Dynamic Compression Questions
Thread Starter
Joined: Sep 2012
Posts: 257
Likes: 18
From: Colorado Springs, CO
Dynamic Compression Questions So this isn’t your typical “will this can work with my application” thread as I have been running my current cam for a while but I’m looking to turn it up and there are a few ways to go. If this is as far as you make it, at what point does dynamic compression TYPICALLY become an issue with boost?
The car is a 2001 Z06 (auto swapped) and the basics are a 370ci with flat top pistons, 243’s, 232/247 112.5+5.5 cam with all supporting mods, return style dual fuel pump system, ID850 injectors, dual nozzle meth, and a Paxton SL1500.
I absolutely love the low end torque the current cam has because it was spec’d to make up for my elevation in Colorado. The problem is that the dynamic compression ratio is ~9.2:1 (~11:1 static). This is obviously a calculation as I don’t know my deck clearance but it’s a good ballpark. My decision point is to: switch cams (did a 2 piece timing cover when I did the blower for this reason), swap in a set of 317 heads that I already have, or switch to e85. My question is for the guys that have experience with higher compression ratios and boost and when it became an issue? Reading the plugs (BR7EF) at ~16-19* timing (lower around peak torque) with 7lbs of boost without meth, it could have taken a couple more degrees most likely. Hopefully I provided all of the necessary info and I look forward to hearing some of your experiences.
The car is a 2001 Z06 (auto swapped) and the basics are a 370ci with flat top pistons, 243’s, 232/247 112.5+5.5 cam with all supporting mods, return style dual fuel pump system, ID850 injectors, dual nozzle meth, and a Paxton SL1500.
I absolutely love the low end torque the current cam has because it was spec’d to make up for my elevation in Colorado. The problem is that the dynamic compression ratio is ~9.2:1 (~11:1 static). This is obviously a calculation as I don’t know my deck clearance but it’s a good ballpark. My decision point is to: switch cams (did a 2 piece timing cover when I did the blower for this reason), swap in a set of 317 heads that I already have, or switch to e85. My question is for the guys that have experience with higher compression ratios and boost and when it became an issue? Reading the plugs (BR7EF) at ~16-19* timing (lower around peak torque) with 7lbs of boost without meth, it could have taken a couple more degrees most likely. Hopefully I provided all of the necessary info and I look forward to hearing some of your experiences.
Thread Starter
Joined: Sep 2012
Posts: 257
Likes: 18
From: Colorado Springs, CO
Thanks for the reply! I’m not necessarily looking for people’s opinions on what they think it needs and I’m certainly not going to let someone tune my car through a forum haha, I’m more looking for information from people who have went against the grain and used strong “n/a” cams with centrifugal setups. As I said before, I love the low and midrange provided by the cam and it seems to compliment the boost curve of the centrifugal supercharger but at some point I feel that I will run out of octane and I’m just curious as to when that “typically” happens in setups like this.
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Joined: Feb 2015
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DCR is only a small part of the equation assuming you are wanting to avoid detonation. Fuel octane, IAT, and cylinder temps, pressures and CC design (softened chambers) are key contributors to achieving MBT without knock.
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Thread Starter
Joined: Sep 2012
Posts: 257
Likes: 18
From: Colorado Springs, CO
Thanks, the cam card is based on .050” and I doubt calculating it with the .006” specs is going to get me to the widely accepted ~8.5:1 dynamic compression anyways. Please don’t get too tied up on my build specs and math, I want to hear about YOUR success/failures with higher compression and boost. For the guys that replied, what is your current compression ratio (static/dynamic) and at what point, if any, did you decide to lower your compression and go more boost? What was your deciding factor on that? Was it purely guidance from someone (forum or an engine builder) or were you at a point of having to run such low timing or something similar that YOU made the decision?
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