Well autozone teamed up with a local tuner for parking lot dynopulls. I waited 2.5 hours for one since I'd never done one. No tuning. I'm not sure what to make of this. I was expecting higher though..This was a dynojet and is RWHP. I saw some crazy stuff like a 496 pegleg truck which made 802 torque but a little over 300 rwhp. One thing I noticed about mine was torque still climbing after Hp topped out. You guys tell me what you make of this good or bad. Alot more tuning to do? I had no idea what to expect but I was thinking both HP and torque should have been higher. This was a 5000rpm pull. HP on the left
torque on the right.

383, gm hot cam 218 228@ .050. ebrock RPM heads
12cc dish pistons, 670 avenger, 700R4.
Seems like the car use to pull harder..
In case its not ledgeble..314 torque 284 rwhp
http://home.hot.rr.com/importtech/chevelle/383engine/dyno1.jpg

another view. (http://home.hot.rr.com/importtech/chevelle/383engine/dyno2.jpg)

Anybody with a similar combo..
What would this equate to a 1\4 ET

Stick shift or automatic?

Originally posted by Slowpoke70:
Stick shift or automatic? 700R4 with cheap 2400 coverter..(I built it..maybe thats the problem graemlins/waving.gif )

Your cheap 2400 converter might be skewing your dyno readings. Remember, it is reading HP at the wheels, so it'll only be as accurate as your drivetrain is efficient, and the converter is where a lot of that efficiency goes down.

If your car loses 35% through the drivetrain, you'd be making about 383HP at the flywheel.

And you might be losing even more through the drivetrain.

35% loss would be pretty huge! although with a faulty converter anything could be possible. I don't know squat about reading the graph but i am sure someone will be able to here

The RPMs that things happened at look about right, for that small cam; peak torque at 4300, peak HP at 5000. I would think the numbers should be higher though.... but I doubt the trans or converter have much to do with it. Also, since that is a FI cam with a wide lobe separation, will reduce the peak torque from where a correctly chosen cam really should be.

A dyno pull is almost useless as a tuning aid, without a wideband O2 hooked up. If you don't know whether you were rich or lean, it's pretty hard to know what to do to dial it in. It would be my guess though, that you were lean below 4500 RPM, and rich above that; that being typical of what happens with a carb that's not big enough, as yours is not.

I'd guess you're in the high 13s like 13.8 to 14.0 with a 3300 lb car; adjust your guess from there according to your car's weight.

Originally posted by RB69SS396Conv:
The RPMs that things happened at look about right, for that small cam; peak torque at 4300, peak HP at 5000. Actually its the other way around which makes no sense to me. Horsepower is on the left side of the graph as I read it.. I'm totally in agreement though that the numbers seem low in either case. I never heard the car miss at all. As for the carb it was setup by THE CARB SHOP in CA. The jetting they came up with is kinda weird to me but might support what you've stated. It has 65F and 75R. This thing ought to run better than 13.8 but by those numbers I think your probably in the ballpark.

No, you're reading the graph wrong. Regardless of which side they put the torque axis and the HP axis on.

HP = torque x RPM / 5252

The lighter-colored curve that goes up fast, stays sort of flat, and then slowly tapers off, is torque; the one that rises continuously is HP.

If THE CARB SHOP didn't have the whole car and motor, and put it on a chassis dyno with a wideband O2, then it isn't tuned to the car. It might be well-built and all that; but it isn't matched to the rest of the setup yet.

Hey thanks

I've learned something aready...That does make a bit more sense..Still think numbers could be alot better. FWIW I pulled a few plugs this morn, and look pretty lean. Appreciate the response.

284 rwhp is fairly typical for the 383's we see in street cars, maybe a little on the low side.

Who drove the car on the dyno? It looks to me like the throttle was feathered until 3500 rpm or so. This is one problem with automatic trannys - nail it too hard and it will downshift.

Your cheap 2400 converter might be skewing your dyno readings. Remember, it is reading HP at the wheels, so it'll only be as accurate as your drivetrain is efficient, and the converter is where a lot of that efficiency goes down.The dyno reading will be as accurate as the dyno can make it, regardless of the drivetrain efficiency. This would be like saying he should have 800 hp but the poor thermal efficiency of the engine makes the dyno tests inaccurate.

