Background: In 2003 I had my car dyno tuned at Speed Inc with the following combo:

Combination Motorsports Stage II heads, 54cc chambers
Comp XE 224/230 cam .536"/.544" 112 LSA
Comp 987 valvesprings
52mm TB
Unported, stock intake
GMPP CAI / Trickflow elbow
Hooker LT's
Mufflex Y
Hooker Catback
Motive 4.10's in stock 10-bolt

That setup yielded 366 RWHP / 355 RWTQ:



I was pretty satisfied with the numbers, but I wanted a bit more power. So I called up Cam Motion and talked with some folks about getting a more aggressive cam. I was fine with sacrificing street manners since I only put about 3000-5000 miles on the car in a year.

Here was the cam that Cam Motion recommended: 234.5/242.2 .575"/.596" @ 112 LSA

Most of you will recognize that this is very close to the GM 847.

I installed the cam and made a few tweaks to the setup. I returned to Speed for a re-tune last week with the following combo:

Combination Motorsports Stage II heads, 54cc chambers
Cam Motion cam
Comp 977 valvesprings, installed at Comp's recommended height
58mm BBK TB
Ported intake manifold (runners and TB opening)
30# injectors
GMPP CAI / Trickflow elbow
Kooks LT's
Kooks Y
Hooker Catback
Motive 4.10's in stock 10-bolt

I was personally shooting for about 400 rwhp. However the car fell extremely short: 368 RWHP / 337 RWTQ!




I'm in shock, but I'm not giving up. I just need to figure out why this setup didn't make more power.

Before I start swapping parts, I have some general questions:

1. Jim at Speed mentioned that the fuel pump is dying and that I was losing fuel pressure. The car is up on jackstands and I'm taking out the tank as I write this. What kind of power loss would I see from that problem alone?
2. Is this cam just too big for stock cubes? I was under the impression that with my top-end and headers the motor would be able to move enough air.
3. The bottom end has 65,000 miles on it. However, it burns almost 2 quarts of oil in a little over 1000 miles. The last time I checked compression (around 2005) all cylinders seemed even. Could this be causing a huge power loss?
4. Could valve lash contribute to this problem? The car does not appear to be hesitating.
5. Is there any reason to believe that plug/wire selection might be robbing a few hp?
6. When I went on the dyno my 10-bolt was having some serious issues. Could that have contributed to power loss?

Like I said, I'm not happy with the numbers, but I am determined to learn from my mistakes and learn how to put together a fast car. Any advice would be appreciated.

EDIT 1 -- I just checked my notes from the machine shop. Chamber size was 54cc, not 58cc.

 

what lifters are u using?

Your rockers/valve lash could be too tight, and i dont c y a bad 10 bolt wouldnt be robbing u of power. But u are losing almsot 40rwph . U should def be at the 400rwhp mark.

Valve lash is a common power robber when people do cam swaps.

reason y i asked what lifters is that Comp lifters only require 1/8 turn after zero lash as where stock replacements require 1/2-3/4.

 

This comment comes up a lot. I have heard that the looser you can set a rocker without it clicking is ideal. I have my stock lifters set at 1/4 PZL. I have been told looser and I have been told tighter, it just get confusing.

 

If I had to guess I'de say your heads are holding you back, What do they flow? And what head gaskets are you running? 58cc chambers is pretty big for the stock bottom end.

 

I don't have flow numbers on the heads. They have 2.00" / 1.56" valves.

Lifters are the original factory ones.

 

I'd readjust the valves, take it to the track and see what it runs as long as your fuel ratio is right and then take it back to the dyno.
Comp R's are not just a blanket "1/8 turn past lash..." I believe it is .004 to .006 past lash. Depending on what studs you are using can vary your adjustment.

On that first dynograph... What happened after 6200rpm?

 

Guys, that first dyno chart looks like mine did, when I had valve float. Only his torque line is flatter that mine. I fixed the valve float with a nice set of 06' Comp 918s.

 

Yeah, this is a case where just switching the valvesprings on the first setup would have you much farther ahead, considering your down almost 20 ft lbs at peak and 40 ft lbs @ 3000! Just wondering does the car feel slower untill you "get on the cam"?

Bret

 

One more point. I too had those 987s before the beehives. They didn't work to well.

 

With the larger cam I bet your dynamic compression ratio took a hit. That would account for some of the lost power in the low range. Maybe you should have milled the heads some to regain the compression?

 

Personally, I'd go back to the first cam, with some Pac beehive springs.

 

Not quite!

 

Um considering stock is 54cc then yeah, and if he didn't use a thin head gasket his compression is going to be way too low, expecially for a cam that size.

 

Pretty big to me is 64, or 76!

 

58 versus 54 isn't going to make that big of a difference....certainly not going to put the compression too far out of wack for that cam. It is too low for optimization, however IMO. What's the quench? What final DCR did you end up with?