Need educated guess for right prop for 21' Chris Craft with 600hp
05-31-2014, 08:28 AM
#11
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scare up a spare alpha lower. when this one snaps, use that as reference point for max throttle...but with that light hull, it isn't as bad as running it on a 24 or 25 foot boat. but that little hull will also get air pretty easy. i would try the paid for ballistic 24 and see what u have before investing in anything else.
06-02-2014, 10:09 AM
#12
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technically speeking your adding 280hp minimum, and conservatively you can gain 1mph per 20hp, so thats 14mph gain, 55+14=69mph top speed. figure in 15% slip, 1.5r @ 6000 rpm = 21p prop.
Start with a 21 to see how it handles the power, im guessing that the minute you go to plain off with a big prop that drive is going to snap.
back in the day my father swapped a out a 350 for a 454 in a wellcraft nova xl with an alpha, then broke 3 drives coming out of the hole, too much torque
Start with a 21 to see how it handles the power, im guessing that the minute you go to plain off with a big prop that drive is going to snap.
back in the day my father swapped a out a 350 for a 454 in a wellcraft nova xl with an alpha, then broke 3 drives coming out of the hole, too much torque
06-04-2014, 04:49 AM
#13
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Hmm...I might start with that 21" but I was maxing it out even with the old (new) 350 (around 300hp)...
although that's a little hard to evaluate since the old fuel pump didn't keep up with the demand and it stalled the engine within 5 sec of full throttle...It worked ok to about 80% of WOT.
Within those 5 secs I managed to see 5500rpm (according to rpm gauge) and speed close to 50 knots (47-49 knots)
And now with much more power and raised X dim I feel that the right pitch -should be- around 24"-> 28"
And I know that the hole shot with big torque IS bad with the alpha...but as I mentioned with my current setup the engine is not on boost (at least not much) when the boat rises to plane..that should help a bit.
I'll start with the balistic and see how it performs...
Juzzi
although that's a little hard to evaluate since the old fuel pump didn't keep up with the demand and it stalled the engine within 5 sec of full throttle...It worked ok to about 80% of WOT.
Within those 5 secs I managed to see 5500rpm (according to rpm gauge) and speed close to 50 knots (47-49 knots)
And now with much more power and raised X dim I feel that the right pitch -should be- around 24"-> 28"
And I know that the hole shot with big torque IS bad with the alpha...but as I mentioned with my current setup the engine is not on boost (at least not much) when the boat rises to plane..that should help a bit.
I'll start with the balistic and see how it performs...
Juzzi
06-04-2014, 07:11 AM
#14
I would not use the aluminum prop, i was thinking a 21 mirage or a mirage plus, from what your telling me you where getting 25% slip thats high, my calculations are for 15% which would be acceptable. If you only have those props to test then the balistic would be the best choice.
06-19-2014, 07:03 PM
#19
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I'm guessing to be making the kind of power you say it makes, that engine is going to be spinning some serious rpm's. My guess is around 65-6700 rpms. With that said, I doubt your alpha will last one wide open run. As for prop, I would think a 21 pitch. I don't think there is any way your going to spin anything more than a 23 at the rpms that engine will need.
A few years ago I had a Formula 242 with a 330 hp 454, top end was around 53 mph with a 21 mirage. I then replaced it with a 540 hp +/-, 427 designed for my application. The new engine made max hp at 6100 rpms. I started with a labbed Mirage Plus 25. I got 4600 RPMs and 56 MPH. I then tried a 23 Mirage Plus, I got 5300 rpms and 62 mph. Then I put on a 21 Mirage plus and got 6000 rpms and 69 mph. So in the end i used the same prop, just spun it a lot harder. Now you are using a supercharger the way it sounds, so it may change a few things but I say you are going to be around a 21 or 23 Mirage. Don't even think about using an aluminum prop. I wouldn't waste your money on anything bigger until you see where the 21 and 23 put you. As you can see from my results, the 200 rpms per pitch rule doesn't work when you're way out of your RPM range. Seeing that your engine was built for a Corvette with a hotter cam that engine is going to need to be spun really hard, probably too hard for a boat. I would get the specifics on the engine other than just what the max hp is. You need to know at what RPM it's making that power. I don't know much about LS1 engines, but as you will learn on this forum, what works in a car, rarely works in a boat.
Also what were you using to calculate your speeds, your boats speedo?
