Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
Is anybody using silent choice with this cam?
Do you have to go to Switchable/Mufflers instead?

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

I have Lightning headers and silent choice and NO reversion.
I do run my exhaust almost dry though.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

I still have the Gil setup and I'm concerned about suck'n in water. :(

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

I also run 741 straight up. Straight headers with dumps before transom. (Almost dry) I run older Gaffrig switchable mufflers.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Silent Choice, Gil/Merc exhaust, Crane xxx741 cam. Dry as a bone.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

If you change your tails to a dry setup with the gills, you'd be ok. I wouldn't want to try it with a wet riser though. I know that I can get mine to revert with Lightning headers. And they dump further back than the gills did.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Dennis/Strikin',

I agree with Cord, convert your "wet" system to a "dry" system. Have your tailpipes extended ALL the way back through your transom and at least 6 inches out and have the water dump at the very end of the tailpipe. That way you will have a nice, one piece stainless steel tailpipe without all the wet system rubber hose stuff on it as it will look much nicer, less stuff to take apart without the rubber hose and hose clamps, etc, etc and it give it a much cleaner appearance to your engines. Actually, there are a few different ways you can dump the water out and still make it a "dry" system. I know a guy who can weld some extensions on your tailpipes. He does (or at least he did) all of GIL's tailpipe work for several years and he is very good and his pricing is extremely reasonable. His name is Bob from Lake Precision Welding in Ohio. He has done work for me and my cousin and it turned out very well. Bob's number is 440-639-1444.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

I have the 741 and stock gil exaust, and have never had reversion.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

I have had Bob that Kaama mentioned above do work on a set of tailpipes I had, he does awesome work reasonable.....he can also build you tubular risers any style or length.....Fred

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

There are other factors to look at. What is the size of the motor? Aftermarket or ported heads? In a 454, that cam is almost guaranteed to revert. With a set of wild heads on a 502 it will revert with the silent choise risers.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

At present my engine is a 502 with Brodix Plus2 CNC heads.
The cam is somewhere around 598in/615ex lift.
I bought the boat already setup like this and that's all I know about the cam until I pull it out and get numbers.
I want stroke it out to 540 and use the same heads with MAYBE 741 camshaft.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Mine are 540s with stock hp500 heads. No reversion. I was worried about it also.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Im running twins with gil exhaust wet,no reversion y pipe and silent choice 509 cubic inch

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

502s, GM rect port heads, CMI elbow tops, silent choice, 741 cam, B&M blowers, no reversion..

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

a 741 with factory mag exhaust WILL have reversion. I learned the hard way!

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

502 , Brodix bb2plus ported heads, 741 crane on 114 l/s, EMI with ss risers and silent choice and procharger no reversion.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Bigger engines will tolerate bigger cams and revert less. A 540 with those parts may work ok. Keep your idle up. If you spend too much time at 6-700 rpm, that could give you a problem. But don't be surprised if it happens. My 540's with the next size larger cam ( Crane 651) and AFR cnc heads reverted like crazy. If I loosened the tailpipe- manifold connection, water poured out in a steady stream. And my tailpipes didn't dump the water until after the transom.

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Some (not all) of the posters of the 741 not experiencing reversion are forced induction applications. The comparison is not apples to apples with N/A and should be addressed in cam selection. In a N/A motor the probability of reversion is significantly higher than forced due to the differences in the pressure differentials during the portion of the overlap period ATDC. Exhaust reversion (not intake reversion) occurs after the piston reaches TDC (beginning of intake cycle) and is descending in the bore, reducing pressure across the piston crown, at a time when both intake and exhaust valves are open. At low RPM (N/A) the pressure differential is:
Intake column> combustion chamber< exhaust tract
Allowing both exhaust gas and water back into the combustion chamber
As RPM increases the inertia of the intake and exhaust columns increase so:
Intake column> combustion chamber> exhaust tract
Negating exhaust reversion.

At low RPM in forced induction applications:
Intake column> combustion chamber> exhaust tract
The intake column is pressurized increasing the fill rate/pressure of the combustion chamber (blow through) and effectively restricting the exhaust charge/water from reverting past the exhaust valve back into the combustion chamber.
A cam profile that shows no sign of reversion in a forced induction application will have a much higher probability of exhaust reversion in an N/A application.
Bob

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

Wouldn't it be just considered a NA motor at idle since there is no boost? That idle is when the reversion is a factor, correct?

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

US1 Fountain,
Not necessarily. With a roots type supercharger for example, even at very slight throttle openings when the blower is technically not "making boost" the rotation of the rotors generates enough energy in the intake column to show an increase in the VE of the engine which counters the tendency to revert.
Bob

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

rm,
If the same motor is n/a and has 12 inches of vacuum at idle and then you add a blower and it has 12 inches of vac at idle then no difference correct? I do agree that a blown application off of idle is different. Vacuum is vacuum with or without a blower dont you think?

Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
 

HP,
Simply stated manifold vacuum is not the cause of exhaust reversion. This can be seen by a mild (duration) cam with less overlap that does not revert and hold, say, 18” manifold vacuum, where a more aggressive cam, with a higher duration and the resulting increase in overlap will have a greater tendency to revert water and only carry say 10” manifold vacuum. We reverse engineered this concept as it pertains to blower motors. While exhaust reversion is a design/engineering consideration when building a motor, only in the marine environment is exhaust reversion a mechanical factor due to the fact that many marine engines utilize cooling systems that place water in the exhaust tract. We know the consequences of water entering the combustion chamber due to reversion. The running engine, from carburetor to exhaust tips, is a series of bi-directional pulses and pressure differentials. Exhaust reversion occurs during the overlap period when the entire tract, from carburetor to exhaust tip, is open and under the correct conditions these pulses bring the discharge (and water) back into the combustion area. It appears that the supercharger being placed in this tract disrupts these bi-directional pulses enough to counter exhaust reversion. If anyone has experienced reversion with a blower motor I would be interested in the specifics.
Bob