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Always wanted to fab something up where youre using a base/tray such as a mopar that had a flange with bosses for any runners you could think of, plenum etc. Hogans I believe sells all kinds of stuff to get started .
Is 89transam still around, remember that project and one where he made his own crossram type runners...not sure he was happy with it. Maybe it was a taper issue on the runners? Looked impressive
That TPI is on Dyno Dons Iroc 400 to the ground and passes smog? If the paint was better Id have bought that car in a hot second it was a steal for all it has going on .
Spent the last two days enjoying my Vette only for it to no longer start today, just means more CAD time for me.
I want to take some time and clarify somethings, starting with the process, the prototypes will be printed on a consumer FDM 3D printer, I've had great luck in the past in using the printed parts as a consumable form for fiberglass and carbon fiber., but my end goal is to lost polymer cast the final product and call it a day.. That means that the prototypes will be somewhere in the $10-$20 range, with the castings barely adding to that. Secondly, the goal was never to make 300-400BHP with this intake design, the goal was to make an easily reproducable intake without sacrificing too much of the L98's identity apart from slow. This will be done based on theory, what has worked in the past from aftermarket vendors, forum member experiments, various white papers, and some of it just common sense. Right now I am heavily leaning towards what is basically a larger volume, split plenum super ram, reduced length runners, a stockish base or a redesigned one with the edelbrock proflo mounting profile. I'm still in the research stage, but so far, I have the stock plenum CADed up, minus the IAC inner passages if there are any, and mock runners, within the next couple of weeks I'm aiming to have the stock base with all external features done, it is rather difficult as the only intake I have is the one on my vette, so I'm reverse engineering everything from pictures and known dimensions. From there designing, printing, and validating the above ideas. I'm still all ears for suggestions, feedback and other links, I really do appreciate the feedback, it really does help steer this intake into what is hopefully the right direction. Moving forward I'll be posting more detailed info for each respective component, but this really is still in its infancy, I haven't gone beyond napkin math and have yet to crack open the text books for reference, but tommorow night I'll try to get a nice and detailed post with the basic layout of how I see things going, but everything is subject to change.
Thanks all.
Initially, the idea was to have one butterfly per bank, but looking at what the stock to 58mm throttle bodies flow, it would only be feasible to use a 58mm or else the throttle body would be the limiting factor airflow wise. The split plenum works two-fold in this case. I'm planning on using a plenum volume upwards of 210CI, and while this will help the engine breathe in the higher rev range it can destroy low-end throttle response and power. The split plenum is a compromise, it sacrifices some of the benefits of the plenum's massive volume in the higher revs for better low-end power and throttle response. The next part is where things get murky, I was taught that your plenum volume should be anywhere from 40%-60% of total engine displacement for engine breathing purposes and/but it should be closer to 4 times your runner volume, the impulse from the valve events would then be reflected at the opening of the runner into the plenum, but too large of a plenum would absorb the wave rather than reflect it, I know for a fact that this heavily relies on an even fire engine which the L98 is not, but I'm wondering if it could provide some benefit, this is the part where I really have to dig into it and see how the math works out. It's a really delicate balancing act, but what intake isn't.
I'm planning on using a plenum volume upwards of 210CI, and while this will help the engine breathe in the higher rev range it can destroy low-end throttle response and power. The split plenum is a compromise, it sacrifices some of the benefits of the plenum's massive volume in the higher revs for better low-end power and throttle response.
Yeah? How big is the Super Ram's plenum? How is throttle response on Super Ram equipped cars?
Originally Posted by ThatOneKid
the impulse from the valve events would then be reflected at the opening of the runner into the plenum, but too large of a plenum would absorb the wave rather than reflect it, I know for a fact that this heavily relies on an even fire engine which the L98 is not, but I'm wondering if it could provide some benefit, this is the part where I really have to dig into it and see how the math works out. It's a really delicate balancing act, but what intake isn't.
Yikes.
*THIS ARTICLE doesn't mention one word about plenum volume. Their demo engine for the article used individual throttle runners, opened to atmosphere. That's about as big a plenum as you can get.
*The L98 most definitely IS an even firing engine. There is a power pulse, every 90* of crank revolution.
*If you use a split plenum: 1. I don't think you'll get the effect that you're looking for if it's divided before the TB; in that case, both sides can "see" each other...2. With a truly divided plenum, you will have syncopated intake pulses on each side or the plenum...unless you re-route all the runners as is done with a dual plane intake such that you get 180* intake pulses on each "side" of the plenum.
