WOT different RPM's
 

With my boat that running twin 454's at WTO I get a 1-200 rpm difference, however at anything less both engines are the same. I've not had my props blueprinted so I guess that could be a possible cause, any other ideas?

Tach discrepancy. Trim. 1-200 rpm I do not thin is reason for concern

The trim is dead on for both drives so I'm pretty sure its not a trim issue. So is this pretty typical? When I had the 330's in the boat it would always get the same RPM at WOT, with the new engines there is a slight difference. The only reason I'm asking is if one engine is losing power at WOT then I'm certainly scrubbing some speed. I don't think it's the tachs either as they are the same all the way until I have everything wound out.

Understandably so but the 1% at 3000 rpm is a smaller number than 1% at 5000. I don't know typical tach discrepancys but wouldn't be surprised to find one especially the higher in rpm. I would imagine even a **** hair of difference in drives meaning 1/8 inch could make a difference. Again they mechanical cables and at speed a little more play in one pin could be enough o make a slight difference.

If your rpm is let's 5000 and your talking a 150 rpm avg difference that would be like a 3% variance. Minimal I would think. I'm no expert just going with logic. You also have mechanical issues such as plugs, throttle cable, rotor, cap, plug wires, plug gap. A gazillion possibilities and I think you'd end up chasing something that isn't there. 400-500 rpm. Might be an issue. 100-200 I doubt it.

I had a small nick on one prop, had it repaired they also said that they balanced the prop now that side runs 200 rpms faster

Throttle cable may need adjusting. Have somebody move the throttle all the way forward and look inside the carb and make sure it's opening all the way.

I had the same issue only at Wot, once props were labed and blueprinted they are dead on now. I was told this is common where 2 of the same props are not perfect from the factory. Trying switching the tach wiring and props from each side and see if the rpm change follows

Most tachs turn to crap and start to give false readings about three years out ...... check those out before you start spending big money and if you have to buy new ones look at Autometers - They make a marine line and you can call them toll free any time. Good luck...



Jim

Twin 454mag MPI's in my Formula when I run a set of 30's they are off by 200 rpm, when I run my 28's dead a-s on.. Had the 30's labbed and it got a little better... Found out you can have big dif. in Bravo-props..

My Tachs are only 2 year old Livorsi's so I don't think its a tach issue. The props are Hydromotives- I plan on sending them off to Brett as soon as I can get on the water and get some data.