How does supercharging affect target DCR?
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
How does supercharging affect target DCR?
For the sake of argument let's say the target pump-gas DCR is 8.5:1. So we cam the car accordingly based on static CR, IVC, stroke, etc. Do the same rules apply for a supercharged combo? Is that why popular thinking with a 9.5:1 blower motor has most guys camming it with about 220/230@.050 duration (to keep the DCR up with the lowered compression)? Is there any affect at all to target DCR when boost and meth injection are part of the equation?
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
For the sake of argument let's say the target pump-gas DCR is 8.5:1. So we cam the car accordingly based on static CR, IVC, stroke, etc. Do the same rules apply for a supercharged combo? Is that why popular thinking with a 9.5:1 blower motor has most guys camming it with about 220/230@.050 duration (to keep the DCR up with the lowered compression)? Is there any affect at all to target DCR when boost and meth injection are part of the equation?
PR = (boost / 14.7) + 1
This is the very simple way to look at it and not complete picture.
Mike
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
If I wanted to dealve into it a little deeper, is there a source that might make it understandable to a simple mind?
Safety Car
Joined: Sep 2006
Posts: 4,075
Likes: 6
From: Wilmington NC
I just bought the book "Supercharged" by Corky Bell on Amazon for about $23 and it has all this info and a lot of other good info in pretty simple form. It was a recommendation by Forum member PowerLabs.
Last edited by j_digi454; Dec 19, 2010 at 11:54 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
Not sure I'm following what you're saying. DCR (Dynamic Compression Ratio) is the measure of the 'actual' dynamic compression ratio the engine experiences while running. DCR applies to normally aspirated engines as well and it has everything to do with the effects of cam timing on static compression ratio. A motor with 11:1 SCR can have 8:1 DCR. So, if the optimal DCR for a pump gas N/A engine is 8.5:1 to stay out of detonation, how does the pressure ratio associated with adding boost affect that optimal DCR?
Thread Starter
Drifting
Joined: Jun 2008
Posts: 1,565
Likes: 111
http://www.empirenet.com/pkelley2/DynamicCR.html
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
Pat Kelley's DCR calculator is a great resource....
http://www.empirenet.com/pkelley2/DynamicCR.html
http://www.empirenet.com/pkelley2/DynamicCR.html
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
Not sure I'm following what you're saying. DCR (Dynamic Compression Ratio) is the measure of the 'actual' dynamic compression ratio the engine experiences while running. DCR applies to normally aspirated engines as well and it has everything to do with the effects of cam timing on static compression ratio. A motor with 11:1 SCR can have 8:1 DCR. So, if the optimal DCR for a pump gas N/A engine is 8.5:1 to stay out of detonation, how does the pressure ratio associated with adding boost affect that optimal DCR?
Mike
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
Pat G. specced me a blower cam a few months back. It was for my iron block forged 6.0L in my GMC daily driver. Maggie blower at 8psi. Specs were 214/224 116LSA. Static c/r is 10.5 and he calculated the dcr at 8.15. He also did the cam in my vette 219/231 .607/.617 115lsa. I looked a little last nite, but couldn't find the recommendation sheet that shows the exact timing events and dcr on that set up.
Safety Car
Joined: Mar 2006
Posts: 4,448
Likes: 4
From: Sarasota Florida
St. Jude Donor '06
The DCR on a boosted engine is a lot higher, which is why we pull so much timing, and/or add octane and/or add meth compared to the same engine NA.
When I was designing my setup I made a spreadsheet that incorporated a DCR calculator along with the timing and octane formulas from Kenne-Bell's website. It allowed me to see (at a rule-of-thumb level) the interactions between boost level, SCR, cam timing, ignition timing, and octane requirements. Once I thought I had what I wanted I ran the resulting cam and SCR by some genuine experts and they seemed to think it was pretty much spot-on for my application. But it's not running yet so who knows?
When I was designing my setup I made a spreadsheet that incorporated a DCR calculator along with the timing and octane formulas from Kenne-Bell's website. It allowed me to see (at a rule-of-thumb level) the interactions between boost level, SCR, cam timing, ignition timing, and octane requirements. Once I thought I had what I wanted I ran the resulting cam and SCR by some genuine experts and they seemed to think it was pretty much spot-on for my application. But it's not running yet so who knows?
