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RV8R999

Well Known Member
I'm going to attempt to describe this idea and see if anyone has tried it:

create two separate plenums, one for each pair of engine cyl by creating a baffle running along the inboard cyl fins. cover the rear and side with alum or composite leaving just the inlet open. Seal the inlet with normal baffle material. The inner baffle can be extended all the way to the inner cowl inlet section and cut to match the contour of the upper cowl inlet ramp thereby eliminating the need for the section of baffling which spans the forward portion of the engine just aft of the spinner.

The hard part is fabricating the inner baffle section to account for both cyl, and the 4 valve rod housings.

Surely someone has done this? If so, do you have templates for a lyc O-360? :)

Thanks,

Ken
 
Wow

I really like those plenums in the pics. They really look like they would be very efficient. I wonder how much more trouble this would be than using the regular vans baffles?

bird
 
A friend of mine had done it and was experiencing serious cooling issues. I believe the air that enters the loft inlet is much more then the right side. He end up removing the middle section and make it one big plenum and has solved some of his cooling issues.
 
Performance results using this style plenum setup have been extremely poor as to cooling... many have tried this set-up. I've still got the templates for this plenum design in the hangar but will no longer experiment with the design.
 
settles that

Well that's settled quickly, looks like I'll stick with vans design, I'm sure there is a reason they have the baffles setup the way they do. Its hot here in Louisiana with high humidity sometimes so I need the best cooling setup possible.

bird
 
LifeofReiley said:
Plenums are not bad, I've got an alumium solid top I'm running now and it performs AWESOME! :)
Click to expand...

I have to agree. With the old engine and standard Van's setup, it took me a long time to balance my CHT's. They all were right around 364 to 367 in cruise. Climb was another story, I could cruise climb it at 500 FPM w/o any issues but much more than that and I could bake #3.

With the new engine and James cowl and cooling plenum the cruise CHT's are between 365 and 375 without messing with anything. The extended hard climb CHT's don't go above 405*F, which is very acceptable.

The price difference between the James cowl / plenum and Van's cowl is right around $100. However, the James cowl / plenum does take more work to setup.

Would I do it again, you bet!
 
Overall, there's too much focus on the "plenum or no plenum" question. A plenum alone will not improve speed or cooling as compared to a really well done standard flap baffle. An upper plenum is way to minimize the leakage of high pressure air, and nothing more.

There are some additional features which may or may not come with a plenum installation, and those features may have their own effect. A good example might be a well done internal diffuser behind the intake, should you be of the high Vi/Vo persuasion. However, you don't need a plenum to install optimized diffusers. It is an independent feature.

A plenum matched with poor inlet shape, poor inlet sealing, or poorly fitted cylinder and cylinder head baffles won't work worth spit.

The OP's question here is simply two independent plenums or one. Either can be made to work, and in fact both kinds have been out there flying for years. God is in the details.
 
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