Ken2

Hey guys.
Been searching over the forum and there is so much info its overwelming.

I have a little different senario for you guys.

Currently running a 302, in a marine application.
It is EFI, the motor is a 95 or 96. Puts out 220 HP according to the specs.

I want to convert to Carburetor. Most likely a Marine Holley 600-650
I have GT40 heads currently, but I'm willing to change/upgrade if needed.

Shooting for 300 HP, while still having equal bottom end as the current setup.
Don't really want to turn the engine much over 5K.
5500 would be about as far as I'd like to go.

I'd like to stay with the same heads, but if I need different ones, thats ok.

What specific intake and cam should I go with?
Is 300 HP feasable while still having a reliable engine?

This motor is going to turn 3500-5000 rpm for extended periods of time.

Tell me what I should buy

wydopnthrtl

300hp limited to a 302 and 5000 rpms is going to take higher compression, ported heads, a specific camshaft, and a stroker kit. Or.. boost it with a SC or turbo.

Keep in mind that the 302 is a short stroke setup. IMO you could get there by increasing the stroke, a cobra intake, headers, a 650-700 carb, a special made cam shaft w/matching valve springs, & roller rockers. W/O porting the heads you *might* get there. I don't really know for sure but I'd port them if possible.
The cam is not much more expensive than an off the shelf cam so don't be afraid to do this.

Having been into boating myself. I'd take a different approach because that longer stroke engine might over power and cavitate the prop at low speeds.

Personally I'd want a long and increasing TQ curve from the engine and just step the prop down in pitch to keep the water speed where you want it. Basicly.. spin the engine faster to go the same speed.

mjr46

you won't hit 300 with out a head upgrade, I assume this is in a boat??

Ken2

Yes, its in a boat.
I was trying to stay away from aluminum heads, but maybe if I have them anodized that would help with corrosion.

Propping isn't a problem, I actually own a propeller company, so I an always get that dialed in later.

Are AFR 165's the best to go with? or are there lots more to choose from?
I see the Edelbrock performer RPM, upper kits with heads, intake, cam, etc... supposidly getting 360+ HP
http://www.edelbrock.com/automotive_.../2091graph.jpg

didn't know if that was realistic or not.

I just didn't think it would be very good to turn this motor with a stock bottom end up to 6K for extended periods of time. (5 - 10 minutes)

wydopnthrtl

You could have your iron heads done by this guy in Fla. http://www.hunterstyle.com/thumper/

It looks like the power curves in your link are making the power vs rpms your wanting. Maybe contact them to see what they can do for maranizing (sp?) the heads.
You could also do a closed radiator system like a car... if the engine room is open. Seems like a lot of work though.

I bet the thumper heads a good bottom end balance and the other things to support the cam would get you there. Especially if you'd be willing to spin it a little higher.

If the bottom end is factory stock.. I would not be all that concerned about 6000 rpms. But if your going to rebuild it.. you could buy a high quality scale that can go down to 0.1g and static balance the parts yourself. Get them all weighing the same and then send the (unassembled) bottom end (less the block) to a professional who can rotationally balance the crank. Get a good harmonic balancer and you can spin it to 6000 all day long. And in reality the bottom end could be spun much higher with forged parts. I wouldn't even be scared of 7000rpm with good balancing on stock parts. Remember.. this is a short stroke setup.
The shade tree way... find your lightest rod / pin / piston combo and make the others match it for weight. Get a good harmonic balancer for a stock bottom end and 6000 won't be a problem. Professional preping of the crank can't be beat though.

Something else to consider is oil and piston to wall clearance. Take a look at what mercury marine specs for their 5.0 and 5.7 engines and make yours match. (assuming 25W-40 marine type of oil)

Also... with times at those extended rpms, make sure to ask about the lengths of the valve guides. Often times when people port heads they cut them down or use bronze. I'd stick with the stock steel / iron ones and keep them as long as possible. Talk to the cam guy about it. Point being.. the shorter and softer the guides.. the shorter their life. And if they do get egg shaped high rpm power is where you'll see it the most.

The last engine I built I did this to the bottom end. (5.4L modular engine w/forged parts) Even with its longer stroke I could spin it to 7500. And the bottom end wasn't the limiter. ;-) I spent $300 on the scale and about $1100 on the cranks straightening - machining - balancing. That bottom end was bullet proof and I cared not how high I spun it.

If you choose to do this yourself. Send me a PM. I've got lots of tips to help you balance the parts w/o compromising their strength.

Ken2

Its a very small boat, so closed system is out.

I may be giving shooting you a PM when I get started.

As long as the bottom end doesn't look screwed up, I was going to leave it as is.
The motor has about 400 Hours on it. They are "Hard" hours, but I would think its still in pretty good shape.

As for that link, it did look nice, but I didn't know if that was just "advertizing" or if the Edelbrock top end combos actually put out what they claim.
I'm going to give them a call to see if they can do something to help with corosion.

Thanks for the info so far !

Ken2

Trying to get up to about 70 MPH with 2 people in the boat.
I only need about 50 more HP to get there, but don't want fall short.

Currently specs say its 220 HP at the prop with fuel injection.

I have been told that just going to carb would likely get me there.
I've just never upgraded heads and tried to match the cam, intake, heads, and springs for a specific result before.
I've always dealt with "stock" stuff in the past.

Here is the boat http://www.youtube.com/watch?v=523BvHsn4AI