I have an 89 Full Size Blazer. I went to autozone to pick up a base gasket for my throttle body and adapter plate. The normal tbi gasket is too small for the throttle body that I have. I have some pictures of the TBI, but I was wondering if anyone could help me identify which throttle body this is, or maybe what vehicle it originally came from. This unit was installed prior to me buying this vehicle and it was running so I know it works. It just isn't the regular TBI for this year/model vehicle. There are some pictures from each angle for help in identifying this part.

Also I measured the interior bore of the venturi and the one that I have has a 50mm bore, but the one that should be on this year's motor is 42.5mm That's about an 8mm difference! Any help would be appreciated.

Is there any way to just get a similar gasket and cut the excess piece that would otherwise constrict the butterflies, or is there a specific bore sized gasket for this?

 

if your truck is a 5.7 (350) the bore on your throttle body should be 1- 11/16 opening , the tbi you have may b for a big block chevy ,the tbi bores are a bit bigger , hit your local junk yard n pick up the rite one , the big block tbi will work good if you bore out your intake , both tbi have the same bolt patterns , get the the smaller one and rebuilt it , very simple to do, dont move the idle screw it should b factory sealed with a metal plug ,

 

I put it back on with a regular gasket, and it constricted the butterflies as I though. So I'm going to cut the excess with a razor and try to get it as precise as possible so that it will work. After that, this unit needs need throttle shaft bushings. I'm going to see if I can get my local machine shop to do it.

 

So your intake is bored to match the throttle body? You may have some minor drive-ability issues if the ECU hasn't been reprogrammed for the different airflow characteristics.

Looks like it's a rebuilt (bored&modified) 5.7 throttle body. The shrouds are missing on the throttle bores (this is a good mod). Doesn't look like you have an injector pod spacer, though. It's a plate that sits above the base and raises the injector pod by 1/2". It's like $20 on ebay, or easy enough to make with material and a decent shop.

 

theres your problem lol

since you have it off you might be better off taking it with you too to match up the gasket. try a better parts store too

 

You don't like autozone? The one I have here in town has very knowledgeable people working there. Anyways, my buddy suggested just getting a gasket from a 454 tbi unit and maybe that would fit. The ECU has been reprogrammed for this larger tbi which is why I wasn't able to switch back to the normal 42mm tbi unit. The guy who owned it before me put a Summit Racing intake manifold that requires a special adapter plate for the tbi unit. I'm just trying to find the gasket that matches the tbi unit. I did cut this gasket back some, so I'm going to try it out.

Hey it worked! Its not stumbling anymore, but I did have to swap the IAC valve on the tbi unit because it was doing some erratic idling. But all is well now. So I just gotta fix my brake lights and my steering column then I can get this thing back OFF the road

 

You have a carb intake with tbi adapter plate.

I wonder if you might have vortec heads (from 96+ 350's)? If so, FYI, you MUST use the vortec spark plugs when you replace your plugs (long-reach ac delcos, for 96+ trucks). You can't use the vortec plugs in tbi heads, though (too long, will contact the pistons).

Easiest way to tell is by the bolt pattern on the intake. vortecs only have 2 intake manifold bolts in each corner, tbi heads have a line of bolts equally spaced along each side.


You can switch to a 42mm throttle body if you need to for some reason; the drivability won't be much of an issue stepping down in size being tuned for more air flow.

The chip you have provides a bit more fuel when you open the throttle blades because you get more air with less tps voltage than a factory 42mm TB. I'm sure there are other mods in the chip, but that's the gist of what has to be changed when going to a 454 TB. In tuning, it's called TPS AE [acceleration enrichment].

 

I went to check, and I do have vortec heads on this motor. You're saying I have to use special plugs for this. I'm planning on upgrading the ignition with a hotter coil, msd module, and msd cap and rotor, then some better plug wires. I was not aware that I needed different plugs for this though.

 

I'm using ac delco R44LTS plugs in my vortecs; NAPA stocks them. Just use a '96 suburban as the application for plugs. I think the 96+ 4.3 blazers use the same plugs, too.

I've heard a lot of horror stories about msd coils burning up, so carry a spare.

I'd like to upgrade to a distributorless setup like the 4.8/5.3/6.0 engines, but I'm not sure exactly what's involved and I haven't yet found a cheap junkyard ignition system to tinker with it.