Plenum & Injector Housing Porting

[jss06c6]

Gents,

Thanks to Constantine, I've got a spare Plenum and pair of Injector Housings to port without shutting #473 down. I've read, with great interest, Keith's (KJL) thread on Corvette Forum. My goals are the same. I've got a '91 and my Plenum looks identical to Keith's. However, the one I got from Constantine shows straight pipe nipples just below the TPS, versus the rear one being curved. Is this something to be concerned about? I was also surprised to see that the Injector Housings were "chamfered". Obviously there was an attempt to eliminate a sharp edge at the transitions from the Plenum and the Heads..

I'd like to get a "junk" injector to verify how much I can take off the primary boss. I understand it can essentially be completely removed, just want to get an eye on it before I put a burr to it.. If anyone has a junk one laying around, I'll be happy to pay to have it shipped..

Got everything cleaned up. Here's a few photos showing the chamfers and the injector bosses.. Would appreciate some guidance on the pipe geometry (not sure what these two are, will need to check my docs)..

[jss06c6]

Can anyone shed some light on my question regarding the piping configuration difference on this plenum and the one in my car? The rear pipe on mine is curved back toward the underneath side of the plenum.. Do I have to replace this tubing to match the geometry on my '91, or simply adjust the hose configuration to enable me to install it?

[A26B]

Yes, you will have to change the rear pipe. The 2 straight pipes are for 1990 only


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[jss06c6]

Thanks Jerry! Is it available somewhere? Is it installed with something like JB weld?

Much appreciated!

Steve

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[Marc Haibeck]

Some injector housings were machined with chamfers to compensate for core shift in the castings. The correct port center is at the top of the chamfer. This problem was solved in '93 when the chamfer was blended 1.5 inches into the port for a smooth transition. This was a part of the 405 hp upgrade.

The crankcase vent flow restrictor configurations are different on the '90 verses '91 and later injector housings. To make your '90 housings compatible with your '91 cylinder heads you need to drill the small holes in the '90 flow restrictors to at least 3/4" to remove the restriction. When you are shopping for the EVAP tube at Jerry's, look at the injector housing index 10D3 on the 5th page of the Intake section. It shows the unrestricted crankcase vent ports. If they are not drilled out the engine will be double restricted because the restrictions are also in the cylinder heads for '91 and up.

[jss06c6]

Thanks very much Marc. Looks like these injector housing castings were pretty far off then. Found the tube on Jerry's site.

Steve

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[A26B]

I have a more in-depth review of the different Injector Housings on my website under the Category "Technical Data." Here's a link to it. There's no charge for any of the Technical Data, just put it in your cart & checkout like you would for parts. Afterwards, you are authorized to download it and save it to your computer if you like.

http://www.jerrysgaskets.com/fuel-in...housing-guide/

[jss06c6]

That's great! Thanks very much Jerry...

Merry Christmas everyone..😊

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[jss06c6]

Resurrecting this older thread as I'm now starting the top end porting work. Port matching the plenum and injector housings has been straight forward on three sets that I now have. While I haven't put a burr in the castings yet, I'm happy with the relative alignment between the plenum and the injector housing runners.

I can't say the same about the primary runners between the injector housings and the heads. They are considerably off centerline. With no porting, there is a shift between the two resulting in a sharp step, which would really hammer the flow pattern. The offset isn't there with the secondaries, only the primaries. Placing the gasket on the head, then comparing it to the injector housing quickly shows the very poor port matching..

If my '91 is anywhere close to a representative example, I understand why the LT-5 responds so we'll to top end porting..

I'll try to get a couple of pics tomorrow morning to post for illustration.

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[XfireZ51]

Steve,

Yeah GM left a lot of meat on that bone.