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moparbarn
06-27-2007, 03:31 PM
i am setting up a k&b 3.5 ob, 13 mm crank, turbo head with a prather mod kit and tuned pipe. the kit has you remove the carb and turn the front housing into a venturi. the ex. throttle will mount on the ex. port, between the cylinder and the pipe. am i wasting my time? any tricks needed to make it work? tom foley, have any thoughts? you've seen a lot more of this stuff than me.

AIRWALK
gettin' old ain't for sissies

crazy horse
06-28-2007, 05:24 PM
I still have a old 3.5 that was ext. throttle. Way back when, I bought the kit to convert it to a carb. To this day I think the old setup was better. I never put a pipe on it but I did save the old hardware. After I got the 7.5, I never messed with the 3.5 much after that. I'd like to see how yours works with a tuned pipe. I might have to clean up my old 3.5 Hot Shot:D

moparbarn
06-29-2007, 10:46 AM
i posted on intlwaters, also. the response there has been positive. i'm going to try it and see. i'll keep you posted. waiting on parts, be a few weeks. was your ex. throttle stock? if you want to go back, check out 707 specialities, they sell a nicer ex. throttle. then google 'california mod' for the lower and fr. housing mods. a lot more power available that way. or find a prather mod kit for 3.5 k&b's. prather's gone, but hyperformance has bought their stuff, they might have some, or start making them again. or they pop up on ebay occassionally. i have the instructions for one, the parts aren't hard to find to do it. let me know, i can send you a copy.

AIRWALK
gettin' old ain't for sissies

moparbarn
07-10-2007, 08:42 AM
i have 2 pipes, an equi and an irwin, the basic motor, a rek carbon/resin lower and a k&b lower cut for a pipe, pipe timing piston and cyl., and the prather mod kit. waiting on crank and bearings. can't wait to get it assembled and try the different combos of parts, pipes and props. gettin' close, more to come-soon.

crazy horse
07-10-2007, 04:23 PM
I found the paperwork on my old 3.5, It came from K&B with the slide valve. I even have the factory linkage kit # 8572 and the assembly instruction sheets. I can't remember how many years I ran it that way. I bought a Perry for it and at that time K&B had a kit to convert a 3.5 to a intake throttle body using there carb or a Perry. Keep us posted it sounds like fun.:D

tunnelhead
07-24-2007, 06:23 PM
In my old A-Hydro racing days we would grind out the exhaust cavity in the "foot" and remove the venturi and install the needle valve directly in the setscrew holes leaving a huge intake. Combine this with the exhaust throttle and they sure ran up top... A bit rich on the low end though :p

The piston/sleeve "fit" was really important in those days too. It wasn't uncommon to have a motor that required a wrench on the flywheel to turn it over by hand.

moparbarn
07-24-2007, 06:44 PM
In my old A-Hydro racing days we would grind out the exhaust cavity in the "foot" and remove the venturi and install the needle valve directly in the setscrew holes leaving a huge intake. Combine this with the exhaust throttle and they sure ran up top... A bit rich on the low end though :p

The piston/sleeve "fit" was really important in those days too. It wasn't uncommon to have a motor that required a wrench on the flywheel to turn it over by hand.
that's what was called the california mod. prather started making a kit to do it. that's what i'm using, except with a tuned pipe. have a powerhead on a REK carbon lower, just have to fit the header. should be ready this weekend (i hope). if i get it in the water, i'll post some pics. still waiting for the disc to my dvr, and i can post video:D .

tunnelhead
07-26-2007, 07:20 PM
Well I am out here in the west, so if it was the calif mod then I can see where that came from.

I went off into cars for a few years and now I'm too old for the fast crowd but I keep looking at the boats and know I can still build great hydro's. I might just have to put some of this radio gear to use....

moparbarn
08-07-2007, 07:46 AM
man, what holding you back? get out that radio gear and find a hull. burnin' nitro is tons of fun:cool: . i've made a few changes to my setup on my motor. as it stands now, i've got a turbo cut crank, turbo cut head, modded cylinder, RADICALLY modded case (a lot of port matching and transfer work), light flywheel, venturi front housing with speed needle, rek carbon lower, and 2 different pipes (and irwin stamped & a john equi 'S' pipe)and headers ( 1 macs & 1 homemade). i realize i'm building a hand gernade, but most of the parts have come in bigger deals or trades, so not a lot of $ invested:cool: . the crank was cut and balanced for the rod and (skirt cut) piston, so maybe the vibrations that usually come with the turbo cuts won't be an issue.i have run it in another milder motor, wasn't any worse feeling than stock. and, since K&B cases are known for cracking, i've devised a stud girdle (sounds kinky:D ) for it. i had read that 2 piece mounts will cause case failure in ib's. should use 1 piece mounts, to take strain off of the case. not an issue in ob's, but high performance applications can cause the same issue. case will crack on the bottom, on the casting line. i've got a bunch of aluminum steering arms that mount across the case, from mount lug to mount lug. i use 1 stock for steering, and another (without the ears for steering) bolted in the other 2 mount holes. i hope it will add some strength/stiffness across the case. these changes, and losing my pond, put me back another week or 2. losing the water REALLY SUX, see the thread i started about it. pretty sorry folks out here:mad: .