TomZ

iTrader: (2)

Joe, I pressaure tested the risers and they're good. Valve adjustments are good, too (they're a little on the loose side). Being the off-season now, a leakdown test wouldn't hurt, though I haven't seen/heard any signs of valves leaking.

When we were out this past weekend, I kept the idle high (1500-ish) when docked and leaving her running (parking the truck, etc), and had no trouble with cylinders dropping. When a cylinder does drop, I good rev will bring it back to life.

And just to mention... my oil looks good. There aren't any signs of water intrusion into the oil at all; nice and clean. So whatever amount of water it is that's coming through seems to be minimal... just enough to be an annoyance at this point, though it is something I want to correct.

I'll order son new manifold gaskets this week. Anyone got a good part number for a well-sealing gasket? The heads are Dart 360s.

SB

iTrader: (1)

Don't you have 454 or similar ?

That size intake runner could have so much dead airflow for that motor that reversion is more likely.

14 apache

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[QUOTE=TomZ;4499944]Joe, I pressaure tested the risers and they're good. Valve adjustments are good, too (they're a little on the loose side). Being the off

The exhaust gasket used on 1075 mercruiser are made by cometic MLS only set you will ever buy again.

TomZ

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Can you explain a bit more in depth?

Have been over the use of these heads with a number of knowledgeable folks, and no one has ever brought up this. And though these heads are overkill for the displacement, the engine is very responsive with, and shows no signs of laziness. The blower helps a lot here.

HyFive578

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The 525EFI cam has a fair amount of overlap on the exhaust cycle. I've been battling reversion on my two rear motors for three years now. I would definitely recommend going to full length tails.

Black Baja

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The Dart 360 heads is what's killing you. With those heads on a 454 there is no air speed in the intake at idle and it will re-vert like crazy. Put smaller heads on and I would bet money it goes away.

TomZ

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I'm not an expert here, but my understanding is that the supercharger, even though it's not making boost, is still moving air. In a NA appliacation I could see what you and SB are saying, but with the blower I don't think this is the case. Can you further elaborate?

I know the head is not optimal for the displacement, but they're what I had and hey've worked really well so far with the blower, on the dyno and in the boat. If needed I'll fix the exhaust to compensate.

Thanks!

Black Baja

iTrader: (2)

A 454 that spins 5,500 rpm is going to want a cylinder head with a cross sectional area about 2.28sq in the heads you have should be in the neighborhood of 3.6sq inches. So, what ends up happening is the airspeed in the intake is very lazy. Why? Well simple air moves a lot faster through a small hole than a large hole. Why does this become a problem? Well, when the cam is in overlap the air is not traveling fast enough through the intake to clean the cylinder out and the exhaust gasses start backing up in the intake and this reversion is pulling the water back up the tailpipes. But we have a blower on top... The intake is subject to atmospheric pressure until the blower starts making boost. At this point the only thing the blower is doing at idle is protecting the boosters in the carb from the intake pulses that travel back up the ports when the valve shuts on the compression stroke. If there is some run time on your motor I'd be willing to bet if you pulled the blower and inspected the intake ports that there is carbon in the intake ports. Making the exhaust fully dry is only a bandaid.

HaxbySpeed

Too much initial timing can cause reversion. Dump some timing at idle before getting too crazy.

mike tkach

iTrader: (3)

except for the last part i 100%agree.my thinking is it is cheeper&easier to go with dry pipes than changing cylinder heads.if their is no water in the exhaust water reversion is no more.