Side effects of adding phenolic spacers under intake

[Viper488]

On for example the Viper engine, if I were to add say 1/4" phenolic spacers under each runner to head port connection, how much higher would that raise the manifold? 1/4"? More/less? I'm also looking for advice of which particular type of phenolic plastic I should buy with a continuous useage temperature rated high enough to hold up in a near-engine environment. I'm aware of, and working on, the other sources of intake manifold heat soak. I just need info about the spacers often used under carburetors. How high they'd raise the intake, how thick the carburetor types usually are, and what type of phenolic plastic to look for.Thanks

 

[patprimmer]

There are two types of plastic that I have seen used as manifold to carburetor insulators.

All under carburetor ones I have seen are Phenolic composite and are a simple spacer design and can be in a number of thicknesses. Factory examples tend to be about 1/4" thick as this is thick enough to be reasonably effective and tough enough, but has minimal effect on bonnet clearance.

This phenolic composite is readily identifiable by the brown colour which is the natural colour of phenolic resins. These are normally wood flour filled, and cotton fabric reinforced. The colour and texture of the wood flour can normally be seen once you know that is what you are looking for, and the reinforcing fabric yarns can also be seen in places.

The only inlet manifold to head insulator I have seen is that used by GM on their 3.8 litre 90 deg V6. It incorporates the gasket and is in glass filled nylon, probably type 6.6 nylon, but type 6 should work and type 4.6 would be best, but 4.6 is probably not available in sheet form, and I suspect you do not want to spend $20,000 or $30,000 on a mould.

I would use phenolic composite sheet unless the ports are very close together like a SBC, then I would use glass filled nylon 6.6 or a maybe a Fiberglas sheet.

The change in height is simple high school geometry, so draw it up and work it out, or just fit the components together, use appropriate spacers made of whatever is convenient, then measure the result.

Regards
pat pprimmer@acay.com.au
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[Viper488]

I was thinking I should mock up something similar out of wood to see what happens. Mostly because I'm now wondering if the addition of the phenolic will change the angle the intake meets the heads at slightly...that wouldn't be good.

Earlier today I saw a Superformance Cobra with a 1" carb spacer at a cruise. The Cobra'd been sitting about 15 minutes and the engine was still hot..but the carb was almost cool to the touch

Later a friend with a turbocharged Roadrunner showed me his canvas based phenolic spacers he had along with him...

I'll work on it.

 

[finman]

I think the material you are looking for is called TUFNOL it's available in many different grades. I've used it on motorcycle carbs to stop the things getting hot, it works a treat.
As for any changes of Geometery at the port I can't assist however you could machine the Tufnol spacer at an angle to get things back to normal.
The stuff machines easily, but make sure you don't breath in the dust particles.