Thread: 81 corvette engine (need opinions)

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I would like some input on a few thoughts I have.
I own a 81 corvette, and it is 100% stock. The problem is that I planned on owning this car for a year or two, and then selling it. It is a realy nice looking, not butchered car, but the problem I run into upon occasion when I find someone interrested in buying it, is that it is a 190hp car, which means, it is a slug!!! Looks wonderful, but a true dog.(I bought it becasue I like the 1980-1982 body style.)
Anyway here is my idea. Since I want to keep the engine looking as stock as possible( COUNTY CORVETTE IN WEST CHESTER PA SAID THIS ENGINE WAS ONE OF THE CLEANEST THEY HAVE SEEN).. I have a set of older 64cc heads that have been milled .030 and the intake was milled as well, for proper fit. The headon it now are 76cc and it has dish pistons.Total of 8.2 cr.
My plan was to put the other heads on the car, raise the CR a little( I would guess it would be about 9.3 with 64cc. I have a heavy car with high gears( 3.08)posi. Next I was considering the comp cam extreme 262 cam. I would think with a higher CR and that cam that it should at least get out of its own way. Last, I was going to have Carb USA rebuild my electronic q-jet ( It is leaking at the the butterflies ect, needs rebuilding badly) What do you think? I am fairly sure the original cam is something like .390 lift and very short duration. Remember, I am tring to keep the original look, but get a noticable gain on the power.
If it really matters, I have a test tube in the place of the cat, and new mufflers, so it flows okay. Need some back presure for bottom end. Any suggestions would be helpful, but remember, I want the stock look, and Brodex heads and holleys aren't stock. Thanks..

Building CR will make a huge difference and the cam swap definetly won't hurt. You could stroke that motor and gain a lot of hp and torque and use internally balanced parts and look completely stock.

P.S. Exhaust back pressure for low end torque is a myth.

I think you're on the right track, that motor's biggest defficiency is the compression ratio which will be corrected with the 64 cc heads. The car is light enough that it could be made fairly quick even on the 3.08 gears. I just turned a 15.37 quarter mile at 88 mph in my '76 truck and that was with 3.07 gears, stock converter, and a small block that idles so well you'd swear it was stock. It runs 89 octane, too. I was also shifting at 4500 rpm and the cam doesn't even make peak power until 4700 and should rev to about 5500. I used Comp's XE256H cam, which is a step smaller than what you picked. Because you're car is lighter, you should have no problem getting away with the next step bigger cam on the same gears as me. Now, I topped it off with a pair of Vortec heads and an Edelbrock Performer intake. Other than that, my combination is pretty much what you picked out. I'm running a stock Q-jet and a stock HEI (one of the reasons I was shifting at 4500). With an upgrade to the valve springs, ignition, and some 3.73 gears, I feel like I could be in the mid 14's and thats on a 350 powered truck that runs 89 octane and gets 16+ mpg on the 3.07 gears.

Honestly, other than repairing what age has taken a toll on, I wouldn't touch it. Finding any 25 year old car that hasn't been molested is extremely hard. Is it the most wanted Corvette? Far from, but being in it's original condition is what will let that car hold it's value.

If someone else isn't happy with the power, let them buy the car from you so they can invest the money that will never be recouped when you go to sell the car. I'd see about joining the Corvette Club if you haven't already.

Originally posted by Swifster
Honestly, other than repairing what age has taken a toll on, I wouldn't touch it. Finding any 25 year old car that hasn't been molested is extremely hard. Is it the most wanted Corvette? Far from, but being in it's original condition is what will let that car hold it's value.

If someone else isn't happy with the power, let them buy the car from you so they can invest the money that will never be recouped when you go to sell the car. I'd see about joining the Corvette Club if you haven't already.

I agree, and that if a buyer would happen to notic the heads had been changed, he could walk away.

if the car is a numbers matching car then leave it alone . but that doesnt mean you cant do a good rebuild, just dont swap heads intake and such, you can open the cylinders a little to like .020 over, add new rings and bearings, maybe new cam, and get some work done on the original heads, like 3 angle valve job, maybe new valves ,guides and seals.
you would bring the hp up a little and still have a numbers matching car.

Originally posted by fordsfairlane
I agree, and that if a buyer would happen to notic the heads had been changed, he could walk away.

if the car is a numbers matching car then leave it alone . but that doesnt mean you cant do a good rebuild, just dont swap heads intake and such, you can open the cylinders a little to like .020 over, add new rings and bearings, maybe new cam, and get some work done on the original heads, like 3 angle valve job, maybe new valves ,guides and seals.
you would bring the hp up a little and still have a numbers matching car.

.020 over cylinders?

Would the older 64 cc heads have the neccesaary accessory bolt holes for your emmisions, alternator, and A/C ?

I've bought and sold 2 '76 vettes. It takes a very special buyer to care about the heads. The key matching is on the block pad and the pillar. If they match, good for 95% of vette guys.

I say, unless the car has under 60K on it, go for it.

Originally posted by erik erikson
.020 over cylinders?

sorry. thats a typo. should have read as .030 over cylinders

Originally posted by JayDog69
Would the older 64 cc heads have the neccesaary accessory bolt holes for your emmisions, alternator, and A/C ?

