Hey folks, I'm looking to throw a little more $ at my problem and would like opinions and advice.
I have a mostly stock (exhaust is now full dual) 1975 L-82 4-speed and I'm looking to add some HP on the cheap. A local craigs's lister that I've dealt with before has a stock 1980 aluminum intake for $25 and some very low mileage (< 1,000) heads from a 290hp crate motor for $150.
To my novice eyes, these look like good deals and great places to start, nice and easy, just a top end replacement, how hard can that be. I'm just wondering if I'm going to get the HP increase through added compression and flow, and reduced weight. Or if I'm just going to give myself the largest self-induced migraine.
What are some compatibility issues I should look out for?
Vette(s): 1981 Blue Ice Met. w/pearl ghost flames
3.45 Dana 44.
If you do decide to buy that stock aluminum intake, be sure you look closely at the areas around the coolant crossover passages. The metal is thin and over the years the antifreeze can corrode it a hole in it.
I had this issue with the stock aluminum intake on my '81. I was going to sell it and upon cleaning it up I found the previous owner boogered it up with some J-B Weld and painted over it. Needless to say it went into the scrap pile.
GEN III 5.7L "LS6" Engine swap TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes Borgeson Steering Box Born 8/1981
The stock heads on the GM 290 hp crate motor are worse than the 882 heads on your L82. They only have 1.94 / 1.5 diameter valves with pressed in studs and no guide plates while your L82 would have the 2.02 / 1.6 diameter valves and I believe screw in studs and guide plates. Both sets of heads have 76 cc chambers so no increase in compression either. Be careful adding more hp to a 38 year old engine too; previous owner of mine hopped up the top end on mine and this summer I took the bottom end out of it.
The heads ended up being a mid-70's, nothing-special pair with non-matching casting numbers.
When I looked them up I saw that the valves were indeed smaller than those on my 882's as Case75 pointed out. The intake also didn't have a place for my manual choke's hot air pipe, so I passed on the deal. Converting to electric is probably not that hard but I really prefer to change as little as possible, especially when visible.
Now mulling over the idea of a new cam, which comes with a whole other set of considerations I'm finding out.
My gaskets are leaking a bit, as I suppose 38 year old gaskets do, so I'm planning to replace them this winter which is really putting me in the "as long as I'm in there" state of mind. An expensive state, as I'm sure you all can attest to.
Thanks again, your advice and knowledge is greatly appreciated!
I've been there with mine. I was in a quandary for years about what I wanted to do and how far I wanted to go. I'd go back and forth between doing what you're proposing to rebuilding everything to crate motor and then back to just bolt-ons. My hand was forced when I was replacing harmonic balancer and I broke the hold down bolt off in the end of the crankshaft. I had original block bored and other machine work done and pretty much replaced the top end with vortec heads and all other new stuff. You're in a little better situation than most of us are/were since you're starting with an L-82 which has higher compression than us poor saps with L-48s. Low compression motors don't seem to respond too well to cam upgrades and possibly even some of the other stuff like exhaust. I put 2 1/2" true dual magnaflows on mine before I did anything to the engine. It sounded better, but not much else. It never seemed to run as good after I did that and it sure felt like it lost some low end grunt. My advice is go big or do nothing. Cam upgrade by itself may not be ideal and new heads can create other problems as Greg points out. (I had the top end rebuilt on a Honda once and that part of it was great, but it started burning oil like crazy -- better compression sealing at the valves was causing oil to go past the worn rings.) If it were me I'd keep the original block, freshen it up a bit with a bore or at least a hone, and then upgrade cam and rework or replace the heads. Most likely you can keep the original crank and maybe rods. Another benefit is you will be able to get new cam bearings when you do this.
Your car is great, love the color and only 1664 green ones in '75. Throw in the L-82 4 speed and you probably have a pretty rare car!
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: firstname.lastname@example.org, 112 LSA, Eagle Steel Crank.
Dave has said what I meant to say. Take his advice and make sure the bottom end is strong enough before working on the top end. And he's right, not many green '75 L82 4-speeds out there so take good care of that block.
Thank you, thank you! All great information. So if I go in, I'd better be prepared to go all-in. Think I'll go with the freshen-up and keep it mostly as-is, and spend my time and $ on the suspension.Age and fluid leaks have dried, cracked and eaten away just about every piece of rubber.
The other day, my 5yr old son was working on a lego project. He built a vehicle with a drill-bit type nose that was supposed to spin when he rolled it. He finished it but the nose didn't spin. This brought him to tears. I calmed him down, told him we would fix it and explained to him that "when daddy works on his corvette for a long time and it doesn't work like it's supposed to... he cries too."
Vette(s): 1980 Black/Black L82 Coupe
1974 Medium Red/Silver coupe
Your L82 probably has about the same power as that 290 GMP. Your rating is net the engine is gross. I have a 1980 L82. I have appreciably more power, but I don't think it is because of any major internal changes. The power drop from 1974 to 1975 was about 35HP. I think most of it is due to changes in intake and exhaust. Last month I loaned my car to Flowmaster. They used it to design their new low back pressure exhaust from the exhaust manifolds back to the tips. In return< I now have the first of the new exhaust system. They will market the new system in about a month. I seem to have about a 10% power gain from lowering the stock exhaust backpressure. No dyno test but it gets going a lot faster. Sounds good too.
Perhaps a lower back pressure cat converter would let your engine be more of what it wants to be.
Vette(s): 1971 350 270 hp roadster millivanilli red, black interior, white rag top, white hard top, I've had it 18 years and intend on giving it to my son for his 25th birthday(another 18 years from now)
There are a lot of great after market heads out there that can give you the upgrades you need, cam, heads,intake and carb will run you $2000.00 in parts,if you shop smart you can get them cheaper.Don't forget the ignition system,that can make all the difference in the world !
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