C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

86 Plenum Thickness?

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Old May 27, 2005 | 09:44 AM
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Default 86 Plenum Thickness?

I need to remove some material from the underside of the plenum in the area of the EGR valve (Clearance issues with large tube runner install). How much material can I safely remove?
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Old May 27, 2005 | 12:06 PM
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not much.... 1/8" max.... you may want to see if you can remove some material from the EGR valve...

perhaps thin down the mounting base? I donno... how much do you need?

My bigger concern is why must you grind anything... those aftermarket tubes shouldn't effect anything.
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Old May 27, 2005 | 12:12 PM
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The plenum clearly sits lower with the large tubes than with the stock runners, thus the interference. 1/8" Just might do it, though. Jim @ TPIS says he's never run accross this before. Maybe it's just an oddball set of runners. Probably not much I can do with the EGR valve.
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Old May 27, 2005 | 12:21 PM
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I would hold off... wait until one of the TPI experienced tuners pop in.
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Old May 27, 2005 | 12:22 PM
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Yea, something's definitely wrong. Those runners should not cause any interference with the EGR and the plenum shouldn't sit any lower either.

Who's runners are they?

I'd send them back to have them checked.

As far as the EGR itself, you can remove it, install a cover plate to block the hole and have it turned off in the PROM. That's what I did on my 86.

Jake
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Old May 27, 2005 | 02:54 PM
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TPIS runners.
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Old May 27, 2005 | 03:39 PM
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Originally Posted by geezel
TPIS runners.
Can you post a photo of the runners and the interference?

If not, I'd send them back to TPIS to be checked. You may have been sent the wrong ones.

I don't know where the EGR mounts on other years/models, but could they be for an 'F' body?

Jake
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Old May 27, 2005 | 03:47 PM
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Originally Posted by geezel
The plenum clearly sits lower with the large tubes than with the stock runners, thus the interference. 1/8" Just might do it, though. Jim @ TPIS says he's never run accross this before. Maybe it's just an oddball set of runners. Probably not much I can do with the EGR valve.
Are they the Accel runners? They are shorter than stock.
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Old May 27, 2005 | 04:13 PM
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I bought them from another Forum member who claimed TPIS Part no. 500-503 which their catalog says is good for 85-88. The interference is at the top of the EGR valve / bottom of plenum. I'll do more investigation after the long weekend.
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Old May 27, 2005 | 04:16 PM
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Originally Posted by geezel
I bought them from another Forum member who claimed TPIS Part no. 500-503 which their catalog says is good for 85-88. The interference is at the top of the EGR valve / bottom of plenum. I'll do more investigation after the long weekend.
Can you lay them next to the stockers to see if the TPIS runners have a tighter radius?

Jake
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Old May 27, 2005 | 04:30 PM
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All I can say at this point is that they are LONGER as measured along the outside radius of the tubes. I suspect a tighter radius would be tough to detect by eye, but the interference tells the story about the final height of the plenum.
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Old May 28, 2005 | 04:46 PM
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Originally Posted by geezel
All I can say at this point is that they are LONGER as measured along the outside radius of the tubes. I suspect a tighter radius would be tough to detect by eye, but the interference tells the story about the final height of the plenum.
Can't you just mate them up to each other?

For example, if you take a coffee cup and set it on the counter. Then take another coffee cup, turn it upside down and set in on top of the first cup.

Using one of each, align the bolt holes on one end and see if they still align on the other. Or try measuring the distance between one upper bolt hole and one lower bolt hole on the stock runners. Then do the same on the other TPIS runner. See if there's a difference.

I'm just brain-storming this problem trying to visualize a way to detect the difference between the two.

Jake
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Old May 29, 2005 | 09:50 AM
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www.hotrodlane.cc has a nice egr blockoff plate.
I even passed emissions without the EGR.

http://www.hotrodlane.cc
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