Always thought the plenum on the L98 was too small...if I had the $ i wouldnt be opposed to buying a larger one and modifying the hood.Dreams are free though!
Post up on your project
If you ever did up some polymer big tube runners Id be "in" for a set.
The amount guys are asking for old aftermarket runners are nuts.
Yeah? How big is the Super Ram's plenum? How is throttle response on Super Ram equipped cars?
Couldn't find anything on the super ram volume except for how much people love it, and nobody seems to have complaints on the .throttle response. If you have a volume I'd love to hear it.
Originally Posted by Tom400CFI
*THIS ARTICLE doesn't mention one word about plenum volume. Their demo engine for the article used individual throttle runners, opened to atmosphere. That's about as big a plenum as you can get.
I'm glad they don't mention it, their credibility would really worry me if they did since infinite volume and infinity tend to wreak havoc on math. By common definition the plenum is a common volume post throttle body where the air charge's velocity is reduced, lower velocity means higher pressure (Bernoulli's principle); this comes with the added effect that the larger the plenum the smaller your throttle body can be, as long as you don't mind the loss in throttle resolution in low-speed applications. ITB's arent relevant to this at all, for those all you worry about, is CFM, and charge inertia (that why they have the huge stacks on there). But keep in mind there is a reason ram tube intakes that extreme that aren't on daily driven cars, they suck to drive, but are great for binary throttle operation. The whole point of a large plenum is to make up for the lack of air in periods of throttle transience while filling in the gap of reduced flow from the time the throttle butterflies open to the time there is sufficient velocity through said butterflies to sustain the engine's performance.
Originally Posted by Tom400CFI
*The L98 most definitely IS an even firing engine. There is a power pulse, every 90* of crank revolution.
You are absolutely correct, I misspoke, I was referring to the unevenness of the induction pulses per bank.
Originally Posted by Tom400CFI
*If you use a split plenum: 1. I don't think you'll get the effect that you're looking for if it's divided before the TB; in that case, both sides can "see" each other...2. With a truly divided plenum, you will have syncopated intake pulses on each side or the plenum...unless you re-route all the runners as is done with a dual plane intake such that you get 180* intake pulses on each "side" of the plenum.
Again you are absolutely correct, but as I said before I am planning on using the stock throttle body for the initial go around, as the individual bores on a stock throttle body cannot flow enough to sustain a bank above 4400 RPM, in theory. In a streetable car, the split plenums seeing each other does make the split plenum less effective, there is still airflow through the plenum at all times, and this should be enough to combat reversion from plenum to plenum. While correctly timed pulses would constructively interfere and increase the pressure behind the valve at the time of a valve event, there is a diminished effect constrained to the runner's volume and that is what I am trying to harness, all in this is an experiment. Net gains may not be as high as a no-compromises intake, but it will be better than stock.
I have and notice how they're talking about huge plenum volumes hurting drivability, this is where that 40%-60% of engine displacement comes into play, I am at the upper limit of 60% and as previously stated the plenum volume is one of the things that will take multiple tweaks to get right. Nothing is set in stone.
I appreciate the feedback, pushing me to rethink some ideas has definitely shown me where I need to focus my research more.
Originally Posted by cv67
Always thought the plenum on the L98 was too small...if I had the $ i wouldnt be opposed to buying a larger one and modifying the hood.Dreams are free though!
Post up on your project
If you ever did up some polymer big tube runners Id be "in" for a set.
The amount guys are asking for old aftermarket runners are nuts.
A decent 3D printer is only $300, I really push for everyone to get one because it is one the most versatile tools I own, that's why I have three . Let me know what size runners you're thinking of and I'll see what I can do, I'm getting ready to decommission my Vette for a week to pull the intake and finalize dimensions, then print and test fit a stock printed plenum and runners to see how close my model is.
Last edited by ThatOneKid; Aug 30, 2020 at 09:40 PM.
It's been a while, work really consumed my time so I just got back to this project this week. So far I have CADed the passenger side runner, all flange dimensions are pretty accurate, but the runners on the other hand are as close a match to the 3D scan as I can get, there is some weirdness with the runner to plenum flange interface, specifically with the EGR tube, but I've elected to continue CADing the rest of the intake and then go back and fix any inaccuracies. If there are any volunteers with a spare intake who wouldn't mind taking a few photos for me so I don't have to remove my intake piece by piece, please PM me, that would exponentially speed things up. Next on the list is the stock plenum, should be done pretty quick, perhaps by Monday if all goes well.