Hmm, guess I was wrong. Always thought power was lost through the drivetrain before it got to the rear wheels where the dyno is getting its readings?

At least I learned something new today.

Power is lost everywhere from the radiator to the rear end - friction losses, windage losses, pumping losses, wave pressure losses, thermal inefficiency, etc.

The graph is definitely wrong - horsepower and torque are equal at 5250 RPM, no matter what. On your graph, the two lines cross well before that.

On the other hand, even with the error, the only thing I'd take away from this pull is that you have a rough idea of what your car is capable of. You can really only truly compare your car's numbers to the other cars tested on the same dyno using the same calibration.

Ryan

The dyno isnt wrong. Check the second link, and the HP axis goes to 300, and the torque axis goes to 325. This is why its not crossing at 5252.

Originally posted by -SS454-:
The dyno isnt wrong. Check the second link, and the HP axis goes to 300, and the torque axis goes to 325. This is why its not crossing at 5252. I can't tell for certain from either view exactly where they cross. 5252 is where they must cross, doesn't matter how you read the graphs, if they're accurate horsepower and torque are always equal at 5252 rpm. I don't know if measuring at the real wheels vs the engine has any impact on it, can't see how it should, but that's it. It's not open for debate, I didn't make the rules. It's the math formula used to derive the 2 and that is not open to debate.

Slowpoke70, you're not wrong. There is a power loss in the drive train. That was the big change, when it appeared that cars had a lot less horsepower. They switched from 'gross' at the flywheel, to 'net' at the rear wheels. There can be a big difference.

They cross at 4700...One thing for sure the numbers are too low for this motor. Everything I have read this motor should make 400FWHP anyway.
I'm not greatly concerned as I'm moving to an
aftermkt tpi (http://www.firstinjections.com/products.htm) Maybe it will be a better match for the cam. Kit should be here in about 2 weeks. Then maybe I'll get a little more serious with turning.

Slowpoke70, you're not wrong. There is a power loss in the drive train. That was the big change, when it appeared that cars had a lot less horsepower. They switched from 'gross' at the flywheel, to 'net' at the rear wheels. There can be a big difference.

It seems to me that factory power ratings have always been flywheel power raings. Early ratings were without any accessories, in the 70's the ratings were with all accessories.

Finally,

It DOES matter if the HP axis is different than the Torque axis, that changes where the line is on the graph. If the HP and TQ were on the same axis range (say 300), then it would have crossed at 5252. And just like onovakind67 said, gross was flywheel horsepower with no accessories, and net is with accessories.

The only point I was trying to get across is that there is a big difference between HP taken at the wheels and HP taken at the flexplate/flywheel, especially in a car with a lot of slippage in the drivetrain. Hence the reason we always hear "Stick shift cars get more power to the wheels".

So his 284RWHP is not going to be close to the HP the engine is making at the flywheel.

Its sorta just semantics (well, maybe 1-2% power) but IIRC that SAE net horsepower is measured at the end of the driveshaft with the engine and all accessories installed in the car. I don't think its at the rear wheels.

.02

matt

Originally posted by Finally:
...5252 is where they must cross, doesn't matter how you read the graphs, if they're accurate horsepower and torque are always equal at 5252 rpm...Finally - your second statement (hp = torque at 5252 rpm) is correct, but the first statement is only true when the scales are identical. In this case, if you check the values for hp and torque at approximately 5250, they both appear to be about 280. QED!

Originally posted by 383Malibu:
Finally - your second statement (hp = torque at 5252 rpm) is correct, but the first statement is only true when the scales are identical. In this case, if you check the values for hp and torque at approximately 5250, they both appear to be about 280. QED! Yes I see on the second view that they are using different scales for hp and torque. In that case you have to compare raw numbers. Actually you don't need the hp line at all. Since you can only measure torque and must derive hp from torque and rpm.

As for SAE NET hp, sorry I mis-spoke. SAE net hp is still measured at the flywheel but includes all accessories like, full exhaust, water pump, alternator, emissions stuff