After doing a search on siamesing the intake plenum to match slp runners, I came across 1bad91z's post on why it should not be done. Something about an slp engineer saying that it would cause uneven air flow to the cylinders. However, I have read many other posts from members who have siamesed the plenum.
Is siamesing the plenum okay or not?

 

I would not do it. I'm going to have to side with SLP engineering on this one!

Just open up the ports (port match to TPIS big mouth gaskets).

 

Not only did I siamese the plenum, but I did the BBK big tube runners and the intake manifold too.

I even removed most of the divider walls in the runners and plan to cut them open to get at the remaining walls.

My next plan is to buy another plenum, cut out the underside and have it re-welded about 2-1/2" lower to increase the plenum volume.

Check on this board for the thread that MadMax began to get the experience of others, some excellent photos and comments too.

Just my experience.

Jake

 

Jake, let us know the out come of increasing the size of the plenum. Allen

 

only problem with that is the EGR and the regulator are in the way. EGR isn't a problem. but the regulator you have to have.

 

EGR is a problem,mrr23. You can't jsut remove it, or else you will have detonation problems. Increasing the plenum volume sounds like a lot of work for nothing. I doubt the plenum is the weakest link in anybody's intake track.

 

I think that's a great idea. No need for EGR and you can just relocate the regulator. Let us know how it comes out.

 

Yes need for EGR. The ECM advances timing when it applies EGR, without it, the combustion chamber gets too hot, detonation occurs, and you have big problems on your hand. EGR doesn't affect performance when you are flooring your car, so it's not hurting quarter mile times or seat of the pants enjoyment. So why cause the problems associated with dumping the EGR system when you could just leave it and be fine.

 

How does the ECM KNOW when the EGR valve opens when the EGR valve is 100% mechanical? We are talking about a TPI and/or TBI set up right? I will agree with you (partly) on the combustion chambers getting "hotter" but I personaly havent had problems with detonation on cars in general. Just my .02. Hopefully someone WILL correct me if Im wrong....

Dan

 

The ECM operates the EGR Vacuum Solenoid, which opens the mechanically operated EGR valve, so its not 100% mechanical.

 

thanks for correcting me..
never knew that...

Dan

 

Further, the ECM doesn't have the ability to know if EGR is actually flowing. So it just assumes that when EGR is commanded, EGR flows. If you just pitch the EGR valve, the ECM can't tell.

Scenario: You are cruising on the highway: 80 MPH, 2500 RPM. Ignition timing is at lets say 40 degrees. EGR is commanded at 50% duty cycle. Since the cumbustion chamber will now cool down, the timing is advanced 2 degrees, putting timing at 42 degrees. BUT YOU PITCHED YOUR EGR VALVE IN THE GARBAGE CAN! Who needs it, right?

Since there is no EGR flow, combustion chamber temps do not cool down as expected but timing is still advanced. Detonation starts to occur. So just retard timing back to 40 to make it go away, right? Wrong! It is a lot harder to stop detonation than is is to cause it. So timing is retarded maybe 8 degrees to stop it, putting total timing at 34 degrees BTDC. Because of this, gas milage is poor at this very moment, as well as decresed performance.

So in trying to gain performance, you have actually hurt performance.

 

A great link, check it out.
Understanding EGR

 

just burn a new chip, simple. How would it cause uneven airflow anyways?

 

Cause the divider walls separate the air-flow to the front and back tubes of each runner. Removing the divider wall will throw more air torwards the back tubes of each part of the runners. (Back tubes that will get more air, are cylinders 3,7 and 4,8). Kinda similar to the air flow distribution problem of the LT-1 (or mini-ram style) intakes.

The above information was told to me over the phone from an engineer at SLP.

 

This topic still makes no sense to me. The air is being drawn into the runners not fed into the plenum through the TB, therefore the theory that air will be "thrown" towards the back runners makes no sense.

Each runner draws the air into the cylinder from the plenum, the plenum maintains a certain amount of air to fill the needs of each runner, and the TB needs to supply enough air for the plenum to do just that.

If what the SLP "engineer" said was true, then what is the purpose of the "siamese" part of the runners? I would assume it's to decrease runner length and increase plenum volume, no?

 

First, your ecm verifies the egr valve is open by way of the temp sensor on it. It isn't very reliable, hence the false code 32's coming up every once in a while, but it does have a way to verify its operation. Regardless, you'd be a fool to remove it w/out a custom chip, and in that case it wouldn't be a problem at all.

