GM 292 in place of MCM 250

[Fordiesel69]

Which year 292's will work in place of the 250 I6? I am seriously going to start my search.

What about height on the 292 block, will the exhaust rubber mate up or will a custom piece need made (longer).

How many have pulled this off?

 

[Bt Doctur]

Re: GM 292 in place of MCM 250

bored .030, mild cam, 4bbl manifold, needed to go to a 1.50 drive . Only change was because of the taller motor/head was to add a piece of wet exaust hose in place of the oem rubber one.

 

[ziggy]

Re: GM 292 in place of MCM 250

i've no personal info on this subject, only speculation.

my first question would be, if it's such a good idea, why did mercruiser only go with the idea for 1 or 2 years? they sure changed their attitude awful fast. maybe it was because it was only mated to a mercruiser II drive and the II drive was a bad idea, i don't know. but before ya attempt the switch, it might be a good idea to find out why merc. changed there minds so fast. might be some insight as to weather ya wanna proceed or not.
since it was only mated to a II drive. i would think there would be compatibility issues between mc-1 and mercruiser II. what they are, i don't know.

i've been on iboats a long time, you too fd. i've never seen anyone say they did that conversion. lots that say they want to do the conversion. but i've never seen one thread that says they did it and got away with it.

myself. i'm a poor boater. reliability is very much on my mind. my 250 cid works well, it's known to work well, even beyond well. you've seen it said before, the 165hp L6 250cid mated to a mc-1 drive may be one of mercuruisers best success stories. it's a very desirable package. i see no reason personally to open a can of worms and change it's desirability and reliability.

fwiw, i've read more than once that the 292 w/4bbl is thirsty. imho, that'd be a down side. the 165 can be thirsty too if yer on it all the time, but if ya use judgment with your throttle hand, ya can keep the fuel consumption down to satisfactory imho.

i do wish you good luck in your adventure.

 

[kilowatts]

Re: GM 292 in place of MCM 250

Hi Ford:

I posted the following entry some weeks ago in a similar thread. I can't help agreeing with Ziggy who loves his inline 6 almost as much as I do, but on the other hand...


Hi Guys:

If I might make a few comments with regard to the elusive 292! I've been wanting to bolt up a 292 for some time now and I'm convinced it's easily done. I think the issues are:

(i) Height of new block and clearance issues both for the boat and the electrical harness
(ii) Height of block and exhaust pipe extension required
(iii) Lack of "ears" on the new block for motor mount
(iv) Different motor mount placement
(v) You'll need to fabricate a new exhaust boot
(vi) Suitability of a pre-alpha water pump to supply enough cold water to the system
(vii) The 292 uses a lot of gas


I think the issues are easily solved but the last 2 are what's kept me from going forward. I'm so happy with my L6 250cu in 165 as I feel it's ideally matched to my boat that I can't quite see the utility at this time. I don't want to spend more money on gas, for obvious reasons, and I'm not sure the impeller will provide adequate water flow to cool the bigger block. It would be nice to have the "bigger six" though!

Perhaps someone who knows for sure whether the issues I brought up are indeed correct could comment? There must be a reason Mercruiser didn't use the Pre-alpha outdrive.

kilowatts

 

[HT32BSX115]

Re: GM 292 in place of MCM 250

Which year 292's will work in place of the 250 I6? I am seriously going to start my search.

What about height on the 292 block, will the exhaust rubber mate up or will a custom piece need made (longer).

How many have pulled this off?

Howdy,


I went thru the same gyrations when I had my 230cu-in // MC-1 powered Mark Twain.

It appears that the 230/250/292 share the same deck (heads are interchangeable)

You have to ensure that the engine mounts will work. I couldn't be sure that the 292 damper would fit in the front Mercruiser mount though.

The deck is about an inch taller so you have to accommodate that with a longer exhaust tube rubber or otherwise.

It's absolutely do-able. I don't know if it's worth it. You can build up a pretty good running 250.

Since there's not a lot of marine 292's, you would probably have to use a 250 head and/or intake manifold (watch the compression when you do that.)

http://inliners.org/main.html are a good resource.


