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  1. #1

    Default Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    OK, GM was [and still is, I believe] building the 2.5 liter and 3.0 liter engine in Mexico simultaneously. MerCruiser used the 2.5 [old 153 cubic inch Chevy II / Nova] block for a 120 hp motor and the modified 3.0 liter [183 cubes] engine with 4" bore as a 130, 135, and 140 hp rated motor. The 3.0 liter crank is different...larger rod journals and the 3.0 liter rods are shorter. Question is: did they cast two different blocks, or just one thick-wall casting that could be bored to either 3_7/8ths or 4 inches? Reason I ask is I have a 2.5 block I'd like to use to replace a cracked 3.0 engine.

    BTW, what's with the ratings on the 3.0...did they have to downrate this motor and if it couldn't really put out 140 hp does that mean the 2.5 isn't capable of 120, either?

  2. #2
    Join Date
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Question is: did they cast two different blocks,
    Ayuh,... It won't work....
    Any Grease is Better,... Than No grease at All....

  3. #3

    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Two different blocks, eh? I wonder why they bothered keeping the 120hp motor in production, then?

  4. #4
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    where are you measuring the hp from ?

    The flywheel or the prop ?

    You ain't gonna put componets from a 3.0 in a 2.5.

    And i don;t know if you can bore out the cyl. say 30 thou. and find rings and pistons.

    What i did when my 2.5 went was find a 140, same series motor.

    In my case i found a 85' 140 my 2.5 was a 85'.

    There are plenty used good motors out there find a fresh water one if you can doesn;t matter make you can just use the mani and riser off your old motor.

  5. #5
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Quote Originally Posted by Volvo351 View Post
    Two different blocks, eh? I wonder why they bothered keeping the 120hp motor in production, then?
    Ayuh,... Probably for the same reasons there were 305s, 'n 350s....

    Demand, 'n marketing....
    Any Grease is Better,... Than No grease at All....

  6. #6
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Quote Originally Posted by Volvo351 View Post
    I wonder why they bothered keeping the 120hp motor in production, then?
    they didn't
    the 2.5L version hasn't been made in over 20 years
    Last edited by hystat; 01-02-2011 at 02:27 PM.

  7. #7
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    alot of 120 / 2.5 were used in forklifts, little bucket jobbers. Postal trucks / vans.

    Also nova's and chevy II's.

    3.0 were never put into a auto, never.

    Stambolis the ice machine uses a 3.0.

    The best thing that ever happened to my boat was the 2.5 went and i installed a 140. The 20 extra horses makes my boat feel better, better gas milage, just a whole different boat.

    Whatever you do don't install another 2.5 take the time and find a 140.

  8. #8

    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    That's funny..... I had a Bayliner 18 1/2' "Eagle" with 140 in it. The 3.0 is a 180 / 181 CI motor, basically the same motor as the old Chevy Nova 153, with some refinements on the head and such and different bore. Used chevy small block pistons (don't remember which ones) after doing all the measurements and accounting for a .030 overbore, when I rebuilt the motor, called Dave Crower from Crower Cams and he confirmed it's the same as the 153 "bump stick", but a different profile. He "heel ground" the cam for me (because there was no such thing as blanks for that one) for a slightly different profile and supplied std Crower / Chevy profile lifters, springs, retainers and keepers. I used 327 valves in the head for the valve job and ported it. Been a while, but think the drive was a 1.88 : 1 ratio and prop was 14.5 x 21", I think. Converted to electronic ignition (an automotive conversion kit for the Prestolite distributor, back then, marinized with silicone sealer. HAHAHA. Hey, it was a long time ago).

    After it was all said and done, that little 4 banger was impressive. Made that 18 1/2 foot Eagle run low 50's MPH w/ 1/2 tank of fuel and just the driver, and cruising around all day while using just 3 1/2 gal per hour. Pretty speedy, for the day, and economical too. Kinda miss that simple little motor.

  9. #9
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    My friend has the 3.0 in a 92' 19' Bayliner cuddy classic. It does better then 45. 19 pitch prop.

    Mine is a 19' Citation heavy boat, cuddy. With the 2.5 i could just about make 25, turning 4600 rpm wot on a calm sea and 2 men onboard. 15 pitch prop. If i had 4 people onboard then i had to install a 13 pitch prop to get to 4200 rpm.

    With the 140 i turn 4600 at wot and do close to 40 or a little better on a calm sea. 17 pitch prop.

    I usually turn 3200 rpm and do about 30 my back just can't stand the pounding and at that speed i'm in my comfort zone. My speedometer is not that accurate, and my tach i think is off also. Being a 86' i'm ok with the way it is.

    I go out 5-6 hours and burn about 9-10 gallons of gas, can't get any better then that. Some of that time is drifting, or most of that time is drifting.

