Dynos and "False" Readings Question...

Hi,

I've read a few dyno tests with TDI owners. Some guys make the runs in 4th gear. Others say to use 3rd because it pulls harder. Since most cars have a 1.000 4th gear ratio, I thought the idea was to use 4th gear in order to give that 1:1 ratio between the engine and the wheels. Then factor in the 17% loss with the transmission.

But many TDI owners are using third to get the higher torque readings. Since 3rd gear is obviously a lower gear ratio than 4th, isn't that multiplying the torque that's applied to the wheels? Are 3rd-gear torque numbers actually inaccurate? Someone please explain...

All my dyno runs have been in 4th gear and with a 15% transmission loss.. This was recommended by the dyno shop...

I'm not sure about 3rd pulling harder than 4th.... That's not the point... the point is to get as close to 1 to 1 gearing as possible.... Atleast on my NB it's .97 to one...

Gary M

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Stealth TDI:
But many TDI owners are using third to get the higher torque readings.<HR></BLOCKQUOTE>

It would be more accurate to say "But many TDI owners are recommending the use of 3rd gear to get the higher torque readings."

Hmmmm.... Last week, I got something like 290# of torque using 4th gear.... Don't think I need 3rd gear to "make" the numbers look better...

At the Atlanta GTG, when we go to the Dyno, we will suggest they use 4th gear.... I've not seen a 3rd gear run listed anywhere... But I suppose we could try one, just to see what happens...

Gary M

I made three runs at the dyno shop today and the guys there said they had heard of doing it in 4th gear, but never use the results from those. I did three runs - 2 in 3rd gear and 1 in 4th. The run in 4th gear took too long and made the curve really long. Both of the 3rd gear runs were pretty consistent (114.3 and 113.0 hp.)

Once I can post the results, I'll put them out there.

Kevin

Since Oldman owned a dyno shop, let me jump in.

The 15% figure is for mag racer to toss around. The true loss figure is a function of torque and RPM with RPM being far greater. i.e a GS-R Integra is losing more HP at 7500 rpm and 150 HP than a TDI at 3500 rpm and 150 HP. So forget trying to get engine HP out of wheel HP. Just take it as is "wheel HP"!

On gassers, turbo motors put out far more wheel HP on a non-load dyno like the dynojet, a program load dyno like Bosch or Mustang that can loar the engine will show a HUGE drop in HP on any turbo gasser motor.

All dynos run correction factors and they are NOT the SAE factor that OEM rates engines at. Bummer but true. That said, forget about CFs as they are just used by guys trying to show how has the bigger err I mean more HP. If your dyno is running a large CF have two graphs made, 1 as measured and one with the CF. Large is anything out side 5% IMO.

Evl Dzl,

It takes me about 14 seconds to make a 4th gear run... You should see a Civic on the dyno... Takes FOREVER to get those 3500# rollers going...

As for correction factor... The software and data that I get from the Dyno jet allows me to view my runs with any of the 5 CF (including the so called SAE) or NONE.... Whatever you choose to use... just make sure you document it...

Oldman, Is your's a mustang or Dynojet brand ?!?!? Just curious...

Gary M

It was a dynojet. Maybe my next shop I'll go to a Mustang!, I'd rather have the extra money for a mandrel bender. Since the Mustang dyno is far more accurate and you can get coast down powerloss, nobody wants to use them. The dynojet is far better for the dyno racers out there.

Gary, agree just be sure others out there know about correction factors. One other thing the correction factors DON'T work for turbo motors no even close. In general on turo cars the CF should NOT take into account altitude or barametric pressure. As turbo motors in general lose far LESS HP than a NA motor. Of course on turbo motors with limited compressor wheels, this loss can be far MORE but I won't go there today.

So here I stand so far $300.00 I have a setof injectors for the wife's future auto TDI, she still has her mind set on a gasser BMW. I have enough HP to blow 95% of the TDI out there into the weeds (almost all the 4 banger eco boxes) and I'm at 55 MPG going into spring where I need no a/c and no heater defroster, toss in red line MTL, Amsoil 3000 and the light weight spare (a can of fix a flat) I'm never more than 10 miles from home, more break in miles. I think 57 MPG is in reach! Man I love this TDI, I get more HP and the MPG goes up. Try that on a gasser!