What gears?

Hey guys I have a question about what gears to run in our pulling truck. I am looking for a formula or a way to calculate what gears I need. I can post up the info if needed. Anyone with this knowledge I would be grateful if you shared. Thank you.

njstang87 wrote:Hey guys I have a question about what gears to run in our pulling truck. I am looking for a formula or a way to calculate what gears I need. I can post up the info if needed. Anyone with this knowledge I would be grateful if you shared. Thank you.

What wieght class, what CID & mods., how much horse power, Auto or stick .all these play into it, but I dont think there is any sure fire method to calculate the correct gear ratio without trial and error... In my experience a good 20-25 to 1 ratio works for me ,( trans gear ratio x transfer case ratio x gear ratio ) I have done best with 4:10 gears..................

[/quote] What wieght class, what CID & mods., how much horse power, Auto or stick .all these play into it, but I dont think there is any sure fire method to calculate the correct gear ratio without trial and error... In my experience a good 20-25 to 1 ratio works for me ,( trans gear ratio x transfer case ratio x gear ratio ) I have done best with 4:10 gears..................[/quote]

6200 lb. class. Probably around 500 horsepower or so. Its an automatic (Allison AT545). Probably running 35" tires but have 33"s on hand to help get wheel speed up. We have had it out to a few pulls and the thing just won't come up in rpm. Wee have pulled a best of 220' and the thing didn't get over 3,000 rpm. It has 4.10's in it now. I believe the problem lies in the converter but we spent $1000 on it and it was supposed to be 4,000 stahl.

We were thinking about going with 5.38's or something in that neighborhood.

I know there is alot of Difference between Mud trucks and Pulling Trucks but with 5.13's my truck was turning 5000 RPM less than a truck length into the pit '

Btw im running 38's though

njstang87 wrote:

What wieght class, what CID & mods., how much horse power, Auto or stick .all these play into it, but I dont think there is any sure fire method to calculate the correct gear ratio without trial and error... In my experience a good 20-25 to 1 ratio works for me ,( trans gear ratio x transfer case ratio x gear ratio ) I have done best with 4:10 gears..................[/quote]

6200 lb. class. Probably around 500 horsepower or so. Its an automatic (Allison AT545). Probably running 35" tires but have 33"s on hand to help get wheel speed up. We have had it out to a few pulls and the thing just won't come up in rpm. Wee have pulled a best of 220' and the thing didn't get over 3,000 rpm. It has 4.10's in it now. I believe the problem lies in the converter but we spent $1000 on it and it was supposed to be 4,000 stahl.

We were thinking about going with 5.38's or something in that neighborhood. [/quote]

thats a heavy class,, 35 tires I think is pretty tall,,, what gear you pullin in , low or high on the transfer ?? how much timeing you got in the motor, what carb,, whats the cam ?

If your stall was supposed to be a 4000 and the engine only got to 3000 rpm their is most of your problem, you never got to your torque curve, Most engines making good power are a pig 1000 rpm below their torque peak.

It never had a chance to show out.

what gear you pullin in , low or high on the transfer ?? how much timeing you got in the motor, what carb,, whats the cam ?

We start in first but the thing shifts on its own. We are trying to figure out how to make the allison only shift when we want it to. We have ran low and high in the transfer, with better results in low. It has a predator carb on it. Still trying to find the cam specs but we ordered it from Lem a while back. It has lift somewhere in the mid to upper 600. The motor has 12.5 compression.

IDT-572 wrote:

It never had a chance to show out.

Definitely agree with that.

njstang87 wrote:

IDT-572 wrote:

It never had a chance to show out.

Definitely agree with that.

You can't decide what gear to pull until the engine is leaving the line up in the power curve. When you get it to do that , heck it might be geared to low.

You have no idea what it wants at this point. Get the converter right first then chase the ratio you need..............

Thanks Blake I can understand what you are saying but wouldn't gears do the same thing by helping get the rpm's up? Anyone know someone that can work on a allison valve body?

Yes Gears will help bring up the RPM's (which is prolly why you did better in low range) BUT what Blake is saying is if there's another reason your engine wasent turning up rather than not enough gear, with 4.11's 35's in low range and a 'healthy engine' you should of easily got over 3000 ROM out of it

with a tall tire and the trans shifting, you will never get all your rpm, I think you need to work on keeping it from shifting,, Im runnin 1st and low range ,thats the norm, and gets the best results............

Thanks for all your responses and knowledge.

