What year plenums for the L98 are interchangable.

How much gains can be brought from porting the stock plenum. Thanks.

 

I was under the impression that all plenums, runners & intakes were cast aluminum on the L98, the main difference in the set up was the cold start valve, but I don’t believe it affected the plenum more the runners & intake.

 

They are cast aluminum.

I believe you can interchange all the TPI plenums except for '89 & newer. '89 is specific for '89 since there is no hole in the face of the surface TB mounting area as in other years and there is no extra hole for the 9th cold start injector. The plenums for 85-'88 have an extra hole in the plemum which is not present in 89+ plenums. So no I don't believe you can use and 90 plenum in an 86 unless you block off the cold start injector tube in the runner.

Below are some pic of an upper intake I've been working on

Face of an '89 plenum cranked up to 58mm:


Side view of an '89 plenum w/o 9th injector hole (siamiesed):



SLP runner porting in progress:


Plenum with a new face lift:

 

85-88
89-91

 

Wrong again
As stated by engle1147 ;
1989 is one year only model , no cold start but no provision for the MAP fitted to the '90-'91 models!

Check out the 3 different plenums shown here

http://www.hotrodlane.cc/Streetstories/choosingtpi2.htm

 

85-88 will work. Thanks everyone!

 

Engle....what kind of gains do you expect to see with your porting? powerband? what cam are you going to run? I see myself doing what you are doing in the near future with my stock iron heads and stock throttle body and the slp runners. I have already ported my plenum and have a slightly hotter than stock summit g5000 cam and 1.5 rollers. I want to get my RPM up a notch. I may attempt porting the base also.

 

Corvetteplenum.com said if they do the highest porting, it will be like a superram with the stock TPI look. I am anxiously awaiting Engles reply as well.

 

My opinion but just doing the plenum is not going to make that big of a difference, the weak link in the TPI system, runners would be 1st, base intake 2nd, plenum would be 3rd. in a perfect world do all 3 parts same time.

 

Nice looking work

 

Im not looking to break any land speed records with the new setup....the idea is to make the "TPI" all it can/could be while still staying with the TPI (L98) intake setup. I fully understand the limitations of the TPI and don't expect anything above what it will do. The car ('89 vette coupe) is an automatic and used as a daily driver (city 99% of the time). The car will never see RPMs above 5200 and spends most of its time down low so I'm trying to play towards the TPI strengths if you will. Like most builds, this has been a long ongoing process...it has taken many months to collect all the parts needed for my build. Most of the parts for this build have come from CF members or through local contacts...and you'd be suprised at what you can acquire and build for just a few hundred $. The 58 MM BBK TB is a bit of a over kill but I picked up for less than $100 and my stocker is shot. See my personal profile for a current list of mods. This TPI upgrade project will take some time as I'm currently in the middle of and interior swap/upgrade although I did manage to get the SLP runner pictured above fully ported out yesterday.

Other related engine parts that have been acquired and are soon to be installed:
1.6 RR Crane Gold
ZZ4 Roller
V Springs & retainers
Hi-Flow Intake

Items still on the wish list include:
3000 Stall Converter
Trans cooler
Head work
Paint job
NO2 150hp wet kit

"My opinion but just doing the plenum is not going to make that big of a difference, the weak link in the TPI system, runners would be 1st, base intake 2nd, plenum would be 3rd. in a perfect world do all 3 parts same time"

so I have this also:

 

Thanks I'm doing the valve covers the same way as the plenum. It is just dupli color rattle can, some sanding and clear coating. I'm more of a "go" rather than "show" kinda guy and the black keeps the dirt from showing as bad.

 

You and I have the same goals, my car is a 4+3. It's hard to get a deal on a performance base, so I am considering porting my own. I am also going to get a better cam, my last emission test for this car is in a few weeks, so off goes the cat also. I agree that all 3 should be ported, and maybe the heads to make it an even 4. That is a heck of alot of porting.

 

aluminum is everywhere! I bought the intake already ported/polished from a CF member...so I can't take credit for it....I'm sure it has a few hours of porting time on it. One of the water neck bolt holes was stripped in the intake (which I knew about) so I got it for a song. I welded it back up and re-tapped the hole then cleaned up the ports to match the gaskets and added paint and she's ready to go.

 

when you buy runners and stuff 89 is not all by itself, and I think the plenum part is pretty stiff chance.

 

The TPI intakes main limit for high horse power breathing is the long runner length which is good for low end torque.

The Supperram uses very short runners which help the engine breath to much higher rpms.

Unless you dramatically shorten the TPI runner lengths, it'll never come close to the Superram intake.

 

Porting a set of heads is not something I would do on my own, way to easy to mess them up in my opinion. When I had the top of motor apart was thinking about doing the plenum but with stock runners its not worth the time.

 

There are alot of things that I should not try, but I can't help myself. I think I could do a fair job on a light porting of my heads as long as I go into it with some education on what to do and what not to do. If I fail....I am out a set of used iron L-98 heads, which I now own 2 pair of. I have seen many write ups on how to go about doing it....but that makes me far from an expert. I will know alot more about it when I am done (I hope).

 

Having a extra pair is nice, I tend to do my own work also, except I refuse to lay on my back under the car unless its something minor. Good luck with your project

 

Oil changes are minor.