Scarab1988

Hello gang.
Does anyone know the horsepower loss between the flywheel and the tires on a '96 Corvette with an LT-1 , with a 4L60E ( I've been told that is the stock transmission my C4 came with ), Dana 36 with 3.07 gears ?
It's supposed to have 300 rear wheel horse power ( minus ? from age ).
I've sent this question to a couple of websites that their forte is baseline Dyno testing, then changing heads, cam , headers, intakes / fuel injection, then re-dyno testing to show the modifications results in increased power.
Have not heard back from them ....... yet, but it's been quite awhile, so I'm not optimistic.
I've been told you lose between 125 to 150 horsepower depending on who you ask.
Do any of you folks know the answer to this question?
It would suck to go put a new 400 flywheel horsepower engine in the car, and end up going slower.
Thank you in advance for your help.

John A. Marker

With an automatic transmission you will loose abut 15% from the flywheel to the rear end. Also be aware that Dynos are different. The Mustang dyno is known for being stingy on numbers. But at the end of the day, it is just a number. What important is how does it perform when your at the track.

vader86

On a dynojet, you can expect about 15% loss for a manual, 16-18% for an automatic.

vette196

Does a good torque converter (more efficient) make a difference in HP loss?

bjankuski

a stock lt1 auto will make 260 to 270 hp at the tires on a good day, 300hp was the flywheel rating.

GREGGPENN

Factory ratings are not rear wheel.

Scarab1988

In 1972, GM changed from measuring horse power at the flywheel, to measuring rear wheel horse power. When did they change back to measuring horsepower at the flywheel?
​​​​​​Thank you for the estimated percentages of horsepower loss. Is that based on the assumption of the engine being 300 flywheel horsepower?
I have been out of building race cars for a long time, but from personal Dyno experience, I know it takes 75 +/- horse power to drive a stock turbo 400 with a basic shift kit. That transmission consumed 75 horsepower whether it was bolted up to a 300 horse power motor, or a 500 horse power motor.
Has anyone run any dyno tests to see specifically what a 4L60e consumes?
Thank you gang

84 4+3

It is my understanding that a 4l60e/700r4 is around 18% drivetrain loss. That's just a rough number. Could be 16 could be 20. The viscous coupling plus all the moving fluid resists changes in motion yada yada so as you hit it it takes more away, more energy to spin those parts. As for dyno tests, pretty much every darn vehicle gm has built since 96 or so has used a 4l60e if it had a v6 or v8 in front of it minus the hd pickups so I'd guess if there isn't a scientific test here I'm sure somewhere else there is. Hot rod has probably done an actual test test I'd guess...

Tom400CFI

No they did not. They changed from measuring a blueprinted engine on a dyno, that had long tube open headers, no exhaust, no accessories, an optimized carb and ignition tune, and other little tricks to maximize power...and measuring that at the flywheel, to measuring the engine as installed; meaning, with exhaust for that car, all accessories, emissions equipment, factory spec jetting, timing, coolant temp, all accessories installed, etc. AS INSTALLED...but still measured at the flywheel.


Never. They've always measured from the flywheel.


​​​​​​It's based on typical known flywheel ratings, vs same car, typical RWHP ratings. I think the number is actually less than 10%...but people typically quote ~15% loss from flywheel to tire.


There is now way that is true. You could MAYBE make that claim (X hp) at an RPM...but the trans isn't going to take the same hp at 2000 RPM as it will at 6000 RPM. I can't believe any modern auto would consume 75 hp .....and the dyno numbers prove that they don't. bjankuski above, stated that a stock LT1 typically makes ~265 RWHP. We know it's a 300 hp engine at the crank, so the trans, + d/s, + rear diff, + wheels and tires consumed ~35 hp.

bjankuski

As stated in 1972 gm changed from gross rating to net rating. Gross was measured at the flyheel but there was no accessory load, no air cleaner and open exhaust. Net rating is measured at flywheel but as the engine is installed in the car, air cleaner, exhausr, accessory load.

to figure wot power loss you can assume around 15% power loss. The higher the hp the greater the number will be. A 1000 hp drag race engine with a high stall convertor, steep gears, and turbo 400 can drop 150 through the drivetrain. That same turbo 400 behind a 350 cruising down the highway at 60 mph with street gears and a stock stall may only drop 5 hp through the drivetrain. It depends on power in and combination.

MatthewMiller

It probably doesn't change the percentage loss as power changes, but the percentage of loss should increase with increasing rpm (which, granted, may be the way extra power is achieved). The loss to friction force increases linear to the increase in input force (crankshaft torque, in this case), so the percentage stays the same. However, IIRC the loss of friction increases with the square of rpm, so that a doubling of rpm quadruples the friction losses.

To the OP, there is another kind of loss to consider on any inertial dyno (Dynojet being a prime example): losses to engine and driveline inertia. These dyno measure power by measuring the engine's acceleration of a known inertia (the drum of the dyno). However, the engine also has to accelerate it's own rotating mass plus the flywheel/clutch or torque converter, driveshafts, tires/wheels, etc. All of those things rob a bit of the acceleration. The lower the gear the pull is made in, the faster the acceleration of the driveline relative to the drum, so the greater the power loss. That's why pulls are supposed to be standardized to as close to a 1:1 trans ratio as is available (usually 4th gear).

Scarab1988

Awesome feed back !!!
When. I said it took 75 +/- horse power to run a turbo 400, that was the max net result over the whole RPM range.
I believe I still have the Dyno printout somewhere. If I run across it, I'll take a pic and post it..
I guess I should have explained that better. Sorry.
Very interesting about where the horse power is measured. Next time I see my old auto shop teacher I'm gonna tell him he lied to me 40 years ago.
😀
Thank you all again for tech support.

vader86

Not really no.

My PI Vigilante transferred basically the same amount through my 700 as did the stock TC.

MatthewMiller

A torque converter should not result in any loss on a brake dyno if it is locked. On an inertial dyno, the rotating mass of the t/c will cause a small loss. I don't know how much they weigh, but I would think it's similar to a clutch and 20lb flywheel or thereabouts. If the t/c is unlocked, then there may be a bit of slippage that causes a small loss of power. Although at anything close to peak power rpm, even a non-locking t/c should be slipping very little, if any. It would be at lower rpm where lots of slippage and torque multiplication occurs.

BTW, if you ever see a dyno sheet from a chassis dyno for a car with a very loose converter, the graphs can look very interesting. You get this massive torque figure at low rpm, which falls continuously through the rest of the pull, and the power curve can often be a nearly flat line. That torque curve doesn't represent the engine's torque, but rather the multiplication at the wheels. The power curve does represent the engine's power (minus whatever driveline losses), because the engine itself is operating close to its peak power rpm for the whole pull.

vette196

How do you like the vigilante? I have to get a TC for my build and its either Vig or Yank

Tom400CFI

Mine did too. (One of them, anyway).
*To have tq, you need a small cam, small valve, small head, 2 barrel 400 small block.
*If you do a top end on a high milage engine, you'll "blow the bottom out of it".

^Those were two of his favorites.

Tom400CFI

This is true, and one reason why chassis dyno numbers are a tool..."evidence" if you will of where you combo is.

I've had/stlll have 2, 400hp/400tq cars; an '06 'Vette, and an '05 CTS-V GM rated both at 400/400 as installed, at the flywheel. But the 'Vette dyne'ed ~30 more hp at the wheel. Why?

Lighter drive train. Caddy has a 45 lb flywheel, plus clutch, it has a ~50 lb driveshaft, it has 14" rear rotors, heavy, 18" wheels and big 6 lug hubs with big bearings. All that consumes hp to accelerate. At a steady state both cars would show about the same RWHP.


.

vader86

I wish I could have gotten the 2000rpm TC out of the 86 and put it in the 88 instead of this Vigilante, because I drive on the street and an aggressive TC that locks up higher is not really the best for driveability on a street car.

The first one had a lot of shudder at lockup, felt like going down a gravel road. Called PI and they replaced it. The 2nd one has been fine.

Tom400CFI

For a data point, THIS GUY just did 278/336 with an auto.

bjankuski

On that dyno, on that day with whatever setting were chosen. The real point of a dyno is to compare changes to each other on the same dyno to see what your changes did. It is hard to compare actual dyno's to each other because you are not sure how they are set-up. As long as the set-up on the dyno you are using is the same each time you use it the changes will be shown.

Let me point out that in my area we have two dynojets and two mustang dyno shops other then the shop I use. Each one of the other shops dyno's will read different numbers because over the years they have changed their calibrations to reflect the numbers they wanted to show. Hopefully they leave the calibrations alone after they changed them so back to back runs on different visits are at least useful and not biased one way or the other.

Too many whiners out in the world expect to see real high dyno numbers and they complain when they do not get the numbers they expect to see. So what does the shop do, they change the dyno reading to display higher numbers so the customers are happy. Write, wrong, who knows, but it keeps customers happy and the shop gets return business.

I was at a dyno day competition a few years ago with a shop that had a brand new Mustang dyno installed. On it witnessed a Mustang owner complaining bitterly about the low reading on his Mustang because even though he won his class his 365 ish RWHP was too low and it should have been in the 410 RWHP range. He made a big fuss over this in front of 30 people. On that same day I dynoed my Firebird and it made 306 RWHP which was low from a dynojet reading but on par for a Mustang dyno. I run mustang dyno's at the shop I tune at and I looked at the roller mass numbers entered into the program calculations and it was as it should have been at 1850 LBS. Fast forward 6 month, I went back to the same shop for quick tuning session and ran my Firebird in the same configuration as before to get a baseline run and it showed 370ish RWHP, I then looked at the roller mass and it was set at 2250 lbs. It was changed to show higher numbers so people would not whine. That is why you need to be careful comparing different dyno's to each other.