  10. #10
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Quote Originally Posted by chiefalen View Post
    My friend has the 3.0 in a 92' 19' Bayliner cuddy classic. It does better then 45. 19 pitch prop.
    weird...
    my 1992 Bayliner 18.5' cuddy ran 36/37 gps. with the 3.0 with a 19P prop
    maybe I need to go on a diet.

    It now does 46/47 since I repowered it with the V6

  11. #11
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    You think my friend is bs-ing me on how fast he goes ? Could be, hmmmm this summer i'm gonna bring my own gps it tell me everything speed and such.

    People all lie about how big the fish was, how fast the boat goes how big there male member is, how long they can keep it up, can't trust nobody.

  12. #12
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    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    every hull is different I guess.... I have a hard time seeing 45... and it doesn't add up for a 19P prop and 1.98 ratio...would have to be a 23P to get that speed behind 1.98 gears unless he is well over the 4600 rpm

  13. #13

    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Quote Originally Posted by 04fxdwgi View Post
    That's funny..... I had a Bayliner 18 1/2' "Eagle" with 140 in it. The 3.0 is a 180 / 181 CI motor, basically the same motor as the old Chevy Nova 153, with some refinements on the head and such and different bore. Used chevy small block pistons (don't remember which ones) after doing all the measurements and accounting for a .030 overbore, when I rebuilt the motor, called Dave Crower from Crower Cams and he confirmed it's the same as the 153 "bump stick", but a different profile. He "heel ground" the cam for me (because there was no such thing as blanks for that one) for a slightly different profile and supplied std Crower / Chevy profile lifters, springs, retainers and keepers. I used 327 valves in the head for the valve job and ported it. Been a while, but think the drive was a 1.88 : 1 ratio and prop was 14.5 x 21", I think. Converted to electronic ignition (an automotive conversion kit for the Prestolite distributor, back then, marinized with silicone sealer. HAHAHA. Hey, it was a long time ago).

    After it was all said and done, that little 4 banger was impressive. Made that 18 1/2 foot Eagle run low 50's MPH w/ 1/2 tank of fuel and just the driver, and cruising around all day while using just 3 1/2 gal per hour. Pretty speedy, for the day, and economical too. Kinda miss that simple little motor.
    Might of been 327 pistons?? After some research, they seem to be the only ones close to the 3.0. Shave .020 off the top to get CD and .230 off the skirt to get total length and it seems they will work. 100 bucks for 8 new ones is alot cheaper than buying 3.0 pistons.

    Mild recessed?

    Let me know if you recall which ones you used.

  14. #14

    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Sorry, was a LOOOOOONG time ago and can't remember precisely which ones. They did have the 4 valve relief notches in them. But you are correct, they were 327's and I used the thick S/S head gasket to make up the for the slightly taller piston dome and keep compression ratio in check. Did not cut anything off skirt. Checked for interferance after rough install. Clearances were very close, but not to a point where there would be contact. Someone back then actually said the 180 / 3L was like half of a 327, parts wise, so I kinda went on that assumption and did a whole lot of homework and comparisons. Much to my surprise, he was right.

    Buying a bunch of Hi Perf aftermarket 327 parts was way cheaper than Merc label stuff. Besides, Mercury/Keikhoffer used to make the HOT Chevy engines for GM. Sooooo, the old "Parts is parts" addage applies. Back then, Chevy HiPo parts suppliers were as plentifull locally as cell phone stores are now. Couldn't swing a dead cat without hitting one, and the parts were cheap.
    Last edited by 04fxdwgi; 02-11-2011 at 06:24 AM.

  15. #15

    Default Re: Boring GM / Chevy 2.5 Liter to Replace 3.0 Liter Block

    Quote Originally Posted by 04fxdwgi View Post
    Sorry, was a LOOOOOONG time ago and can't remember precisely which ones. They did have the 4 valve relief notches in them. But you are correct, they were 327's and I used the thick S/S head gasket to make up the for the slightly taller piston dome and keep compression ratio in check. Did not cut anything off skirt. Checked for interferance after rough install. Clearances were very close, but not to a point where there would be contact. Someone back then actually said the 180 / 3L was like half of a 327, parts wise, so I kinda went on that assumption and did a whole lot of homework and comparisons. Much to my surprise, he was right.

    Buying a bunch of Hi Perf aftermarket 327 parts was way cheaper than Merc label stuff. Besides, Mercury/Keikhoffer used to make the HOT Chevy engines for GM. Sooooo, the old "Parts is parts" addage applies. Back then, Chevy HiPo parts suppliers were as plentifull locally as cell phone stores are now. Couldn't swing a dead cat without hitting one, and the parts were cheap.
    Thank you for the info.!!

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