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hello,

I have a plan to put a K motor into a mk1 miata. Some targets I have for this engine is to make 300whp on ITBs and have it rev to the moon, up around 10-11k.

I bought a dirt cheap hurt k20a2 that i have been pulling apart to get a feel for the platform and i have been learning a lot.

I think I want to do a Frankenstein using a k24 block, k20 crank and a k20a2 head and a sprinkle of goodies to make the power.My hope is the short stroke of a k20 crank with the tall deck height of the k24 block will let me get a low(ish) enough piston speed and also let me use a much longer rod to get a higher rod ratio.

is there any compatibility issues with my plan? does the k20 crank fit in the bottom end of a k24? also, are there any off the shelf rods and pistons that will fit this idea well (that are pretty light weight but not alloy)

another route could be a destroker crank. if anyone makes a 1.8L crank? that would let me move down a class :)
 

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Arouse the DAMPFHAMMER!
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...targets I have for this engine is to make 300whp on ITBs and have it rev to the moon, up around 10-11k....using a k24 block, k20 crank and a k20a2 head and a sprinkle of goodies to make the power.My hope is the short stroke of a k20 crank with the tall deck height of the k24 block will let me get a low(ish) enough piston speed and also let me use a much longer rod to get a higher rod ratio.
Welcome to K20a.org Henry Collingwood!

Now I got you in my edited version of this post. I was going to build a 86x68 K16 engine for 1600 ccm class, parts cost of 18,000 Euro without work and alternation of load parts. This engine was spec'ed to be safe up to 12,000 rpm with 270+ [email protected],500 rpm. Likely we change to a cheaper platform not to exceed 25,000 Euro. Now you have a number what is necessary for around 170 hp/Liter. Your aim is around the same hp/Liter area, just with an 86x86 engine, just the crank, pistons and conrods are some of the shelf aftermarket parts, saving you some 5000 Euro.

With the 86 mm stroke you run in some series dynamic issues: crank assembly forces get really high. The taller block height isn't for all of them an advantage. It depends on the weights of piston and conrod assemblies. It isn't just a transfer of rod-stroke-ratio of high speed engine like an Formula 1 engine into a K-series, while the Formula 1 Pankl rod was around 155 mm at a rod stroke ratio of more then 2.5:1 the K24-block rod would be around 158-163 mm long (piston height!), but the forces at 11,000 rpm at the rod bolts are already higher as on that Formula 1 engine at 16,000 rpm. If you look at that Pankl rod an Mahle Piston you see a lot of design work to make it more stable at around 245 g piston assembly and a roughly 390 g conrod. ONE cylinder assembly cost more than your engine will cost. You can fight weight down, but you can't increase reliability in that manner F1 did. Finally you need to put big effort in a 50 h lasting engine: alu or smart designed steel rods, low piston height pistons (two ring or three ring system) and then the head. What makes it inhaul air for 345 hp at flywheel makes the port inefficient down low, what is needed on a hill climber, so the compromise where the engine performs cost investment into customized exhaust and intake as well as valves and ports.

It would be recommendable to go to an 90x78.5 (= custom crankshaft) or 87x84 (F20C crankshaft), it would reduce the dynamic load in the crank assembly and give more room to the head design to achieve the flow numbers and combustion velocity which is needed. The 231 mm block height of the K24 would provide some advantages, but not in all engine setup cases on that project.

How many race hours do you need it before overhaul?
 

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Welcome to K20a.org Henry Collingwood!

Now I got you in my edited version of this post. I was going to build a 86x68 K16 engine for 1600 ccm class, parts cost of 18,000 Euro without work and alternation of load parts. This engine was spec'ed to be safe up to 12,000 rpm with 270+ [email protected],500 rpm. Likely we change to a cheaper platform not to exceed 25,000 Euro. Now you have a number what is necessary for around 170 hp/Liter. Your aim is around the same hp/Liter area, just with an 86x86 engine, just the crank, pistons and conrods are some of the shelf aftermarket parts, saving you some 5000 Euro.

With the 86 mm stroke you run in some series dynamic issues: crank assembly forces get really high. The taller block height isn't for all of them an advantage. It depends on the weights of piston and conrod assemblies. It isn't just a transfer of rod-stroke-ratio of high speed engine like an Formula 1 engine into a K-series, while the Formula 1 Pankl rod was around 155 mm at a rod stroke ratio of more then 2.5:1 the K24-block rod would be around 158-163 mm long (piston height!), but the forces at 11,000 rpm at the rod bolts are already higher as on that Formula 1 engine at 16,000 rpm. If you look at that Pankl rod an Mahle Piston you see a lot of design work to make it more stable at around 245 g piston assembly and a roughly 390 g conrod. ONE cylinder assembly cost more than your engine will cost. You can fight weight down, but you can't increase reliability in that manner F1 did. Finally you need to put big effort in a 50 h lasting engine: alu or smart designed steel rods, low piston height pistons (two ring or three ring system) and then the head. What makes it inhaul air for 345 hp at flywheel makes the port inefficient down low, what is needed on a hill climber, so the compromise where the engine performs cost investment into customized exhaust and intake as well as valves and ports.

