Dyno'd it - not happy at all....

[DZEE'S LX]

My Mustang club rented a day on the dyno so I finally got some #'s to chew on.

Best number was 252 which is way lower than I expected. At 18% loss that puts me at 297 at the crank. The dyno operator said the number is already calibrated for our 4200 ft elevation but I'm not completely convinced of that because the correction factor on my printout was 1.15 while other cars on the same day were 1.16. I'm wondering if that might have been a correction for temperature or humidity? This is all wishful thinking cause I'm just looking for an excuse to add more to the number.

What was strange to me is that I was running too much fuel pressure. After the 2nd run he said my a/f was way fat and told me to take the pressure down. I had guessed at 48 psi thinking that with my mods I could use the extra fuel at top end. I asked him what to set it at and he said 38. I didn't really believe him and set it at 42 cause I had it stuck in my head that I MUST need more fuel. Anyway, I went from 247 to 252 on that last run. He said I probably would have picked up 10 - 15 if I let the engine cool. It sat there on the dyno idling for a good 5 minutes while I got my tools out and adjusted the pressure. He said the whole engine was probably completely heat soaked during that 3rd run.

So my question is, how can it be that lower fuel pressure means more power? The guy running the dyno is a longtime 5.O dude and he says his highly modified (no pwer adder) engine puts out the best numbers at 44 psi. (and I'm sure he tunes all the time on the dyno since he is a part owner).

??

More fuel pressure doesn't necessarily mean more power. It's finding that perfect a/f mix that makes the most power. Since you are N/A...the leaner the better. The trick is to get it to run fairly lean, but with not going so lean that you are experiencing detonation.

[Rev]

What were the A/F numbers? They should be graphed below the HP/Torque curves on the dyno sheet print out (assuming a DynoJet).

Rev

[DZEE'S LX]

They didn't print out. A few cars later they were showing up on people's sheets so he must have not printed everything correctly when I ran. Mine was one of the first cars and I was the first one to request a/f.

He said the ration looked good on that last run. I could have run it again later on in the day when my name came back up on the list but I couldn't stay that long. I'm wondering if I really should go down to 38 like he said. Don't know if it will make much difference but I guess I'm still surprised that lower press is good. I installed the FPR so I could up my pressure but now I find myself back down around the stock setting.....

What pressure are you guys running ...?

I'm embarrassed to admit it, but due to emmissions I'm still running my stock h-pipe with converters. I know that is a restriction but how much......?

[red82gt]

At higher altitude, you'll need less fuel than someone at sea level. I drove my car to Yellowstone national park and kept my carb jetted for my 850 ft elevation. At 6000 feet, I could hardly get the car to start and it was tough to keep it running.
No matter what correction you use, when you're at 4200 feet, the car is going to respond and only make the kind of power it's capable at 4200 feet, you can't tune it to sea level specs. Even though you didn't get the right #'s that you wanted, at least you came away with information, which is the whole point of using a chassis dyno.

[tarmon8r]

All chassis dyno's are different. You can not compare numbers from one dyno to the other, they are just tools to use at your disposal for generating numbers. As long as you continue using that particular dyno for changes and seeing results. That is why every magazine you read, they try to do a baseline dyno before any changes, cause the dyno's will be different. But I agree with Red82Gt on your altitude.

[Dark_5.0]

There is alot more to how much fuel your engine gets than just fuel pressure.

Pulse width- On mass air cars the pulse pattern of the injector can be lengthend or shortend to add more fuel to match the air flow that is metered by the amss air sensor.

With your mods 19# injectors @38psi will easily handle it.

[~The Jester~]

Rule of thumb to remember: Lean is fast, Fat is safe. This holds true for all, but us nitrous guys take it to heart. Like mentioned before, you want it to run as lean as you can, but without detonation. All an internal combustion engine is, is a big air pump. Get the air in, and get it out as fast and efficiently as possible. The fuel makes the air mixture explosive, and that's what drives your air pump. Extra fuel in there takes up space that we could put more air in, and actually takes longer to burn. Once the flame front starts across your combustion chamber, too much fuel means it's still burning even after your piston is long gone. Then we have too many spent gasses to get rid of on the next stroke as well. There's A LOT more to it than that, but in a nutshell more fuel WILL NOT make more power, unless you add more air to go along with it.

