Gear Question for the Racers Smarter then myself

[pacman1967]

I am building a 350 with a weiand 142 blower, the cam is .488/.510 114LSA 234/244 degrees of duration and a Holley 750cfm carb. I am running a turbo 350 tranny, with stock gears. I am running a 315/60/15 M/T ET Steet tires out back. I am not sure what gears to run in it. I wanna be spinning about 5500rpm thought the lights on a 1/4 mile track. I was thinking about a 3000rpm stall also. Its going into a 85 shortbox. Its gonna see some street use but mostly gonna be my track toy. Any help and information would be great. Thanks in advance.

[Blue Rat]

What does it turn now through the lights rpm wise, an what gear?

[Marv D]

Making some assumptions...... Power wise I think your going to be capable of mid 12's is a total WAG. and probably around 105-110ish.

A 315-60 is a 29.7" tire

and a decent street / strip convetor is going to have ~10-12% loss in the traps

that assumed, the math says....

3.73 gear = 4800-5100 in the traps

4.10 gear = 5300 - 5600 in the traps

More importantly,,,, 4.10's will be around 3500 on the freeway at 75mph, where 3.73's will be about 3100.

Without an OD it's always sacrafice somewhere....


3.43 or 3.73 would be my choice for a street driver,, 4.86 for the track so you get that thing up around 6600-6800 in the traps so it can make some power

[pacman1967]

Well I haven't had the truck to the track yet, and I wanna stay at around 5500prm to be safe and keep away from possible valve float. The blower starts to loses effeciency after 5500rpm do to heat and that toward the top of the cams rpm range also. Thanks Marv D. and 12's is the goal with this little set up, and out here in rural nebraska we don't have too many freeways, this ol gal will never see over 65 on the high way.

[pacman1967]

What is everyone's opinion on B&M Holeshot convertes? I was looking at a 3000 rpm stall.

[RatPwrd72]

I vote 4.10's for the rear...

I think there are better converters out there than the B&M's. I'd be on the lookout for a used, high-end unit.

[fastwillie 696969]

i dont care for b&m torque converters ,tci ati ,monster ,steve evans custom made ,detroit converters for some others
im running everything tci on my 72 turbo 400 transbrake

[GMR-PERFORMANCE]

I think that a set of 3.73 would work the best for all around use. Marv beat me to the math. However if the bug really bites you and you want the truck to really hook a set of slicks will get you there. However they are going to grow a fair amount, thus more gear is the safe bet, but street use suffers at least hwy driving will. since you said not much street use but a track toy, hit the gearing for all you can. 4.10 would be my choice. I love gearing!!!

A good convertor is worth its weight in gold, vs the el cheapo ones. And a ask me how I know deal is do not run one with out a anti ballon plate, and no trans brake on the stock TB 350 cast hub... not unless you want to see inside the trans from out side that is.

Gearing is the starting point from there you get to play with stall speeds.. advertised stall speeds are just that ,... its all about the set up. 3000 is not much really but never ran that small of a blower on a sbc either.. I ran a 4200-4500 for my old 355 in a s-15 truck with 4.56 gears most strip than street.

A blower will push the power out past what the cam is stated to do. In fact a blower cam needs duration and that is about it. Open the door fill the cylinder and make boost. We just complete a 120 CI harley engine with 14 lbs of boost on a pro charger it makes 222 hp and 175 tq. So do the math on what you can do with that set up. I ran a very large duration cam shaft to allow more time to fill the cylinder. take that and the car stuff I have done it has always come back to amount of duration vs time to fill the cylinder as rpm's increase.

Good luck on your hot rod truck sounds like its going to be fun.

[Marv D]

I tell ya, for convertors it's hard to beat the Jeggs house brand. We put a $220 Jeggie 3600 advertised stall in a buddys 74 Nova with a 434,, he's footbraking to 10.3's. Stages at 3000, Says best he can see on the tach it flashes to 3800-4000. It's been in the car for 5 years spinning a 10 year old Hughes street/strip TH350 . The 3500-3800 is a loose convertor for street, but they have tighter ones too.

http://www.jegs.com/p/JEGS-Performan...50793/10002/-1

[pacman1967]

Thanks Marv, I will look into that Jegs unit and it will help keep me in budget. Thanks for all the info guys.

[hotrod 80]

With the tall tire i vote 3.73 . My buddy has the 3500-3800 Jeg's in his 67 Camaro and it works good .

[pacman1967]

Well guys here is the little jewel that caused all the questions, thanks everyone for all your help, I am going to be useing a 4.11 gear set and the jegs stall that Marv D. suggested.

[Marv D]

Those little 144 blowers are pretty nice on the street is what I hear (I have never had anything with mechanical boost) Might want to be a bit conversative with the stall. Making more torque dow low with the boost your going to drive through the convertor more than you would n/a. e.g. what may be a 3000 stall behind a normallly aspirated small block might go 4000 with 5psi force feeding it. Blower motors are agressive in the torque department

[pacman1967]

well I ordered a jegs 2700-3000 stall we will see what happens

[GMR-PERFORMANCE]

Should work very well. As Marv stated the Tq input is what makes the convetor work, its hard to nail it dead on the first go round. With a blower motor shooting under for stall is a good bet for normal use. ...