i've seen some cars run around 11:1 compression on FI with about 12 psi. just wondering if anyone has tried this on a z. i know that is better for lower compression when going FI just wondering if there would be any advantages.

 

i have 10.5:1 compression and am having trouble getting 11-12 psi. arent that many advantages except some more power down low.

 

Unless you run 100octane or greater fuel, there are no advantages, and quite a few disadvantages. I tuned KTaylor's car above, and with his high compression pistons, 10-11psi was the safe limit on pump gas. Anything greater would show too many knock counts, and is unsafe for sustained street usage.

 

+1

I'm running stock compression, and 13-14psi...but also running 100 octane as Sharif suggests.

 

Which pistons are you running.

 

JE Pistons

 

Thats the stock bore though right.

 

Stock bore or .020 over. We arent sure becuase the car was purchased used.

 

i see alot of people with the stock compression which is around 10:1 and they run around 8-12 psi. just wondering if you run this psi on a built motor with about 11:1 and tune it for 93 but i'm guessing that the motor would last a lot longer with 9:1 and be alot safer.

 

stock is 10.3 CR

 

yep

 

i dont believe it would be any safer.

 

I was running 15lbs boost with 100oct.. but make a wrong move and misshift like me and your motor is gone...So if you don't want to live on the edge...run a built motor with a lil lower comp. and you'll be all good...give Sharif a call...

 

But I doubt it was the high stock CR that killed you -- I would think it was caused by inadequate valve springs, and con rods for 9000 rpms.

If the car came with a 9:1 CR I think it would have still blown with what you did to it... What do you think?

 

I agree. No way the stock rod bolts are going to hold at 9000 rpm regardless of CR.

 

I believe the orginal question was about compression ratio and boost.
In laymans terms:
Your octane roughly gives you the maximum temperature it can stand before it will self ignite (aka knock). That temperature gain comes from the combination from your boost and your compression ratio (PV=nRT). So as you go up on compression you must go down on boost w/ a given octane of gas. As my friend (who is a professional drag race car builder) says, FI is the cheap way to gain horse power. It is much more expensive per hp for NA.

Octane is acting as an auto-ignitian suppression, but there are others. The only other one that comes to mind is water/methanol.
Maybe, we could just put a diesel engine on the car and we could be running insain compression ratios w/ FI!

 

I agree...but everything contrubited to the failure....The rods were streched from the over rev....

 

How goes the new set up?