Second, air in motion has inertia and likes to take the straightest path possible regardless if it is being pulled or pushed. This is going to give more air to rear most ports of a siamesed intake, although I can't imagine it would be enough to cause problems. As one bad Z said this would be similar to the situation in a LT1 or similar style intake, but I wasn't aware of these manifolds having air distribution problems??? I was under the impresion that these were alot more efficent than our TPI's at doing what they do (distribute and meter air and fuel).

 

is siamesing the plenum okay or not, let stick to the question asked. I have SLP runners and I would like to know what would be best for flow.

 

Thanks for all the replies, but I concur with SLP-GTA. I port/gasket matched my intake, heads and runners and I'm about to pull my plenum. I still would like to get more opinions.

Anyone siamese the plenum and have problems with the engine?

 

Well, I can only speak for myself.

I took the advice of SLP and I did the following:

Port matched the Plenum's TB openings to 58mm bores (matching my throttle body) and knocked down the EGR walls in the front of plenum.

Port matched the openings on side of plenum to match TPIS big mouth gaskets (still leaving plenum runner openings walls in tact).

Port matched the openings on top-side of runners to match TPIS big mouth gaskets and finished siameesing the top part of runner about an inch further back from where SLP stopped.

Port matched bottom side of runners to TPIS big-mouth gaskets (going as deep as I could into the runners).

Port matched SDPC intake base to TPIS big-mouth gaskets (going inside the intake as deep as I could).

And finally, port-matched bottom side of intake base to match my ported vortec heads.

As far as siamesing the plenum, that's your call. I wouldn't do that if I were in your shoes though. I would do the above (like I've already done).

 

I think you are very confused about this probably due to lack of experience in disabling EGR systems. Your advice may scare people from even trying it, and worse yet continue on the trail of misinformation by telling others the same thing. I don't feel that it's best to post up information like that when you've never tried it and do not know. For those who have blocked/disabled the EGR, we already know it's completely harmless and will cause zero problems. Benifits range from lowering the intake charge temperature to keeping the intake, chambers, and plugs cleaner.
Thank you.

 

305sbc-
Sorry, but the tone in your last post is just asking for a flaming.

First off, what good is a lower intake charge temp due to the removal of the EGR system (which I am not saying is even true) when combustion temps were actually lower with an EGR system installed and functioning correctly?? Ask anyone who knows, from personal experince or just from research in the right places, and they'll tell you that you'll actually pick ZERO hp by removing an EGR system off a car that was designed with one in mind in the first place. Besides, JakeJr isn't trying to tidy up the inside of his engine by minimizing carbon build up, he is trying to delete the EGR system to free up room under the plenum.

Telling someone it's 'harmless' to pull off a component that is vital to drivability without telling them the required steps to do so correctly is a pretty lame thing to do, regardless if you didn't know any better when you did it to your car. I suggest you and anyone else who isn't clear on what this system actually does takes some time to do some reading in the articles below (305sbc-I have noted the sections in those articles that specifically counterdict what you said, thank you.):

Bottom section entitled 'Other Notes':
http://sethirdgen.org/egr.htm

First section entitled 'EGR Theory':
https://www.thirdgen.org/newdesign/t...diagnose.shtml

Now back to the actual point of this post. Many folks on this board have siamesed their intake and reported a gain in high end hp (a search on this will keep you busy for a while). With the risk of pissing other people off by telling them it's the wrong way to go about it, I don't think this is a good idea. The fact of the matter is that the rest of our car (TC lock-up, cam, heads, shift points, gearing, ect.) is designed around low end torque and not high end power. So unless you have modified the rest of your combo (or plan to) to make use of a higher powerband it's pointless to only make one part capable of it. If you have changed the intended range of your combo than you obviously spent some money to do it and you should continue to spend money on an intake that is designed to make power at a higher engine speed(ie. HSR, MINI, SR, RJ, ect.) rather than butchering one that wasn't. But this is just my opinion, and I do understand the fun of trying to work with what you have out in your garage, but if you want to put together an effecient combo you need to use components that work together. So in summary, for the people that started this post, do a search. I ahve read through many a long @ss post that give the ins and outs of doing what you are talking about. Another good place to get some theory behind what is going on inside your intake is here:

http://www.grapeaperacing.com/GrapeA...ntaketerms.cfm

 

Does anyone have any dyno # on siames the plenum and runners. It sounds too much work for maybe a 4-9hp gain. I understand what 1bad91z is saying. I know more air into the engine make more power, but will making the runners and plenum larger decrease the velosity of the air if you don't have the right size cam to pull the air in?

