new and got a couple questions

[skinnysfd]

Alright guys heres the deal... I have a 1970 gmc pictured below and want to set it up for drag raceing 1/4 mile. so far my best time has been 14.05 and i know i have around 3:11 or so gearing in the rear end. it also a one wheel wonder. i have the motor built as well as a built tranny in it. the motor has been dyno'd at 400-450 hp motor alone . now i want to run in the low to mid 11's for starters and go from there. i have a 100 shot nitrous avaliable and am running only a 2200 stall convertor right now. so im thinking going with a 3200 stall ( because motors dyno sheet showed 3500-6200 is the power range) and putting in a different rear end with different gearing. so my question is ... Am i on the right track in this thinking? If so whats the best gearing for these trucks and what rearend? ford 9", chevy 12 bolt??? also wondering if i should go 4:11 or 4:55 whats yalls experience and any other advice is welcome and needed. Also going to be putting fuel tank in the bed as well and getting it out of the cab.

[TBONE1964]

The first question you need to answer is with a 3:11 gear, does the truck ever make it out of second gear at the end of the quarter? Are you shifting it at the end of the power band (6200rpm) and if so what is the RPM at the end of the run? If it is only pulling to 4500 then put a lower gear set in it.

If you are at 6200 at 1000 ft then you need to put a higher gear set in like a 3:08 or even a 2:70. I dought this is your case.


I agree with you on the stall speed of 3200 if your power band starts at 3500.


My personally opinion on rear end selection for a truck would be a dana 60 only because they are heavy and strong and you will need both.

What is your tires selection? Are you getting hooked out of the hole? This is hard to do with a truck because of the weight balance.

[skinnysfd]

beign a one wheel wonder right now im running a cheater slick and once i heat it up im fine with traction and beign hooked. now as far as getting out of second gear no hell my last run i barely got into second so i know i need lower gearing. Also would a full locker be the best option or would a limited slip or air locker be better??

[TBONE1964]

If you drive the truck on the street a lot, stay away from full locker. They are a pain to maneuver around in parking spots and tight turns. A stock posi should be fine. I don't know that much about air lockers except they need a source of air and a lot of hardware.

[Tinkermc]

Well first thangs first-welcome to the forum!!~!I would think 411 would work well and 455 may be a bit of run out before you trip the lites. Then it's a nice lookin rig.

[PanelDeland]

WELCOME!!! If you're going to street drive the truck at all,don't use a locker.I would guess a 4:11 rear gear would be a good start along with a posi especially if street driven.Moving the tank to the rear and probably the battery would also help.The next thing is to put the front end of the truck on a major diet.11's are entirely possible but may be a stretch with your current engine combo unless the truck is strictly strip.You'll need to set some goals and parameters for the truck and go from there.

[skinnysfd]

i used to have jeeps for wheelin so air lockers arent to bad to install and once i get the build done probably wont be on the street much LOL. So dana 60 huh? what would you think for gears then? 4:10's ???

[skinnysfd]

would dropping the front of the truck 2" and rear 4" help at all??

[WIDESIDE72]

If you are on a budget you could find an original 3.73 rear axle assyand swap it in. You might get lucky and find one with a posi. They are out there. IMO, the next option at your power level would be to buy 3.73 or 4.11 gears and deciding if it is going to be primarily street driven or mostly a track truck. A street truck with ocassional track use would do well with a posi. If mostly track use a locker is better.

The problems with a Dana 60 or Ford 9" is also what makes them so durable. They are heavily built to withstand abuse. If you are planning even more power than you are making now, a Ford 9" is a solid choice. The dana 60 is tougher, but takes even more power to turn.
I forget where but there was an article in one of the hot rod mags comparing a Ford 9", dana 60 and 12 bt rear axle. The car made around 500 hp and the different axles were swapped in with identical gears ran the fastest times with the 12 bolt, as power was not wasted turning all of the big heavy parts in the ford 9" or dana 60 . They did admit that the 12 bolt was not a sturdy as the others, but at that power level, it was the best choice for rhe quickest times.
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[TBONE1964]

I do agree with wideside72 ion the dana60 / 9 inch / 12 bolt debate. The reason I suggested the dana 60 is because of its strength and weight. The weight is really needed in the back of our trucks for traction. If you think it is hooking good now, then I would consider a 9 inch. The problem with 12 bolt GM rear ends for racing is the carrier has such a big window in them and they love to crack. It really depends on how you use the truck a majority of the time. I think also that a 3:73 or a 4:11 would get you close to the gear you need.

Have you ever used a desk top dyno program? It is a pretty accurate program for the computer that lets you plug in your numbers and will give 1/4 mile times. I am not sure if they still have them but mine was a DOS program made by Mr Gasket. I had it years ago and it was usually very close numbers.

[67_C-30]

If the engine is making its peak at 6200, you don't want to go anything lower than a 4.11 with a 28" tire.

We made over 300 passes on a truck 12 bolt with a set of Richmond 4.10's and an Auburn mini spool at that power level and with nitrous up to 159 shot with zero issues.

On the HP, what exactly do you mean by it dyno'd at 400 - 450? That's a big variation. A true 450 engine with a 100 shop will get you in the high to mid 11's, but its gonna to be tough to get to low 11's, even with a 100 shot in a heavy stock suspension truck.

The truck below dyno'd at 441 HP at the crank, and we got 12.30's out it on motor and a best of an 11.88 at 113 with 100 shot.

[skinnysfd]

never tried the desktop dyno ill do some checking on it . Only thing im wondering is now that i go with lets say 4:11's and a locker and a 3200 stall am i going to hook as good because now im in my power range right off the bat? or am i gonna do all this and then be into a traction problem??

