Quote:
Originally Posted by A26B
Principal Advantage: Thermal insulator for plenum, to impede heat soak from the engine
Other Advantage: Marginal increase in air circulation under plenum, aids in cooling of plenum & DIS Module.
Disadvantage: 1/4" spacers frequently result in intake contact with underside of hood.
Disadvantage: Requires some bending of vacuum line to PCV top connector.
Disadvantage: requires 2 sets of plenum gaskets. & longer bolts
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^^^ what he said. I'm not doing this for any performance impact, and I doubt the claimed benefits of plenum insulation are even measureable!
I just need the spacers to improve the transition interface between the housings and plenum. What happens, in my case, is a slight decking of the block, combined with skim cut on the cyl head deck, and a thinner MLS gasket = the heads sit fractionally lower. The plenum ports no longer line up perfectly with the housings, so I need to fix that. We're talking millimeters here.
One added consequence, the extra 1/4" or so should move the natural tuned length of the intake slightly lower (perhaps 100 rpm). Peak torque on Build 1 was 5800 rpm, which is more or less where the factory HP peak was, and where the stock runner length is tuned.