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Buy the car, not the engine. The engine is one of the easiest things to change (though not the cheapest). Lots of speed shops can swap in a crate motor, or rebuild one, if you can't. Paint and rust are the hardest to fix, and it seems that fewer and fewer places know how to properly work on Corvettes. Condition matters a LOT, especially if you are unable to do most of the work yourself.
It also matters where you live. 1980 is great for modding (last year without a primitive computer). If you live in CA, your choices are more limited.
So please post photos of what you are considering!
Last edited by Bikespace; Aug 28, 2020 at 06:49 AM.
Well, since all you picked are smogger engines, almost anything will be an improvement.
You're going to have to be more specific on your changes - compression, runner size, etc.
It's not realistic to try to calculate the improvements when there may be NONE. The wrong heads, cam, etc. can actually cost power.
The components you mention are not very specific. What compression are you looking for? What size heads are you looking at. Fast road cam? What is that. There are several thousand cam grinds out there. If the components are mismatched you could have a real dog of a motor that makes crappy HP. Select the right parts and you could have 350-500HP. You need to be more specific.
Out of the three.....buy the Big Block......
If you know what you are doing......you can make a hard running Vette with the stock 454.....all it needs is headers, camshaft and timing.
It is on my bucket list of things to do in my life.......the 74' 454 had so much potential it wasn't funny.......and people know about as much of what was going on with the 74' as they do now.
It may have low compression but overall, it is a big block large displacement engine.......and the dollar vs. performance ratio is much better......The trick is finding a nice one. These cars seem to be a magnet for the "engine enthusiast" crowd who like to turn idle screws and set timing by ear........
That said.....the 80' L-82 4 speed is a better running car than the 76' L-82 4 speed out of the box.....but very little was change on the core engine from 73' to 80' so both have the same potential for mods.
Understood, as I mentioned unfortunately I am not the least bit mechanically minded.
I would be honest with yourself on what you want and set a budget. Find someone who knows engines and buy or have one built that works. Just throwing high performance parts together usually results in poor performance. If your not comfortable find some who is knowledgeable about this.
IMO, the most significant "smog" change occurred MY1971 when ALL motors' compression were drastically reduced from MY1970 levels.
In my opinion it was the 75' Cat mandate which strangled every single car available from any manufacture.
A 1975 400 Trans Am would run one second faster in the 1/4 mile with headers and duals......
A 79' 425 Caddy DeVille would run 1.5 seconds faster.....
It is interesting to note that a 71' LT-1 350 made the exact same power on a dyno as a 70' model because the larger chamber compensated for the 1.5 points lost in compression. (A bone stock LT-1 was really like 10.5 to 1 measured). The 71 head just flowed better due to intake valve unshrouding.
The 70's were bad but nothing is worse than the 1981 model year of anything. Ford, GM, Chrysler.....just terrible. Ford's VVT carb, Chryslers "Lean Burn" 318/360's with 2" single exhaust, the 81 Turbo T/A, CCC on ALL GM products and lower ratings, The GM EFE carb heater gasket, Ford killed the 302 that one year....255 was all you could get in a car. Z/28 was Automatic only......pretty terrible year.
BUT.....most of the "core" engines and transmissions were unchanged......and ALL of the tried and true Hot Rod stuff works on them.....A 360 in a Diplomat ran about 17 seconds in the 1/4.....that exact same 360 in a Dodge shortbed truck ran low 15's.......trucks were the fastest "cars" you could buy.
The reason I remember this so much is that all of this junk was on the Used Car lots in 1987 when I got my drivers license.......by the time these cars were 6 years old, most of them ran like crap and you had to figure out how to skirt around the "electronics" to make them right........my local GM salvage yard ran out of 1980 carbs and distributors for just about anything, especially the 3.8l Buick V6 G-Body cars......the local mechanic shop had a cottage industry converting them to pre-81' spec.....I got my girlfriend an 81' Monte Carlo that was perfect in 1995 with 40,000 miles on it with the 229 Chevy V6 and the IMCS shorted out almost immediately.....I tried to convert it but NOBODY had a carb or distributor anywhere....(Internet was no help then).
EFI solved all of this by 82' in most applications.....by 89, there were no more carbs available on anything. The 88' Monte SS was the last carbureted vehicle ever sold on US soil.....and it had the CCC.
Sorry for the rant.....but it is relative to the history of Vette's in these years and I hope it helps people understand a few things.
Jebby
Last edited by Jebbysan; Aug 28, 2020 at 11:57 AM.
Are not all the engines in C3s smoggers after 1971? 🤔
Not really! Yes the compression came down but try and run a 70 LT-1 with 11:1 compression on gas at the pumps today..Good Luck.
