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Blower help, ideas

Old 08-06-2007, 09:55 PM
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Baddog
Im looking at putting a 250 on mine. Did you have to modify the hatch or back seat?

Originally Posted by BadDog
Sounds like you have something wrong. I have a B&M 250 on my 502, here is my basic setup on my Force 235.

Timing 30 degrees total with a base of 10
Carb by Nickerson, single 1050 reworked to something.
Belt with 5/8 showing on tension rod
AZ 120 thermostat, crossover with small bleed holes to headers when stat closed. Water temp (measured just at port forward fitting of manifold) 120 at cruise 125 WOT. Never varies from 40 to 85 degree water.
Water pressure 15 to 20 depending on water temp and speed
AC MR41 plugs
Holley Black fuel pump, no check valve, 9 psi at WOT
3x21 oil cooler with Mocal T-stat. Temp gauge in pan, 180 at 3000, 200 at 3500, 235 at WOT

Boost gauge generally shows 1 lb. vacuum around 3000 and builds gradually to 4 to 5 from there. If your belt was slipping I think you would smell it. From your numbers I would not run it further until you determine where the power is being lost. Might be lean or else the rotors are not sealing well enough to make any boost. Not sure where you should start checking but get someone to assist that does. I believe you only get one shot to do it wrong with a blower motor.

Keep us posted as to what you find but I would start with doing some plug readings from 3000 up at 500 rpm intervals. Check fuel pressure while running and get that boost gauge on there. Check timing from idle to 3K and up.

You should be running about 76 to 78 with that setup.
Force 235
stock 330 56 to 58
stock 502 415 hp 64 to 66
502 w/headers and single plane dart 67 to 69
502 w/B&M 250 at 5 psi 78 to 80

My 235 did not like the 4 blade prop, lifted the stern too much. The best prop for the 235 seems to be the Mirage Plus. I still have issues with bow lift. The faster you go the more the nose plants. Scrubbing a lot of speed off. BudMan shaved the hooks off his and it did not seem to make much difference but he is only running 60. Once I get over 65 you can fell the nose dropping as you add throttle. You have to over trim a bit to get the bow to carry and then feed some throttle in. Once you get the bow up drop the trim a touch to hook the prop back up and feed it more throttle to 75. At that point over trim a touch and rock the wheel slightly to Starboard and back to straight, this seems to put it up on what little pad the hull has. Once up on the pad it will wind out to 80. That hull was not meant to go over 65 or so. I think I can avoid all that trimming nonsense with the right prop but I have not addressed that yet. Might just have to change the address of the hull to fix it.
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Old 08-07-2007, 06:00 AM
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Have not played with any other props. Still running the stock 27 MP. Might have it tweaked for more bow lift but for now it is fine.

Yes, you will have to make a small cutout behind the rear seat to clear the blower snout. Back seat then gets a tad cut off the rear edge and upholstery re stapled. Not a big deal. You also need to shave the lip of the rear seat support to clear the blower case. Very easy to do with a dremmel tool.

I will see if I can get some pics up.
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Old 08-07-2007, 08:07 AM
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I cut a small slot in my back seat for the blower snout, but I really diod not need it..on my setup there is no need to do anything to the (seat) because it does not fit all the way back to the support ( where the slot is)...I had to knotch out the inside a little too where my carb linkage is, but in all it was about 15 minutes with the dremmel tool..but still a very tight fit..I will be down at the boat this Thursday, I will take some pics and post them on Friday night. My boat is a 26' 6" 265 Force, but I think they were the same as the 235's from the windshield back...my boat has the teak external swim platform, so that could have made a difference somehow..and I also have zero effort controls..those were the two biggest differences I see in most of the late 80 early 90 models......I also have the Power Boat mag from their first test on the 265 back in 1987..it is in prestine condition...shows my boat running 53mph with 454 330 hp..& 54-55 mph with twin small blocks...best thing about that mag is they have alot of other boats tested, a twin engine, twin turbo Fountain is one of the coolest I have ever seen..it looks bad ass!
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Old 08-07-2007, 06:26 PM
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That would be great if you guys can put up pics.Thanks
Are you guys running the 3"belt?
Just looks like there is not to much room to add a blower crank pulley.
Did you guys have to cut the hatch on the inside?

I already put in a bigger fuel pick up and lines from the tank and a return. I take it you guys did that to.
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Old 08-07-2007, 07:04 PM
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Yes, I did all the fuel line upgrading stuff..no, no need to cut the hatch at all & there is plenty of room for the lower pully to bolt on..3" serp belt is what I have..you can see the engine in a picture above in this thread..I just did not have the seat pushed back yet..you have to use 8" or less flame arrestors or they will hit the seat back...mine are 8" dia & I have about 3/8" clearance
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Old 08-07-2007, 08:18 PM
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What did you guys do for the thermostat housing?
Looks like no brackets/acc.s have to be moved for idler?
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Old 08-07-2007, 09:05 PM
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Well, not sure what you mean exactly..you use a different intake for the 250 B&M..it has the idler bolted to it along with the t-stat housing..do not run stat though....that is the problem I had...too much water pressure kept blowing out intake gaskets...
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Old 08-11-2007, 02:22 PM
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Here are the pics I promised!Send me a PM with your email and I can send you more pics if you need some...as you can see, there is plenty of room for the bottom pulley...

Last edited by Bajapred; 09-13-2007 at 06:17 PM.
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Old 08-11-2007, 09:40 PM
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Did you ever find the pullies you were looking for? I have some old style 250 B & M ones.
John B
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Old 08-11-2007, 10:46 PM
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Thanks for the pic.
Did you install the crank pulley while the engine was in the boat?

Originally Posted by Bajapred
Here are the pics I promised!Send me a PM with your email and I can send you more pics if you need some...as you can see, there is plenty of room for the bottom pulley...
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