How much % loss is there from the crank to the wheels in a th400 aut approx?

1969

 

The h/p loss should be a constant amount at a constant speed, as any driven accessory. Though it would vary in relation to a less powerful motor when accelerating, as the loss would vary with the friction of the parts in contact, and that would vary with the torque being applied. 60-80 h/p is a standard loss through a drivetrain at peak.

 

Something around 15% loss for the transmission. The converter is just a huge fluid pump that makes a lot of waste heat; then you have frictional losses, etc. The THM400 was pretty inefficient....but very effective and robust. Total drivetrain loss with a 400 in the system is probably between 20-25%.

 

recently had my stock 72 BB with turbo 400 dyno'd on a dynojet. Factory 270HP, RWH was 236HP.
I'd Say a 12% loss from advertised to actual on mine

 

I agree with this assessment as I have done engine dyno and chassis dyno tests on the same motor, with a turbo 400 you are looking at 25% maybe even more, with my brand new TKO 600 I was at about 23%. I am talking gross HP ( engine dyno no accessories ) to chassis dyno

Also remember this is C3 specific, don't apply these estimates to any other car, a C5 for example might only lose 15%

 

Yepp..

I dynoed my ZZ502 at 526hp at 5500rpm no accessories (superflow). So today i have electric fans, electric waterpump, electric fuelpump, and I am thinking that maybe a 25% loss would be pretty near reality..

So around 395 hp to the pavement!

 

We recently had a dyno day at a local shop and they've found 15% to be a good rule of thumb for both auto and manual transmissions cars. I suspect that general rules of thumb are about as good as you're going to get

 

15% loss from advertised Net HP I assume. And were most of the cars newer ?

 

15% loss from what the engine was making at the flywheel per the dyno operator - and IMHO, these guys know their stuff. All new stuff; C5-C6 'Vette's mostly.

 

I've always heard 10%-20% loss at the rear wheels. My 75K1500 dynoed at 500HP at the flywheel and made 411 at the rear wheels. About 18%. That's pretty good considering it had to run through the 700r4, and an NP203 transfercase to 35" tires.

 

The actual % will depend to a large extent on the type of dyno used to get rear wheel HP and maybe even on how the particular dyno is calibrated. I had my '73 (w/TH400) dyno tuned this summer on a Mustang dyno. Shop owner knew his dyno required a 30% correction factor to get from crank to rear wheel HP. He said most other dynos are in the 20-22% range.

DC

 

MotorHead is correct....I have also done engine dyno and chassis dyno tests on my 427 SB with Turbo 400 (3000 stall) and 3" exhaust on the car. Engine dynoed 628 hp, and rear wheel hp measured 490 hp.....that calculates to 22% loss to the wheels.

 

Why do the newer cars lose less power to the wheels? I can't believe there is any difference in the transmissions (manuals anyway). I would love to hear an explanation.

 

From 72 and up the HP (neto) start to measured at RW so your car is not tuned good, you get -12% then what it should be at RW or you have some options (PS, A/C...) so it's OK.
Until 71 the HP (grose) was measured at the crank and the loss was with manual trns' ~15%-25% and with auto trns' ~20%-30%, it's depend on the options the car has.
Avner

 

Difference was the inclusion of the accessories, exhaust routing, STP differences, etc.

 

'72 net= at the fly wheel with acc and exhaust.

 

So it all depends on your question???!!!
1) What loss would you see on a RW to an engine dyno?
2) How would you estimate your net or gross motor number if you tested on a rear wheel dyno?

Most engine dynos are gross #'s. Most RW Dyno's just vary... alot sometimes.
Newer vehicles have much more efficient drivetrains and accessories. An old school motor through a TH400, PS, alt, Water pump, fan, ac, smog will be down much more than others. Then a stock pulley system from a 366 truck motor is very different in drive ratios for the accessories than say a DZ 302, L79, L88... There are 4 blade fans and 7-8 blade fans... It never ends.

 

This is true. But, on an old car you can get rid of most of that sh-- that you are saddled with. My Vette uses an alternator and high performance water pump on one belt and drives through a 5-speed manual. I actually pulled off the a/c and sold it to a forum member.

While I recognize that new cars also use just one belt, try to find one without a/c. My car gets very good power to the ground on the dyno for what it is and I attribute this in part to a lack of parasitic losses.

 

Sure, as do I. I will have a very streetable old school motor that is Naturally aspirated on pump gas car that will run solid 10's by spring/summer.

My only point was that the losses are driven by many variables. RW #'s are your best apple to apple comparison for pure HP #'s from a car. Motor building is fun too and a engine dyno is the only way then. But take it to the track for a reality check.