Dynoing auto's in 2nd
 

I seen some enthusiastic email about how stupid shop techs are for dyno'ing automatics in "2" vs. 3'rd gear. I asked my friend who is a hardcore Honda tuner who has the industry standard Dynojet dyno about this and I got an interesting answer for you guys.

He said that the dyno is RPM based. Not based on gear ratios. He said that there would be a difference in running a car in 2nd vs 3rd but the difference would be very small. Something on the order of 1-2 WHP. He said that on an auto tranny like our Maxima's, with only 1, 2, and D, a third gear run would be very difficult to do properly. "2" would be the best gear selection to do a dyno run in. My old car, an auto Civic, had 1, 2, D3, and D4. This car's tranny can do a 3rd gear run with no problem because it had a 3rd gear provision.

Well, I hope that this somewhat quells the debate over this issue.

Re: Dynoing auto's in 2nd
 

:confused: my 2k2 max has 1, 2, 3, D----and now i'm more confused as to what gear it's supposed to be dynoed in--people here were saying how much carboys sucked for not doing it in third and now you saying it doesn't REALLY matter--would the hondas being RWD make any difference??--people who know, please respond
thanks

Re: Dynoing auto's in 2nd
 

D3 in your Honda is the same is O/D off in which both will cancel any gear higher, 4th gear, while still being able to use the gears lower. Regardless, a proper dyno should be done on the gear that is closer to a 1:1 ratio, which is 3rd gear on the Maxima.

You should still always do a dyno in the gear closest to 1.00:1, though. A DynoJet dyno will correct for gear ratios so that you don't get massively inflated power numbers if you make a run in a lower gear, but it still can't account for the fact that the losses in the tranny increase the further you get from 1.00:1. After correcting for gear ratio's, a 2nd gear dyno run would still probably be lower than a 3rd gear run (for an auto).

The important thing is consistency, though. Your friend is right, the difference would be small, but I think it'd be more than 1-2 whp. Maybe 1-2 whp on a Civic, but the Maxima has double the power. When you're trying to dyno things that only give you 5-10 fwhp you need as much accuracy as possible. If you dyno in 2nd for baseline and then mod and dyno again, just be sure that you dyno in 2nd gear again, otherwise you'll skew your results. Same thing for other gears.

Dyno's are difficult to do on automatic transmissions period, because of their natural tendency to want to downshift on you and spoil your run. I'm not sure if the Maxima is this way or not, but the Accord V6's tranny will lock itself in 2nd gear and not downshift to 1st if you leave the shifter in 2. So to test mods for low-end performance we have no choice but to dyno in 2nd. But for top-end tests we usually use 3rd gear and just get the car cruising on the dyno at a speed where the shift logic won't knock it down to 2nd when you go WOT. That's about 60 mph for us - 3300rpm. When you hit it the torque converter comes out of lockup in 3rd and shoots up to about 3800rpm and then we take that up to redline.

Dyno's are much easier to do on stick shifts :)

Re: Re: Dynoing auto's in 2nd
 

It does matter. On a car with 255HP, I think it'll make more than a 1-2 HP difference. As for gears...

00-01 1 => 2k2 1
00-01 2 => 2k2 2
00-01 D (O/D Off) => 2k2 3
00-01 D (O/D On) => 2k2 D

This carboy place, if I remember properly, also didn't use SAE correction, and also didn't even have a fan on your car, and didn't even have the hood open. If I've got this right then trust me, Carboy still sucks!! :D

Re: Dynoing auto's in 2nd
 

Sorry but tell your friend to take some DYNOJET training because he doesn't know what he is talking about.

The gear closest to 1:1 is the gear that will show the ACTUAL hp in the most ACCURATE reading. 3rd gear on autos with OD off and 4th in 5spds. This is a industry standard of doing this.

Re: Re: Dynoing auto's in 2nd
 

Sorry Russ, he's worked on a Dynojet for 4 years and building race cars is his life, but you go ahead and take him to school about a dyno. Yes, 3rd gear is best but how are you going to get an auto max to redline in 3rd? And what's this with 4th gear on a 5 speed?

PS - I'm still looking for that stock manual Maxima in the So Cal area! Whoever it is gets a free intake and dyno, in 3rd gear :laugh:

THANX :)

Re: Re: Re: Dynoing auto's in 2nd
 

Easy, turn off OD and it will bounce off the limiter at 125~mph. Sorry I have worked and helped many dyno sessions in 5 years. I may not work at the shop but I know how they work. I would never take my car to someone who says that about a 4spd automatic. LOL. What do you not understand about 4th gear on the 5spd? That is the proper gear for dynoing.

3rd gear will show about 10-15hp less in some cases but alot more TQ because it will wind out that gear MUCH FASTER. 4th gear takes more time to wind out, it gives the equipment time to see the actual correct readings.

4th gear is closest to 1:1 on all cars.

The torque converter does not lock up in 2nd or 1st gear so you don't get the best power transfer. In 3rd and 4th (O/D) the TC is locked. You should dyno in 3rd for an auto....

I was the one who did a dyno run with Carboy initially. Just for the record, the hood was open and the fan was running for a good 5 minutes before each run.

But the fact remains, it wasn't SAE corrected and it was run on 2nd gear.

I'm sorry, but I have to jump into this one.

Russ and Steve are right - some points:

1. To get the most accurate reading as possible, the gear ratio should be as close to 1:1 as possible.

2. In auto trannys, this is usually 3rd gear.

3. In manual trannys, this is usually 4th gear.

4. For auto trannys, it is very important to use 3rd ALSO because in 2nd or 1st gear, the torque converter does not lock up (as in most cars), so you are loosing power there as well.

5. BIG fans should be run with the hood open.

6. For comparison and accuracy, results should be available in SAE corrected form.


THE ABOVE POINTS ARE STANDARD PRACTICE FOR PROPER DYNOS.

If your friend (or any other "dyno" shop or pro) does not know, use or agree with ANY of the above points, I would fully question their expertise (on dynos - not engine building) and walk out the door.

Your friend is not correct, an auto should be dynoed in 3rd on the Max, and there will likely be a significant difference. On C5 corvettes, some memebers have done dynos in both 2nd and 3rd trying to get the highest HP reading... the 3rd gear dyno usually is 15-25 HP higher than the one done in 2nd.