I'm 100% with you and totally into alternative long-runner intakes, too.
I don't understand why you would go with curved runners, though as that's one of the problems with the TPI intakes. -ESPECIALLY if you're talking about a 2nd injector up runner you want those runners to be STRAIGHT. -A Holley Dominator can stage the injectors; and only run the 2nd up-stream injector when needed and at WOT. If the runners are straight you might even be able to have "pencil" style injectors in the plenum squirting into your bellmouths and get max evaporative cooling, BUT you do need to size the runners slightly larger to make up for volume lost to fuel evaporation.
The dual plenum / split plenum intake with dual throttle bodies is, IMHO a GREAT idea and it's been proven on the LS engines with the Edelbrock X-ram and Fabricated Holley Sniper "dual plenum" intake: https://www.holley.com/products/ls_p...s/parts/820242
The Holley Sniper dual plenum intake produces more average HP than any other LS intake tested by Westech so far.
-Having the valley plate seal off the valley and then being able to mount the runners directly to the heads would make everything MUCH easier. If you're looking for a properly long 18"-22" runner, your runners and plenums will end up on top of the valve covers.
-I think 1989GTA's long runner project found that 18" with around a 2" diameter runner is PERFECT for picking up the strong 2nd reflected wave (10% boost vs. 7% from the 3rd wave).
An aluminum intake valley cover can be purchased with a thermostat housing in them, and everything which gets you started quickly. It also helps to keep heat down in the runners and with all that you're talking about, octane / detonation quickly becomes a limitation so every degree of IATs helps.
I don't think a large plenum volume is as detrimental as you think; there's a great thread on YellowBullet on exactly this subject and I think a lot of the "classic" advice here isn't standing up to the test of time. Getting the right plenum shape to avoid having the rear cylinders run lean, like on a TPI intake is more important, IMHO. (Especially with SBC cooling having issues with the rear cylinders and between the adjacent exhaust valves -those rear cylinders hotter AND leaner don't do you any favors.)
I've got a FIRST TPI + Holley HP engine build waiting to go in my C3 right now, but there are limitations that just can't be overcome with those curved runners and the plenum.
This project has been put on the back burner for a while, I decided I was gonna LS swap my vette as that's the most affordable way to make good power in these cars, so have been slowly collecting parts and researching the swap. The plus side to that swap is I'll be able to fully 3D scan the TPI intake and recreate it in CAD to make a TPI base compatible intake which is the direction I have decided to go. What I have come up with so far is a 2.75-inch runner with a 2* taper, and just over 17-inches in length, the result of that taper brings you to a 1.6-inch runner diameter at the runner-base interface. It's a simple way of making do with what's available, no need for modifying the base apart from a port and polish, and you can still get great results as if it was siamese'd or large runner intake. The taper would, in theory, allow the L98 to have nearly identical low-end power while allowing it to breathe in the high end. That's where the wishful thinking stops though, the runner length and diameter makes it incredibly difficult to package well, 3D printing does solve the manufacturing issue, but most consumer printers would only be able to print this intake in multiple pieces, which then means sanding epoxying and reinforcing the intake. I'll also be losing my testbed L98 in my own corvette so apart from making the design available and maybe manufacturing one for somebody interested, that's as far as I can develop.
By common definition the plenum is a common volume post throttle body where the air charge's velocity is reduced, lower velocity means higher pressure (Bernoulli's principle); this comes with the added effect that the larger the plenum the smaller your throttle body can be, as long as you don't mind the loss in throttle resolution in low-speed applications. ITB's arent relevant to this at all, for those all you worry about, is CFM, and charge inertia (that why they have the huge stacks on there). But keep in mind there is a reason ram tube intakes that extreme that aren't on daily driven cars, they suck to drive, but are great for binary throttle operation. The whole point of a large plenum is to make up for the lack of air in periods of throttle transience while filling in the gap of reduced flow from the time the throttle butterflies open to the time there is sufficient velocity through said butterflies to sustain the engine's performance.
. Let me know what size runners you're thinking of and I'll see what I can do, I'm getting ready to decommission my Vette for a week to pull the intake and finalize dimensions, then print and test fit a stock printed plenum and runners to see how close my model is.
