School Me On Torque Converters
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From: Lancaster, MA
School Me On Torque Converters
I'm in the process of getting all the plans laid out for my winter project, a 1977 Trans Am. I'm going to be dropping a built 383 (somewhere around 415-425hp when all is said and done) in matched with a race prepped th350 trans. Now, what torque converter do I need or should I say what stall speed do I need? I'll be doing 97% street driving with that occasional trip to the strip. I have no idea how to figure out the converter.
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I'd like to add a website for you to check out. I was a member there (still am) when I owned my 97 Firebird Formula, lots of knowledgeable people there, especially with the 2nd generation like yours.
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It really depends on where that engine makes it's power. A 383 generally starts coming on hard at 2300-2800rpm, so you want a stall speed somewhere in the middle of that range. A 2500 would be good, but it needs to be a 2500 at your engine's power. A torque converter that is rated at a 2500rpm stall behind a stock iron duke would be about a 4500rpm stall behind your engine.
You'd be best to have the engine dyno'd, then send the dyno info to a reputable torque converter manufacturer/rebuilder. You will spend more money, but it'll be right and will make all the difference in the world.
You'd be best to have the engine dyno'd, then send the dyno info to a reputable torque converter manufacturer/rebuilder. You will spend more money, but it'll be right and will make all the difference in the world.
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From: Lancaster, MA
Thanks for all the info. and yes Phinxter, I am going the easy way out I know. It's already got a Chevy 350 in there now. If it was a numbers matching car I'd be keeping the stock motor and building that up.
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GM factory converters stall in the 1200-1600 range, IIRC. And stall (and flash) speed vary greatly with the power input.
The 383 platform is a "low speed torque motor", as opposed to a "high-speed HP motor". Small-block valve trains aren't capable of speeds over 5000 RPM without a LOT of work, and then they're generally useless for anything UNDER 3000 RPM or so.
If you're going to drive this for any length of time at any one time (anywhere approaching daily-driver, for instance), you're not going to want anything over 2200-2500 or so, and even that's pushing it. But if you're going to drive this once a week to the Sonic on Saturday nights, you could probably tolerate something as high as 3000. But then you run into the problem of having very little "room" in your RPM band before the motor tops out.
I played a little with the converter in my last Chevy truck, and learned the hard way that while it improves takeoff and full-throttle performance off the line, if you don't have a motor that can take advantage of the higher RPM, the higher stall is almost 100% wasted.
-blaine
The 383 platform is a "low speed torque motor", as opposed to a "high-speed HP motor". Small-block valve trains aren't capable of speeds over 5000 RPM without a LOT of work, and then they're generally useless for anything UNDER 3000 RPM or so.
If you're going to drive this for any length of time at any one time (anywhere approaching daily-driver, for instance), you're not going to want anything over 2200-2500 or so, and even that's pushing it. But if you're going to drive this once a week to the Sonic on Saturday nights, you could probably tolerate something as high as 3000. But then you run into the problem of having very little "room" in your RPM band before the motor tops out.
I played a little with the converter in my last Chevy truck, and learned the hard way that while it improves takeoff and full-throttle performance off the line, if you don't have a motor that can take advantage of the higher RPM, the higher stall is almost 100% wasted.
-blaine
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You're quite welcome. 
When you only have enough cash to tweak your daily driver ONCE, you learn all you can before you finally get around to pulling the trigger.
Unfortunately I pulled the trigger a little TOO soon.
One might ask why you're using a TH350 instead of a TH400, or a 700R4?
-blaine
When you only have enough cash to tweak your daily driver ONCE, you learn all you can before you finally get around to pulling the trigger.Unfortunately I pulled the trigger a little TOO soon.
One might ask why you're using a TH350 instead of a TH400, or a 700R4?
-blaine
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From: Lancaster, MA
I'm still up in the air about the tranny, but it has a TH350 in there right now. It's all set up for it and ready to just drop a stronger one in there. I still have to talk with my mechanic friend who will be doing the engine and tranny building with me and figure out exactly what we are going to do about the tranny.
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In the For What It's Worth Department, the 700R4's 3.08:1 first gear is better for getting a heavy car moving; however, without some careful engine/tranny management, that 1st-2nd shift can be a doozy, because it uses the "GM Standard" 1.52:1 2nd gear. That large a jump can be hell, trying to keep power going across it.
But the flip side is that you get the OD 4th gear, which will keep engine RPM's manageable when cruising.
-blaine
But the flip side is that you get the OD 4th gear, which will keep engine RPM's manageable when cruising.
-blaine
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From: Lancaster, MA
That's what I like about that tranny for it.
