Intake manifold

[pike hunter]

I have a Mercruiser 5 Liters 1992 serial #: OD709798. Actually with a Mercarb 2 barrels with electric choke. I would like to upgrade with a 4 barrels. A friend of mine gave me a marine Rochester 4 barrels MCM 260/270, 1347-8292; that carb was on a 350 Mercruiser and was running fine before a bad winterization that cause the block to crack. He also gave me the flame arrestor and the trottle bracket. The only thing missing I beleive is the intake manifold. That carb doesn't come with a electric choke. I know we should always use marine parts but for a intake manifold can I use a automotive one or do I need a specific marine intake? I want to keep the cost low. If you have any advise on where to purchase one let me know.
Hope I was clear enough.
Thank you

 

[Bondo]

Re: Intake manifold

As long as it's Cast Iron,+ Fits the 87/96 Bolt Pattern,......

Ayuh,...... Any of them will Work.........

 

[FreeBeeTony]

Re: Intake manifold

pikehunter.........send me an email.

I have a 4bbl intake you could use.
Also have the matching Weber 4bbl if you want it.

The intake/4bbl came off a '92 350 Magnum that was FWC'd.

removed email address

 

[John_S]

Re: Intake manifold

The hi-rise cast-iron will bolt on the 305, but will it be good match for it? Its good for the 350, but might be too much for the 305. Just something to consider.

If you are in fresh water or you are not raw water cooled, look at the Edelbrock Performer. It has provisions for stove type chokes and Q-jet bolt-on. There is also an air-gap Performer, but you would need to convert to electric choke.

If you are raw water cooled, and boat in salt, you will need a cast-iron manifold. Only other one I know of, is the standard low profile one. As Bondo says, make sure you get the one that matches your year heads.

Expect a fuel line change, and some minor carb tweaking, going from a 350 to 305. The good news here is that the Q-jet came on both, so you will be able find out what jets/rods/hangers/adjustments Merc had for the 305. I haven't looked at them in a while but believe it is minor.

 

[FreeBeeTony]

Re: Intake manifold

Didn't pick-up that your engine was a 5.0.......John maybe be right about the carb being too much. I believe my carb is the 750 (4 equal size barrels), my manifold is the GM high rise cast iron.

Hey John...........how did you make-out with your 4bbl conversion? Which carb did you use?

 

[John_S]

Re: Intake manifold

The Webers that came on the 305 4brls, were 625 cfm, not the 750cfm of 5.7LX and 350 Mag. Being they are vacuum secondaries, and will only flow what your engine needs, a 750 could be tuned to work. There will not be a good starting point provided by Merc though, and it will never be as responsive as the smaller carb.

Your Q-jet is 750cfm too. It will not flow anywhere near that on a 305 running 5K rpms or less. It too has vacuum secondaries, and will only flow what you need. If the Q-jet is tuned such that you can cruise on the small primaries, you may actually see your gas milage improve over your current 2brl set-up.

If you go the hi-rise route (which I don't recommend) make sure everything will still fit under the dog house. Actually, you would want to make sure for any aftermarket intake, too.

 

[John_S]

Re: Intake manifold

Tony, I stayed 2brl this season! :$ and I speak from experience on checking the dog house height! The cast-iron high rise, weber 750, and K&N was not going to fit. A half inch mifgt as well been a foot. I sold the intake and carb on ebay. Being I missed last season due to work, I didn't want to loose any of this season with allot of other tuning and adjustments, as well. The smart tabs did get installed and they are great.

The 4brl is still in the plans for this winter. Probably will settle on a Edelbrock Perfomer and 1409 carb.

 

[FreeBeeTony]

Re: Intake manifold

Too bad about the 4bbl conversion John........I remembered you were contemplating it.

Oh well..........I still have the carb/manifold if anyone is interested. I put them on ebay and never got any bids! Maybe I should try again.

 

[pike hunter]

Re: Intake manifold

The Webers that came on the 305 4brls, were 625 cfm, not the 750cfm of 5.7LX and 350 Mag. Being they are vacuum secondaries, and will only flow what your engine needs, a 750 could be tuned to work. There will not be a good starting point provided by Merc though, and it will never be as responsive as the smaller carb.

Your Q-jet is 750cfm too. It will not flow anywhere near that on a 305 running 5K rpms or less. It too has vacuum secondaries, and will only flow what you need. If the Q-jet is tuned such that you can cruise on the small primaries, you may actually see your gas milage improve over your current 2brl set-up.

If you go the hi-rise route (which I don't recommend) make sure everything will still fit under the dog house. Actually, you would want to make sure for any aftermarket intake, too.

The fact that if the Q-jet is well tune it can save gas is the main reason why I want to move forward with that solution.
Can I use a intake from a automotive Chevy block with the same bolts patterns (model with the valve covers that have the bolts in the middle instead of around it?)
What year of motor should I look for? Many blocks from those years are fuel injection.

 

[Bondo]

Re: Intake manifold

Many blocks from those years are fuel injection.

Which is Where the Problem lies,.........

Aftermarket or Marine are the Solutions...........

 

[pike hunter]

Re: Intake manifold

Many blocks from those years are fuel injection.

Which is Where the Problem lies,.........

Aftermarket or Marine are the Solutions...........

I'm sure there is a chevy block maybe in the truck departement that where using a carb instead of a fuel injection.
I don't compromise habitually for marine parts vs auto parts but for a intake 'come on' I will call a few scrap yard tomorrow and try to find something if "possible"
Thank you all for you're answers and effort.

 

[John_S]

Re: Intake manifold

I have heard of people slotting the center bolt holes on pre-87 intakes, to fit the 87-96 heads. Can't say how well it works, but you should be able to research it and find more info. A decent machine shop should be able to tell you if it is possible. There are ton of pre-87 carbed cast-iron manifolds that haven't turned to dust yet.

 

[No show]

Re: Intake manifold

I have a Mercruiser 5 Liters 1992 serial #: OD709798. Actually with a Mercarb 2 barrels with electric choke. I would like to upgrade with a 4 barrels. A friend of mine gave me a marine Rochester 4 barrels MCM 260/270, 1347-8292; that carb was on a 350 Mercruiser and was running fine before a bad winterization that cause the block to crack. He also gave me the flame arrestor and the trottle bracket. The only thing missing I beleive is the intake manifold. That carb doesn't come with a electric choke. I know we should always use marine parts but for a intake manifold can I use a automotive one or do I need a specific marine intake? I want to keep the cost low. If you have any advise on where to purchase one let me know.
Hope I was clear enough.
Thank you

I need that carb if you want to sell it,I mean if you decide not to use it
thanks

 

[dan t.]

Re: Intake manifold

slotting out the center bolt holes works just fine , make up a sleve that goes between the bolt head and the manifold with one end at 90 degrees, the other ground to conform to the man ifold,put a flat washer between the sleve and the manifold. works good, I have a manifold from a 1966 327 on a 1992 305 , 6 years no problems

 

[erikgreen]

Re: Intake manifold

Since this thread is from 2006, I'd bet he's fixed the problem, and the carb is sold at this point