My new engine is on its way and the dyno results were pretty good.
Max BHP was 422 on the dyno.
What BHP should i see at the wheels of my 85 TA?

PM

 

What transmission are you going to be using? With an auto, I'd think about 350-375 at the wheels would be pretty attainable.

 

Sorry,should have said...T56 6speed manual
PM

 

Probably about 360-380 then. Figure 10% power loss and you're right at 380.

 

I dunno whats with using % all the time... not knocking anyone, but I mean, look at it this way:

If you use the 10% figure, a 500hp engine would lose 50hp to drive a tranny. The same tranny driven by a 300hp engine only uses up 30hp.

That cant be right, can it?

It will take (to pick a random number...) 30hp to drive it, regardless if the engine has 300hp or 500hp or whatever.

 

Actually, the truth is somewhere in between....

There are things that are a constant source of loss (?? ... bad combination of words), such as the auto trans pump; doesn't matter what the engine HP is, the pump uses up x amount of power. On the other hand, there are also things such as friction in the ring & pinion; the harder those are getting smashed against each other as they rub, the higher their loss. So the true number will end up being a combination of both HP-independent and HP-dependent losses.

For reference, there's alot more that goes into what an engine makes after it's been put into a car, compared to what it makes after installation, than just "drive line loss". On the dyno, there's no power steering, often no water pump, no alternator, etc; there's a more or less unlimited supply of fresh cool air; the exhaust is usually far less restrictive than what's in a car; etc.

A guy I knew owned a chassis dyno, and one of his racing buddies owned an engine dyno. They had alot of friends in common. These people would build a motor and get it tested on the engine stand, then put it in their cars and tune them on the chassis dyno. According to the chassis dyno owner, the lowest difference he had ever seen between an engine stand # and a chassis #, was 22%. He said most stick shift cars would show about 25% difference, and most auto cars about 28%. Those were of course cars with relatively good exhausts and stuff, like you'd typically find people on this board using who were serious enough to get their engines dyno'ed on a stand; not a bunch of factory 2-barrel exhausts.

Alot of this has also to do with the way it's measured. Engine stand numbers are often steady-state, while chassis numbers are usually measured while allowing some fixed rate of change of RPMs, typically 300 RPM/sec, to duplicate the condition of accelerating the car (as opposed to running a generator at 3600 RPM for hours on end or something). The faster the engine is allowed to rap up, the lower the measured HP # will be, because then the inertia of things that spin will consume a greater proportion of the engine's output.

So, if I was the kind that was bold enough to predict the future, I'd say that a motor that does 422 HP on the water brake, should realistically be expected to put about 320-325 HP to the wheels, in a real-world car using normal measurement techniques.