A few years ago I had a Formula 242 with a 330 hp 454, top end was around 53 mph with a 21 mirage. I then replaced it with a 540 hp +/-, 427 designed for my application. The new engine made max hp at 6100 rpms. I started with a labbed Mirage Plus 25. I got 4600 RPMs and 56 MPH. I then tried a 23 Mirage Plus, I got 5300 rpms and 62 mph. Then I put on a 21 Mirage plus and got 6000 rpms and 69 mph. So in the end i used the same prop, just spun it a lot harder. Now you are using a supercharger the way it sounds, so it may change a few things but I say you are going to be around a 21 or 23 Mirage. Don't even think about using an aluminum prop. I wouldn't waste your money on anything bigger until you see where the 21 and 23 put you. As you can see from my results, the 200 rpms per pitch rule doesn't work when you're way out of your RPM range. Seeing that your engine was built for a Corvette with a hotter cam that engine is going to need to be spun really hard, probably too hard for a boat. I would get the specifics on the engine other than just what the max hp is. You need to know at what RPM it's making that power. I don't know much about LS1 engines, but as you will learn on this forum, what works in a car, rarely works in a boat.
Also what were you using to calculate your speeds, your boats speedo?
Last edited by endeavour32; 06-19-2014 at 07:40 PM.
08-12-2014, 03:43 AM
#20
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I have not seen the actual dyno sheet from the seller...but he beeing a friend of mine for years I doubt he would feel the need to elevate the numbers...
The rpm for the max power with LS1 is usually in the range of 6200-6500...but I'm not going to spin that high...I plan to keep the max rpm between 5500-6000.
The 24' formula that you have/had is quite a bit bigger boat than mine 21' chris ...I would guess 1000lbs more weight...so it would need a lot more torque and LS1 charged or not might not be a optimal for it...
My own goal is around 70mph / 60 knots AND keeping the engine rpms right at or below 6000.
I use the Navigator program on ipad (GPS) to check the speed
Juzzi
The rpm for the max power with LS1 is usually in the range of 6200-6500...but I'm not going to spin that high...I plan to keep the max rpm between 5500-6000.
The 24' formula that you have/had is quite a bit bigger boat than mine 21' chris ...I would guess 1000lbs more weight...so it would need a lot more torque and LS1 charged or not might not be a optimal for it...
My own goal is around 70mph / 60 knots AND keeping the engine rpms right at or below 6000.
I use the Navigator program on ipad (GPS) to check the speed
Juzzi
I'm guessing to be making the kind of power you say it makes, that engine is going to be spinning some serious rpm's. My guess is around 65-6700 rpms. With that said, I doubt your alpha will last one wide open run. As for prop, I would think a 21 pitch. I don't think there is any way your going to spin anything more than a 23 at the rpms that engine will need.
A few years ago I had a Formula 242 with a 330 hp 454, top end was around 53 mph with a 21 mirage. I then replaced it with a 540 hp +/-, 427 designed for my application. The new engine made max hp at 6100 rpms. I started with a labbed Mirage Plus 25. I got 4600 RPMs and 56 MPH. I then tried a 23 Mirage Plus, I got 5300 rpms and 62 mph. Then I put on a 21 Mirage plus and got 6000 rpms and 69 mph. So in the end i used the same prop, just spun it a lot harder. Now you are using a supercharger the way it sounds, so it may change a few things but I say you are going to be around a 21 or 23 Mirage. Don't even think about using an aluminum prop. I wouldn't waste your money on anything bigger until you see where the 21 and 23 put you. As you can see from my results, the 200 rpms per pitch rule doesn't work when you're way out of your RPM range. Seeing that your engine was built for a Corvette with a hotter cam that engine is going to need to be spun really hard, probably too hard for a boat. I would get the specifics on the engine other than just what the max hp is. You need to know at what RPM it's making that power. I don't know much about LS1 engines, but as you will learn on this forum, what works in a car, rarely works in a boat.
Also what were you using to calculate your speeds, your boats speedo?
A few years ago I had a Formula 242 with a 330 hp 454, top end was around 53 mph with a 21 mirage. I then replaced it with a 540 hp +/-, 427 designed for my application. The new engine made max hp at 6100 rpms. I started with a labbed Mirage Plus 25. I got 4600 RPMs and 56 MPH. I then tried a 23 Mirage Plus, I got 5300 rpms and 62 mph. Then I put on a 21 Mirage plus and got 6000 rpms and 69 mph. So in the end i used the same prop, just spun it a lot harder. Now you are using a supercharger the way it sounds, so it may change a few things but I say you are going to be around a 21 or 23 Mirage. Don't even think about using an aluminum prop. I wouldn't waste your money on anything bigger until you see where the 21 and 23 put you. As you can see from my results, the 200 rpms per pitch rule doesn't work when you're way out of your RPM range. Seeing that your engine was built for a Corvette with a hotter cam that engine is going to need to be spun really hard, probably too hard for a boat. I would get the specifics on the engine other than just what the max hp is. You need to know at what RPM it's making that power. I don't know much about LS1 engines, but as you will learn on this forum, what works in a car, rarely works in a boat.
Also what were you using to calculate your speeds, your boats speedo?
