Low Comppression?Rebuild Help-

[sledmonster]

I have a 83' Rude 150 carbed up to a 175 ..I think...
I have just put the motor into use on 16ft 77 77' side winder with michigan michigan 23 23' Ballistic Four Blade Stainless. Ran 49mph 49mph, Rpm is unknown. I thought this was a little slow so a comp. revealed 75psi 75psi on 6cyls 6cyls. Is this to low? rebuiled rebuiled are there good tunersrebuilders tuners/rebuilders vancouver vancouver that are known? If not does recommend recomend american american company that i send it out to?

Possibly looking for a little more power as well

Thanks

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

sorry about the doubling up not sure what happened there?

 

[tschamp20]

Re: Low Comppression?Rebuild Help-

terretts!?

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

not sure happened in spell check
any help?

 

[tashasdaddy]

Re: Low Comppression?Rebuild Help-

don't use it, it's been messed up

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

care to elaborate there?

 

[emdsapmgr]

Re: Low Comppression?Rebuild Help-

How did you take your compression readings? Did you remove all plugs when taking the reading? If you take it with 5 other plugs in, you will get a low reading. Normal readings closer to 90-95 per cyl. You might try a can of Engine Tuner before you decide to rebuild.

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

I took my readings with the other 5 plugs out, as well with them in didnt see much difference. Are the reeds a possible area,ie. if one was damaged? my main consern was the lack of power. She just didnt want to rev out. I dont think im over pitched either.

 

[Dhadley]

Re: Low Comppression?Rebuild Help-

Without a tach it's impossible to know if youre overpropped or not. My guess is that if it's all the way down on the transom the 23 is a bit optimistic. The 75 lbs compression may not be that bad depending on which heads and gaskets ou are using. The 175 carbs aren't helping in this case.

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

I think the motor should be lifted, the cav plate is 1.25" below the keel I was trimmed all the way in and could feel the boat riding on the cav plate , ( i think) it was very unstable. The motor also a custom lower unit aluminum nose cone and leading edge. The motor was an old bass boat engine.
How high should I be going?

 

[Paul Moir]

Re: Low Comppression?Rebuild Help-

This is an almost completely ignorant answer since it comes from ignorance of both racing and V-6 engines, but as I understand it, low static compression readings are caused by raising the intake or exhaust ports. Raising the ports is a tactic used by some in an attempt to increase the performance of an engine. This is somewhat analogous to modifying the cam on a 4-stroke engine.

DHadley didn't mention it, so now I've got doubts about it.

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

thanks for that ,now too interpret

 

[Dhadley]

Re: Low Comppression?Rebuild Help-

Paul, you're absolutely correct about port timing. OMC was notorious for having pretty good intake porting but pretty consertive exhaust port timing. Raising exhaust ports (to a point) will indeed increase power and reduce static compression readings. Thats why a lot of stock loopers had low static compression but lots of power.

We're assuming, maybe incorrectly, that his motor has stock porting. Good point!

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

the motor deffinitly has been dinked with as shown by the leg work, it looked to me like they ported the lower leg to increase exaust flow? but later welded those holes shut.

 

[Dhadley]

Re: Low Comppression?Rebuild Help-

What do you mean by ported the lower leg"?

 

[sledmonster]

Re: Low Comppression?Rebuild Help-

there where longitudinal ports milled from the exaust pasage out about half way down the leg that where welded up. I couldnt see any other purpose.