OK, so I've been looking around, and it seems like the best way to make power for free with the TPI is to cut up the Plenum and intake, right? Well, maybe not technically, but you guys know what I'm talking about. Siamesing everything, porting and polishing everything, (see madmax's intake manifold, holy ***!) etc.

Well, I was looking at a site earlier today (I forget whose it was, a 91 maroon Formula with yellow lettering on the doors, looked pretty sharp), and saw the TPI plenum up close for the first time.

HERE'S THE ACTUAL IDEA: seems to me, if you're going to bother siamesing (is that a word?) the runners, why not siamese the plenum? There's what, 10 holes, in pairs of two? TB, then two pair on each side, right? So what if you cut out the middle section that seperates the two holes in each pairing? I've never had the plenum in my hands, or seen the gaskets or bolt holes, etc, so this may be a total pipe dream, but could it maximize airflow? I mean, why have siamesed runners if the air has to go through 2 seperate holes to get there?

Just a thought, let me know what you all think.

-Reno

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89 Formula

 

That's a good question. Anyone?

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'87 Trans Am:
(Engine)
305 TPI
180 Degree Thermostat
JET Fan Switch
TB Bypass
Accel 300+ 8.8 Racing Wires
Accel Super Coil
Bosch Platinium Plugs
Custom Ram Air with K&N
Removed Emissions Equipment & Cat.
(Stereo)
Full Kenwood Excelon System

Member at kyfbodies.org

 

****** on a frigging *****!!!! I just read that massive thread on madmax's siamesed stock TPI base! Holy ****! Sorry, that was some wild stuff there for free! Speaking of porting maniacs...

Anyway, could someone explain to me loss of torque in a TPI unit with freer breathing? I've been thinking about SLP runners, siamesing both ends, siamesing the paired ports in the upper plenum, and now, a dyno proven gain of siamesing the base. Other then about $500 in dremel bits, what would the negatives be here? I'm just not seeing ANY after reading madmax's thread (which, BTW, should be edited into a tech article).

So, who can shoot this idea down? Will it provide substantial gains on a stock 350? Madmax did it with stock runners, too, seems like a killer sleeper mod...

-Reno

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89 Formula

 

do you guys have the website for madmax id like to chech this out

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91 formula
305 tpi
borla exhaust
white face gauges
home made cold air
tpis airfoil

 

It's here on the boards, check my post about the uncluttered TPI engine bay, and there's a link to this massive thread about it.

-Reno

 

Check on Dan's (ws6transam) reply to siamesing negatives here: https://www.thirdgen.org/messgboard/...ML/002392.html
As for connecting the adjacent runners, of course you would want to do that. Here's what I did:
There are more pics and an explanation on my page.

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Bob '89 Ram Air Formula 350
Last(lost)Member of the Elusive Great Lakes Crew
My car's homepage

 

Yup, that's what I'm talking about. Would it help to do it at the TB ports, too?

Also, what a link! Daniel's response seemd more theological/philosophical then technical! Lots of interesting ideas there...

-Reno

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89 Formula

 

Whoah, RCR, just checked your site, excellent idea with the "air foils" in your intake! Man, you TPI guys are licensed lunatics with dremels, huh?

Dumb question: What does the lower end of the stock runners look like? Obviously, you can siamese the top end a bit, but what about the lower? If you could do both, why buy aftermarket ones? Just a thought...

-Reno

 

I don't think it would hurt or help to remove the center between the throttle body, as long as the holes match the tb size.

I run a setup almost identical to madmax's and with the zz4... I have no complaints on bottom end torque.

 

Well, I see it like this.
its good to run a dremel on the inside of the plneum just to get rid of casting flash. The smoother it is, the easier the air flows. Thats easy enough to understand.

The intake base. I like the siamessing idea. Like I was saying earlier I am going to do that to my 87 with the ZZ4 cam and see how it comes out.

Id skip the stock runners though. I dont remember the diameter but in comparison to the aftermarket ones, they are tiny. The best ones to get I think, would be the Arizona Speed & Marine semi-siameesed runners. People seem to have good results with those.

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-86 IROC
a few mods
this years goal: 10.50 @ 130+ mph
-=ICON Motorsports=-

 

I wouldnt cut them out completely, unless:
On the part where the TB attaches, you are running a monoblade TB. Otherwise, there is a sharp edge (90 degrees) left by the TB with the missing section. Ideally, you want it to taper to a knife edge.
The part where the runners are, you wouldnt want to do that unless you are running siamese runners or you round the edge of the runners facing the airflow. It would be hard IMO to get a good transition there from the runner to the plenum if you cut that part out and rounded the edge of the stock runners. Since you were thinking about siamese runners, cutting it there will be ok.

 

That's exactly what I did to the plenum and runners. No loss of torque and probably big power gain with the cam I have now (can't confirm though)
Rick


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'88 GTA 350 (very rusty)
Check out my car here:
www.fortunecity.com/silverstone/brabham/42/