Technical Cadillac 390 head dowels for intake, how critical are they?

I just scored a 2x4 intake for the 390 Cadillac I am building. It has 2 holes drilled for the alignment dowels on the heads. They are diagonal from each other, one on each corner. The deal is one of them rubbed completely through the topside of the intake. I was thinking of welding both of them up and re-drilling using the intake gasket as a guide.

Looks like someone has taken a file to mine in the past, so the original hole dimensions are long gone. A fellow hamber has a better one with good holes I can get dimensions from. Just wondering how critical this alignment is? Is it just there for the original 70 lb intake? What if I never drilled the holes and left the dowels out?

 

The intake gets a bolt on each end of the flange and is clamed down in the middle correct? The dowls are probably more for helping to install the intake than for any other reason.

 

Yeah. You can see the bolt holes outboard and then some notches on the inboard side.
I ***ume the dowels are for alignment, since this intake doesn't sit in a saddle like the sbc. I didn't realize that they we even there until I noticed the hole rubbed in it.

 

One thing that we forget is that a lot of that stuff is used at the factory to make it easier to ***emble.

 

That is a definite possibility.

 

I remember "back in the day" we were racing a 427 Camaro and we installed the heads without dowels so we could slide them out from under the intake without removing the intake and messing with the timing. Cant see why you would have to use them on your intake.

 

I was wanting to deck the block and wondered how that would affect the geometry and alignment on those dowels.

 

That depends on far you deck the block. I decked the block recently on a BBC build to zero the pistons and then I took the heads down to dial in the compression ratio, the result was the intake had to be milled to align the bolt holes and set the intake down on the gaskets. Normally I don't have to go to that extent.

 

What is the ratio of material to be removed from the intake manifold to say, .030" on the heads or block surface?

Merv Furtado had a chart...Think he did the geometry...

 

Dunno yet. Haven't made it that far. I was just thinking I may zero deck it to get the quench right. I believe it has a similar deck height as a sbc. I may have to look at the water crossover tube that attaches to the heads as well.


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[QUOTE="Roothawg, post: 12035247, Is it just there for the original 70 lb intake? What if I never drilled the holes and left the dowels out?[/QUOTE]

Cool manifold, great find. right on.

You are exactly right, the nubs are just to hold the intake gaskets on and help you position the incredibly heavy stock manifold while standing over the 6 foot long engine compartment with your pencil arms (mine are more like Ticonderogas than anacondas anyway)


Here's a close up


This manifold is a bear, I always leave the carbs on when I pull it because I'm lazy


Always use the metal gaskets (here is where the pin goes)


I used these Offy cardboard gaskets, and the exhaust portion of the manifold burned them away in short order, so the engine exhaust would shoot out. If you are blocking the exhaust portion off that might not happen, but if the plates got hot enough it might.


Rock on

 

Thanks for the info.

 

At work I just rebuilt a 365 Cady. What the dowels are for is to locate the intake ports and gasket to the head ports front to rear. The way that the factory intake is bolted down if you didn't have the dowels then the intake can be slide front to rear about a 1/8 inch. If it was me I would make some makes with a marker to check if it all lines up when using the dowels first.
Then make adjustments from there.

 

you should find an un damaged intake..... an give that one to me!

 

Good idea.

 

I think Cadillac are the same a Olds . 0167 off the intake for every .010 off the deck.

 

Wonder who would known for sure?

 

Hey root,
Look at this pic. Instead of welding them up and re-drilling them they could just be slotted like the original.

 

The old 'rule-o-thumb' is that for 0.005" off the combustion side of the head then take a strong 0.006" off of the intake gasket side. If you cut the intake manifold then you have an odd-ball manifold and an odd-ball head...cylinder head that is......
This is for a 'normal' 90° v-8.
If you have intake manifold like an LA Mopar then you also may need to do 'something' about the end seal areas as this gap will shrink by about 0.008".

There is a nice chart on this site:
http://www.crankshaftcoalition.com/wiki/Milling_cylinder_heads

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