What needs to be addressed, in order, to get the LT1 engine to be able to rev higher.

Is it the valve train that's the main limiting factor? Crank and pistons?

What could be reasonably attained?

2nd Question: What's a good estimate, or established figure, for drivetrain loss between the engine and wheels on an LT1 M6 car?

 

Fred is likely about to drop a bomb of knowledge, but I will tell you what I know. The stock lifters, 3/8th rocker studs and springs are prone to valve float at higher RPM. Back in the day, AFR came out with a kit they called HydraRev that was intended to help stability, but it was still recommended to work on the springs/heads. LS7 lifters are the current replacement for our engines and have been shown to support 7k RPM. You would also want to change your rocker studs to 7/16, and upgrade to roller rockers. From there, the spring selection is going to depend on the over all build.

The bigger question is why more RPM? You will need heads that flow enough for the RPM to be a benefit, and cam that can use it. One thing always leads to another

 

The easy one first - I had the advantage of seeing the results for my engine on an engine dyno with full exhaust, and then on a chassis dyno. Losses, logically, varied with HP. There are "constant" losses (mass) and "variable" losses (friction).. With a manual gearbox, as HP increases, loss as a percentage decreases. I lost my original file on this, but remember the results fairly well:

At 490 flywheel HP (all motor) loss = 13.3%

At 614 flywheel HP (1st stage N2O) loss = 12.5%

At 762.5 flywheel HP (2 stages N2O) loss = 11.9%

Engine dyno did not include:
- alternator
- power steering pump
- A/C compressor (deleted from vehicle, so not a factor)

Drivetrain loss is affected by mass of the components behind the flywheel. My setup for these pulls was:
- McLeod Street Twin w/ steel flywheel
- Mark Williams 3" chrome moly driveshaft
- Strange 12-bolt w/ 3.73 gears, Eaton HD posi
- OZ Monte Carlo 17x9.5" wheels w/ 275/40-17 Goodyear GS-C tires
- factory spec lubricants, no synthetics

For bolt-on engines, closer to factory HP, I generally use 13.5 to 14% when helping people estimate injector requirements, etc.

There are other variables....
- dyno acceleration of engine RPM/second
- type of dyno
- consistent use of correction factors

Factoid - the T56 was replaced with a TH400 with non-locking converter (gears were 4.10, wheels were 17x11 AFS ZR1/GS replicas w/ 315/35 BFG Drag Radials) Loss at 762.5 flywheel HP increased to 22.3%. But the torque multiplication of the converter and elimination of my clumsy shifting made up for the difference, performance wise..

 

Good to know all. In reverse...

I was using 15% loss so I was close in that regard. It's interesting that the actual measured loss varied like it did.

I'm pretty sure I'm flowing pretty good as I have the LE2 head work by Lloyd Elliot, he ported my intake, and I've got the 58mm tb. I'm running 1.6 true Scorpion roller rockers, Comp Cam lifters and pushrods. And long tubes, no cats, 3" exhaust.

I do have ARP rocker studs but I think they're still stock
size. Also I don't have guide plates which I probably should do. I've dyno'd up to 6400 with no adverse effects and I was gaining power. I know the times I had on the drag strip I went over 6400 and AFAIK I didn't have any detrimental effects either on the run or afterwards. I've since bought a shift light and will install before any track time.

My T56 has been rebuilt and beefed up some by RPM Transmissions in Anderson, IN and I have the Strange 12 bolt so I'm pretty covered there I think.

More RPMS makes the wheels turn faster and gets more out of each gear.

Fred, I'm curious why you put in 3.73s when everyone keeps saying 4.11s or 4.56s are the way to go. If I'm reading right the 3.73s we're with the m6 and then you went 4.11s with the a4?

 

If you are not running guide plates now, then you have self aligning rocker arms, do not guide plates with these rockers as it will cause binding.

If you were on a dyno and were not seeing the power curve roll over, you should be okay to go a higher on the RPM. Valve float will cause the power to drop at RPM which you would have seen in the dyno. I would also assume by the parts you listed that your push rods are hardened? If not, that would be the next weak point.

 

Because I made a mistake.

Was too concerned about gas mileage. Bought the Strange in 1997 or 1998. After I had it for a while, I realized the 4.11's would have been a better choice.

 

I think we might should frame this! Lol

 

Hey... I will admit to many mistakes . Things I should never have bought/installed soon after buying my 1994 Formula brand new:

- Hypertech Power Programmer

- ASP underdrive pullies

- adjustable fuel pressure regulator

- throttle body airfoil

- Electromotive Super Direct Ignition / Opti Eliminator

- Taylor 409 (10.4 mm) Pro-Race spark plug wires (to go with the Electrmotive)

- JBA shorty headers, CARB-EO

- ACPT 4” carbon fiber drveshaft

They say “we learn from or mistakes”...... Damn right ! But it’s a costly education.

 

No Fred, don't say shorty headers!

 

It's truly helpful for us that you have tested and evaluated those products. Therefore they aren't mistakes but rather field use reviews. Some of them intrigue me like the under drive pulley system.

That could actually be a good section; the "Seemed like a good idea" forum or stickie. It could include some of the free mods.

Bad profucts/mods and why they are not recommended.

 

Do you remember the WS6.com website, where the owner did dyno testing of a lot of the free mods/low cost bolt-ons? If newbies would just read through that it would show them what works and what doesn’t. Unfortunately it doesn’t show the downsides of some of them - charging problems w/ underdrive pulleys, throttle body airfoils that block the idle air passages, etc.

WS6.COM LT1 Trans Am

 

no I didn't know about that info. I'll check it out.

 

Fred,

I remember reading another thread where you mentioned your regret with the 3.73 gears so when I changed my rear end ratio last month I went with 4.11. I am one of the newbies that got a step ahead from your experience. Thanks!

 

Thanks for the positive feedback!