Jim 86 IROC

Several people on this Forum, I believe "MadMax" was the first, have done this mod. The depth reported was 3 1/2".

I am in the process of siamesing my stock intake base and have read some cautions about going too deep and losing low end torque. So I'm now at about 1" deep by 1" wide on the openings.

Has anyone done this mod and have test (dyno or time slip) data and dimensions of the holes between adjacent intake base runner tubes? If so, what other mods were in place at the time of the tests.

Thanks much for any info.

Ed Maher

Sorry but nobody has done any actual scientific testing of how far in one needs to go and if there is evena significant trade in powerband by altering the divider length. It seems the minimum most people are going in is at least 2 inches or so. The base going on mine is cut a good 2.5" into it. This seems like a good minimum start though as it still leaves a fair amount of divider length to act as the runner, yet a decent sized 'plenum' for both runners to feed from and to take care of the transition form the runners.

smokin87iroc

i went 4 inches and i am down like 3 rear wheel torque from where i started when i was stock. 265 stock and like 262 now.
however that is a peak number. also keep in mind both of those are with the stock chip. with and ed wright chip or some custom prom tuning i feel that i could be at the 280 mark.
what i can feel on the street is worse that what is shown on paper though. i do bog if i don't drop the clutch. i don't have any 1/4 mile times yet but i should soon.
with that said
the top end advantage is well worth it. i can feel the difference once i break 3500-4000 rpms
also i have 3.08 gears and will be moving to 3.73 which will eliminate my bogging problem and get me to my powerband quicker.
2.5 to 3 inches is a good start and you can see what you wanna do from there.
when i do my 350 or 400 block i'm gonna go some more. probably to just in front of where the injectors are. but i'm also gonna get a big cam and do some prom tuneing.
Andrew

Jim 86 IROC

Thanks for the feedback; for the first pass I'll just cut into the stock runner mounting flange about 1/2" to bring the total cutout to about 1.5"x1" or about the same area as the runner crossection.
I can always take out more but tough to put it back, since I don't have a heliarc setup.

BTW, I'm modifying a used base & runners that are they're going into my L98, not the IROC's LB9. The L98 has the "free", exhaust, ignition and cooling mods in addition to 1.6:1 RRs.

I'm looking for a cost/power effective alternative to LT base & runners. These give about 10-15hp for $900 whereas the siamese base mod gives (in theory) 30-40hp and will cost me $300 for used parts & tools.

After I get some track/dyno data, I'll be baaak.

tpivette89

definately let us know. i am planning this mod next in my 89' Vette and would like to know how it performs at the track as well as the street. BTW i plan to go in 3 inches when i port my base

Jim 86 IROC

tpivette89, it's going onto the L98 in my '88 Vette; I'll post results on the C4 forum as "65Z01", well as here.

I considered going deeper but don't want to lose the TPI tuning. I'll will give up a little top end breahing to keep that low & mid-range torque.

What's your schedule to try out this mod?

ThirdGenZ28 92

Would anyone recommend having a TPIS base siamesed that will go on a stock internal L98?? Im gonna have the entire set up w/ SLP runners port matched with TPIS LT gaskets, is this enough or should I consider a modest siamesing of the base as well while Im there??

Jim 86 IROC

I was going to use my AS&M LTRs with the siamesed stock base but concerned about possible loss of velocity at low RPM; so decided to start with stock runners.

I would consider the same issue, loss of velocity, with siamesing a BM base for use on a 350, it might be ok on a 383 or larger. Also that's an expensive piece to experiment with!

Swapmaster

Figure what air flow you need and go from there. A manifold which
flows more air than needed will hurt torque. A manifold that flows
not enough air will hurt Horsepower.

Everything down to the base is irrelivant on a TPI motor as long
as the upper components will outflow the heads. The base is
where I would suggest tuning the motor. The base runners are
about 6.5" long. A dual plane manifold has runners between 6"
and 8" long. A single plane manifold has runners between 3" and
6" long.

If the plenum and runners will outflow the heads then the 6.5"
long base runners become the restiction, This is good because
we can then tune them make the engine perform the way we
want to. We can siamese it to shorten the runners and raise the
power band or we can just port it to enhance midrange power
depending on what we want the motor to do.

