Looking for another 500 rpms!
#1
Registered
Thread Starter
![Default](/forums/images/icons/icon1.gif)
I've got an 87 Formula 242 that I'm looking to get another 500 rpms out of my current engine so I can jump up one more prop size. I'm currently spinning a 21 Mirage and would like to spin a 23 Mirage Plus. I'm able to get 6000 rpms out of my current engine which is a 439" BBC that has around 525 hp. I currently am running a Weiand Stealth intake with a holley hp 950 and I'm curious if I switched to a single plane and ran a supersucker spacer if I could realisticly pull the extra rpms that I'm looking for? I'm only getting 62 mph and would really like to get to at least 65-67 mph. I know other guys that are getting 62 mph with a stock 502 mag (415 hp) in the same boat so I'm curious if there is something else I should be looking at, it seems I should be going much faster... As it is I'm getting about 21% prop slip which seems really high for this boat. Most are around 15-16% slip.
#3
Registered
Join Date: Aug 2005
Location: Between A Womans Leggs in IL
Posts: 6,306
Likes: 0
Received 1 Like
on
1 Post
![Default](/forums/images/icons/icon1.gif)
the first thing i would do is try another carburetor,,i think that 950 hp is to big for your motor..i would look for a 800 and try that first..i jetted my 355 in my donzi rich until i gt on the water and then started playing with jet sizes,just from going down 4 jet sizes on the secondaries i picked up 300 rpm's..im running a 750 hp style carb..
#4
Crazy Energy
![](https://www.offshoreonly.com/forums/images/icons/platinum_member_star.gif)
Join Date: Aug 2007
Location: Oklahoma God's country no one else wants it.
Posts: 4,334
Likes: 0
Received 1 Like
on
1 Post
![Default](/forums/images/icons/icon1.gif)
the first thing i would do is try another carburetor,,i think that 950 hp is to big for your motor..i would look for a 800 and try that first..i jetted my 355 in my donzi rich until i gt on the water and then started playing with jet sizes,just from going down 4 jet sizes on the secondaries i picked up 300 rpm's..im running a 750 hp style carb..
#5
Registered
![](https://www.offshoreonly.com/forums/images/icons/platinum_member_star.gif)
Join Date: Mar 2008
Location: Vancouver BC
Posts: 1,181
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
Patrick's carbs are usually right on. How was the air fuel on the dyno and what RPM was peak power?
Last edited by HaxbySpeed; 09-07-2010 at 09:48 PM.
#6
Registered
Thread Starter
![Default](/forums/images/icons/icon1.gif)
the first thing i would do is try another carburetor,,i think that 950 hp is to big for your motor..i would look for a 800 and try that first..i jetted my 355 in my donzi rich until i gt on the water and then started playing with jet sizes,just from going down 4 jet sizes on the secondaries i picked up 300 rpm's..im running a 750 hp style carb..
As for the dyno, I never dynoed the engine... Once the season is over I'm going to pull the engine and get the thing dynoed so I really know what I'm dealing with.
Last edited by endeavour32; 09-07-2010 at 09:51 PM.
#7
Crazy Energy
![](https://www.offshoreonly.com/forums/images/icons/platinum_member_star.gif)
Join Date: Aug 2007
Location: Oklahoma God's country no one else wants it.
Posts: 4,334
Likes: 0
Received 1 Like
on
1 Post
![Default](/forums/images/icons/icon1.gif)
I'm pretty sure the carb is the right size I had prosystems build it for my engine combo. It flows 830 cfm's. The HP numbers are very misleading and do not equal flow. I did have to jet the carb up do to a lean issue that ruined two pistons. I do find it odd that the carb gets ice cold when I'm running the boat which causes a lot of condensation. Is this normal for holleys?
As for the dyno, I never dynoed the engine... Once the season is over I'm going to pull the engine and get the thing dynoed so I really know what I'm dealing with.
As for the dyno, I never dynoed the engine... Once the season is over I'm going to pull the engine and get the thing dynoed so I really know what I'm dealing with.
Think about how an aerosol can gets cold when you spray its contents.
#9
Registered
![Default](/forums/images/icons/icon1.gif)
first off your small cu in big block is not a good boat set up, boats need lots of torque, thats why stock 502's run close, while your engine will make the H/P on the dyno you may never see benifits from them in the RPM range that you run in, also spinning outdrives in excess of 6k is going to be a issue at some point. That is a heavy boat for it's size and a high torque engine will perform much better...
#10
Registered
![Default](/forums/images/icons/icon1.gif)
Start saving your money for a 4.25 stroke rotating assembly. Guys that want to go fast in boats like yours usually build 540's. To get the most out of your engine, I would use a Victor Jr. Super Sucker made my engine go very lean. I use a 4 hole spacer.Then try more props. Maybe get a 23 Mirage plus labbed. Make sure the hull is straight with no hook. Maybe try a -2 shorty outdrive.