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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:
After a short search I found some inspiration for my block calculations at Doug's threat (http://www.k20a.org/forum/showthread.php?t=114024) and at NtegraDryvr threat (http://www.k20a.org/forum/showpost.php?p=839411&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:
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!
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 (http://www.k20a.org/forum/showthread.php?t=114024) and at NtegraDryvr threat (http://www.k20a.org/forum/showpost.php?p=839411&postcount=11)

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
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/s²) 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 :wink:. 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!