Swampmaster, very interesting explanation of intake filling dynamics; I've had a hard time trying to picture the process.

If I did the math correctly the phasing on the other cylinders is 1 1/2Pi whereas on the 5/7 pair it's 1/2Pi. So the 5 intake is closing as the 7 is opening. In the 5/7 intake pair there will be wave motion phasing to perhaps minimize the potential power mismatch with the other cylinders at higher RPM and perhaps a little detuning of the intake charges at lower rpm.

I know that Edelbrock TES has various dia. header tubes (1 1/2" & 1 5/8") to broaden the tunning band but I suppose that effect is minor compared to the issue here.

But please enlighten me on how a Sun scope can determine balance between cylinders. What does it monitor? Sounds like a great idea.

I have a Mr.Goodwrench friend in Barberton, OH and I think he may have a scope. Since the potential imbalance due to 5/7 reversion/phasing has concerned me maybe I could have him check it out after I get the mod installed. If the scope is a fairly common test apparatus, it would be worth while to have it checked here in NY.

This is a agreat thread. I would realy like to enjoy the benefits of this mod but don't want to put my motor at risk, at least no more than racing does anyway.

 

Im not sure the 5-7 is enough of an issue to worry about. Theres problems in the whole setup with the TB being in front, it will starve the rear cylinders because they are in the back(especially #8 hiding in the plenum corner), the fronts see some starving because of the larger bend they have to make, etc etc...

If I have time and am bored, I'll have a balance test done. I suspect there is going to be some difference but nothing major.

 

Cylinders 5 and 7 are 45* apart. They will both be at peak
draw at the same time, this is the problem with these two.

I know those cylinders will fill differently than the rest but
whether or not it will cause a problem, I don't know.

Durring a ballance test, the scope will cause one cylinder at a
time to miss and then calculate the rpm drop from each cylinder
and give you the percentage of loss per cylinder.

This tells you which each cylinders are weaker than the others
and by how much.

 

I would like to see the results of this test. I suppose a set of
large tube runners would lessen this effect over a set of stock
runners.

 

Hmm, I didn't consider the potential imbalance with a stock intake; but too late now to get a balance check run. I'm about to remove fuel rail and base. But a balance check after the mod seems like a good idea, thanks for the info on how it works.

Madmax, are you talking about a balance test on the motor with siamese base or stock base?

My stock cam with 1.6:1RRs has an intake duration of 213deg at .050". The phase difference on the other three pairs is 3Pi/2 (270deg) so no overlap there. But with a Pi/2 (90deg of crank angle) there is substantial overlap. It looks like #5 will be closing through the point of max flow as #7 is reaching it's point of max flow. The #113 Al Vette heads reach max flow at about .350" lift ar roughly 120deg apart. I wonder if this is why the larger base plenum seems to work well (bigger air resevoir to draw from at high rpm)???

 

The only combo that would have imbalance issues would be a
siamesed base used with non siamesed runners. That is the only
setup that would create an imbalance.

 

FWIW anyone still following along with
all the physics... 8-)

My Alternator died on the dyno Friday, I
tried 3 runs, but the fuel pump was only
getting about 10V and the O2 readings were
in the double-digits by 4000rpms.. I couldn't
even get the motor enough fuel to rev beyond
5500.

So sorry to report that there's nothing to
report... 8-(

Butt dyno is working, but I hesitate to post
that graph... 8-)

mike

 

Mike, sorry to hear about your bad luck. Maybe you'll get another shot at it with a good alt.

 

Well I think the effects will be the same siamese base or not, even if you are running a stock intake the 2 runners take air in from the same spot and I'd imagine theres some overlap going on there as well. There are quite a few intakes out there that have starvation problems due to design, I dont see it as anything significant.

If it matters, I have about 4000 miles on the siamese setup and the plugs all look the same. If there was a real problem, those cylinders would be running rich due to lack of air and it would show up on the plugs. It doesnt.

 

Madmax, what are you using for runners and throttle body?
And did you cut a factory base or an aftermarket?

 

Stock on all counts. No airfoil, didnt even have the EGR wall removed.

 

I had thought of the 5-7 issue a while ago, and had actualluy considered leaving them LTR. Then i came around and talked myself into the idea that at worst 5-7 basically have an h-pipe between them. They still have access to the same amount of runner, but now you're just balancing pressure between the cylinders (and adding volume to buffer) Thats not that different than what the other cylinders have. If anything the imbalance can't be worse than the other natural imbalances of the intake IMHO.

I would love to seea balance test on it though to see for sure. I've heard of that before, i know it's built in on at least some OBD II cars where it will periodically run a quick test while cruising or idling.

