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boatnt

02-01-2019 10:28 AM

Twin engine question

So helping out a buddy with an engine build, he’s got a twin engine boat big block GM EFI engines, hurt one Cylinder in the block so he needs to go 30 over, question is has anybody done this before? one engine stock the other engine 30 over, do they run the same or are they out of sync?Is 30 over enough to notice a difference?

beaver 3

02-01-2019 12:16 PM

there will be no difference.

14 apache

02-01-2019 12:19 PM

Sometimes I will only go bigger on a few cylinders just to save the blocks. If it's just one hole see if it will clean with a .005 piston if they offer it.

f_inscreenname

02-01-2019 12:43 PM

Quote:

Originally Posted by 14 apache (Post 4670735)

Sometimes I will only go bigger on a few cylinders just to save the blocks. If it's just one hole see if it will clean with a .005 piston if they offer it.

Had a Jasper motor that had 3 different size pistons in it. Really pissed me off trying to do a refresh.

14 apache

02-01-2019 12:54 PM

Quote:

Originally Posted by f_inscreenname (Post 4670741)

Had a Jasper motor that had 3 different size pistons in it. Really pissed me off trying to do a refresh.

lol ya that would piss me off to. Only reason I do it to save room if it ever fails again. Did one each block had 2 big pistons and 12 small ones piston people made 12 big ones they had to make 8 more small ones.

mggdoors

02-01-2019 01:13 PM

Quote:

Originally Posted by f_inscreenname (Post 4670741)

Had a Jasper motor that had 3 different size pistons in it. Really pissed me off trying to do a refresh.

mental note to self. Never using jasper

Baja Rooster

02-01-2019 01:56 PM

I know JE makes some pistons that are just a few thousands over stock if a good power hone will clean them up. You’ll never notice any difference with one engine bored over.

ThisIsLivin

02-01-2019 04:44 PM

I bought a boat that sat in storage so long the cylinders rusted so badly the rings wouldn't contact the bores all the way around. I ordered a set of Diamond pistons at 4.565 to clean it up no problem.

14 apache

02-01-2019 05:28 PM

Had a boat with 454 one side and 510 other side ran same rpm on top end. 510 had more mid range.

Rookie

02-01-2019 07:17 PM

I had to pull one of my 550HP 454's last summer and put in a spare Merc 420 I had laying around. There was ~600RPM difference in the engines. A little under 3/4 throttle on the 550HP and the engines were in sync.

You won't notice the difference with 0.030" Put the power steering pump on that engine...

getrdunn

02-01-2019 07:18 PM

Just an FYI. His boat won't go in circles if your wondering. lol

boatnt

02-02-2019 07:42 AM

Quote:

Originally Posted by getrdunn (Post 4670798)

Just an FYI. His boat won't go in circles if your wondering. lol

lol

getrdunn

02-02-2019 10:24 AM

Quote:

Originally Posted by boatnt (Post 4670837)

lol

I couldn't help it. I use to always concern myself with "identical" twins but realized their rarely identical anyway. Some cases you can dyno two of the same exact builds and be off 10-15 hp at any given rpm. Have him refresh the ugly ginger and be good to go. Like rookie said it would be a plus to be on the power steering side. I would imagine he will be doing a complete refresh including valvetrain inspection etc. As long as it's out might as well give it a complete bill of health.

Maybe pull its mate mate next season and refresh. Did he mention the hours by chance?

ezstriper

02-03-2019 07:54 AM

Quote:

Originally Posted by f_inscreenname (Post 4670741)

Had a Jasper motor that had 3 different size pistons in it. Really pissed me off trying to do a refresh.

years ago jasper was good..then they turned to crap..and I mean crap,had a engine few years back acted like blew a head gasket, pulled it down to find they had welded the head in the combustion chamber and weld came out ! Talked with jasper and was told they have to use about everything they get back due to availability on cores, stopped used them.

f_inscreenname

02-03-2019 11:48 AM

Quote:

Originally Posted by ezstriper (Post 4670942)

Mine came with a boat I bought. The seller pointed out the tag on the motor "Jasper" as a selling point. The boat was a wreck and I got it for a song anyway but was shocked on how a simple refresh turned into a nightmare.

Full Force

02-05-2019 05:15 AM

Sleeve it, then they will be the same.... cheap to do..

Full Force

02-05-2019 05:17 AM

Quote:

Originally Posted by getrdunn (Post 4670857)

if built right they will be the same, my Mistress engines were 1HP and 3ft lbs apart.. same dyno, same day.

boatnt

02-05-2019 08:50 AM

Quote:

Originally Posted by Full Force (Post 4671225)

Sleeve it, then they will be the same.... cheap to do..

Yep already done that, but unfortunately when you sleeve a cylinder you take the chance of distorting the cylinders next to it and in this case it did ,so That is the reason I’m thinking about boring it so I don’t keep repeating the sleeving process

Knot 4 Me

02-05-2019 09:16 AM

My 496 MAG was bored .030 over when I had it rebuilt a couple years ago. Otherwise everything put back bone stock. Dyno'd at 390 HP fully dressed with wet stock exhaust. You shouldn't see any difference.

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