888 / 302 intake manifold

[Aloysius]

Re: 888 / 302 intake manifold

I see lots of 302 4 bbls. in boats..Pleasurecraft was a large supplier. Used a low rise manifold, probably stock production.

As I stated, disconnecting my secondaries doesn't make any difference under 3500 rpms or so, and the stock 2 bbl. is pretty large already.

 

[mkast]

Re: 888 / 302 intake manifold

Print it so it's readable.

 

[haulnazz15]

Re: 888 / 302 intake manifold

While I agree that the 351w produces a lot more torque than the 302, it makes me wonder why the 351w used the 1.32 while the Chevy 350 used the 1.50. I don't think their HP/TQ are more than a a few hp either way in a 2-or-4bbl configuration. Either way, the 4bbl carb isn't going to help things much since the rochester 2bbl that is likely on his 302 isn't going to add much of anything.

 

[Haut Medoc]

Re: 888 / 302 intake manifold

While I agree that the 351w produces a lot more torque than the 302, it makes me wonder why the 351w used the 1.32 while the Chevy 350 used the 1.50. I don't think their HP/TQ are more than a a few hp either way in a 2-or-4bbl configuration. Either way, the 4bbl carb isn't going to help things much since the rochester 2bbl that is likely on his 302 isn't going to add much of anything.

Good question, but why are the only other applications for 1:32's on the BBC's?......

 

[mkast]

Re: 888 / 302 intake manifold

It would appear 1.32 or 1.33's are used in high torque applications.

 

[89cruisers]

Re: 888 / 302 intake manifold

well arnt the secondaries opened based on throttle position?...if so then when I open the throttle up, the secondaries will open allowing more power for the engine..thus allowing it to overcome the gearing better

 

[Haut Medoc]

Re: 888 / 302 intake manifold

well arnt the secondaries opened based on throttle position?...if so then when I open the throttle up, the secondaries will open allowing more power for the engine..thus allowing it to overcome the gearing better

The best you're gonna do is get 215 out of it even with a four barrel, & even then you will need to be engaging the secondaries all the time, & we all know what that doe$ to ga$ con$umption.....
You are trying to reinvent the wheel here, when what you need is a 1.50 drive.....
No matter what parts you throw at it, you won't properly overcome the wrong ratio.....

 

[Haut Medoc]

Re: 888 / 302 intake manifold

Not too mention what the internal condition of the engine is if it has been 'lugging'.....
Have you done a compression check?....

 

[89cruisers]

Re: 888 / 302 intake manifold

well from what I was getting from the previous owner the engine was just put in before I bought it, and compression is even across all cylinders (right around 110 dry and with other plugs still in) I can see what your saying about fuel usage, however I cruise at around 25 which the secondaries should still be closed...the top end is for when I would have the...special guests on board lol

 

[Aloysius]

Re: 888 / 302 intake manifold

The secondaries open on demand, not necessarily throttle position. The 302 engine only pumps 151 cubic inches of air per revolution..period. If the existing carburetor is big enough to flow that much air with no restriction, adding a bigger carburetor won't help.

well arnt the secondaries opened based on throttle position?...if so then when I open the throttle up, the secondaries will open allowing more power for the engine..thus allowing it to overcome the gearing better

 

[89cruisers]

Re: 888 / 302 intake manifold

Well I do know that a 4 barrel on a 302 does indeed help for the starndard use of adding a 4 barrel when the gearing is proper

 

[haulnazz15]

Re: 888 / 302 intake manifold

Well I do know that a 4 barrel on a 302 does indeed help for the starndard use of adding a 4 barrel when the gearing is proper

You have to separate your knowledge of auto 302's versus the marine versions. Flowing more air and fuel by going to a 4bbl carb on an auto works better because you are able to get the rpms up into the 6K+ range. Your 302 should top out around 4200rpms, so you just won't see much benefit in the bigger carb. As was mentioned, the 4bbl 302 only eeked out around 215-220HP in the marine versions, so that extra 20HP or so on the top end isn't going to produce much additional power, especially in the range in which you are currently have problems.

