Upgrading my 300xs

[TUNNEL T]

merctech , the poppet valve and tuner is in a sense is drying the exhaust right?you say you noticed a stumble off idle did this hurt your holeshot at all . also talked with simon not toolong ago about more mods for our motors and he told me too hang tight he's workin on it!

[merctech5591]

hey guys been away for the weekend on my action with my boy. i have made no progress in testing as the boats been at liberator for the last month and a half getting buffed, a new windshield and a custom bimini top.

tunnel t , i have not been able to get the stumble out of the motor. also if you chop the throttle it will on ocasion stall and have to restart. at this point i would love to go back to the stock tuner or try a hydra-tec tuner and check that out. do not cut your stock tuner it is almost 3500 if you ever have to go back to it. i realized this after the fact. at this point untill simmon comes out with something diff i would just upgrade the flywheel and ecu. i have noticed the last that the mid was starting to turn white probably from the extra heat inside the can. if your real picky keeping your motors clean the popet diverter is going to cause u a lot more time cleaning a waxing.. i will update some more after i get the boat back..

[hotdaddy27]

hey guys been away for the weekend on my action with my boy. i have made no progress in testing as the boats been at liberator for the last month and a half getting buffed, a new windshield and a custom bimini top.

tunnel t , i have not been able to get the stumble out of the motor. also if you chop the throttle it will on ocasion stall and have to restart. at this point i would love to go back to the stock tuner or try a hydra-tec tuner and check that out. do not cut your stock tuner it is almost 3500 if you ever have to go back to it. i realized this after the fact. at this point untill simmon comes out with something diff i would just upgrade the flywheel and ecu. i have noticed the last that the mid was starting to turn white probably from the extra heat inside the can. if your real picky keeping your motors clean the popet diverter is going to cause u a lot more time cleaning a waxing.. i will update some more after i get the boat back..

That is great info. I am sorry you had to learn the hard way...sometimes that is part of the "game" though. Been there and have the receipts to prove it!

Looks like the diverter is off the list, I can't deal with white spots.

Keep up the good work.

HD

[R.grover]

have 15inch midsection one a wile back just put a good running 300xs powerhead on my 300promax midsection with cut 300promax tuner and found flatspot when u planted ya foot off idle. ran at idle and other rpms ok. Have talked to hydrotec in the past and said his tuner on 300xs didnt idle well.
Just been running kilo runs today with 300promax with popped devider and it boiled the paint on the midsection and i melted the plastic inserts on my large propshaft hubs.

Love to hear feedback from others

[Skatin]

I have been running Poppet Diverters on all 3 motors for quite some time and haven't had any issues whatsoever.

[bigboy]

I wonder if you were able to shave some weight by going with the 15" mid?

Thx

[Maritime_Eng]

So after all the modifactions you made what was the best mods and what was the worst? I see you added a Hydrtech tuner and was wondering if you gained any on the top end with the tuner? My 250xs's are going to be out of warranty in the next year so I am starting to do my research.

Thanks
Don

[merctech5591]

well for my application i felt the best mods were flywheel and ecu upgrade. motor ran like a top and would pull the same prop 28 thropy to 6700 were as before 6350 was the most it would turn. after cutting the tuner and adding the poppet valve dump i ran into a wall. motor would stall by chopping the throttle, and has a bad miss at 1000 to 1300 rpm.the hydro tec tuner is sitting on a shelf and has not been touched. im sure this winter the mid will be comming apart again for a tuner swap.

[jpf091959]

This is a good thread. I have two stock 300xs that will be out of warranty (Fall 2011) I am starting my search for upgrades. Do you have access to a dyno. I am running 34"cleavers upto 6100 rpm, my goal is 6300-6400 rpm. Curious about hp increases or do these changes just change the shape of the curve. Hoping for increases throughout.

[MarylandMark]

3/10/2011 my warranty runs out......

Hopefully now with some warranties expiring, the aftermarket market will pick up for us 300xs'ers!

[DRHOBACK]

This is a good thread. I have two stock 300xs that will be out of warranty (Fall 2011) I am starting my search for upgrades. Do you have access to a dyno. I am running 24"cleavers upto 6100 rpm, my goal is 6300-6400 rpm. Curious about hp increases or do these changes just change the shape of the curve. Hoping for increases throughout.

what size is your boat? seems like with your climate you would be able to spin 28 or larger pitch as starting point to maximize rpm's.

[jpf091959]

Sorry typo, 34" three blade cleavers.

[DRHOBACK]

that sounds more like it, actually doing very good to turn 6100 with 34's. I too am watching this thread with interest.

[jpf091959]

I was really hoping for 110 with a pair of 300xs. I am sure with the right conditions in saltwater I might see 110. Not to whine but want more. Anyway if there are ideas out there I would like to hear them.

[merctech5591]

i would deff try the flywheel mod and wait on the ecu mod. if your turning 6100 i feel a 200-300 rpm increse is in the flywheel. you will not beleive the weight reduction from stock . try it you have nothing to loose.