Frankenplenum
 

Several years ago I bought a plenum from phrogs that was missing the MAP sensor ears. I Siamesed that the Inj housings and the heads....with small intake cams(222 .415 primary/236.425 secondary) I made 441RWHP/7100RPM; that's untuned.

Since then I ported the inside of the plenum removing all of the water passages and guts(There are significant blockages to the #1 and # 2 intake ports, etc. Added a 63MM TB.....

I decided that now I am going to add volume to the plenum; I will be cutting off the roof unshrouding the runners adding an inch, and cutting the bottom off and doing the same.

I am also going to do some air intake testing.....I know people say there is nothing there, but I want to try a few ideas.

Here is where I started with the Siamese
http://i134.photobucket.com/albums/q...f/DSCN3804.jpg

Re: Frankenplenum
 

Sounds like an interesting project, Lee.

Have fun and Good Luck.

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The LT-5 Plenum is know to be too small.....on a manual trans car you really want at least 1X the CI of the motor, some say 1.5X. I also know that in testing larger plenums did better during engine development....approximately 55-80 additional cubic inches are needed.

A lot of people told me the plenum roof would not clear the hood, however I have 1.14inches in the front and 2" in the back. I think the issue is raising the entire plenum and not just the plenum body....the runners might hit the outside of the raised section of the hood; but the plenum box has room...I also have no AC.

I would like to have unshrouded the #7/#8 runners but the fuel rail is a challenge

Re: Frankenplenum
 

I like it when someone tries to do what others say they shouldn't.

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Lee, keep in mind the engine twists when you accelerate, it will lift one corner. Sounds like you'll be real tight. I like where you're headed with this. MORE POWER wuh-wuh-wuh.

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A High Rise Hood would solve some of the height issues.

Be interesting to see what could be done.

Keep Us posted, and We like pictures.....

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Interesting project. I've been pondering something similar; thinking about using a split air box, vis a vis the Coyote's "Y" approach and straightening the runners; reducing that (90º) bend into the IH. (I believe it was Grahm (?) that said they were able to increase the 90 LT5 output to something well north of 430 chp by straightening out those runners some, IIRC. But, anyway, let's face it: GM isn't going to be coming up with anything for the LT5s. It's up to us ZR-1 loyalists to do it. And, so learning from what others are doing with the DOHC motors is a good place to take notes, I recon!:cheers:)

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Put some silly putty under the hood and see if it touches anywhere.

It might hang on long enough haha

I remember that plenum.
Pretty sure it came out of tommy morrisons stash

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Way ahead of you phrogs, nabbed my daughters playdo and checked it...put the enture can shape on the plenum and dropped the hood. lots room

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Lee:

What about those people who put on the phenolic plenum spacers some years ago complaining about rubbing holes in the hood?
If I recall correctly, those spacers were only 1/2 inch or so, surely what you've got planned will need more room than that.

'Crabs

Re: Frankenplenum
 

I wonder if eliminating the common plenum entirely would be of benefit? This would require 8 t-bodies. and 8 velocity stacks. I always wondered how those systems on teh older hot rods really worked. Individual runner length is easily individualized.

Complex as all heck, but would look cool poking through the hood!

Re: Frankenplenum
 

Yup! A sheet metal box(s) with shortish curved (funnel) runners... I haven't crunched the numbers yet for the runner/air box dimensions yet, but a Toledo hood (or the like) is prolly going to be part of the answer.

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I wonder if the runners are hitting, I am only raising the box...

As far as run a velocity stack setup, shorter runners make it more difficult to keep the car at idle.

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It makes me happy to think that an aftermarket plenum may one day be made available by a savvy member of the brotherhood that will give our cars even more umph. :happy1:

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I'm one of those people. They're still on there. The spacers are only 1/4", and it does rub enough to take the under hood paint off at the front.

This sounds like a job for one of those 3D printers...a big one that can use some heat resistant plastic.

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What part of the plenum is rubbing?

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Pete used a Hogan sheetmetal plenum on Kevin's 441 several years ago. I believe it really didn't offer much improvement.

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I wonder if the volume was sufficient...also velocity stacks might have helped flow....intake runners that share a wall with the plenum generally have flow opportunities....

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But that Hogans was a short runner intake.. Lee is looking to keep the runners as they are and expand the 'box' if I understand it correctly

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Correct, in terms of the plenum volume I had 2 Engineers from the program tell me thats were the most potential was; and in looking at intake development on Porsche, Audi, and the Coyote motor I saw comments on flow improvements on "unshrouding" runners from an intake ceiling/wall.

I will also add that there was a ZR-1 race car with a raised roof plenum in another country with a documented 15hp increase due unshrouding of the roof side of the runner.

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Is this for the black car? if so.. wanna sell your hood?

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My hood has chipping paint in the center, someone dropped the hood on something at some point, but I am keeping the stock hood

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The parts that scrape are, the ribs on the plastic intake duct, and I'm not sure what you call it but it's the sheet metal shroud around the throttle mechanism. The actual plenum does not hit.
The intake duct ribs could be swelled up a bit from stock because I have one of Mark Colplon's stainless liners inside it.

Both of these areas aren't real bad. Just enough to take the paint off, not enough to scratch the fiberglass.

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Good feedback, thanks Bob!

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I can offer an opinion on that sheetmetal intake. I did have it flow tested, and it was 2 to 6 cfm better than my (highly) modified plenum and housings. That was with the TB and Airhorn attached, and the other ports taped.

From what I remember, Pete and Kevin said it lost a ton of torque almost all the way through the rev range, only crossing over >7000 rpm. I could be wrong on that--its been awhile.

