I want to cut the runners off my intake manifold and use aluminum sheet metal to make a better intake manifold. I did some testing with a steamer and little to no steam was coming out the first runner. More came out the 2nd and 3rd runner. And then the 4th, 5th. and 6th were about equal. I could port out the runners and make them shorter for better top end. And use a very big throttle body like a Q45 or Pathfinder without any kind of adapter plate. And it would save like 10 lbs! That way you don't have to worry about flanges or anything.

 

just make sure that it will hold the boost and not explode on you.

 

Yah I got some guy in Houston to help me. He has made these kind of intake manifolds for f-bodies and other cars.


What gauage sheet metal should we use? Edit: he said 5/16

 

I've often wondered about the 4th gen intake manifold and that very sharp turn the air has to make at the first runner. The air has to make more than a 90 degree turn, about 100-110 degrees, I think. That can't be good for flow distribution.

I'm interested in what you come up with.

 

I mean NO STEAM came out of the first runner. I know there is more air coming through than the steamer but the steamer is pretty powerful. Its almost like with that intake manifold, you are running on 5 cylinders because barely any air is coming in that back right cylinder.

 

are itb's out of the question?

 

In reality it's not as bad as that since the no. 6 (or is it the no. 5?) piston is sucking the air into the cylinder. But the volumetric efficiency for that cylinder might still be a point or two lower than other cylinders at high rpm when the air is coming into the plenum at a pretty fast rate. At low-mid rpm there's probably no difference.

 

to add to that, not all six cylinders are on the intake stroke at the same time so the air really is not being distributed everywhere at once.

 

so what creates the vacuum in the intake manifold that makes air only go ing to 3 cylinders at atime or whatever.

And the only time steam came out of the first runner was when the large volume before the runners was completely full of steam and the amount of steam coming out of the first runner vs the other runners was 1 x 100.

 

This is basically going to cost me like $100. The guy has all the tools. Just going to try it out if it does not work its going in the trash. A guy in town told us that the nissan cast aluminum is very hard to weld, its hard to get penetration. So it might not work.

 

pretty much anything cast is hard to weld without the right machinery. so are you using the flange part of the stock manifold and then welding custom runners onto that, or are you making the whole manifold from scratch?

if you hack the stock maniold it will more than likely get quite messy, not to mention if it sucks you will have to get another manifold to go back to stock (unless you have one already). if you have access to a machine shop i think you will have much better results making it from scratch. by using the bottom of the stock manifold you are already restricting yourself to half of the original design in which case it may be difficult to get the final result you desire. the best way to make the manifold would be to have the flange made (or maybe you might be able to find one that fits somewhere...) and then group all the cylinders that are on the same stroke by having some sheet metal walls inside the 'master' casing. this will result in all the air that comes in through the tb to go into the passage with the least resistance - in other words, by creating seperate channels for cylinders that are on the same stroke, all air that comes through the tb will only go into the runner leading to the cylinders that have the intake valves open. thus, there is relatively little wasted air, much less disturbance in air circulation (air is not going through runners that it has no need to go into), and ultimetly far more effecient utilization of product.

i hope that made sense. the design would be a little tricky -especially figuring out how to shape the runners - but not really expensive at all since sheetmetal is pretty cheap as it is. the only thing that would run you some money would be the flange, unless you can get use of a machine shop for free, in which case all you have to do is buy a half inch block of metal and drill the holes where needed. you could probably even use the stock aluminum flange if you cut it in the right place but then you are restricted to the direction that the original runners are already facing therfore not acheiving full effeciency. sorry if all this is something you have no intention to do. i guess i just had a suggestion and started to type and this is what became of it. all in all, i wish success to you in whatever you end up doing. im sure it will turn out well.