[67_C-30]

BTW, if you are racing with 20 wheels on the truck, Don't!

[skinnysfd]

Originally Posted by 67_C-30

If the engine is making its peak at 6200, you don't want to go anything lower than a 4.11 with a 28" tire.

We made over 300 passes on a truck 12 bolt with a set of Richmond 4.10's and an Auburn mini spool at that power level and with nitrous up to 159 shot with zero issues.

On the HP, what exactly do you mean by it dyno'd at 400 - 450? That's a big variation. A true 450 engine with a 100 shop will get you in the high to mid 11's, but its gonna to be tough to get to low 11's, even with a 100 shot in a heavy stock suspension truck.

The truck below dyno'd at 441 HP at the crank, and we got 12.30's out it on motor and a best of an 11.88 at 113 with 100 shot.

sorry i couldnt remember the exact numbers but when we built it we just put the engine alone on a dyno and it was in that range. im not home so dont remember the exact numbers. So maybe what your saying is im going to have to start changeing suspension and possibly a different motor as well? I mean im happy with 12's just think 11's would be a whole lot cooler lol. Im new to the whole drag raceing thing so sorry for all the questions

[skinnysfd]

and yeah i dont run the 20's on the track lol i have a set of 15" wheels i throw on but think ill need a different setup on that too.

[67_C-30]

Originally Posted by skinnysfd

never tried the desktop dyno ill do some checking on it . Only thing im wondering is now that i go with lets say 4:11's and a locker and a 3200 stall am i going to hook as good because now im in my power range right off the bat? or am i gonna do all this and then be into a traction problem??

That depends on your tires. Sticking a truck is much harder that a car, but doable if you have good tires. If you are sticking an engine that actually has 450 with one tire, I'd guess you do need more converter. You should be having traction problems now if everything was matched up.

[skinnysfd]

Originally Posted by 67_C-30

That depends on your tires. Sticking a truck is much harder that a car, but doable if you have good tires. If you are sticking an engine that actually has 450 with one tire, I'd guess you do need more converter. You should be having traction problems now if everything was matched up.

thats what i was thinking because if i dont heat up the tires alot and i mean alot i will spin for quite awhile . Actually this past weekend on my last run i didnt hook on the start and spun for a little while. What made me want to do gears mainly was because on really tacky days the truck almost bogs down at start because the gears are so high then at around 1000 ft or so she finally gets the rpms up. So ill start some checking for some 4:11's and a good rear end. also where if any parts sources do yall recommend getting parts for you guys trucks??

[67_C-30]

Originally Posted by skinnysfd

sorry i couldnt remember the exact numbers but when we built it we just put the engine alone on a dyno and it was in that range. im not home so dont remember the exact numbers. So maybe what your saying is im going to have to start changeing suspension and possibly a different motor as well? I mean im happy with 12's just think 11's would be a whole lot cooler lol. Im new to the whole drag raceing thing so sorry for all the questions

Not a problem, man. There's a big learning curve with drag racing, but my best advice to anybody starting out is to get a log book (or make you own a in a tablet) and document everything you do. Don't make 3 or 4 changes and go to track. Change things one at a time if possible so you can see the true effect.

The single most important thing is make enough passes on any given combination to find its best time. Instead making the huge mistake of aimlessly changes a bunch of stuff and throwing parts at it, run the truck while changing launch RPM to find the best 60ft times, and then change the shift points to find the best MPH and ET. Document everything you do in your log book when you come back to the pits.

You'd be surprised that sometimes an car/truck may be way faster at leaving a 1800 on the converter and shifting at 6000 may be faster that stalling up 2500 and shifting at 6500 RPM.

I've seen people gain a half a second by learning how to drive their car.

Find

[skinnysfd]

yeah i understand i got alot of work and learning ahead of me and my boy loves it to so he will love all the test and tunes. I forgot to ask also since im doing a stall that high do i still look into a transbrake? or is it not necessary? i have line locks but those i understand really shouldnt be used for launching??

[67_C-30]

Originally Posted by skinnysfd

thats what i was thinking because if i dont heat up the tires alot and i mean alot i will spin for quite awhile . Actually this past weekend on my last run i didnt hook on the start and spun for a little while. What made me want to do gears mainly was because on really tacky days the truck almost bogs down at start because the gears are so high then at around 1000 ft or so she finally gets the rpms up. So ill start some checking for some 4:11's and a good rear end. also where if any parts sources do yall recommend getting parts for you guys trucks??

On parts, I search Jegs/Summit/ebay for whoever has the best prices at the time on quality parts. I've bought Richmond gears from all three sources at different points. I really believe you'll be fine with your 12 bolt, unless you have aspirations to go really fast (10's or slow) or plan to use high levels of nitrous in the future. At that point, I'd go 9".

[67_C-30]

Originally Posted by skinnysfd

yeah i understand i got alot of work and learning ahead of me and my boy loves it to so he will love all the test and tunes. I forgot to ask also since im doing a stall that high do i still look into a transbrake? or is it not necessary? i have line locks but those i understand really shouldnt be used for launching??

A transbrake is not normally used on a that low of a stall speed. When running 3000 - 3500 converters, I always tried to stall the car to around 1700 or 1800 at so the converter could flash at least a 1000 RPM on the launch. Instead of pulling it up until the converter is trying pull, we stall it as low as the engine would without hesistating so the engine would free rev as much as possible and shock the tires when the converter engaged. This simulates the effect of a transbrake somewhat on a street car.

[skinnysfd]

awesome i appreciate your input as well as everyone elses keep the knowledge coming i got a lot to learn and i guess some money to spend lol. Now i just gotta hide it from the wife hahahahaha