Math for gearheads

[TN farmer]

I am interested in finding out what my speed will be for upcoming truck pulls. I want to compare 4HI in 1st gear at the rev limiter to 4LO 2nd & 3rd. I have changed my tire size and they measure 32.5" tall.

Any help would be appreciated I never did like word problems.

[Jelisfc]

Who needs math with the power if the internet? smile.gif

Try this site and good luck. http://www.4lo.com/4LoCalc.htm

[TN farmer]

Jelisfc, Thanks for the info but now I need to know the ratios of the Allison in 1st-3rd. Also I need to find out what the transfer case ratio is for hi and lo.

[GMCTRUCK]

Last fall at our area fair they had street class pulls and a lot of diesels showed up. One of the guys I know wanted to pull his bone stock 2002 2500 CC SB 6.6 Allison in 4 hi. Even after we all told him to use 4-lo he still did it. He put a smile on every Ford and Dodge guys face when in the first heat with a relatively light sled the truck strained about 10 ft and then stopped turning the tires. Don't pull in 4-Hi. 4-HI is 1:1 and 4-LO is 2.61:1.

[ 02-12-2003: Message edited by: GMCTRUCK ]</p>

[CPMac632]

I'd say most of the time you will want to pull in 4 hi with the hot juice. Low range will kill the power trying to shift all the time. The transfer case ratio in my 6 speed truck is 2.72 to 1 low range but maybe it is different on the trucks with an allison. Also some trucks have the power limited in low range at least all the 6 speed trucks that I have seen do.

[BowTieDmax]

With a fireplace mantle full of trophys from last years truck pulls. I could only say USE "HI". Other wise you will loose up precious distance letting the allison shift up and down.
Once the weather gets better and I can get my buddy to come out and play with his tech. 2. I whanna try locking the allison in 2nd gear and pulling 2nd gear "HI RANGE" (how about this John Kennedy will the tech 2 do this)
As for speed, I just went out on the road and let it govn. out in each gear I was wandering about. Its works alot better than doing the math.

Oh yeah! I've converted 2 going on 3 cummins to duramax owners since last years truck pulls. Gotta love it. Once again, For winning results DO NOT USE LO!!!

[TN farmer]

BowTieDmax, Did you ever pull with the HOT juice? What about the front end, did the IFS want to hop or any thing? I assume you must have hit the limiter in 1st if you are thinking of pulling in 2nd? Robert

[Jelisfc]

Allison ratios

First 3.10:1
Second 1.81:1
Third 1.41:1
Fourth 1.00:1
Fifth 0.71:1
Reverse -4.49:1

More specs at http://www.allisontransmission.com/product/series/1000series_specificationsheets***p

[Kennedy]

Just look at it in terms of MPH by selector.

In other words, go to max RPM in each gear to see what mph you get...

[TN farmer]

JK,

What do you think, will the trans take care of itself in HI range 1st gear with the HOT juice? Most posts I have read the guys were using 90hp. Robert

[ 02-13-2003: Message edited by: TN farmer ]</p>

[BowTieDmax]

TN FARMER
Last year I had the 90 hp juice. Yes my speed was limited to the rev limiter. So thats why I want to use 2nd gear this year. Every pull I did I never came close to losing power even when forward momentum stopped.
As for the front end. I had no hop at all but I had the rancho 9000's set to "5". And I had put a rachet strap from around the steering center link and the cross over frame. This was done to keep the exsessive "toe in" from happening when I started down the track.(Have someone stand at the end of the track and film your pull without this and you will see what I mean) Plus more so with bigger tires the front right wheel would whobble from the crappy idler arm. (Jack up right front tire and grab wheel at the 9:00 & 3:00 position and wiggle to see what I mean)
This year I hope to have a locker in the front so that will probably be worse. I am also going to make up a better quick install thing to replace my "strap".
I quess my biggest worry this year is the hot juice because my EGT's with the 90hp were past what my 1500 deg gauge would read. And I hope that the predator is out by summer and it stacks well with the juice. Paul
:D

[Jelisfc]

BowTieDmax, Not to switch subjects but how do you like the Pro Comps in the snow and what wheels do you have?

Thanx.

