View Full Version : need 1000 rpm
glashole
05-08-2007, 09:04 AM
I need to gain 1000 RPM
after the new motor switch etc I am having difficulty getting the motor above 4500 RPM
I have trimmed the boat to max and this is the highest I can get
the new motor is supposed to start really working between 4000- 6000
motor is a carberated 502 approx 500 HP
right now i am running a Blackhawk drive with 31: props 1:50 gears
I have put it out there to anyone willing to part with a set of 29's on another post, as I think that might bring it up there (this is the question)
I also have a drive that will have 1:36 gears (not yet installed) but I don't think this will give me the RPM's I need but rather slow the motor down
I am looking for suggestions with regards to options :)
does anyone have a set of 29's or 27's that I could try out for a quick blast at the AOTH?
should i be looking at something else
regards
Shea
Shea you need to look into the motor, 500HP is more then you had something is not right!
Phil
glashole
05-08-2007, 09:25 AM
I am thinking maybe the torque curve is different
mrfixxall
05-08-2007, 09:25 AM
are those the oe props you had with the old engine? if so like mop said theirs somthing wrong in the engine,,,,mabe the rockers are to tight??
glashole
05-08-2007, 09:34 AM
with no load the motor will run up to 6-7000 rpm
I do have a smaller spark arrestor on it
I have a free-er flowing one showing up in the next couple of days
however it didn't seemed starved for air
98shovel
05-08-2007, 10:39 AM
what cam/carb is in the motor
whats the total ign. timing are where does it come in
did u check to see if u have full throttle at the carb if its a vac. sec carb are the sec. opening all the way ,the 1.36 will hurt your rpm
Conquistador_del_mar
05-08-2007, 11:12 AM
Shea,
I have no idea what boat you are trying to run a set of 31" pitch props on or exactly how efficient the Blackhawk drive system is, but I can tell you that if you could turn 31" pitch props at 5500RPM on a conventional drive with a typical 10% slippage with a 1.5 gear ratio, then you would be doing at least 97MPH. I know the Blackhawk is quite a bit more efficient (less slippage) so you would be doing well in excess of 100MPH. By my rough calculations, you will need to drop down to around a 25" set, although you might be able to turn the 27" set if your cam really starts to kick in at the upper 4000RPMs. The other 1.36 gear set will result in needing even lighter pitch props. I run a 29" Hydromotive Q four blade prop at 5300RPM on a Bravo 1.5 drive for a top speed of 93MPH on my 23' Eliminator Daytona powered by a 600HP blower engine. Bill
I need to gain 1000 RPM
after the new motor switch etc I am having difficulty getting the motor above 4500 RPM
I have trimmed the boat to max and this is the highest I can get
the new motor is supposed to start really working between 4000- 6000
motor is a carberated 502 approx 500 HP
right now i am running a Blackhawk drive with 31: props 1:50 gears
I have put it out there to anyone willing to part with a set of 29's on another post, as I think that might bring it up there (this is the question)
I also have a drive that will have 1:36 gears (not yet installed) but I don't think this will give me the RPM's I need but rather slow the motor down
I am looking for suggestions with regards to options :)
does anyone have a set of 29's or 27's that I could try out for a quick blast at the AOTH?
should i be looking at something else
regards
Shea
glashole
05-08-2007, 11:23 AM
blackhawks tipically have more slippage as they are a surface drive
you say those number's like there is something wrong
seriously I don't expect that high of a mph
BigGrizzly
05-08-2007, 11:50 AM
The stock Blackhawk had 415 hp and turned 31s props. If you reall want to turn that drive at 6000 or 7000 the drive will come apart. The drive isw not capable of those sustained RPMS! We have done many 502 with quite a bit more HP than that and they all worked at 4000. So I am going to say something is really wrong but I don't have a clue
Rootsy
05-08-2007, 12:27 PM
welp if you can't find any 29's you could always have your 31's cut down a bit or regear the BH to a 1.65:1... or figure out what is wrong with the motor... trouble with "estimating" what an engine is going to put out is that it is just that.. "estimating"... 500 crank hp on a dyno (or computer simulation) with tubular headers is NOT 500 hp at the crank with stainless marine or imco's or such...