It would be recommendable to go to an 90x78.5 (= custom crankshaft) or 87x84 (F20C crankshaft), it would reduce the dynamic load in the crank assembly and give more room to the head design to achieve the flow numbers and combustion velocity which is needed. The 231 mm block height of the K24 would provide some advantages, but not in all engine setup cases on that project.

How many race hours do you need it before overhaul?
Does the s2000 crank fit in either the k20 or k24? I remember reading something about the head gaskets matching between the engines which would suggest you could put an S2k head on a k24 block ? I believe it was on an old hybrid racing article
 

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hello,

I have a plan to put a K motor into a mk1 miata. Some targets I have for this engine is to make 300whp on ITBs and have it rev to the moon, up around 10-11k.

I bought a dirt cheap hurt k20a2 that i have been pulling apart to get a feel for the platform and i have been learning a lot.

I think I want to do a Frankenstein using a k24 block, k20 crank and a k20a2 head and a sprinkle of goodies to make the power.My hope is the short stroke of a k20 crank with the tall deck height of the k24 block will let me get a low(ish) enough piston speed and also let me use a much longer rod to get a higher rod ratio.

is there any compatibility issues with my plan? does the k20 crank fit in the bottom end of a k24? also, are there any off the shelf rods and pistons that will fit this idea well (that are pretty light weight but not alloy)

another route could be a destroker crank. if anyone makes a 1.8L crank? that would let me move down a class :)
4piston makes stroker kits for the k20/24 if you contacted them they May be able to make you a custom
Length combo but I would expect it to be expensive
 

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Arouse the DAMPFHAMMER!
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Does the s2000 crank fit in either the k20 or k24? I remember reading something about the head gaskets matching between the engines which would suggest you could put an S2k head on a k24 block ? I believe it was on an old hybrid racing article
Yes, it does. It is the 87x84 (F20C crank) engine I recommended above. There is a machine work to do on the shaft outlet to get a fit into the shaft machined. Beside that it is a direct fit. This would be a nice 2 Liter engine, which is maybe the cheapest beside the 86x86 1998 ccm configuration. All other stuff is much more expensive in the 2 Liter area. The cheapest and most powerful is, if class allows, the 90x99 one, then the 89x99 (more reliable, less powerful).

Do you have a further specification to get this condensed more down to reality Henry Collingwood?
 

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375hp at the flywheel of a 2.0L motor is a tall order. Get out your checkbook!

 

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Arouse the DAMPFHAMMER!
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It started very interesting @Henry Collingwood. Would be great to read if your plans get into real shape and what approach you took. I really would appreciate your feedback here @Henry Collingwood.
 

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Arouse the DAMPFHAMMER!
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Such kind of topics are those I got a member here. More of these would be really nice, because this is what K-series is about: high revving, most powerful in allmotor-style.
 

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Such kind of topics are those I got a member here. More of these would be really nice, because this is what K-series is about: high revving, most powerful in allmotor-style.
Yes Indeed. They are about the NA high revving. Many people overlook the fact the 86x86 is Honda's version of a pure square racing engine for endurance racing and road course racing. Even the Honda Euro Accord R was a heavy chassis with a 86x86. I think the world stubbled apoun the K24 with a K20 head accidently and obviously it made big NA power. The K24 was built for the touring type engines and daily driver low end torque. Of course in order for the K24 to be better it needs K20 parts. This off balance is great for making power but bad for the industry and maintaing a 100% opportunity for a Acura or Honda car owner to get the parts for service when they need them on time or in the future. Kswap the world is not a great concept for the industry either. At some point, Honda will make a decision based on "money" if they continue to make parts for cars over two decades old. Kswap the world is a "race to the bottom reality" soon to meet.

This one of the reasons I replaced every working sensor and mechanical assembly on my engine and transmission the best I could. I now have 100% working used back-up parts for my build. I have a nice display of OEM parts, even oil pumps, rocker assemblies, and more. I am getting ready for it. I have the opportunity to get another complete K20a2 longblock. I do want a RSP head at some point, my RRC IM is on the way.
 

