Holley aluminum heads on 68 302 block - drill waterpassages?

86sebring · May 15, 2005

I installed Holley aluminum heads on my '68 302, but I have been having issues with overheating and I can't figure out why.
So I removed the heads again to check the HG and it was on right.
But I found something else. The 68 block has a small water passage in at 12 o'clock when looking from the top down. The original heads have that same passage . But the Holley heads do not have that whole, instead there are larger triangular wholes more towards the bottom right corner, about 5 o'clock.
I attached 2 pictures.
http://img148.echo.cx/img148/9040/compareheads0wg.jpg
http://img148.echo.cx/img148/851/block9zv.jpg
Is that the reason for the overheating issue?
Can I just drill the wholes myself and do I need all of them?
thanks for the help, this is driving me nuts, I already missed some of the best days driving this year.

stangman67 · May 15, 2005

When i installed my Performer RPM heads, i had to drill the block with a 1/8" hole on each bank. See the triangle next to the part you circled on the new heads? I had to drill the hole right below those on the two front cylinders. Edelbrock called them steamholes.

HistoricMustang · May 15, 2005

stangman67 said:
When i installed my Performer RPM heads, i had to drill the block with a 1/8" hole on each bank. See the triangle next to the part you circled on the new heads? I had to drill the hole right below those on the two front cylinders. Edelbrock called them steamholes.

Very good stangman.

I had to do the same thing with my "early" style block when installing the Edelbrock RPM's.

Just wonder how many Stangnet'ers may not have done this procedure.

HistoricMustang
www.historicmustang.com

86sebring · May 16, 2005

Anybody else have any suggestions?
thanks

coolblue65 · May 16, 2005

Like Stangman and Historic said, I too have the early block and had to drill those holes into the block before installing my trick flow heads.

Is it possible you got heads for the wrong application? Is there a part number somewhere on there that you can check?

Paul619 · May 16, 2005

coolblue65 said:
Like Stangman and Historic said, I too have the early block and had to drill those holes into the block before installing my trick flow heads.

Is it possible you got heads for the wrong application? Is there a part number somewhere on there that you can check?

I also have trick flow heads. It should have said something in the directions for it, if it didnt just take your new head and use it as a template. Align the gasket with the dowels and mark the holes on the block with a white out pen. When you drill them be patient it is a PITA. also you may want to inspect you old head gaskets and intake manifold gaskets and see if you had positve seal on them. if you didnt have a good seal on the intake that would also cause overheating. oh and make sure you flush out your block after you are done those shavings will do wonders if you kno what I mean.

hope that helps

Great68 · May 17, 2005

I never had to do any drilling when I installed my AFR's...

Come to think of it, I don't even remember my block ('68 302 block) having those holes...

65ShelbyClone · May 17, 2005

The small holes at the top(lifter side) of the bores isnt the problem, its the triangular holes between the bores. See how they're offset on the heads compared to the block? This is my latemodel roller block next to your early Mexican block for comparison:

View attachment 514466

86sebring · May 17, 2005

Thanks a lot for all the responses.
When looking at the pics, it makes sense to drill the triangular holes into the block.
Too bad I already drilled the small holes at 12 o clock into the heads and torqued them down :damnit:
Can I re-use those nice $95 Felpro gaskets or do I need to buy another set?
I didn't start the engine yet.
Also what size need the holes be (1/8?) and how deep into the block?

coolblue65: I bought those heads used, but rebuilt. No instructions with them.

Paul619: I did not use a torque reading when bolting down the intake, but I made sure it was not too tight. I heard too many stories of stripped threads in the heads due to overtorquing the manifold. How can you tell if you had a tight seal?

Thanks

Paul619 · May 17, 2005

86sebring said:
Thanks a lot for all the responses.
When looking at the pics, it makes sense to drill the triangular holes into the block.
Too bad I already drilled the small holes at 12 o clock into the heads and torqued them down :damnit:
Can I re-use those nice $95 Felpro gaskets or do I need to buy another set?
I didn't start the engine yet.
Also what size need the holes be (1/8?) and how deep into the block?

coolblue65: I bought those heads used, but rebuilt. No instructions with them.

Paul619: I did not use a torque reading when bolting down the intake, but I made sure it was not too tight. I heard too many stories of stripped threads in the heads due to overtorquing the manifold. How can you tell if you had a tight seal?

Thanks

you cant use the head gaskets again you need a new set. the steam port just neetd to be as big as the hole on the gasket use that as a guide. what kind of manifold do you have? I can try to find the torque specs on it

86sebring · May 17, 2005

thanks Paul, the manifold is a Edelbrock Performer.
How many holes would I need to drill, all 8 or just the front 2 and how deep ?
What kind of drill bit works best for the block?

65ShelbyClone · May 17, 2005

86sebring said:
How many holes would I need to drill, all 8 or just the front 2 and how deep ? What kind of drill bit works best for the block?

I would say all 8 and deep enough to go through the deck and into the water jacket. A steel drill will work on the iron block, but you may need more than one if it goes dull(iron is really abrasive as a metal). Since I've never actually done this, wait for others to confirm before you go poking holes in your block.

Wait a minute, if you already drilled the heads, wont that work instead?

coolblue65 · May 17, 2005

Have you tried contacting holley and seeing what they suggest?

mustangracer · May 17, 2005

Drilling the holes in the head at 12 o'clock works well enough. I did it on my late model p heads due to some overheating issues, and it ended my problems with 100 deg 95% humidity in SC

86sebring · May 18, 2005

Thanks everybody for the input. Since I already torqued the heads, I decided to put everything back together and see if the overheating problem went away. I will post the results here soon.

86sebring · May 20, 2005

Ok, got it back together tonight and ran the engine for a while, definitely much improved. No more instant overheating, although after I went for a spin, the temperature did rise to about 195° while the fan was spinning.
So I guess I still need to work on the cooling system a bit more and also double check the timing. But drilling the 8 holes in the heads definitely helped a lot.
And the little sebring goes like stink now

Thanks again for all the input

Holley aluminum heads on 68 302 block - drill waterpassages?

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