Evacuation Setup - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 04-16-2017, 12:36 PM Thread Starter
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Evacuation Setup

We have a '70 455 +.40 in a 4-speed car with headers. A long time ago, I had but in an "evacuation" setup that consisted of a 1/2 pipe @ a 45-degree installed at the header collector, with a 45-degree angle end and a "notch" at 45-degrees to create a "vacuum". To this, we connect an EGR check valve and ran a hose up to a connection (-10AN) on one valve cover.

The questions are:
Should we still use this setup (street car with 2.5 full exhaust with cross-over "X" pipe)?
If so, should we run a hose from each valve cover to a "T" to the one hose running to the EGR?
Or, the one valve cover - one hose setup that it was
This motor / head / cam combination has never been run (yet).....

Thanks in advance,

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post #2 of 3 (permalink) Old 04-16-2017, 05:07 PM
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Not needed. The evacuation system is really for race engines that spin high RPM's to take advantage of them. Your stock EGR valve should work just fine, so no need to go crazy with the evac system UNLESS you just want to add it because you want to.

Found this warning: "Remember they do not recommend using this set-up with mufflers. The whole idea behind them is to remove built up pressure in the engine by creating vacuum. Muffles create back pressure. That being said I did have mufflers bolted on my collectors earlier in the year before I blew them out and to some extent I still had vacuum but I didn't have a complete exhaust system. "

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post #3 of 3 (permalink) Old 04-17-2017, 09:31 AM
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In the mid 80's had a 468 Chevelle street/strip car (barely streetable), the idea with the Moroso header evac setup was to aid ring seal, but as Jim mentions only for use with open headers. Building a racecar, am sure there would still be some advantages, ESP with loose ring clearances.
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