Ok here is the skinny. I have a C5 with a super low compression motor. I am running a Callie's Dragonslayer crank, Compstar H beam rods, ARP studded hardware assembly, Diamond pistons and rings with lowered ring landings, Comp Camshaft and springs specs on cam are 218/229@50 112 center and 526 lift, the heads are ported and polished but are other wise stock LS1 heads. The intake is a FAST 92mm but is very much ported with a 102mm LS2 throttle body. The supercharger is a Procharger D1SC with a 3" custom pulley. I run a full 8 rib pulley system with a ATI Superdampner crank pulley (that of course is pinned). There are two high output Racetronics fuel pumps located in the tank, the second fuel pump is called for when 8 psi is attained. Also @ 7 psi I inject 100% methanol via a 150 psi pump, Mfg is Snow Performance with a 625ml/min nozzle. Siemens DEKA 60 lb fuel injectors, Centerforce clutch and pressure plate, 3/4 " stainless steel headers with a 3" X pipe and Corsa Tiger Shark exhaust, no cats. There is no mass air meter, tuning is by Jeremy Formato and he uses speed density tuning.
With all of that said the displacement is still 5.7.
The problem is we were on the dyno yesterday and all is well and making 623 rwhp @ 4800 rpm then we cannot hold the 15 psi of boost. All of a sudden the boost drops off to 12 psi. It doesn't seem that the problem is belt slip but really am not sure. The BOV is a new one from procharger rated @ 0-25psi. I want to run 20 psi but how can i find out why the boost is not consistent? This motor combo should develop 730 rwhp. Can anyone help. By the way this one fun ride!

 

More info.

What do you mean by super low compression ? as if you are lower than say 9.0:1, then you are far too low.

Boost suddenly dropping off could be either belt slip, or something like a boost leak ( BOV leaking for example )

You have no need for a TB that size either, that is massive. Stock is more than adequate.

Probably no real need for meth below say 15psi either, even more so as you state "super low compression"

So what is your CR ? What sort of intercooling do you have ? Any details of the blower drive ? Any signs of black dust indicating belt slippage ?
What sort of belt are you using ? Is it installed correctly and all tight ?
What about air filter/induction ?

And I personally dont think the 60lb injectors would be ok for your final goals of 700rwhp+

 

9 to 1 is the compression, I am in south Florida and the meth cools the intake temperature besides helping the octane content of the combustion air. So far I do not see where the injectors are beyond their pulse rate (they are now @ 68%). No black dust, new belt Gates 8 rib, installed correctly with variable tensioner active and set according to ATI specs. After reviewing the issues for a few days I believe that there are leaks at this higher boost generated around the existing hoses, they are a few years old. Also they have those worm screw clamps. I will replace all hoses and change the clamping devices to an industrial type. Any ideas on where to locate these clamps?
Thanks
Ed

 

Worm drive clamps are fine. You only nead more, if the hoses are actually blowing apart.

Although if you wanted T-bolt clamps, Im sure some of the site sponsors could supply.

 

Cap off the tubing after the blower and at the TB. Pressurize and listen for leaks. Check ANY rubber elbows for tears. Verify you do not have an inlet restriction. Let us know the results.

 

with a D1SC and a 3" custom pulley, its more than likely belt slip with a 3" pulley. On my buddy's car we see 15-17psi of boost with a 3.75" pulley on a D1SC(750rwhp) and A&A's new bracket, stock size 8 rib balancer and 5.7ci. motor. Your better off with a bigger crank balancer pulley(8" pulley) than such a small 3" pulley..

 

I agree. If the dyno graph has peaks and valleys (highs and lows) then you are seeing belt slippage. We typically see belt slippage problems when trying to use a blower pulley any smaller than a 3.55. Bob

 

When you say bigger crank pulley...do you mean the blower pulley? I'm confused.

 

Got under the car and started to tighten clamps. Some of them were several turns loose. Tightened all of them up. Back ti dyno.

 

Ment bigger overdrive crank pulley. 8" Innovators West balancer, it overdrives all the accessories and blower by 10%. Lets you run a bigger pulley on the supercharger and still spin it faster..

 

I would say it sounds like belt slip mine had the same problem at 12-13 psi 3.85 pulley, then I got the new A&A style bracket and a 3.75 pulley and the boost is now at 17psi and no SLIP!!

 

 

Another vote for belt slip, 3" is tiny especially for a D1. 623@4800 is going to be a lot more than 730 when you get the issue fixed methinks