I'm currently planning some upgrades to the Camaro's engine. I have a new set of RHS aluminum heads and a stouter Comp roller cam. I'm trying to figure out whether I need to make some short block changes as well.

With resepct to DRC, I searched, but did not see, any discussions about rules of thumb for supercharged engines.

I ran my numbers through both calculators and the results are as follows:

Pat Kelly's calculator: DCR = 6.33:1 (8.2 static)

rbracing calculator: DCR = 7.5:1 (N/A) and 12.1:1 (9 pounds of boost)


It looks like rbracing's calculator does the following to account for boost:

14.7 + 9 pounds of boost
----------------------------- = 1.61 "adjustment" factor
14.7 atmospheric pressure

Applying the correction factor to Pat Kelly's calculator results = 10.2 DCR under boost.

Obviously, the under boost number is outside of the range Pat recommends (7.5 - 8.5 on 91 octane), but I would think that any supercharged engine would be outside of the range.

is there an acceptable range DCR for boosted apps? id like to see intake air temp (intercooled vs non) and density factored (climate, water injection, etc) in somewhere. know anyone wit these kind of calculations?

thanks

My main concern is making sure that the engine is not a dog while driving around without boost. However, I do understand that the engine can only be built one way: perform N/A without or perform under boost.

Gene,
What type of blower are you going to do?

I had all the same questions and more 3 years ago when I began my project.
Did countless seaches, talked anyone I could, and found nothing that was real diffinitive. I tried 14 lbs of boost on a 9 to 1, EFI, intercooled SBC, with 35 degrees of total timing, on 91 octane. It detonated! Not audible but there were specs of aluminum on the plugs.

As we all know every combo is different, but I have some basic thoughts on what works with most centrifugal superchargers.
At 8.2 static, 9 psi, pump gas, and take out 3 to 5 degees of timing with between11.5 & 12 to 1 AFR under boost, should work ok. There are so many variables, post more details. EFI or carb, Roots or centrifugal, intercooled, pump gas octane or race gas?

Maybe Jody and others will chim in, its mostly opinion and a little experiance on my part. Any questions I'll be happy to try to help. --Bill.

Bill,

Please click on the website link in my signature. All of the car and engine specs are there. I have outlined my planned changes below.

The current combination of parts has worked great. I have had the blower on for almost 8 years (I bought my blower when the P600 was the only model Procharger made!). The engine runs great, I would just like a little more power. My goal is another 100 HP on top of what the engine already makes with the same amount of boost (9psi).

I know the L98 heads have probably cost some power, so I bought the 200cc RHS aluminum heads (RHA bought ProTopline). Also swapping to a set of Doug's 1 3/4 primary tube headers. Planning on 3 inch exhaust pipe from headers to an "X" and then 2.5 inch from the "X" to the tailpipe.

The new cam is a Comp hydro roller with the following specs:

Lift = .541/.541 with 1.5 rockers
Duration at .006 = 280(I)/294(E)
Duration at .050 = 230(I)/242(E)
LSA = 113
Intake CL = 113

Will be updating valvetrain to include Comp ProMagnum roller rockers and Comp pushrods.

The only other planned mod at this time is a hydroboost booster to replace the vaccum assist on the power brakes.

I would really like to build a 383, but that is not in the cards at this time.

I've actually never figured DCR on a blown motor. I do know the charts you see on BDS, etc. are very conservative as far as how much boost can be run on pump gas.

At 9 to 9.25:1 compression you should be able to easily run 9-10 psi of boost on even 91 octane, with timing close to 30 degrees total, maybe more. Keeping the A/F in the 11.6 to 11.8 range provides a bit more safety factor without costing much power.

As far as your cam it will benefit to have 10-12 degrres more exhaust duration @ .050 and a bit wider LSA (114 or so). That cam is fairly mild but will work well.

Are you changing blowers? With the P600B you are limited compared to their newer blowers, but the cost to change at this point is a bit for sure. I started having issues with my P600B when I tried to run over 9 psi. By swapping heads and exhaust you may have to spin the blower faster to maintain the same boost, so watch for belt issues.

Jody

Is the 10-12 degrees more exhaust duration the same given stock heads vs aftermarket?

thanks

Is the 10-12 degrees more exhaust duration the same given stock heads vs aftermarket?

thanks


Even good heads like the extra exhaust duration with a blower, but if it had an excellent exhaust port it would not be as critical.

Jody

Ok Gene,
I see the specs, and your changes will work well to get the motor to beathe more.
Like Jody said, you will need to spin that P600 a little faster to maintain your boost level.
Can that be done? Smaller blower pully would do that, but then there is a possibility of belt slippage. Try it, you might need to upgade the blower later.

Good luck. --Bill.