Assuming your throttle body, plenum and runners will outflow
your heads then we can as be sure that:

At 6.5" long, the stock base runners will still provide plenty of
torque.

Porting through the restrictive center area of the runner will
dramaticly improve power while moving the power band up some.

Siamesing it will move the whole power band up. The deeper you
cut the higher the power band will move

Ed Maher

Within a month i should have track times on a siamesed base on an internally stock 305. If it gives me reasonable gains then it should do the same for any other application.
You probably wouldn't stand to gains much on a stock engine with a siamesed aftermarket base vs. leaving it alone. But once you start getting into any real mods it will only shine that much more.

Guest

I dont know that 1-1.5" is going to do anything at all. Its like you are cutting a window in the side of the airflow path, probably not a whole lot of air is going to make that turn most of the time. I think Mike Davis originally went about 2", then went more, 5"? Its on his website I really dont remember. For the poster above asking about a TPIS base, it was an Edelbrock base he cut. The good thing about cutting so little is you can always cut more if you want. Its quite a bit more difficult to put it back.

tpivette89

im gonna take the Vette down to the track just one more time next week to try and squeeze some better #s out of it before i do the porting. i figure itll probably take me a few weeks to do the whole intake, as i work alot and go to school, so im kinda pressed for time. i may not even do it at all, because i am thinking of trading in my Vette on a LT4 or ZR1. im itching for a 6speed

CHRISMAN2000

iTrader: (1)

Has anyone ever gotten some dyno results from a siamese setup?
350 or 383?

Jim 86 IROC

That's the info I was looking for. I've only seen hand drawn plots, not actual dyno graphs.

Assuming my project works out on time slips my dyno data will only show results from ~3,200rpm up, due to my A4.

Guest

Yep. Check this post out:

https://www.thirdgen.org/techbb2/sho...hlight=siamese

These are the actual dyno sheets, they arent 'hand drawn'. The comparo sheet I 'hand drew' with excel, taking data points off the dyno sheets. Mike Davis also has some sheets up I believe, and I know he has a chart comparing the two. Both his engine and my engine are 350's.

Jim 86 IROC

Madmax, you ARE da man.

It looks like the old post that I lost access to, and much more.

Thanks much for putting up this link and much of the info therein.

And, yes, it was a stroke of inspiration to begin this mod several years ago.

85MikeTPI

iTrader: (2)

.... I'm finally heading back to the dyno this
Friday and will report back after cutting
another 2-2.5" out of my base. I made
it back to the track already and picked
up 2MPH, but the dyno will tell the real
tale..

mike

http://www.eecis.udel.edu/~davis/z28...13baseporting/

Jim 86 IROC

85MikeTPI, I assume that's with the ZZ4.

So now you have only about 2" of separator?

What ET & trap speed did that + 2mph come from and with how much separator remaining?

I"m very interested to see how you do with even more removed. Any other mods between the prior runs and this Fri?

85MikeTPI

iTrader: (2)

Yep, I had forged pistons installed (std. size)
in the ZZ4 last Summer/Fall when #7 cracked.

The separators left in the base are 2-2.5" now.

The ET's were all 12.0x at 111.x consistantly
in street trim. I 'cheated' an 11.94@111 last
Dec in cold/windy day with alot of weight removed.
My best in street trim before was 12.2x @ 109.
(before meaning before cutting the base more)

Most all my mods this Winter were weight/cooling related to prepare for RoadRacing. The only
engine mods were the extra cutting of the base
and the changeover to CompCam 'R' lifters for
the higher revs.. (p/n 875-16) (So the dyno
should only show changes as a result of the
base cutting)

((oh yeah, I did upgrd to 30lb/hr SVO injectors
after the drag runs showed me running out of
fuel with the new base @ 6000rpms))

mike

My mods/times etc are kept up on my MAFB page
under the link in my Sig.

Jim 86 IROC

So looks like you picked up about 20hp on a 380hp motor, that could use the extra air at upper rpm. Hmm.

As we know that larger runners and base on a bone stock LB9 or L98 has little benefit.

