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-   -   420trs Blower upgrade (https://www.offshoreonly.com/forums/general-q/200666-420trs-blower-upgrade.html)

TylerBurich 12-28-2008 09:45 AM


Originally Posted by TomFTM (Post 2766285)
get your self some bm 250's ,( a little larger blower than the 177) you can run one 850 or a one dominator or two 750's. You should always use a larger blower when possible. You can spin that larger
blower slower and create less heat... also, you can use the larger
blower down the road if you choose to make more power.

What kind of power will i see out of my motors with the 250 blowers and 850 single carbs? I want to take it easy on my trs drives but i only boat on a small lake so i won't be "airing it out" on big water. There is a pair of 250's in the classifieds but i will need the single carb adapters and maybe a different crank pulley?

TomFTM 12-28-2008 10:17 AM

I had a 84, 38 Cig years ago that had 420's. I changed heads to merlin cast irons , changed cam , bolted on bm 250's with single 850's boost referenced , msd ing, stainless marine exhaust and ran 5 lbs of boost. This set up made about 575-600 hp and pushed the cig to 72-73 mph . I also ran trs drives . I would get about 150 hrs on drives before they would need to be gone through. I would go through drives before they blow due possibilty of losing a gear case..These motors had about 600hrs on them when I sold the boat.. They are very reliable if set up right. Tom

ezstriper 12-28-2008 10:41 AM

the weiand's work very well I did one of those engines this season, any way the marine blower(blower itself the same) gives you the special thermostat housing, 10 rib belt, and one of 2 different lower crank pulleys depending on if you have a aluminum or steel lower crank pulley. power wise my 489 with that blower, ported 781 oval ported heads, 8-1 comp, comp blower cam, made 525 @ 5500 4psi, 610 @ 5500 6-7 psi...you will need to boost referance the carb and rejet...Rob

TylerBurich 12-28-2008 10:49 AM


Originally Posted by ezstriper (Post 2766324)
the weiand's work very well I did one of those engines this season, any way the marine blower(blower itself the same) gives you the special thermostat housing, 10 rib belt, and one of 2 different lower crank pulleys depending on if you have a aluminum or steel lower crank pulley. power wise my 489 with that blower, ported 781 oval ported heads, 8-1 comp, comp blower cam, made 525 @ 5500 4psi, 610 @ 5500 6-7 psi...you will need to boost referance the carb and rejet...Rob

as for boost referencing, what will need to be done to my 850's in order to work properly with the 250 blowers?


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