Can I put 4barrel on Mercruiser 165

rabristol

Seaman Apprentice
Joined
Jul 20, 2007
Messages
42
I have an inline 6 250 cid mercruiser. I would like to put a 4 barrel rochester on it. Can I do it? Whats involved? How much extra horsepower will it get?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Can I put 4barrel on Mercruiser 165

With time and effort anything can be do. It's likely only to increase fuel consumption rather than increase power.
 

bigblocksarefun

Petty Officer 3rd Class
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Jan 27, 2008
Messages
81
Re: Can I put 4barrel on Mercruiser 165

It is possible with the right manifold...the 292 came with a Q-jet. You might look at maybe 10-20 extra hp? Make sure you have a manifold similiar to this one.
osco8759-2.jpg
 

Don S

Honorary Moderator Emeritus
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Re: Can I put 4barrel on Mercruiser 165

Mercruiser tried it for ONE year, then gave it up. Wonder why????
Yes the manifold MIGHT accept a 4bbl carb in place of the normal adapter plate which comes in either a 4 or 6 bolt pattern. I see that Osco manifold pictured above is the 6 bolt version.
 

bigblocksarefun

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Re: Can I put 4barrel on Mercruiser 165

Mercruiser tried it for ONE year, then gave it up. Wonder why????
Yes the manifold MIGHT accept a 4bbl carb in place of the normal adapter plate which comes in either a 4 or 6 bolt pattern. I see that Osco manifold pictured above is the 6 bolt version.
Nope, I don't wonder or care why. Yes, these particular manifolds WILL accept a 4 bbl, specifically a Q-jet. See below.
2945_1.jpg
2eff_1.jpg

2c20_1.jpg
 

Don S

Honorary Moderator Emeritus
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Re: Can I put 4barrel on Mercruiser 165

I didn't say you couldn't put one on it, I said Merc only tried it for one year and gave it up.
 

bigblocksarefun

Petty Officer 3rd Class
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Re: Can I put 4barrel on Mercruiser 165

Personally I don't know if I'd put a 4 bbl on a 250, maybe a fat 2 bbl like a 500cfm. A 292 is at least approaching small block territory.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Can I put 4barrel on Mercruiser 165

The limiting factor on that engine is the airflow thru it. You can put the biggest carb you can find on it. If you cannot get the airflow into and out of it it won't make any (or very little) difference.

You can only suck only so much air through the engine (non-turbocharged)

When you get to a carb that is too big the limit is then valves and exhaust (and actual pumping losses)

Mercruiser did the R&D for you. You're probably better off to stick with a 2 bbl.



Cheers,


Rick
 

bigblocksarefun

Petty Officer 3rd Class
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Messages
81
Re: Can I put 4barrel on Mercruiser 165

I'm waiting to see how it runs, if I don't like the way the 4 bbl performs, I'm throwing a very small 4 bbl or a 2bbl. Gotta redo the floor first hehe.
 

ziggy

Admiral
Joined
Jun 30, 2004
Messages
7,473
Re: Can I put 4barrel on Mercruiser 165

if ya do some research. ya'll find there aint to much to do to a marine 165hp L6 to improve it.... put it to specs and be happy.........
 

wca_tim

Lieutenant Commander
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May 28, 2007
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1,708
Re: Can I put 4barrel on Mercruiser 165

Without major additional work, the inline 6 won't use much if any airflow beyond the stock carb. IF you went with an aftermarket cam, major head modifications (porting, valvetrain, etc...), and exhaust, and you planned to spin it up to over 6000 rpm's, my math says you MIGHT get to the point where you could put a small 4 barrel to good use... but then again, if you did that, power below 2000 would be akin to a lawnmower engine... Not trying to be a smart ***, but it's just way more cost effective (and easier) to swap to a larger engine than to pull real gains out of a straight 6. Parts are out there but are expensive and hard to come by...

Although I've never personally had one of these in a boat... it should be bulletproof and give decent power and good fuel economy in stock trim.

imho
 

bigblocksarefun

Petty Officer 3rd Class
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Re: Can I put 4barrel on Mercruiser 165

That's why I looked for a 292, figured it was the best upgrade I was going to fit. The engine compartment has absolutely no stock provision to put a V-8 (or I would've put a FWC 5.7 hemi in there) without EXTENSIVE work. Besides, this boat is low buck all the way.
 

bomar76

Lieutenant Commander
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Messages
1,963
Re: Can I put 4barrel on Mercruiser 165

(or I would've put a FWC 5.7 hemi in there)


And where would you have bought the imaginary manifolds for it, along with the other little things like a coupler, USCG approved injection system, ignition system, starter....ad nauseum ?
 

bigblocksarefun

Petty Officer 3rd Class
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Re: Can I put 4barrel on Mercruiser 165

Dude...I AM the USCG...who is gong to board me when I do the boardings? (J/K!) Seriously though, I'm a CG mechanic, its my job to figure stuff like that out. If mounting it had been viable, I would've found a way. Luckily, alot of mopar small block type stuff bolts on the periphary (alternator, starter, tranny, etc.) - lots of mopar small block marine engines around. But its a moot point anyhoo.
 

