MatthewMiller

Tom, I think if you fully siamesed them from top to bottom it should do some of what you're asking for. Helmholz theory says that increased runner area does increase the rpm of the resonance, and you'd be more than doubling it. What is confusing to me is how the valves "see" the runners in this scenario. Or maybe more correctly how each of the (now just) four runners "sees" the intake valves. Two valves per runner now, so the question is there ever a point where both valves are open at the same time, even a little. For instance, the 1 and 3 valves are paired to a runner but they are 270* apart in opening, so I think they would never both be open at the same time at all. In that case, whichever of them is open is just seeing a much bigger runner volume, and so the Helmholz theory says you've significantly raised the resonance rpm. But the 5 and 7 valves open 90* apart, so they should have some overlap to one another. I frankly don't know how this would affect things, but it's hard for me to believe it doesn't. I'm guessing that it cancels a fair amount of the resonance effect, or at least makes it a lot "fuzzier". What I wonder in that scenario is if the AF tuning for cylinders 1/3 needs to be different than 5/7, which is not happening with the factory EFI system. IOW, do you end up with an imbalance in mixture from one pair of cylinders to another?

Partially siamesing the runners is even more confusing to me. I would think that you shorten the effective runner length with respect to Helmholz tuning, but again there are complicating factors.

Tom400CFI

I think you're onto something here. I'm probably giving up on this idea. I recall, years ago "1989TransAm" on Thirdgen was working on a high RPM high hp TPI solution. I recall that he'd tried a heavily ported and further Siamesed set of SLP runners in order to shorten runner length and raise the RPM range. He lived in Cali and had to stick with CARB cert'ed parts that pass visual. I think he and "Dyno Don" and a couple other Cali residents were working on this project. Cuisinartvette probably knows who I'm talking about.
Anyway, I recall that they didn't meet their goals, RPM wise or HP wise with the massively gutted SLP's and they weren't sure why. They ended up welding and porting, raised runners and other methods to reach their goal...I don't recall the outcome. Point is, "shortened" runners via ported SLP's didn't get them what they were expecting, IIRC.

MY feeling is this; while you can cut the divider back (in an SLP runner) the end result is not what I'd call a runner with a mouth that is "opening into a plenum"; the mouth of the runner is totally shrouded on ~270* of it's circumference and the remaining part is typically tapered So your "mouth" is a huge, angled-to-the-sound-wave, oval. IDK how that "gradual" mouth opening lends itself to being a place for a helmholts wave to "bounce" off of...like it would off of the air space in a typical plenum which is fully exposed to the entire mouth of the runner. I think the SLP runner would have to "baloon" toward the plenum where you cut the divider back to, so that would be a defined transition from tubular runner, to plenum space.
My guess is that cutting back and porting and SLP helps....but not a lot b/c the runner "mouth" isn't fully exposed to the plenum...and it still behaves somewhat like a long runner -because it somewhat is.

I agree that 5/7 have an interesting problem that would affect tuning/running with a siamesed solution. IDK how you'd manage it. Get a different intake where the mouths don't affect each other.

If a bunch of folks posted and said that they'd picked up 1000 useable RPM with ported SLP's....I'd start shopping seriously for some. But that didn't happen so I think the solution is a mid or short runner intake. I want something that looks cool/different since it's in the Kart....it's "front and center". Wish I could find a T-Ram!

MatthewMiller

It's down to there being a difference between a runner opening to a common plenum with all the other runners, vs effectively opening to a common runner shared by just the adjacent runner. I guess it would sort of be the same concept as a "tri-Y" header.

And just to be clear to those following along, on the other bank the 8/4 cylinder pairing would have the same problem as the 5/7, whereas the 6 and 2 cylinders are spread 270* apart.

84 4+3

If you want to try something different, mercury racing used to have an efi style manifold that was similar looking to the LT5 one. They designed it after they learned the flaws in the original piece but I can not for the life of me remember if it was small block or big block. All I know is it looked cool but it should for the most part be plug and play, if you could find one...

KyleF

Don't forget the head intake port also factors into the length. Its the total distance from the plenum to the valve.

In the end, you have long runner designs from the 80's, Short Runner designs from the 90's and mid lengths like the LS1. All have benefits and compromises.

Tom400CFI

I think that one you're thinking of is for a BBC. I like the way it looks...good suggestion. I've been looking at THIS. It's not extremely sexy, but it is different and I was thinking a fabricated aluminum plenum box on top with ribs CNC'ed into it, could look cool. And it's definitely in the realm of a "mid length" runner intake. Looks like easy porting too.



Yep, I know. I was thinking if you ported the SLP's back to just about the lower, then you'd just have essentially the head port and lower....about 11" or so of runner. But it doesn't seem to actually work that way in practice -at least from what I've heard about the SLP's.

MatthewMiller

That looks somewhat like a Holley Stealth Ram. I'd be interested to find out more about that. My guess is that it will be hard to come by good data on this intake regarding flow numbers. I also wonder if it would fit under a stock C4 hood?

cv67

Siamesing never gave a sotp gain it just seemed to perhaps give more plenum area
I remember 89 TAs attempt at welding up his own runners dont think he was happy with it.
Bet if it had the type of taper the LSx runners do he woulda. Neat threads miss seeing stuff like that.
If you took enough out of the SLP runner you could almost mimic the superram effect. Ported heavily they can really make about any sbc make big tq!

drcook

Wouldn't it be less expensive just to convert a LT1 intake per the instructions link I posted above ?

