Thanks again for all the help guys. Do you think Ill find an improvement with installing the Gils? I have dart heads and intake , 850 holley and a mild hyd cam. It dynod at 490 hp at 5200. I will install a roller setup next year. But everyone tells me I need the exhaust more. Thanks....sj

stevejohns,

Several years back I installed a set of Gils on my 502 with roller cam. I fired on a test stand to hear it run and check things out. After 5min of run time I found the oil in the pan was milky.. I drained the oil and refilled it.. 5 min run time same thing. So I thru on a set of stock manifolds and the problem went away. That is when I heard of reversion. The Gils I had were extended pipes that had the water flow enterning the exhaust stream at the end of the pipe. Acutally the inner pipe was enlarged to meet with the ID of the other pipe. In this transistion where three holes about 3/8" if I remember correctly. The water was sprayed into the exhaust stream and it was actually being sucked up the ID of the inner pipe at an idle. Well I blamed the situation on the roller cam that I had. To solve the problem I changed the end of the pipes. I had to shorten the pipes anyway, so what I did was to shorten the outer pipe, which extended the inner pipe about an inch or more past the outer pipe. I put spacers on the inner pipe to block the water flow equal to the three 3/8" holes. You dont want to weld the outer pipe to the inner because of difference of expansion in the two pipes. With the water entering the exhaust stream before the end of the inner pipe it eliminated the reversion proplem. I used rubber exhaust hose to connect the pipes to the tips in the transom. Worked good untill I got my CMI's.
So this may be what your friend is referring to about the Gils. With any combination cam timing exhaust length, water introduction are all factors. It depends how it all works out. Also my Gils had the turbolators installed and the water flowed right past them. As always any leaks compound the problem.. So presure check for leaks before you buy.. Good luck.. Hope this helps.

Dick

Dick;

Are you saying that you had reversion with the Gils but not with stock Mercruiser Manifolds?????

hmmm im really starting to think about different manifolds. I was considering gils cuz there is many around from people taking them off 500hps. Maybe EMIS , IMCOS or Stainless Marine

I found a good $$ on a new set of EMIs here all brackets and hardware... 1050.00. I think Ill go with those. thanks again.. sj

Some of the 500's had a problem when Mercury used the 4 inch riser after they went to the six inch riser the problem stopped. The cam overlap determines if there is going to be a problem at idle speeds.