Yorcci

I have siamesed the openings into runners from the plenum and I also matched the throttle body and plenum to the gasket. This is what I have done already at the plenum side:



The throttle body from this:



into this:



Then, I found a different gasket for the TB; with the opening



So, is there any harm or downside, if I take out the visible aluminum outside the gasket, between the openings at the plenum side? Increased turbulence or less turbulence? I'm guessing less turbulence, but does anybody know?



I should lift the engine back into engine bay by the end of the week and I'd like to have 'everything' done before Friday. (There are other minor things yet to do... like installing lifters, pushrods, rockers, the intake manifold etc., but that all takes just a few hours, no biggie )

leesvet

I would think that divider/partician is necessary for the air metering for that center passage. Thats idle control air I believe, and removal could effect how well it can manage the idle.

I've never seen it totally removed. No benefit as far as flow...thats limited by the TB bore and what can possibly pass thru the baseplate and head runner. Even the ductwork ahead of the TB has something to say about how much and how fast the air flow is..


The plenum work does look good !
is that a stock TB? if it is, that would be the limiting factor for that engine.
Find a good 52mmTB. A 58 is pointless unless you have bored it to 400ci or more. Be prepared for some "tune" changes...

cv67

Ive removed it plenty of time no problems. Did it help, who knows without back to back testing. Probably not is my guess

vetteoz

Only the 85 - 88 intakes with CSI have that port that feeds air through a runner cast on the underside of plenum , down a tube on drv runner into holes in the ports of the base
Was deleted on the 89 - 92 non CSI intakes and the air from the IAC dumped out into the plenum directly behind the TB blades so obviously not related to idle control

Yorcci

Yes, that's the IAC opening at the TB, but I just don't see how that divider would/should/could have any effect on the idle air flow, since the needed air isn't that much.

Yes, it's stock TB. As for the limiting, these flow test numbers beg to differ http://www.gmtuners.com/flow/index.htm

And yes, I'll have it tuned, since there are some other modifications also, like bigger runners, porting every inch from plenum, runners and baseplate/intake manifold and gasket matching.

Yorcci

Thanks for the info! I've wondered so long time about those small holes in the baseplate (In this picture in the foreground):

Cliff Harris

In the first picture, the holes on the right just behind the gasket are for the EGR. There was a bump in front of them to create a venturi effect to suck in the exhaust gases.

My recollection is that the triangular-shaped opening between the throttle bores was for the cold start injector. Somebody else needs to verify this...

383vett

Minirams don't have that divider. I would think it's not necessary. Only back to back testing will give the answer.

vetteoz

As I stated above , was only used on the CSI equipped intakes so reasonable to assume it directed air there to dilute and distribute the fuel from the CS injector when cranking over

Yorcci

100%

Just wanted to get the answers the easy way, if somebody would already have had some hard data...

Anyway, I'll probably just leave it as it is, at least for now. There are more important issues, which demand pretty urgent attention. For instance valve covers

Yorcci

No EGR on my machine...

383vett

I'd drop all work on the plenum divider immediately and address the valve cover problem. Those things are UUGGGLLLYYYY.

cv67

Off an 89 no cold start injector.
Pretty sure it takes EGR gases from the small passages in the runner (and also from the base)
Its been awhile since Ive worked on one so the memory is foggy