at equal VE or BMEP at peak power and same rod bolt tensil stress.

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...It would lack the down low torque in 1st and 2nd gear but that also is a positive (reduces drive train stress).


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Originally Posted by BlackNDecker View Post
...What are the theoretical rev limits for the two motors?
Depends on budget (= parts), application (= duration and profiles of load and engine speed), mis-shifting likeliness and so on. For the case I calculated it (endurance race application, lower budget range) the 86x92 it's 8936 rpm and for the 89x86 it's 8635 rpm. The 92 mm stroke engine has the higher peak acceleration (vectorial), but the higher mass of the piston of the 89x86 engine overcompensate this. I took the piston weight approximation out of Wiseco's catalog for the K20 list.

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...You're prediction would suggest that bore size makes a bigger difference than stroke on the smaller motors? This seems counterintuitive.
That's a good question and definitely something I wanted to clarify for me. You gave the perfect example above for the 2140 ccm case (89x86 or 86x92). The 92 mm stroke engine is with 6 whp in front, because the higher piston weight, which has an higher impact on redline than rod weight and a bit higher acceleration. Something I wouldn't have expected. K20actr.J likely have seen this with an smile . Not calculated is the friction within the F = m x a (Newton's 2nd law). Maybe a variation of the barycenter of the rod could clear about the significance to know the measured barycenter.

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Originally Posted by BlackNDecker View Post
...And when you mention the f22 or BC2.2 crank, are you saying that more power would be made with an 86x92 motor compared to a 89x86? (Assuming both would have a similar displacement).
Yes, about 6 whp more for the stroker.
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Old 09-20-2017, 11:08 AM   #18
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Default Re: Review with a different approach

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Originally Posted by BlackNDecker View Post
...more power would be made with an 86x92 motor...
An idea would be, having an 92 mm crankshaft, a stock rod and a piston with a

piston height = 212.09 - 139 - 92 /2 = 27 mm

You only would have to buy the crank and pistons (if bearing clearances fit). Adding the maximum bore for the stock block you would have a real 2.2 liter engine (2188 ccm). As pistons are bought anyway for that version it would be a good update for the 86.5x86 engine I already have, but adding 20 whp and a nice lift of the torque line over the entire revving band. Now I understand K20actr.J why he did it, I just wouldn't like to use the InlinePro-stroker kit, as it consists of a adapted rod length-wise. Your purchasing list would be: crank, rod, piston.
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Old 09-20-2017, 12:33 PM   #19
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Default Re: Considerations on a K20 small block endurance build

Another advantage of the 92 mm stroke, the dome volume of the piston get reduced by 3 ccm, which supports a better flame initiation and propagation, once squish is done properly. Actually I have 9 ccm Mahle piston (12.8:[email protected] ccm head volume), looks like a 14.5:1 CR piston dome of a 88x99 mm stroke engine...86 mm stroke engine would really profit from a smaller head volume flame speed-wise. This would help to reduce knock and increase the capability to run ignition timing at MBT (mean best torque of the ignition timing hook). Crapy fuel feed engine need it more than the high octane stuff, like E85.

Endyne is able to weld head volumes without loosing flow capacity, they even increased it after the finishing.

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Old 09-20-2017, 02:49 PM   #20
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Default Re: Considerations on a K20 small block endurance build

What do you think about the Brian Crower 92 mm stroker kit? Just wondering because you mentioned the inline pro kit but not the BC kit.
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