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Unread 08-06-2009, 06:20 AM   #1
attworth
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Intake Manifold connected to Exhaust manifold - delete?

The motor is a 79 258. It has/had stock everything. The intake manifold bolts to the exhaust manifold directly below the carb - some sort of air regulation something or another.

The bolts in the exhaust manifold were toast, and a fella was nice enough to let me have his exhaust manifold that he will not be using.

This new manifold came off of a 84/85 model 258. Everything looks basically the same. The major differences are EGR and O2 provisions, and no air tubes above the manifold. The biggest difference is the lack of the connection to the intake manifold.

Now - people run headers all the time, so there has to be some plate made somewhere to block off the hole on the bottom of the intake. Does anybody know where I can find said plate? I've been looking around and have come up empty handed.

Thanks!

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Unread 08-06-2009, 06:44 AM   #2
Rob Abel
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I have the same setup and am not crazy about it either. This summer, I blew the intake/exhaust gasket and it took me awhile to figure out what was going on.

I'd suggest just making a blockoff plate out of 3/16 or 1/4 inch steel plate. Put the gasket in there, tighten up the bolts and you should be good to go providing you can fit the exhaust man. in.

Good luck.
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Unread 08-06-2009, 06:52 AM   #3
John Strenk
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You don't need to block off the hole on the bottom of a 79 intake, it's just used for heating the floor of the intake manifold when the engine is cold. Kind of like the electric manifold heater used in the later water heated maniflds. there is a diverter in the exhaust that will direct exhaust gasses onto the bottom of the intake when it's cold. There should be no leaking between the two manifolds. You might have to check the EGR valve if you are using now. You could disable that if you have too. Bu don't worry about any leaks. No block off plate needed.

Fort Worth Texas? Probably don't need any more heat on the intake.

I'm suprised the later exhaust manifold fits without a lot of trimming.
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Unread 08-06-2009, 06:55 AM   #4
attworth
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Quote:
Originally Posted by John Strenk View Post
You don't need to block off the hole on the bottom of a 79 intake, it's just used for heating the floor of the intake manifold when the engine is cold. Kind of like the electric manifold heater used in the later water heated maniflds. there is a diverter in the exhaust that will direct exhaust gasses onto the bottom of the intake when it's cold. There should be no leaking between the two manifolds. You might have to check the EGR valve if you are using now. You could disable that if you have too. Bu don't worry about any leaks. No block off plate needed.

Fort Worth Texas? Probably don't need any more heat on the intake.

I'm suprised the later exhaust manifold fits without a lot of trimming.
Ahh, that's what it is for. Makes a lot of sense now. I removed all the air heating devices on another car I used to drive here without any ill effects.

The later exhaust manifold is much smaller physically than the current one. It's more streamlined and "header" looking than the large blocky one from 79. There's a ton of room where the diverter doesn't exist.

I'm going to plug both the EGR and O2 bungs.

Thanks Mr. Strenk, always a big help.
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Unread 08-06-2009, 08:18 AM   #5
CSP
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Another thing to watch out for with the newer exhaust manifold.

The intake and exhaust are held to the block with bolts and heavy washers that clamp it via shoulders on the manifolds. The shoulders on the newer exhaust manifold aren't as thick as the older one, so the shoulders won't line up properly with the shoulders on the intake manifold. Without some sort of shim to make up the difference in thickness, you'll never get the new manifold clamped tightly against the block. I have no idea how you would keep a shim in place anyhow.

Be sure to check this out before you try to install the newer manifold.
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Unread 08-06-2009, 08:24 AM   #6
John Strenk
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Cut a washer in half and weld, braze, solder the parts onto another washer untill you make up the difference. Or find some thick washers and start filing.
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Unread 08-06-2009, 08:25 AM   #7
attworth
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Good to know, thank you. I'll be sure to check fitment before I do any work on it.
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Unread 08-06-2009, 09:01 AM   #8
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You can also pile up a weld on the low side. This makes a pretty good shim without having to go the washer approach.
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Unread 08-06-2009, 04:05 PM   #9
keith460
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McMaster-Carr.com has large thick washer in stainless steel that you can use. They are called "fixturing washers" and I used them to replace the OEM washer that hold the intake/exhaust manifolds in place.

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Unread 08-07-2009, 06:21 AM   #10
attworth
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Quote:
Originally Posted by keith460 View Post
McMaster-Carr.com has large thick washer in stainless steel that you can use. They are called "fixturing washers" and I used them to replace the OEM washer that hold the intake/exhaust manifolds in place.

What kind of paint did you use on those manifolds? Looks nice.

Thanks for the recommendation on the washers. I was wondering where I might find new ones.
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Unread 08-07-2009, 11:27 PM   #11
carnuck
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Use the later intake. It increases the air flow about 10% over the earlier one.
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Unread 08-21-2009, 06:02 PM   #12
ctm
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Hesco has manifold washers too, pricey though

Hesco Inc. - High Performance Engine Service

dealer part number is 33004255 if you want to go that route
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Unread 01-17-2012, 06:49 PM   #13
DENVAR03
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john
i have a 1986 nuttered,and weber carb.the s shaped egr tube was kinked when engine was taken apart for rebuild.can i cap the 2 threaded holes the egr s shaped tube came off of??

thanks dennis
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Unread 01-18-2012, 03:51 AM   #14
John Strenk
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Yeah but I don't know the thread size. A lot of people just pinch off the pipe to seal it.

Personally I like running the EGR valve. Keeps me from pinging with the cheap gas they sell around here.
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Unread 01-19-2012, 02:51 PM   #15
DENVAR03
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thanks
went to jeep and bought a new s tube,38.00,but i will keep the egr as you said.

thanks dennis
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