Gary Lewis Posted July 29 Share Posted July 29 My understanding has been that running manifold vacuum would be better for idle cooling characteristics …… recall Bill or you mentioning that The vacuum source won't change cooling if it is the same every time - assuming the same idle RPM. The beneficial cooling comes when you have ported vacuum with the temp below a certain point and manifold vacuum if the temp goes over that point. When you hit that temp the added vacuum will raise the idle RPM and, therefore, help cooling. But unless you firmly have your foot on the brake you may start creeping forward as well. Link to comment Share on other sites More sharing options...
viven44 Posted July 29 Share Posted July 29 My understanding has been that running manifold vacuum would be better for idle cooling characteristics …… recall Bill or you mentioning that The vacuum source won't change cooling if it is the same every time - assuming the same idle RPM. The beneficial cooling comes when you have ported vacuum with the temp below a certain point and manifold vacuum if the temp goes over that point. When you hit that temp the added vacuum will raise the idle RPM and, therefore, help cooling. But unless you firmly have your foot on the brake you may start creeping forward as well. Yes that makes a lot of sense... the stock vacuum diagrams for a 460 are configured purely for manifold vacuum though. The only difference between hot/cold is the presence of a V REST while cold and straight manifold vacuum when hot... Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 29 Share Posted July 29 Yes that makes a lot of sense... the stock vacuum diagrams for a 460 are configured purely for manifold vacuum though. The only difference between hot/cold is the presence of a V REST while cold and straight manifold vacuum when hot... Right. There's something about the VREST that I don't understand. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 29 Share Posted July 29 Right. There's something about the VREST that I don't understand. Neither one of you are looking at the dashpot (throttle positioner) that comes on trucks with AC or automatics. Link to comment Share on other sites More sharing options...
viven44 Posted July 29 Share Posted July 29 Right. There's something about the VREST that I don't understand. VREST is supposed to keep the distributor from leaking vacuum, remember ? Just kidding.. I am still embarrassed Link to comment Share on other sites More sharing options...
viven44 Posted July 29 Share Posted July 29 Neither one of you are looking at the dashpot (throttle positioner) that comes on trucks with AC or automatics. I have grabbed just about every Holley 4180 I found on one of these 351W/460 and tossed it into a storage bin and dropped in a Edelbrock so I have no idea how these were configured or supposed to work stock Nothing against those Holley, I am sure they are wonderful. I don't intend to learn all carburetors.. or at least there isn't a need yet. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 29 Share Posted July 29 VREST is supposed to keep the distributor from leaking vacuum, remember ? Just kidding.. I am still embarrassed Vrest keeps the distributor from advancing or retarding too suddenly/abruptly. It provides hysteresis in the loop, where the VCV pulls in full manifold vacuum instantly (and -in my truck- increases idle speed) Link to comment Share on other sites More sharing options...
viven44 Posted July 29 Share Posted July 29 Vrest keeps the distributor from advancing or retarding too suddenly/abruptly. It provides hysteresis in the loop, where the VCV pulls in full manifold vacuum instantly (and -in my truck- increases idle speed) Yes its amazing what a little orifice can do. It allows vacuum to get through from the main reservoir to the destination (intake to the distributor) but the micro fluctuations are "too big" of a signal to get through that orifice Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 29 Share Posted July 29 Yes its amazing what a little orifice can do. It allows vacuum to get through from the main reservoir to the destination (intake to the distributor) but the micro fluctuations are "too big" of a signal to get through that orifice So call Vrest a damper.... Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 29 Share Posted July 29 I have grabbed just about every Holley 4180 I found on one of these 351W/460 and tossed it into a storage bin and dropped in a Edelbrock so I have no idea how these were configured or supposed to work stock Nothing against those Holley, I am sure they are wonderful. I don't intend to learn all carburetors.. or at least there isn't a need yet. The 4180 is technically a Motorcraft carb. It was never offered by Holley, and doesn't wear a 14 or 15 series number, but you can read that on the front bowl of every one... Link to comment Share on other sites More sharing options...
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