Hey guys, putting a set of rams horns on a sbc. Out of the 6 bolt holes in the manifold 4 of them are 1/2 diameter and only take a 3/8" bolt. The other 2 (center holes) are the correct size for a 3/8 bolt. Am I missing something? All my manifold bolts are 3/8 with no shoulder.
should be fine. sometimes they are tight fit and someone may have made the holes bigger. i have had trouble with bolting them to later heads. they bolt up ok to 283 and 327 but may be tight on later 350.
Are they too small or too big? If they are too small its likely just scale that has built up inside the holes.
You can always make some bushings . But take your time align it correctly , tightener up and forget about it .
Yea, possibly what Dustin said. Some of the later years, they started making them with thinner walls to help save weight. What happened to MANY small Chevy manifolds, was that they warped enough to not fit the bolt holes any longer. Many of all the designs of manifolds were drilled with larger holes during the light weight casting era. You may even have a set the the car owner drilled larger because HE couldn't get all of the fasteners in. Remember to use anti-seize compound on the threads. Even under the head of the cap screw. Mike
If the end bolt holes are the correct size everything should line up. Just use 3/8 bolts with flat washers on the center holes.
[QUOTE="... I have had trouble with bolting them to later heads. they bolt up ok to 283 and 327 but may be tight on later 350.[/QUOTE] I've had two different sets on my 400. Changed to the 2-1/2" Corvette rams horns some years ago. Both sets fit fine.
Exhaust manifolds are one of the most misunderstood parts of an engine.... As the manifold heats up, it needs to do two things: 1. Move around 2. Dissipate heat To help it move around, Chevy made the end holes larger, and also used lock tabs and thick washers on the mounting bolts. To help it dissipate heat, Chevy decided not to use gaskets between the manifold and the head. This lets some of the heat from the manifold go into the cylinder head, where there are coolant passages, so the heat gets put into the radiator eventually. Many guys re install the manifolds without the lock tabs, and they add gaskets. Neither of these practices are a very good idea.