STL94LT1

My heads/cam LT1.

353 rwhp trapped 117 mph
374 rwhp trapped 119 mph

All of the talk about LT4's being underated. Stock M6 LT1's seem to dyno 30 hp less than LT4's. So, I guess that also makes LT1's underated.

Same day same dyno I witnessed a stock LT4 dyno 296 rwhp and a stock M6 LT1 dyno 272 rwhp.

Tom400CFI

My LT1 did 279 RWHP. Either it's more than 300 hp...or I've got some ridiculously efficient driveline.

SurfnSun

Tom400CFI

Say what? Who was comparing? What was being compared?

SurfnSun

Tom400CFI

Ahh...I wasn't making that comparison...or any. STL94LT1 threw out there that maybe LT1's are under rated too. IDK that they are in general...but I threw my data out there just to show that maybe some are.

SurfnSun

yeah, my comment wasn't exactly pointed at you but I should have been more clear. I think the problem lies in the assumption that a 15% correction factor is accurate for a manual transmission. While we all use it it's probably on the high side. I also think there are probably a lot of generous dynos out there. Correction factors never seem to overcome either perfect air or extremely bad air there's always a difference.

Tom400CFI

I agree with everything you just said....especially the correction factor that we all use; I think it's bogus. Based on my observations, it's more like 7%-9% drive train loss.

As for dyno's being on the high side...I'd say that is quite possible...even quite likely. But if they ALL are high, then comparisons can be somewhat valid. I don't doubt the numbers that I observed b/c my results at the drag track have been aligned with the dyno numbers. Everything seems to "jibe". But if you really want to know, trap speeds don't lie.


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bjankuski

I do not want to get too far off target but the correction factor all depends upon what combination is being tested and the dyno's being used. My 555 BBC drag race engine made 774 HP on the engine dyno and 636 RWHP on the chassis dyno. 636/774 = 18% drive train loss. This was a powerglide combination with a 5000 stall. Car weighs 2550 with driver and runs 8.70's at 151 MPH. Math says it should be 725-750 HP to run this ET.

Tom400CFI

Surfnsun and I were talking about stick shift cars. But even they are affected by variables...the largest being the weight of the drive train, IMO. My C6 (LS2) did 361 wheel, Our CTS-V (LS6) did 338 at the wheel (same dyno). Why the big diff? V has a 45 lb flywheel, a 40 lb drive shaft 14" rotors, heavy wheels....heavy. And there goes your power on an inertia dyno.

MatthewMiller

And U-joints in the half shafts have to soak up a little power, too. I was going to suggest that the 15% "correction" is probably often bogus, but may in fact be closer to accurate for any ZF6-equipped C4 due to the 40lb dual-mass flywheel and fairly heavy wheels. Even in 4th, I imagine the drivetrain mass soaks up a little power (though not nearly as in 1st or 2nd). If I find some spare time (hah!) I will have to try to put some math to it one of these days.

OTOH, my own C4 at least doesn't seem to have a lot of rolling friction. Even with sticky 315 tires, it seems to take very little to move it by pushing (or very little grade), and it seems to roll forever in neutral.

856SPEED

I have also heard the final gear ratio in the differential will have an impact on rwhp dyno tests. Some have told me a lower gear ratio vs. a tall gear will show more torque and lower hp numbers all else being equal. But I honestly don’t know for sure.

Tom400CFI

Maybe. I'd love to see the calcs on this.



That is true. A lower gear ratio will typically hurt the final number (tq and hp) b/c the lower ratio allows the engine to accelerate faster. Doing so you consume more hp in the acceleration of the rotating assy, FW, etc.

rocco16

I wouldn't consider the LT-4 to be rare in any sense of the word. Certainly there aren't as many LT-4's as there are LT-1's, but they put LT-4's in a lot of cars....and not just Corvettes.
I would say stock C4 LT-4's put out somewhere between 340 and 350 hp. Keep in mind that there is NOT a lot of variation between production engines....certainly not more than about 2%....so claims of stock LT-4's dynoing at more than 350 hp are to be taken with a grain of salt.

rocco16

Same day, same dyno, I witnessed a stock LT-4 dyno 311 rwhp and a stock LS1 (1997 C5 M6, rated at 345hp) dyno'd at 314. This was at sea level and about 65 degrees F.

rocco16

And I think you're both right.

rocco16

Still a fun thread....

cv67

Car making at the tire whats claimed at the crank...here we go again. Sorry guys bs.
I dont think they are any kind of rare ooh ahh collectible. Good part is a simple hotcma minor headwork headers they can run pretty well.
I see a lot of fs ads with guys wanting huge money for a mid mi C4. Good luck as a nice C5z is in the same price range
With that said if I found the right deal on an LT4 Id keep one as a daily beater.

KyleF