Big rods vs small rods in looper built as a ski motor.

[neveredge]

OK, I have a 2.7 omc that is being bored to 3.0 and I have a set of lightened pistons for it.

I am not looking for all out speed and the motor is going to be ported to stay under 7000 rpm. I may even use a 6700 rpm limited pack.

I am looking for snappy low end performance and I think the lighter small rods would help provide this along with the light pistons. Will the volume lost by the small rods be overcome by the fact that they are so much lighter than the big rods? Or vise versa?

[Dhadley]

I've used the light rods and light pistons in many motors like youre building and have always been impressed with the way they run. Especially at idle and especially the V4's. In fact I wouldn't build one without the light rods and pistons. You'll be glad you did.

[H2OPERF]

Late rods will be fine sounds like your going to be fairly stock,to be honest though don't think u will really notice the diff unless your running on a really light boat with a small wheel.Personally i like the big rods thier bullet proof, turn mine 82-8400 all the time.dave

[neveredge]

I am comparing it to what I have experienced with crossflows. In other wise identical motors on a 1200 lbs. hull the motor with the lightened pistons and wristpins had a very noticable difference in out of the hole performance.

I could feel the difference in how the motor with the light parts shoved me back harder in the seat than the other motor. Granted, the boat was not run back to back or even in the same month but the prop and load was the same. It was actually a little warmer when we ran the light piston motor.

The motor should produce about 270 hp at the prop at around 6700 rpm after it is finished. It isn't going to be a race motor so if the light rods will show a bottom end improvement then it would be worth it to me. After all, the sensation of speed to my passangers is going to be the acceleration and not watching the speedo eek past 100.

I also want a good boost of power to knock my kids off the tube!!!!!!!!!!!

[MrG]

If it was finger ported or if you got a 2000 Fict and take the boost port and finger ports to the rod slot like the 3.3 it would be a rope breaker ��

[MrG]

[Instigator]

Who’s dyno chart?

To me, the biggest things w/the small rods is, if you pop one, which you will if you’re learning to do your own tuning (ask me how I know) the small rods break and saw your block in half.

If you have time/money in porting, etc, it’s an expensive oop’s.

The big rods won’t break, so normally you can repair the block.
Replace a sleeve, maybe a little welding and your back on the water.

Ive bent a large one but never broke one.

Performance wise, I’ve turned them both 8300+ many times and saw no difference.

Even if I’m giving up a bit of spool up time, Ill give it up to not cry after sawing my favorite block in half.



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=MrG;3322424][/QUOTE]

[racer]

If you lower the finger on a 3.0 to the bottom like a behind the liner 3.3 you have to cut the sleeve which then leaves less sleeve at the bottom than a 3.3 and the lower part of the cylinder will not stay round. For what it sounds like you want IMO just do a good clean up and fill in the idle relief hole. This will give you good low end and stay reliable. As mentioned the small rods will live under 7K but will break a lot quicker than the big rods if you have an issue.