starsnstripers

Lieutenant
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Messages
1,330
Re: Can I put 4barrel on Mercruiser 165

I'm running a 250cid L6 also and I wouldn't try putting a 4brrl on it. However the 292 L6 I just picked up will be installed next year with a small 4brrl on it for about 200hp. Why merc only did them for one year in 69 is unknown to me. Maybe i'll find out huh? Thats the plan I think it will be a nice set up with good torque and hp. I think a 4brrl on a 160hp 250 is like overkill. But let us know how it goes, i've never tried it or know anyone who has. Good luck! "stove bolts r-us" :D
 

Don S

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Re: Can I put 4barrel on Mercruiser 165

Dude...I AM the USCG...who is gong to board me when I do the boardings? (J/K!)
A little story about the CG.
When I was working in Alaska , we used to perform the maintenance on their Volvo diesel powered small boats (bouy tender boats).
We had one in that we were repowering from the old Merc diesel to a Volvo 41 diesel (about 4 years ago now) while upgrading the electrical system, I found the nav lights were, well, how should I say this.......... a little less than legal.
They had a sailboat all in one light mounted on the top of an aluminum pole backwards. The red and green showed aft, not forward.
I called the contact and explained the situation, and they asked if I could fix it so it would pass the CG exam, I said yes and fixed it.
Being in the CG, does not mean you suddenly know all the rules and regulations.
 

bigblocksarefun

Petty Officer 3rd Class
Joined
Jan 27, 2008
Messages
81
Re: Can I put 4barrel on Mercruiser 165

A little story about the CG.
When I was working in Alaska , we used to perform the maintenance on their Volvo diesel powered small boats (bouy tender boats).
We had one in that we were repowering from the old Merc diesel to a Volvo 41 diesel (about 4 years ago now) while upgrading the electrical system, I found the nav lights were, well, how should I say this.......... a little less than legal.
They had a sailboat all in one light mounted on the top of an aluminum pole backwards. The red and green showed aft, not forward.
I called the contact and explained the situation, and they asked if I could fix it so it would pass the CG exam, I said yes and fixed it.
Being in the CG, does not mean you suddenly know all the rules and regulations.
You're absolutely right. Even after 12 years. Never said I did. But I know where to find it, and that's all that matters.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Can I put 4barrel on Mercruiser 165

I sure hope your better than most USCG techs I work behind.
station Hatteras and Oregon inlet guys are good at SAR and aides to navigation but they really outta but the tools up.
there is no way you can get outta boot camp, go to a week long tech course and go work on mercs,volvos,evinrudes mercs and hondas and yamahas.
just aint gonna happen.
myself,other than 6 years as an FC in the USN and 6 years programming and setting up CNC lathes and mills, I have done this wrench turning gig since I was 15. I am now 46 and still learn daily. I have worked for chevolet dealers,ford dealers,yamaha,Honda,Tohatsu,Suzuki,merc/mariner,Force and OMC.
been doing Volvo and mercruiser since the late 80's.
thats the nice thing about staying in one area and going to any and all training schools you can find, if shop A doesnt want to increase the bennies shop B and C will get into a bidding war for your service :).
 

bigblocksarefun

Petty Officer 3rd Class
Joined
Jan 27, 2008
Messages
81
Re: Can I put 4barrel on Mercruiser 165

Been all over it for 12 years, trying to get what i can before the next 8 show up. That week long course is in the middle of a 12 week course that teaches a bunch of the BASICS (MK school is literally designed to give your average retard minimum mechanical knowledge). They only recently switched over from teaching old style OMC 2 strokes (which we hardly have any of anymore) to the 4 stroke Hondas most of our orange boats (25', 27') are running. One of the problems is alot of the time, to get a specific engine school that the CG doesn't have (Honda, Mercury, Yamaha, etc.), you have to go to a civilian school, which means the unit you are at has to foot the bill out of budget, rather than the big pot of $$ that is set aside for training & schools service wide. Case in point: the station I was at in FL had a 23' SAFE boat. This poor thing came saddled with 115 Johnson 2 strokes (right before Bombardier bought OMC). Vastly underpowered, within 3 mos to a year, they started blowing up at stations all around us. No one got to go to OMC school. The Group replaced them with Yamaha 115 4 strokes. Better engine, better fuel economy, quieter, but now the boat couldn't get out of its own, way, much less anybody else's. Surf? Forget it, we'd die. No one got to go to Yamaha school once they found out how much it would cost to send a few of us.
 

bigblocksarefun

Petty Officer 3rd Class
Joined
Jan 27, 2008
Messages
81
Re: Can I put 4barrel on Mercruiser 165

We picked up a different boat, same size but with Mercury 150 2 strokes; faster boat, high strung engines. No Mercury school either. With the newer stuff, its getting to the point where no one wants to pony up to train our guys on how to do it instead of coming down to the local marina/shop and paying to have it fixed. The cutter fleet is some cases has gotten this way too. It sucks.
 
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