7.4L- Should I bore it out??

klawton55

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I have an 89 Sea Ray with a 7.4l mercruiser, I have pulled the motor and was planning on resealing it along with new rings. I was getting some blow-by and figured as old as it is I figured it was about time. I have it tore down and everything looks good and I got to thinking that maybe I should bore it out. I would like to have more power but not sure if this would gain me a whole lot.

So my question is, will having it bored out give me noticeable increased power? Last year I installed a dual plane intake and it did seem to run better but that is the only thing that has been done to it. I am looking for input and suggestions before I spend the money on having it bored. Thanks.
 

Bondo

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Re: 7.4L- Should I bore it out??

I have an 89 Sea Ray with a 7.4l mercruiser, I have pulled the motor and was planning on resealing it along with new rings. I was getting some blow-by and figured as old as it is I figured it was about time. I have it tore down and everything looks good and I got to thinking that maybe I should bore it out. I would like to have more power but not sure if this would gain me a whole lot.

So my question is, will having it bored out give me noticeable increased power? Last year I installed a dual plane intake and it did seem to run better but that is the only thing that has been done to it. I am looking for input and suggestions before I spend the money on having it bored. Thanks.

Ayuh,.... Not nearly enough Info,....

Have ya mic'ed the cylinders,..??
Checked their Roundness,..??
How many hours on the motor,..??
What's the bore measure at,..?? is it still Original, stock,..??
Saltwater, or freshwater run,..??

An overbore is Just to get the cylinders back to Spec, for roundness, 'n to clean up imperfections,...
There's No real horsepower increases from an overbore,...

A BBC can stand up to 'bout .125" overbore, til the block is junk,...

Btw,.... Reringin' it, without cleanin' up the bores, is usually a waste of time, money, 'n effort,...
 

alldodge

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Re: 7.4L- Should I bore it out??

I have an 89 Sea Ray with a 7.4l mercruiser, I have pulled the motor and was planning on resealing it along with new rings. I was getting some blow-by and figured as old as it is I figured it was about time. I have it tore down and everything looks good and I got to thinking that maybe I should bore it out. I would like to have more power but not sure if this would gain me a whole lot.

So my question is, will having it bored out give me noticeable increased power? Last year I installed a dual plane intake and it did seem to run better but that is the only thing that has been done to it. I am looking for input and suggestions before I spend the money on having it bored. Thanks.

With a worn engine it would be safe to say you will need to bore it. Over time the rings wear the cylinder and most time not a perfectly round cylinder. You may be able to get by with a 0.010 bore. You do this so the new rings will seat correctly. If you had a micrometer bore gauge you should see the bore is no longer a perfect circle. The top of the cylinder should also have a slight grove, and if this is not removed you will break your new rings when it is started.

As for power increase, there will be an increase and how much depends on size of bore and ability to burn fuel. The old comment "there is no replacement for displacement".
 

haulnazz15

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Re: 7.4L- Should I bore it out??

At a minimum have the cylinders mic'd/honed, but a light bore (say .020 or .030) may be necessary to get the cylinders back in shape. There won't be any significant power increase, especially when it's put in a marine-application. If a .030 bore was done, the 454 becomes a 462, so you added 8 cu inches. Not much of an advantage there.
 
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wrench 3

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Re: 7.4L- Should I bore it out??

I'm with haulnazz15. Get the cylinders mic'd. If they're OK, deglaze and install new rings. If they're not, go with what ever over size the machine shop recommends. Not for horse power but just to have the engine working right.
 

Scott Danforth

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Re: 7.4L- Should I bore it out??

boring will not get you any power as was mentioned, only getting you back to the fit spec.

However since you have the block out for a rebuild, piston shape, combustion chamber shape (heads), cam, intake, etc. all can be fiddled with to get you more power.

your engine builder should be able to help.

However if you have an Alpha drive, you may want to reconsider adding power.
 

wrench 3

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Re: 7.4L- Should I bore it out??

However if you have an Alpha drive, you may want to reconsider adding power.

Since he's calling it a 7.4 he most likely has a Bravo. The Alpha was designated a 454 Magnum. But with the change point being in 1988 it could go either way.
 

klawton55

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Re: 7.4L- Should I bore it out??

I apologize for not having the measurements ready I am in the process of measuring them. I was also going to at minimum have the cylinders honed before installing new rings. I wanted to see if it was worth boring it out, but by the sounds of it, it will not benefit me to have them bored out.

