94sylvan

I've seen mention of it several times here on various threads, but never a discussion devoted to extending stock exhaust risers to increase the water introduction point. Does anyone have experience with this? It seems like an inner pipe extension could be welded to the riser elbow with a piece of rubber tubing over to create the longer water jacket. A baffle (reversion ring) could be fabricated on the new outlet end to further reduce reversion chances. I have GLM manifolds (small block chevy) and would like to go more aggressive with cam if I can find a solution for exhaust. I'm eliminating my thru prop, removing the Y-pipe, and installing side exit tips due to a low swim platform so I will have a 90 degree elbow close behind the riser. Does Imco have a riser that would solve this without buying a complete exhaust?

BUP

iTrader: (9)

Corsa for 90's or whatever turns / bends and Merc or GLM extension riser blocks that fit in between your riser and manifold to raise the waterline height to aid against reversion.

AllDodge

iTrader: (1)

First I don't see anyone welding to cast iron, next the flexible rubber tubing will not hold up and have other issues. To help with reversion adding riser extensions will help
http://www.mercruiserparts.com/bam/s...31954/7585/180

f_inscreenname

You need something like this but you can only do it the SS risers (BBC).

94sylvan

Yes, that is exactly what I'm trying to do. Are those the 6" extra tall SS risers from IMCO? where did you get your elbows from?

Trash

Some of the elbow/riser combos from Merc for small blocks were stainless steel. Not all were cast iron. Second, a vertical component in the exhaust prior to water introduction does not aid much in regards to reversion. Water introduction as far away from the highest point in the exhaust will be the most benefit.

f_inscreenname

I have a guy I think I met on here that will take my 496 SS risers and makes them any size I want. The last set I had shortened so a BBC would fit under the hood of a Donzi 18. The picture is from my classic race boat where the front motor sits real deep in the hull. Had to use two 6" extensions to make the height right so it wouldn't back flow into the motor (the rear motor is almost the same). I hated the extensions so I had those risers extended accordingly and now have six 6" risers and two 3" risers sitting on a shelf where they should be.
PS, the work I had done on both sets in the race boat was cheaper then one set of 6" extensions for the same exhaust and looks much cleaner.

f_inscreenname

Here is the short set for the Donzi

94sylvan

Trash, who makes the longest tail riser stock off the shelf that will bolt up with a GLM cast manifold? I can't go dry thru hull straight back due to transom shape / swim deck so I need enough room to elbow sideways.

Trash

I wish I knew. It is problematic for SBC folk. The only thing I can tell you is that I've gone as far as a 221/230 @.050" on a 114 LSA roller cam and it doesn't revert with GLM manifolds and stock Merc stainless steel elbow/riser.

I'm not recommending you go dry either but the solution you seek with the stock manifold is elusive. I wish that weren't the case.

I'm just thinking out loud at this point but does anyone know if the Stainless Marine riser/elbows would bolt up? I don't think so but I haven't tried it.