E-Bodies.org Cuda Challenger Forum

Need some advice! I am trying to bolt up my Edelbrock RPM Air gap intake manifold (new) to my Edelbrock performer RPM heads (new) and can get the bolts started on one side, but not lining up on the opposite. See picture. Should I grind out the bolt holes a bit larger? Any help is greatly appreciated!

You say the intake is new. Has the heads been decked ?

Are you using a gasket or sealer on the end rails?

Heads are new as well, not decked. Using sealer for the end rails

Sounds like a question for edelbrock .

Might be worth measuring the thickness of the intake gaskets. There are a few different thicknesses available that account for the geometry change when decking the heads. Usually the difference shows up as slightly misaligned bolt holes.

They're the 0.060 Edelbrock gaskets

Do you know if the block has been decked? If it has been cut very much the intake may need to be cut as well...

That I do not know. I'm guessing the best thing for me to do would be to have the intake milled a bit and see how the alignment is. Only problem is, how much??

Not sure how far off the alignment is, but, first thing I would do is to determine if the gaskets are too thick, or too thin and then look at alternative gaskets.

The gaskets are .060", I haven't found anything any thinner than that, the orientation of the holes indicated the gaskets needing to be thinner, but again, haven't found any thinner than .060"

If you just set the manifold on the heads with no gaskets, do they align ?

Another thing to try is if you have a stock oem manifold, give that a test fit and see how the alignment is. I had a similar issue with an aftermarket intake and ended up removing some material for fitment. If you end up doing so, be sure there is no interference with the bolts to the heads/manifold as you may end up cracking the intake at the attachment holes.

One other time this was an issue as they machine shop took a few thousandths off the heads. Again, i had to do some slight modifications for the intake to fit. I know you said all is new, so check out the intake very closely with an oem and keep us informed on what you find.  :popcorn:

Block deck height & targeted  compression ratio changes  required .035 I had to have shaved on a new M1 intake. The bolt holes on 1 side looked like late quarter moons prior.

Yes they align just fine without the gaskets

Quote from: Cbridgewater on January 01, 2023, 01:40:41 PM
Yes they align just fine without the gaskets

If the holes line up without the intake gaskets, wouldn't that be the appx. amount you would need milled off each side of the intake?

Your simplest solution is to oval the intake manifold bolt holes so it fits with the gaskets you have. Hotrodders have been ovaling intake manifold holes forever using a die grinder and a carbide burr. Afterward, as you pull down the intake with the bolts, the gaskets will slightly compress which will improve alignment. Many choose to leave out the front and rear cork seals and just use Permatex Right Stuff to seal the end rails. Edelbrock recommends not using cork as it causes the misalignment problem you are experiencing. Leaving out the cord end rail seals gives you clearance to get the intake manifold bolts started without cross-threading or pulling the first thread from the head. See this video: https://youtu.be/1lKI9HNn0kg?t=268 (https://youtu.be/1lKI9HNn0kg?t=268)


The greatest concern is whether your block has been decked enough to misalign your intake manifold port to cylinder head port. Milling that intake port surface without knowing what has been done to the block is a guess at best. Here is a video showing port matching using the gasket.
https://www.youtube.com/watch?v=n5xicOb-ChM (https://www.youtube.com/watch?v=n5xicOb-ChM)
You can confirm port alignment by marking your intake manifold gasket while installed on the cylinder head and again while installed on the intake manifold. 
You may find a mismatch or may be surprised to find that the intake manifold port is slightly smaller than the cylinder head port which helps prevent a step mismatch from intake to head port. Edelbrock knows this when they engineer the intake manifold port dimensions so it is not typically a problem area.