I've bought and sold 2 '76 vettes. It takes a very special buyer to care about the heads. The key matching is on the block pad and the pillar. If they match, good for 95% of vette guys.

I say, unless the car has under 60K on it, go for it.

yes , but even I have ran into the type that must have everything perfect.

my example. I have seen barret-jackson auction in where Craig Jackson had pointed out what was original and not on a car. and yes he did notic on one car that it had a numbers matching engine but the car had a few aftermarket parts on it. while he did say that the original pieces could have brought the car up in the price range.

just because you maynot care if the car is original, doesnt mean a prospective buyer maynot care either.

I serched many places looking for an original numbers matching 50's chrysler with a factory hemi, but mostly when I find one the engine has been modded and that turns me off from buying it, the sad part is that in finding what Im looking for I would have paid double the asking price. to get a car that can be restored into factory new condition.

I think what Erik is getting at is that there is a major misconception about boring an engine .020, .030, or even .060 over. The increase in displacement is pretty much insignificant. In fact, the only reason to bore an engine over in those increments is to straighten out the cylinder walls so your rings don't wear out prematurely. It is not a performance modificatin.

Now that you mention .020 over, yes he should have the engine bored .020 over. I don't know why anybody would bore an engine .030 if they didn't have to. If you bore an engine .020 over, you can bore it .040 on the next rebuild, then .060 on the third. If you go .030 over, you only get a second rebuild at .060. You significantly shorten the life of you engine block which is a crime because good engine blocks are getting harder and harder to find.

I understand about the original parts, ect. Another option I had was to nicely remove the original intake and carb, and A>I>R pump (almost as a whole unis with removing as few bolts as possible), us Flat Rate Techs are good at that,hahaha.. Anyway, I could simply remove the cast iron intake and computer controler Q-jet and put them in a nice storage box. I have an issue with the Q-jet, as it needs rebuilding CORRECTLY, and I am not the one to do it. I was considering Carburator USA in New Jersey, or the Carb Shop in California.NJ $195, CA $300. HUMMM. They both seem very confident in thier work. I know the Computer controled carb is not the best, but in all honesty all the computer does is control the misture at idle. At WOT it does nothing. Need some opinions on that. Should I have the carb rebuild and use the stock intake, or should I save it, and run a Edelbrock and a Holley? Would I really gain that much more with the after market setup? I personally think Q-jets if done correctly are better for daily drivers, and when you want the power it is there.
Another thing I came to realize. I was at my friends machine shop today looking at the heads I have there. They have th ebolt holes like my old ones, but I forget the casting numbers. I think I might have made a mistake about the 64cc chambers. I think they are more like 67cc chambers. There was a set of camel backs next to them, and these ports were a little bigger, but much smaller than the 76cc chambers. Anway, to make up for that, I figure I can run a .015 steel shim head gasket. I think that will be good for about 4cc per cylinder verses the stock gasket from GM or Felpro.
Anymore feed back would be helpful. I know I said it should look almost 100% stock, but if some MINOR changes in apperence are made, and could be corrected at need be at a latter date, that would be fine.
Oh, and one more thing. The xe262 vs the ex268 cam. Do you think the 268 cam is going to make me loose alot of bottom end torqe vs262? Has anyone used either of these cams in a fairly heavy car with a stock converter and hiway gears in the rear??
I would like the car to run a high 13 low 14. Do you guys think I am out of line?? Let me know. Give me some combinations ...

All old generation heads had 6 bolt holes for the intake, the new ones have 4. They did away with the two in the middle. Also, the bolt holes are not perpindicular to the head on the Vortecs. Check the casting numbers on those heads, Vortecs had 906 or 062 as the last 3 digits of the casting numbers. On the outside, where the accessory bolt holes are, Vortecs have 3 triangles in a sawtooth pattern. If your heads show none of these characteristics, you do not have Vortecs. My new engine got my truck with highway gears pretty close to the 14's and I know it's got a lot left in it and that was with just the XE256H.


Look closely at this picture and you can see 2 of the 4 vertical bolts for the intake and the sawtooth pattern on the front of the head.

someone on here might have the link to what im talking about.

there is a web site that has a list of most if not all engine block and head numbers, and it shows what the hp rating of the head or engine was acording to the numbers stamped on the heads

I lost the link, but will try to find it. there are just way to many heads out there to remeber which are better than others.

www.mortec.com is the link I was looking for.

I will give you an example of what I had done.

a friend gave me the engine out of his truck, I didnt know much about it so I went looking to this link and found the engine casting number was #3970010. from 69-80's the head numbers are #3998993. with 75cc chambers

but I had noticed that the 60cc chamber head numbers, and made myself a list of them and went to a few boneyards. and found a good rebuildable set for $20. each, and at that price you cant beat them.

Okay, the heads ar in fact 67cc chambers. I figure with a .015 steel shim gasket, I can lose another 4cc's verses a stock gasket.
That should bring cp ratio to about 9.3 to1 . Next, I want this car to really pull out hard, even though I have 3:08 rear gears. I am considering going to the comp 262 cam verses the comp 268 cam. What do you think. And last but not least, I was gonna have "carbusa" rebuild my carb. Any suggestions on another carb rebuilder?? Let me know, thanks.