Cheers,


Rick

 

[kilowatts]

Re: GM 292 in place of MCM 250

Hi Ford:

I just looked for another posting I made in this regard and came up with this:

Hi Guys:

There are several differences with the 2 engines apart from the obvious displacement and engine height:

(i) The 292 was mated to a MCM Mod II drive which did not exhaust through the hub so the exhaust boot would need to be redesigned.
(ii) The 292 drew raw cooling water through the hull via an external belt driven pump so you would need to be sure the impeller in the outdrive would be adequate.
(iii) The 292 had side mounting brackets to allow for the operation of the water pump so the brackets would need a retro-fit and redesign.

In my opinion it should be possible to fit a 292 to a pre-alpha drive using all the MCM 165 marinizing parts only if the raw water pump in the drive provides enough flow to cool the engine.
On the other hand, there must have been a reason for Mercruiser to discontinue the program after only one year and also to use the Mod. II drive when they had so many pre-alphas available.
I think the 292 would be a fine marine engine with lots of low end torque but I understand they are a very thirsty engine and at the end of the day it would be much more convenient to install a rebuilt V6 which are cheap and plentiful.
On the other hand, it would be nice to have the fastest 6 on the lake, eh?

kilowatts

I'd be really interested in finding out how well this project works going forward so please post as much as you can.

KW

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

I think I will follow Ziggy's advice on this one. I will wait it out for somone to do it first!!!!!!!

I am just utterly blown away as to how my 18' w/ I6 performs during acceleration. However top speed is limited to 42 MPH. The more I think of it, the 292 may not help top speed at all. It may help mid range cruise @ a lower RPM, the I6 design may simply limit the top speed. They were never meant for high end.

I wonder how hard it would be to find a merc 292 already dresssed. Probably dreaming.....

 

[kilowatts]

Re: GM 292 in place of MCM 250

Hi Ford:

I think you're right, a 250 inline 6 sure is hard to beat, eh?

I almost bought a Mark Twain online with an original running MCM 200 inline six. I would have towed it from somewhere in the midwest back to Vancouver but I chickened out at the last moment. I think the reason was the Mercruiser II drive which only lasted a very short time and parts are simply impossible to find. That and the gas consumption was very high. Then I advertised on Clist for a 292 and received several replies but again I chickened out as I'd just finished rebuilding yet another 250! Then I saw a fully dressed and running OMC 292 version but the seller wanted too much.

After all of these gyrations I think I've come to the conclusion that what I have is about perfect for my purposes, so why futz with it? All in all Ziggy's right with his analysis when he says the 165 and No. 1 drive may be one of the best things Mercruiser ever did.

On the other hand....

kilowatts

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

If I knew I could get 10MPH out of the top end I would be more serious. But I definatly don;t need anymore low / mid power. With the 18' glastron hull, its the fastest planing boat I have ever driven.

PS- When loaded with 5 people, and cruising at 4100 RPM, my 250 also uses a TON of fuel. I blew thru 17 GAL to go 15 miles. It really was working hard as we had about the full capacity in the boat.

 

[kilowatts]

Re: GM 292 in place of MCM 250

Hi Guys:

Nothing I like more than talking about the big six, eh?

I may be wrong but after all I've read I don't think it's possible to get another 10mph. It has to do with more than just the engine but hull, prop, water conditions and on and on.

In order for your inline six to perform using less gas you can't be running at WOT fully loaded. Just back off the gas and run at 31-3500 and you'll use a lot less. My friend and I checked our boats last year and they make between 6 to 7 GPH in mixed speed cruising on calm freshwater. He was trolling this week and used a lot less, although he didn't measure it. I've made guesstimates while in the ocean and found I use more depending on the state of the waves.

Late last night when I couldn't sleep I was looking at an automotive enthusiasts website and read about 292 Chevrolet engines in trucks. They seem to do about 10 - 11mpg under normal use in stock trim and use more gas when hauling a load. Just imagine what the fuel consumption would be in a boat when the motor is always under load! I think you'd get the performance of a chevy small block but the fuel consumption of a big block, exactly the wrong combo, eh?

