Intake manifold problems with Comp Header

[Canadian510]

Hey everyone,

Ran into a problem with my new comp header in that none of my intakes will fit with it lol. Tried using the Canon intake that came with my 45's but it doesn't seem to be long enough the flange where the carbs meet the manifold hit the runners. Then tried my edelbrock intake and the bottom of it hits the middle two runners as well.

I'm assuming I need a Nissan Comp manifold to go with the header or is there another option?

[defdes]

How much interference is there?
There's a race car trick which involves tapering the face of the manifold that meets the head which tips the carbs upward so there is a more direct shot of fuel/air to the combustion chamber.

[Byron510]

John's trick mentioned above works for many of the intake manifolds. Usually it's the #4 exhaust that seems to interfere with the comp manifold. It's intersting that the center two hit on one of your manifolds.

Just another point of interest to save heat ache later; make sure the intake and exhaust manifolds are the same height where the stud and heavy washer crosses them both. If the manifolds are at different heights, one doesn't get cranked down tight enough, and usually it ends up in an annoying exhaust leak. So either machine/grind the higher manifold to match or use a stepped washer to make sure the clamping pressure is equal on both components.

Byron

[Canadian510]

Cool thanks for the tips both of you. I'm currently in ontario for work so I'll message dad back home and see if he can whip something up. Tapering the manifold definitely sounds less expensive than buying a new one lol

[Canadian510]

Well finally got the manifold back from the shop after a few months wait and the damn thing still won't fit. #4 runner is the only lasting culprit, still needs almost an additional 1/4 of an inch where the carb meets the manifold.

Anyone have any tricks up their sleeve other than bashing the hell out of my beautiful (and damn expensive) header?

[Byron510]

Definitely don't hit that header for all the reasons you mentioned above.

Did you have some more angle milled into the manifold? That should do the trick.

Byron

[okayfine]

And if that was the last resort, I'd make friends with a TIG welder and cut-n-shape the #4 until it fit versus bashing.

That said, bashing in other applications has no effect on HP:
https://www.youtube.com/watch?v=azPKIjx ... rE&index=7

[Canadian510]

The manifold currently has the mounting surface milled 2.5 degrees but apparently milling it more won't solve the problem, according to my dad who's at home with the car and trying to get it finished for my vacation. Says the angle of the runner would just keep interfering and the top edge would be getting awful thin.

And watched that video awhile ago, hard to believe that has no effect on power haha.

[defdes]

How thin is the flange along the top edge? I remember mine being close to 6.5mm.

[tfm1066]

I used the Edelbrock manifold, I removed(milled) the water passages off the bottom and then made 1" extensions. Then add 1" tabs to the header it works great and allow's @ 1/4 distances between the header and manifold for a heat shield. However on a DCOE type manifold it might push the carb's out to far. The spacers were very easy to make.

[Canadian510]

How thin is the flange along the top edge? I remember mine being close to 6.5mm.

That might be my issue then, mine's nowhere near that thin. Called my dad and he's running it back out to the machine shop to increase the angle to see if that solves the problem.

One question,with the flange being that thin are you worried about the manifold cracking with the weight of the carbs at the end?

[defdes]

It's a pretty widely used modification in race application, pressure is distributed pretty evenly about the casting. I never had any issues in 5 years racing the car.

[Byron510]

Just a side note on the angle machining;

Make sure the spat faces on the intake and the seats on the shared stud washer are parallel with the new machined face on the manifold.

I have not needed to do this modification on any of the manifolds that I have used in the past as I have had the luxury of having Nissan Comp intake manifolds on hand to use with my Nissan Comp headers.

However I do see an issue with the fasteners than needs to be corrected when angle milling the manifold. You could imagine that if the two are not parallel, then a significant amount of stress would be placed on the studs/bolts when torqued down. I would also think that the twist in the studs/bolts could also lead to backing off of the fasteners as well. Just a thought while you have the manifold at the machine shop.

Since I lack in a good drawing program, this is my 15 second sketch on the back of a scrap envelope - just to give a visual of the idea.

Byron

[Canadian510]

Thanks for all the help everyone! Decided to go the spacer route and it seems to be working well. Picked up some longer bolts and made some spacers to keep even pressure on the manifold and header. Got the car fired up and runs great!