Elevation has a HUGE impact on horsepower, but really more-so in naturally aspirated engines.

 

Hp numbers mean very little as their credibility will always be in question. There are different dyno machines that will give different hp figures. Some people run em in 3d, others in 4th. Some people put ice on their ic for a higher read out, others can add hp when doing sae corrections.
The true way to calculate hp is to know the gear ratio, the final drive ratio, the tire dimensions, and weight of the car. You then do a run from whatever speed to whatever speed and calculate it that way

 

I've raced evo 600hp cars and have put several lengths on them. I've raced 505hp z06's and only pulled a couple lengths, I've raced 505hp m6's and put bus lengths...
I raced a 640hp s/c viper srt-10 and put about 5 lengths
I've raced 500rwhp supra's and have been murdered... Martin 590hp ruf will destroy my car
A stock 996 gt2 would probably be neck and neck with my car

And keep in mind my pos is rwd and making a bit over 500 to the wheels

"Rwhp" is really meaningless ... You have to have the whole package

Proper tuning
Proper suspension set up
And most importantly GOOD tires

With all that being said, can any of you reply to my tire tread already ?!?!

 

The motor itself makes whatever power it does. It doesn't know/care what gear is being used.
The gear a dyno operator would use, would have more to do with controllability and efficiency.
A higher gear means there is less likelihood of spinning the tires on the rollers, and the pull will
be longer. As to efficiency, car manufacturers design their gear boxes to have the most
efficient gear be used at the speed the car will spend most of it's time, or be measured for
fuel economy. So if you want to see the highest power number on the dyno readout, choose
the most efficient gear (least internal loss). That doesn't mean the car *is* more powerful.
You will still get less power to the wheels in the other gears. And note that if the dyno says
400 awd horsepower, that's only in the best gear at the exact best RPM. 99% of the time,
you get less, and mostly significantly less. You beat someone off the line at the stop light
because you put down 108hp at 2000rpm, when the other guy was only putting out 86hp...
Joe

 

yes, most dynos overcorrect for both NA and turbo cars. turbos loose lots of power but not as much as NA cars. Hipo NA engines loose less power than low performance engines at altitude as well.

 

Let's not forget the old adage of heat soak. In the TT, even with fans on everything, a 5th gear pull results in extremely high IAT's as you just cannot get enough air going through the ICs on the dyno. AS others have mentioned, the closest to 1:1 is the gear you want to use unless it exceeds the speed limit for the dyno. 4th is the gear to use on the Porsche.

Justin

 

Yes, there may be a speed limit for a dyno, and air to the intercoolers is
certainly important for our cars, but IAT's are not a function of gearing.
If you don't have enough cooling air to maintain the intercooler temperature,
it will rise in temperature, raising the IAT, and the longer the pull, the hotter
things get, and needless to say, the higher the gear the longer the pull. So,
if you cannot cool the ICs enough, then the shorter the pull the better,
which would suggest running as low a gear as possible to get it over with
ASAP. If you do have sufficient air, we are back to the gear having no
thermal relevance.
A one-to-one ratio of crankshaft-to-tranny output shaft rotation is also
of no relevance except as it *may* indicate the gear that is most efficient.

 

so I can do a 1st gear dyno pull then....


Oh, yes, the scoundrel Tune. Run the car on dyno with no cooling fans. Provide NO tune, and run car after with fans, bam, 60 hp gain....$1000 please

an engine provides the horsepower it's going to provide depending on which dyno you use..........

 

This is true, to an extent. I actually prefer a Dynojet as the numbers are not AS manipulatable as some others. The dyno is a tool, that's all. If you baseline the car(or a similar car), make changes to it, and dyno again(on the same dyno), then you are using it as a tool. If you actually use it as a "rolling road"(to quote our friends from across the pond) for tuning, then it is being used correctly. If you are just looking for bragging rights, then.... well, it's still being used correctly. However, it is not an end all, be all. Best way to tell who is making more power is to race them in a closed environment, of course.

Justin

 

Justinn I'm surprised you aren't a fan of DynoDynamics dynos! Accurate numbers, a test mode that will not allow you to dork with the corrections and won't let the engine just zing, a pretty good tie down with the trapeze in back, ability to HOLD power for actual tuning and not just a numbers run, easily controlled from within the car via their handheld, pricing that included many of the "extras" that other dynos charge for (last I priced), ability to show minor torque differences in REALTIME unlike any other I'd used (especially DynoJet's I'd used with big rubber brakes), and best of all if things get whacky you can use the BRAKES without fearing you'll be shot off the end like a plane from a carrier! 2 days of using one of those on my car and I was sold sold sold! Sadly comparing it's numbers to those taken on a Dynojet is serious cold water in the face and is probably partially why one of the members here thought the kit they had gotten wasn't properly delivering power. When I first saw the sheets mounted on the walls of the shop that dyno'd my Supra I snickered thinking "no problem" - until the first pull. Ouchie, that stung! Apparently American ponies are smaller than Aussie ones?

