poncho@home

Wouldn't siamesing the base create alot of turbulance unless you had fully siamesed runners? I keep on reading people suggesting to siamese the base 1-2" in, siamese the runners 1-2" in and port match the plenum, but how would that work? Siamesing I assume is designed to decrease the runner length, therefore raising the peak power in the rpm range, right? So how would siamesing the base help unless you had siamesed runners? Can you visualise what I am saying? You'd almost be creating a mini plenum in the middle of each runner!! I'm sure that can't be good...

92 zzz28

The idea behind siamese porting the base and runners is to allow for more air to get into the cylinders. We all know that TPI engines in stock form are not known for high RPM output. The TPI does offer excellent low end response. THe siamesing helps to move more air into the engine so high RPMs are possible and powerful. You will not change your runner length by porting the base, just open it up some to benefit the RPM window of your powerplant.

Did you check out the pictures from the tech article on siamese porting? CHeck it out, maybe those pictures will show what I mean.

poncho@home

I understand the idea behind providing more air for the engine, and the idea behind siamesing runners, but what I don't understand is the idea behind siamesing the base....The air enters plenum > enters individual runners > enter siamesed base > then re-enters individual runners in base?

Can you see what I am getting at?

I took a look at the article, it's talking about siamesed runners...that's ok...I understand that....what I still don't is the people that are only partially siamesing the runners and also the base!!!

Bort62

Siamesing the base Allows for each Intake Runner ( valve side ) to Draw from Both TPI runners.

Simple as that. The deeper and wider you Siamese it, the Better it will work as the restriction for the intake charge being pulled from the opposing runner will be less.

Yes it does Shorten Runner length.


My Siamesed Base Works well, and pulls easily to 5300 RPM.

Havent taken it higher really.

poncho@home

What else did you do that would impact on the engines ability to breath? Or is it all attributed to the siamesed base?

blue86iroc

iTrader: (2)

I'm going to do this mod when my engine gets a little more radical. Right now, the internals are bone stock. What thread did you read on siamesing the base? Here are three to check out:

https://www.thirdgen.org/techbb2/sho...threadid=47263

https://www.thirdgen.org/techbb2/sho...threadid=98960

https://www.thirdgen.org/techbb2/sho...hreadid=140646

GTA91

iTrader: (1)

Well, hell. My stock intake/TB/runners pulled to 5300. Now I've got a siamesed base (3" or so) stock runner/TB, with a LT4 hotcam and other stuff and it only pulls to maybe 5500. I know what this guy is saying and asking. I agree and I think my car would breathe ALOT better with FULLY siamesed runners to match my base! Just IMHO

Bort62

I doubt your car made appriciable power at 5300 RPM with the stock TPI.

FWIW, my (and every other I have compared ) Stock Tach Read ~ 500 RPM high at 5000 Rpm +.

When I say 5300 RPM, that is as measured by Datamaster through the ECM. My Tach said something in the range of 5700 or so.

So while your factory tach said 5300 RPM, you were likely sitting around 48-4900.


But that aside, Of course with a fully Siamesed Runner, its going to be better. That's not really the point.

I can honestly say that I am now Running out of Cam before I am running out of intake. It pulls just as hard and just as high with the TPI as it did with the Performer RPM. Im using a Comp XE262H, wich at 218/224 Is done just in the 5500 RPM range. A Local friend of mine Using a Weind intake w/ holley made max power at 5300 RPM with the same Cam, in the same Motor (Lg4)

236 RWHP Through the L69 Exhuast manifolds. Not Too shabby.


No track Data yet on mine, because it is Raining. Give it a month and we will see.