I bought the Holley 108-70 heat shield, and it didn't come with any instructions. It came with a 5/16 non-metal carb spacer, the shield, and a carb gasket.

What is the order of installation? Is it:
Manifold, spacer, shield, gasket, carb?

Does the spacer need to have gaskets on either side of it? If so, I need a couple more gaskets....
Thanks for your help!

What you're calling a spacer is just a thick base gasket with nylon inserts to control crush.

I have a (now discontinued) Genuine GM heat shield of similar design but for Q-Jet style flanges. The gaskets are stapled to the aluminum heat shield. That unit has the firing order stamped into the aluminum of the heat shield, which of course would face "up". With the stamping facing up, the thin gasket is on the bottom, and the thicker gasket is on top, next to the carb.

Can someone elaborate on what a carberator heat shield does?
I assume it is to keep the hot air from the engine being sucked right back in the engine?
How effective are Carb heat shields? Do they make them for Q-jets?

I was thinking of making some kind of cold air induction on my car.

It's a sheet of aluminum between carb and manifold that blocks heat from the manifold from warming up the carb excessively. It is shaped to clear the throttle linkage and such, and has a pair of gaskets to seal it.

You used to be able to buy them through GM, but they've been discontinued. There was one part number for 4150-style, straightbore carbs, and another part number for Q-Jet style carbs.

Holley made a very similar unit--almost identical--for straightbore and for spreadbore carbs. Holley's spreadbore unit is now disco'd, but the straightbore is still available using the part number in the first post.

http://store.summitracing.com/egnsearch.asp?Ntk=KeywordSearch&DDS=1&Ntt=HLY%2D108%2D70&x=18&y=13&N=+115&searchinresults=false

My set up is a '68 Chevelle with a ZZ502/502. The problem I was having was that when I tried to restart the car after driving somewhere, it acted like it was flooded (difficult to start). I called the Holley Tech Line and described my problem - the tech rep at Holley suggested that I make a heat shield to place under the carb. He described what was happening was that the carb fuel bowl (primary/front bowl) was getting "heat soaked". The heat was causing the fuel inside the bowl to expand, and when it expands, it "pushes" the fuel out of the squirter, into the engine, causing the flooded engine. I installed a GM heat shield, and the problem was solved. :)

When the engine was warmed up/hot, I was actually able to hear a slight "perculating" sound (like the old coffee pots made) when I removed the air cleaner, and I could actually see the fuel being belched into the engine. After the heat shield - no more problems. Also, the Holley heat shield appears to be "identical" to the original GM heat shield, with the exception of the Holley logo stamped into it. Not positive if they make one for a quadrajet, but I would be willing to bet they do.

Kent
'68 Malibu ZZ502/502
ACES #5102

Thanks for the reply Schurkey, I should have followed up earlier.

Well, I tried to install it like you said, but unfortunately it won't fit without a little work. I have a 350, with an rpm air gap manifold, and a 750 dp. The shield wouldn't fit down onto the manifold for 2 reasons. It hit the waterneck, and would also rest on top of the 90 deg (low profile...) vac fitting on the manifold behind the carb for the brakes.

I had a 3/8" alum spacer under my carb before, to allow the rear bowl to clear the vac fitting. With the alum spacer under the carb, the shield will fit. I will need to do a little trimming off the front, as it still wants to rub the water neck. It's probably important for resisting the heat transfer to use the thick insulated gasket provided with the shield. So hopfully, the hood will close with all those spacers under there and the air cleaner installed! :)

Not positive if they make one for a quadrajet, but I would be willing to bet they do.

GM--and Holley--did make a Q-jet shield. Both companies have disco'd them.
Holley's p/n was 108-69 (vs. 108-70 for the straight-bore version)

'Course, all you need is some sheet aluminum and a thick/thin pair of gaskets. Trim the aluminum to fit your engine.

I found and bought a NOS GM HS for a Holley. Two weeks later found that they are being repopped with a retail of around $30. Comes with the gaskets and shield. I think it was NPD who has them online- C-3726-100A. Don't ask what I paid for the NOS.

I've seen the NOS on e-bay and their costly, and yes it's NPD that has them (repops) as a newly listed item.

The vacuum fitting can be changed for one which has the ports out the sides instead of up and out. I'm going to install one on my 427 this winter.

I usually make my own, A few years back I made a template from a HS that my friend had on his car. I bought a 4x4 a sheet of .063 6061-T6 from a local recycler for $8. It takes some time to make but what can I say Im cheap. :)

Are they really repops, or just the Holley shield without the Holley packaging?

First Guess: Nothing special. Might as well buy the Holley shield for ~$25

Yes, it has the GM PN stamped right on the top just like the NOS version. I'm a bit confused, in regards to the order of things. I had emailed Holley and they replied that it was the thick gasket, plate, thin gasket, then carb. When I mocked things up there was barely enough room to get a PCV hose in there. I'd prefer using the GM plate and just need to confirm that the sequence is: thin gasket, plate, thick gasket then carb?

My GM Q-Jet shield would go on with the thin gasket against the manifold.

Since without the heat shield, the thick gasket would be directly under the carb, I don't see a problem with installing the thick gasket against the carb, and just adding a sheet of aluminum and a thin gasket underneath the thick gasket.

Thanks. Makes sense.