2 bolt main vs 4 bolt main

[Cptkid570]

Hey everyone,

I’m pricing replacement engines for my 1985 26’ Searay. Currently has a Mercruiser 260 (350 chevy).

The shop is quoting me an extra $100 if I want the reman engine to have a 4 bolt main versus 2 bolt main.

The boat is already underpowered with the 350 chevy motor in a 26’ boat.. (I’m not going with a larger/more expensive motor).. so, I was thinking that it would be best to stick with the 4 bolt main so that the motor may be a little stronger.

Is there a big difference between motors that have a 2 bolt main and 4 bolt main? Do marine applications always have a 4 bolt main? Is this an area that really breaks down much?

 

[Haut Medoc]

Re: 2 bolt main vs 4 bolt main

Most of the bigger ones have four bolt mains....
The demand of marine use is the reason...
A marine engine works much harder than an auto engine during it's lifetime....
I would go with four bolt mains for sure........JK
Guess I'm wrong.....:$

 

[Don S]

Re: 2 bolt main vs 4 bolt main

Most are 2 bolt mains, even the new Merc and Volvo MPI 5.7's pushing 320 HP are only 2 bolt.
You won't gain anything using 4 bolt mains unless you run 8 or 9,000 rpm all the time.

 

[mkast]

Re: 2 bolt main vs 4 bolt main

I would have to agree with Don.
Two bolt mains have been in marine engines along time,
making more hp than the one you're building.

 

[Bondo]

Re: 2 bolt main vs 4 bolt main

Ayuh,.....

The Bottom End of a Small Block Chevy is Not it's weak point at All........

Even the Hot Rodders will pull 450hp out of 2 bolt blocks.......

Save your $100.00,+ Throw it in the Gas Tank............

 

[Cptkid570]

Re: 2 bolt main vs 4 bolt main

thank you so much for your advise everyone

 

[FreeBeeTony]

Re: 2 bolt main vs 4 bolt main

If the boat is underpowered with the 350...........how about considering building a 383 Stroker?

I'm really curious to see what the guys will say.

I know the stroker will have more torque..........but will the drive handle it...........assuming you have an Alpha.

Maybe a 383 Stoker block w/ Vortec heads..........

Would still be a SBC...........I must have cabin fever!!

 

[John_S]

Re: 2 bolt main vs 4 bolt main

http://www.gmperformanceparts.com/E...Id=HT383&engine=HT 383&sku=12499101&engCat=sb

No need to build a stroker either. Many places selling crate long blocks.

This is a rather mild one with 340hp and 435lbs torque.

 

[180shabah]

Re: 2 bolt main vs 4 bolt main

You have a heavy boat and an alpha drive, you need to control the urge to build a high output engine unless you don't mind frequent drive replacements

 

[waterone1@aol.com]

Re: 2 bolt main vs 4 bolt main

For decades it has been well accepted that a four bolt main is a stronger engine. For as little as $100 additional, you get a four bolt main......GO FOR IT !

 

[Cptkid570]

Re: 2 bolt main vs 4 bolt main

I agree that I need to control any urges to over power my alpha drive.. and to be honest, I'm not a speed freak.. well, I may be, but my wife isn't.. so, I doubt I'll be driving it over 25mph very frequently. I'm not concerned about beefing it up. And... as tempting as it would be to drop a 454 in there, I love how much room I have in the engine compartment.

 

[FreeBeeTony]

Re: 2 bolt main vs 4 bolt main

I'm just curious what the opinion of the guys is.........could an Alpha drive handle a power plant such as what is pictured above? Doesn't produce much more than 300HP but alot more torque..........

 

[mkast]

Re: 2 bolt main vs 4 bolt main

If I remember correctly, the Alpha 1 was rated at 300 hp.
When installed on the big block 454 and the 255hp 351 four barrel Ford, the gear ratio was 1.32 to 1because of the engine torque issue.

 

[Flukinicehole]

Re: 2 bolt main vs 4 bolt main

I have a 400hp/355 2bolt in my boat. No problems.I`ve put nox on 2bolt mains in cars never had a problem.

 

[FreeBeeTony]

Re: 2 bolt main vs 4 bolt main

What drive are you running with that 400HP SBC?

 

[Flukinicehole]

Re: 2 bolt main vs 4 bolt main

Alpha1 built by Tim at TOP marine in patchogue.

 

[FreeBeeTony]

Re: 2 bolt main vs 4 bolt main

Is there something special about your Alpha?

 

[Flukinicehole]

Re: 2 bolt main vs 4 bolt main

Dont know he said I should have no problem biggest thing is gunning it out of the hole. I was there when he went through it to check it out last year.There were no problems he even showed me how to go through it myself.I used it this year but not to much as I put another boat together so it didnt get in the water until August. So far so good.I dont know if I will get 1000 hours out of it but there are no signs of metal in the oil.

 

[FreeBeeTony]

Re: 2 bolt main vs 4 bolt main

How about your SBC?...........

Where are the 400 HP coming from?

 

[Flukinicehole]

Re: 2 bolt main vs 4 bolt main

350 2/bolt mains forged pistons flat top with valve reliefs.67cc Dart sportsman deads with 2.05 intake valves, ported ,polished.Crane cam,Edelbrock performer RPM intake. I want to go with through hull exhaust but this is in a 24ft.walkaround and I want to keep it quiet for the family. Most power comes from the cylinder heads, they are the key.Boat gets on plane fast enough for me plenty to get a skier up.From 2400 rpm up it pulls real hard.