I need some advice I want to put a 3.90 rear end 13.48@101mph 1/4 mile with the 3.42 The car is a street/strip and don't see a lot of highway Here my setup 1973 buick 455 (0.020 over) stage 1 piston ta stage 2 se head ta-310 cam th400 tranny(full manual) b&m nitrous holeshot 2400 coverter dave's small body hei(locked and phase) msd blaster 2 coil msd 6al-2 programmable sp1 intake holley hp 1000 carb innovate wideband 3'' exhaust with flowmaster 40 in a 78' chevy nova 8.5'' 10 bolt 3.42 posi rea
need advice on rear end ratio change I need some advice I want to put a 3.90 rear end 13.48@101mph 1/4 mile with the 3.42 The car is a street/strip and don't see a lot of highway Here my setup 1973 buick 455 (0.020 over) stage 1 piston ta stage 2 se head ta-310 cam th400 tranny(full manual) b&m nitrous holeshot 2400 coverter dave's small body hei(locked and phase) msd blaster 2 coil msd 6al-2 programmable sp1 intake holley hp 1000 carb innovate wideband 3'' exhaust with flowmaster 40 in a 78' chevy nova 8.5'' 10 bolt 3.42 posi rea
Honestly I dont think you'll gain much, if anything, except RPM. 3.42 is a good gear for a Buick with a mild build.
Re: need advice on rear end ration change Good idea. Please report back on your findings. I imagine people would need more info to tell you if it will make you any faster though... tire height, vehicle weight, etc... what RPM do you clear the traps at now?
Re: need advice on rear end ration change the engine is in a 78 nova full interior I leave the trap at 2300-2500 The car weight 3750 pound tire: 275-60-15(27.99) hoosier quick time
What is your 60' times? You need better traction,this alone will take your qm time down,and a gear will only make it worse. You want a 1st gear ratio multication best case senerio of 9.5:1(closest to it with available rear gears),for a street/strip car,you take first gear ratio of your T400 of 2.42 X your gear ratio of 3.42,this only gives you a first gear multication ratio of 8.276:1. With a 3.90:1 rear gear this will put you closer to 9.5,@ 9.4379:1,if your engine can handle the extra rpm at the end of the track,and regular driving. A T350 with a 3.73 rear gear would be better,with a 9.4752 1st gear multication ratio(closer),and you don't lose as much HP with a T350 than you do with a T400.Of coarse it will have to be built to handle the extra torque,but will free up some ponies.Or a 200R4 built to handle the torque,with the gear you have,you'll end up with a 9.37:1 ratio,with overdrive that will make your final drive gear a 2.29:1,and with the light weight of your car,and the monster torque of the 455,you'll be just over idle at highway speeds,and the engine won't lug. You'll probably see over 20+ MPG on the highway also,and better around town over 45 mph,something to think of. Usually by using the 9.5:1 1st gear multication ratio for a street/strip car,this gives you the best launch,while keeping it streetable in final drive ratio(some combos are better than others,just depends on what you want to do with the car),unless you use a powerglide with a 1st gear ratio of 1.73,you would need a 5.49:1 rear gear(not very streetable). Now,to tuning,your set up that you have now in that VERY light car,should already have you in the low 12s!!(even with a stock 455,you should be in the mid 12s!!) There's something not dialed in,that any gear change is going to fix. You should try dialing in what you have before you change your gear.(JMHO) Like your timing curve,A/F ratio,plug wires...so on...and so on. With a bad plug wire,you may be running on 7 cylinders,and that's why your not running the way it should.Could be a fouled out plug also,this will do the same. If all is good,a compression test may be in order to make sure the engine is in proper working order. Keep us posted on what you find,and good luck. I had a 75 Nova years ago with a mild 350 with a T350 tans,and a 3.55 rear gear,that was in the high 12s,a 455 should blow this combo away! A stock Buick 455 is only 60 pounds heavier that a stock sbc,and doesn't come close to making the same torque. A friend of mine has a 72 Skylark with a 455,with some home porting done to it on stock heads(I think his cam is close to what you have also),with a T350 tans,and 3.73 rear gear,a B4B intake and a Q-jet that runs 11.60s(a 9.4752 1st gear multication ratio with a T350's first gear ratio of 2.54:1,running slicks,and suspension setup very well) all day long,and pulls the front tires off the ground ever so slightly,and that car is at least 400lbs heavier than that Nova,check your tuning/suspension.
looking at your engine combination i would think your E.T should be in the twelves with the 3.42 gears. I had far less engine and 3.36 gears in a 4000 lb car and was running low 12's, and that was with poorly ported cast iron heads, a KB 113 cam and a performer intake. oh yea a quadra-jet also, i think your slow Times are due to something else other than gear ratio unless your at 10,000' elevation
Re: need advice on rear end ration change At the end of the run you are at 2500? Or do you launch at that RPM? I like a 3.42 gear for a street car, but generally the 3.90 will bring you through the traps at 4000-5000 rpm depending on tire size and keep you in your peak power band (and thats a very big SWAG statement) So yeah, try it!
I'd like to know what the actual compression ratio is. The combination of low compression and that ultra tight torque converter will hurt you pretty good. Put a good quality 3000 to 3500 torque converter in that car and I bet you will pick up 3 tenths or so. Certainly more than you will be from that rear gear change. Converter and compression ratio aside, that car should run much harder than that.
Unless you know all the measurements, you don't know your compression ratio. Head cc head gasket thickness piston to deck clearance piston dish cc
Hmm. I have unported SE1 heads, a roller version of the 310 cam, SPX intake, 3.42 rear gears, and I cross the line right at 5,000rpm (manual trans) at 106-108mph. My '77 Skylark weighs 3,810lbs with me in it. I've been thinking of throwing more gear at it too, like 3.73's but 3.90's aren't out of the question if I do swap gears. My best run has been 12.95 @ 108mph, but I ended up running out of fuel pump capacity and I have to work on my launch technique as my car was dead hooking the drag radials and that pass I brought the rpms up to 2500rpm and dumped the clutch and it instantly dropped to 1500rpm and just pulled through it from there. I've ran a pile of 13.3x's at 106mph. My suspension and launching technique have a lot of room for improvement.
If your "burning tire in all gear" I don't think the 3.42 ratio is the problem. Work on the suspension its not hooking. Check your stall speed with that so called nitrous converter. Maybe you need nitrous to stall to 2400. A true 2400 stall with that cam should work fairly well. As mentioned you should be in the 12s with what you have. Good Luck Bob H.
