Short block…. Compression ratio?

[Gregory347]

19 A10 with Procharger P1X, 4.5 pulley for 10-11 lbs of boost. Car will be pump on street and ms109 at track. Need a new short block due to ring land failure. Does it make sense to lower compression and if so what’s ideal?

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[engineermike]

This has been hotly debated several times. The long story short is it depends completely on the fuel. If you want to optimize performance when knock limited then it will make more power with low compression. If you want to maximize efficiency on ms109 then higher compression will make more power.

 

[Gregory347]

Got it… street car 98% so optimize performance with pump… was thinking 10-10.5

 

[turnswrench]

19 A10 with Procharger P1X, 4.5 pulley for 10-11 lbs of boost. Car will be pump on street and ms109 at track. Need a new short block due to ring land failure. Does it make sense to lower compression and if so what’s ideal?

Dang the ring land broke on 10lbs? Sorry pal.

 

[Gregory347]

Thanks….good thing it wasn’t the crank….lol

 

[engineermike]

I’ve spent way too much time thinking about the optimum boosted Gen3 pump gas compression ratio and where i seem to keep landing is 10.5. You can actually hit 11/1 using the mahle drop-in 12/1 pistons and thick cometic head gaskets.

Keep in mind that you have to fuel the airflow not the power. At 10.5/1 you’ll have to raise the boost about 2 psi to break even on power. But you have to supply 6% more fuel as well. If you want more power you can raise boost a few more psi but need more fuel still.

Also don’t forget that a custom tune will be needed to get the most out of it. Brenspeed has a YouTube vid out there where he makes good power on a gen3 at 9.5/1 so he may have experience tuning it. I’d like a shot at it myself, TBH.

 

[SolarFlare]

Ideal in my opinion is stock compression.

 

[Cory S]

Building mine again after ring land failure this year.(2nd time) Keeping it 11:1.

 

[K4fxd]

Building mine again after ring land failure this year.(2nd time) Keeping it 11:1.

I would think you would learn

 

[Cory S]

I would think you would learn

First was the original engine. 2nd was fresh stock short block, and the stock ring gaps don’t like big power on gas. So yes, this build with a piston upgrade, will have ring gaps for boost…..So, I’ve learned yes….

 

[K4fxd]

So, I’ve learned yes….

 

[Gregory347]

Only spoke to 1 engine builder so far, Mike at L&M Engines, and he suggested 11:1.

 

[Barrel]

I went with 11:1 twice. Would do it again if I had the choice in front of me. I do run E85 full time, though.

Check out TKM if you're still shopping builders. They built mine and did a truly excellent job.

 

[Gregory347]

Check out TKM if you're still shopping builders. They built mine and did a truly excellent job.

are you sleeved?

 

[Mach9310]

My stock engine failed on pump gas and 11 psi. I went with RPG and they build their motors with high compression (12:1) as well. Sleeved block. As long as you have the proper fueling (E85) you should be ok.

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