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onesubdrvr
06-25-2005, 09:10 PM
OK,

:bonk: :pizza: :toiletpap :eek: :toiletpap :sombrero:

New drive for the Ragazza is going to be a 5.7l Cobra - the old drive was a 4.3l so my gear ratio is going to 1.41:1 from 1.68:1,.....bigger change than I thought it would be,....

How much do you think this will change my engine RPM. With the Turbo I-22p, I was able to turn 5200-5300rpm. I'm hoping that I'll be at about 4600-4800, any guesses?

Thanks
Wayne

Mr X
06-25-2005, 09:23 PM
I would guess more like 4300-4500

DonCig
06-25-2005, 11:23 PM
This may help you. I would guess around a 400/450 rpm difference.http://www.go-fast.com/sterndrive_gear_ratios.htm

DonCig

penbroke
06-25-2005, 11:37 PM
Assuming a FLAT power curve and no other changes:
1.41/1.68 x 5200 = 4364 RPM

Frank

onesubdrvr
07-20-2005, 08:42 PM
Assuming a FLAT power curve and no other changes:
1.41/1.68 x 5200 = 4364 RPM

Frank

Hmmm, flat power curve,...

well, If I'm making more torque at lower RPM's (385 lb-ft) @ 4364, vice 330 lb-ft at what I was running (5200rpm), am I to assume that I will most likely turn a little faster than the above less complex calculation?

My dyno sheet shows peak hp (340) @ 5000rpm, so really, I was a little less at the RPM's I was turning, and peaktorque @ 4000rpm (400 lb-ft). This based on valve opening / closing based at .050".

With valve opening based on open to close, peak hp 355 @ 5500rpm, peak torque 385 lb-ft @ 4500rpm).

I guess what I'm really trying to figure out (and I know water time is the best way), but am I going to have to try a whole new pitch of prop, or will my Turbo I 22p be OK? Where do I want my RPM's to be?

Just curious, boat comes home Friday!! :hyper:
Wayne

Cuda
07-20-2005, 10:24 PM
I'd say you want it at the peak horsepower.

onesubdrvr
09-16-2005, 04:16 PM
OK, the results are in,...

Turbo I 22p, 1.43:1 ratio - 4500rpm, 60mph

I read on a different thread (and make sense) that you want to prop at RPM for peak HP, and cruise speed at peak torque RPM.

My engine peaks HP @ 5500, Torque @ 4500 so it looks like I want to change prop to gain 1k RPM :boggled: ?

If so, I'd go from a Turbo I 22p to a 17p? (using the 200rpm / 1" pitch rule) any input here?

I'll probably throw the stock "Viper" 19P SS on for this weekend and see what gives, but I'm interested in what y'all think

Wayne

Cuda
09-16-2005, 04:35 PM
Props are a black science. Each boat seems to be a law unto itself. I'd try to borrow a few, and see what happens. 60 with your setup now sounds pretty damn good I think.

Keep in mind, props AIN'T cheap! :frown:

blackhawk
09-16-2005, 04:37 PM
OK, the results are in,...

Turbo I 22p, 1.43:1 ratio - 4500rpm, 60mph

I read on a different thread (and make sense) that you want to prop at RPM for peak HP, and cruise speed at peak torque RPM.

My engine peaks HP @ 5500, Torque @ 4500 so it looks like I want to change prop to gain 1k RPM :boggled: ?

If so, I'd go from a Turbo I 22p to a 17p? (using the 200rpm / 1" pitch rule) any input here?

I'll probably throw the stock "Viper" 19P SS on for this weekend and see what gives, but I'm interested in what y'all think

Wayne

I would think you'll want to be around the 19" range for 5500 rpm. I'd throw the Viper on and see what she does. I like the Viper props.

onesubdrvr
09-16-2005, 05:14 PM
Props are a black science. Each boat seems to be a law unto itself. I'd try to borrow a few, and see what happens. 60 with your setup now sounds pretty damn good I think.

Keep in mind, props AIN'T cheap! :frown:
Joe, those are 3 of the mose true statement I've ever heard!!

It is pretty good (speed wise), but VERY slow out of the hole (even though I don't gun it). And, if what holds true (torque and hp), that means I'm cruising at 60mph!! not too shabby :bonk: - Just kidding, I know that I need to prop at HP to get cruise speed at cruise RPM's!!

Wayne

onesubdrvr
09-16-2005, 05:16 PM
I would think you'll want to be around the 19" range for 5500 rpm. I'd throw the Viper on and see what she does. I like the Viper props.
I'll tell you, I must have a VERY bland boat, of the 3 props I've tried, other than RPM and Speed differences, the hull acts pretty much the same (ie pourposing, chine walk, etc),.... but there again, I am pretty mild in HP,.... and although I do see some pourposing, I can easily trim it out. I'll try the Viper this weekend.

Wayne