Need Help, Comp. Ratio for Boosted 427ci - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Vicster · 08-31-2021, 07:22 PM

I need to decide between, Diamond 2k -20cc pistons, which will give me 9.25-1 comp ratio. Or Wiseco -32cc pistons, which will give me 8.50-1 comp. ratio with a 0.070" head gasket. I think that I can get 18psi from a Kong 2650 over driven to it's max rpm, because of the cam and heads I have. The higher comp. will have better low rpm throttle response and the lower comp. will allow 3 more psi without pulling as much spark in the tune.
I have the diamond pistons already, will swap them out if a lower comp. ratio if it is really needed. Block is at shop so I have about a week to decide.
I am hoping that others with experience will chime in.

Robmnrd · 09-02-2021, 09:09 AM

Oof... Admittedly I don't have experience with a build of this capacity, but I think a couple pertinent questions to ask would be what fuel you plan on using and if this beast is track-only, drive to/from track, weekend street beast, frequent driver, or near-DD?

Vicster · 09-03-2021, 02:20 PM

Quote:

Originally Posted by Robmnrd

Oof... Admittedly I don't have experience with a build of this capacity, but I think a couple pertinent questions to ask would be what fuel you plan on using and if this beast is track-only, drive to/from track, weekend street beast, frequent driver, or near-DD?

Hello,
Fuel is 93 octane with boostane to bring it up to 104 octane, unable to find E85 in my area (have used the web sites and drove around looking). I want to break 200mph in the standing mile and it is a weekend street beast that will see some track time.

After some thought I am thinking that the 9.25-1 comp ratio would suite me better as I really like snapping people's heads back when I leave the line (so to speak). How often do you really see 7500 rpm on the street...

I guess I could compromise and get the Wiseco pistons but bump it up to 434ci at 8.75-1 to 9.0-1 comp ratio.

Thanks for replying

DrkPhx · 09-03-2021, 09:24 PM

If I was building that motor I go to 10.1-1. Better efficiency so you can run lower boost and less timing for a safe reliable set up, but that's me. You need the actual deck height to get the true compression ratio.

Vicster · 09-03-2021, 09:41 PM

Quote:

Originally Posted by DrkPhx

If I was building that motor I go to 10.1-1. Better efficiency so you can run lower boost and less timing for a safe reliable set up, but that's me. You need the actual deck height to get the true compression ratio.

Hello,

You are correct, The machine shop is aiming for 9.240" deck height as it comes 0.002 to 0.005" taller from Dart for finishing machine work. My rotating assy. comes to 9.240" so deck height should be 0.00" with the Diamond pistons and 0.005" deck height with the Wiseco pistons.

Thanks for replying

Robmnrd · 09-04-2021, 09:55 AM

If you'll be mixing your own it will likely be very consistent and safe to run, so I'd say go ahead with the higher compression ratio as it will better fit your street-enjoyment of the car (You are right, snapping necks is a lot more fun than trying to find a place to run a motor like this up to 7500rpms safely and without catching the attention of the police..).

Looking forward to pics/vids when the time comes, too!

Vicster · 09-11-2021, 10:21 PM

Thanks for the replies and the votes! I will stick with the Diamond pistons!

View Poll Results: Which pistons for boosted engine?
Diamond -20cc, 9.25-1 comp. ratio	6	75.00%
Wisco -32cc, 8.5-1 comp. ratio	2	25.00%
Voters: 8. You may not vote on this poll

08-31-2021, 07:22 PM	#1
Vicster 1000hp is NEVER Enough! Drives: 13' ZL1 Join Date: Jan 2013 Location: Seattle Posts: 665 View My Garage	Need Help, Comp. Ratio for Boosted 427ci I need to decide between, Diamond 2k -20cc pistons, which will give me 9.25-1 comp ratio. Or Wiseco -32cc pistons, which will give me 8.50-1 comp. ratio with a 0.070" head gasket. I think that I can get 18psi from a Kong 2650 over driven to it's max rpm, because of the cam and heads I have. The higher comp. will have better low rpm throttle response and the lower comp. will allow 3 more psi without pulling as much spark in the tune. I have the diamond pistons already, will swap them out if a lower comp. ratio if it is really needed. Block is at shop so I have about a week to decide. I am hoping that others with experience will chime in. Last edited by Vicster; 09-01-2021 at 11:53 AM.

09-11-2021, 10:21 PM	#7
Vicster 1000hp is NEVER Enough! Drives: 13' ZL1 Join Date: Jan 2013 Location: Seattle Posts: 665 View My Garage	ENDED Thanks for the replies and the votes! I will stick with the Diamond pistons! Attached Images

09-02-2021, 09:09 AM	#2
Robmnrd Drives: 2013 ZL1 Join Date: Aug 2018 Location: Texas Posts: 110	Oof... Admittedly I don't have experience with a build of this capacity, but I think a couple pertinent questions to ask would be what fuel you plan on using and if this beast is track-only, drive to/from track, weekend street beast, frequent driver, or near-DD?

09-03-2021, 09:24 PM	#4
DrkPhx Drives: 2013 Triple Black ZL1 / 2006 TB SS Join Date: Feb 2011 Location: MN Posts: 2,250	If I was building that motor I go to 10.1-1. Better efficiency so you can run lower boost and less timing for a safe reliable set up, but that's me. You need the actual deck height to get the true compression ratio.

09-04-2021, 09:55 AM	#6
Robmnrd Drives: 2013 ZL1 Join Date: Aug 2018 Location: Texas Posts: 110	If you'll be mixing your own it will likely be very consistent and safe to run, so I'd say go ahead with the higher compression ratio as it will better fit your street-enjoyment of the car (You are right, snapping necks is a lot more fun than trying to find a place to run a motor like this up to 7500rpms safely and without catching the attention of the police..). Looking forward to pics/vids when the time comes, too!