I promise, if you swap out the outdrive for something with a 1.50 gear ratio and a prop that has your WOT rpms at 4200 you will be happy. If you still want to add some extra grunt, throw the 4bbl carb on and a dual-plane intake manifold after you do the outdrive.

 

[89cruisers]

Re: 888 / 302 intake manifold

After doing some research, the marine 4 barrel 302 was generously rated at 225hp, and considering the 351 that was on it was a 233...id say that would be sufficent?...and found on this site are people who did the upgrade to a 4 barrel and are happy?

 

[Aloysius]

Re: 888 / 302 intake manifold

Believe what you want. I've only got 2 of 'em (302's), rebuilt 'em, monitor them with vacuum gauges, gotta distributor machine and tweak 'em constantly.

Which brings up a good point. If you haven't optimized what ya got, you're wasting your time.

But hey, it's your engine.

 

[89cruisers]

Re: 888 / 302 intake manifold

Im not trying to debate, im just trying to learn...and so if the 4 barrel version makes 225hp, and the only difference is the carb, then it seems logical a 4 barrel does indeed help?

 

[a70eliminator]

Re: 888 / 302 intake manifold

I only know of 1 factory 302 4 bbl and that was in 68 so where are you getting 302 4bbl HP rating specs?

 

[haulnazz15]

Re: 888 / 302 intake manifold

The point here ISN'T the HP rating, it's the TQ rating. The 302 @ 215HP is making nearly the same torque as a 351w@233HP. We're not saying that adding a 4bbl intake/carb won't be beneficial, but it's not likely the primary reason you are having issues right now. I had a 233HP 351w with the 233 drive, and it did great, however when it came time to rebuild I went with the 4bbl option just to get that extra 30-35HP. I didn't do it because I thought it was going to help me plane out quicker or get more top-end speed, because it take a lot of HP increase in a boat to make much of a dent in actual performance.

 

[Aloysius]

Re: 888 / 302 intake manifold

Since horsepower is strictly a function of torque and rpm (hp=torqueXrpm/5252), there is NO difference in power between a 2bbl and a 4bbl. at lower rpms...the "horsepower" is just rated at a higher rpm. A bigger carb helps ONLY when the existing carb restricts flow.

Optimize what ya got. Make sure the timing advance and total advance is spot on. small block fords usually require alot of timing advance..big bore, not much turbulence. Make sure the engine is in good shape. Make sure the intake air flow is not restricted.

 

[JasonB]

Re: 888 / 302 intake manifold

If I were doing a tear down of the motor, I would also have the heads checked for smog bumps. You never know what someone put on a motor over the years. That said, I agree with others that the 4bbl isn't going to overcome the torque issue. The 351 is simply a longer stroke motor making significantly more torque. Even if you get a prop to get you out of the hole faster, you will still be asking a lot form that 302 and will likely be lugging it = short life. Hunt for a new outdrive, or find a 351 to drop back in. Beware though, I think a 351 uses a wider exhaust Y pipe?

That 15+" diameter prop seems a bit steep as well since I'm used to running 14 1/4 or 14 1/2" dia.

A70, in the mid 70's Mercruiser offered the 302 with a transmission/outdrive setup and it was rated at 225hp with *I think* a 450cfm Holly. There was straight inboard version rated at 215hp as well.

 

[haulnazz15]

Re: 888 / 302 intake manifold

The 351 is simply a longer stroke motor making significantly more torque. Even if you get a prop to get you out of the hole faster, you will still be asking a lot form that 302 and will likely be lugging it = short life. Hunt for a new outdrive, or find a 351 to drop back in. Beware though, I think a 351 uses a wider exhaust Y pipe?

Agreed. However, I don't think they use a different y-pipe. The 1/2" of extra deck height won't affect much on the y-pipe. I'm sure the difference is covered up by the rubber exhaust connections from the y-pipe to the riser.