cp5899

iTrader: (1)

Tim explained my sex life to a T.


80's in a 235 force is extremely fast!! Was the busted bearing and rod due to detonation? Your right about the clearances under the in front of the motor. I looked into it and there is enough room in both areas. I used that as a "if it won't fit I won't buy it", but after looking online and calling velocity it will fit. Did he have constant issues? How about his outdrive?

I did get the address for the gaskets, but I've put a hold on ordering anything else until I figure out if in staying n/a or going with the blower. I just bought a set of 4.500 wiseco small dome pistons that I will have to sell and have to go back to my je flat tops


Thanks budman

Budman II

iTrader: (1)

He actually ran trouble free for a few summers, but toward the end he did bust a drive, and then he had the infamous episode where the rod let go - fortunately it was right at the end of the season. He was running about 4500 RPM when it let go - managed to limp back to the dock. He was lucky to salvage the block, but I think he had to have it sleeved. I don't recall detonation being the issue on this one - most likely just metal fatigue after many hours of hammer time.

The rod bearing was a strange one. He was heading home and had a guy pull next to him in a Fountain who wanted to play. He leaned on it and then heard something, and limped home. It actually sounded like a lifter ticking, but they eliminated that after some searching. Finally decided the engine had to come out, and when they disassembled it, a con rod bearing had been hammered flat like a penny on the railroad tracks, and a piece of it that was sticking out was coming around and hitting the block. That was the ticking sound they were hearing. Not sure if they determined if detonation was the issue for sure, but sounds like a likely culprit to me.

He had nickerson set up the carb according to the specs he gave him for boat weight, RPM range, etc. It was pretty much plug and play after that. I highly recommend finding someone who is an expert on supercharging to set it up for you. At this power level you are running with the big boys, and tinkering with it if you are not sure what you are doing can get real expensive, and leave you on the trailer all summer.

You touched on another issue: driveline parts. Tim managed to keep his XZ alive for quite a few hours, but he was religious on his fluid change intervals. Also, a 235 is not nearly as much hull as a 280, although the 280 is a much faster hull. You have to figure on the driveline getting hammered with any major power upgrade. Also, with a blower you have additional moving parts to contend with - I think Tim also sent his blower off to be rebuilt at least once while he had it.

He will tell you it was a lot of fun having the blower, but it certainly wasn't cheap!

Budman II

iTrader: (1)

Also, if you are going with a power adder like a supercharger, you may need to look at different (larger) clearances for piston-to-bore, first and second rings, main and rod bearings, etc. You will probably want to consult with the bearing, ring, piston manufacturers for this.

eddie

iTrader: (7)

Shoot me an offer, anything is possible.

cp5899

iTrader: (1)

I've had a few twin turbo and supercharged small block setups that I've built and ran 10-14psi in cars, but nothing that had to live in the 3500 and up rpms for any length of time like a boat motor. It seems like 4-5 psi would be nothing for a big block. (At least that's what my inner voice is telling me) Most of my forced induction experience is with small block fords and the lack of head bolts and blown head gaskets still gives me nightmares.


Thanks again for the insight. I'm going to think it over a little more before I make the decision.

Budman II

iTrader: (1)

Definitely run the cometics with head studs if you are going SC.

MILD THUNDER

iTrader: (3)

I wouldn't be worried about reliability as I said. You have to look at the big picture. Mercury, and tons of other builders, have used blowers with great success, and reliability wasn't a concern. The old 525sc, 600sc, and 800sc's were very good engines. Theyd go hundreds and hundreds of hours before teardowns.

They key is a proper combination of parts, and as I said, proper tuning.

The 250 blower works well, I ran them. Also ran the 177, and now running the 420 B&M. All on the same engine combo. All I can tell ya, is from day 1, the engines should have had the 420 Blower. They idle much better, make a ton more power, but most important, they make so much less heat, which is the key. Plus the blower internals will last longer, since they are spinning at half the rpm of the smaller blowers.

The 250 with a single carb, has very poor fuel distribution. Pretty much no matter what you do, you'll have certain cylinders fat, and the others lean. So if you go that route, you really need enough fuel to keep the lean cylinders safe (front cylinders).

Don't let the twin carb setups scare you. Most people automatically assume twin carbs=less mpg. This isn't true. If the engines tuned to a certain AFR, it doesn't matter if you have 1 carb, or 4 carbs, its consuming the same amount of fuel. I actually think Im getting better economy with the twin 850 carbs tuned with a wideband, than the 250 tuned off plug readings.

If you shop racing junk, ebay, craigslist, or here on oso, i'll bet you can find a nice 420 B&M for a very good price. Probably real close to what you'll pay for a 250. Then down the road, when 600HP isn't enough, the 420 will support 800-900hp no problem. An 8-71 would also be great, but they are harder to find in a complete package for short money.

cp5899

iTrader: (1)

Thanks for all the info everyone. As much as I want to go the blower route right now, I'm not sure its the right time. With my current budget for the project (originally didn't have a blower in it) I'm concerned I would have to skimp on certain items to make the blower fit into the budget and I really don't like doing that. If I were going with the blower I would like to go with some good rods, dual carbs, etc and I can't swing all of that right now. I'm trying to have the boat done for mid april so time is running short already. I think I'm going to stick with the original plan and build a strong N/A motor for this year since I've already bought dome pistons and everything thus far has been geared for a N/A build. I do think I will start a blower build from scratch over next winter.

I really appreciate the amount of response and personal experience that everyone has offered to the thread.


I would love to find a set of alum heads to replace my 088's if there is power to be had going with an alum head over the 088's.

Thanks again everyone!!

Craig

Rookie

iTrader: (4)

I'm curious to this combination as well. Besides the weight of the aluminum heads I don't see any gain over your Dart heads. I see that you are going to use the Sniper Jr. intake. I don't know much about the Jr. but on the regular Sniper I've seen the Plenum volume is large. I believe it pushed the power band out higher than a Dart intake and also hurt its lower end torque. I know some stuff is just the right combination of things and this might work great.
Please keep us informed. The dyno #'s will be great, but I'm more interested in the real world in the boat #'s.

ezstriper

and if you run in salt water would not consider aluminum heads...waste of $$$$ they will be killed in 3 years...and never make the power of the blower...