Thinking about a gearing change

Six_Sloww · Jun 25, 2014

Jared @ River City Diesel said:
Too legit. 3.31 and a grizzly locker FTW?

Is the 3.31 the gear to go with for drag racing?

I've never driven a 6.0 with anything taller than a 3.73

Trqmnstr · Jun 25, 2014

Six_Sloww said:
I worked with mike when he worked at deans sellers in Troy, MI. I also worked with chuck who was his lead tech, and he's the guy that took over the shop (rolling coal customs). I know some stuff, it's just the minor details.. Nbd, now that I'm turning the bolts on it I'll find out everything I need to know.

Sounds like youll have it all figured out on your own then. I did know a chuck that was a tech from the romeo area also. Cant remember his last name tho, i do recall he built a hell of a cummins, iirc it was a 24v but im trying to recall from over 10 years ago. Ive been out of Mi for too long.

KCTurbos · Jun 25, 2014

Six_Sloww said:
Here's another graph that doesn't cut off

Please excuse my lack of knowledge for the track... I am just getting into the track events and have been studying this very subject.

Would the reason to drop down to 3.31 gear ratio be so that you don't shift into OD (6th gear) when going down the track? That way you keep the 1:1 drive ratio and have 1 less shift to worry about?

To help pick your tire and gear ratio you can use this site. Go to the calculator for "Transmission Ratio RPM". Then start playing around. You don't want the truck to be shifting as it hits the end of the track. You probably want to be pretty close to the end of the rpms band where you make your most power. If you pick the wrong ratio then you might hit the end of the track at too high/low of an rpm
http://www.ringpinion.com/Calculators/Calc_RPM.aspx

Currently with a guesstimated trap speed of 111mph with 32.5" tires and 4.30 gears you will hit the end of the track in 5th (really 6th) at 3500rpms

Currently with a guesstimated trap speed of 111mph with 32.5" tires and 3.31 gears you will hit the end of the track in 4th (really 5th) at 3800rpms

You can guess and check with your mph and gears until you get the ratio that will best suite your needs

In regards to you dyno graphs. They all seem to have similar curves... but way different numbers. That is okay because the curve and rpm can tell you a lot.

Your power curve seems to come on really late??? That is probably why the gear ratio got changed, to help put the power to the ground earlier. Your peak torque is at 3500rpms... that is pretty late in the rpm band. Also at 2500rpms you are only make a max torque of 450ft/lbs... I would imagine it should be much higher than that (more like 700-900). Most 6.0 dyno's that I have seen make their peak power between 2700-3000 rpms. Even an s475 should have peak tq at around 3000rpms???

I have not driven the truck but from the dyno graph I would imagine the truck is pretty laggy and smokey below 2500 rpms... by 3500 it is probably a complete monster. That would mean in 1st gear that if you floor it at anything under 10-20mph it is probably smokey and laggy... 25-30mph in 1st gear is probably a ton of fun... the problem is if you change the gear ratio to 3.31 then the power will not really come on until 33-38mph. Which does not matter much at the track but for daily driving it can get annoying... that also means when cruising on the freeway you will be way under the turbo, truck will have high egts and probably feel gutless.

Take that all with a grain of salt... I love dyno graphs and study them a lot. I know numbers can vary from dyno to dyno but the curves and RPM range are usually pretty similar.

Is there a chance that something is wrong with your truck? Maybe tuning or a leak?

What A/R turbine housing do you have?

Six_Sloww · Jun 25, 2014

KCTurbos said:
Please excuse my lack of knowledge for the track... I am just getting into the track events and have been studying this very subject.

Would the reason to drop down to 3.31 gear ratio be so that you don't shift into OD (6th gear) when going down the track? That way you keep the 1:1 drive ratio and have 1 less shift to worry about?

To help pick your tire and gear ratio you can use this site. Go to the calculator for "Transmission Ratio RPM". Then start playing around. You don't want the truck to be shifting as it hits the end of the track. You probably want to be pretty close to the end of the rpms band where you make your most power. If you pick the wrong ratio then you might hit the end of the track at too high/low of an rpm

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

Currently with a guesstimated trap speed of 111mph with 32.5" tires and 4.30 gears you will hit the end of the track in 5th (really 6th) at 3500rpms

Currently with a guesstimated trap speed of 111mph with 32.5" tires and 3.31 gears you will hit the end of the track in 4th (really 5th) at 3800rpms

You can guess and check with your mph and gears until you get the ratio that will best suite your needs

In regards to you dyno graphs. They all seem to have similar curves... but way different numbers. That is okay because the curve and rpm can tell you a lot.

Your power curve seems to come on really late??? That is probably why the gear ratio got changed, to help put the power to the ground earlier. Your peak torque is at 3500rpms... that is pretty late in the rpm band. Also at 2500rpms you are only make a max torque of 450ft/lbs... I would imagine it should be much higher than that (more like 700-900). Most 6.0 dyno's that I have seen make their peak power between 2700-3000 rpms. Even an s475 should have peak tq at around 3000rpms???

I have not driven the truck but from the dyno graph I would imagine the truck is pretty laggy and smokey below 2500 rpms... by 3500 it is probably a complete monster. That would mean in 1st gear that if you floor it at anything under 10-20mph it is probably smokey and laggy... 25-30mph in 1st gear is probably a ton of fun... the problem is if you change the gear ratio to 3.31 then the power will not really come on until 33-38mph. Which does not matter much at the track but for daily driving it can get annoying... that also means when cruising on the freeway you will be way under the turbo, truck will have high egts and probably feel gutless.

Take that all with a grain of salt... I love dyno graphs and study them a lot. I know numbers can vary from dyno to dyno but the curves and RPM range are usually pretty similar.

Is there a chance that something is wrong with your truck? Maybe tuning or a leak?

What A/R turbine housing do you have?

That about sums it up.. The truck is a monster once it's lit, but smokey until then.

Also the truck is pretty fun on the street, but the huge downside is I'm locked up in OD by 45 mph, so once that happens if I'm not completely lit the fun is over. I can delay the shift with t/h a little but it still locks up too early for the street.. I know I can play with the tuning but I can't help but notice that most people that make a track truck usually drop to a numerically lower gear rather than the other way around.

I think I may have a drive pressure leak, and I know the stock up pipes and egr cooler are holding me back.

As far as the A/R on the turbo I actually don't know, if I had to guess its likely just comes on a box stock s366.. That's one of those little details I won't know until I tear into the truck.

I won't be changing gears until after all the lag issues are solved, I have a feeling that once this truck is running properly I'll be trapping close to redline in 5th (technically 6th)

I'm just trying to educate myself on how to properly gear a truck that will see a lot of track time, especially because racing on the street isn't my thing.