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4 Barrel Manifold for 6-Cylinder 165

4

427435

Member
Did anyone make an intake manifold for the old 165 hp, in-line 6 Mercruisers? The intake and carb look like the same ones used on the 120 and 140 hp, 4 cylinders. I would like a little more breathing on top end.
 
Intake and card used on a four cylinder is NOT the same as a six cylinder.

Also the 250 cubic inch gm motor used in marine is the basic motor used in gm auto's. That bieng said any six cylinder GM 250 cubic inch intake will bolt up.

A holley 390 cfm may be had in marine??? Cant go too big on the cfm's for a six banger......without valve and cam changes......
 
I believe MERCRUISER used a 6 cylinder " truck " inline 6 ---292 cubes or there abouts.--------Came with 2 carburetors.
 
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You may correct I did not have my books available when making pervious post. There was a guy from the north east here, I think new hampshire who was very heavy into the six inline motors....

Here is a exert from merc manual # 1
 
And no the 165 was a inline six cylinder with a Single Rochester 2 bbl. carb (two air/feul adjusting screws). I personally have never seen a 4bbl on a inline six stock motor.

They were stock on some of the imfamous inline 4 cylinder (470) with the Big block ford head..........
 
I believe that " truck " MERCRUISER 292 came with 2 carburetors.----------Not sure if that manifold will fit the 250 cube machine.
 
I personally have never seen a 200 inline six mercruiser. I believe all I have ever seen first hand is the 140 hp inline six and many many 250 (165hp) inline sixes.

The 292 must have been a good power plant. I also think the odd balls from the exert I posted the inline six ( 140, 150,160 and the 200 hp) were most likey used way back pre '70's definately pre '80's anyway. They seem to standardize the 250 ci 165 hp as the typical for many years.....

I am not sure how many here have much experience pre 70's. I have only handled a few. They had some wierd designs back then......Most here seem to be in the late '70's early '80's to present knowledge base.

As far as the original post goes there are a ton of six cylinder resources out there as they are commonly used for auto racing and other things. Many parts sources also. I do not know of any myself but have seen reference to them in the past.
 
If you check on line yu can get the model numbers for any of the 4 and 6 cylinder engines (Mercs/Chev) between 1970 to 1980. My boat runs twin 165 in line 6 which have the rochester carb.
 
I have seen a 4 bbl on 250 cid in a B modified stock car years ago and I seem to remember it being an Eidlebrock manifold.
 
merc never had a production 4 barrel manifold on the inline 6 cylinders. You can find many for auto applications but they are intake only and the marine stuff is usually integrated intake & exhaust in a unit casting. They did make a dual carb manifold but it had the really old "B" rochesters on it. I'm sure you can buy a custom one provided the budget is large.

Kghost's time frame is pretty close. They were predominant thru the 60's. Guess I'm old enough to have actually owned (& rebuilt) a 165 with a I drive. Have only seen a 292 based 200 hp i/o.

Why would you want a four barrel? Even at 4000 rpm, you don't need more than 300 cfm. The "standard" 2GV will flow that at WOT and a bit more if you clean them up. A quadrajet will flow that thru the primaries so there really isn't a need for a four barrel unless you are going way beyond stock.
 
The rpm at WOT is 3900-4000 and I would like to be able to get a little more rpm and speed out of it. The carb is the same as the 120 and 140 hp, so I'm thinking that may be the limiting factor. From what I'm hearing here, it doesn't sound promising as I don't want to divorce the intake and exhaust manifolds.
 
427435 said:
The rpm at WOT is 3900-4000 and I would like to be able to get a little more rpm and speed out of it. The carb is the same as the 120 and 140 hp, so I'm thinking that may be the limiting factor. From what I'm hearing here, it doesn't sound promising as I don't want to divorce the intake and exhaust manifolds.
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Ayuh,... Drop 2" of pitch on the prop, 'n Enjoy what you've got....
 
maybe the op is looking in the wrong place for the cause of low wot rpm.

I " believe " recommended wot is 42-4600 rpm.

So your only 200-600 rpm off the mark.

IF The tach is correct. Is it ? You checked it against a know shop tach that is correct ?

So say the tach is correct !Compression is what ?

Fuel pump is giving what psi ?

Water in the hull wet stringers ?
 
chiefalen said:
maybe the op is looking in the wrong place for the cause of low wot rpm.

I " believe " recommended wot is 42-4600 rpm.

So your only 200-600 rpm off the mark.

IF The tach is correct. Is it ? You checked it against a know shop tach that is correct ?

So say the tach is correct !Compression is what ?

Fuel pump is giving what psi ?

Water in the hull wet stringers ?
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I'm pretty sure the recommended WOT is 3900-4300 rpm, and I'm just at the lower side of that. Acceleration is fine with a 21" stainless prop. I also had a 19" prop on it and that resulted in 4300+ rpm and no more speed.

I don't know about the fuel pressure, but I can run at WOT for a significant length of time without any problems. Compression is in the 130-140 area. Don't know about the tach, but the engine "sounds" about right. The boat is aluminum and dry inside.

I'm just looking for a relatively easy way to get another 300-400 rpm out of it with the 21" prop.
 
I'm just looking for a relatively easy way to get another 300-400 rpm out of it with the 21" prop.
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Ayuh,... It Ain't gonna happen...
Drop to the 19" prop to get the rpms up... You're lugging it at 3800rpms at Wot...

That motor won't mind a 4400/ 4600rpm Wot, so long as you don't run it at Wot for extended periods...
 
bondo said:
Ayuh,... It Ain't gonna happen...
Drop to the 19" prop to get the rpms up... You're lugging it at 3800rpms at Wot...

That motor won't mind a 4400/ 4600rpm Wot, so long as you don't run it at Wot for extended periods...
Click to expand...

Why drop to a 19" prop?? As I posted, I have already tried that and it did nothing for my top speed and caused the engine to run at a higher rpm (noisier and thirstier).
 
What kind of prop? rebiult or brand new?

A rebiult prop will not have the cupping like a new one will there fore you will basically over rev with no real increase in speed.
A propperly cupped prop will continue to give more speed.

You are dealing with a marginal motor so high speed and power are really not on the menu.......
If the motor has never been rebiult it is also old.....many many issues at play.

Propping a boat with the right one and even a special high performance one can make your experience as different as night and day.

Some boats I have seen and driven where the owner purchased a high performance prop ($600+) made a dramatic improvement. 5+ mph increase...acted like a passing gear in a auto........made the boat a whole lot more fun.
 
the 200hp 292 Mercruiser in 1969 used a Quadrajet carb...

I thought all the 165's had a manifold that could accept a 4 BBL by removing the adapter plate

158759.jpg
 
hystat said:
the 200hp 292 Mercruiser in 1969 used a Quadrajet carb...

I thought all the 165's had a manifold that could accept a 4 BBL by removing the adapter plate

158759.jpg
Click to expand...


Well that gives me some hope.

Another thought I had was finding a 2 barrel with more flow capacity.
 
Holley makes a 500 cfm 2bbl that is more than that 230 can burn with stock cam, and compression ratio. About 350 cfm is probably plenty.Not much sense running in a semi flooded condition and leaving a black smokescreen behind.
 
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