Building a long runner intake manifold

carcrafter22

carcrafter22

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I am going to be making a long runner intake manifold but have a few things to decide on first and would like some help.

This will be for my isuzu 3.9L and it comes factory with a short runner aluminum intake manifold with a very small inlet in the middle. I'd like to build something with a large plenum and large opening that is at the front I am also considering making the plenum a tapered design as well as tapered runners. My thinking is I am raising my rpm a good bit and shoving alot more air into this little engine so and intake could help a bit.


Biggest questions
1. What material to use? I'd like to use aluminum (6061 or 3003-h14 but that may be too soft???)
2. I could use stainless but I'd rather it be light, is alumium not good for our high boost diesel apps? 80psi roughly.
3. What thickness should I make the runner walls? I am thinking .125 but will this hold up against 80psi? The head flange is 1/2" and 1/4" for the plenum parts.
4. Any suggestions on forming or buying runners? I have read alot of info on this and I like the idea of using round tube then making a metal die and pressing it into the tube to form a rectangular runner but would love to hear some suggestions. I know I could alsway form, cut and weld the runners but that is alot of extra welding thats not needed and nice one piece runners would look much cleaner.

Anyway thanks for helping. Lets hear what you guys think.
 
In general long runners and high rpms don't mix if packaging is of no concern which isn't generally the case. Ofcourse it's quite possible the factory short runner intake's runner length is for rpm currently way out of the range you're trying to run in due to packaging constraints. If you want to build your own manifold I suggest looking into a program called PipeMax by Larry Meaux (forgive my mispelling if I have). Go over to speedtalk.com and search him and the program. Not sure if things need to be changed for diesels or not but it's an extremely useful and creative program which may give you some of your answers. Good luck.
 
1/8 " aluminum should be fine if it's round or square wall tubeing. But remember just because it works on a non boosted application, dont mean it will in a 80psi application. there are guys that really know this stuff out there. good luck.
 
DIESEL_POWER said:
But remember just because it works on a non boosted application, dont mean it will in a 80psi application.
Click to expand...

Exactly! From my very limited understanding gained through a little experience and more reading runner lengths/exhaust pipe lengths meant to operate within a certain rpm range rely on pressure differentials to impart their resonance tuning phenomenon. Obviously with boost you are changing things quite substantially.
 
I have been reading about the pipemax program and lots of folks recomend it, its hard to find any info for boosted apps espcially the large numbers a diesel sees. I guess since I'll be making it myself and have pretty much all the materials (except runners) if I blow it up due to boost I'm really only out my time.

I also see your point on a long runner and high rpm but its not going to be super long runners. Here is a pic of what I have planned its like one of the banks dual intakes for a duramax engine. Google Image Result for http://www.roadraceengineering.com/parts/magnus_intake_manifold/magnus_intake_manifold.jpg
 
FWIW, my first attempt in 6061 1/8" buckled and bowed out. I added 3/8" pins to keep it together and it's happy now.
 
Thanks Brandon just what I wanted to know. What do you mean by pins? I guess I need to start looking at some 1/4" material for runners. That means I will be welding my own runners up I guess.
 
I have a huge plenum style made out of aluminum. The pins run across the 3" span between the two plates where the gap between perpendicular surfaces is >2".

There's eight 1/4" pins in this picture and they pulled though the backside.
DSCF0734s.jpg


the bulge:
bulge.jpg

pulled_pins.jpg
 
Thanks for the pics I see what you mean now. I am making the plenum out of 1/4" 4" OD tube with a flat floor made of 1/4" also, the runners will probably be made out of 3/16" and formed on a sheet metal brake and press. I plan on using the 1/2" for the manifold to head plate. Thoughts? I am thinking this will be about the minimum I can safely get away with while making the lightest/strongest intake I can.

I did consider making one from stainless but I dont have any of it laying around and its considerably heavier. I wish I knew how much heavier it would be.
 
This is ridiculously light. I lost 20lbs on the nose this year by cutting the intake off and making everything aluminum even though I added a 56lb primary and hotpipe to the mix. I would make the head plate >1/2". Mine pulled like crazy when it was welded. I milled 1/8" off the middle to get it flat after welding.
 
if you anneal the aluminaum it will soften it substantially, then weld it and bake it in an over for half an hour to an hour at 350dg, it will bring back up to around a t5 hardness and eliminate alot of stress in the welds. 1/8th inch in the runners should be plenty thick due to fairly small surface area compared to the pizza box joefarmer is using.
 
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