Anyway, if I could own a dyno of my own that is what I think I'd want. Heck the thing is supposedly light enough it can be moved around a shop or put away when not needed without having to have a forklift on premises. No pit required, no lift required..... A shame they were rare as hen's teeth when I was tuning DynoJet's are great for WOT numbers, DynoDynamics is what you want when you want to tune an engine across a wider spectrum of behaviour IMO. I'm sure you've used one, was there something about them that I missed that sucked? I never heard great things about Mustang dynos either - especially realtime torque capability - has that improved? I only ever had pulls on one once so no real data of my own regarding them just opinions from people I respected. If I could have afforded a DD and had a place to put it where neighbors wouldn't want to kill me.... I thought we were all going to go deaf that weekend stuffed in that tiny garage up in PA!

And yeah, a race is the best way to test one car's power against another but a dyno is much much easier to test various modifications back to back seeking improvements. I wish more of that sort of testing was done and documented in the P-car world.

To answer the OP - we used to use whatever gear was closest to 1:1 without overspeeding for just WOT power runs. For "tuning" that wasn't always just WOT we used 3-5th to hit as many load areas as possible at varying speeds. <shrug>

 

don't get me wrong.... The dyno dynamics line are fine for the lower hp cars(sub 1000whp), but they are able to be manipulated(numbers wise) if the operator so chooses. I actually like the capability and price of them. For Load tuning, they are great.

Mustang Dyno's also have good load bearing technology with the current eddy current capability.

Even the new Dynojets have an option of eddy current loading.

I wasn't clear in the previous post. Whichever one you choose(brand), you need to continue to use the same brand when comparing the modifications. Use it as a tool, not an ego inflator.

Justin

 

All of my dyno pulls have been in 4th gear on a RWD dynojet dyno. In fact the dyno I use is the same dyno Tommy (Autobahn) uses to dyno most of his Supra's on. Justin has had experience on the same dyno as well. My only complaint about dynos is you can go to 2 different dynojets and dyno and get different numbers (on the same day even) with SAE corrections. I've been told it has to do with exact tire placement, number of dynos that have been made, version of software, etc.

Regardless Justin has a good point, the dyno is a tool (I use it to reassure myself that the car is running right only because I get use to the power of the car VERY quickly LOL!) Some people use it as a bragging right, but when it comes down to it... The track or a heads up race is going to be the true determining factor of whos car is actually faster. That is why I care about my track numbers over even 60-130 times because the car with a better gear setup will always do a better 60-130 because of less shifts, and time the car is actually in a "power band".

 

Yep. People get very sad and accusatory when one dyno gives
them 'less horsepower' than another. Talking about 'crank' or
'flywheel' horsepower is another pure ego booster. What you
get at the wheels is what you get.

 

Yep. Dynos are complicated machines with a difficult job and shifting environmental
factors. They are like fine Swiss watches. Any man who owns an expensive
exclusive, Swiss luxury watch knows what time it is. Any man with two or more
expensive, exclusive, Swiss luxury watches is never sure...

Joe (who has two watches which connect via radio signals to the N.I.S.T.
atomic clock in Colorado 6 times a day to sync up, so they are accurate
to within 8 hundredths of a second at any time :P )

 

For fun email DynoJet and ask them for the formula they use on their dynos to calculate power. Unless something has changed recently that's not something they will tell you. WTF? Mustang and DD will apparently tell you - go figure. I agree that using it as a tool is the way to go, stick to one dyno and don't sweat what other dynos give to others, DynoJets are consistent run to run on the same machine in my experience. I also agree that HP at the wheels is what matters, to heck with figuring out "flywheel power". Yes it's bigger but most of us ought to be dealing with the same drivetrain losses anyway...

Justinn - yeah I'd forgotten you're a baller playing with toys over 1K! Not much is going to hold THAT back! Full pulls FTW on hardware like that for sure. Trying to hold it back would just burn it down. I only ever got to help tune on one car, turbo V8, making that kind of power. Amazing what kinds of spooky weird things that can go on - I'd never seen an intake manifold SWELL (or sweat!) before! Left a plug wire off, dropped a hundred+ horse and spent 5mins freaking trying to figure out WTF we'd broken! lol I'd love to start a war stories thread someplace appropriate to talk about funny stuff like that. Still tuning the alky RX7 with a gas mask?