|04-24-2007 06:24 PM|
re: What rear end gear ratio to choose?
To all that have participated in this discussion, I really appreciate the advice! At this point, I believe I'm going to keep the B&M 2400 stall converter I got (I don't know if this is considered a cheap converter or not?), hook a beefed up TH400 up to it ('cuz I got a good deal on one) and test drive my friend's '67 Chevelle (stock 396, TH400 & 3.73 posi) to see how that drive train feels. If that feels fun on the street and manageable on the freeway, I'll consider installing a 3.73. If that doesn't feel right, it looks like the advice from this conversation has tended to lean toward something in the range of 3.42 to 3.55 as being more "reasonable" for a street car, which I find eminently logical.
|04-11-2007 09:09 AM|
|MIKE FROM SM||I used to run 4.11 with a 28" tall tire in my Chevelle with a 396. It was loads of fun and ran great. The freeway sucked though. I would most likely go with the 3.55. The lower gears will make your convertor stall less. The problem you are having with your convertor is because you have a cheap one. A good quality convertor will not stall high unless it is flashed up there. I have a 6000 stall convertor and I can cruise it around with no problems. When I leave a stop light, it doesn't stall past 2500rpm.|
|04-11-2007 08:47 AM|
curtis i agree.
gearing in a race car is a necessary evil. i know too many people who were so unhappy with a 4 series RP swap. in the end their cars sat, or girlfriends made them sell. to really take advantage on the streets you need an OD trans.
|04-11-2007 03:14 AM|
|curtis73||Agreed. Since its a street car, I'd go no more than 2400. Without knowing all the cam stats its tough to guess, but I would shoot for a rear end ratio that gets you the target cruise RPM you want. As Ozz1967 said, you'll have TONS of torque available. My 400-horse 454 has a TH400 in a very heavy 73 Impala Station Wagon with huge 255/70-15 balloons and I'm running a stock converter that stalls at about 1800 with 2.73 rear gears. I left things alone and I thought for sure I'd be changing them out, but three years later its still like it is. I'd be happier with 3.08 or 3.23s, but the ability to cruise at 75 mph all day at 2400 rpm and still haul ***** from a dead stop is pretty nice so I left it alone. If I do anything I'll throw in my Gear Vendors that's been gathering dust and then go with 3.42s, but the stock converter is working great. My cam specs are 218/224 @ 50|
|04-10-2007 10:02 PM|
maybe i just like cars that drive right
3.73-4.10 ( no OD) are terrible on the street. take your daily driver out. put it in second, and drive at 60 mph. is that cool ?? cruising at 3500 rpm is no fun. garranteed police attention in my town.
3000-5000 stalls are rediculous on the street. no fun part throttle either.
its always some hillybilly hotrod. i like a balanced car that drives right.
a race car is a race car. they sound cool, and are fast. they dont belong on the street. you cant cruise at 4500 like a boat to buddies house. you just cant.
a muscle car has incredible on demand power at any time. mastering the open roadways at all speeds. they fall short on the race track. sometimes you wont even get into 4th, i think thats a good thing.
|04-10-2007 12:45 AM|
With a BBC you are going to have GOBS of torque. I don't know how much exactly but running a 2500 stall with 3.73 gears you are going to get off the line in a HURRY!!!! I mean smoking!
What he means by fighting it at the light (as I figure) is that you'll be having to stomp on the brake to keep the car from going anywhere. It'll WANT to go forward.
For true street with a TH400, especially since this is going to be basically a daily driver...I'd personally go with a lower gear, say 3.32 or 3.42. You'll be much happier around town and It'll give you good highway with that 1:1 final gear. Not to mention with the torque you'll be shoving to the pavement with the 454 you won't burn all the rubber off your tires just easing it into first gear. With a 3.73 and up you won't be able to keep tires on the thing.
|04-09-2007 09:15 PM|
I think if your not going to be going to the track at all you would be happier with 3.55 even in the city and if you do happen to go on the highway you will be able to drive a little faster.
It is really up to you in the end but I think 3000rpm at 67mph is a little much. and if you don't have a lock up converter you will have a little bit of slip witch might put you around 3100-3200rpm at 67mph.
|04-09-2007 05:26 PM|
I'm running a 2400 stall on my vette.
it's got a 450hp 500ft/lb 434 a TH400 and a 3.70 rear end. I've driven it >200 miles on the highway, went racing and came back.
I Get a little bog on the track, no bog on the street, just tire smoke
I'm torn on more converter or solving the bog with a shot of NO2
More converter would definitly make it faster...
|04-09-2007 04:30 PM|
rear end gears
Not stock but not a high stall, 2000rpm or a little less. Built to 69 LT1 specs with edelbrock performer heads and intake.
|04-09-2007 01:36 PM|
re: What rear end gear ratio to choose?
OK, it looks like I'm going to a slightly beefed up TH400. Based on the calculator you suggested (by the way thanks!), with a 3.73 it looks like 67 MPH at 3000 RPM. A little high, perhaps, but workable as street car? A 3.55 gets me to 70 MPH at the same RPM.
So a 2400 converter is pretty conservative? Will going to a 3.73 dampen the slipping effect?
By fighting the engine, do you mean having to "punch" the engine to get an reasonable rate of acceleration?
Yes sir, it's a street car. TH400. Cam is a Lunati with a .54 lift in and .55 lift ex. The guy who built the engine indicated that this engine's torque curve is at a higher RPM, which (if I understood him correctly) is the reason he selected a 2400 converter. Sound correct?
Yeah, an overdrive would be cool! Solve all the problems! Are you running a standard torque converter?
|04-08-2007 12:29 PM|
I have a 69 Malibu and I run a 3.73/1 behind a 700R4 transmission. that gives me 1800 RPM at 60 MPH in OD and I still get the acceleration and torque in 1st-3rd. The 700R4 will handle 500HP easily especially if it's not a race car, just a hotrod
|04-08-2007 03:15 AM|
Wait... we're talking about a 400+ hp BBC? That doesn't require that much of a cam. I'm making almost 400 from a 454 with a 218/224 cam and I run a stock converter in a 4500-lb station wagon.
I think a stall that is slightly above stock should be fine in most cars for a BBC.
Anyway, Rodney... if your main purpose is street and you will see any highway use, pick a gear ratio you can live with. If you post the transmission you'll use and cam specs we can guess on torque peak which means you can predict best cruise RPM on the highway. We can also use torque peak to determine the stall speed and a ratio that will make the best of your launch and acceleration. From there its up to you to pick the ratio that will fit your driving style. For instance if you say you're picking a powerglide with its really high 1.76 first gear, that's a lot different than using a 700r4 with its 3.06 first gear.
|04-07-2007 06:43 AM|
If you choose a converter with too high a stall speed you will find yourself fighting the engine at stop lights. 2500rpm would be more streetable IMO.
|04-06-2007 11:35 PM|
Yea, 5000 is a little much of a converter.
BUT a 3000 stall is a pretty good for a fast street car.
You gotta remember a stall converter isn't a switch, it doesn't just suddenly lock up at 5000 ( or whatever) rpm.
And at part throttle it transfers power to the trans just fine.
|04-06-2007 10:53 PM|
What kind of transmission are you using? Need to know to suggest gear ratio.
Try out this table out just type in your info and it will do all the math for you.
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