 

GM ODBII ECM's do detect misfires and do tell you what cylinder
is doing it but I don't know how it does it. I had a 96 S10 Blazer
in Thursday with a miss and hooked up the scanner and it said
the miss was on #6. Sure enough a quick check found the plug
wire laying on the exhaust all burned up.

I don't think it does a balance test but it probably determines it
by calculating it from the distributor reference pulses versus the
rpm drop, It must figure what ingition pulse the rpm drop is on.

Any large roll away type scope should do a balance test. I had an
old scope that I sold a couple of years ago that would do it and it
was ancient.

Snapon sells a hand held ignition scope that does that kind of
stuff but I have not bought one yet, it's about $2,000.

 

Yeah, OBD II takes use of the crank sensor and the cam sensor to determine what cylinder is not pulling it's weight when a misfire is present. It can use the same sensors to perform a balance test. But it doesn't really do a balance test on its own. It just logs how many misfires it accrues during run time for each cylinder. IIRC (and it has been a while since I have messed with an OBD II car), the system can indeed do a balance test, but you need to interface with the PCM with a Tech 2 or similar scantool and run through the test. AFAIK, the PCM doesn't randomly run balance tests on the engine on its own.

 

This is by far the best thread I have ran into yet. I'd like to start off thanking all of you guys that are putting in the time and effort to try new things and share the results with the rest of us. All of the info seems to be geared towards a naturally aspirated engine. What effects would doing the siamese base have with a supercharged engine? I have a stock bottom end, a ZZ4 cam, and stock TPI except I have 30lb injectors. I'm putting on some TrickFlow heads this weekend, and I'm considering doing the siamese porting. I have an ATI ProCharger with 9psi boost. Would this mod be any good for me?

 

you are in uncharted teritority
since you are under boost you really won't feel much if any difference.
it is possible that it could but i really don't see it doing much of anything since you are pushing air in already.
i don't think it would hurt anything to try if you want but don't expect huge gains or anything
let us know how it goes if you decide to try it.
Andrew

 

you guys wanna talk airflow, read this pdf i have on my server
http://www3.bc.sympatico.ca/nickscorvette/AirFlow.pdf

its 373k and you better be well versed in math to understand the formulas. Im working on an engine simulator similar to desktop dyno, and ive read more about volumetric effieciency and thermal dynamics than i ever wanted to know.

Also read this
http://www.seas.upenn.edu/~meam100/handouts/Thermo.pdf

 

Well I got started on a spare intake a few days ago. Here's a pic of what I had done a few days ago. It is almost all done now..... Just matching the head ends up to a Felpro 1205 now. Just thought I would share

 

Looks good Matt. How deep did you go and what are you using to cut? For anyone that cares I'm going 2.5 to maybe 3 inches, so I guess we'll see how that works out if I ever get the car going again.

 

here's what i've done. i left the divider at the runners because i'm not doing anything to the runners. i did cut the divider all the way to the head side. left the divider at the head as you all did. to promote smooth transition into the head.

 

Thanks. That is 4" deep from the runner mounting surface to where the divider starts. I used a carbide grinding bit (just a generic one from the local hardware store - actually a kit with interchangeable heads and two different length shanks for the bits to mount to). I did the entire intake ( I finished it up today) with one conical bit..... I used gear oil to lubricate the bit and it worked perfectly. The heavier oil stays on the bit better and keeps the AL from sticking in the teeth and cools the bit down so it doesn't get dull.... My plan is to smooth out the bottom of the SLP runners on my car so the transition into the base plenum area is clean. I might even take the upper divider walls of the SLP runners down a bit more as well. I took them down about an inch from the way the come when I built the engine last spring....

I had actually only planned on going like 2-3 inches on this intake but after seeing the pics of Mike Davis' manifold (and knowing how well his car performed), I just couldn't keep the grinder off of the piece.....hehe. I just kept grinding and grinding until it looked to me like the heads had really clean "views" of the runner openings.... I have the whole thing all cleaned up now and I ran a wire wheel through it as well to smooth it out and it looks awesome!! It's a good bit lighter than when I started as well . I'll try to post another pic when I get a chance (no digi camera, myself - I borrow from friends from time to time ).....

Unfortunately it might be a while before I get it on my car as I really want to do new lifters while I have the intake off and I am totally out of money.... I just had to pick up a fuel pump and a new MAF and that stuff took pretty much all of the money I had, so.........

 

i have problems with mid range torque exscpecially in 3rd gear what can i do to increase that torque. Thanks

 

here's the dyno of mine. you can see at 3500 rpm it jumps up. then still peaks at 4400 because of the stock runners.