300 cfm carb for 302 mercruiser??

[conk3416]

I have a 300cfm holley 2bbl carb on my 302 mercruiser engine. I was wondering if i should go up to a 500cfm carb or will the 300cfm be enough? I just bought the boat and i am new to the whole boating thing. I am good with automotive but marine engines i am finding out are quite a bit different. Just wondering if anyone knew.

Thanks Andrew

 

[frank246]

Re: 300 cfm carb for 302 mercruiser??

The horse power on the MCM 302 is restricted by the carb.
You did not mention the year but 302 mercuiser was 188Hp back in the days.
The Mercruiser 302 uses 351 heads and a 351 cam.
I run a 302 fitted with a 4 bbl edelbrock performer rpm intake manifold topped with a 600cfm vac. sec. Marine Holly carb, Hei electronic distributor and 0.04 gaped plugs.
The secundaries make the difference!!
For standard rebuild better go with the 450 cfm, 4bbl intake and upgrade to point-less ign.
Be sure to be safe, use marine certified parts!

 

[conk3416]

Re: 300 cfm carb for 302 mercruiser??

the motor is a '73. I have already upgraded to the hei distributor. Will the 450 carb give me more horsepower? Is there a big difference between the 2bbl and 4bbl? I am only using the boat for tubing and wakeboarding, so a little more horsepower will not hurt.

Thanks Andrew

 

[WizeOne]

Re: 300 cfm carb for 302 mercruiser??

Tubing and wakeboarding is usually done at lower speeds where you have trouble keeping the boat on plane without increasing the speed to an uncomfortable level. This is not a power issue. Look into SmartTabs, they will lower your planing speed and give you much better speed control at the lower speeds.

That being said, yeah a 450-500 cfm 4bbl would be ideal for your stock 302. You just want to stay out of the secondaries as much as possible or your mileage will go to h*ll. But the increased power will be there when you need it.

 

[conk3416]

Re: 300 cfm carb for 302 mercruiser??

yes i am trying to get on plan as fast as possible. I would like to stick with the 2bbl for mileage, would a 500cfm 2bbl have a noticeable difference or am i wasting my time? What are the smart tabs? I am new to the whole boating thing.

 

[WizeOne]

Re: 300 cfm carb for 302 mercruiser??

Again, a 500 cfm 4 bbl would give you more kick when you need it. It would be nice to have but if you had to do just one or the other, I would do the smart tabs, or at least do them first. You can buy them here on iboats.

http://www.iboats.com/Boat_Parts_Ac...**********.532665599--submit.x.27--submit.y.7

Here is the manufacturers website. The have a good little vid.

http://www.nauticusinc.com/smart_tabs.htm

With smart tabs on my 20 ft 302 with 5 people on board and a tuber out behind, I can stay on plane at 2000 rpm. The Tabs are worth their weight in gold, IMHO.

 

[conk3416]

Re: 300 cfm carb for 302 mercruiser??

thanks to everyone for there help. I am planning on upgrading to to the 4 barrel intake and carb soon. Probably the 450cfm. Thanks again Andrew