Do gears affect Dyno Numbers?
 

I haven't gotten a clear answer on this yet.

Technically when you step up your gears from say 3.55 to 4.10's your putting more torque to the rear wheel right? So wouldn't that increase your torque and HP on the Dyno?

Re: Do gears affect Dyno Numbers?
 

Actually, I've heard the opposite.

A loss of 3 - 5 rwhp is what I've seen reported, but this is also in-line with simple dyno/car/engine variation from one day to another.

I've never seen anyone report a power/torque gain from lower (higher numerically) gears...

I always believed that there was a slight loss as well. Tim of Modular Powerhouse confirmed this when I asked him. It is nothing really to worry about though, for a loss of a couple of hp, you are picking up a few tenths.

Off this topic but Tell me about your Pro-M 95 mm MAF and the JLT RAI.

Does this integrate with the shaker? Any stalling problems?

Well, since you want to hijack your own thread I'll be happy to tell you. The Pro-M/JLT combo that I have has given me absoluely no stalling issues, or any issues whatsoever. It does not integrate with the shaker though so if you want to keep that functional go with either the K&N or the MRT. I cant tell you if the Pro-M increases horsepower, but 3 of the 4 strongest N/A (as far as dyno numbers go) automatic Machs that I've seen here run an aftermarket meter. "cmylxgo" is the only one that didn't at the time that he made like 280hp STD. Jim Vaccaro, BlackMach, and I all are in the exact same range and use a Pro-M. I firmly believe that I'll dyno quite a bit higher once I can figure out what in the heck is killing my power at 4800rpm (see my dyno in this section of the forums). Personally I say whatever has a bigger hole and lets more air go through, makes more power IF you have the means to burn it better, and get it out of the back of your car faster. But you will need additional mods and a good tune to see the benefits of adding an aftermarket meter. Just buying one and putting it on will not really do you any good except for adding a $250 ornament under your hood.

Hope this helps, but it's just my opinion.

you are increasing the speed at which you're spinning your transmission and rear end assembly by upping your gears, therefore the resistance is higher = more drivetrain loss. you will be dynoing lower.

You are also multiplying your torque by a different amount (4.1 instead of 3.55), but the dyno takes that into consideration; they will ask you what gears you're running.

dynoing an auto is the best thing to see this... it's very common for them to be dynoed in 3rd, where their 1.0 gear is, however, they can't hold that gear at say, 40 mph/2000 rpm to start in it, so they will end up inevitably starting in 2nd, and getting a good upshift, then keep going into 3rd till redline. 2nd gear is usually at the beginning of a dyno of an automatic car, and you'll be able to see it as being quite a big jump at the beginning (50-100 hp) then the regular dyno graphs show... basically 2nd gear on an auto is what would happen if you don't tell the dyno operator that you've got 4.10s and he keeps the 3.55 ratio in there. it'll show that you're making 600 hp, but your dyno will end at 3500 rpm :p

Both shops here in Houston that I've used say that there is no difference between the 3.55/4.10 gears. One of the shops did a before/after dyno to prove it. Of course if you are talking about a 5 hp loss, that's only 1.6% of the motor's power.

I watched my buddy get his LS1 dyno tuned last friday at Carolina Auto Masters. He went from 3.27's to 4.10's. We asked Creech about it and he said that you should lose anymore than 5hp, but you'll pick up a little torque. Creech is well known in the south for his work with LS1's. I don't see why it would be any different on our Mach's.

Re: Do gears affect Dyno Numbers?
 

HTH...

I found this on IMBOC.com;

QUESTION:
A car having 3:27 rear end gears is placed on a DynoJet chassis dyno and
has a dyno performed. Then this same car is taken off the DynoJet
chassis dyno and has the rear end gears changed to 4:10. The car is then
placed back on the DynoJet chassis dyno and another dyno is performed.
Will the second dyno show a loss of horse power caused by the 3:27 to
4:10 gear change?

ANSWER:
Yes. This has been a long standing debate among car enthusiast, so I
recently emailed DynoJet and asked this exact question. Below is the
response I received.

