888 / 302 intake manifold

89cruisers · Oct 12, 2010

Hey there everyone, I'm looking to put a 4 barrel carb on my 302 to help overtake my incorrect gearing. I seem to remember reading that the mercruiser 302 used 351 heads on it, but im not completely sure. Can anyone spread any light on this, and if so does that mean I need to buy a 351 intake manifold?

Thanks

Don S · Oct 12, 2010

Re: 888 / 302 intake manifold

What gear ratio are you trying to overcome?

Aloysius · Oct 12, 2010

Re: 888 / 302 intake manifold

The 351 is physically wider...a 351 manifold will not fit a 302. The difference between heads is the water passages, and determines the intake gasket used.

Bondo · Oct 12, 2010

Re: 888 / 302 intake manifold

Don S said:
What gear ratio are you trying to overcome?

Ayuh,.... I believe it's a 302 tryin' to turn a 351 ratio,...
Can't buy a prop small enough to bring the rpms up...
Mod. 1 Merc...

Haut Medoc · Oct 12, 2010

Re: 888 / 302 intake manifold

You need an intake that fits a 302.....

4bbl for Mercruiser is pretty rare....

89cruisers · Oct 12, 2010

Re: 888 / 302 intake manifold

This boat originally had a 233 which would have a 1.5 ratio, but the 351 was replaced with a 302 wich doesn't have the power with the current setup to go past 3000 rpms with a 15x16 4 blade prop. a 888 ratio is right around 1.7 I believe, but I don't want to spend the money to have the gears swapped, and still have a fairly slow boat. So then then answer would be use a 302 intake and intake gasket?

Haut Medoc · Oct 12, 2010

Re: 888 / 302 intake manifold

Like Bondo said, if you are trying to turn a 1:32 by putting a 4bbl on it, it won't work.....

Aloysius · Oct 12, 2010

Re: 888 / 302 intake manifold

A 4 bbl. won't make much difference under 3500 rpms. Running my 302's with the vacuum secondaries disconnected, I only notice a difference at 4000 rpms and above..and that's with a small 450 cfm 4 bbl.

There's no substitute for cubic inches.

89cruisers · Oct 12, 2010

Re: 888 / 302 intake manifold

in the classic mustang application adding a barrel to a 302 has done wonders, so I have faith it should be able to overcome atleast some difference in the gearing, and if not...then I have a great powertrain for when swapping the gears out anyways. Just want to make sure to buy the proper manifold since I read somewhere that the 888 used 351 heads. I've seen a used 4 barrel merc 302 intake for $125...but if that goes I wana know what automotive manifold to buy

Bondo · Oct 12, 2010

Re: 888 / 302 intake manifold

Haut Medoc said:
Like Bondo said, if you are trying to turn a 1:32 by putting a 4bbl on it, it won't work.....

Ayuh,... The 1.32s are gettin' hard to find,.... NLA gear sets..

Probably trade it for 2 1.50s, which Should be on a 302....

Btw, Haut, I've got another 1 sittin' in the yard,... Complete 302, 73 model...

JasonB · Oct 12, 2010

Re: 888 / 302 intake manifold

An 888/302 2bbl 188hp should have a 1.5 gear ratio. I'm pretty sure the 2bbl 351/233hp also came with the 1.5 gears as well. The oddball may have been the 4bbl 302/225hp, it used a transmission in front of the drive I think.

My 2bbl 302 w/ 1.5:1 gears pulls a heavily cupped 19 pitch prop quite well on my 19' bowrider.

Many of the 888's came with 351 heads, but the manifold is still a 302. The extra deck height of the 351 block is much of what makes the wider manifold necessary for a 351 application.

zbnutcase · Oct 12, 2010

Re: 888 / 302 intake manifold

89cruisers said:
in the classic mustang application adding a barrel to a 302 has done wonders, so I have faith it should be able to overcome atleast some difference in the gearing, and if not...then I have a great powertrain for when swapping the gears out anyways. Just want to make sure to buy the proper manifold since I read somewhere that the 888 used 351 heads. I've seen a used 4 barrel merc 302 intake for $125...but if that goes I wana know what automotive manifold to buy

Yes the 888 has 351W heads. But you can use any 302 intake manifold. Just use 351 intake manifold gaskets. And a lightweight, lightly loaded mustang compared to a boat is apples&oranges

haulnazz15 · Oct 12, 2010

Re: 888 / 302 intake manifold

JasonB said:
An 888/302 2bbl 188hp should have a 1.5 gear ratio. I'm pretty sure the 2bbl 351/233hp also came with the 1.5 gears as well. The oddball may have been the 4bbl 302/225hp, it used a transmission in front of the drive I think.

