88 Irocz 305 TBI to 350 carb questions
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Joined: Apr 2005
Posts: 2
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Car: 1988 Irocz
Engine: 5.0
Transmission: 700r4
88 Irocz 305 TBI to 350 carb questions
Hey guys, I'm wanting to pull my 305 from my 88 Iroc, and I'm looking at a 350 a friend of mine is selling. The question that I have is, what has to be done with the computer? I don't know what all it controls and what it dosen't. It controls the tranny right? What sort of horsepower can a 700r4 tranny handle? what about the other sensors and what will i have to do to make it all work. Or would I be better off just geting a th400 tranny and just not use the computer at all. Any help would be great!
Joined: Mar 2000
Posts: 43,187
Likes: 46
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Welcome aboard.
I assume you're talking about retaining the TBI. If that's the case, most of your questions would be answered on the TBI forum, particularly the stickies at the top of that forum.
The typical approach with the TH700 is to help it out a little with a shift improver kit (Transgo is pretty popular in these parts), Corvette servo, and .50" relief valve. Check out the Transmission and Drivetrain forum for that info.
I assume you're talking about retaining the TBI. If that's the case, most of your questions would be answered on the TBI forum, particularly the stickies at the top of that forum.
The typical approach with the TH700 is to help it out a little with a shift improver kit (Transgo is pretty popular in these parts), Corvette servo, and .50" relief valve. Check out the Transmission and Drivetrain forum for that info.
Thread Starter
Junior Member
Joined: Apr 2005
Posts: 2
Likes: 0
Car: 1988 Irocz
Engine: 5.0
Transmission: 700r4
The 305 is TBI. The 350 is going to be carb. I guess my main question is, is it easier to remove the computer and get a new tranny or get the computer reprogrammed to work with the 350?
Joined: Mar 2000
Posts: 43,187
Likes: 46
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Okay, I completely misread your post.
The ECM doesn't control the transmission. The only interaction it has with the tranny is to lock the torque converter clutch during cruise conditions. Otherwise, the transmission is self-contained just like they had been for decades before.
The transmission forum has many discussions about how to get the TCC to lock without the computer. You can buy a kit (a bit pricey at around $150 last time I checked), or rewire the system inside the pan to lock up the converter in 4th gear. You can also rig up a vacuum switch (the heart of the ready-made kit) to disengage the clutch under heavier load conditions.
The main thing you need to do is duplicate the TBI throttle shaft geometry for the throttle valve cable that goes from the carb to the transmission. Get that wrong, you'll be rebulding a transmission. Info on that on the tranny forum as well (and hits the Carb forum from time to time).
The ECM doesn't control the transmission. The only interaction it has with the tranny is to lock the torque converter clutch during cruise conditions. Otherwise, the transmission is self-contained just like they had been for decades before.
The transmission forum has many discussions about how to get the TCC to lock without the computer. You can buy a kit (a bit pricey at around $150 last time I checked), or rewire the system inside the pan to lock up the converter in 4th gear. You can also rig up a vacuum switch (the heart of the ready-made kit) to disengage the clutch under heavier load conditions.
The main thing you need to do is duplicate the TBI throttle shaft geometry for the throttle valve cable that goes from the carb to the transmission. Get that wrong, you'll be rebulding a transmission. Info on that on the tranny forum as well (and hits the Carb forum from time to time).
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