How gear affects dyno numbers

[Dbunch9]

So I put a gpi ss3 cam and head setup on my car 2 years ago, had it dyno tuned and it made 450/415 which I always thought was low compared to the other numbers I see online with the same setup so I thought I’d have it dynod again at a different shop but this time around I have 3.91 gears in the differential and it made 475/467. Now while the first numbers are lower, the hp/tq split looks pretty average and now they look way to close together. Does anyone have experience with dynoing different gears on the same setup? I feel like the HP is normal but the Tq should be more like 430-440.

[POWERFREAK]

Don't worry so much about the dyno #'s...different dynos and weather conditions will give you different numbers, as well as different gear ratios...they can result in a different amount of "driveline loss" in HP.

[Dbunch9]

I’m not super caught up in numbers, but I got it tuned by a guy I found out afterwards is a questionable tuner, so I was unsure if his tune was bad or the dyno read low. But now I feel like my numbers are a little out of whack on the torque side so I’m kinda just curious how much the gear affects the numbers. I’m not worried cause I know how my car performs against other cars

[Greenhornet2]

Well did the second shop dynotune it or just run it on the dyno? You would see if it was a tune that made a difference if they ran a baseline pull first. going from dyno to dyno you can see very large sweep in numbers but I believe a lower gear will make for a lower dyno number if run on the same dyno same day no changes. They are just numbers and mean almost nothing by themselves especially in those small margins. It's just a good tuning tool and I guess bragging rights. My car last year was dynotuned at JRE 575whp then I did a dyno day on a mustang dyno and it was 595whp, no changes were made. Its a ballpark number. Numbers that matter are at the track

[Dbunch9]

No tune change just dynod today on the old tune. I care a lot more about trap speed than dyno numbers. Only reason I’m bringing this up is because I thought if one dyno reads higher or lower than the other, the hp/tq split would stay the name. I went from low numbers and average split, to average hp number but abnormal high torque

[InFiD3ViL]

Shouldn't 3.91s cause a slightly lower trap than stock gears? How would the gears affect dyno numbers...Would they?

[Dbunch9]

I’ve only seen people gain mph and lose ET with gears but I haven’t been to the track to say from experience. I’m also not really sure why gears change dyno numbers either but I’ve heard people say it

[Roader]

Who did the previous tune? Lot of “tuners” in that part of Florida.

To put this in perspective when I lived in Tampa. Shop A mustang Dyno (who did tune) showed me a graph with 430ish rwhp. Shop B with a dynojet (went for dyno day) had me at 403 rwhp. Was it weather conditions or did the first shop fudge the numbers to make it Look better?

[Greenhornet2]

Originally Posted by InFiD3ViL

Shouldn't 3.91s cause a slightly lower trap than stock gears? How would the gears affect dyno numbers...Would they?

They affect dyno numbers if it's not calibrated for those gears same way running in 3rd would be different than running in 4th. In the 1/4 if he's getting out of the hole better he'll trap higher with the 3.91s is what he means not speed on the dyno

[POWERFREAK]

Originally Posted by Dbunch9

I’ve only seen people gain mph and lose ET with gears but I haven’t been to the track to say from experience. I’m also not really sure why gears change dyno numbers either but I’ve heard people say it

from what I understand, different gear ratios will cause different amounts of "parasitic loss" (crank hp vs rwhp). It shouldn't make a huge difference, but results may vary. Different types of transmissions, differentials, driveshafts/axles etc...will also change the #'s.

[Dbunch9]

Yeah I guess the new gear ratio tricks the dyno into thinking it has more torque, but the gear also has More parasitic loss so the torque is a little high and hp a little low. Idk just thinking out loud, either way I’m happy with the car and it beats the cars that it should.

[pnwdan]

I would agree that the parasitic loss would be less and the drivetrain as a whole would be more efficient allowing for more WHP. Other than that, I dont think the gears can do anything more or less.

[acammer]

Originally Posted by InFiD3ViL

Shouldn't 3.91s cause a slightly lower trap than stock gears? How would the gears affect dyno numbers...Would they?

More ratio usually only helps mph. If it takes you from a place where you were only make two shifts to a place where you make three shifts and finish out of the power as you go through the traps I could see it hurting trap speed. For my bolt on car going from 3.45's to 4.10's (no other changes) picked up about 1-1.5 mph even though I was making an additional shift. It definitely was easier to launch (even on street tires).

With the cam, I can't imagine not having the 4.10s. I'd run a 4.56 if we could get it.

[christianchevell]

Reading up you would usually find that higher gear ratios usually cause numbers to go down on the same dyno....( it has to be programmed in when changing them to the equation), anyway its formulated off the torque and your working it higher RPMs with the gears and that makes it feel more in the seat of the pants. Different dynos can be way different, mustangs are the "heart breaker"; they do load bearing as in actual driving, others mainly are not load bearing and give higher numbers.....and it can vary a lot so don't sweat it ; that's what you would find and most likely if aggressively cammed well you should be around 450 torque to the rear with a manual; and less for a automatic, the GPW cams spec out good and generally you should look at what others show for the similar with similar mods....Good Day