The 233 Drive was a 1.32 gear ratio, not 1.50. I do agree with you that the heads for 302/351 are identical as far as size/measurements are concerned, it was the porting/valves/combustion chamber that differed. The intake manifold should remain the same 302. I wouldn't want to use 5.8L heads anyway because most of them post-75 or so are larger volume chambers which reduced the compression ratio and thus the HP output.

I would switch props as much as you can to try and make up the difference. If you're still not happy, go buy an SEI outdrive at 1.50:1 ratio and sell the 233 drive to recoup some of the money.

89cruisers · Oct 12, 2010

Re: 888 / 302 intake manifold

well in a previous thread about my rpms not going above 3k, engine checked out so was told gearing is different between the 888 and 233, I know comparing the two is a bit dfferent, i'll just stick with my example of a 3.7 2 barrel is 170 and a 3.7 4 barrel is 190. thanks for that intake and gasket info. but yeah like I said...even if adding it doesn't help atleast im al setup for later...anyways, im youngs and still have to learn from my mistake

Haut Medoc · Oct 12, 2010

Re: 888 / 302 intake manifold

Bond-o said:
Ayuh,... The 1.32s are gettin' hard to find,.... NLA gear sets..

Probably trade it for 2 1.50s, which Should be on a 302....

Btw, Haut, I've got another 1 sittin' in the yard,... Complete 302, 73 model...

I'll be right over......

Don S · Oct 12, 2010

Re: 888 / 302 intake manifold

Bond-o said:
Ayuh,.... I believe it's a 302 tryin' to turn a 351 ratio,...
Can't buy a prop small enough to bring the rpms up...
Mod. 1 Merc...

I assumed the same thing, just thought I would ask and get verification from the OP first, instead of posting some WAG and hoping for the best like everyone else.

JasonB · Oct 12, 2010

Re: 888 / 302 intake manifold

found this chart: http://www.seilermarine.com/info/mercruiser-drive-ratio-chart.htm

Mercruiser Sterndrive Gear Ratio Chart

Mercruiser R-Style Sterndrives (1969 - 1983)
Engine HP Liters/CID Cylinders Gear Ratio Tooth Count Year
2.5 Liter 120 2.5/153 4 1.98 20-24 1969-1983
2.5 Liter 130 2.5/153 4 1.98 20-24 1969-1983
165 165 3.7/224 6 1.65 24-24 1969-1983
470 170 - 190 4.3/262 4 1.84 17-19 1969-1983
215 - 233 205 - 230 351 8 1.5 20-22 1969-1983
260 260 5.7/350 8 1.5 20-22 1969-1983

JasonB · Oct 12, 2010

Re: 888 / 302 intake manifold

Ok, I stand confused. Found this as well:

Mercruiser 888 1.50 1971-1977 3106717-Up GLM18100
Mercruiser 225-S 1.50 1974 3856268-4200499 GLM18100
Mercruiser 233 1.32 1975-1977 4200500-Up GLM18100
Mercruiser 898/228/260 1.50 1977-1982 4782330-6225576 GLM18100
Mercruiser 250 1.32 1977 4791300-4898729 GLM18100

My question is, why use a 1.32 ratio on a 233hp 351 when they used the 1.5 ratio on everything else? Was this something for heavier cruisers?

89cruisers · Oct 12, 2010

Re: 888 / 302 intake manifold

Thank you for finding that, becuase that does greatly explain why my 188hp is having such a hard time moving and haulin, that is what I plan on doing next spring if the 4 barrel and or a 15.5x13 prop doesnt make enough difference

Haut Medoc · Oct 13, 2010

Re: 888 / 302 intake manifold

JasonB said:
Ok, I stand confused. Found this as well:

Mercruiser 888 1.50 1971-1977 3106717-Up GLM18100
Mercruiser 225-S 1.50 1974 3856268-4200499 GLM18100
Mercruiser 233 1.32 1975-1977 4200500-Up GLM18100
Mercruiser 898/228/260 1.50 1977-1982 4782330-6225576 GLM18100
Mercruiser 250 1.32 1977 4791300-4898729 GLM18100

My question is, why use a 1.32 ratio on a 233hp 351 when they used the 1.5 ratio on everything else? Was this something for heavier cruisers?

The 351 produces a lot more torque......

888 / 302 intake manifold

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