the deep

iTrader: (8)

Very good thread , i'm learning every day hangin around here........

Philm

I spin my 598ci N/A with a hydraulic setup to 6000rpm all the time, and would have no issues with going to 6200rpm if it was still making power that high.

It probably wouldnt live long at all if I threw a 36" prop on it and lugged it down to 5000-5200rpm. The heat in the chambers would lead to detonation, eventually getting everything so hot that the end result would be preignition, and I would wind up with an expensive paperweight.

Baja_man

So help me out here......and this may be more prop question than engine. My current engine has rev limiter set @ 5600 rpms....was stil make power all the way up till then but torque started to drop at 5300ish. My current prop i can only spin to 4900.....maybe 5000 if its over trimmed. This prop is in stock form. It doesnt make sense to me to be able to drop prop pitch and still be faster with a lower pitch prop but at only 4900 i am leaving 80+ hp on the table. Would i benefit from dropping pitch and running higher rpm?

MILD THUNDER

iTrader: (3)

In my opinion, yes, I'd go down in pitch to get the wot rpm where the engine makes the extra 80hp. While you may not gain a bunch of speed, i would think your engine/drive would be happier.

Im guessing that if I posted this poll 15 years ago, we probably wouldnt see as many people turning 5600+rpm with pleasure boat engines. Seems that todays valvetrain technology opens things up a bit for us, campared to the old flat tappet hyd cams and light spring pressures.

mike tkach

iTrader: (3)

i spin my 540,s in my cat to 6200 rpm,but normal crusing at 65 mph is around 3300 rpm,the nice thing is the way it accelerates from 60 mph on up,if i prop it to run 5200 rpm max,it is not getting to its max powerband and acceleration is poor at best,plus detonation risk increases from lugging .just my opinion,but it works for me!

drpete3

So here is my dilema. Having engines built as we speak. Builder says ok to run at 5600 rpm and my mechaninc wants me at 5200 WOT. Guess i need to ask them more questions.

MILD THUNDER

iTrader: (3)

Give us some details on the builds pete. Many mechanics are just that, mechanics. I'd listen to the builder on what's best for the engines.

Keith Atlanta

Wayne, you are leaving almost 90 hp on the table. Look at your dyno sheet. Prop down to get that power out.

drpete3

what details are needed? heads, valves, lifters, pistons? Im unsure what you need to know

MILD THUNDER

iTrader: (3)

Dyno sheet, valve springs, cam specs, lifter style, cylinder head model, etc