Thread: sp383

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Im new here, Otis is my handle, I live in az. Nice weather now but couple of months it going to be hot. Im working 1985 silverado,we are 2nd owners got from a neighbor in 1991. This truck has orignal paint and never been wrecked and is not trailer queen we have over 230000 miles on her. I looking to put a sp383 in the truck. I have 7004r tranny now. I hoping this will be enough trans for this engine 435 hp 445ft/lb t. All help will be appreciated.

Welcome to CHR Otis!
At 230K miles, I wouldn't trust the tranny. But it can be built to support the new motor.

Welcome to CHR Otis:

I think that you should seriously think about replacing the transmission. With 200K miles on it there’s bound to be some wear and fatigue. Stock 350 in the ’85 trucks put out 175-210 HP with 275-300 lb-ft of torque. A conservative 383 roller build will be in the neighborhood of 350-400 HP and 425+ lb-ft of torque. The stock 700R4 is good for 300 HP and 350 lb-ft of torque when new and tight. Unless you run some very skinny tires that will spin forever the first time you nail the pedal and the tires lock up and you bang second or third you’ll split the converter, dump the fluid all over the street, and be hearing some real bad noises.

Heavy duty rebuild on a 700R4 is good for well beyond the horsepower and torque a 383 will deliver in all but extreme race configurations.

My two cents.
Glenn

Glenn is dead nuts on the money, beef the tranny......

The other thing about using an overdrive tranny and hot rodding the motor is that you have to make concessions on the cam and the static compression ratio. If the crank is going to turn at 1700-1900 rpm's at cruise in 4th gear, then the cam will have to be up into its operating range at that point in order to make good gas mileage. I mean, that's the intention in the first place, to make good fuel mileage with an overdrive transmission, right ?????

So then, you can't use a big hot rod cam that, for instance, makes power from 2500 to 6000 and expect any kind of gas mileage, because for gas mileage, the cam will need to be efficient at the rpm's the crank is turning in 4th gear (1700-1900). A cam that begins making power at 1000 rpm's (with an operating range of 1000 to 4500) is the type of cam that you will want to use to insure fuel mileage. Otherwise, if you use a hot rod cam, then you will not need an overdrive transmission and could make the truck work with a TH350 or TH400. The cam you will want will probably not exceed 204 degrees duration @0.050" tappet lift and will want a 9.00:1 static compression ratio. Any higher static compression ratio will want more cam, which will not work with your overdrive transmission.

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That's the issue I had with my 69 nomad. I couldn't use overdrive below about 70 mph.

I was going to change the gears, but sold it first.

Hell, I've got the same issue with my 2001 Indian chief. Next time the sprockets need to be changed, I'll go smaller on the back sprocket, and boy will it be a neck snapper off the line then.

Originally Posted by firebird77clone

Next time the sprockets need to be changed, I'll go smaller on the back sprocket, and boy will it be a neck snapper off the line then.

If you think about this for a while, you'll realize that for increased neck snap, you will need a LARGER rear sprocket or a SMALLER front sprocket. A smaller rear sprocket will give you increased top speed, but it'll take longer to wind out.

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Yup my Harley Softtail with a 1989 evo motor had the rear sprocket replaced by the former owner to a tooth smaller to cruise at 70mph with less vibration. Bike had no top end speed or get up and go, dangerous on a bike, a quick throttle can save your life. So I had the heads modified, and a hottter cam put on. After that it was like the transmission was changed as to what gears I cruise in with the vibration comfort level. I think in my case I need to go back to a stock rear sprocket, but it does excelerate like a scalded cat now! Hard to know when and where in the power band you need to tweak any machine, especially a bike, depends where your riding, for me when I do the coastal roads, speed is not necessary, your riding at lower speeds, and need to work thru your gears, but California interstates are a different matter. Used to be 70 mph was plenty fast, but now days the maniacs out here cruise 85 in the slow lane, which means they ability to accelerate fast when merging onto the hiway. It seems most new cars seem to be much faster, and handle better, so the average idiot can and does go faster than they should, which also leads to problems when it rains! Lots to think about!