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Extra 95 Cubic Inches


mfg
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I have a 400CI Chevrolet V8 that was removed from My 1973 Avanti (RQB1967) and overhauled last year. It's ready to go. I was planning on installing it in My '85 Avanti (RQB4234) as soon as I can get around to it. I think the '85's original 700R4 transmission should be able to handle the extra torque over the 305 engine. Opinions? In the '73, this 400 engine was originally bolted to a strong Turbo 400 transmission.

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The 700R4 IIRC will handle 400-425 ft-lbs of torque. They were built to handle truck installations so unless you plan to get seriously jiggy with it, I wouldn't be too concerned.

If your emissions 400 has over 300 or so ft-lbs I be surprised. Now if want to tear out the emissions cam and intake system then you would be getting closer.

IAC, I think you should be fine. Even if it were to break it costs the same to rebuild it to a higher torque spec then as now.

JMHO

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A 700R4 is a very stout transmission should easily handle the increase in power and torque as long as it's in good mechanical condition. It may require a different torque converter to match the engine specs.

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The 700R4 in the '85 seems to be in excellent condition. The car was parked for years, and has relatively low mileage (around 59K). As to the torque converter...I think I can use the converter that's in the '85 now, but I will have to use the flywheel that came on the 400...which has balance weights welded to it for the external balancing this engine must need. The vibration damper up front appears to be specially balanced also.

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Yes, you will need both the flex plate and the balancer from the 400 as they are the only externally balanced SBC's. I would use the existing converter as you are and go from there. Be sure you have a trans cooler either in the radiator or aftermarket.

I have a 383 stroker going into my 74 and the limited driving during construction really indicates the pull of that SBC.

Should make a nice upgrade. Bob

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I have a cheap rebuilt 700R4 behind my 400 SBC with all the emissions stripped off. Your combo should work fine...even with bigger tires, it is difficult to put the engine torque to the ground with the light Avanti rear weight. You will spin the rear wheels before you over torque anything in the power train.

If you do not have the lock-up pin in your convertor, suggest you install with a switch of some type (I just have a toggle). Reduces highway RPM 200-300 and makes tranny run cooler.

I did not change the cam in my 400, but tuned with about 18 ° of advance...much more torque, more throttle response, and runs cooler even in 100° Texas days.

Joe

Edited by Devildog
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Thanks very much for these tips guys! I'll be using the efficient dual snorkel air cleaner with air inlets down at the valance this '85 was built with, and I've purchased a like new Edelbrock carb and performer manifold combo for this 400 engine.

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mfg, I had the THM 400 trans swapped out of my 76 400 powered Avanti for a rebuilt 200R4 and have had no issues with the trans. The 400 motor was rebuilt minus the smog equipment and warmed up as well. There has been no problem with the trans handling the 460 ft pounds of torque it was running after being rebuilt. The flywheel was retained, but the torque converter was changed to a "small block" type converter that used the inside set of holes on the flywheel instead of the outer set of holes. Its a good idea to go with the dual snorkel type air cleaner to run more cold air into the motor. I first used an open type air cleaner but later changed to a single inlet unit and utilized the cold air routing in the fender of the 76.

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mfg, I had the THM 400 trans swapped out of my 76 400 powered Avanti for a rebuilt 200R4 and have had no issues with the trans. The 400 motor was rebuilt minus the smog equipment and warmed up as well. There has been no problem with the trans handling the 460 ft pounds of torque it was running after being rebuilt. The flywheel was retained, but the torque converter was changed to a "small block" type converter that used the inside set of holes on the flywheel instead of the outer set of holes. Its a good idea to go with the dual snorkel type air cleaner to run more cold air into the motor. I first used an open type air cleaner but later changed to a single inlet unit and utilized the cold air routing in the fender of the 76.

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