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Arouse the DAMPFHAMMER!
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Many people overlook the fact the 86x86 is Honda's version of a pure square racing engine for endurance racing and road course racing.
BTCC, STW, DTM and many other racing scenes used square near bore-stroke-ratios, which is not bad up to around 9000 rpm as limit for 2-liter-I4-engines. Opel/Vauxhall had a square design in the C20XE, the Renault F7R 2-Liter engine was under square with their 82.7x90 dimensions, the Audi engine EA113 was also under square with 85x88 (at a 88 mm bore pitch!), the STW engine of BMW, called S42, had 86.5x85 based on the M42B18 (84x81). Renault won more then 50 % of the races of 1997 I think with this under square design. But remember these engines were limited to 8500 rpm per rule book and made end of the 90'ies all around 305-320 hp. None of them made more then 26 m/s mean piston speed or more then 40 m/s peak piston speed. These are quite well experienced values for todays of the shelf quality material in the lower comp piston area.

The F7R engine or the F4R engine of Renault was a real beasty boy, 200 [email protected] and 215 [email protected] rpm in series. This is quite a step up of the K20A2 engine and competes directly with the JDM version with 225 [email protected] rpm and 215 [email protected] rpm. The rod-stroke-ratio was just the same with the K-series, despite the 90 mm stroke because of the bigger block height. That this worked quite well even with the tiny 32.3 mm OE intake valve (83.7 mm bore!) size. A different approach as the K-series does have it with the 35 mm valve. Finally I don't know what sizes they utilized in the race version, e.g. if bore was increased to favour a shorter stroke and bigger bore for more air, but the basics are different to square design and was great success.

I've calculated the piston pin and rod tensions as well as the forces around the crank drive as well as normal force at the liner-piston-skirt for my DAMPFHAMMER HD engine to analyse how these went on when engine speed is pushed further to 10,000 rpm. The F20C1 setup is quite racy with the over square design, the long rod approach and 2 mm lower stroke helps allot to reduce side force and piston speeds. It's understandable that many racers go this route with the 2-Liter-10,000 rpm area. But to be honest, for the 330 hp approach it isn't necessary. For my 360 hp approach it would help, but it means a huge invest. The R/S-ratio of 1.82 won't be reached with the 84 mm stroke in a 212 mm block height, would be 1.67 to 1.71, depending on compression height, that means allot on the alternation of load side as well on the friction side. The way to go to 89x80 would be attractive on the alternation of load side but would loose much of the mid range torque. Joe McCarthy's 90x78.5 approach is way above the valvetrain capability, which I would limit to 10,500 rpm. The head for that engine need to be borne, as this thingy need very tight ports to come to live. I am convinced Joe focused much on the side load and mean piston speed, but power wise this thing is limited. It made with huge valves a bit over 300 hp at flywheel at around 9700 rpm, but that level can be achieved well around 8000 rpm with a stock near head. He designed it for endurance and the 5 miles on the salt. It was a safe approach. Today we know 10,000 rpm based on a 86 mm crank for circuit are not the limit when built and designed correctly. But keep in mind this are 28.7 m/s (~5600 ft/min) mean piston speed, that's an enormous load on pin, rod and bolt's, you need to be very very light in parts to stand this.

The NASCAR cup engines are in a similar but bit lower range at 10,000 rpm because of their bigger rod-stroke ratio. Now as they as speed limited the play of the game get's really nasty regarding rod-stroke-valve size design, fighting for the best wide torque bandwidth to get faster into peak power out of the corner, designing resolution is 50 rpm. These guys do a great job for the V8 system and brought the valve spring development over the years to an point were we are today. The US market has some of the best valve spring companies, just because NASCAR always screw up power with the valve spring engine speed capability.

Finally, the by the OP aimed 350 hp at flywheel are quite interesting, with ITB's very challenging. I would even say, none in the market would reach it with pump fuel just with ITB's only on intake side. The top dogs at drag racing where rod-stroke-ratio's down to 1.43 are used and alcohol fuels are allowed reach out for 180-190 hp/Liter, which would be 370 hp. But that is not transferable, as the 86 mm bore is used for the head already and it's huge 35 mm double valves. You would need to do a 80x99 engine in a K20 block and go down to a 1.4 rod ratio, which shrouds the valve hugely. So that concept of low rod-stroke-empowerment of alternation of load doesn't work here. The concept would need around 10,800 rpm to get into that range where those huge ports are on spot and then you need a let's say 500 rpm safety range to redline, which would be at 11,300 rpm. These piston rings would sing you a song about oscillation because of the almost 8000 g piston peak acceleration, which is still lower at a 106 to 108 mm stroke engine at 9500 rpm, where the 180-190 hp/Liter came from. So that concept also doesn't work. The 2-Liter engine is the real challenger for peak power competition as power comes from different sources as the typical top dog drag race engine from JBM, 4Piston, DragCartel, ... came from.

