1990 Throttle Body on 2g Intake

[Cox Abele]

I have a 90 Laser that I bought without a head. I had a 2g head around that I had machined to work on the 6-bolt block, so naturally I'm also using a 2g intake manifold. Now that I have the car running, I have a massive problem with the parts combination.

As it turns out, the 2g intake mouth doesn't have enough material to allow a proper seal of the 90 TB's FIAV and IACV veins, resulting in a massive boost leak (if I can ever get to that point) but also idle surge issues that don't allow me to set idle or CAS timing.

Has anyone ran into this before, and is there a method to seal the flanges without disabling the IACV?

 

[1990TSIAWDTALON]

My 90 TB (fresh rebuild) wouldn't seal on my Evo3 intake so I had to go with a different 1g TB and wire the TPS and FIAV from it to the 90 harness. I don't know what year mine is I just know it is a 1g. I had to hog out the intake for the bore size so it would open up all the way too. My 90 TB leaked horribly for the same reason yours is. .

 

[Cox Abele]

I already opened up the intake, so I'm good there. I've read a few bits and pieces indicating that if I want to run the later 1g TB that I'd also need to install the later fuel rail.

I'm considering getting some sheet metal and making my own plate in the shape of the 90 TB gasket, then sandwich between the TB and intake and a pair of gaskets. Besides welding and having the surface flattened, I can't really think of another way to make it work, but I'm all ears.

 

[1990TSIAWDTALON]

I run the 91+ fuel rail and the 91+ TB for a perfect seal.

 

[Cox Abele]

Well, I've done the impossible I guess and managed to get a 90TB onto a 2g intake.

Since there will be others that attempt this and unknowingly run into the same issue, here is where the problem stems from:

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The vein that is used for the FIAV and ISC extends between 1/8"-1/4" past the flange of a 2g intake manifold's throttle body flange. If you look closely, you can see some of my copper spray that "falls off" right where the vein is no longer in contact with the intake manifold.

My solution seems to work pretty well, but may have issues with higher boost levels. I cut a piece of 22 gauge sheet metal I picked up from Home Depot for $8.00 in the shape of a throttle body gasket.

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This blocks the vein. I used a little RTV smeared thinly on the TB itself only around the vein, then sandwiched the plate between two gaskets. The issue with this is that the sealing potential is reliant upon the adhesive used and rigidity of the metal. I could see using 16 gauge steel with no ill effect, but didn't have the patience to work with something much thicker then 22 when I had no idea if it would work or not. Everything bolted together just fine and the vacuum leak has been solved.

I BLT'd to 10 psi with no leaks. I am just trying to get the car to run at this point after all, but this is a solution that has held fairly well. I could see it becoming a boost leak at higher pressures, but thicker steel could be used, or the obvious- swapping to another throttle body and the sensors/pig tails.

Below my index finger in the picture, there is also a small hole in the throttle body. It could be tapped and have a machine screw threaded in to provide additional clamping to the plate. I didn't opt to do this either, but greatly considered it.

Either way, I did what RRE says couldn't be done.

 

[1990TSIAWDTALON]

Yep same problem I had and if I didn't have a spare TB it looks like something I would have tried too, good job. I would worry at high boost levels but rtv has held BOV's on without any bolts believe it or not. Best of luck, keep us posted on how long this holds up.