So I finally had the latest build of my engine tuned yesterday and the numbers were waaay lower than they should be. It was tuned by Mayhem Motorsports in Raleigh, NC and made 475/450. I was expecting hp to be in the 525-550 range.

Specs on the engine:

2000 Corvette Z51, M6 T56, 3.42 3 rib diff

402 LS2 (4.005" x 4.0")
- Callies Compstar crank/rods
- Wiseco pistons/rings, -8cc dish
- GMPP CNC LS3 heads with Comp Cams 921 springs (installed height verified), milled .036"
- Cometic 4.085" .045" thickness head gaskets
- 11.5:1 or so compression
- Comp Cams 875 lifters with (I believe- I can't find my notebook) .020" preload
- Comp Cams 7795-16 Hi-Tech pushrods, 7.375" measured for .020" preload
- Comp Cams 235/250 .621/.595 115+4 spec'd by Martin @ Tick
- LS3 intake/LS2 throttle body
- return style fuel system conversion
- Holley billet rails
- Aeromotive 13101 regulator set at 58psi plumbed after the fuel rails
- all Fragola PTFE braided stainless lines
- stock GM fuel supply line
- 60# Deka injectors
- KB BAP set to turn on at 4" of vacuum
- Melling 296 oil pump
- Edelbrock Victor water pump
- under drive pulley
- MSD plug wires
- NGK TR55 plugs
- LS7 MAF in a 4" housing mounted at the throttle body
- Vararam
- Comp Cams billet tensioner
- ARP rod bolts, head studs, and main studs
- AIR delete
- LG Motorsports Street Series 1 3/4 headers 3" collector
- Corsa dual 2.5" Tigershark exhaust
- no cats

Driveability was great from what little I drove it. After I got home from the tuner it sat until this morning when I blew a power steering hose- which will be here Thursday and will be installed on Friday morning.

I honestly do not know where to look. I was told by the tuner that I need larger primary tube headers and that they would net me probably most of my missing hp because LS3 port heads need a larger exhaust than cathedral port heads.

I want to be clear- I am NOT, in any way, bashing ANY of the companies whose parts are in it or have done work to it.

Here is they dyno sheet

 

I would say you aren't too far off with that compression. I have the same compression in a ls6,434ci and I make 572/568. exhuast is fine, bigger doesn't equal better. and LS3 heads do need a bigger exhuast valve than intake valve, but not more lift in the cam.

 

5750 rpm seems low to hit hp peak. As long as it not running out of fuel, I would go with the larger headers and a fast 102. I don't think your power guesstimate was unrealistic. Did your tuner say what similar set ups were getting? Stingy Dyno?

 

Just curious....is that enough preload (20) ?

I thought the target was always 60 with 40 to 70 thou being ok.

I'm rebuilding my 402 now with Wiesco pistons (had diamond previous). I have my preload close to .0058.

 

the ONLY HEADER you should possibly consider is a 1 7/8'. the 2" will hurt your car more than help it. you might consider a larger intake manifold. Personally, I wouldn't stress about dyno numbers until you run it down the track, unless you are building a dyno queen.

 

I think .020" is too much for the 875 lifters. I think you want to do a max of .010" with those. The CC 850 lifters should be around .040" preload.

 

The recommended preload for 875 lifters is 0.00" - 0.0125" . 0.20" was the closest I could get given available pushrod lengths. I am not 100% positive that it is .020, I am going to pull a valve cover and remeasure.

 

Comp cams isn't very good with communicating the correct preload. I called multiple times for my 850 lifters and it ranged from .020"-.080". I was running .080"ish and I just swapped out to .045"ish in an attempt to quiet down the valve train. It did seem to work.

 

Do you have the graph of the air/fuel ratio? Most tuners plot that under the HP/TQ graph

 

I do not. I am going to see if they can email me it and the tune file itself if they saved it.

 

Have you talked to Martin ?
He is pretty sharp on combos.

 

I have been talking to him quite a bit, right now he suspects it may be the lifter/pushrod combo.

 

From your list of data I have some questions:

- What is the chamber volume of your cylinder heads?

- How far above or below the block deck are your pistons?

- Whose rocker arms are you running, and what is their ratio?

- Who made and what is the underdrive ratio of your crank damper?

- Do you have flow numbers on your cylinder head's intake and exhaust ports?

And from your list I would suggest that you get rid of that Comp belt tensioner and install the standard GM spring loaded belt tensioner. And, if you go back into the engine, sell the Melling 296 oil pump, and purchase and install a Melling 10296 pump.

 

Chamber volume is 63.5cc +/- .5cc

Don't know offhand, my notebook with my engine data is MIA, but I do know they do come out of the bore some

Stock GM rocker arms

ASP 941020 under drive pulley, which I believe is 25%

GMPP CNC LS3 heads, PN 88958758 flow data from GM- I don't have any independent flow data on them.

Lift______Intake______Exhaust
0.039____27.612_____21.037
0.079____60.714_____44.679
0.118____ 87.3_______75.053
0.157____24.341____103.872
0.197___161.414____127.083
0.236___195.628____147.451
0.276___223.566____167.097
0.315___251.641____186.501
0.354___275.218____206.322
0.394___294.406____222.84
0.433___311.917____234.353
0.472___327.475____242.617
0.512___340.917____247.045
0.551___348.538____249.514
0.591___351.323____252.371
0.630___359.135____255.246
0.669___365.137____257.451

The pump is a 10296. The 296 is a Chrysler 2.7L pump that will definitely not fit....

What is wrong with the Comp billet tensioner? The GM tensioners fail all the time...

 

Thanks for the reply, and thanks for your service.

A quick calculation, assuming that your pistons are 0.010" out of the hole makes your static compression ratio 11.44:1. The block grows 0.010" from ambient to 190 degrees F. That reduces your static compression ratio to 11.18:1.

Next, LS3 heads use a 2.16" intake valve. An intake valve that large is significantly shrouded with a 4.005" bore. You won't achieve the 365 cfm intake flow with your bore size. That hurts power output. You MAY pickup some top-end power with L.G. Motorsports 1 7/8 inch Super Pro headers, but you will give up low and mid-range torque. Right now you are making approximately 1.18:1 horsepower per cubic inch at the rear wheels. You should not expect 525 to 550 rwhp. That's between 1.31 and 1.37 horsepower per cubic inch at the rear wheels.

I have a 451 with 12.0:1 static compression, a 4.185 inch bore, 413 cfm intake ports, a Mamo-ported F.A.S.T. 102 intake manifold, L.G. 1 7/8 inch headers, a Mamo specified 244/252/.732"/116 degree +3 solid roller lifter cam, JESEL 1.8:1 roller rocker arms, etc. and I am making 1.33 horsepower per cubic inch at the rear wheels.

Also, if you get back into the engine get rid of the crankshaft damper and purchase and have installed an ATI 10% underdrive damper - 917278.

I have had the stock GM belt tensioner on my 02 Z06 for 12 years without a failure. The spring in the GM tensioner is DESIGNED to exert the correct tension on the drive belt and the accessory pulleys.

You have a beautiful Corvette. Enjoy it.

 

I appreciate any help I can get. While I do like to think I know a lot about performance, there are always people that will know more than me and only a fool would not want to reach out to them and seek help.

I guess what concerns me more than the peak numbers is where the power peaks at. 5750 seems rather low to me, as I was hoping for 6200.

Honestly, my goal was to run 10.5 on motor and 9.xx on spray. If I can run 10.5 with the power I have now I will be happy.

I do intend to move up to a 3" exhaust, either the Kooks or LG and see where my numbers are from there as I know the 2.5" has to be a restriction. I called LG and talked to them about my headers and they said while the 1 3/5 Street Series isn't the best for high hp, it really wouldn't be that much of a restriction where I am at. They said the 2.5" is hurting me far more than the Street Series headers ever would.

For me, I have always known the military was my calling in life. For all this country has given me serving it is the least I can do.

 

If you want more top-end from your engine, have your engine builder retard the cam 4 degrees. But, understand that you will lose low and mid-range torque. Drive the car for a while and see how it feels to you. If you like the sharp throttle response that your present setup give you don't change anything. If you feel the engine dies on you and you drive most of the time with the engine at or above 6,000 rpms, bump the cam and install 1 7/8 inch L.G. Motorsports headers.

Good luck with your engine and thanks again for what you do.

M.O.S.: 05C40, a long time ago.

 

The power doesn't really start coming on until 2000-2500, I will probably put 3.90s in it when I rebuild my 3 rib with C6 Z06 internals. The headers will probably be upgraded at a later date. Hitting the track on Sunday so we shall see what it will run.

Right now pretty much the only thing I am willing to do inside the engine is swap the lifters/pushrods. I may go with TFS GenX LS3 heads down the road but I have a hard time thinking it would be worth it. From what I have read they are only worth like 20-25hp over the GMPP CNC LS3 heads.

Hindsight 20/20, I should have just went and bought a 454LSX long block and be done with it lol...for as much as I have in this haha. I am tempted to get a semi-finished LSX block and have it finished to a 4.005" bore so I can keep my rotating assembly, sell my current block/heads/intake and put some 6 bolt LS7 heads on and a supercharger....IF I don't build my '55 Nomad.

First thing I NEED to do is rebuild my diff. Gears are whining like a Private having to work a weekend haha!

Thank you for your service.

91B3P5W currently, 11B2P in another life lol