custom intake plenum

[ks71z28]

I have a Holley Stealthram and want to build a custom carbon fiber plenum. The Stealthram's volume is 246ci, and my motor is 383ci. It equates to approx 65% of the engine displacement. I have seen recomendations of from 50-150% plenum volume to engined displacement. I know a TPI system is too small and it is around 45%. The motor makes 450hp and revs to 6200 rpm. Any resources?

thanks

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[Blown353]

I don't have the experience with intake design to comment on a specfic or ideal plenum size for your application but I can offer some observations, General guidelines are the larger the intake plenum the better, at least when it comes to top end power; however too big of a plenum results in lazy low RPM and no-load throttle response. My intake has a plenum volume of about 775 in^3. When "Blipping" the throttle at idle in neutral the engine responds somewhat lazily under 2000rpm because of the large plenum volume, but as soon as the engine is under load the throttle response is fantastic-- and that's what matters. I have seen several sheet metal intakes on 500ci drag engines with plenum volumes in the 1600-2100 in^3 range, but their "service" RPM range of 6500-9800rpm range is what is driving that manifold design.

Now for what I can really offer advice on-- making a carbon fiber plenum. CF for the plenum is fine, but make sure you use a resin that is resistant to oil and gasoline vapors-- otherwise that nice plenum of yours may collapse on itself one day from engine vacuum when the resin degrades from oil/gasoline vapor exposure. You also want to make sure the resin you use has a service temp rating high enough; otherwise if your intake and/or underhood temp exceeds the Tg of the resin the intake once again will collapse in on itself from manifold vacuum. Also, the shape of your plenum will have a HUGE difference on the wall thickness requirement. Say you make a large box-style plenum about 16" x 10" x 6" and your typical peak engine vacuum under coast down is 22 in/Hg. That's an effective pressure differential across the plenum of 11 psi; which may not sound like much, but that 16" x 10" lid needs to be able to withstand 1760lbs of force because of the manfold vacuum. After you build your plenum I would highly recommend capping it off and either pulling a vacuum (20 in/Hg minimum) or pressurizing it with about 15psi and measure it for displacement (you'll want to create about a ~15 psi pressure differential to simulate operating conditions, even a bit more would be good); you'd be much better off finding out that it's not strong enough on the bench than having it break on the car and the engine either injesting pieces of plenum or effectively running wide-open.

Troy

[Kenova]

........ Also, the shape of your plenum will have a HUGE difference on the wall thickness requirement. Say you make a large box-style plenum about 16" x 10" x 6" and your typical peak engine vacuum under coast down is 22 in/Hg. That's an effective pressure differential across the plenum of 11 psi; which may not sound like much, but that 16" x 10" lid needs to be able to withstand 1760lbs of force because of the manfold vacuum.
Troy

Try this experiment to witness the power of a vacuum: Take a paint can (empty of course) and drill a small hole in the lid. Run a vacuum line from your daily driver to the hole in the paint can making sure you have a tight seal. Fire up the engine. Odds are the paint can will collapse, if not right away, then when you give it a light poke with your finger .
Ken

[Blown353]

True, although in the case of the paint can, being a cylinder it has quite a bit of hoop strength; however that hoop strength goes away as soon as it buckles somewhere (i.e. poking it with your finger.) There's a reason pressure vessels are usually spherical or cylindrical, and hoop strength is it.

I play with vacuum (and pressure) every day at work curing lots of expensive composite parts, and know the results firsthand. Also, if you think vacuum and a paint can is cool, Try taking a rat that is stuck to a glue trap and put him inside a belljar then hit him with instantaneous 29" of vacuum out of a large accumulator tank. ("accumulator" tank being used loosely here as you really can't accumulate vacuum...) Almost as fun as dipping it in liquid nitrogen and then throwing it as hard as you can against the concrete outside... (do I really get paid to do this stuff? LOL)

Troy

[ks71z28]

I appreciate the advice, which is exactly what i was looking for. I do realize the materials engineering behind a piece like this, I am a manufacturing engineer. It is the functional design that I was unsure of. My goal is a plenum that is NOT mistaken for a TPI set up. Sorry but if one more idiot asks if my motor is out of a TPI Vette! Plus I like to mess with things. I do appreciate the input from and educated source.

Keith

[Matt@RFR]

Keith, have you called Hogans or Wilsons? They may be willing to help out, since niether make composite manifolds that I'm aware of.

[Blown353]

I appreciate the advice, which is exactly what i was looking for. I do realize the materials engineering behind a piece like this, I am a manufacturing engineer. It is the functional design that I was unsure of. My goal is a plenum that is NOT mistaken for a TPI set up. Sorry but if one more idiot asks if my motor is out of a TPI Vette! Plus I like to mess with things. I do appreciate the input from and educated source.

Keith

FYI, the lower portion of my intake is a Holley Stealthram that has been severely extrude-honed; the intake flow is now in the range of 305cfm per port. Works fantastic. There are a few pics on my webpage under the EFI conversion section. I've never been told it looks like a TPI intake. Just wanted to give you some ideas...

Troy

[jeff351]

Hi

My 1st real post here, I am in the early stage of building a TT460. This thread is along the lines of what I am looking for, but where can I find info on calculating shape and size of a plenum?

[Kenova]

I play with vacuum (and pressure) every day at work curing lots of expensive composite parts, and know the results firsthand. Also, if you think vacuum and a paint can is cool, Try taking a rat that is stuck to a glue trap and put him inside a belljar then hit him with instantaneous 29" of vacuum out of a large accumulator tank. ("accumulator" tank being used loosely here as you really can't accumulate vacuum...) Almost as fun as dipping it in liquid nitrogen and then throwing it as hard as you can against the concrete outside... (do I really get paid to do this stuff? LOL)

Troy

Got video?

Ken