Hey all,
Been tossing the idea around of 3D printing an experimental plenum and some runners to "fix" some of the weakpoints of the TPI intake. I know this topics been beat a million times, so I'll say right now I'm not trying to make the intake flow more, I'm trying to make it more efficient or a better fit to the 350.
Ideas so far:

• A true split/divided plenum, I'm targeting a 105- 125 cubic inch plenum volume per bank, I'm trying to get the plenum volumes to be 4 times the runner volume, which seems to be the magic number when it comes to Helmholtz resonators and open volume wave reflection. With the TPIs already being low RPM beasts this should only add to the effect and may improve midrange throttle response.
• Secondly, I'm looking at adding bell mouths to each runner, due to the space constraints of needing up to a 250 cubic inch plenum, it does look like they will need to be integrated into the runner, not the best option, but it will be much better than the current 90* transition in the plenum. This will most likely be the only mod targeting increasing flow, again, not changing runner diameter, or volume, just helping the runner do it's job to the best of its abilities, I know the stock base is the restriction in the system.
• The above mods were basically the free ones, easiest to implement, but the next one I'm looking at is placing the injectors in the center of the curve of the runners. This isn't even close to realistic with the batch fire system and stock ECU so this is really just an idea based on theory. With this change I'm trying to get better charge cooling from fuel atomization, but it requires different injectors, full sequential injection to prevent pooling, injector angle optimization, fuel timing, basically a laundry list of supporting mods. From what I've read, the narrowest place in the runners is where the injectors are, so removing and welding up the injector bungs might even allow for consistent runner cross section from plenum to valve, but I have no experience with these intakes so who knows.

I'm planning on starting with the plenum, tinkering with it for a couple of weeks, finding what works best, if I do find anything worth the time and effort I may even try a lost polymer aluminum casting, but I'd love to hear some feedback on the above ideas, anything I do come up with I'll upload to thingiverse and link back here.
Thanks

 

Injector location is to spray at base of intake valve when it is open. With the stock 23* cylinder head there is a compromise. L98 is somewhat of a dead horse 28 years out of production. Now a EFI "ram" style intake for 15* - 18* SBC cylinder head there maybe a market for.

 

Why not go all out, and try to duplicate the LS style intake ?

 

I think the biggest issue for the RAM intakes is getting a ram tall enough to be able to harness some if the intake harmonics. In a stock vette you'd maybe be looking at maybe 3rd and 4th order harmonics with an 8 inch runner with some top of the head math. But if anyone has an intake base for the 15*-18* heads and doesn't mind sharing dimensions, i don't mind CADing something up and sharing. I'm really just trying to make the most out of my L98 on a budget.

This is actually one of the things I was considering doing, but I havent found a good source on runner length, ive seen everything from 14" to 17". The other issue is temps, the material im looking at printing the prototypes out of softens at 80*C and with the coolant running through the manifold that means a very short test time. If I can find a solution to the coolant and temp problem, a FAST style intake becomes pretty trivial, it would be awesome to just be able to pop some bolts and swap in some shorter or longer runners. I'm looking at doing a top down approach to see what the engine does and doesn't respond to all that well, and yhen using what ive learned to create the "ultimate" L98 intake, or atleast an intake that doesn't choke off the engines full potential.

 

yrs ago was going to do an improved plastic LTx inake but was cost prohitive...esp to make it 50 state legal and sell
The material is called Nylon66 or something like that which GM and all the other mfrs use.
Couple guys on speedtalk.com would know more. Maybe a different take on a superram?

 

Yeah, im not trying to make anything 50 state legal, really just putting the science down to improve my own car and make it publicly available for anyone wanting to do the same. Nylon 66 has a glass transition of 70*C, the good stuff is PA6 with glass fiber reinforcement, but it's only available in pellets, not consumer 3D printer friendly. Right now the best solution is looking like a resin reinforced 3D print, and with that comes the possibility of doing CF or fiberglass in the post print.
I havent read into the super ram at all before but I'm looking at something pretty close to the super ram.

 

Check www.thirdgen.org for ideas. I think they've tried almost everything over there.

https://www.thirdgen.org/forums/tpi/...be-runner.html

https://www.thirdgen.org/forums/tpi/...struction.html

 

15 and 18 deg heads typically flow way more than a TPI ever could plus you need different pistons I wouldnt go there.
Do your experiment for a Gen 1 let us know what you come up wtih.

 

I've spent alot of time on the third gen forums, it's actually where I got the idea of doing this. The people over there have come up with some crazy ideas for intakes. Ive lurked here and there trying to educate myself on the TPIs and get ideas on how to makeine go faster for cheap . The thread about the DIY cross ram gave me the basic idea of how I envision the intakr to look in stage 3 (plenum to base redesign) .

This is basically exactly what im going after, but rather than the plenums be outboard, they'll be inboard with the injector rails outboard. But... if i can find a way to package this design so that'll fit under the C4s hood, im all for it. Just really got to get it into CAD and measure all my clearances.
Will do, hopefully I get my car back from paint quick enough to do a quick tear down and get some dimensions.

 

The path I took on my prior '88 was:
-52mm TB with plenum port matched
-rounded plenum transitions into runner tubes
-ported runner lower ends into TB base and siamesed the runners so that each cylinder would pull through two runners.

The result was no loss on power at launch RPM and a substantial gain on the high end. Enough to usefully raise the shift points to nearly 6k RPM.

Your idea of a dual plenum is an interesting idea. Worth hearing the results of your experiments.

 

Interesting, did you just break the edges or were you able to do smooth transitions? Did you port the base at all or were was the siamesing and runner porting good enough?

