Dropping some weight on a HP500 carb?
 

I love the way my boat rides with the SBC in it, but I'm thinking about a HP500. Is it possible to make a HP500 Carb weigh close to a SBC? I boat in fresh water only. If I swap out the factory iron heads with aluminum ones how much weight will it drop? I believe the HP500 already has a aluminum intake. What about the exhaust, is it iron or aluminum?

Is your SBC all stock with cast iron intake, heads, and exhaust ?

All stock except for edelbrock performer EPS aluminum intake, still has iron heads and stock exhaust, the iron log manifolds. Circa 1981. Was thinking about an intake, cam, aluminum head and aftermarket exhaust rebuild on the small block but now and considering a HP500 since a few have come up for sale. but wanna see how close I can get the weight.

About the only places to shave some weight is going to be aluminum heads and a crossover kit to eliminate the cast water pump

Maybe build a stroker SBC?
That said, the 24-7 hull has been home to lots of BBC engines. Hard to beat the torque a big block makes.

A lot of 24 Outlaws and 25 Active Thunders with Big blocks that run very well. Maybe there are other things (weight) you could move forward for better balance?

I'd be leaning toward an LSX powerplant.

Yep what he said ^^^^

If this is a 24/7, why do you want an anorexic boat? The weight on a short straight bottom will help the ride. If you have your heart set on light, go with the LS platform.Its easy to get more hp than a blue hp500

I second that motion.

Heres some weights I found. All listed with bravo drive package.

350 MAG MPI = 1025lbs

454 MAG MPI= 1177lbs

502 MAG MPI= 1189lbs

So, lets say you have a difference of 165lbs between the 502 mag, and 350 mag. Now you put aluminum heads on the BB, and lose 70 lbs. Then, you install aluminum exhaust manifolds, and lose another 70lbs. Now, your real close to the weight between the two.

With that being said, 165lbs really isnt much. People act like a small block is several hundred pounds lighter. Like its some paperweight compared to the big block. In a strip car, that may be alot, in a boat, I wouldnt EVER trade off the minimal weight savings, for the power production and powerband of a big block. Probably why I'd be 95% of the boats on oso have big blocks in them.

For chits and giggles, go throw a few sandbags in the bilge of your boat, and do a back to back run with and without them. See how it feels. I'll bet you wont feel much of a change in handling or performance. But strap in a big block making an extra 150ft lbs or HP, and I bet you'll be grinning from ear to ear. The power gain will more than offset the weight difference. The added power will make the boat feel much lighter. I know at 60mph my boat feels like a tank. At 90mph, it feels like a sports car. A simple change in prop style can easily lift the extra 165lbs off the stern, or vice versa.

Aluminum heads, intake, exhaust will shave off huge weight..... I used 496 aluminum exhaust with SS risers and those alone compared to cast iron manifolds and risers will save you at least 100lbs..... With aluminum heads and intake as well I had to convert to closed cooling as I am in salt water so there is some weight added back in for the heat exchanger but it's minimal compare to even one cast iron riser..... I figure my 502 weighs 250 less than an original factory setup. My 26ZX sits very high in the back as a result and I am having an issue with getting the bow to come up and ounce on top of he water..... It rides kinda flat even trimmed up but it is very smooth and stable...... Build up a fairly mild 540 that runs good on 87 octane and makes over 600HP all day long without even berthing hard..... Use as much aluminum as You can on the engine and you can have big, reliable power with fret handling...... Go for it!

My 350 in a 206 formula has stainless marine exhaust and aluminum intake, 125 pounds lighter on the back. I took the 125 pounder platform off and it had trouble carrying the bow and would blow out at speed. Bigger diameter prop fixed it but is 1-2mph slower now.

My point is all boats react differently, but you may find you actually like a little more weight in the back.

Move the cooler to the front and leave the old lady at home, problem solved :boat:

I'd be all over the HP500...assuming you have a Bravo drive.

The aluminum manifolds are 80+lbs lighter than the cast iron stockers.
edit in: Oh, you asked and no one came out and said exactly, the HP500 stock came with Gill Aluminum exhaust manifolds and stainless risers.

Speaking of which, you'll need to move the exhaust holes in the transom.

Anyhow, a 24X7 (as others are saying) is begging for a big block. A HP500 (stock) will make a massive difference in your boat. 500cid vs 350cid....nothing to think about there.

Kind of the same line of thinking I was having for my 19 footer.

I currently have a mild built 355 sbc with CMIs that is maybe at most 325 horse.The only real money I have in it is the exhaust the crank is cast and the heads are just some opened up stocks with 202.

So last month when you were seeing running BB 420s for sale all over here for cheap it got my thinking . Why not sell my running sbc for 800 and try to get enough money out of my CMI to buy a nice set of BB stainless marines.
Than buy a used runnung 420 and just do a budget refresh on it and have an easy reliable 420 horse instead having to get into some expenses to build a winding stroker sbc that would need some real heads to achieve that power and would be at the limit of its potential where the 420 with some heads or a blower or both could be in the 500 to 600s.

The extra weight is nothing as I hold 55 gallons of fuel just leave out a few.

Very interesting.

If he has Bravo's already - will need to change the gear ratios and if he has alpha's then he needs bravos in which will add some weight back to the mix along with extra cost of all of that..