Upgrading Engine
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6th Gear
Joined: Jul 2024
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Upgrading Engine
I have a 1974 L48 and going to change out the engine to a 390 HP crate engine, have a Muncie 4 speed and stock rear end. Any
one have any feed back if the trans and rear end can handle it
thanks
one have any feed back if the trans and rear end can handle it
thanks
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From: Sunshine Coast, Queensland, Australia
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You can break anything if you treat it badly. However right around 400HP on street tires and you should be fine.
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i ran mine with a 430 hp 327 and raced it, the tranny and rear end were fine. ITs the torque on the bottom end that will tear up your driveline, not the HP at the top end. I doubt a small block would hurt it unless its a 383 or bigger. If its a big block then you should look at the torque. If its below 450 ft/lbs you should be good
Intermediate
Joined: Jan 2019
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From: Seabrook, NH
I am in a similar position, about to swap in a crate 350 with a stock Muncie & rear on a 1974 corvette. Will there be any adapters or parts I should order in addition to the engine to facilitate the swap? Anything required to get the crate to bolt up to the transmission? Any good maintenance to do while down there? Any surprises waiting in the engine bay. This will be my first swap.
Is my vette stock?? HAHA
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If its a gen 1 or 2 small block crate motor it will bolt right in place of the gen 1 you are removing
Le Mans Master
Joined: Oct 2007
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From: RI, Now Franklin/Nashville TN
A Gen 1 SBC crate engine will hook up to your 4 speed with zero issues.
I upgraded/rebuilt my OEM 78 L-82 4 speed back in 2014, guessing around, to 425-440 Gross HP (roughly 375-380 Net HP). Your 390 Gross HP Crate engine is about 325 Net HP, at best, which is easily within the rated HP/TQ range of your Muncie 4 speed tranny.
How do I know that fact? My engine builder who did my machine work and short block build on my L-82 who also worked for GM for 16 years, 30 years ago, AND is a mechanical engineer by training told me that my weaker Super T-10 tranny (than your Muncie) can easily handle the bigger HP of my engine. I am over the 325 Net Hp/TQ limit for a Super T-10 (Muncie 4 speed would be substantially higher), but he cautioned me about stomping the throttle versus rolling into the throttle. 11 years on, no issues! The limiting factor is the HP/TQ made by the engine along with the RPM made for both, more than the cubes......
I upgraded/rebuilt my OEM 78 L-82 4 speed back in 2014, guessing around, to 425-440 Gross HP (roughly 375-380 Net HP). Your 390 Gross HP Crate engine is about 325 Net HP, at best, which is easily within the rated HP/TQ range of your Muncie 4 speed tranny.
How do I know that fact? My engine builder who did my machine work and short block build on my L-82 who also worked for GM for 16 years, 30 years ago, AND is a mechanical engineer by training told me that my weaker Super T-10 tranny (than your Muncie) can easily handle the bigger HP of my engine. I am over the 325 Net Hp/TQ limit for a Super T-10 (Muncie 4 speed would be substantially higher), but he cautioned me about stomping the throttle versus rolling into the throttle. 11 years on, no issues! The limiting factor is the HP/TQ made by the engine along with the RPM made for both, more than the cubes......
Last edited by jb78L-82; Dec 23, 2024 at 07:33 AM.
Racer
Joined: Dec 2006
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From: Swansea IL
The factory put the same Muncie 4 spd and rear end in the big block cars. 454’s came stock with 500 ft/lbs of torque.. I don’t think a warm smallblock is going to tax the driveline unless u have some drag radials n u abuse the dead stops.
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Is my vette stock?? HAHA
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the L88 had a much stonger M22
Racer
Joined: Dec 2006
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From: Swansea IL
The M-22 had straight cut gears but the aluminum case was the same as the M-21. So while the internal gears were stronger, the case was not. The L/88 worked thru the same driveshaft and iron differential, so no advantage there either. U could say the driveline was overbuilt for the majority of the available engines.
I believe that small blocks, with street tires, will not tax the driveline. That assumes ( u know how they spell that) the trans n rear end are up to factory standards and not severely worn n out of spec!
I believe that small blocks, with street tires, will not tax the driveline. That assumes ( u know how they spell that) the trans n rear end are up to factory standards and not severely worn n out of spec!