While we like these engines, they are after all over 30 years old and designed to consume gas at 35 cents a gallon. A lot's changed since then.

kilowatts

 

[HT32BSX115]

Re: GM 292 in place of MCM 250

PS- When loaded with 5 people, and cruising at 4100 RPM, my 250 also uses a TON of fuel. I blew thru 17 GAL to go 15 miles. It really was working hard as we had about the full capacity in the boat.

You have something wrong with the carb NO 250 cu-in should use that much fuel in a boat that size!

My 454 doesn't burn that much even at WOT!!

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

30 yrs old and still overbuilt. Nothing wrong with the carb, just running it way too hard that day. So hard in fact I ended up loosing some drive oil. Still have no clue where it went.

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

Well I found a 265ci and a 292ci used for marine (mercruiser) in a big 40' boat. Engines were pulled and boat scrapped. Carbs have been sold but manifolds are still on them. I am kinda thinking if the motor mount holes are there I will snatch them up. Then to find 4 barrel carbs........

I wonder if I can bolt my 250 2 bbl manifold on and just re-jet the carb. I know its only 2bbl but it could be modified I guess.

These engines just kinda fell my way, otherwise I was kinda forgetting about it. Now Im back to thinking.........

 

[Oshkosh1]

Re: GM 292 in place of MCM 250

You have something wrong with the carb NO 250 cu-in should use that much fuel in a boat that size!

My 454 doesn't burn that much even at WOT!!

How big were the people? Did you have a whole NFL offensive line in there? You have SERIOUS problems...NO WAY should you be getting just over 1MPG even at WOT.

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

Well I found a 265ci and a 292ci used for marine (mercruiser) in a big 40' boat. Engines were pulled and boat scrapped. Carbs have been sold but manifolds are still on them. I am kinda thinking if the motor mount holes are there I will snatch them up. Then to find 4 barrel carbs........

I wonder if I can bolt my 250 2 bbl manifold on and just re-jet the carb. I know its only 2bbl but it could be modified I guess.

These engines just kinda fell my way, otherwise I was kinda forgetting about it. Now Im back to thinking.........

3...2...1... and back to the topic at hand.

 

[kilowatts]

Re: GM 292 in place of MCM 250

Hi Guys:

According to Mercruiser Service Manual No. 1, the MCM 292 had a standard Rochester 2 barrel carb. I don't think adding a 4 barrel will do anything except use more gas!
Can you please take pictures of the engines as I'd really be interested in seeing the "Bigger Six" in the flesh.

kilowatts

 

[dan t.]

Re: GM 292 in place of MCM 250

In its stock form in a mid 60s pickup the 292 used the same single barrel carb as the 250 just jetted a little richer, a4 barrel would be a waiste of time, a 292 will only flow about 400 cfm, a 2 barrel is all you need.

 

[daydreamer1252]

Re: GM 292 in place of MCM 250

fordiesel......remember these motors ran across them in wreckers and school buses....here is a thread I found it has some info about fuel mileage http://www.jalopyjournal.com/forum/showthread.php?t=100479

Two comments I found interesting..."...7 mains ... V8 parts fit ... 292s get 11 MPG in an empty pickup or a loaded dump truck..."

This I know is sooo very true...... and

"...he put a 292 in, and it actually gets better mileage now that he put a 4 bbl, mild cam, and headers on it--they must be starved in stock form with a 1 bbl."

enjoy and keep us posted.....

 

[Fordiesel69]

Re: GM 292 in place of MCM 250

Looked at a 265 and also a 292 today. Will post some pics tomorrow. I wonder if it would be bad to swap the 250 front harmonic balancer onto the 292.

 

[dan t.]

Re: GM 292 in place of MCM 250

Dont know about the 11 mpg, I had a 63 chev 4x4 1/2 ton with a 292 and I seem to recall 16-17 mpg, and thats Imperial gallons. If you could find a 400-450 cfm 4 bbl carb it probably would work good, if not I would stick with a 2 bbl. The ballancer should fit, ballance is the same, belt groove spacing might be different.