In the intake test (SuperRodder), semi-siamesed large tube runners did not perform nearly as well on the top-end as a SR. Because the runners are the same size and because the divider was removed to the same spot (as the SR runners end), the big difference has to be in the plenum config.

The SR has a much larger plenum which means the air "stack" pulling into each runner is distanced much further from the runners on the opposite side. A logical conclusion would be to assume the force of air being pulled in opposite directions begins to affect each other at sufficient velocity.

BTW: This question is out of curiousity for very high power setups. It has nothing to do with trying to uncover a potential problem with factory cars. (I might have given the wrong impression?)

 

I hate to ruin this thread, but what the hell are you talking about? The LT5 was a marine engine that the ZR-1 got as an afterthought?

And my original post was tongue-in-cheek

 

Some guys must just post without taking Corvette history 101.

 

Bob are you a L-98 hater now that you have an LT-5?

 

It does defy logic... must be a distribution problem of some sort. Air flow can be real tricky and the least little thing can sometimes disrupt it.

 

As was mine,didn't think you were going to bite.Merry Christmas

 

LOL, never! I hated it well before I had the LT5.

Just kidding, I think they are fun. A lot of fun for the money anyway, and decently fast when you step on it. I think how happy someone is with the L98 depends greatly on their expectation, though. If you've had other fast cars, it may be a let-down. I had an "iron duke" Chevy Celebrity when I bought mine. So I thought it was a rocket ship. At least until I had run-ins with other cars like Mustangs, Supras (presumably there were still stock ones around back then), Impalas, and such. In fact most anything performance oriented could hang, except other 80's cars like 5.0s and F-bodies.

For me though the car was fun, decent on gas, and pretty reliable. And it didn't kill me or anything.

 

I agree. And, this thought still is in my mind. To some degree, it's keeping me from choosing another LT runner setup.

If the negative pressure waves of exhaust can travel all the way back thru an exhaust system to positively effect flow on adjacent cylinders, why can't "negative" pressure in a plenum affect ports that are only a few inches away? When the car is at very high rpms, the force of the air going down the tubes much be significant.

The SR probably overcame it because there's so much more distance across (from opposing tubes).

CC mentioned the runners are staggered. That's only partly true. When you look at a mega-ported plenum (on corvetteplenum.com, you can see right thru the damn thing. The center two runner ports pretty much line up.

Until someone provides a more reasonable explanation why the SR works so much better than ASM siamesing, I have to believe I might be right (or at least partially right).

gp

 

It generally relates more to air velocity through the runners. I'll type in a longer explanation with some math tossed in later.

 

http://www.thirdgen.org/techboard/al...t-efi-intakes/

-- Joe

 

I know it also has to do with the runner length and diameter..... but that issue is with the runners. I'm talking about the plenum.... keep up...

 

I didn't need an invitation....

 

..... could be the plenum size, or volume. The stock plenum thins down to about 3 1/2". Maybe it's just too small to feed hi RPM. Like a Spacer under a carb/intake, more plenum area often picks up the top end some.

 

"very high power setups"

Not usually mentioned in same sentence as TPI.

 

Well we pretty much have it all covered. I know it comes up a lot over here, but theres no stickies here. We've got a large amount of data over there.

-- Joe

 

I signed up and perused "your" forum for the past few weeks. You do have some nice stickies and good (forum/thread) organization. Kudos on that. However, I've never seen a reference to the question I asked -- making this particular reference seem somewhat lame.

From my perspective, it becomes a little like an advertisement for another forum -- the kind of advertisement that got some other members (here) banned.

Maybe I don't understand the rules....

 

The superram works by having a different length runner. I don't have the numbers in front of me. The shape of the plenum is more incidental to allow for the midlength runners.

 

seeing as this thread got dug up from the bone yard.... I don't think that was the reason. for some things I look at that board, and camaroz28, as good resources. I use all information gathering possible when trying to learn about something that has already been done (pros and cons).

I remember once reading that there were negative affects using siamese runners and it was NOT a good idea. TO me none of these intakes are that perfect, and the first thing that comes to mind is the location of the TB, and it's relationship to the runners. AS an example, If one is concerned w/a more even distribution of air, something similar to a victor jr. type intake would be better as far as I am concerned. Other things that would contribute to better overall efficiency and performance would be an input from each cylinder to the ECM.......

 

SLP reps say siamesing causes "turbulence". And, that's why they found that a minimal (siamesed) slot provided the best improvement. (Personally, I suspect that removing plenum obstructions between runner ports would accomplish the same thing as their minimal slot). When they talk about turbulence, I have to think they are talking about a disruption in the harmonic pressure wave traveling up and down the intake tube?

If you look closely at the Super Rodder intake test, the siameseing did produce some of the change expected. The TPI hump was lower in mid-range and the peak of the curve did move up until 5300 rpm. Something appears to have disrupted the high-end performance at it neared the 5k rpm range because the high-end performance did not equal the superram. It was better than the TPI, just not as much.

(Obviously, this could be an error in tuning, intake seal, or some other issue. I didn't want to assume the lack of error).

One reason this is important, is because I like the superram curve the best of all intakes listed (for street). I like the LT TPI and HSR as second choices for different reasons. I don't like the actual superram due to lack of availability and complaints. This siamesing seemed like the only reasonable alternative to getting there. If my guess was correct, having a (partial) divider welded inside the plenum seemed a possible "cure". (Mind you, this is my own, personal schemeing).

I understand what you are saying about intakes in general. I'm also aware of the front-intake problem with even distribution. (I've seen where the rear cylinders typically run leaner and about 100 degrees hotter). I assume that's where individual monitoring of the mixture (by the ECM) could compensate via their respective injectors.... But, then the rear cylinders would be "stronger".

gp

 

in that case why not add a throttle body on each runner?