This mod may be similar, except that it changes the filling dynamics at the valve ports. Though you have effectively shortened your runners to the length within the heads, air must still be drawn down the runners from the plenum. There may be some ram tuning between your open base and open plenum. So the dynamics is still not the same as say a short runner LT1 setup.

Anyway, looking forward to your time slips from this Fri.

I8AStang

I noticed that a few posts about runner lenght and being a restriction. Runner diameter is a restriction not length. The runner length is tuning for a particular rev range. Obviosly When you siames the runners, you shorten them, increasing the rpm the engine is going to achieve peak volumetric efficiency. Decide what rpm you want the engine to make peak torque (stock runners are about 3500rpm, using simple equations it comes up 3300rpm, so the math does hold true). A good book to read on the subject is "A Scientic Approach to Intake and Exhaust Tuning", I think, I can post the ISBN number when I get home. What you are doing with inlet and exhaust systems is making pressure waves overlap (it is not a steady flow). When you change lenghts, you change the time it takes for a wave to come back. The math wouldn't work quite right with the siamesed runners because it isn't individual and whole plennum like stock, it is plenum, almost a plenum, and individual. Also don't forget to include the lenght of runner in the head, as the equations are plenum to valve. I don't think everything can be answered with math and equations, but it really helps to understand the physics of what is going on.

Ed Maher

I8Astang, it's all well and good to think about physics, however you have to remember that an intake is a VERY VERY VERY complex system. What you are talking about, ram tuning is just a very very small part of the equation. If you don't think runner length is a restriction then i'm not even going to get too deep into this since apparently your 'physics' experience is rather limited. Runner length is a restriction b/c as velocity increase, so does the frictional losses of the column of air moving through it. That is why LTR TPI doesn't make good high rpm power, as you try to move more air faster, you have more and more loss of energy into friction in the runner. Also, with the plethora of turns and angles the air has to make from the TB to the head also present significant losses.
By using a siamesed base however, you effectively cut losses from the turns in the plenum / runners in half (actually not half, but like i said, this would be math for a grad student who's into this stuff to handle) since it now has 2 paths to supply the mini-plenum you create in the base. Now the base is free to act as the intake and let the heads / cam breathe how it was designed. Early testing even on a stock 305 (madmax) shows a real and measureable gain vs. stock.

I8AStang

I did not say it wasn't a gain, I said the gain wasn't from a restriction. You "tune" the engine for the desired rev range with length, then after that the runner has to be capable of flowing the air, obviously losses increase with length, but we are talking differences of inches, not feet. If it is still a problem then you make its diamter larger (then fluid flows slower, less frictional losses, like I said, diamter and wall surface finish are the real issues, not length). If you make power by shortening the runners it WILL be at a higher rpm. I have spent a decent portion of the last few years of my life attempting to understand the physics behind it, and it is very complex (mainly when you are talking about how the cylinders in a multi-cylinder engine "talk" to each other, that is way beyond grad level). The wave tuning portion, neglecting how the cylinders influence each other, is very simple. The intake and exhaust pressure behave very simalar to a sin wave, make your intake valve open on a peak and you exhaust open on a trough. On an LTR TPI, this happens in the 3-4k range. As it spins faster, these ups and downs in the wave start hurting, not helping you, hence the torque curve starts to drop like a rock. Shorten the runner and this happens at a higher rpm, so the engine gets more air. The optimim diamter will change with runner lenght. I wasn't hostile, I thought I introduced information that may be useful. When the early experiments regarding single cylinder test engines were done, they did them with huge lengths, and still made great peak torque very low rpm. Obviously you must make peak torque at a high rpm for large horsepower. I also thought there may be someone here who really wants to understand the physics of what is going on, hence the reference to the book. What understanding I do have comes from good sources, and I am not just some goober who likes to make it sound like he knows something, if I came across that way then I apologize. Runner length becomes a restriction when it is overly long without sufficient diamter, make it larger and it is no longer the restriction.

Ed Maher

Nothing wrong with a good debate. I still see length itself as a restriction, just as i see the bends and poor transitions as restrictions. True you can increase the diameter, effectively reducing velocity and the frictional losses associated there, however we're not talking about theory, we're talking about real world application of parts. The largest diameter set-up you could run, AS&M runners and aftermarket base still prves to be a tremendous limitation when you're trying to make power. Look at a car like Kevin91Z's for proof of this.