What is the 1st gear ratio in the transmission and what trans case are you using. If you give me those numbers along with the rear end ratio, I'll tell you what your final is. Also, Shifting is a bad thing here in Indiana. The tracks are too good to do that with a gas motor. Also, if you are only making 500hp, you need a 28 or slower final with those 33 or 35 tires if you are going to build some rpm. And if your going to get serious, get rid of the auto and go with a stick/clutch setup.

Several things come to mind here. 1st. When you built the motor, did you dyno it or are you guestimating it. Also please tell me what heads you are using and what they are flowing, and what headers and carb. All this makes a difference because you could have too much cam for the heads or too much carb or not enough carb or too small of tubes on the headers or... well you get my point.

AP

The first gear ratio is 3.45:1
differential is 4:10
Using the New process 205
Guestimating horsepower
Heads were ported by Fred Flagle @ Indy Cylinder Head using the PI castings I cannot at this time remember the information on the work, which was performed back in 1988.
Using the Allison because at the time it was unusual to hear of a pickup with one, and at this time I want to make it work.
I have also a smaller set of tires stock size which was is my opinion a cheaper way to get wheel speed up but have never ran them. Was at the time sorting out the drive line weak links and replacing them as they broke.
I have been schooled by Lem Evens on the engine to a point, just nothing really to show for it.
Father and son project as the story goes. Just want to pull at the local fairs without going bankrupt.
Thanks
Dave

Headers are by Hooker 1 7/8 tubes 3 inch collectors open.
Carbureted by by one single Predator plumbed for juice but never used
I at this time do not even know if the were flow tested, the only numbers I can remember it that the were CC'D

Your final is 27.72 if you pull on the low side of the transfer case. Don't bother with the high side. The final is not bad with 35's if you had 800hp. PI heads can be decent heads but not in the same league as Cobrajets. What is the cfm of the Predator carb? Also, did you say what the cubic inch of the motor is?
Have you read the plugs to see if there is a fuel issue?

I went down the route of an auto when I first started pulling and the reality is if you want stay with the auto, you MUST have 80-100hp more than the other guys to be competitive and if you are pulling against Helms and Rothrock and some of the other top trucks stock/altered trucks in Southern Indiana, you need 521ci+ making 800 ponies with a clutch to hang with them boys (yes in the "stock" class) also you need to have your motor built to turn 8000 rpm.

Bottom line is Don't waste any more time and money with the auto. Ditch it and put a stick in period! You could put in an NP435 and would be mutch better off that what you have.

I am not trying to discourage you, just trying to save you alot of money and time. (what I wish someone would have done for me).

Thanks for the info
466 cubes
Predator carb claims 930 cfm
plugs look decent
It would be nice to have more inches but the accountant says stand pat. The one reason I want to compete with the run what you brung league. Since you have incurred the bumps and bruises it is nice that you share the wisdom with us. Johnson and Bartholomew counties have the shade tree group of trucks that I try to run with, nothing to exotic.
Will look into stroking another block but again this one is built and we were trying to make a go of it in the form that we have presently.
I already have the new process, original transmission. What clutch and pressure plate would you recommend, at least I can venture back looking into a manual, need pointed in the right direction.
Dave

Call Travis at Travs4x4 for a clutch. Super guy to deal with. http://www.network54.com/Forum/228279/thread/1258424255/last-1262878732/TRAV'S+4X4+CLUTCHES+AND+BELLHOUSINGS

I totally understand the cash flow situation. That's why I gave up and sold out last fall and I had a top 5 truck in our association. I just couldn't afford to keep upgrading to stay towards the top of the class. Now I'm enjoying life with a much lower blood pressure and stress levels. I am working on a Pro Street drag truck project as time and money allow and I don't feel any pressure to get it done. And when I want to hop on the motorcycle and go for a ride, I go. The wife has even started asking to go for rides which is much better than fighting with her over money going to the puller.

Also, someone with more knowledge than me may pipe up, but I'm thinking you might have more carb than you need for that combo.

In case you don't have this information regarding RPM/wheel speed, you might find it useful.

I took the 2nd gear ration for a np435, low side of an np205 and your 4.10 rear gears, and 35inch tires and your 3000rpm
Your calculated wheel speed in MPH is 12mph

Now lets drop to a 31inch tire and estimate that you'll pick up 2000rpm. Your calculated wheel speed is now 17mph
In your situation, going to a 31inch tire is the better option given your budget.

This analogy holds true whether it's an auto or a manual. That said the benefit of the manual is less hp loss through the transmission and you get to come out at a much higher RPM then with the auto. (it comes out at a lower rpm and has to climb).
Truck pulling is about momentum and most are won in the first 100ft, so you have to get up to speed as quickly as possible and that is where the manual shines.