Q&A

Ask Away! with Jeff Smith: Building an L83 vs. LS Swapping an ’84 Corvette

We upgraded an iron truck 6.0L engine using stock pistons with a very mild 219 degrees at 0.050 Comp cam and mildly ported 5.3L truck heads to increase compression. With a stock LS6 intake, this engine made 475 hp and 440 ft.-lbs. of torque. Not bad! (Image/Jeff Smith)

I have an 1984 Corvette 350 that’s a real dog. What is the best way to get more out of it? I’d like to get 300 horsepower or more. — J.W.

Jeff Smith: The ’84 Corvette was the first year of the C4 body style. Chevrolet carried over the ultra-lame 350 c.i.d. L83 engine that was rated at 205 hp and 290 ft.-lbs. of torque.

Adding insult to injury, this ‘Vette was cursed with what Chevrolet called the Cross-Fire EFI system which featured dual throttle bodies on what could generously be called a cross-ram manifold vaguely similar to the dual four-barrel intakes offered on the ’68-’69 Z/28 302 c.i.d. engines.

It didn’t take long for wags to tag the Cross-Fire as the Cease-Fire. It wasn’t a very good system.

The L83 has some good bones as a basic long block but is encumbered with a restrictive induction system and conservative cam timing.

The problem is improving the breathing on this engine while maintaining its emission legality. That process is fraught with road blocks. There actually is a performance dual cross ram intake manifold called the Renegade that is supposed to improve power. This item isn’t cheap at more than $600 but it does retain the EGR valve.

There are other ideas that will improve power like opening up the exhaust side with headers.

Hedman makes an emission-legal 1 5/8-inch primary tube header that looks pretty good and this will likely improve torque and horsepower. However, burdened with a stock Cross-Fire intake, power will still be limited.

If you wanted to stay with the basic engine, then a mild emission-legal camshaft, E.O legal aluminum cylinder heads, and a step up to a Tuned Port Induction (TPI) intake system would be in order. This would require using a later model chip-based factory computer. At this point, an aftermarket EFI controller (while technically not emission legal) would be a very smart move.

There are a couple of retro-fit EFI systems available. We really like Edelbrock’s Pro-Flo4 system both from its simplicity and also because it is affordable. Edelbrock does not yet offer a retro-fit conversion EFI ECU and harness assembly for a multi-point application without an intake but that could change. Fuel Air Spark Technology (FAST) does offer a stand-alone retro-fit kit so you could use their FST-302000 that sells for around $750 and along with a TPI manifold.

The TPI manifold isn’t known for its power production either since it uses very long, restrictive intake runners. This could make upwards of 300 hp bolted to your existing engine.

If you went with a mild cam upgrade and headers, this whole package might make 325 to 350 hp.

A better upgrade would be to use one of the old ACCEL SuperRam intake manifolds. If you can find one, these are good intakes originally designed by the late John Lingenfelter. This manifold will bolt in place of a stock TPI using the same fuel rail and throttle body.

A far more powerful idea is to yank that small-block and consider swapping to a late model LS engine.

Even the early LS1 engines are far more powerful than your L83. The 1998-2000 LS1 346 c.i.d. engines were rated at 345 hp and later upped to 350 hp with 375 ft.-lbs. of torque.

At this stock level, that is a near 75-percent power increase over the stock Cross-Fire. Not only do you gain an enormous amount of horsepower, but the torque increase is substantial as well from 290 to 375 ft.-lbs. Even better, the LS1 is all aluminum which reduces engine weight by roughly 100 pounds.

Of course, this is not just a bolt-it-in-and-go affair.

The Gen III/IV LS engine family is substantially different than the small-block Chevy, but there are enough similarities that this swap has been accomplished successfully. The best route would be a complete LS1 or similar engine with an F-car oil pan. It would take too much space to go through all of the details here, but there is information out there on the web regarding this swap.

Then you could use something like the Edelbrock ProFlo4 ECU and stand-alone harness that would be inexpensive, robust, and with self-learning technology it would tune itself in a matter of a few hours and save the cost of tuning.

As you can tell from our enthusiasm, this LS swap makes the most sense to us.

Technically, it could be made to be emissions compatible (except in California where the rules are stringent about engine swaps).

Just about everywhere else, you could perform this LS swap, retain the catalytic converter and with near-stock components have a performance platform while not spending a ton of cash. The early C4 Corvette is near the bottom of the desirability scale for Corvette enthusiasts but that will change as time wears on. With an LS swap, an investment now in building a performance version might just pay off in the future.

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2 Comments

  1. Pingback: Ask Away! with Jeff Smith: Building an L83 vs. LS Swapping an ’84 Corvette

  2. Ok, I’ll be a man and accept looking like a goof ball or worst. I’m over sixty, and quit frankly easily confused by all the acronyms GM has to their engines. Also just as silly when I was a kid, laying on my back on a gravel driveway replacing clutch’s In solid lifter big blocks.
    So today I have a pristine 1998 GMC Sierra 1500 four wheel drive, only 100k and looks like new. I would like to place a modern LS platform engine in it, but the brakes go on every time a look at the hundreds of different GM motors. I’m not adverse to rebuilding it, with can, timing, and head upgrades. I simply need a target engine to look for.
    When I ask a younger individual, all I hear is put an LS in it. The guides I see here are great, but it would appear an LS engine also has another acronyms associated Or attached to it. So does that mean a gen lll LS in a certain vehicle is also referred to a L79 as an example.

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