Optimal compression on a built motor?

[cobra gt 07]

I am researching the potential of doing an engine build down the road, in order to take maximmize and take full advantage of my current set-up. I noticed that it seems like quite a few people choose a compression somewhere in the 9.5:1 to 10:1 area.

Stock compression is 8.45:1, which has worked out well on my stock engine.

What is considered the best compression ratio on a built modular that is going to use a supercharger, and why? At what compression ratio does it become risky?

Thanks

 

[CPRsm]

That all depends on fuel and over all power output goal. If you are still going to run pump gas, then the target power will have to come down. But general rule of thumb is the highest CR you can run to hit your goal on the octane you want. Or you can run 10-1 with 9 psi and take it easy on the street while still making probably 600+rwhp. Pulley change at the track and get stupid.

 

[bull3441]

I am researching the potential of doing an engine build down the road, in order to take maximmize and take full advantage of my current set-up. I noticed that it seems like quite a few people choose a compression somewhere in the 9.5:1 to 10:1 area.

Stock compression is 8.45:1, which has worked out well on my stock engine.

What is considered the best compression ratio on a built modular that is going to use a supercharger, and why? At what compression ratio does it become risky?

Thanks

i asked the same question to Michael @L&M. his answer was , i stay with 93 oct than i'd only see about a 15whp increase bumping the compression to 9.5:1 vs stock CR. he felt i shouldn't go over 17psi on pump gas whether i used his Diamond or Manley 2618 pistons. race gas was a different story obviously. yesterday i put a $10k deposit down for a motor build. as of tonight i think i'm gonna pull the plug and go with L&M instead. i wanted to stay local in the invent an issue were come up, but L&M has built a lot of modular motors and know what works on the GT500. just my 2 cents.

 

[DMotorsports]

You'll get at least 10 different answers on this one. Here's my 2 cents: just keep in my mind that as compression and boost go up, you'll be flirting more with possible detonation. If I were building an engine primarily for street duty, I would go with something in the 9:1 - 9.5:1 range. On the other hand, if I were building something strictly for track use with race fuel, I would probably go with something around 10:1. There are guys that run even higher compression than that and put down some very impressive numbers. However, you'll have a difficult time convincing most engine builders to go higher than 10:1 on one of these boosted engines. They have their reasons....

 

[rdsnk46]

9:5:1 street strip, moderate boost(17 psi) with 93 oct sholud net colse to 700 wheel, add octane/timing and boost make 850rwhp

 

[thebull]

I agree w Andy. 9.5 to 1 for all around great performance. I think when you go much higher the tuning window closes...More chance for an easy f-up.

I don't think you can wrong with L&M I've heard nothing but good things.

 

[bull3441]

I agree w Andy. 9.5 to 1 for all around great performance. I think when you go much higher the tuning window closes...More chance for an easy f-up.

I don't think you can wrong with L&M I've heard nothing but good things.

Bull, who built your motor?

 

[thebull]

Bull, who built your motor?

Thunder Autosports probably built a few hundred mod motors over the years. He's local and we have been friends for 20 years.

 

[bull3441]

Thunder Autosports probably built a few hundred mod motors over the years. He's local and we have been friends for 20 years.

would you mind listing your internals? as you have mentioned you've run 46psi and have laid down huge power for a street car. it might be helpful for guys doing research to see what the KOTS uses.

 

[thebull]

would you mind listing your internals? as you have mentioned you've run 46psi and have laid down huge power for a street car. it might be helpful for guys doing research to see what the KOTS uses.

CP pistons, stainless rings, BIG piston pins, Oliver rods, Arp fastners, melling high volume oil pump, manley valve springs and tit retainers, and cometic head gaskets (lock wire in the block). I buy all my parts from Dale at Propower and have for the last 20years. 561-901-0262 he is the man!!!!

 

[cobra gt 07]

Thank you guys for your posts. My car is and will be a street and strip animal. I made 676 RWHP on pump gas with a stock engine @19 pounds of boost. Looking to make around 900 RWHP and get as close to an 8.999 pass as possible, at the same time knowing that my built engine will hold up against anything I throw at it.

Sounds like a 9.5:1 might be something to look into

 

[bull3441]

CP pistons, stainless rings, BIG piston pins, Oliver rods, Arp fastners, melling high volume oil pump, manley valve springs and tit retainers, and cometic head gaskets (lock wire in the block). I buy all my parts from Dale at Propower and have for the last 20years. 561-901-0262 he is the man!!!!

when i was on Modmax site it seemed like they supplied your parts. that's one of the reasons i asked. hats off to your builder.