Avoiding reversion?
 

OK we have been talking about cam choices for a while and one of the big factors is always reversion...I have EMI fanifolds and Merc silent choice now but the silent choice is going away!I'm going to switchable mufflers in the spring. Is there ways of limiting the ammount of water runnig through the exhaust to minimize the possibility of reversion? I think Tinker did it with his maybe he can enlighten me.....pictures would be good Steve.

ttt

Too Old has it down !:D

Pictures wont show what I did.
I have 1992 engines and I removed the cover off the thermostat housing and then removed the shield that holds the thermostat down and then drilled two 1/4 inch holes behind the shield into the area where the water inlet hose enters the housing. With these bypass holes the cold lake water will bypass the thermostat and go right out the exhaust hose ( hose that goes to the bottom of the manifolds ) This way the exhaust gets water even when the engine is cold so that the rubber hoses don't burn up.
I then run the hoses that went to the top of the exhaust out the back of the boat. I built some dumps that spray this water onto the top of the drives to cool them since it is almost lake temp. I don't have any chalking on my drives and I don't have ugly drive showers.
My exhaust runs very dry and is VERY loud in open mode. ( I have silent choice )
You can adjust the temperature of your exhaust by the size of the holes but no smaller than two 1/4 inchers.
Do not drill the thermostat or your engine will run cold at idle and low cruise.

Steve the question then is do you think this will help avoid reversion?? will it allow me to run a bigger cam with my Emi exhaust?

I have oft contemplated a reversion free hp exhaust system for boats...somthing along the lines of the old "Baja Bug" exhaust, only taller....the extended into the air pipes would have a Big Ed Daddy Roth look and could double duty as a ski tow, grab handles, even bimini framing. I've yet to do a patent search, however.

ya,keep your lobe separation back on your cam choice!

I've often wondered what effect, if any, mufflers have on reversion. Any comments?

It has always been my understanding, (and I'm sure that someone will tell me that I understand wrong) that the volume of water mixing with the exhaust (especially at speed) has very little to do with the water ingestion problem called "reversion". Camshaft LSA (Lobe Separation Angle) has a GREAT DEAL to do with it. The less LSA you can run, (like 110 deg. or less) the more HP you can make BUT the more reversion you are subject to; especially at idle. So dry pipes with a separate cooling water dump is the best answer as long as you don't need the water for silencing purposes. Going to a cam with a 113 or 114 deg. LSA will allow you to dump water in and even use a switchable exhaust divertor system and idle all the way out the channel without reversion worries. The downside is, of course, that cam doesn't make as much HP. Now you got decisions to make. Luck!! --- Jer

The only time you will have a problem with reversion is at low RPM.
The drier that you keep your exhaust the lower chance you will have any reversion.
Reversion happens when at low rpm the piston is moving back down but the valve is not yet closed and the intake valve is starting to open. This can cause reverse air flow from the exhaust into the engine.

reversion is from the lope of the cam at idle speed, hook a vac gauge to your engine at idle with a big cam in it and watch the needle, it's moving around, now bring it up in rpm's say around 2000to 2400rpms and the vac gauge smooth's out, use longer risers that dump the water futher back in the risers and make a smart cam selection and you will not have any problems

If you are concerned. run just enough water through the exhaust to keep from cooking the rubber. Dump the rest overboard.

Dyno,
Don't worry about opening the LSA to 112. While you may loose 6-8 hp peak over the same cam ground to 106 LSA , the impact on average hp and torque throughout the range will not be significant. A positive is a broader, flatter torque curve that will make the boat much more enjoyable and easier to drive. Remember reversion is a byproduct of overlap, and overlap is a function of both duration and LSA so both must be considered in your selection.
Bob

Stupid question but what if a person were to take and bypass the water coming out of the exhaust headers and run it into some buns on the pipe its self to keep the noise down, this way the water is on the downwaard side of the headers instead of being collected at the bottom of the headers.

Info -- that is how mine is riged now. I usually have to change the rubber connection hose yearly.

Hard -- The water doesn't enter the exhaust stream untill after it turns the elboe at the top of the header on manifold type or short tube headers. You need water going through the header to cool it and keep the rubber hose from burning up. The problem is that merc injects way too much water into the exhaust strickly to quiet it down.
Most of the water that is pumped out of the lake doesn't even go into the motor.

Dyno, get the stainless pipes to go along with your EMI manifolds, and tell them you want the water outlet nipples at the tail pipe to allow you to run them dry. No water out the stack, no reversion.

Dave will that cook my manifolds???it needs some water right?

No, the manifolds still will have water flow. The only difference is in where the water exits the system. Water flow still exits the manifold via the 1-inch hose from the manifold (you have this plugged on yours because the water passes through the riser gasket) to the stainless riser. Typically this water then exits the stack right at the outlet but nipples can be added on the stack just inside the transom so that the water can be dumped via a thru-hull fitting. The system still runs as cool as before but this way you have dry stacks. Remember that the stainless risers eliminate the 4-inch rubber hoses in your system.

Dyno maybe you should get on my list for switchable muffers. If you liked the gauges you love the mufflers!

bajalion so what you got????? I'm not privy to this subject??

I guess my attempt at some friday afternoon humor was a flop....maybe some of you guys are too young to remember "Big Ed Daddy Roth"....I was hoping for at least one ":D " or even a ":rolleyes: " would have at least been acknowledgement!:hothead: :cool:

Yes I'm too young but I remember the cool cars and shirts when I was a kid (I'm 40)

http://www.ratfink.org/

What you got man!!!

Dyno call me at work this afternoon or home night. I sent a PM to you. I will not be here for the rest of the morning.