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HP to Weight ratio


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Posted

As far as car classification goes, is the hp to weight ratio measured at the crank or at the wheels? If your using a chassis dyno it's measuring from the wheels. I'm trying to class my 1999 Mustang Cobra and I'm not sure what is the base class I start from. I think TTC with the *.

Posted

its done by wheel horsepower

 

note - for TTA and below you must meet points limits AND adjusted whp/weight limits

Posted
I'm trying to class my 1999 Mustang Cobra and I'm not sure what is the base class I start from. I think TTC with the *.

That is correct per the 2009 rules:

 

Ford Mustang Cobra ('99 & '01) TTC* 3285

Mark

Posted
its done by wheel horsepower

 

 

And for RWD or FWD vehicles MUST be from a Dynojet. Not only do numbers vary significantly from dyno brands, but environmental factors can have a big impact as well.

Posted

The rules don't say (anywhere I see) whether it's 'uncorrected' HP or 'SAE'. I would make an 'ass'umption, but that would make a 'you know what' out of me.

Posted
The rules don't say (anywhere I see) whether it's 'uncorrected' HP or 'SAE'. I would make an 'ass'umption, but that would make a 'you know what' out of me.

They say in section 6.4.2 Dyno Testing Procedures on page 28 of the 2009 TT Rules. Really, they do!

 

Mark

  • National Staff
Posted

It actually says it twice in that section. Yes, SAE correction. Smoothing Factor 5.

Posted

I would definitely take it to a dynojet! my car put down nearly 220RWHP on a dyno dynamics. I took it to a dynojet and the SAE correct HP is 197HP. From what the dyno guy said a lot of these dyno's results can be messed with pretty easily.

Posted

Most people don't understand that chassis dynos are just rough measuring sticks, and nothing more. If you're trying to tune your engine, then just make sure that you're using the same one over and over. If the rules say that you can only use a specific one, then make sure that you do. I know of people who take their dyno queens to different shops because their car "makes more power on the other brand of dyno." Duh.

 

Non-specific example: It's like building a house and having 2 measuring tapes that each show a "foot" as being 2 different lengths. As long as you stick to using the same measuring tape throughout construction, everything will fit together, although the final result will be scaled up or down a bit compared to a house that used the other tape. If you switch measuring tapes halfway through construction, then you have no idea where you really stand and the roof might never cover all 4 walls. If the building code says to use 1 specific tape measure, then you had better make sure that you use that one, no matter how big or small the house may be when you are done.

 

Mark

Posted
Most people don't understand that chassis dynos are just rough measuring sticks, and nothing more. If you're trying to tune your engine, then just make sure that you're using the same one over and over. If the rules say that you can only use a specific one, then make sure that you do. I know of people who take their dyno queens to different shops because their car "makes more power on the other brand of dyno." Duh.

 

Non-specific example: It's like building a house and having 2 measuring tapes that each show a "foot" as being 2 different lengths. As long as you stick to using the same measuring tape throughout construction, everything will fit together, although the final result will be scaled up or down a bit compared to a house that used the other tape. If you switch measuring tapes halfway through construction, then you have no idea where you really stand and the roof might never cover all 4 walls. If the building code says to use 1 specific tape measure, then you had better make sure that you use that one, no matter how big or small the house may be when you are done.

 

Mark

 

Nice explanation. What size is the gov't stick?

 

Dynos depend a good deal on accurate weather - being close to an airport to get correct density altitude prevents the guessing. A lot of tuners fudge the weather to show dramatic improvements. Racers fudge the weather to show the sheet to the TT Directors .

Posted

my car dyno'd right after RA (got it tuned) did 10 hp/10 ft/lbs less on the same dynojet than it had just previously done. only change was heavier (street) rear wheels/tires and 15w50 oil vs 5w30. (which may have accounted for all of it). it was actually cooler on the 2nd session, it was very hot/humid the first session a month or so back

 

the delta after the tune was 10 hp/10 ft/lbs and a bunch more mid range torque and a much smoother curve. I could have really used that at RA

Posted
my car dyno'd right after RA (got it tuned) did 10 hp/10 ft/lbs less on the same dynojet than it had just previously done. only change was heavier (street) rear wheels/tires and 15w50 oil vs 5w30. (which may have accounted for all of it). it was actually cooler on the 2nd session, it was very hot/humid the first session a month or so back

 

the delta after the tune was 10 hp/10 ft/lbs and a bunch more mid range torque and a much smoother curve. I could have really used that at RA

 

 

where did you go?

Posted

dynolab

 

I will used Balanced if/when I go next time. didn't realize how close they were to me

Posted

Since DynoJets measure whp based on the angular acceleration rate of a fixed mass, heavier wheels will show less whp (and heavier oil will show less whp too). Make sure you use the lightest wheels you will use in competition when getting a dyno for TT/PT competition if you are close to the limit.

Posted

Hi Im am new here trying to build a C4 Corvette for TTA. Im not new to racing, just the NASA TT format. Anyone know of a dynojet in the Cleveland area? Also, where can I weigh my car so I know what HP Im limited to?

Posted
Hi Im am new here trying to build a C4 Corvette for TTA. Im not new to racing, just the NASA TT format. Anyone know of a dynojet in the Cleveland area? Also, where can I weigh my car so I know what HP Im limited to?

Dynojet locations:

http://www.dynojet.com/dyno_centers/list_automotive.aspx

 

For scales, you will have to get creative if you want a ballpark weight. Try race shops, local tracks/dragstrips, truck stops, transfer stations, the dump, recycling centers, etc. Note that some of these scales go in coarse increments (sometimes 20 lbs), so the weights will neither be exact nor official.

 

Mark

Posted
Medina:

http://www.backstreetper.com/" onclick="window.open(this.href);return false;

 

And in a pinch you could use a truck-stop scale. $9 around here.

 

Thanks! I will have to see if they can dyno tune a L98 as well.

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