All of the aftermarket and homemade plenum plates I've seen are aluminum. Being an excellent conductor, an aluminum plate will transfer heat from the hot engine oil to the incoming air. Cooler air, being denser, will make more power. So...

How about a homemade plenum plate of say, phenolic plastic? This stuff is used for carb spacers to reduce heat transfer. Why couldn't it work as a plenum plate? If it really was a good idea, I would think someone would have done it already. Any idea why it wouldn't work?

Also, how thick can the material be? I've read that 1/4" aluminum is the way to go. Just how thick can the plate be before it interferes with something? Can I use 1/2" material?

Thanks for any ideas, suggestions, etc.

 

It could, but the idea with replacing it with aluminum goes back to the original problem. The stock plate is steel, so it expands and contracts at a diffrent rate and at diffrent temps then the aluminum intake. With these diffrent expansions is where the gaskets get ripped and leaks start. So going with an Aluminum plate makes the expansion rates very similar, minimizing the risk of ripping the gasket and causing a new leak. Using plastic will probably cause the same original problem of diffrent expansion rates.

 

way to throw some knowledge, socha!!!
i've been wondering why the plenum has been such a problem

 

The basic idea of plastic in the intake manifold is sound.

A 'performance' intake manifold for the 5.2/5.9
that would be
all plastic (probably fiber re-inforced Nylon 66 or similar)
pickup less engine heat
have smoother walls in the passages
have NO plenum plate at all on the underside
and have longer individual intake runners than the current 15.5 inches
would be a very good upgrade!

Such a plastic intake manifold would essentially be like the current factory 5.7 Hemi manifold.

I bet that somewhere there is an ex-Chrysler or DCx retired engineer who could tell you exactly what the dimensions would be.

 

the plenum problem is the same kinda problem i had witht he head gasket on my old dodge spirit.

 

Why would you want the runners longer?

 

For those of us who use it as a work truck

 

What are the problems with the plenum? My manifold is off, should I replace my stock plenum?

 

Factory runner length is pretty good. Going shorter will give more higher up and take some low end but I really don't see how going longer would make much of a diffrence in the low end, it would just zap the high end. So when you use it has a work truck and want to pass on the highway good luck

 

Kikidbird, do a search here, you should probably replace it if it's already off. They tend to develop leaks.

Socha, thanks for the informed reply. I was aware of the expansion difference, but still thought there could be a way to do this. I have no idea of the expansion characteristics of phenolic resin, though. What do you think of a "laminate" with aluminum as the main plate, and a plastic overlay? That's one reason I wanted to know how thick I can make the plate.

Hank, your intake idea is interesting, and on topic, but I have no plans to design a new intake. I might be first on your list if you make them, though! I'd want a shorter runner, though. I plan to shorten my stock runners, clean up the inside, remove divider, if any, and maybe port match, as some others here have done.

I used an I/R thermometer to check my (exterior) intake manifold temp. It showed 180 f, the same as my radiator showed! That made me wonder if these intakes have coolant passages. Seemed like quite a coincidence. They don't as far as I've been able to gather.

Can anyone tell me how thick the plenum plate could be made? Even a rough estimate would be good. I'd just like to have all my materials ready when I do this. I'd like to do it in a weekend.

Thanks.