Modifying a mercury 250 efi for 300hp

[rico649]

Good Day Guys,
I'm currently in the process of trying to squeeze maximum hp out of my 2001 mercury 250hp 3.0 . I currently have my computers at Simon for re programming and want to send out my heads this week to cut to 300Promax specs. I'm looking at upgrading my reeds and also exhaust tuner. Can you guys give me an opinion on the best reeds to go with? and also is hydro tec exhaust tuner worth any gains in hp?

 

[atc250r]

I have a 250 EFI as well. I went with a 300 ignition box and Chris Carson Marine reeds. You'll be hard pressed to find anyone with anything bad to say about those reeds or that shop's customer service. I just cut the stock tuner in mine. Most discussions I've read say there's no power gain in an aftermarket tuner. I just cut mine for a little more noise.

 

[rico649]

Ok, thanks. I spoke to CCM yesterday about their reeds. He told me they were a great upgrade over stock but I wanted a customer's opinion Appreciate it. I'll order them today. With the 300 ignition box upgrade, I know your rev limiter is raised to 6400 rpm, did you get any noticeable power gains besides for more revs? e.g can you spin a bigger prop to a higher rpm?

 

[atc250r]

I did reeds, 4 butterfly intake, and 300 box. Picked up about 4 mph with same prop. It was tapping the limiter somewhat regularly before and has tapped it once or twice again with the new set up so I could probably swing a bigger prop. I've got a bigger one to try but haven't had a chance. It's basically at the point that the boat is pretty damn fast for what it is and I can still pull the kids on the tube even with several people in the boat. If I go to a bigger prop that 2 mph isn't worth the loss everywhere else.

John

 

[rico649]

Ok, kool sounds great. are you still running the 24p prop?

 

[atc250r]

Yes. Picked up 13 mph since I bought the boat with a 200 Johnson with the same prop.

 

[rico649]

Ok, I think I'll stick with mines. Can't wait to get my computers back to see if I can spin my 24 choppa over 6k, that should give me some good gains in mph. The acceleration on the 24 is crazy kool, just sucks at top end. hopefully that all changes

 

[atc250r]

I haven't been too impressed with a chopper on mine (open bow version of yours). I maybe have more tweaking to do but the Trophy is better everywhere so far.

 

[rico649]

ok, I found a trophy 24 on craigslist but can't get in contact with the owner. Guess ill try again tomorrow. My computers arrived from simon today along with my solid mounts. Installed them this afternoon. So tomorrow I'll go for a test run see if I can notice a difference in performance. Hopefully by next week, I can find a shop to send my heads out to get cut. Everyone turn around time is like 2 weeks. Which is kind of too long for me. I'm wanting more like 2-3 days.

 

[atc250r]

Remember, these aren't like a lot of 2 stroke heads that can just be milled down. I believe the o-ring grooves need to be removed cut. If you're doing all this work and it's a lighter hull than mine you may want to go with a 25 or 26 pitch instead.

 

[rico649]

Just got out the water trying my buddy's 26 choppa. Got 73 mph gps by myself and 71mph with a passenger. That's with Simon computers, everything else stock. My reeds should be here on Monday so once they arrive, I'll go for another run

 

[rico649]

Ok. I ran my boat today with my buddy 26p chopppa. Simon computers n everything else stock. Did 73mph by myself n 71 mph with 2 people. Half tank of gas. My next mod will be heads. Do you know if the 250 pro xb heads have a different cc from the stock 250 efi heads??