Hello I have been told a few times by various people that a dyno run in 3rd gear will give a higher reading then a run in 4th gear ... I have seen people post up graphs where both gears looked much the same.

The shop I go to usually do's 3rd gear runs for some reason can someone shed any light here.??

 

Someone must know?

 

a gear is a torque multiplier so when you have it in 3rd gear you are going to have a higher number than 4th b/c of the steeper gear ratio.

4th gear on almost all cars are 1:1 or very close to it so thats why you want to dyno in 4th

 

Gear ratios trade rpm for torque. The higher the gear ratio, the higher the torque reading. The higher numerical value, the faster you'll travel through the rpm band. The lower the numerical valve, the slower you'll travel through the rpm band but the more torque you'll transfer out. The power doesnt change, its essentially power in=power out. The transmissions have 15% drivetrain loss, so that has to be factor in.

 

Thanks for the reply's so its the torque reading that would be higher not the horsepower?? Is that correct

 

Yeh the torque @ the wheels is higher in 3rd gear then in 4th. But the dyno doesn't know what kinda gears ur car has. The dyno only knows rpm and mph. it uses those to figure out what gear u have then divides it out as if u didn't have a transmission and gives u the #'s you see on a print out. 3rd/4th gear dyno #'s should be the same, or very close. I have actually heard of 4th dyno'ing higher then 3rd because of the added load on the motor.

If u were to calculate actual torque at the wheels through the tranny, 1st gear would be about 4 times as high as what u read on a dyno print out, 2nd is around 3 times as high, 3rd would be around twice as high and 4th would be about the same. thats why they say 4th is almost a 1:1 ratio.

 

Good topic!

So I should be dynoing in 4th with my JDM S1 transmission?

Reason I ask is I'm going this Saturday morning...

 

Power in=Power out

Gear Ratio=Number of teeth of gear 1/Number of teeth of gear 2

Gear Ratio=Tin/Tout

Gear Ratio=Rpm out/RPM in

For example the LS transmission:

3rd gear: Gear Ratio=Gear 1 (counter)/Gear 2 (main)=33/26=1.26:1

4th gear: Gear Ratio=Gear 1 (counter)/Gear 2 (main)=30/29=1.03:1

Now apply Gear Ratio=RPM out/RPM in at 4,000 rpm for example.

3rd Gear: 1.26=RPM out/4,000 RPM out=5040

4th Gear: 1.03=RPM out/4,000 RPM out=4120

Now apply Gear Ratio=Torque in/Torque out at 122 ft lb (engine torque going into transmission)

3rd Gear: 1.26=122/Torque out Torque out=96.8 ft-lb

4th Gear: 1.03=122/Torque out Torque out=118.44

This is all hypotetical, but it shows you that 3rd gear gains more rpm but less torque, where 4th gains more torque less rpm.

 

I just phoned the tuner, yes IRepD thats correct third actually gives a slightly lower HP reading tuner said 4th gear is more efficient by about 1-2% so you will get a slightly higher reading in 4th he said the lack of gearing has something to do with it. Yeah the torque certainly does multiply in the lower gears.

Cheers all, Boosted Hybrid I almost understand what your trying say

 

good info guys

 

so 4th gear would yield better hp...someone explain the tq please i cant think right ...jsut plain and simple please

 

**** numbers--- whats better for TUNING?

 

Just to keep it simple, the gear ratios ratios multiply the torque so the lower gears having higher ratios give much higher readings for torque. Yeah 4th gear is best for an accurate torque and hp reading.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turbozxi &raquo;</TD></TR><TR><TD CLASS="quote"> Yeah 4th gear is best for an accurate torque and hp reading. </TD></TR></TABLE>

like i said, who cares about numbers... PC racers??

what is better for spitting out a more reliable a/f to the wideband sniffer?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">Power in=Power out

Gear Ratio=Number of teeth of gear 1/Number of teeth of gear 2

Gear Ratio=Tin/Tout

Gear Ratio=Rpm out/RPM in

For example the LS transmission:

3rd gear: Gear Ratio=Gear 1 (counter)/Gear 2 (main)=33/26=1.26:1

4th gear: Gear Ratio=Gear 1 (counter)/Gear 2 (main)=30/29=1.03:1

Now apply Gear Ratio=RPM out/RPM in at 4,000 rpm for example.

3rd Gear: 1.26=RPM out/4,000 RPM out=5040

4th Gear: 1.03=RPM out/4,000 RPM out=4120

Now apply Gear Ratio=Torque in/Torque out at 122 ft lb (engine torque going into transmission)

3rd Gear: 1.26=122/Torque out Torque out=96.8 ft-lb

4th Gear: 1.03=122/Torque out Torque out=118.44

This is all hypotetical, but it shows you that 3rd gear gains more rpm but less torque, where 4th gains more torque less rpm.

</TD></TR></TABLE> all this sounds pretty good. but i would not dyno a low hp car in 4th gear. i would dyno a high hp car in 4th gear, other wise a high hp car will spin tires in a lower gear and will not get an accurate reading. also in a high hp car it will a sample more af points. thats about it . anyway good post boost hybrid

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by delvtecsol &raquo;</TD></TR><TR><TD CLASS="quote">

like i said, who cares about numbers... PC racers??

what is better for spitting out a more reliable a/f to the wideband sniffer?</TD></TR></TABLE>

Well numbers do reflect on how well you have done the job would you prefer a dyno readout without them? To answer your question there would be no difference after all its an A/F ratio thats all.

 

When I dyno'd my car we were doing all the pulls in 3rd gear. I wanted to try a 4th gear pull to see if the added load changed anything. Everything stayed the same and I made withen .2hp of the pull before. Dont remember if it was higher or lower, wasn't much difference.

 

You will want to dyno in whatever gear is closest to 1:1. It'll give the most accurate readout of engine power without gearing swaying the results. Usually for our cars 4th is the best gear.

 

I know from experience dyno in 4th gear is best in these transmission G3-GSR, 90-91' LS, and JDM S1. (I don't really know about the others)

 

when i got my car dynoed they asked me for my final drive ratio and the 3rd gear ratio. Do all dyno places do that??

 

i've been to 3 places, and not one has asked.

maybe they knew what is was (doubtful), or just don't care (most likely)