Tom400CFI

IDK if it would fit under a stock hood. My guess is "no"...with that plenum. I think you could fab a plenum that is lower/wider though, that would fit. Something more like the shape/size of a super ram plenum.

Thanks for confirming my memory. I agree....those old threads were bad assed.


Eh....maybe. That intake is $500 which isn't bad...but I have an LT1 intake sitting on my shelf, so yeah, that would be cheaper. But since this is for the Kart, and the engine is "right there" for all to see.....I'm looking/thinking for ideas that are different/cool looking etc. A TPI is cool looking. I already have that covered with the stock intake, IMO. But the power curve in the kart is worthless. I want to extend the RPM range (don't actually need more power...just more range), so I wondered about heavily ported SLP's which would keep the "cool TPI look"....but it doesn't sound like they'll do what I want; mimic a mid length runner intake.

I don't think the LT1 intake looks cool. It looks "neat and tidy"...compact, even....but not cool. So, I'll keep looking/thinking....

84 4+3

That's a vortec style lower actually. Interesting but it has longer runners it appears.

MatthewMiller

Coolest looking intake is the old-school look of Hilborn, but converted to EFI. But it would probably cost more than the rest of your car...

KyleF

Not true. The SLP runners still hit a base that crosses over from one side of the engine to the other. The "Ram" style manifolds do not. So, not only do you lose length on the runners themselves, but also in the lower intake manifold.
Cutting the SLPs still maintain this length in the lower manifold and what you end up with is a mid length design and effect. The Miniram, Stealth Ram, Super Ram, etc. all remove all this length and you end up with just about 5 or 6" (I can't recall correctly) that performs well over the entire band but gives up a tuned torque peak or any kind of tuning. This is why LS guys still got to a more straight shot manifold for racing or high HP combos. Changing nothing else about the engine other than this allows the engine to make more peak HP at the trade off of lower end torque. If you are geared low, you never see this and enjoy the upper HP, but if you had an 86 TPI auto (Peanut cam) and a 2.73/2.77 rear... going to a mini ram won't make you so happy.

We all know on here, its the combination and how it all works together. Not about individual parts. The car running the best 1/4 mile time or posting the biggest number on the dyno won't be the best to drive two hours to a car show in. Have to build for intended use.

You can't really cut and weld the factory ones, but the SLP casting allows this. I have seen a few that cut them completely open, remove the centers, port and polish everything up and weld the outer shell of the casting back up.I am familiar with the guys referenced doing this (I also have an Iroc... the reason I am in the TPI discussions my 'Vette is LT4). They may have not achieved their goals, I honestly don't remember any threads detailing this, but I know doing this makes more HP. Probably not as much as a miniram.

In the end, I think if you plan on seriously racing a TPI, you have to go to a ram style manifold.

I don't think this is a flaw in the original design. You have to go back to 1985 when the TPI was released. Nobody was making big emissions legal HP for the time or doing great on fuel economy.

The 700R4 of the time had a very deep first gear
Most of the Cars came with either a 3.08 or 2.77 Gears in the Camaros
A lot had 305's
Should I mention what crossfire was like.

The TPI by making low end torque coupled with the 700R4 allowed a IROC with a 305 making 195hp feel strong coming out of the hole and provided really good punch. Plus would kick the crap out of anything built the previous 10 years (Stock). Yes, it had it's limitations, but for 35 years ago, it was a dang good system.

Remember, a 5-speed G92 car (305 TPI, T5, Hard Top, 3.42 gear) with a good driver was able to run with an LT1. Stock to Stock. Especially if said LT1 was a T-Top Auto with a 2.73. Not bad for development in the early 80s and limited processor and memory capability.

The TPI gets a bumm rep now 35+ years on. When you look at what an 85 IROC or Corvette was to a 50-55 Chevy (Reliability, Maintenance, Performance, Handling, Safety). There is no surprise what a new Camaro/Corvette is to an older IROC. I think the TPI was an amazing system for it's time.

KyleF

Aesthetics are a hard thing to argue because they are subjective. Nothing looks better than a TPI to me.

drcook

Webers look pretty cool also and are a little less expensive, not much, just a little.

Tom400CFI

Yep...that definitely looks wicked....but that is candy that I can't afford....and it doesn't really fit w/in MY Kart's theme; home/DIY.

No, I need to find something cheapish or cheap, interesting looking and different. Something that has shorter runners and people ask, "What's that!?" would be ideal.


I'd be beyond thrilled if I had this sitting in front of my kart's windshield...

84 4+3

the runner geometry on those hilborns is actually very similar to the one tom posted. Minus the shared plenum of course. But yes, that is one of my favorite looks along with the original cross rams. Just something about it I guess lol.

Red 91

Tom, just trying to follow along and I Im thinking duel quad or tunnel ram. In the past I worked at a race shop and we fabbed a sheet metal intake for a v6 with 3 webbers. Anything can be done, just is it worth the time and effort. Good luck!

Tom400CFI

I'd like to stay EFI....but I've thought about ideas like that (dual quads) also. Thanks!

84 4+3

What about the ram jet?