True or B.S about the bubble back x-flow?

[audiobill5]

True or B.S.?

I heard from a customer today the bubble back x-flow was created as a cheaper way to power Bayliner boats in the day?

When I look at the parts breakdowns it looks like there were a few years of the bubble backs and a few years of the flat back OMC engines around in the 1980's.

Were the flat backs both loopers and x-flows?

I just traded my 55 looper for a buddies 110 bubble back, I think I done good (?)(he had a smaller boat the 110 was to big for)

Are there x-flows that are not bubble backs?

I heard somewhere (probably here) that the bubble backs' exhaust sounded meaner, any truth to it?

thanks!

[flabum1017]

Bubble backs were created long before the '80's......... and definately not for the bayliners.................

All the flat backs and bubble backs were crossflows..... in the mid- eighties, the looper 120' and 140's came out.... the exhaust housing were molded into the block on the loopers......


Bubble backs and flat backs sound the same unless someone drilled the midsection...

[perfmarine1]

BS all of it except for your trade. Most older 150-175-200 were flat back,then only 235 150 xp-gt and 2.6 xp-gt were bubble back. Then the changed hp rating from crank to propshaft and then more were bubbleback but only x-flow. As flambue said all looper were bubbleback it was cast in.

[audiobill5]

So a looper can have the rounded back between the cylinder heads on a 4 cyl?

I'm trying to figure out what I got, the numbers are missing.

I believe it to be a 4 cyl 1988 110 HP, definately has the rounded back hump w/ 1-5/8 carbs.

Thanks

[rockman69]

I'm trying to figure out what I got, the numbers are missing.



A pic would help...

(2) 2-barrel metal carbs or (4) single plastic? Dont think they ever made 1 5/8" xflow carbs...

[flabum1017]

Those might be 1 3/8" not 1 5/8" if its a crossflow. The crossflow will have a rounded bubble back and the loopers have a more squared bubble back, also, the loopers will have a "V-4" or "V-6" cast into the bubble back............. This is a crossflow.....257126

[lokinutz]

aluminum 2 bbl carbs - crossflow
plastic 1bbl carbs - looper

[audiobill5]

Hey Thanks so much, lokinutz!
I had some pics to download but you answered the question.

Why did OMC change in and out of the x-flow and the looper?
Are x-flows better for low end?, high torque?, efficiency? Or maybe just OMc's bottom line at the time?

In about the 110 HP range did the x-flow or the looper do better against the Mercs of the day?

Great info here
Thanks,
Bill

[lokinutz]

Sorry audiobill5, I thought about it and need to change my post. Later crossflows do come with plastic carbs, BUT, no factory production non-race loopers had aluminum 2bbl carbs. Some looper F1 V-8s did, but we aren't really talking about that stuff. So, if you have the aluminum 2 barrel carbs, and its a standard production non-race use engine, it is a crossflow.

Thought I would correct that before racer came along and fixed it for me!:thumbsup:

[200VEGAS]

loopers were more powerful. and were known for better fuel economy. i think a 120 looper is 120 at the prop and not the crank like crossflows

[audiobill5]

Thanks for the detail.

So all x-flows are bubble backs?

Why did OMC change internals and make x-flows?

[lokinutz]

Nope. Crossflows are either bubble or flat back.
Loopers I guess would kind of be a bubble back, but the exhaust chest is cast one piece in block, not removable like the x-flow. (although some cut the exhaust off to grind and change the exhaust, then weld back on)
Crossflows are the old design. Less efficient and make less power than loopers, although OMC and a few manufacturers made them for a very long time after the looper became the standard in power/efficiency.

[Nd.stream]

Il go out on a limb here the term looper refers to loop charging of the cylnders verses cross flow charging . The easy way to tell the differnce is all cross flo engines have removable covers on the out side of the block and a cover that unbolts over the exhaust. On all omc lop motors I have saw (fishing / non race) there are no removable covers over the transfer and exhaust chest

[powerabout]

BS all of it except for your trade. Most older 150-175-200 were flat back,then only 235 150 xp-gt and 2.6 xp-gt were bubble back. Then the changed hp rating from crank to propshaft and then more were bubbleback but only x-flow. As flambue said all looper were bubbleback it was cast in.
all 235's were bubble backs

[Forkin' Crazy]

Nope. Crossflows are either bubble or flat back.
Loopers I guess would kind of be a bubble back, but the exhaust chest is cast one piece in block, not removable like the x-flow. (although some cut the exhaust off to grind and change the exhaust, then weld back on)
Crossflows are the old design. Less efficient and make less power than loopers, although OMC and a few manufacturers made them for a very long time after the looper became the standard in power/efficiency.

I'll bite. :) I've gotten close to 5mpg in my Allison, light load, 29" wheel and easy on the go pedal. Running up just to where the boat airs out good.... 65-70mph. You are right on the less power. Damn thing only runs 94mph! ;)

[flatsboat 21]

chiming in......the bubble back is actually called tuned exhaust . it was an easy way for omc to adjust torque and horsepower. a your 110 can easily become a 120 with carb change or a 140 with lg carbs and tuned exhaust (bubbleback} because of so many port,carb,tuner, configurations theres no telling what u have or need......all tuned exhaust omc motors were great motors, strong and crisp!!and yes they call it a two thirsty five for a reason lol.....ps you have just begun your journey my friend good motor !!!!

[terry taylor]

It took more space to design a more efficient pulse tuned exhaust hence the bubble. But to some maybe a ( bubble) fetish, they were forever blowing :cheers:BUBBLES:eek::eek:thanks.

[VectorPat]

chiming in......the bubble back is actually called tuned exhaust . it was an easy way for omc to adjust torque and horsepower. a your 110 can easily become a 120 with carb change or a 140 with lg carbs and tuned exhaust (bubbleback} because of so many port,carb,tuner, configurations theres no telling what u have or need......all tuned exhaust omc motors were great motors, strong and crisp!!and yes they call it a two thirsty five for a reason lol.....ps you have just begun your journey my friend good motor !!!!

The 140 crossflow became the 110/115 when everything went to the propshaft horsepower rating. The 110/115 then had the bubble back exhaust and carbs of the 140. The flatback 115 became the 90. Im thinking that was in the 1985 model year and thats when the loopers started coming out.

[71V153]

The 140 crossflow became the 110/115 when everything went to the propshaft horsepower rating. The 110/115 then had the bubble back exhaust and carbs of the 140. The flatback 115 became the 90. Im thinking that was in the 1985 model year and thats when the loopers started coming out.Yup! And that's roughly when VRO was introduced too. Late '84 actually, I think ...

[agood1]

Hate to drag up an old thread, but I have a bubble back 115HP in my Whaler Jet boat (stop Laughing we use it as a tender). I pulled it apart and sent it off to be bored and the shop found a crack behind cal #4. They say it cannot be fixed....and apparently this block is difficult to find. Any ideas on what I can use instead?

[perfmarine1]

Hate to drag up an old thread, but I have a bubble back 115HP in my Whaler Jet boat (stop Laughing we use it as a tender). I pulled it apart and sent it off to be bored and the shop found a crack behind cal #4. They say it cannot be fixed....and apparently this block is difficult to find. Any ideas on what I can use instead?
What is cal#4- And what is a whaler jet boat,is it a jet outboard? They made millions of 115s you should be able to find one. Post a pic of that crack.

[agood1]

Nevermind