Rear Wheel Horsepower?

Hello Fellow Tacoma Junkies and Addicts:

Does anybody know what the percentage of loss of horsepower is from the Net Horsepower rating to actual Rear Wheel Horsepower? The muscle car people claim that it is about a 20% loss for a manual transmission and a 25% loss for an automatic.

Thanks in advance for all of your potential replies.

Take it easy,
Paul

 

I had my 2nd Gen RC 5-lug, which has the 2.7L and automatic transmission. I had my truck dino-tested at the 2017 Carlisle Truck Nationals and it shocked even the guys operating the dyno. My truck has 159hp at the block, and it also had about 75,000 miles on it at the time. The guys at the dyno expected my truck to be putting down about 120hp at the rear wheels, but it was making 132 at the wheels!

 

It's going to vary depending on the tranny, and it's going to vary again depending on what gear its in. 25% is as good a number as any.

 

There's a lot of factors when considering loss of power through the drive train. Most auto trans will suck 20%-30%, manual will take 15%-25%. Depends on how fresh everything is, how it's built, what clutch/converter you use. In our race truck, the motor is hard mounted for minimal torque shifting. Some guys will even say premium oils help save power. I don't know how true that is but, when you're dealing in hundredths of seconds, every little bit helps.

 

Rough estimates are just that!

 

20-25% seems to be pretty reasonable, based on all the Motor Trend shows I watch...

Although I've never really been all that concerned about horsepower numbers - I guess that's why I drive a 14 year old Tacoma, lol...

 

FWIW...

In 1962 I put a 1960 325 HP Buick engine with a 1957 standard Buick transmission into a 1953 Ford. After a few months the mechanic at the Buick dealer put the vehicle on the dynamometer. It registered 85 HP at the rear wheels. He said it would probably read a bit higher but he didn't want to take a chance on it climbing out of the rollers.

I figured 125 HP absolute maximum at the rear wheels. That's about a 61 HP loss from the engine to the rear wheels. I don't figure much has changed since then. (The old Ford ran pretty good, but it couldn't beat a hot 283 Chevy in the quarter mile...)

 

That math doesn't quote work out... I assume a typo somewhere?

 

It depends how many stickers you have

 

is the engine rated at 190HP at the crank? Because I want to say on a dyno it usually does 160 stock

 

That sounds about right. ​

Most HP ratings are at the output of the crank.

 

Here is what I understand about horsepower ratings. Gross Horsepower is measured at the flywheel without any engine amenities installed as well as no exhaust manifolds. When I am using the term amenities, I am referring to power steering, alternator and air conditioning. This is how horsepower was measured until about 1970. Then they went to Net Horsepower, which is horsepower measured at the flywheel with all of the engine amenities installed including the exhaust system. Rear wheel horsepower is the actual amount of horsepower at the rear wheels or drive wheels.

 

Hey, you're right! Don't know what I was thinking about the math. The "61 HP" should be "200 HP". I wonder how much of that 325 HP was advertising BS...

325 HP at the flywheel of a "perfect" engine minus the A/C, PS, exhaust, etc. That's about what - 250? 275 HP? Then there's the drive train loss - I can't really figure that one out -

Anyway, 85 HP at the rear wheels of a 325 brake HP engine was kind of a bummer for me...

 

Was kinda wondering why you seemed pretty happy with those numbers, lol...

 

There’s actually quite a few stock dyno tests done if you google them for the 3.4.
Most are 140-150 horses at the rear wheel.

That’s about 20-25 percent

 

This, and being a vet of different dyno’s the numbers are +/- 15 hp for ea dyno that is different as not any 1 dyno is gonna give the same numbers. My vote on best hp accuracies is hub mounted dyno’s with wheels off, hubs bolted to water cooled dyno’s, instead of the treadmill style which showed higher hp every time I have a tune. I had 168 hp on a 256,000 mile 3.4 maintained to the teeth with headers and full exhuast no cat, w/elbow mod and freshened injectors from r/c injection. I can recommend good dyno’s across the US if needed. I also believe good synthetic oil helped me keep the engine in shape w/early changes @ 3k.

 

Well you probably gain 10-15 hp from the headers and full exhaust less cat I would think