"The 4:10 gear will show less horsepower than the 3:27. The reason is
due to rate of acceleration changes. The rate of acceleration is quicker
with the 4:10 because of torque multiplication being increased to the
rear wheel. The horsepower will show less because the targeted RPM is
met before the horsepower has a chance to overcome the rotational mass
(dyno, drive line, etc.) or moment of inertia in speed. Because the
speed is decreased and the RPM is met faster, the horsepower never has a
chance to catch up with itself, so to speak. The overall ratio of 1:1
will always produce the most horsepower on the chassis dyno. Having said
this, a similar problem can occur with horsepower loss when the rear
gear is too high. The horsepower is being absorbed in just trying to
keep the rotational mass spinning. Please keep in mind that your
engine's horsepower never changes but what gets to the dyno or drive
surface does. If you have any further questions please don't hesitate to
ask. Thank you."

For us automatic owners who increase the stall speed on the torque converter, I found this on the Precision Industries web site:

"THE TRUTH ABOUT DYNAMOMETER READINGS AND HIGH STALL TORQUE CONVERTERS

There is a misconception and a lot of misinformation about the poor vehicle performance numbers that are generated by testing a car with a high stall torque converter on a dynamometer. Most people that are not familiar with how a torque converter operates will automatically think that the torque converter is inefficient. This is totally false and the following facts are why you should not believe the dynamometer numbers while using an unlocked high stall torque converter. All late model dynamometers have a software program that commands the loading and speed of the vehicle over a certain period of time while making a test pull. The software used in these dynamometers is setup to be used with a locked 1:1 connection between the engine and the rear wheels, such as using a standard shift transmission in 3rd gear or when an automatic transmission has the torque converter clutch locked. When an unlocked high stall torque converter is used to make the pull and the dynamometer software has not been changed to allow for the fluid coupling differences the dynamometer readings will all be bogus. For instance, the low rpm torque readings will be high due to the torque multiplication of the torque converter being run in partial stall. Likewise,the high rpm torque readings will be low due to the long period of time the dynamometer takes to allow the torque converter to transition from partial torque multiplication to a hydraulic locked condition. The only cure for this phenomenon is to rewrite the dynamometer software to prevent this from happening. Torque converters with a low STR or low stall are not as adversely affected by this phenomenon. The high rpm transition problems never occur when the vehicle is being driven or raced normally. Therefore, worrying about what the dynamometer numbers are is a total waste of time. If your dynamometer operator refuses to alter the software to give correct readings then the only things you can do is (1.) lock the torque converter clutch and do the testing, (2.) use the readings you get with an unlocked torque converter as a baseline and continue to tune the car like normal until you get the best numbers remembering these are just numbers and not the actual horsepower and torque or (3.) use a dynamometer shop that gives you the service you deserve for your hard earned money. The only really true test of the performance of a vehicle is to take it to the track and see what ET and MPH the car will run."

thanks for everyone's input on this :)

nice thread!

Good read guys, thanks.:THUMBSUP:

Re: Do gears affect Dyno Numbers?
 

You learn something every day!!!

Re: Do gears affect Dyno Numbers?
 

All of the above answers are excellant and provided the information that was asked for. There is also another explanation that is easier to wrap you head around. Our drivetrains are geared in such a way that the driveline is in a 1:1 ratio in 4th (manual) or 3rd (auto) and thats the numbers the dyno uses to do its math. When you change the gears from 3.55 to 4.10 (or 3.90, 4.30, etc.) you are unable to get to that 1:1 ratio... thus the "discount" of horsepower. The lower the gear (numerically higher) the greater the loss of horsepower... according to the dyno.

Some, not all, dyno packages are able to compensate for the gear change, but the operator won't know to make changes unless the owner of the car provides that information.

Just remember the dyno numbers in and of themselves don't mean anything. They are only valuable in that they, first, provide a baseline number that is used to measure relative gains/losses achieved by making modifications to the car.

The only accurate measurement of horsepower is by going to the track and running the 1/4 mile. By having the racing weight, ET, and mph, you can compute the REAL horsepower.

