I was looking at some intakes and add says that it fits
up to 1986 SBC. What is the difference in intake manifolds between
pre and post '86 SBC?

 

as far as I know early 86' was still iron, and late 86' first came the aluminum heads, and maybe like 5 more hp.

 

Not sure what intake your looking at but late model 1986 Corvettes L98 & up use aluminum heads. Beat me to it pologreen1

 

pretty sure we'll all say the same thing

 

The center two bolt holes on each side are at a different angle on the later heads. I do not remember what it is, but I think it was something like 87 degrees verses the "older" style where all the bolts go in at the same angle, what ever that angle is. It's like the corners, two at each location, go in at an angle equal to the angle of the intake to cylinder head. The "inner" two on each side go in almost straight down. Then of course you have the Vortec heads where they do not even have the two center bolts on each side.

 

Only on the late iron F-body heads.

Alum Vette heads have the old style bolt angle so any SBC intake will fit.
The angle difference on the 2 center bolts is no biggy; people just enlarge the holes and run a washer to use one on the other.
Some intakes come multi fit with an elongated hole and a tapered washer so can be used on either.

 

Great, thanks for the infos!

 

Late 86' and all 86' convertibles had aluminum head which added 5 horsepower and a good deal of weight reduction.

 

centerbolt vs perimeter valve covers as well.

 

I have an early 86, Sept. 85. I believe it originally came with the first set of aluminum heads, and they were cracked, and the dealer replaced them with Iron heads.
I believe this because my front tires with stock wheels scraped the hood on bumps.
I switched to 113 heads, and the scraping stopped.

Here's the deal:
1. on corvettes, the bolt patterns never changed between early and late heads.
2. The egr pipe was designed for the aluminum heads where the 85 engines had the egr using the heat crossover in the middle of the heads that was eliminated from the aluminum heads due to cracking.
3. 86's iron heads had the crossover passages, but were unused.
4. the 113 heads have 58cc chambers, and the iron chambersare 64cc.
5. The rocker covers were centerbolt on aluminum, but perimeter on iron heads.
6. The rockers on the iron heads were standard Chevy issue, but the aluminum heads had guided rockers with unhardened guide plates.
7. The iron heads have only one accessory bolt hole in one end, and three bolt holes in the other end, and can only be installed one way due to the accessories installed on the vette.
The F body cars had basically the same heads as the aluminum corvette, except they were iron, and had a center couple of bolts that were at different angles. THe F body intakes are different from the corvette cars (Y).

 

The late production coupes received the aluminum heads. Some say only the last 8500 or so cars got them Early aluminum heads had cracking problems so they were not introduced until the convertible was available.

If your car has them, it's possible they were installed later on. A build that early would have gotten cast iron heads. But it's also possible that you may have gotten a car that was used by GM and later sold to a dealer for resale.

Tire scraping sounds like another problem. There was no change to tires and wheels between 84 and 87 in terms of tire size and available rim widths. And the weight difference should have been not more that 30-40 lbs. Even the base springs would have handled that. Sounds more like weak/bad shocks or a hood alignment problem.

 

As I was told, the early production 86's had aluminum heads, but they were suspended due to cracking. The dealers replaced the cracked heads with iron, and they went on their merry way.
In the wrecking yard, I came across an aluminum headed 86 that the yard had purchased from an old gentleman.
When I questioned the owner of the yard, he said the old man had stated he had purchased the car as it sat, presumably with those heads on it, and when the engine failed, he parked it for 15 years, then sold it to the wrecking yard.
I tried to buy those heads, and when I had gotten them off, the coolant was jelly that was almost impossible to remove completely.
I returned the heads, and they sent the heads out to be dipped, but when they came back, there were 2 cracks per head , both in the same places in both heads.
I asked for different heads, and got 1124 heads in their place, and the second set came with roller rockers for my trouble.
As for the scraping, I don't have that problem anymore since I put the aluminum heads on it.
Anything could be the problem, but having an early build date, swapping heads fixed the problem, and the hood fits good.
When I got the car, I put Bilsteins on it figuring the shocks were weak, but the problem continued till the head swap.
Go figure.

 

He's asking about the intake, not the heads.

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