I wish i had the energy to really get into a good discussion on this. Perhaps later i'll have some time and energy to get into it. Whats important to note though is that none of us hopping on the siamesed base bandwagon could give less of a care about the effects of ram-tuning. In fact, madmax's original post about his base was titled 'anti-tuning the tpi' in reference to his (and now our) desire to eliminte the effects and instead run an anti-tuned short runner intake that lets the cam and heads dictate torque and power characteristics. I see a siamesed base as a 4 plane intake with a nasty spider TB feeding the 4 hollows.
As for changing the divider length in the base, i don't think this will have major effects on the powerband of the engine. For example, ike davis's car obivously picked up some good power by hacking more out of his divider, but could a 20hp diff be accounted for with just the effective runner length change, or a combination of the shorter runner also having less of a restriction since it has a larger mini-plenum to feed from, and less overall small diameter runner in it's way before the head. The latter seems to make the most sense since 20+hp doesn't come very cheaply at the power level he's at.

MikeS

Keep debating guys. I wanna read it. Gimme a number for that book, I'll read it too. Any other sources for intake theory? I'll read them too.

Ed Maher

If you do some searches i think i posted a bunch of relevant theory a while ago. Try using words like efficiency and loss and harmonics, etc to narrow things down...

Jim 86 IROC

With today's PC power it is possible to model wave motion in intake sysetems. Desktop Dyno does this in rather simplistic fashion; their Dyno2000 sw doesn't effectively model intakes that deviate far from several standard designs. They mention more expensive (than $50) software available to model new designs. I have Desktop Dynos, ISBN 1-884089-23-2 that came with my early sw version. It provides some insight into the complexities of intake and exhaust air movement.

With the machined dual plenum setup I would think that the dual shorter runners feeding the lower plenum still provide a ram-tuning effect of somewhat diminished amplitide (slower air since two feeds) tuned to a slightly higher rpm due to the shorter effective runner length.

Though I have a Physics background I have not the ability to accurately do this modeling and program it into my PC. I'm trying to understand how this new manifold design compares to existing types to get a "feel" for how it will effect various TPIs (L98, LB9, modified, etc).

Thus this search into the world of innovation and experimentation called "hot roddiing". I realy thank you guys for the informative responses.

I8AStang, please provide the author or ISBN # of that reference. I'm currently beteen jobs now and find this very interesting reading.

I8AStang

ISBN# 0-83760309-9
This book was written about 20-30 years ago, and while some of the info is dated, the ideas are not, just the technology to implement them. The reason I read it was my automotive powerplants professor (who is head of research and development at Robert Yates Engine Manufacturing, he only teaches that one class) suggested I read it, as it is informative without being overly complex and theoretical. Hope someone finds it helpful, thanks.

RedIrocZ-28

Hey guys, I was just reading over this and pondering a lot of things in my head. Here are my thoughts.

-Runner length shouldn't be the main point of discussion, yet. The REAL problem are the bends the moving air column must travel. If someone were to come out with a manifold where its like a gradual turn starting at the plenum through the runners down through the base and straight into the head... DEAR GAAD IN HEAVEN WE'D HAVE SOMTHING! Think about a piece of flex tube in your head, now bend it so its this gradual curve entering straight into the head port. Anyone up for a building a prototype?

-Wall finish I do believe plays an important part here. I noticed that the inner plenum is all "marbled" shall we say, the runners are smooth, and the base is again kinda "marbled." A nice teflon coating would be great wouldn't it? The fluid dynamics of this whole system are amazing... if only there was a way to reduce friction.

-Tuning this new system. I have read about the waves bouncing back to the plenum from the back of the valve and then being smacked back down to the opening valve again by a closing valve on the other side of the manifold. (Kinda hard to explain what I mean, I8ASTANG knows though). GM did a lot of research to tune this intake system even with all these flaws in it. Now if one were to do a gradual turning air column manifold/runner setup where the inner surfaces were going to cause less friction, I would assume that one would also have to retune the system.

But why do all this when there are the LT1, LS-1, LS6 and whatever intakes? Why don't ya just supercharge the TPI system and negate all the inherent problems and broaden the powerband?

