TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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why is there a tpi plenum difference [look at pic]
Hello
I was just looking at some pics when i noticed the the grooves on one plenum extended much farther than the grooves on another.if you look closely on one the grooves end at the begining of the first two runners. and on the other the grooves go even farther than that.
I am not sure as to why this is. maybe it is a vette/camaro, bird difference or maybe they changed the look slightly one year. All that i know for sure is that both my 89 iroc and 90 gta have plenums with grooves like the blue one.
It isnt anything important but i was hoping just out of interest if someone could shed some light on the subject.
I don't see any differences in those pictures. But in the later third gen years GM was phasing out the L98 parts and switching everything over to the LT1. So when the factories ran out of L98 parts, some third gens wound up with LT1 runners.
The MAF systems have a different plenum than speed density systems. The difference in grooves made it possibly to quickly tell what year car it came from. The longer grooves were used from 85 - 88, and the shorter were used on 89 - 92. The other thing that made them different is the earlier plenums had a passage for the cold start injector, they also had a cut out in the front for the IAC. The later plenums did not have this, in 90 - 92 the plenums got a MAP boss for the map sensor.
I don't see any differences in those pictures. But in the later third gen years GM was phasing out the L98 parts and switching everything over to the LT1. So when the factories ran out of L98 parts, some third gens wound up with LT1 runners.
*Edit*
I just noticed you were talking about the plenum.
Maybe it's the same story?
Yeah, they also started using LS1 parts on the last couple years of the LT1 motors because they were running out of LT1 parts.
Yes, to tell the difference between the MAF and SD cars. Maf had longer ribs and were slower, and the SD cars were shorter ribbed but much MUCH faster.
I don't see any differences in those pictures. But in the later third gen years GM was phasing out the L98 parts and switching everything over to the LT1. So when the factories ran out of L98 parts, some third gens wound up with LT1 runners.
I don't see any differences in those pictures. But in the later third gen years GM was phasing out the L98 parts and switching everything over to the LT1. So when the factories ran out of L98 parts, some third gens wound up with LT1 runners.
well, that's what i was thinking but someone posted before seemed to imply that they seperated from the intake like the tpi runners do. didn't sound right.
I dont think the difference is a maf/map thing. MY 89 iroc tpi [maf] and my 90 gta tpi [map] both look the blue tpi pic. The plenums are slightly different because the is a hook up for the speed density on the rear passenger side of the plenum but the grooves are the same.
I side the 89 to 92 tpi plenum statement. I know for sure those look like the second pic .. but as for 85 to 88 i havent seen a tpi in one of those for a while so i couldnt be sure.
so then really all we now need to know is what 88 has.
Speed
Cast into the underside of the plenum, there's an encircled number, which might mean something. From an '85 in a junkyard, that encircled number was 85. And one I have in my garage for porting has an 88 on it(though I don't remember what year car it was from).
But assuming that number relates to the model year, then the 88 looks like the one on the right, whereas my '87's, like everyone else's '87, is like the one on the left(the better-looking of the two, IMO). But I've never had my '87's plenum off, so I can't confirm that its number is 87. Maybe someone else can though.
So if that's correct, then that also would make the SD/MAF plenum comparison inaccurate.
There are several differences over the years of the plenums between the length of the grooves on top, which was more or less for astetics, to the different set ups such as ones equiped with the cold start injector or not, as well as MAF and MAP. I belive there are 3 or 4 variations, and the Corvette had another design if I recall.
__________________ 87 Camaro Z28 Waiting for LS1/4L60E transplant. Tons of TPI parts for sale 2009 Malibu LT 2.4: The comfy daily driver www.GMInsidenews.com www.NJFBOA.org
There are several differences over the years of the plenums between the length of the grooves on top, which was more or less for astetics, to the different set ups such as ones equiped with the cold start injector or not, as well as MAF and MAP. I belive there are 3 or 4 variations, and the Corvette had another design if I recall.
There were three different plenums used through the TPI era-
Quote:
The plenums break down into three groups--'85-88 (left), '89 only (middle), and '90-up (right).
Quote:
The fuel inlets and returns differ between the different years. The '89-91 Corvette fuel rail (left) has a female 16mm passenger-side inlet and a female 16mm return. The '85-88 Corvette (middle) has a female 16mm passenger-side inlet and a female 14mm return. The '85-92 F-body (right) has a female 16mm driver-side inlet and a female 14mm return
Don't forget the three lower intake manifolds-
Quote:
Three intake manifold styles were used on the TPI equipped engines. The '87-91 Corvette intake on the left used a heat-riser tube off of the passenger-side header and has a water crossover at the back to relieve hot spots on the back of the aluminum heads. The middle intake was used on '85-86 IROCs, T/As, and Corvettes with cast-iron heads with outside valve-cover bolt holes (early-style). (The two center bolts on these two intakes are at the same position as the end bolts and will fit the early head-bolt pattern.) The intake on the right was used on '87-92 IROCs and T/As with cast-iron heads with center-bolt valve covers. The '87-95 intakes with the later cast-iron head-bolt pattern can be machined to fit the early bolt pattern. If you want to run Vortec and Fast Burn-style heads, GM and S&P have new TPI intakes to adapt a TPI to both.
So, maybe it would be easy to confuse who had Vette parts versus F-body TPI parts. They weren't always the same!
Quote:
All the passenger-side TPI tubes (top) for all '85-92 models are the same. There are two different driver-side tubes. The '85-88 units (left) had the ninth injector port (arrow), while the '89-92 F-body and '89-91 Corvette tubes (right) didn't.
The maf to sd is mostly true, except for 89. Check out Chevy TPI swapper's guide on page 20. It gives you the run down. There were actually three upper plenums made from 85 - 92. 85 - 88, 89 and 90 - 92. 89 - 92 had shorter fins than the earlier plenums.
Hello
I was just looking at some pics when i noticed the the grooves on one plenum extended much farther than the grooves on another.if you look closely on one the grooves end at the begining of the first two runners. and on the other the grooves go even farther than that.
I am not sure as to why this is. maybe it is a vette/camaro, bird difference or maybe they changed the look slightly one year. All that i know for sure is that both my 89 iroc and 90 gta have plenums with grooves like the blue one.
It isnt anything important but i was hoping just out of interest if someone could shed some light on the subject.
Speed
Here is a link that most of the ID storys seem to originate from:
