Opening up 318 ports to 360 size

[dart_68]

I have a Holley Street Dominator intake that has 318 sized ports. I was wanting to open them up to match the ports on my Speedmaster heads which are 360 sized. It looks like there's enough meat to open the ports to the sides but they need to be taller too. Problem is that the opening them up in height on the roof would leave maybe about 1/8" material. I think that's too thin.

Should I just open them up to the side and not worry about the roof or not open them up at all? A new manifold with proper sized ports is not really in the budget right now.

 

[cudamark]

I'd run it like it is until you can get the correct manifold and swap them. Doing the mods you mention would ruin the resale of the existing manifold.

 

[Garrett Ellison]

I don't think you'll see a lot of benefit because the runners are sized at 318 port dimensions in the plenum, too. Is it the EGR intake or a type Z with the crossover port between #4 & #7? I think you would see more of a benefit by shortening the runner dividers back from the plenum, but I would leave it alone until you get your manifold of choice.

 

[rumblefish360]

Well it, roll the money over to another manifold.
Problem solved, performance increased!

 

[Wyrmrider]

how big a motor and cam on a street build the velocity of the 318 heqds could help where you need it most

 

[Garrett Ellison]

Yes, how's the rest of the build. You'll probably be somewhat surprised with the Street Dominator, every one I've experience with on whatever "street" engine with a 106-109 LSA cam in it with decent to good heads had really strong midrange power from 2500-6500 rpm. But that's also with gearing to match. The 318 sized runners will down tune from that a few hundred rpm on a larger engine but there are worse intakes to have laying around to be forced to use. I'm running one on my 318 (stock heads with 3 angle valve grind) by choice right now. I'm happy I have it but am really looking forward to some gears...

 

[RustyRatRod]

Most of the time, the intakes don't have room to open them up that big. You run out of room on the bottom side of the ports. Measure it and mark it off and see what it looks like.