tomcat

Hi SB:

Glad to help; I knew I was posting for some reason.

The only fly in the ointment is estimating blower drive HP. It goes up as you increase the amount of pressure and flow. A 1000 HP engine could be making 1200 HP and paying 200 HP to the blower. If I was sizing injectors that's what I would estimate anyway, just to be on the safe side.

When I really want to know I spin the (centrifugal) blower on a mule engine. The mule engine isn't supercharged, but by running it on a dyno with and without the blower drive belt, the difference in observed HP is what you lost to spin the blower. I just use a throttle body on the outlet of the blower to duplicate a given boost level. With that pressure and the blower RPM you can get the flowrate from the compressor map. Repeating this experiment at different RPM gives you a real compressor HP curve.

I have also found the estimated compressor HP predicted by Engine Analyzer Pro to be accurate enough for design purposes.

Tom

articfriends

iTrader: (1)

Tomcat,have you spun a centrifugal on a mule motor on a dyno to see what they really take to spin,I'd love to hear what the true parasitic loss actually is at about 10 psi boost,Smitty

articfriends

iTrader: (1)

So SB,you could really put some theory into injector size if you figure you want to make 1000hp,add in the fact the blower uses 200hp to spin THEN add in the fact the blower manifold boost pressure lessens the actual output of the injectore even though you have increased fuel pressure to it,you would need some big mo-fo's ,Smitty

articfriends

iTrader: (1)

Tyler doesn't worry much about bsfc#'s,only actual air fuel ratio's on his wide band 02sensors and egt temp's. I could see in my case why he wouldn't care as I did my own combination/engine package and built it myself. I would think (because I know the bsfc IS a good measurement of effieciency) that he would be very concerned as it would show how effiecient what he's building actually is. He did bend over backwards to help me and worked very hard on making my motor run the best it could on the dyno so I will probably use him again when I freshen the motor but maybe I will prompt him to hook up fuel flow meter. I think the issue lies in the fact you have to measure both supply flow minus return flow on these efi motors to get a true bsfc,Smitty

articfriends

iTrader: (1)

Borrowed a 28 pitch 5blade maximus this week from a fellow oso'er,tried it fri night back to back on the river against my 30 pitch labbed w/ext box w/1" spacer. Incredible cruise but slower on top end by 1 mph and lagged accelerating above 5000rpm's,also tq steered to port even wide open which boat has never done. Drained oil from lower yesterday,no metal from lower gears yet since newest treatment, even after some very long passes at hardy pond last week plus the testing fri and a couple of weekends of boating too. Pulled lower from upper,removed spacer and studs this morning putting lower back up to 1" raised position to try with 28 5 blade before returning it. Took boat out today,pulled fairly well with 5 blade even with heavy load in boat except still takes 10-20 seconds to go from 5000 to 5700. I made a half dozen high speed passes ,was heading in and leaned on it one more time,brought it up to 5000 fairly easy,started leaning on it with throttle to the wood and sheared something off in the drive . I have put 5 or 6 sets of gears in lower after they started breaking thru the hardness but haven't blown up or sheared any gears or shafts in the past 3 seasons. Either something was fatiguing or the 5 blade just pushed something past its limit,we'll see in the next few days,I think a 5 blade is just too hard on my drive with the kind of torque I'm making,Smitty

articfriends

iTrader: (1)

For the 1st time I can remember the oil (75/140 royal purple)I drained out yesterday smelled a little burnt too,it had less than 10 hours on it but they were some hard ones,Smitty

SB

iTrader: (1)

I'd be willing to bet the 5 blade helped reduce some life.

rmbuilder

Smitty,
Did any of the treated components fail or was it collateral pieces? I have additional info on the short run gear-sets we spoke of.
Bob

articfriends

iTrader: (1)

Bob,drive broke last night on the bay on our way in at sunset,won't know what broke until I get some paying work done and can get back to it in a few days but I'm thinking vert shaft. Prop spins effortlessly with no real noise,if gears blew teeth you would feel some serious crunching/binding as you spun it,Smitty

zt260

A stock 30"bravo is really about 29" I realize it’s labbed, but it’s good you could turn the 28" Maximus. What RPMs do you normally turn with the bravo?

What were the slip numbers like? You can almost always raise the drive 1" or more and have better numbers with the Maximus's diameter. Also how about WOT speed with the spacer out?

Dave