I am targeting 6k of usable tachometer so glad to hear its possible, but siamesed runners effectively shorten runner length. Was their a noticeable shift in the torque curve to higher in the rev range.

The dual plenum sounds cool but there's still a whole lot of work to be done, in theory it'll help throttle response, low end torque, and high end power, but we'll see how it all turns out in the end.

 

Research SLP T RAM. You might also look a mechanical cpi manifold layouts. First TPI made large improvement in the TPI manifold, but there is little technical information about it.

 

Good thinking, the T ram is kind of what hes looking to do.
All kinds of homegrown science projects done on 3rd gen over the yrs some helped some didnt.

Bet if you designed some runners like the LSx, with their compound taper and inverted them...used a large plenum it would kick azz...so cut a hole in the hood and make a nice looking scoop.

 

The T-Ram is an interestimg one, the flow path seems so restrictive and yet they seem to have been one of the best intakes out there for the TPI. But it is a mirror image of what I want to do, just cut in half and flipped inside out so that the stock base can be used.

I'm gonna be posting on the third gen forum soon, just want to wait till I have atleast the split plenum designed, and a basic plenum longevity test atleast started.
The LS and LT intakes are some of GMs best work IMO. Can't find it right now, but a few months back I found this white paper with the CFD models of either the LS or LT intake, that entire paper was just profound in how detailed everything was. I dont think I'm quite at the level of those intakes just yet in computational modeling but it is one of the approaches I'm considering, it is definitely the most convenient install and packaging wise. It's all up in the air till i can get dimensions of my car and see what i can fit.

 

See if you can find a used FAST runner , when you really pore over one it makes sense how there can be so much head/runner volume but they still make ok low speed tq and plenty upstairs. Wish I had the ability to fab up a single plane for my 67 with something similar they work great.
Our old runner designs are stoneaged. lol

 

Yessir, the runner design is pretty interesting, looking at the three available runners you can see how they each target a certain RPM range for peak torque by changing the runner length and bell mouth geometry. Our runners are definitely stoneaged, but that just means lots of room for improvement with simple tweaks.
Hey all,
Been working on the CAD and hit a snag, I've realized I have no idea how the plenum side of the IAC works. Is it just a passage that dumps air behind the throttle body, or are there passages under the plenum that coincide with the CSI?

 

Here's what I'd TRY to do, if I could 3D print metal;

Make a typical TPI dimension/looking intake, but install rectangular ports/opening w/a flange, on the top of each (base) runner, just inboard of the injector; about where the runner bends from the "head flange" angle to run horizontally across the valley.

I'd machine a corresponding port/opening w/a flange in the underside of the plenum; one for each runner -8 of 'em.

Then, I'd print 8 runners that would have corresponding flanges that bolt to the top of the base ports/opening w/a flanges and to the underside of the plenum w/it's new ports/opening w/a flange These runners, when combined w/the bit of additional runner in the base portion, and attaching to the bottom side of the plenum, would be very similar to an HAS, Edelbrock Proflow or one of the Mercruiser/Indmar Marine "mid-length" runner intakes.

Then, I'd have two small holes running through the base, rear to front for two shafts. These holes would intersect each of 4 runners, just inboard or the ports/opening w/a flange

On the shafts would hold a flapper/"throttle valve", for each runner, in the base.

Finally, I'd finagle a way to control the shafts/flapper valves such that they'd be in the raised/horizontal/closed position at low to upper/mid RPM....in this configuration, air would follow the typical TPI, plenum>runner>base/runner>head port and be ~24" long or whatever the TPI length is from valve to plenum.
THEN, at ~3500 RPM? 3800? The shafts would both rotate, flipping the flapper valves down, closing off the typical TPI air path in the base, and now becoming part of the "runner floor" for the newly installed "short ram" runner.

TPI problem solved: you got your LOW RPM TPI TOWAK MONSTAH, you got your cool, TPI looks, and you still got a reasonable RPM ceiling, once the valves change and swap you to a shortish/mid length runner intake.

Take this....





...and put short runners like these, inside of it:

 

Why not start where others left off..

https://www.thirdgen.org/forums/tpi/...be-runner.html the thread is multiple pages, has over 30 pictures. They guy actually ran it, passed California emissions testing with it, and it made power from idle to 6300 rpm on a very healthy small block with good heads. It will give you a decent indication of the practical limits of the over 20 inch tpi setups. A lot of work when you could have bolted on a single plane with elbow and had danner the same results. And be mindful that this guy has access to a dyno, machining equipment, flowbenches, and quite literally hundreds of years of engine design experience from all those he has collaborated with.. if you do not have at least the same resources, and skillset? You are going down a rabbit hole and throwing thousands of dollars in to said hole.

 

Gm already did this, it is called the zr1, ford did it with cobra mustang's, Ferrari, Lamborghini and others have been doing it for longer than you or I have been alive. It is wave tuning, if you can tune an intake to say the 2and and 3rd order waves it will have broader power. Runner length has alot to do with it, but is only one piece of the puzzle. No offense but many far smarter and resourceful than you or I will ever be have been down this road with that tpi setups. And have spent far more than an off the shelf intake that just works would cost. If doing it as a labor of love, or a learning experience then yes, do it. But if you simply want a broad range of usable power. Set the engine up to make power from 2500-6500. Then put a turbo on it that will spool up and make full boost by 2500 rpms. It will be more power than you can use with stock suspension and does not have to cost a fortune.

 

More than a few 383-406 cubic inch small blocks that make over 400 tq from 2000 to 5500 rpm on pump gas. That uses short runner intake. The tpi will never do that. Not without spending more than the net gains are worth. Why spend 500 per hp when you can do it for 200 per hp, figuratively speaking.