Conquistador_del_mar
05-08-2007, 12:39 PM
Shea,
Is there a possibility that your drive x dimension is too much - is it running too deep for the drive to run as a partial surface drive? When I installed the Bravo drive on my boat, I talked to some Florida experts to find out exactly how high I could mount the drive and still get up on plane. I am pushing the limit, but I get the maximum top end. I am mounted almost 3" above what the factory recommends as the limit, but it gets up on plane unless I have a full load (then everyone has to come forward for a few seconds). I designed a custom 1/2" aluminum transom plate which I mounted using 1/2" SS button head bolts since I was changing from a Volvo to a Mercruiser drive. I took my chances mounting it so high with the understanding that I could always add an extension to the drive if I went too high, but it worked out perfectly. Bill
blackhawks tipically have more slippage as they are a surface drive
you say those number's like there is something wrong
seriously I don't expect that high of a mph
glashole
05-08-2007, 12:42 PM
I understand what you are saying with regards to the HP being estimated
what you are saying is the motor may be way overestimated and therefore just doesn't have the balls to turn the props?
The motor seems strong at all RPM's and is running really good
4000 RPM with 3 people full tank of gas was 68 GPS (weekend)
at 4500 RPMs it is running 78 GPS with just me (full figured gentleman) and 1/2 tank of gas, calm water (last night)
Bill- I haven't changed the drive from its stock location, all I changed was the motor and the drive worked good in the last configuration
Did it not run up around 80 with the old engine? Sounds like someone sold you a 350-370 hp engine not a 500.
glashole
05-08-2007, 01:47 PM
the old motor was pooched
:( and after disassembly i was found to not have the performance parts it was supposed to
estimated hp on the old was about 350-375 after disassembly
and I could only get it to about 73-74 top
I don't think its me
but believe me I will keep trying to squeeze out as much as possible with relation to trim and tabs etc..
the 4500 rpm was flat out wfo for about 5-6 min and it wasn't going above it until I trimmed a tad to much and it revved up to about 4900 and lost traction and was just shooting a rooster tail
no tabs
Shea I am pretty sure I read that the true BH uses very little if any drive trim. I have an opinion!!! Instead of dumping the buck on the props yank it and put another cam in the beast so it runs like a true BH. Spank me when you see me!!!
Phil
glashole
05-08-2007, 02:58 PM
It has a high performance cam
max trim is between 1/8 and 1/4 and higher than 1/4 is more just a rooster tail
I appreciate everyone's opinions and will continue with my trial and error
It has a high performance cam
My guess is that's where the problem is. Not making enough power to get "over the hump" at lower rpm. What are the specs on the cam?
Another question for the class, how fast do Blackhawks run with the 502/415?
mrfixxall
05-08-2007, 08:38 PM
Tell us exactly what you did to the engine,,,head work, what cuda said about the cam specs(type whats on the cam card) what machine work on the block,piston to cyl wall clearances 3 thou 5 thou?? did you zero deck the block? ring gaps?? did you update the carb and or the jet sizes???
DonCig
05-08-2007, 11:14 PM
I have seen the Blackhawk drive run at slip numbers from 9% to 17%, mine runs around 12-13%. I have read, but can not truly confirm that they tend to run with more slip than a deep water drive.
I have run a 1:36, 1:50 and a 1:65 BH drive all on the same boat and they make a notable difference in throttle response and acceleration. I personally prefer to use the drives in the following order, provided I have a high enough pitch prop to hit my desired top speed rpm.
1. 1:65 with 31's good for around 78-85 mph top end in the 5,000 rpm range.
2. 1:50 with 31's good for around 86-93 mph top end in the 5,000 rpm range.
3. 1:36 with 31's good for around 94-99 mph top end in the 5,000 rpm range.
Usually I see 500 rpm change between the drives with no change in props and I usually see about 400 rpm change when moving up or down between the BH prop sizes. Remember they jump in 2" approx. increments.
I have sent you a pm on my props and BH drive for sale.
Don
glashole
05-09-2007, 07:02 AM
I will get the specs on the cam etc..
RedDog
05-09-2007, 07:11 AM
...Another question for the class, how fast do Blackhawks run with the 502/415?
I think stockers will run 78 to 80
glashole
05-09-2007, 11:37 AM
I have just recieved the boat back from repairs (exactly 1 week to late for Lake George)
the cam was an issue apparently and has been changed along with a few other parts
will retest this evening and see what sort of difference it makes
Shea
glashole
07-10-2007, 10:16 AM
big difference
I am still breaking it in but took it up to about 4900 and it is working awesome with the 31's
we took the motor to compete merc 500 specs using a merc 500 cam and roller rockers and lifters etc..
motor is mint :)
thanks to all for your opinions and info
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