[andy669]

If you take a trip back there, have him print it out. Everything from the runs should be saved. 1.15 sounds about right for the correction factor. I have seen numbers that high, here, in the middle of July when its 100 degrees.

The guy operating the dyno sounds like he did everything correctly. The only other thing I do is look at the uncorrected numbers.

Andy

[DZEE'S LX]

Thanks for all the info!

It was a Dynojet 248. I will see if I can get another printout with the a/f ratio.

Anyone have any idea of how many ponies might be hiding in my stock h-pipe & cats?

[Dark_5.0]

Originally Posted by DZEE'S LX

Thanks for all the info!

It was a Dynojet 248. I will see if I can get another printout with the a/f ratio.

Anyone have any idea of how many ponies might be hiding in my stock h-pipe & cats?

Probably 15-20RWHP.... You should have ditched that crap long ago

[red82gt]

Holy cow, those are about all I'd expect for numbers through a stock H-pipe. With exhaust like that, it's no wonder you don't need any more fuel.

[DZEE'S LX]

I know, I know......
I've basically left it alone because of emissions.
There are many people around here running offroad pipes but they either have a way of passing the test or they swap their cats back in temporarily. Haven't heard of anyone getting busted for running without cats but I understand it can be very expensive.

I haven't wanted to get into that game but I guess I need to do something.

Any opinions on the differences between going with an offroad pipe vs high flow cats?

Is it true that I will lose bottom end torque or hp with a better flowing exhaust? What about the 2 1/4 vs 2 1/2 pipe diameter, what's best?

[Dark_5.0]

I imagine you will pick up a ton of HP and Torque.

You wont notice a difference in power running high flow cats or an off road set up the only difference will be that it will be much quieter with cats.

You want 2 1/2 or even 3 inch exhaust.

[Dog5ohfun]

If you are worried about emissions get a nice aftermarket h or x pipe with cats. There is not a big difference between high flow and offroad h pipes. Do not get 3 inch exhaust. When I ordered my Spintechs the rep told me that 3 inch pipes are a way to big and offer no backpressure on a 302 which equals no torque which equals no fun. Good luck with the Dyno tuning

[Dark_5.0]

Originally Posted by Dog5ohfun

If you are worried about emissions get a nice aftermarket h or x pipe with cats. There is not a big difference between high flow and offroad h pipes. Do not get 3 inch exhaust. When I ordered my Spintechs the rep told me that 3 inch pipes are a way to big and offer no backpressure on a 302 which equals no torque which equals no fun. Good luck with the Dyno tuning

I have a 2 3/4 exhaust system that goes to 3 inch after the H section and I made 295 ft lbs at the wheels.

With a good H/C/I package 3 inch exhaust is sweet IMO.

[red82gt]

Don't bother with the 3" pipes unless you go to a set of headers with a real collector. You'll neck down for a shorty header collector and then open up into the big 3" pipe killing your velocity. The 2 1/2" stuff is more readily available (especially with cats). I'd bet that you'd see a 20rwhp gain from going to a high flow cat pipe.

[Rev]

Originally Posted by DZEE'S LX

My Mustang club rented a day on the dyno so I finally got some #'s to chew on.

Best number was 252 which is way lower than I expected. At 18% loss that puts me at 297 at the crank.


??

Actually, you can't just add 18% to get the flywheel number. The easiest way is divide by .82.

252/.82 = 307 at the crank.

Not a huge difference but it's a little better.

Rev

[Ackbar00]

Hey, dont fell to bad. When I took the turbo stang, I was rewarded with 368 RWHP! WHat a crock! Sometimes, turbo stangs have trouble making boost on the dyno, and mine only saw 5PSI. As soon as I left, it saw 14-15 PSI on the street, so I know it makes a bunch more than what it put down. Makes it fun to **** with the ricers at home, "My god, you have all that money in your car and only made 368. hahahah, My friends cousins brother has a CRX that makes almost that much!" Hehehe, if they only knew.....

Originally Posted by Dark_5.0

You want 2 1/2 or even 3 inch exhaust.

Get the 2.5"...but please, DO NOT GET 3" EXHAUST! Unless you are making like 500hp. 3" exhaust will do nothing for you. You'll lose tons of torque and have less power at lower rpms.