As jebby said, the real problems started with the crap emission control equipment in 1975, primarily the pancake restrictive cat and 2-1-2 exhaust which is essentially a single exhaust. Take any engine from 71-80 in a C3, especially the SBC Gen 1, tune them correctly with a dual exhaust, and the car will run pretty decently as compared to the early C3's, for the most part. Add headers, Top notch aluminum heads with 10:1 compression total, roller cam, and a 355 L-82, like in my 78, will smoke a 69/70 L-46/LT-1...no problem.....
To the original poster, I believe you might be the same gentleman that posted another thread about choosing between a c6/7 or a c3.
Im sure there are plenty of people that are not mechanically inclined that own a c3. I can’t recommend the union of c3 ownership and lack of mechanical inclination, let alone the desire for major performance upgrades with the same scenario.
Modifying a car for more performance, often exposes other weak points in a car that will subsequently need more attention.
if you are going to go down this road, I’m going to agree with Jebby in seeking out a 454 car. The bigger cubes will be an automatic advantage in craving more performance that will come more easily, in a milder package.
However, keep in mind as I mentioned in the other thread... these cars are old. Stuff will break and other stuff will need attention just from age anyway.
It’s certainly possible that you will enjoy owning a c3, and are not opposed to paying someone to make the car into something you want it to be, and paying someone to maintain it. It’s also way more likely that the overall satisfaction of owning a newer car will be greater.
How about this gem?.....that came on 81' Caprice 305's? The relay for them would stick and melt the grid......dropping **** right into the engine. 20 minutes with a 1980 spec gasket would pickup a butt load of response at low speeds......all S-10 2.8l V6's had them as well as CCC 3.8l V6 G-Bodies......fun times. Not exactly sure why anyone services these....but you can still get new ones!
Jebby
Last edited by Jebbysan; Aug 28, 2020 at 12:12 PM.
MY1971 per GM published specs SEP 1970 https://www.gmheritagecenter.com/doc...t-Corvette.pdf
LT1 370 330hp/380 360tq, 9:1 CR (but same cam as MY1970)
(approx 10.8% less hp / 5.4% less tq / 18% less CR)
LS5 390 365hp/ 500 465tq, 8.5:1 CR (but same cam as MY1970)
(approx 6.4% less hp / 7% less tq / 17% less CR)
======================================== ==
Lowered comp LT1 lost some 2 points of compression, lost some 40 hp, lost some 20 tq
similar reductions & results across entire GM line beginning MY1971
The drop in compression led the way for those many power-robbing changes which continued for several years until computer-aided design and improved on-board computers brought us to today. Where even grocery-getters' direct-injected motors w/ variable valve timing run 13:1 compression on pump gas and make Big power. It's been a learning process for automakers; still is. I suggest rate of change is greater today than ever. Oh, got my license prior to 1970.
Last edited by 71chimera; Aug 28, 2020 at 02:05 PM.
MY1971 per GM published specs SEP 1970 https://www.gmheritagecenter.com/doc...t-Corvette.pdf
LT1 370 330hp/380 360tq, 9:1 CR (but same cam as MY1970)
(approx 10.8% less hp / 5.4% less tq / 18% less CR)
LS5 390 365hp/ 500 465tq, 8.5:1 CR (but same cam as MY1970)
(approx 6.4% less hp / 7% less tq / 17% less CR)
======================================== ==
Lowered comp LT1 lost some 2 points of compression, lost some 40 hp, lost some 20 tq
similar reductions & results across entire GM line beginning MY1971
The drop in compression led the way for those many power-robbing changes which continued for several years until computer-aided design and improved on-board computers brought us to today. Where even grocery-getters' direct-injected motors w/ variable valve timing run 13:1 compression on pump gas and make Big power. It's been a learning process for automakers; still is. I suggest rate of change is greater today than ever. Oh, got my license prior to 1970.
This is the rub....not one 70' LT-1 made the advertised power.....they made about 355-360....I have built them, period correct, even with enhancements....360. The 71'-72' makes the same power on a dyno. It just does.....the valves being unshrouded were worth that much airflow.....about 10 cfm on a bench. The 330 number GM came up with was total BS as was the 370 number in the previous year......
In fact....the 302DZ, the L-79, the L-46 all made about 360 horsepower.....it is all the head would provide. And as a further point, 2 points of compression will not lose 40 horsepower...more like thirty, and to top that off....all of these "11 to 1" spec GM engines had about 10.5/10.6 to 1 actual......I have measured them and done the math. If you zero deck the block, it has 11 to 1.....GM's numbers were based on that....just like any aftermarket piston in any catalog. The trick is to run the 71-72 heads with the 70 pistons and you get about 375.
Jebby
Last edited by Jebbysan; Aug 28, 2020 at 02:24 PM.
Needing Advice About Engine Performance