The approach stated by @Henry Collingwood with the long rod approach (up to around 165 mm for a 3-ring system) doesn't reduce the mean piston speed as stroke is still the same. It will reduce side load and peak piston acceleration, that's all. But it increases rod weight which compensate some of the rpm's. Bolt-wise no single advantage. Pin-wise an advantage, but not the one one may wish. Side-load wise an advantage, but does it count if VE is lowered? This engine just need smaller ports to come to alive at same engine speed bandwidth and therefore it is more limited more peaky, nothing for a Miata RWD regarding control of the rear. I am convinced the 370 hp are possible, but you would invest in parts development as well as combustion process design as these are the weak links for that concept. 300 whp on a RWD none have achieved just by an 2-Liter 4-banger allmotor. You would need at least 5 cylinders, better 6 or 8, to increase engine speed, increase valve area and need to use a more revvy valvetrain (mechanical tappet system) to get 185 hp/Liter on a 2-Liter basis. On a I4 basis you are limited on many areas to reach out this level. I know concepts doing 230 hp/Liter on a simple ITB system out of 2-Liter displacement in NA mode on alcohol fuel, but this is a V8 system based on the Suzuki Hayabusa 1350 ccm heads. Short stroke, huge valve area, a Hayabusa near rod-ratio, and enough play to rev up to 15,000 rpm, does make 460 [email protected],600 rpm and runs the 5 miles on the salt. This concept is indeed reliable, a 370 hp 2-Liter K-series is it not in any case on an allmotor alcohol fuel basis.

What I would recommend is a 1600 ccm concept based on a Hayabusa engine, which are well pushed to 250 hp at flywheel, based on a more reliable concept. It would be also possible based on a B16B basis, but their valvetrain sucks above 10,500 rpm. Mechanical tappet actuation is the key to rev much higher. The Hayabusa head has a nice potential and flows very well, has a much faster chamber then any B- or K-series. In the 1-Liter class I would start with e.g. with the RR1000 BMW, very nice high engine speed design. Here you find much of the V10 F1 engine BMW had learned off.

The DAMPFHAMMER HD is spec'd for the aimed goal, but is far from realization, that money pit need time, or sponsors, to be built and validated.
 

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Opel/Vauxhall had a square design in the C20XE, the Renault F7R 2-Liter engine was under square with their 82.7x90 dimensions, the Audi engine EA113 was also under square with 85x88 (at a 88 mm bore pitch!), the STW engine of BMW, called S42, had 86.5x85 based on the M42B18 (84x81).
This is good to know information about other manufactors, I had no clue this was something popular. I sent @Them Witches a conversation about the 86x86 square design. I noticed that the DAMPFHAMMER has a large bore and shorter stroke to create a longer rod to piston ratio. @Them Witches said I would have to get into a conversation with You about the concept of the DAMPFHAMMER engine and it how closely it resymbols the 86x86 design but is balanced better and has better VE because the pistons do not have to move up and down as much & the port design baseline of the RSP suits the flow characteristics needed to create power with the intake valves having less time to be open in the higher rpm ranges.

I am learning a good deal of information from this forum in such a short period of time reading your build, Lotus's build, some of the other's builds here.
 

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Arouse the DAMPFHAMMER!
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I noticed that the DAMPFHAMMER has a large bore and shorter stroke to create a longer rod to piston ratio....
That's a sequestration question, but it's no secret so I will tell you the details. It's a 86.5x86 engine with a OE R/S-ratio. Nothing special at all. The task was to have a price-worth and competitiv engine concept. With just an usual of the self aftermarket small block it get very price-worthy. It has also an almost stock RSP head despite the intake valves, which makes it also price worthy. Compared to the competitor concepts, which are around 12,600 USD for e.g. the K330 engine for only the longblock you would safe around 6000 USD for the longblock.

As I tuned an K330 engine which had ITB's according 4Piston and a header near to what 4Piston used that engine produced 295 hp beyond 9000 rpm. The DAMPFHAMMER produces 310 hp already at 8200 rpm, which does reduce the built and maintenance cost enormously as well as the DAMPFHAMMER engine uses an Speed-Density based on MAP and IAT system which works well on any altitude compared to an simple ITB system which need well tuned corrections or an improved MAP sensor system to be able to measure that directly and not based on an Alfa-Speed-system. The former reduces also the Tuning costs for altitude adaptions. The concept is there, just need marketing, production verification and customers who race it successfully now to compete and to take a market share.
 
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