My boat does have an Alpha outdrive, and the thought had crossed my mind that I may not want to increase too much unless I change to a bravo. And since it was brought up I guess I should stay with it the way it is and reseal it. Should I think about changing carbs? The stock quadrajet is currently on it.
 

Scott Danforth

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Re: 7.4L- Should I bore it out??

if you have blow by and have the motor apart, you are at the point of needing at a minimum a hone job. most likely a light bore to clean up.

However I would build it back to stock configuration with the Alpha. your motor is rated at 330hp, the Alpha is rated just a bit less.
 

harleyman1975

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Re: 7.4L- Should I bore it out??

That Q jet is one of the best carbs out there. I would only have it rebuilt if it is giving you problems. Don't mess with sucess.
 

haulnazz15

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Re: 7.4L- Should I bore it out??

Keep the Q-jet. No harm in going with a different carb, but you won't gain anything from it. Boat may run a bit faster because your wallet would be lighter, lol.
 

Bondo

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Re: 7.4L- Should I bore it out??

I apologize for not having the measurements ready I am in the process of measuring them. I was also going to at minimum have the cylinders honed before installing new rings. I wanted to see if it was worth boring it out, but by the sounds of it, it will not benefit me to have them bored out.

My boat does have an Alpha outdrive, and the thought had crossed my mind that I may not want to increase too much unless I change to a bravo. And since it was brought up I guess I should stay with it the way it is and reseal it. Should I think about changing carbs? The stock quadrajet is currently on it.

Last year I installed a dual plane intake.

Ayuh,.... If ya Just bought another dual-plane intake, I'm guessin' it's got the Big spread-bore carb flange,...
'n so long as the Quadra-jet is runnin' just Fine,...

No real reason to change anything there,...

'n yer Measurement's of the bores, 'n the pistons will determine whether you can get by with a hone job, or need to overbore, 'n buy new pistons,...
 

klawton55

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Re: 7.4L- Should I bore it out??

I do agree about the quadrajet it has worked great for me, and I don't necessarily need it to drink any more. I have the serial number for my engine where do I find the specs for the block. The number is F124188. Thanks for all the input.
 

alldodge

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Re: 7.4L- Should I bore it out??

I do agree about the quadrajet it has worked great for me, and I don't necessarily need it to drink any more. I have the serial number for my engine where do I find the specs for the block. The number is F124188. Thanks for all the input.

The number you listed is not a casting number, probably a foundry number. The 454 has a 4.250 bore and a 4.000 stroke, Mains are 2.7488 to 2.7495 Rods are 2.20. Look here for more info

Mortec - Chevy Small-Block Casting Numbers, Engine Codes and more
 

klawton55

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Re: 7.4L- Should I bore it out??

Thanks AllDodge. That was the number from the mercruiser tab. The casting number is 10114182.
 

alldodge

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Re: 7.4L- Should I bore it out??

Thanks AllDodge. That was the number from the mercruiser tab. The casting number is 10114182.

Hmmm, that casting number comes out to be a 91 and up Gen V, 4 bolt main, your boat is an 89, looks like it has been replaced before
 

klawton55

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Re: 7.4L- Should I bore it out??

Thats good to know. Thanks. I was wondering about it because it says that gen IV should be a 2 piece rear main and mine is a 1 piece.
 

Tail_Gunner

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Re: 7.4L- Should I bore it out??

You might have a true magnum there if so it quite easy to upgrade but as stated earlier someone replaced the orignal engine. Post the cast numbers on the heads that will determine what can be done and if its a heinz 57. Below are the stock heads.

Casting Number 10114156
Added to Site 2010-12-25 13:03:33 (1159 days ago)
Manufacturer Chevrolet
Category Cylinder Heads
Type Big Block V8
Date 1991+
Notes oval port, open chamber, Gen.V & VI 454, 118cc chambers
 
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Mischief Managed

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Re: 7.4L- Should I bore it out??

You can bore it .030" over, put in a stroker crank (4.250") and shorter rods (6.385") and make it an 8.1. That would dramatically improve power, for not much money.
 

Scott Danforth

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Re: 7.4L- Should I bore it out??

You can bore it .030" over, put in a stroker crank (4.250") and shorter rods (6.385") and make it an 8.1. That would dramatically improve power, for not much money.

and shred his alpha drive
 
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