Edit: G0D is censored? What ever happened to freedom of speech? Wouldn't wana offend anyone and have the administrators sued I guess.... Yet another reason why this country is becoming the laughing stock of the world.

Jim 86 IROC

Easy answer on the last question...$$. I can supercharge my IROC for mid $2k; on the Vette the price nearly doubles.

But mostly it's the desire to use an innovative design that's realy stealth.

JucinGTA

Here was mine
www.geocities.com/softtailduece01

Ed Maher

Guest

I dont think surface friction is as big of an issue as you guys are making it out to be. Even though air behaves a little different than most other fluids, theres not anywhere near as much velocity at the walls, the fastest moving air is away from the walls. Regardless of how smooth you make the surface, the air is still going to travel slower at the walls than it will elsewhere. Theres nothing wrong on a dry intake with making things smooth, but I think its going to be a minor difference compared to what you could do by messing with length, diameter, and transitions.

Ricktpi

I wonder what the effects would be on a Super Ram. Probably not quite as dramatic due to the larger/shorter runners. Any thoughts ?

Ed Maher

I forget the exact term, but madmax is right, air moving past a surface does move slower at the surface. I recall it being called laminar flow effects or something, but i'm sure a physicist/ME has a better term. It's the same reason why the 'ram air' on 4th gens is a farce and why pro stock hood scoops are so far off the hood.

Swapmaster

I am working with air flows right now messing with this flow bench
stuff and laminar flow refers to a smooth flow of air. Broken up
air flow is refered to as turbulent air flow. Drag car hood scoops
are way up there to get up over the air dam effect created by the
nose of the car. The only factory hood scoops I think that actually
worked are the mid 70's Trans Am reversed scoops and like the
Chevelle cowl induction hoods that draw air from the high
pressure area from about the last 1/4 of the hood to the windshield.

Ed Maher

Right, laminar means smooth airflow, but i'm sure there is a concept in fluid flow that stipulates that the air flowing close to an object doesn't move as fast as the air above it. boundary layer or something. Maybe i'm just thinking it's related to laminar flow b/c it will only happen with laminar flow. Turbulent air wouldn't create a boudary layer since it would always be crashing into itself disturbing the boundary layer. And of course the boundary layer actyuually serves to decrease firction since you're in effect getting air / fluid ball bearings on the surface to lube the higher air / fluid.

This is kinda just brinastorming but does any of that make sense to somneone who actually studies this stuff for a living. I have the concept in my head, i just can't name it.

Ed Maher

Man i love the internet. A quick google search on laminar flow boundary layer
gave me http://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.html

check it out, exactly what i was getting at. The air near the surface moves slower, thus friction is less of a concern than a cursory treatment would suggest.

Ed Maher

BTW, for all the people who hate on me. When's the last time you researched a concept you were unsteady on in order to participate in a discussion. It's not like i don't walk the walk.

sIcK pUpPy

Ed, in all seriousness, damn good research, and i'm not just strokin' your ego. You have an abrasive disposition on occasions, but you definately deliver the goods.


Lates,
JD

cort351w

That's why I just scan for your, Vader's, Madmax's, five7kid, and other very knowledgable people's replies when I'm in a hurry

Greasemonkey

Ditto.

Matt87GTA

Ya know, until this post I didn't entirely understand what the big attraction of siamesing the base was..... While nowhere near a physics guru or ME, I can understand how that opening helps get rid of a lot of the problems with how many turns the air has to take and how crappy the runner alignment of all of the components on the stock system is.... And not letting the intake dictate the location of the powerband so much..... This looks very appealing to me.... So on an application like mine (355, TFS 23* heads, LT4 Hot Cam, all the bolt ons, SLP runners ported down about an extra inch, ported and siamesed plenum to match the runner inlets...), would playing with a stock base be worth it? I mean, is the diameter of the runners in the base going to play in for an engine like mine? Hmmm.....

Swapmaster

Matt87GTA, if you are running a stock base, you will see quite a
difference with the mod. Right now the stock base is killing you.

And ED, love ya man, but I wouldn't want to stroke your
ego or anyother part of ya either.

I8AStang

That's a great simple picture of the velocity profile ya got there. I was gonna post something out of my fluid mechanics book, but I would think your picture is more effective than my overly complex picture with confusing differential equations attached. You guys have a good one, I like good discussion.

