vettehardt

I am thinking of building a motor for either my 73 or 76. I run the cars in NCCC auto crosses and have to conform to the rules set up. I run class 2D in which i must keep stock parts but i may intermix between the years/motors in my class. The class is for all low horsepower cars from 71-82.

Now I know there is a killer combination of parts that will net a 10.5:1 CR motor making around 300-320hp. I've been running against these motors for years with my measly 180hp. I can keep up on small tight courses, but long open courses, I can't touch them. This setup includes using the cam and flat top pistons from an 82 crossfire motor, 71 heads and 80 intake.

My thought was to find a 82 short block with the cam and pistons already installed and just put my heads and intake on it and that should be good. The question I have is, are the parts used in the 84 motors the same casting/part numbers as those used in an 82? Is the bock the same casting number? Are the pistons the same design and part number? Was the cam the same lift and duration between the two? I am just trying to figure out if I can start with an 84 motor and still be legal in class.

terry82

they are suppose to be the same motor.have heard that the 84 intake may be good for 5 more hp ,but that has not been proven.the 84 computer is different .but I think everything else is the same .I would ask buccaneer.

derekderek

Date code on block might be a disqualifier...

vettehardt

They don't check the date codes, just casting numbers. I can use the 010 block whether it is a 2 bolt or 4 bolt. I have two 4 bolt blocks out of trucks sitting around that I was going to use for this project, but they both need bored too large. I am only allowed to go 0.030 over including wear.

Dynra Rockets

How do you get 10.5CR out of -3cc trough flattops (464664) and '71 76cc heads? Math doesn't work.

It would have to be 64cc, which was not available in a '71 Corvette, and using a .015 head gasket with blueprint minimum spec milling/shaving to get 10.5CR

vettehardt

I really can't say one way or the other on the math. I am only going by what the people who have built these motors are telling me. Whatever it ends up being, it is much better than what I have now.

Bobo Greybeard

I would do all that I could to avoid the Cross Fire fuel injection of the 82 and 84. The problem is from my understanding is the motor becomes very limited due to the constrants of the intake and cross fire set up. That is why they changed it in 85, the motor was to limited by it. This is what I have been told at least.

Bobo

7T1vette

OP is using an '80 intake (with carb) per post #1.

Buccaneer

I don't believe a word of it...my CF puts 330 to the rear which is roughly 425 at the motor and runs great... ALL CFI.

The 82/84 blocks were both 207 blocks, 2 bolt. I have a 010, 4 bolt in mine now. Cams are slightly different, but not by much. The heads on both 82/84 were also the same 462624. The 82/84 CR is 9.0:1 stock.

Bobo Greybeard

That is impressive with any block of that era. Like I said, that is just what I had heard. I apologize for what appears to be me giving bad info. Those numbers are impressive though. BTW I love the 010 blocks.

Bobo

7T1vette

The engine block isn't going to "make" any power; it just needs to "support" whatever power is made from heads, cam, pistons, and crank. 4-bolt blocks are stronger than 2-bolt blocks, but 2-bolts can handle up to 500 hp/650 ft-lbs with no problem.

If you must use stock parts from that era, heads from LT-1 ('71-72), L-82, or L-98 engines will give you 9.0:1 compression. Not sure how listed era stock parts can make 10.5:1 CR, unless there is a domed piston in there somewhere or it is allowed to mill the heads down.

Buccaneer

Sorry for the highjack to OP
No apology necessary. I just hate seeing negative things about CFI, when it really isn't true. The biggest reason it gets a bad name is that "most" people that have, have had or never had and heard of CFI don't know how to maintain it and end up screwing it up and then the bad mouthing starts. If you take the time to learn how the system works, it is like the energizer bunny, "It keeps going and going..." It's actually rather reliable. Mine isn't anywhere's stock, but not too crazy either.

v2racing

If you have to use original style parts from 71 to 82, here is what I would do. I would use a forged crank available in LT1's, L82's and some truck engines with a 4 bolt block. LT1's and L82's also both had upgraded rods and forged flat top pistons. I don't know if your allowed to deck the block in your class, but if so, go for a a zero deck. If not use the tallest 4 valve relief forged flat to pistons you can find. Combined with a .015" shim gasket, you may be able to get a fairly good quench. I like tight quench, mine is at .034".

For heads the best your going to find is the 487 71 -72 LT1 heads. Mill them to get compression if allowed. A good performance valve job from someone who really knows what they are doing can help a lot on airflow.

If you are stuck with using a stock cam of that era, a repo LT1 solid lifter cam is probably as good as your going to get.

An aluminum LT1 intake would be best, but an L82 would also work.

A 2.5" exhaust with an X-pipe or H-pipe with free flowing mufflers should help a lot too.

Set your distributor up with only 15 degrees of mechanical advance so you can run about 22 degrees of initial advance and around 36 total. Have the advance full in around 2500 rpm. This will help the off corner, response and power.

Take the time to get your AFR corect with your carb. Use a wideband sensor to achieve between 12.5 to 13 to 1 for WOT. If you can't do this part, send your carb to Lars to set it up for you. Tell him what you're building and how you are using it.

Mike