reversion and intake manifolds
11-19-2006, 10:47 AM
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Re: reversion and intake manifolds
Originally Posted by mcrsr
so what do you advise for a mild cam that is reversion free??? i am running very mild comp cams extreme marine cams, anyone have any experience w/ these??
11-20-2006, 06:28 AM
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Re: reversion and intake manifolds
they are in a 32 pachanga, it has stainless marine exhaust, 049 heads, exh discharges forward into a 5" collector, then comes out of collector on bottom w/ 5" hose and out back on hull side, i have an internal flapper in the exhaust, tbolt 5 ign, flatop hypereutectic pistons, compression at 8.5:1, current cams i believe are 272 duration, 515 lift(xm 272 comp cam)
11-20-2006, 07:08 AM
#43
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Re: reversion and intake manifolds
Could you find out exactly what you have for a cam and post it? it will help everyone here greatly.
Also, I'm having a a hard time picturing your exhaust, any chance you have a pic you can post ?
Reason for everyone asking about cam + exhaust is that these are typically the reason for exhaust water reversion.
I couldn't find a XM272 so here's a few close ones.
Comp's Extreme Marine:
Flat Tappet XM270H for Mark IV/GEN V
270°, 286° seat at .006"
218°, 224° at .050"
.505" , .515 " with 1.7 rocker
112°LSA
Hydraulic roller XM270HR retrofit for Mark IV, GEN V
270°, 276° seat at .006"
218°, 224° at .050"
.495", .503" with 1.7 rocker
112°LSA
Also, I'm having a a hard time picturing your exhaust, any chance you have a pic you can post ?
Reason for everyone asking about cam + exhaust is that these are typically the reason for exhaust water reversion.
I couldn't find a XM272 so here's a few close ones.
Comp's Extreme Marine:
Flat Tappet XM270H for Mark IV/GEN V
270°, 286° seat at .006"
218°, 224° at .050"
.505" , .515 " with 1.7 rocker
112°LSA
Hydraulic roller XM270HR retrofit for Mark IV, GEN V
270°, 276° seat at .006"
218°, 224° at .050"
.495", .503" with 1.7 rocker
112°LSA
11-20-2006, 04:43 PM
#44
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Re: reversion and intake manifolds
Going thru some notes, I thought some might find this interesting.
David Vizard writes:
With a typical 280-degree hydraulic cam, the valves (in the TDC overlap position) will be a little over an eighth inch off the seat. This means the piston moving rapidly down the bore in the middle of its induction stroke can draw through the intake manifold and right on through the overlapping valves to that cylinder's exhaust.
If we replace the open plenum intake with a two-plane (180 degree) intake, in one fell swoop, we space out the induction pulses seen in each half of the manifold to 180 degrees instead of 90. This means there is no time when the one cylinder's intake can draw through the exhaust of another. As a result, the intake vacuum goes up by something in the order of 50 percent.
With a typical 280-degree hydraulic cam, the valves (in the TDC overlap position) will be a little over an eighth inch off the seat. This means the piston moving rapidly down the bore in the middle of its induction stroke can draw through the intake manifold and right on through the overlapping valves to that cylinder's exhaust.
If we replace the open plenum intake with a two-plane (180 degree) intake, in one fell swoop, we space out the induction pulses seen in each half of the manifold to 180 degrees instead of 90. This means there is no time when the one cylinder's intake can draw through the exhaust of another. As a result, the intake vacuum goes up by something in the order of 50 percent.
Last edited by SB; 11-20-2006 at 04:45 PM.
11-20-2006, 06:02 PM
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Re: reversion and intake manifolds
Originally Posted by SB
Also, I'm having a a hard time picturing your exhaust, any chance you have a pic you can post ?
11-20-2006, 06:07 PM
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Re: reversion and intake manifolds
Originally Posted by SB
I couldn't find a XM272 so here's a few close ones.
Comp's Extreme Marine:
Flat Tappet XM270H for Mark IV/GEN V
270°, 286° seat at .006"
218°, 224° at .050"
.505" , .515 " with 1.7 rocker
112°LSA
Hydraulic roller XM270HR retrofit for Mark IV, GEN V
270°, 276° seat at .006"
218°, 224° at .050"
.495", .503" with 1.7 rocker
112°LSA
Comp's Extreme Marine:
Flat Tappet XM270H for Mark IV/GEN V
270°, 286° seat at .006"
218°, 224° at .050"
.505" , .515 " with 1.7 rocker
112°LSA
Hydraulic roller XM270HR retrofit for Mark IV, GEN V
270°, 276° seat at .006"
218°, 224° at .050"
.495", .503" with 1.7 rocker
112°LSA
If its either one of these, its barely more than the stock 502 Mag cam. The odds of it causing reversion are nill.
11-20-2006, 06:41 PM
#47
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Re: reversion and intake manifolds
Yes, those cams are mild. Was just trying to jar the memory if he doesn't have them written down.
I know the manifolds, just wanted a pic of the rest of the exhaust. Some funky set-ups get put into into some boats.
He mentioned the exhaust goes " forward into a collector". I took this as going forward to the bow, not the stern. So, not understanding this, I figured pics are in need for a possible better diagnosis.
Like you, just trying to help. Cool thing about forums/internet/etc is being able to post pics. These can really help sometimes.
I know the manifolds, just wanted a pic of the rest of the exhaust. Some funky set-ups get put into into some boats.
He mentioned the exhaust goes " forward into a collector". I took this as going forward to the bow, not the stern. So, not understanding this, I figured pics are in need for a possible better diagnosis.
Like you, just trying to help. Cool thing about forums/internet/etc is being able to post pics. These can really help sometimes.
