Drivetrain horsepower loss

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replicaracer43

replicaracer43

Grumpy Old Man
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Guys, let me first say that I have only ever had 1 engine on the dyno that I built, so I am not real knowledgeable on dyno horsepower of how its calculated. But a recent discussion has made me do some thinking, because what I am being told doesn't seem to add up to what I THOUGHT I knew! What would be the typical drivetrain loss percentage wise, on a typical 727/8 3/4 or a 904/ 83/4 combo, or perhaps even a 4 speed/8 3/4? I do recall the old mopar chassis manual had some information it it regarding the amount of horsepower it would require to run a certain MPH at a certain weight, in the 1/4 mile. And there are various online calculators that seem to mirror the results.......Just trying to learn here guys, so I welcome any input! This is NOT directed at any member/car/engine/track/dyno personally, its to clairify my own knowledge!
 
There is a chart floating around the net on the popular HP loss through various automatic transmissions; I have to say, in an automatic that torque converters have the largest hand in the game of making power to the wheels...


Recently I did a th400 for my truck, used a 1800 stall converter for it; it was ok, a little slippery down low, ho hum... Started making noise so I tossed in a the new hotness Hughes has for stall towing converters to see if it made the noise go away, it didn't, turned out it was the filter wasn't fully seated.

BUT:

That converter makes the damn transfer case shifter want to twist out of the truck every time I look at the throttle; the 5,000 lb truck with a 350 wants to go INSTANTLY off throttle. HOLY PULL!

Totally different rig just from a quality converter swap. These days I've become a believer of being more concerned with a good build and a great converter, over how much bench racing tells me it eats power blah blah blah.
 
I almost have to say"who cares". To move the car, one has to have a powertrain. Choose the components for intended useage, and let the powerloss be what it will be.
But if you really want to know, buy and install one of those windshield mounted accelerometers. They spit out a pretty good result.

As a streeter, and after 3 different cams, I really don't care how much maximum HP at whatever rpm,my combo is kicking out. What I do care about is ET from Zero to 60, and hammer down in 2nd at 30mph.For these I need midrange, and the sooner it comes on,the better.This makes Fun.
Everything else is secondary to me.
Top of second gear is way speeding so I almost never go there.And if it only goes 93 in the 1/8th, well, that's nice.
 
GM
PG 18 hp
TH-350 36 hp
TH-400 44 hp

FORD
C 6 55-60 hp
C 4 28 hp
FMX 25 hp

Chrysler
A904 25 hp
727 45 hp
 
AJ/FormS said:
But if you really want to know, buy and install one of those windshield mounted accelerometers. They spit out a pretty good result.
Click to expand...


Most smartphones already have an Accelerometer chip in them, so a G-Meter App is all that's needed to have a G-Meter in your car.

hope it helps
 
Woods74 said:
GM
PG 18 hp
TH-350 36 hp
TH-400 44 hp

FORD
C 6 55-60 hp
C 4 28 hp
FMX 25 hp

Chrysler
A904 25 hp
727 45 hp
Click to expand...

Absolute numbers are kinda misleading. I mean, I can spin the input shaft of a 904 at say 60rpm, and I don't have 25 hp in my left arm. But say you figured out a way to to have that 904 all tanked up, on the bench, just like it would be in a chassis, I bet I could still spin it up.And I still don't have 25 hp in my left arm, or my right arm.
But lets say you don't like my thinking.
So let's say you have a /6-904 in your 73 Dart.A slanty is NET-rated at about 140hp, right;probably at somewhere between 3000 to 4000 rpm.Let's arbitrarily gross it up to 180 dyno hp.
So just off idle somewhere around 2100, we know it makes at least 45 hp cuz thats what it takes to cruise at 60mph with 2.73s.And since she will do that at something like 30% throttle, we know there is a lot more available at that rpm.
So now lets take half the sparkplugs out. And then,let's guess at how much power she has got left in her at 2100, but with 100% throttle, with just 3 working cylinders.Well first off it has to be less than 180/2 =90, and since we are at 2100,and not at peak hp, it has to be at less than say 1/3 of peak.So I come up with about 30hp So now if the tranny is going to suck 25 of those away , and the rest of the powertrain and accessories suck up 15 or 20, well you are left with less than nothing to move the car.
But I can guarantee you this one thing; If you have a healthy 180dynohp 225, it will still go 60mph on just 3 cylinders. That would mean it is still netting 45 hp or more

So, one would kindof need to see the test parameters, that generated the 25 hp loss.
 
93 in the 1/8 still a good enough for us older saterday night street cruzers.
and just enough to get 3 or 4 BIG tickets with ,if they don't take your car now days.
What do the kids in your town have to do? At least back in the day they new where we all were on fri- sat. nights . Vary sad to see ****** taking over our kids and grand kids .
because they cant go to the avenue and watch the awesome cars cruzing and a few
old guys to teach them a little , well not goin to go into that .
 
As the horsepower is increased the % of loss decreases....

350 hp engine drivetrain 35 hp...10% loss

450 hp engine drivetrain 35 hp ....7.8% loss...

Probably the biggest problem is inflated dyno results...correction factor to get the hp corrected to standard conditions...dyno sheet does not show actual...
 
Another thing...say the dyno says 470 hp at 6500 rpm....so we plug 470 hp into the calculator with 3100 lbs car and the calculator says it will run 11.00 @ 119 mph....ok..

we go to the track...it runs 11.40s at 116...oh ****...

what you only looked at was the Hp at peak rpm,,,,the engine is not running at peak rpm all the way down the track...it gotta launch...it is gotta recovery after each shift rather it is two or three shift depending on auto or stick....engine rpm comes down to let say 5000 rpm....not making peak HP there...so if you take your ET or MPH from track plug into calculator...are you getting peak HP or an average HP going down the track????

1st you got a correct hp number...

2nd you got an average hp number from track results....but the dyno said it made 470 hp....welcome to the real world...
 
70aarcuda said:
Another thing...say the dyno says 470 hp at 6500 rpm....so we plug 470 hp into the calculator with 3100 lbs car and the calculator says it will run 11.00 @ 119 mph....ok..

we go to the track...it runs 11.40s at 116...oh ****...

what you only looked at was the Hp at peak rpm,,,,the engine is not running at peak rpm all the way down the track...it gotta launch...it is gotta recovery after each shift rather it is two or three shift depending on auto or stick....engine rpm comes down to let say 5000 rpm....not making peak HP there...so if you take your ET or MPH from track plug into calculator...are you getting peak HP or an average HP going down the track????

1st you got a correct hp number...

2nd you got an average hp number from track results....but the dyno said it made 470 hp....welcome to the real world...
Click to expand...
This makes sense.......Then, in that case, is it even possible to roughly determine engine horsepower based on a trap speed/weight factor?
 
I thought the rule of thumb was 20%
 
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