Why? My belief is two factors. 1) the runner cross section area was pretty big. I didn't measure it, but visually, most of the runner was oval with no divider. Only like maybe an inch at the head was two separate holes. 2) the runners were exceptionally short, as they have to be for hood clearance in that style of manifold. We need runner length to catch the stronger harmonic waves for best cylinder filling. That's why I didn't go to a sheetmetal manifold on the 427. The stock runner length is pretty good for the rev range we need. Downside is that the runners have to contort to get that length without too much height, if that makes sense.

Anybody got $10k to develop a cross-over style IR manifold?

:cheers:

Seriously, Lee is on the right path by enlarging the plenum. We need more volume for the big motors. Especially because the TB is undersize when you get to that level. I saw over 1" of manifold vacuum @ 7000 rpm. A large plenum box would crutch that a little. Of course, a big billet oval throttle body will help too :-D

Re: Frankenplenum
 

[QUOTE=tpepmeie; a big billet oval throttle body will help too :-D[/QUOTE]


Cobrajet is running a single blade 1640cfm TB

Also remember the LT-5 Dogbone TB; not only was it bigger, but it pushed air down the center of the plenum to better balance airflow to the rear runners.

http://i134.photobucket.com/albums/q...f/DCP_1509.jpg

Re: Frankenplenum
 

Raised/Dropped plenum should compliment my straight through air horn

http://i134.photobucket.com/albums/q...f/DSCN5715.jpg
http://i134.photobucket.com/albums/q...f/DSCN5717.jpg

Re: Frankenplenum
 

With the Hogan's we did loose some low end torque about 20 when you make 450 @ 3500 and you loose 15-20 you barely feel it,anyway the more low end you make the harder it is to stick it to the ground.:)
The low end has nothing to do with high speed runs (1/2 or 1 mile) or even 1/4 after your 60ft.

This was in an automatic and drove just fine could not notice a difference.

It did raise the power to 7k rpm from 6800 it gained 12-14RWHP.

Lingenfelter has sown that we need more plenum volume.
The work that goes into it,is not cost effective,among other issues.

It's like we went from Tune Port Intake to LT1 intake.

Pete

Re: Frankenplenum
 

I don't think to increase the plenum volume will bring a significant benefit. The intake has to many corners and angels. That restrict the airflow. The size limited trottle body and airhorn are additional air restrictors.

With our racing team we removed on a 350 cui LT5 the plenum and installed single runners and put our eye on the correct runner volume, lenght and shape. With stock compression ratio and stock cams but fully ported heads we got around 580 crank HP at 7'500 rpms. It was our first build LT5 for the 2014 racing season. We did first steps and are satisfied with the results.

For the coming season we design new runners and cam profiles and continue our researches.

I hope to see some of you guys this May in BG.

Re: Frankenplenum
 

I anticipate 15hp or so...its actually already been proven when they were developing the LT-5

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On a 350 cu in. engine? Call me skeptical. I think this really benefits the bigger c.i. engines when the TB becomes a restriction. Not sure you'll see that much on a smaller engine. Interested in what you get, nonetheless.

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How big was the plenum on that Aurora V8 indy motor.....opinions vary but some say you need a minimum of 1ci of plenum to 1ci of motor....some say 1.5. Really what you are trying to do is come as close to atmosphere as you can...we will see.

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From Enginelabs....just so one thinks I am full of ****; Todd Berry Custom intake manifold designer

Berry mentions that with custom intakes, the volume of an intake plenum generally matches the displacement of an engine. This means if an engine displaces 500 cubic inches, then the volume inside the plenum is typically going to also have a volume of around 500 cubic inches. Under this type of design, ideally no cylinder is starved for air because the volume inside the plenum is enough to fill all the cylinders simultaneously.
If the volume of the intake plenum is not properly matched and is too small for the application, an engine could develop a stall or sluggish response from an engine at the starting line or after each shift, as combustion events literally draw all the available air from the manifold faster than it can be filled by incoming air. Engines with too small of a plenum may perform well at lower RPM but suffer as RPM increases

Re: Frankenplenum
 

As I stated, I spoke to two lotus developers on the LT-5, they said best results came with a plenum 1 liter larger than stock. Minimum to start with is 350cu...

Re: Frankenplenum
 

That's quite the set of exhaust headers on the Aurora.

You might have trouble fitting them into your ZR-1.... lol....

Keep up the Good Work Lee,

Re: Frankenplenum
 

Convertible LT-5

http://i134.photobucket.com/albums/q...f/DSCN6197.jpg

You can see the roof sat right on top of the runner

http://i134.photobucket.com/albums/q...f/DSCN6199.jpg

Re: Frankenplenum
 

When doing dyno runs, one thing to look at is the MAP value. This can indicate if there is restriction somewhere ahead of the intake. In the runs I have recorded on my 5.7L, kPa at WOT ~ 97-98 and it doesn't drop hardly at all after peak.
That's pretty close. I also check my KEY ON MAP signal because unless u are at sea level, your MAP won't be at 100kPa anyway.
I'm a bit skeptical like Todd but it's good to have someone like you Lee who'll test it out.

Re: Frankenplenum
 

Quotes from LT-5 Engineers

"Lee,
As you rightly say splitting the plenum would lend itself more favorably to even cylinder firing events. The net result of doing this on the LT5 plenum would be more torque up to around 2-3k rpm and less everywhere else. As an aside the LT5 is inherently compromised on plenum volume for high rpm operation in its stock form."


"Hello Lee, we found the best results were from adding a liter of volume to the plenum"