moon2605

Had some work done on my car a few months back. was supposed to be 673hp on the dyno according to the owner of the shop. did not get a readout. Just verbal. Added headers so the car sounded tough. did seem to run better but really had no way to compare until we ran at the mile. had a friend of mine with a 670HP stingray at a half mile event last year run 170 MPH and I ran 160MPH at the same event( before mods). At the Texas mile this April I ran 163 MPH in the half. way off from what I expected. I did run 191 in the Texas mile which is good. during the mods we added a better heat exchanger , water tank, and meth. these cooling mods are doing a great job to prevent pulling timing. just very disappointing to get incorrect info after spending a lot of money with a shop. I think between the new dyno run at a different shop and the comparisons on the half mile I am confident in the 603hp. Just wanted to fuss a little.

Kevin

Maslo

Atmospheric conditions influence dyno runs some. Hi neighbor grew up in Keller and live in Mansfield.

davepl

Chassis dynos are (a) only as accurate as the operator is proficient and honest, and (b) really more useful for repeatable A/B testing.

It's hard to compare from one dyno to the next, because a Mustang Dyno is different from a Dynojet (they shouldn't be, and that tells you a little something).

The biggest difference is the weather. If the operator fudges anything about humidity, temp, or barometric pressure he can get almost any number he wants. -Really- wanted to make 675 but only made 640? Well, just input Denver's elevation, and tada! Of course that's outright deception, and I'm not saying that's what happened here. There are also different correction factors and 3-4 different ISO/J/SAE standards for how to calculate horsepower that cover everything from temp to what accessories and exhaust is connected.

I only have access to an engine dyno, not a chassis dyno, and properly configured they're very repeatable and comparable from one dyno to another. That's because they operate by two different principles:

Engine Dyno:

A big scale is connected to a bar on an engine stand. The engine rotates against a water brake, and when held, the amount of force on the scale is the actual torque. Multiply by RPM and divide by 5252 and you've got horsepower. It's hard to get wrong.

Chassis Dyno:

Drive car on heavy rollers, let car try to accelerate them. Watch rollers to see how fast they accelerate, bust out your Calculus to take the first derivative of the rate of change, extrapolate from that some kind of power number, divide by RPM and work backwards to try to find torque.

As you can see the Engine Dyno has a lot less "magic" in the formulas. In theory a roller dyno should be perfectly accurate, but I don't think the real world bears that out. Which is nothing against chassis dynos, I wish I had one for tuning. I just don't put a lot of credence in the number that comes out for anything other than comparing to itself.

Why hasn't someone yet build a driver's side engine mount with a strain gauge built in? You could have a horsepower gauge (I know our car already does, I mean in general). All it'd have to do is measure the "pull" on the engine mount, do a little basic trig and you'd have your torque right there. Maybe they already exist... if not, consider this my public disclosure :-)

h3mpking

Sorry to hear that, Kevin. Either way, the mods you did are mods you would need to do regardless in support of future upgrades. With approx 20% loss, that puts you roughly at 760 HP motor if your 603ish to the wheel. Your car ran great at the mile and I can not wait to see it run again. Lets get out to the track one of these weekends once the test and tune opens up again. Your Mile speed is right there with the 757 Callaways A8 that just ran in California so your probably right with the 603. Sorry to hear the shop gave you bogus numbers.

BooSSted

Best way to gauge power is to run... Run the quarter run the 1/2 and full mile as you did already. This will validate power. Dyno's will vary from makers and tuners. Jump on a dynapack then a nascar dyno you will truly get your heart broken if your goal is big HP numbers and not time slips.

moon2605

looking at the speeds I think 603 is right on. should have the car back in a few weeks. we will probably do a track rental somewhere. Ill let you know. at the very least hit a TNT. Bad thing is now the nitrous upgrade is only going to be 770 or so. going to be close on hitting 200. may have to overdrive the supercharge. Decisions, decisions. a lot of fun though at the end of the day.

moon2605

I couldn't agree more. Just disappointing to not make the power you paid for. Hopefully this fat shot of nitrous we are adding will move us down the track a little better. at the end of the day I want to get in the high 9s and break 200 in the mile. we are getting closer.

Katech_Zach

Welcome to the world of chassis dynos. It is a daily struggle for me. "Oh, but so and so makes xxxrwhp why do you guys only make xxx?" I'll just go to them because I need a dyno sheet to say xxx for my buddies. And nobody could figure out why my car with "only" 525rwhp would trap at 135mph and the "600rwhp" cars were trapping at 132-134.

/end rant

SurfnSun

Anyone notice the lack of haters in the 202mph thread. Only one guy dared ask the rwhp and he got shut down pretty quick. Its the quietest thread regarding that company I've ever seen. Not mentioning the name here just show it doesn't show up in the search results.

Races are won on the track, not the dyno.

Busa Dave

That is really a good number for the mods you did. 603 is in the park but 670 with headers and meth--way high. I live near you what shop did you use? Might get the car tuned by someone who knows what they are doing to get the most from what you have done. Did not see where you had the CAI replaced. Might give that some thought.

tail_lights

Don't put too much stock into dyno #s. Actual runs at the track and events and races in Mexico (if that's your thing LOL) are what count. 191 at the Mile is very impressive.

moon2605

Thanks, i do have a CAI, have the car at the tuner who did my buddys car. shop in Corpus getting nitrous and a new tune now. The shop i have it now does a lot of nitrous and seem very confident. they have my buddys car running great. he hit 198 at the mile with his c6 z06.

moon2605

Thanks Tail lights. car in a different shop now. looking for 200 in october,

FlamingZ06

Um, yes, they should be different. They are not the same machine. About the only thing they have in common is they are both referred to as chassis dyno's.

And that tells me a little something...

davepl

You lost me. They are different device that if they measured properly should return the same result.

What does that tell you?

Busa Dave

Dave--I thought the same thing. Kind of like having different brands of tape measures that give different readings for the same object being measured...

davepl

I know... beats me, makes no sense. Looks like an attempted slam blew up in his face, I guess.

FastestBusaAround

They should all read the same thing - if properly setup/ built/ calibrated etc...

That's like saying two different rulers give you different measures, because they're made my two different manufacturers.

As far as the only thing they have in "common is that they are chassis dyno's"....that's incorrect. They are all very similar in the way they work and should adhere to some kind of operating standard. Are all weigh-scales going to read differently because they are made by different companies or they look and work slightly differently?

If they did, no one would be able to use them...

davepl

Well, his one valid point is that they're different in one critical sense: one measures acceleration of a roller against momentum, the other measures the ability to overcome gravity against a lever arm.

But like you say, since they both claim to be measuring the same thing (torque) they should crank out the same number even if they use different methods to read it.

I suppose you could have a case where it's not accurate, only repeatable, so you can tune against your own baseline but never compare it to anything else... maybe it reads in NewtonChickens. That's kind of how I treat chassis dynos - great for before and after a change, but I have no idea how many NewtonChickens my car can produce in absolute terms.