Dyno question
 

Does it matter if the run is run in 3rd or 4th gear on our cars?

And... I recall reading somewhere that there's discrepancy between Dynojet type vs. Mustang ones? What's the difference?

thanks!

sub'ing AND not to hijack the thread, but as long as you're commenting.. What's a typical dyno session cost ?

It should not matter what gear you run, the higher gear the better because your run time is longer before maxing out rpm. You need to accurately give the gear ratio including the final drive so that the calculations will run properly thats all. Most places like to run in the gear that yields a 1 to 1 final drive ration so 3rd gear is probably the choice on a stock 930 box.
Accuracy of each type of dyno is all the difference and I am no expert but I know from reading other posts that one type typically overestimates h.p.....cannot remember which....and alot of guys like to hear more h.p. than reality to make the ego feel better.

Power pulls are made in the gear closest to 1:1 ratio.

Tuning pulls are made running through all the gears, and applying loads at various points on the rpm band in each gear, and setting a/f appropriately. Then fine tuning timing

I think we charge $75 for a single setup and power pull, and $150/hour for tuning. Bill handles all that so I'd have to check for the exact #s

Yes different dynos type and mfgs show slightly different power outputs. One reason why SAE corrections are used.... to try and get a level field between all the various mfgs.

Even running the same car on the same dyno can lead to different numbers, i.e. when heat soak starts to rob power, if tire pressures arent correct you might get slip on the rollers, lots and lots of variables.

I have a 4sp stock tranny, and run each dyno in 3rd.

There is a reason they call them Dynojunk. However, if you use a dynojet as a baseline, continue to use that same unit as you make adjustments.

A couple of years ago, I went to local dynojet dyno to test the infamous powerflow intake to see what kind of gains I had (if any). I did a couple of pulls, but his AFR was not working, so I went to another shop across town that had the same model. Although their AFR was working, the pulls were more than 40rwhp lower. I asked how this could be and he said the correction factor used at the first place could have been different. In fact, he asked what HP I would like to see and he would set the CF so I could "show off".

Made my runs in 3rd also. Making runs in 4th will be almost 190mph, which seems a little unsafe to me.

I ran mine last month to establish a baseline - they ran it in 3rd, and it was $85 for 3 pulls. Mustang dyno, and from what I understand they read slightly lower than a Dynojet.

Whatever, I couldn't care less about the net numbers, just the curves and the deltas to come when I get to mods down the road.

An interesting experience tho certainly, was fun.

Does this mean that if a taller ratio (like 4th gear which is more like 0.7:1) will result in different (lower?) numbers?

thanks!

Yes, but the software corrects the number.

Well, maybe this explains the VERY low number I got - 298hp/296ft-lb @ 0.8 bar :(
The only question I was asked is how much does the car weigh.

The same dyno said I had 250hp @ 1 bar when the car was CIS with stock engine internal (but same K27HF and headers) which I thought is very low as even a stock 930 should have that...