What should I do lost RPM, but still same speed
09-13-2005, 03:03 AM
#11
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Re: What should I do lost RPM, but still same speed
Originally Posted by GOODT
prop it right and you should be good to go wouldnt bother with more engine mods unless you have a big pocket then would make more changes but would first I would see what she will do with the right prop!!!!!
09-18-2005, 07:51 PM
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Re: What should I do lost RPM, but still same speed
I'm having the same sort of problem. I've been through numerous props can't seem to find the right ones.
boat is very heavy 11500 dry probally about 15000 lbs loaded with fuel and water. trs drives
running built up 454's with prochargers at 5lbs of boost
1. started with orginal 21p 3 blade props hit rev limiters
2. then went with 27p 3 blade props hit about 3000 rpms then seemed to blow out, just over rev'ed (is it possible transmissions where slipping)
3. then went to 25p 3 blade cleaver props would not move boat at all
4. now running 23p 3 blade runs ok but still hits rev limiter near wot, Still running the same speed as as orginal 454 HO's with the 21 pitch props. 58 mph gps at 5000 rpms. doesn't make much sense but true. maybe getting more slippage don't know
going to try 24p 4 blade next week and I have a set of 25p 3 blade coming in. Was wondering if a large 32p cleaver prop would work, would it move a heavy boat, the 25's wouldn't do anything or is a 4 blade better for a heavy boat. I need something that will lift boat out of water and give more speed. awful lot of money wasted if I can't get more speed out of these motors.
boat is very heavy 11500 dry probally about 15000 lbs loaded with fuel and water. trs drives
running built up 454's with prochargers at 5lbs of boost
1. started with orginal 21p 3 blade props hit rev limiters
2. then went with 27p 3 blade props hit about 3000 rpms then seemed to blow out, just over rev'ed (is it possible transmissions where slipping)
3. then went to 25p 3 blade cleaver props would not move boat at all
4. now running 23p 3 blade runs ok but still hits rev limiter near wot, Still running the same speed as as orginal 454 HO's with the 21 pitch props. 58 mph gps at 5000 rpms. doesn't make much sense but true. maybe getting more slippage don't know
going to try 24p 4 blade next week and I have a set of 25p 3 blade coming in. Was wondering if a large 32p cleaver prop would work, would it move a heavy boat, the 25's wouldn't do anything or is a 4 blade better for a heavy boat. I need something that will lift boat out of water and give more speed. awful lot of money wasted if I can't get more speed out of these motors.
09-18-2005, 10:41 PM
#13
Charter Member # 55
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Re: What should I do lost RPM, but still same speed
Originally Posted by Payton
The 721 cam is the same cam that Merc used in the 420 and 525sc (both 454s) engines. It's not all that bad of a choice.
The cam used in the 420/525sc is a Crane #132561 and is a flat tappet.
The 139721 is a roller and is used in the HP500 or 500efi, can't remember which.
09-19-2005, 09:33 PM
#15
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Re: What should I do lost RPM, but still same speed
Originally Posted by US1 Fountain
I thought the 731 cam is what was used in the 500's?
After a little research, its neither the 721 or 731. Its a grind in between them.
http://www.offshoreonly.com/forums/s...00hp+cam+specs
721 specs 214/222 .553/.576 on a 110 lobe sep
731 specs 226/234 .587/.610 on a 112 lobe sep
500hp cam crane #169611 specs 222/230 .576/.598 on a 110 lobe sep
