Morning all, got bogged down with post searching and
I have a few basic questions about siamesing the runners:
1) What exactly is it, and how is it done?
2) What does it accomplish, and do other mods need to be done to make it work?
3) Any issues with emissions/computer?

Thanks in advance, Joe
'85 stock coupe

 

I'll attempt to explain, as I have done my intake manifold, and soon to do my runners. It si simply taking a die grinder or dremel and making the space between the openings more shallow. Like creating a pocket for the air prior to entering the openings. I have my intake manifold siamesed 5/8 ". It did make a difference with my LTRs in the upper 4K rpm range - pulls a little stronger for longer. Now with the runners, there is a weld behind the openings on each end that you can see, and I wouldn't go past that. The welds are further away from the openings on the manifold end as opposed to the plenum end, so you can go farther in down there. I'm going to practice on my stock runners, then go after my AS&Ms. Other folks will give a better explanation I'm sure. Oh, it gets more air in, a larger aftermarket manifold (or siamese your stock like I did) and long tube headers would be compliments to the mod.

 

Thanks jmrl98!
Thinkinh about finding a spare intake, plenum, & runner set and experimenting with this without taking the car out of commission now that spring is coming. My original plan was to clean up and polish the exterior on a spare set and bolt on at a later date, but I thought it'd be interesting to do this as well.

 

This is not siamese specific, but you may like it.
http://forums.corvetteforum.com/show...ed&forum_id=48

 

GOOD STUFF! Gettin' motivated!!!!

 

I have some pictures of my intake that I am working on would like to post them but dont know how, Can I send then to someone who can?

 

You can host them on www.photobucket.com or email them to me
kalthoffpools@yahoo.com, Ill put them up for you.

 

http://www.geocities.com/softtailduece01/
http://www.geocities.com/jgkov/index.html

 

[
Tried enlarging it, may be a little fuzzy.

 

I sent you a PM so be sure to check it when you can.Thanks!

 

I used a 5/8" dia carbide rasp with a millwaukie electric die grinder and cut down the web between the ports i used the info that Vader posted as the basis for the mods I made. I tried to make the web more square at the back instead of making it pointed.

 

That is what I did to mine. Allthough no one believes me it was good for around 20 rwhp and 17 rwtq over my stock intake on my 383.

Before...


After...

 

I think it could be smoothed out some. What kind of cutter?

 

i'm sure there will an argument against what i say but, in my opinion, with posted numbers on this forum, you can come close to a super ram results by porting the original components. definitely the stock intake is close to the aftermarkets after porting. the runners can be ported, but cannot be shortened which causes problems with horsepower gains. the plenum can be ported, but the high pressure ram effect on an sr can't be duplicated. i think the drawbacks of the plenum and the runners can be somewhat offset by siamesing. but as far as i have read on the net, siamesing too deeply can destroy bottom end, but done correctly can enhance top end horsepower without a corresponding negative effect on bottom end.

i have logically reasoned why siamesing works. this is my opinion, and treat it as such, and i'm only posting it because i've never seen a logical explanation for its effect.----

siamesing (especially the plenum and upper runners), allows the intake valve of the charging cylinder to borrow, or steal, air already pulled down into the runners, and with less resistance and air beyond what is entering the small stock plenum, pull it into the charging cylinder. the lack of resistance may allow the charging cylinder and valve to pull more air than one that is operating in a higher friction environment. this probably results in more air and higher velocities per stroke. i may be wrong, but i don't think i am. logically, this process works on the same principal as polishing the intake surfaces: the less resistance, the faster the flow. also, if the plenum is fully siamesed, it allows the single runner to have a pull at a larger area--this is especiacially important since the airflow must slow as it turns the ninety degrees to enter the runners.

that being said, it is also probably true, that if you do the same amount of detail work on aftermarket products, then you will also see an increase in their flow too. all of this is dependent on wether you have a cam, heads and exhaust that will support that flow. it should be understood that you cannot slap a high flowing component on an engine and expect it to perform to its advertised specs. the whole system must be designed for a specific flow--or the system will not realize it. (i hope i covered my *** with that one).

that's all i've got.


froggy.

p.s.
here's a site that shows how close the stock intake is to improved ones. if these numbers are correct, a small amount of porting should bring them up to aftermarket spec. it also shows the difference in runner lengths and...

http://stealthram.com/flowcomparison.html

p.ss.
smooth flow is important-it equals speed, and speed equals velocity. that is why all transition surfaces should be smooth. the only part that should encourage turbulence in a dry tpi system, is the part after the fuel is introduced--which is why high swirl combustion chambers are so important. in general, the greater the swirl, the greater the atomization, the greater the power gained from the ignition of the fuel/air mixture.

 

"siamesing too deeply can destroy bottom end, but done correctly can enhance top end horsepower without a corresponding negative effect on bottom end"

I have my base only done the same as softtailduece01.
Plenum has TB opening out to suit 58mm , everthing else stock.
95,000 mile 350 (heads never been off ) with zz4 cam and LTs has run 13.1 / 1.84 60ft times so torque is still there.
Never been near dyno , but enough runs to know what it does.
SLP runners made no noticible difference to above combo so in my mind opening the base has the same effect in improving airflow