Carb base heat cross over passage ways

JC2+2 · Poncho Master!

Carb base heat cross over passage ways

JC2+2 · Poncho Master!

4SPEED427 · A Poncho Legend!

I haven't done it but I saw one that someone had tapped and put allen head plugs into it. That looks the same as the 66 setup. I've never had a gasket burn on one of those. You are using the tin shield and the gasket with quite a bit of metal in the gasket material?

JC2+2 · Poncho Master!

I know why it burnt. Had a thick base gasket on top of the tin shield on top of the high temp gasket. So not enough sealing pressure on the tin shield. I didn't think the tin shield would seal against the carb.

65wagon · Poncho Master!

do it all the time, doesn't need to work under the carb, the crossover still works under the intake, and it works just fine in the winter at 40 below. I just use a couple of long bolts and tap them in cat them off at the top you can use some epoxy if you want but they will carbon in over time.just make sure they bottom out in the intake don't put sort ones in. long cant come out. I also use a plastic insulator works better speed shops sell them, along with different tin plates.

-- Edited by 65wagon on Thursday 16th of August 2018 12:09:11 AM

4SPEED427 · A Poncho Legend!

JC2+2 wrote:

I know why it burnt. Had a thick base gasket on top of the tin shield on top of the high temp gasket. So not enough sealing pressure on the tin shield. I didn't think the tin shield would seal against the carb.

I've always marveled at how that tin shield works on the carb, but it does!

hawkeye5766 · Canadian Poncho Superstar!

Hope this is what your asking. Have always blocked off the cross over at the manifold. Only drive in the summer and doesn't discolor the intake. Been a while but used to get the intake gaskets for a 283 with the tin insert with a round knockout in it. If you wanted the heat cross over you'd knock out the round hole on the block off. Not sure if they still make them that way. But found something close on line, mind you this would prevent the choke from working properly.....but I always warm mine up by throtle manually anyways and choke is set open cold.
1957-1965 Corvette FI Intake Manifold Heat Riser Block-Off Plates

-- Edited by hawkeye5766 on Thursday 16th of August 2018 02:56:19 AM

SGS Welding · Guru

Go to google and search

Lars sbc gasket fix

he gives the parts numbers of the

3 gaskets you need to put this together

I did this and have no problems

I have also heard guys drill and tap for pipe plugs

Your choice

both work well

oshawacliff · Poncho Master!

Just spent half an hour reading through Lars sbc gasket fix
Dont have the carb but sure was fascinating reading all of the responses. This fellow is well respected in his field and extremely knowledgeable.

A great read if you have time.
Cliff

long stroke · Canadian Poncho Superstar!

Over the many years of owning small block Chevy's, i have always used the intake manifold gasket sets that have the built in metal block offs. Obviously only on engines that are just used in the summer months. They are extra cost but worth it. I like to keep my intakes looking good with out all that nasty rust that comes with the heat cross over.

65wagon · Poncho Master!

you do need heat under the intake to vaporize fuel, you can block off the one side with out the choke , but it will still burn paint, its a trade off, I find the cross over under the carb gets the carb with our crap fuel too hot especially quads. im running aluminium intakes and leave the cross over open but insulated the carb with a plastic spacer.

JC2+2 · Poncho Master!

I did some reading on that other site and decided to go ahead and plug the holes off. With the holes at 7/16" it was a natural to tap to 1/2 NC. I tapped down approximately 1" from the machined surface. Then made up a couple 1/2 NC set screws 3/4" long. (You could probably buy them as well) Then I bottomed them out with high temp thread sealer. I can now stack a regular carb base gasket over the original tin shield and gasket which now just seal vaccume. I never got a chance to road test but after idling for a while, it didn't seem to perculate in the carb on shutdown like it used to but I'll have to get it warned up good on a road test. Here's a few photos. Not in order of course.

-- Edited by JC2+2 on Thursday 16th of August 2018 11:21:12 PM

65wagon · Poncho Master!

with the old set up my 400 would empty its fuel bowl, switched over to a thick spacer and a heat shield problem gone, it only happened once with winter gas in the tank

SGS Welding · Guru

Bump for norontcan

norontcan · Canadian Poncho Superstar!

SGS Welding wrote:
Bump for norontcan

Thanks, I'm having my Quadrajet 4MV rebuilt so figured I'd look into this at the same time.

GLHS60 · Poncho Master!

I'm sure you know this, but they came with the asbestos type gasket on the intake with the metal shield on top.

No gasket between the metal shield and the carb, especially not the one pictured!!.

Thanks
Randy

4SPEED427 · A Poncho Legend!

I've never been able to understand how a tin plate sealed a carb base but it did...

norontcan · Canadian Poncho Superstar!

Very interesting and informative read. I need to talk to my rebuilder.

SGS Welding · Guru

Bump

4SPEED427 · A Poncho Legend!

I just got my Quadrajet rebuilt at Autoline Remanufacturing in Winnipeg. There is a page in the box that specifically states that when you install the carb, gasket on the intake, then the tin shield, then the carb. I know this has nothing to do with plugging the holes but as JC stated early on here, he didn't think it would seal that way but somehow it does.

Prefectca · Poncho Master!

I plugged those holes on 283 and 327 two barrel engines without having any problems. On the two barrel engines the exhaust passing through would rust away the front mounting studs and they would break off when removing the carb. I brazed a washer onto the stud, and then a nut onto the washer to remove the remainder of the studs from the intake.
Paul

cdnpont · Canadian Poncho Superstar!

Thanks for the Bump Greg, and the link previous Carl.

So the more I read and the more I overthink this (as usual), the more I see 3 trains of thought. One is block it off both sides at the intake. Second is block off the non choke side, and the other is just block the two riser holes. Now, in thinking I'm actually considering driving the 65 all winter. Well, only on dry days of course, but perhaps I will need carb heat?

Seems a lot of the modifications were made to keep the paint nice, some did it due to percolation and others due to gasket or stud deterioration. It is agreed that some heat is needed for proper atomization, and choke spring function, but full on is too much in the hot summer. But on the opposite side, full block off might hinder the choke function and make the engine balky in the cold.

Another though was that really to have the system function as intended, a heat riser valve would have been required. Maybe all that stud and gasket failure, plugging up, coking and boiling happened over many years, and when our cars actually had that valve with a more restrictive exhaust, read full and extremely hot crossover flow. Most of us run a free flowing exhaust now, so I'd expect you'd see less reversion through the crossover.

I think the tin intake block off's as Jim and George suggested might be a good solution. I'd make my own if needed (although my gasket set may have come with them). But I would open them up to make them block off 3/4's of the opening. Let some heat in, but not the full amount. Some heat for choke function and better drivability in the colder months, but a little cooler running in the summer. The better paints of today might even last longer. And I could always add phenolic spacer if she still seems too hot.

JC2+2 · Poncho Master!

You definitely wouldnt want to block the main passage off completely. I guess maybe if you had electric choke and only drove in the summer. What I did doesnt affect that end of it. Just converts it into the newer version of manifold