Well guys I got a dyno appointment!! A local deisel shop that I did not know existed has an eddy current chassi dyno (supposably the most accurate & expensive). I get 3 runs with wideband testing for only $75. Has anyone gotten their truck dynoed? I know my truck came with 200hp/290ft-lbs tq @ flywheel. But what do you guys think drivetrain loss is 65hp for the 4R70W (maybe a few more hp as the power level goes up), or 20% ? Or does anyone know what these trucks dyno at stock?

 

Well, obviously it varies from powertrain to powertrain, but a general rule of thumb is that the rwhp is approximately 2/3 of the flywheel hp for automatic transmissions, and 3/4 of the flywheel hp for manual transmissions. So stock peak rwhp for an auto tranny I would estimate to be around 130. But this is just a guess, however it isn't a complete shot in the dark. In the F-Series Owner's Bible they did a dyno run on a '89 F-150 with a 302 and a manual transmission and the peak rwhp came in around 125 I believe. This was a 4x4 with 32" tires. So taking into account that you have a 2wd, smaller tires, 15-20 more flywheel hp, but an auto tranny, my guess would be around 130. But I'm by no means an expert.

BTW, where did you get your stock flywheel figures? Just curious, because of all the stock 302 hp/tq figures, 200/290 is a new one for me. I know the hp went up for the '95 model years to about 205, but I believe the tq only went from 270-275 lb/ft. I could be wrong, but oh well. Hey, if anything it's better to start with a lower baseline, that way you're getting more power out of your mods. Any ways, I'm really curious to see how you truck does on the dyno!

 

P.S. I read an article in a Mustang magazine about dynos and adding power mods. This guy said that on average, there is roughly a 30% power loss to the rear wheels, but adding hp mods. does not change the quantity of hp loss to the rear wheels. In other words, if you add 20 hp to the crank then you will be adding 20 hp to the rear wheels. His reasoning was that the drivetrain absorbed a certain amount of power, and adding mods. doesn't change this quantity. So if you have 200 stock fw hp, and 130 rwhp, and you add a blower that adds say 75 crank hp, then you will have 205 rwhp according to this guy.

However, this explanation does not sit too well with me. According to his logic, a given drivetrain/powertrain combo eats up a certain amount of hp, no matter what. How is it, then, that most drivetrains tend to absorb 30% of the power on a consistent basis? Furthermore, here is a hypothetical question. Our engines come stock with iron heads, a mild cam, etc. and consequently, our engines produce around 190-200 hp at the flywheel, and 70% of this is 140 rwhp. However, if we add aluminum heads, a beefy cam among other mods and boost our flywheel hp to 275, this is in increase of 75 hp which would put our rwhp, according to the guy in the magazine at 215. This now makes for 78% drivetrain efficiency, up from 70%. Now, if our engines came stock with aluminum heads and a beefier cam, etc., I seriously doubt the engines would still have a 78% drivetrain efficiency. So with the same exact powertrain and drivetrain, we have a discrepancy, or in the mathematical world, what we like to call a contradiction. So, we must look for the premises that are known to be true, so we can decide where the false premise was. I believe that to be the statement that a given powetrain absorbs a fixed quantity of hp. This is my take on this, although I don't have any experimentation to back up my hypothesis.

Any ways, I don't really know how this affects your dyno run, I guess it's just related information that might be of some interest.

 

Yeah thanks alot for the info. It was very interesting.I got the hp/tq numbers from a 95 F-150 brochure. Maybe it was a misprint on the torque. I know Sproket knows the numbers, because he has emailed some guy at ford. Iknow in 94 the 302 has 180 hp. With Mass Air, it either went to 200 or 205., but torque, I just dont remeber. Last time I looked at the brochure it said 200/290, if I could find where I put it, I would take a picture, but I have no idea where it is. I hope Sprocker chimes in with the numbers.

 

Friction increases with speed and since horsepower is basically a measure of how fast you can accelerate it stands to reason that drivetrain losses will be a percentage of your horsepower output. Theres a lot of heavy rotating parts in your drivetrain and the laws of physics say the harder you push on an object the harder it pushes back, so a high horsepower car uses a lot more power to get moving because it is trying to accelerate the drivetrain parts much faster than a low horsepower vehicle. My theory is that when your accelerating off the line, the losses are a percentage of your engines horsepower, when you are cruising at a steady speed the loss will be a fixed number. Since a dyno measures power by how fast you can accelerate a big heavy drum, the dyno will always show the drivetrain losses as a percentage of horsepower.

-Jon

 

That's exactly what I'm thinkin'...although it probably didn't come out that way...:o

 

Ford4ever & TF,

Most of the stuff I have seen shows both factors weigh some, but within most modification windows driveline losses are more or less set per a given rpm. If you do massive mods or a transplant the additional bearing loads, etc from the torque difference will take more power to overcome the driveline, but not a lot.

Driveline and tranny losses also have an effect of changing the output peaks in many cases, if the driveline drag curve isn't flat. This is why some engine combos will have peaks lower than rated rpm. The engine alone may produce peak torque at say 3800 rpm, but in combo with the tranny the peak to the rear wheels might come lower.




Beastie,

Personally I wouldn't worry about the stock baseline at this point. With the 3.31s a truck would hit the rev limiter in stock form anyway so you probably won't find a good comparison with a like optioned truck. Even if you do there are too many variables in weather, dyno's, etc to really use one or two other runs as a baseline compared to yours.

The only factor I would consider is that if anything, our modded 302s should have equal or slightly less driveline loss than the newer 4R70W trucks, which seem to average 60-65 HP driveline losses. This would put the output of a healthy stock 302 at around 135-140 HP at the wheels.

 

Well this is the rule of thumb I have found most easy to use:

Manual Trans - 18% frictional loss

Auto Trans - 25%= frictional loss + hp used for torque multiplication.

Remember a manual directly transfers the power to the wheels; an automatic uses an amount of produced horsepower through a turbine and indirectly transmits power (with exception of full lock up in 3rd & 4th gear if your trans has that feature).

Bottom line is this, nobody cares how much flywheel you make anymore, look at all the magazine tests.

If you are making more than 400 at the wheels, you know you have one bad mother!!!

Just having the base line is the most important thing if you are trying to evaluate the effects of each modification you make.

 

Yeah I have a lock up converter. And wow it is so much better than stock. Not just the stall speeds, but I can feel it lockup and see the rpms drop in 3rd and 4th gear. Yeah I'll just worry about the dyno numbers. Hel Ill be able to take a vid of the run, so if anyone wants to see it, ill get it hosted somewhere.

 

I would be very interrested in viewing it. When are you going to the dyno?

 

This Friday at 8am

 

I'll be waiting patiently for the results