Re: Do gears affect Dyno Numbers?
 

I did not know the T/C was such a factor. Like Jim said "you learn something new everyday."

My 90 GT is a good example. I am runing a PI 3500 stall T/C (AOD & 4.10 's). I dynoed at 247 rwhp/288rwt but I can run mid 12's on street tires @3400 lbs(see sig for details). Using some of the online HP calculators I should be making around 325-330 RWHp which is probably about right.

I knew the dyno readings were wrong-just didn't know why. Thanks for the info.

Re: Do gears affect Dyno Numbers?
 

Lots of good info here. Later this year I'm going with the 4.10's. Sounds like I might want to add the CAI and X-pipe, get a dyno, and then add the gears. We know the gears don't add hp so wouldn't that be a reasonable approach?

:OFFTOPIC:
Now here's another little thread hijack. Our altitude here is going to affect my dyno numbers, right? I'm expecting the dyno to show the rule-of-thumb 20% less HP to the rear wheels than at sea level.

Re: Do gears affect Dyno Numbers?
 

I used to live in Albuquerque and I have before and after Dyno's...of Albuquerque (5000 ft) vs. Florida (sea level)...

Uncorrected 5000 ft was 233 hp
Uncorrected Sealevel was 290 hp Same Configuration

Night and day... Best ET in ABQ was 13.99 @ 101
Now I'm at 12.88 @ 107.68 with a couple extra mods (spacer & CAI)

Get a chip and get your timing advanced... this will help you overcome the altitude a tiny bit, give you an extra 10 hp maybe.

Re: Do gears affect Dyno Numbers?
 

Get a chip and get your timing advanced... this will help you overcome the altitude a tiny bit, give you an extra 10 hp maybe.[/QUOTE]

Forget the chip, it's old technology. Get a SCT custom tune or even just a handheld programmer. Chip automatically voids the warranty but a programmer or tune will reflash the PCM. You can always put the stock tune back in for a trip to the dealer. Why chip it when a reflash yields the same results.

Re: Do gears affect Dyno Numbers?
 

Yeah that's true...

I would definitley go for the custom tune though.

Re: Do gears affect Dyno Numbers?
 

blueautomach,

I just happened to see your problem while reading this thread. They were able to solve the loss of power above 4000 RPM on my car by limiting the knock sensors ability to pull so much timing. If your car is not pinging, it's not necessary for them to pull so much timing. I think mine are limited to only 2 degrees now. I picked up over 30hp above 4000 after this. Hope this helps.

Rob

Re: Do gears affect Dyno Numbers?
 

I have heard that the gears will make your numbers read about 3% lower than actual. This percentage seems high to me! If this were true would my 458rwhp on a Mustang dyno really be nearer 472 if I take into account a 3% difference for my 4.10's?

Re: Do gears affect Dyno Numbers?
 

The lower the gear, the lower the dyno number.

A car with 3.55s will dyno slightly more than a car with 4.10s.

Re: Do gears affect Dyno Numbers?
 

This is a question that i have been wondering about for quite some time, especially since i have recently put my car on the dyno. This may only help me, but if this theory is true, then what do you guys think my car actually has at the wheels? My add-ons are in my signature. My numbers came in at 287hp, 300lb tq. Remember i went from 3:55 to 4:10.

Re: Do gears affect Dyno Numbers?
 

Old thread, but very interesting in my situation...

My '07 Mustang GT is an automatic with a 4,500 rpm stall converter and I swapped the 3.31 gears for 4.10 gears. Double whammy on the dyno based on the info provided above about lower gears and stall converters. To further add to my car's lower dyno #'s, my tuner's dyno is a Mustang Chassis Dyno (vs the more commonly used Dynojet which tends to read higher than the MD). Still very happy with the 351 rwhp and 12.57 @ 110+ mph 1/4 mile performance, though.

Re: Do gears affect Dyno Numbers?
 

my tuner told me to put my gears in before the tune because they would load the motor at diffrent rpms than the stock gears i dont know if thats true but now i wonder what my 318rwhp would be with out 430s and 10.5dds with315s