MikeS

Ed,

You doubted yourself? You had it figured out a good ways up the thread! The only details I can think of to add:

In a tube, the velocity profile (pictured above) is a sideways parabola, with zero velocity along the tube walls, and maximum velocity in the center. Also, if anybody cares, the viscosity of the fluid is a major determining factor in the veliocity profile. Of course, things are all a little different going around a bend...

HotRod

Something has been bothering me for a while. If I siameze the runners completly (weld them) and port the manifold slightly to give a smooth transition would I get the same effect (with a little more plenum volume), or does the double runner effect really help in a way? One more thing, how would a supercharger change the scenario? I know the intake is not supposed to be as important on a blown motor but at what point will it become a restriction. Is it better to run a near stock TPI for torque and supercharge it to allow it to breath? Thanks,
Tyler

Swapmaster

An engine is tuned to a desired rpm range by the intake manifold.
The TPI intake is tuned to peak at about 3500 rpm. It comes on
strong off idle and gives up after about 4500rpm.

The lenght and cross section area of the stock runners from the
plenum to the intake valve, including the head, are designed to
keep the mass of air in the runner moving toward the intake
valve at lower rpms. The way this is designed to work is that at
lower rpms, after the intake valve closes, the air in the runner will
continue to move toward the intake valve so that when the valve
opens again there is pressure at the intake valve from the still
moving air mass to help fill the cylinder.

What happens above about 4500 rpm is that the stock TPI setup
does not have enough air flow due to the small cross section
of the the long tube runners which is what keeps the air mass
moving toward the valve in the first place.

It is easier to look at it in reverse from the head side of things.
When the intake valve opens it allows air to enter the cylinder.
If there were no intake manifold at all, there would be no "ram"
effect from the runner to help fill the cylinder. The engine would
have to reach a certain rpm until shear vacuum from the piston
moving down the cylinder created a low enough pressure in the
2 inches or so of "runner" in the head to cause pressure to
develop at the back of the intake valve when the valve closes.
Only then will the engine begin to develop useable power.

Now, for the intake manifold. When you add large tube runners
or the siamesed runners, you increase the runners air mass which
reduces the air speed which in turn reduces the pressure at the
back of the valve which in turn requires higher rpms before the
engine will start to develop useable power.

Such a vicious cycle.

But, the larger components also raise the rpm limit because they
alow more air into the engine. More air, higher rpms.

Now we will be working with two different setups here so stay
with me.

With siamesed runners (each pair joined as one), the only runner
we can talk about is in the intake base because we just turned
the "runners" into plenum area. Any area which outflows the head
by a significant amount is to be considered plemum area because
its air mass moves too slow to have any positive effect on the
back of the intake valve. Don't forget about runner volume
causing pressure on the back of the intake valve. That leaves us
with the runner volume of the base and head to play with.
Siamesing the base will shorten the runner even farther which
will raise the rpm band higher. The deeper you cut, the higher the
band.

Now, on to the debate. Using non siamesed runners, with a
siamesed base. Each runner in the siamesed base will draw from
two runners connected to the plenum. This will turn the runners
connected to the plenum into plenum area because together they
will outflow the head by a significant amount as to not have any
positive effect on the back of the intake valve which takes us
back to the above paragraph with the siamesed runners. Except
for cylinders 5 and 7. They draw air at the same time so even with
the base siamesed, the runners for those two cylinders will still
act as normal small runners trying to build pressure at the back
of the valve and they will.

You will have cylinders 5 and 7 making power at low rpms and the
rest making power at high rpms. There will be a power imballance
because 5 and 7 will be overfed at lower rpms and underfed at
higher rpms compared to the rest.

Whether this can break a crankshaft at high rpms, I don't know.
A good fluid dampner should avoid that I would think.

Someone with this setup needs to find a Sun scope or equivalent
to do a power ballance test at different rpm ranges to see how
much less power 5 and 7 are making.

I8AStang

I never thought of the firing order on the sbc making 5 and 7 draw air at the same time. That definately could be significant.

Swapmaster

I didn't think of the 5-7 issue either until madmax brought it up one day.