 

Well it's simply because lower intake charge temp increases power output. A higher combustion temperature increases power output. A cleaner combustion chamber allows for higher power output before detonation sets in. I'm not sure I can simplify things any further for your understanding. If you don't get it then I'm sorry.
If I contradicted something else posted on the internet then I'm sorry for that too. I'm not going to go read the endless material and arguing that is posted out there. I'm satisfied with simple test results of others and myself of which I think is credible. I'm sorry to say that you do not fall into that catagory in my book, so sorry again.

 

Its estimated by several companies that siamesing and port matching the plenum to the runners, and port matching the intake base is worth 20 to 30hp.

I don't know if thats peak gain, or at some higher number where flow is really limited.

The estimate for the Arizona Speed & Marine Siamised runners (same as TPIS siamese large tube runners) is a little more than 25hp and 30lb/ft

 

[SNIP]Originally posted by Dustin Mustangs
[B]305sbc-
Sorry, but the tone in your last post is just asking for a flaming.

Besides, JakeJr isn't trying to tidy up the inside of his engine by minimizing carbon build up, he is trying to delete the EGR system to free up room under the plenum. [SNIP]

Just for the record, I removed my EGR and A.I.R. systems years ago along with all the associated hoses and solenoids, etc.

Zero problems.

Jake

 

I read an article last year in one of the mags where over $1,000.00 was spent on a complete "high flow" exhaust system. In back to back testing the engine only picked up 9 HP and slightly less in torque.

Considering that modifying the plenum and runners is virtually cost free; doesn't sound like a bad deal for 4-9 HP.

Most of the velocity and other problems (i.e. loss of low end torque) that use to be associated with open plenum mainfolds, etc., have been resolved due to the more aggressive camshaft ramps that are now being used.

Jake

 

I don't agree with SLP. They also said the casting burrs in the runners were to "reduce turbulance"..

The FACT is SLP's Quality control sucks, the guys on the phone know next to nothing. I've called and asked the same question to 3 guys to see what I'd get, and I got 3 totally opposing answers. Its useless calling them. Most of the stuff they sell, they don't even make (i.e, their camshafts), and the stuff they DO make (the runners) blows goats out of the box.

Now, as far as the physics and airflow are concerned.

I'm not gonna stand up and say "I know exactly what the deal is", but I know SLP doesn't. I highly doubt they spent any time comparing this stuff on a flow bench.

-- Joe

 

The guys you most likely spoke to are just counter sales guys at SLP.

I asked for a manager and that manager transfered me over to one of the head guys in the engineering dept. I left a voice mail and that engineer called me back. This was a little over a year ago though.

He said to smooth and port match everything to the biggest gaskets I could find, but he told me not to siamese the plenum walls due to the explanation he gave me in one of my above posts. I took his advice.

And yes, my runners looked like crap out of the box too. I spent almost ten hours porting them and cleaning them up.

 

I tell ya what.

I have a couple plenums.. I'm gonna run both. A siamesed one, and a non siamesed one. And i'll leave feedback on how they worked.

-- Joe

 

I was told the exact same thing. They didn't have an answer for the terrible amount of core shift though.

 

It's just an overall bad product.

But anyway. I siamesed my plenum. Runners are siamesed partially.. I'm not sure if I should just bring it down to the divider, or gradually divide it.

I also hogged out my edelbrock baseplate last night. Not "finished" (ports are cut but not completly round and blended). I'm curious if there is a good "port diameter" for the baseplate runners.

Next, I gotta match my felpro 1205 gasket and blend the walls.. Then polish everything up and bolt it back together.

 

here's a dyno showing going from stock runners, siamesed stock base and lt1 cam to the fully siamesed (cut divider completely out)SLP runners, Edelbrock base and zz4 cam. http://www.fl-thirdgen.org/mrr23/ima.../dyno14-15.jpg

oh yeah and this was without an EGR. and of course my HSR without an EGR runs 12.13 @ 112. and of course i'm sure john force has an EGR on his motors.

 

That NA?? I'm running a blower. trying to get some restrictions out of the intake to cut down on loss.

-- Joe

 

no, that was on the HSR and 150 n2o. but, it will be soon with the 383 i'm putting in.