HPBCANADA.COM

on the later 56 cu in omc engines (1994 onwards) the exhaust tuner can be modified so ive been told.
But nobody has yet to mention exactly what the benefit of this modification is, and what the modified exhaust tuner
sizes are .

Will modifying the tuner give more top end and roughly what sort of rpm gain.

I have seen a few photo's of the sst60 tuner but that is for a bridgeport engine, would the tuner for the oval port be
totally different to an sst60 ?.

Bottom end I dont have any problems with nor do I have a problem with the mid-range, both of those are more than
enough for my boat, it is the top end I am seeking for a bit extra power.

I thought higher compression would help top end but apparently not.
so my next thing would be to modify the tuner if this would help gain some more top end.

if its not on the tuner, then what is the secret to getting a bit more top end from the oval port 56 cu in. ?

i am not affiliated to any organisations or clubs so no rules govern what i do to my own engines for my use.

Why not look up how to build an sst60? 110hp + on race fuel

he wants to run pump gas... still could do some porting even just cleaning up the ports can make them run better..

Hi BoomerMuskoka

can you elaborate a bit more about cleaning up the ports please.
and remember this is oval port engine, not bridged.


phill

just clean up any slag or casting flaws left in the block with a die grinder. you can port it just dont go crazy on it and dont run alot of compression and you can still wake it up a bit and run pump gas..

and people do run sst 60 motors on the lake on pump gas with soft heads..

How would i get to the ports without temoving sleeves ? On The 56 cu in the exhaust is blind. The old 49 you could take exhaust cover off and get in ther and realy go to work. But these engines are not like that. Maybe need a real tiny grinder and have a go. Would 30 thou up at the top be too much to take off the exhaust port ? Or are we talking much less. I know about getting rid of the casting marks . What i might do is have a practise on my spare block. Thanks for info

Use the SST-60 tuner on the oval port motor as well as the bridgeport if you want more top end. In addition alter the ports to the SST-60 specs (1.450" without chamfer, & 1.393" to top of chamfer). You want to chamfer the upper lip of the exhaust port at about a 30-45 degree angle to the above SST-60 spec.

Yes, it's quite tight and you must carefully grind to spec. in that the ports are blind as you stated. You can then cut head about .060-.080" to get back the compression you'll lose by raising the ports. That will preserve your bottom end and mid range power. Do not change the divergence angle of the tuner to more than the SST-60 or the power band will become very peaky. So if you build your own tuner, keep the same angle and keep the same length of 7.69" from the top of the adapter plate to the outlet of the tuner.

Good luck.

Great info hec2buck.

ive done a sort of diagram and think this is what you mean in diagram A. as in raise the whole port from midway of the oval ?

a bit confused as in the heights, because the SST60 has the deck lowered slightly compared to mine.
so do I still use the sst60 dimrntions, or do I allow for the decked height of sst60 ? as in take it up a touch higher due to my deck
height being a touch higher ? or just stick to the sst60 dims ?

and where exactly would you stop the angled chamfer ? as in at centre line of the sides or ?
do I also need to put a small clean chamfer all the way round the other ports as well to help the rings ?
I take it this is what is meant by cleaning the ports up a bit
( English v American terminology is so very different)

There are many interesting comments on this thread including the one quoted. We saw the change in SST 60 with the Mike W. Special power heads for a few racers. Paul Pitman was dominate in SST 60 with a motor that turned 7700 to 7800 rpm. Then came the Mike motors. Motors that turn over 8300 and made 105 plus hp. The problem was they have a small power band. So he developed his own sleeves. They changed the motor. The horse power was less. 100 to 105. But the curve was flatter. They made maximum power from 6500 to 7900 and still turned over 8000. The SST 60 was designed for a tunnel. By raising ports on the oval port to match the SST60 you are building a tunnel motor.
On a V hull you do not need the high porting. Those that ran a oval port only needed to match port the block and run the large carbs with 79D jets. Those motors turned approx 7500. if you are running a fishing style hull.It will not run well with a tunnel motor.

Yes, but if you match port the exhaust port to the block you end up with the same port height as the SST-60 (1.450"), with chamfer 1.393". So in reality, the SST-60 Spec. was used by those that ran the oval port on V's and turned 7500 rpm. The chamfer is a must and it should peak at the apex of the oval or else you will snag rings for sure. However, as Hounddog said, this might not work on a fishing type boat.