Dyno results before & after tune up.

Tim Bro,

Our relationship was never broken, so no need to rebuild anything.

There are 87-93 mustangs in my area that are superchaged and will blow the doors off of my (and at least 50% of the 40s on this forum) GT40. I have been there when they (and my GT40) were CHASSIS DYNOED and became a beliver in relationship between the darg numbers and machine.

I am trying to build a GT40 that can do drags. So, when I come across numbers that Ross, Rick Merz or Roy have, I become very intereseted.

Calculations, trying to figure out the exact numbers,,,,etc don't mean s*%$ to me. No offence. /ubbthreads/images/graemlins/wink.gif

 

There are only a few things that any one can measure, a dynojet only measures revolutions and time. Everything else is derived from those numbers and a measurement of the mass of the roller.

The data is only as good as your correction factors.

An engine dyno measures revolutions and time with fluid flow and tempature or electric current and voltage for the brake. Once again, the data is only as good as the correction factors.

As long as the engines were tested properly in both situations, the results are equally valid.

Rear wheel horse power may have a better corelation to how fast your car is, but I have not heard of many people that get a new transmission or lighter wheels just to improve their rear wheel horse power figures. They usually blame the engine for the rest of the drivetrain.

If you don't want to be disappointed, don't try a chassis dyno. A 15%+ hit in your horse power always hurts.

Also, lots of manual transmission, front engine, RWD cars in the U.S. have found that drive train losses are about 15% or more. So 300 hp at the wheels is more like 353 fly wheel horse power, not 400. Any dyno opperator can tell you the most favorable correction. That will make you feel better and spend more money. The more hp you make, the more money they make, so some opperators will skew the results to please you (some will have a heater by the tempature sensor to throw off the weather corrections).

 

[Trevor Booth]

Tim , we are on the same wavelength. "work is work done no matter how it is done" (Julius Sumner Miller). The dyno sheet shows kW on the left so presumably it has measured the torque and calculated the kW. You could derive the "torque" figure from the RPM annotated to the graph, But what torque has it measured, has it corrected for the inertia of the dyno, the wheels etc. IMHO the number reported has no basis in science.
Trevor

 

[Trevor Booth]

Hi Ross, HP or kW ( power) is not a measured thing, it is calculated (in this particular case) from the measured torque and the measured RPM. Power is work done over time. The vagaries of a chassis dyno prevent accurate measurement of torque and hence HP. They are great things for tuning your car and trying different things as long as you use the increase or, heaven forbid, decrease as a relative number. I am not suggesting that you pull the engine out each time you want to try something new, but when you first build it put it on an engine dyno and then after installation put it on a chasssi dyno. If you want to get some good results spend the whole day and do runs in differing gears at varying RPM in 500RPM increments. Let the engine stabilise at load before you go up another 500 and so on.
Cheers
Trevor

 

[Howard Jones]

How about the corvette in the rear view mirror's rate of decrease in size. That's the measurement I"M TALKING ABOUT!!!

You can't measure that on a dyno.

 

[Trevor Booth]

Yep, thats the important one, little else matters.

 

[Ross Nicol]

Re: Dyno results before & after tune up.

Trevor
What matters to me is that the 15Kw the chassis dyno told me I had gained at the rear wheels, got me up to 5th place in the final race at Sandown yesterday.You would have to agree a chassis Dyno is a good thing if you do a pre then post run after tuning.
Such a good feeling when that damn Westfield clubman got past me at the start, to know I can blow him away and finish him off on the next straight, oh such power. Thanks for the American muscle chaps. Pretty cheap too.

Ross

 

[Trevor Booth]

Hi Ross, I do agree they are great things for tuning your car and getting a better "number". Keep playing and you will get to the pointy end of the field. "Westfield clubman beating me off the start" tut tut