A bit about the car first. 48 Chevy with a 350. Power pack heads with a holley 670 street avenger. Cam unknown, was installed in engine before I got it. Block hugger headers. 3 speed powerglide tranny. I have got a Chevy 10 bolt with (if my math is right) 2:70 gears. The car is very streetable which I love but I was pretty underwhelmed at our car show last week. It was just vintage drag racing and the car I competed best with was a stock chevy truck with a 283 and a three on the tree. ( No offense if the person who owns the truck hears about this ) I am not expecting to blow everyone away but I think if the track was about 1 mile long I could be doing about 140 ( Call me and idiot but I have had this car doing 140 on the interstate. Lets just say the front gets a wee bit light) I would like to find a happy medium between the street and a little throw you back in the seat torque. My tires are 235 75 R15's There is no more room for a bigger tire unless I do some sheet metal work to the trunk. I do really like the stance so a smaller tire may be an option but not much smaller. My preference would be to stick with the 10 Bolt, but a 9" upgrade is not out of the question. Any suggestions would be appreciated. PS...... in all of the dirt track racing I ve done we always set our valves at 202 exhaust and 182 intake. Is that a safe place to start with an unknown cam or should I buy something new so I know where I am at. Thank again...
A good compromise gear is 3:50 for track and street. Is your cam a solid? If so, I use .16 straight across for valves. Never heard of 202 or 182. Valve sizes are sometimes 202 intake and 160 exhaust on a sbc. Also, powerglides are 2 speed. 3 speeds are eith turbo 350's or 400's. You could get the best of both worlds by going with 4:11's and an overdrive trans like a 200R or 700R.
A 3.25 or 3.50 would give you better pull and may get you better mileage.I'm a Ford guy but see no reason for a Ford 9" unless you plan on serious horsepower and sticky tires,even a regular old 9" does not like that. ROY.
Depending on which 10 bolt you have, there are some options. There are two GM 10-bolts- the 8.5" and the 8.2". The 8.2" is junk, put more gear in it and you will end up breaking stuff. The 8.5" is capable of handling a 4500 pound car hanging the wheels (Grand National), so it should handle your 48 with ease. If you have 2.70s, you won't be able to go into the mid 3s without a carrier change, your carrier is a 2-series, so you would be stuck with 3.08 and smaller gears. Since you don't have an overdrive, I would stick with either 3.08s or 3.42s, that way you don't lose too much top end and gain some quickness. Upgrading to a 9" would be a waste of time, the 8.5" 10 bolt is just as strong in this application. I have an 8.5" 10-bolt in my 4000 pound OT car with over 400 ft lbs.
what he said....4.11s with a a/t o/drive...or 3.70s without. I concur that there is no such thing as valves being set at 202 anything... 2.02 is an intake diameter measurement for sbc, but valve lash is in thousandths of an inch. With that engine, you definitely need to get out of those stock gears you have and get something that will work with the power band of that race motor. You also need to find someway of figuring out what cam you have, or replace it with a KNOWN unit. Are you even sure it's a solid lifter bumpstick? Things will go downhill fast and noisy if you set hydro lifters at 0.016 gap. You're going to spend money on gears, first spend it on a cam that will work with those heads, the torque convertor, the ignition and intake/carb setup. Gears are generally selected AFTER the motor is built. 140mph on the open road is an impressive speed - assuming your speedo is accurate. With that boxy body, you're pushing a lot of air out of the way. I've had (and have) some pretty fast rides - 140mph is hard to hit with a car that's "streetable" even WITH those gears of yours. dj
all depends on how much highway driving you do. You can get away with 3.73 gears in town without too much trouble. If you get on the highway sometimes then 3.36 would be better. You'll see a huge difference going from 2.73 to 3.36, not so much going from 3.36 up to 3.73
You all are correct... its a turbo 350. 140 is fairly fast for the road but that is why i am positive I need a gear change. I do not need this brick to have that much top end. And you would be suprised what a downmountain run in West Virginia and some idoit in his rice burner thinking he could show off to his girlfriend in the pasenger seat. Its a hydrualic cam... and I am not a cam shaft guy so if new is the way to go what research do i need to do to pic a correct one?
I knew someone would say the powerglide is a two speed,You want the best of both worlds use either a 200r4 or a 700.You can go for 3.55 gears ,In first off the line that trans in the high 400 range plenty of dig off line,but with advantage of when it gets into fourth you will be running 1800 rpm at 65/70 .You are right with a dead gear like you have, you topend is high,how is the car setup for stopping .
Stopping is not an issue. Big disc brakes is front and drums in back. I drive mostly around town but I need to able to do 65 / 70 mph as our club takes road trips a few times a year.
My pickup has a 350-375 hp big block mopar in it with an auto, 2.75 gears and 28" tire. My speedo is correct and Ill tell you that 140 mph is quite a reach such that Ive never had it there. It was super quick with the 3.70s but not so cool on the hwy, 3.23 was great on the hwy and was really quick. The 2.75' are nice on the hwy and 3rd is like overdrive, good old lady gears, although its still quick off the line and can do 100 in 2nd no prob it doesnt slam you back in the seat like the 3.70s did.
Hydraulics cams, you adjust with the motor running. Loosen the nut on the rockers until they click, then tighten the rocker arm nut until the clicking stops, then tighten a half a turn more. If the engine is off, you can lossen the nut until the push rod turns freely. Tighten until the push rod quits turning, then a half a turn more.
Yeah a 4 speed is a no brainer for the future just need to find a new checkbook first. One project at a time. Lets not get of on tangent of calling me a liar for 140. Ok so my speedo probably sucks, I was just making the point that it has more than enough speed for the highway. So based on the advice so far I am leaning from that 3.00 to 3.50 range. How about a posi conversion? Are puting in new gears a shade tree mechanics job or a trany shop job? I would consider by mechanics talent above average but by now means a professional.
Remember if you have a 2.70:1 rear gear now or there abouts, you have a Series 2 carrier. DEPENDING on which exact rear you have, as there are several 10 bolts, you might only be able to install up to a 3.08:1 or a 3.23:1 gear. To go higher numerically, or a lower gear final, you will need a ring gear spacer or a Series 3 carrier. If you have an open rear now, and you are not sure how to set up a new differential, look into the Powertrax products from Richmond, if you want a Locking type rear differential. You can install these in about an hour in your driveway with only half a dozen hand tools. TR
try search online for : project33.com click on calculators - helps you figure out what you are looking for
Fwiw, gears were the thing that really f'd up my mileage...went from a 2.52 behind a 700r4, to a 3.54, woke the car UP....mileage went from low 20's to 16 on the highway. If you're seriously considering an OD transmission in the future, either plan on a compromise now, or another rear-end in the future, you can't really have it both ways.
i run a 3.90 gear but i have an overdrive trans, so for your car i suggest 3.55 or 3.73. me, i would choose the 3.73.
You are not a liar if your speedo says your doing 140. Its your speedo giving you the wrong information. Just a common case of mis comunication.
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