[Kennedy]

I ran low range and let it go to 2nd. It sat on the governor the entire way. I am NOT an experienced truck puller, but like I said, look at the mph that can be achieved in 1,2,3L and 1,2H and see what happens. I think that 3L will go faster than 1H and 2H MAY be too much, but remember tracks vary. We are on heavy clay and the tracks bite. I know a V10 Ford tried High and barely spun a wheel! :eek:

[TN farmer]

JK,
I did the math and 3L was 24mph and 1H was 26mph. I think it would be better to pull in Hi without the tranny trying to shift twice and defueling in between gears. That is just my opinion of thinking it would be much smoother. I have allways pulled in low in the past and never had a truck that would hit the governer in 2nd gear Lo range. That is untill now, can't wait.

BowTieDmax,
I may get you to further explain about straping the front suspension. Did you add any weight or block the rearend? This is not allowed at some pulls but nobody checks around here.

Thanks for the replies

[mtomac]

1. Lower the torsen bars all the way down for pulling (This will sit the truck down on the snubbers and give you less suspension travel which is what you want for pulling)

2. Add a steering stabilizer up front (helps cut down on steering wander)

3. Strap the front end (helps to prevent excessive toe in)

4. A blocked or stiff rear suspension via adjustable shocks or air bags (helps eliminate the rear end squatting which drops the hitch height)

7. ARB air locker or Eaton E-locker up front. G80 in the rear (only things available right now)

5. BFG all terrains for harder tracks and BFG mud terrains for softer tracks (they work the best around here)

6. Use HI range (extra speed & less shifting)

7. Get the juice or Hot juice (even in the stock or street class the diesels aren't stock)


The key to transfer sled pulling is to get the sled moving as fast as possible so you will have momentum built up when the box comes up and puts weight on the pan.

[Kennedy]

If you get a light sled on a fast track, 26 mph may be ok, but I haven't had the "cohonez" to try this. 18-20 mph is getting pretty fast. Be prepared to get rear ended if you break at that speed! :eek: The way I see it, in low range I have a fallback gear if needed, where in high you do not. Defueling will not be much of an issue in low range at WOT, and the transfer case should make the load on the Allison less severe with the 2:1 (or whatever the number is) ratio...


Did you calculate these speeds or observe them?


Around here, 35" BFG M/Ts or Bridgestone Dueller are strong especially when siped. I ran my 235 Blizzaks and was 3rd of 3 dmax's similarly set up and similarly geared. The winner had NEW MT's the second truck had 30% MT's and my little tires (and 35 HP advantage) could only muster 3rd.


Again, I am NOT an experienced truck puller...

[CPMac632]

I don't know about everyone else area but the dodge boys around here are pulling a ratio that yields a tire speed of 25 to over 30 mph at the governor.

[BowTieDmax]

Jelisfc
I like the procomps for everything but mud. I have 40,000 miles with alot of burnouts and the still have a "little"tread left. They are on my stock alloys.
Micheal Tomac said it all in this quote:[The key to transfer sled pulling is to get the sled moving as fast as possible so you will have momentum built up when the box comes up and puts weight on the pan]This rules out low range!!
I would just like to add a few things I learned/think is a must:
*Max out rear tire pressure. (more important if your blocked)I am!
*Add the max weight for your class.(the other guys will or wish they did)
*Add the weight as far forward as you can(the front floor boards)
*Max out hitch height
*Build all the boost you can before you take off!!
*I already e-mailed Eaton a couple of weeks ago and they said a locker for are trucks will be out in April. Yee Haa!!That will help
*Blocks are allowed as long as there is a 1" air gap at inspection.Mine are adjustable so I raise them for day to day driving and lower them for the pulls.
*Really helps to have someone film your pull so you can see whats happening on your truck during the pull.
Micheal, Maybe I'll try to get a picture of the "strapping"

[TN farmer]

JK,
I calculated my speed at 26mph and my truck reads 25mph without adjusting for my tire size at the limiter.

What about the EGT reaching 1500 while pulling? If the pull only last ten seconds and the temp comes back down what is the potential for damage?

My next question is there any way to up the rev limiter for more speed without changing the pcm?

Thanks for the help