Upgrades to stock 350 sbc
 

So I'm thinking about an upgrade, something simple to give my boat a little more for cruising around. Its a 1981 24 Pantera with a stock Mercruiser reman 350/260 hp built from a short block (aprox 50 hrs on it) with the upgrades of an Edelbrock Performer EPS manifold (#2701) with an Edelbrock 600cfm marine carb.Running an alpha drive. Current exhaust is 1981 era Mercruiser "log" manifolds with through transom exhaust dumping out right at the waterline half in half out of water with hardin marine mufflers and rubber flappers. So yes I need to upgrade the manifolds but want to keep the thru hull just as it is and where it is for that old school look just like the rest of the boat. Boat currently runs 50-52 mph WOT depending on water conditions with a light load spinning a mirage 23 pitch at about 4000-4100 rpm. She will not pull any more rpm's with that prop.I'm thinking of adding the following:

ProMaxx Performance Heads, SBC 185cc 2.02/1.60/72cc Straight Plug, Assembled w/ spring upgrade. Part#2171 7 (http://www.promaxxperformance.com/in...hevy-1862.html)
Comp Cams XM270HR Xtreme Marine Retro-Fit Hydraulic Roller camshaft
Full roller valvetrain, Comp Cams Pro Magnum Roller rockers 1.52 ratio, Comp Cams Hydraulic Lifters, Comp Cams Magnum pushrods
Edelbrock Performer RPM Air Gap intake
Holley Marine 750 carb

I want to be able to run 87 octane so not sure if I should get the 72cc chamber heads or if I can get away with the smaller 64cc chamber heads? I can also get a pair of brand new Dart Pro 1 heads new in the box from a friend of mine, unassembled for $800, they are 180cc intake runner with 72cc combustion chambers, with Straight Plug. And he also has brand new Dart Pro 1 heads with 200cc intake runner with 64cc combustion chambers, with Straight Plug, same price. Anyone think I should pop for either of those instead of the Promaxx heads? The Promaxx heads are $1100 assembled for the pair with the roller spring upgrade.

Looking for opinions on this setup.

There was a thread a few weeks ago that answers your ? I believe. I would go with the darts if it were me and stick with the 72cc. The 200 head mite give a little more top end but give it up on bottom end. 64cc with the dish pistons( I assume you probably have) would give about 9.2 or so I think. I would say that's pushing it with cheap 87 gas. 180 with 72cc would be good with the parts u have listed at least I think so.

I am looking for a stock 4bbl and intake for a SBC Mercruiser,,,,

Darn I just sold the q jet off my 260 merc. I still got the heads and intake tho. U can get a aluminum intake that has the q jet bolt pattern for about $120 new.

Boat is all covered up right now for the winter, (expecting a little snow tomorrow) i'll have to get into it and get some numbers off the heads, I should be able to run them to tell me what size chamber they have.

Oh and the motor was built from a long block, the Quicksilver Repower tag (forgot I took a picture of it) on the motor reads as follows:
Part No - 87971R5
Bore O.S. - 040
Main Brgs - 010
Thrust Width - STD
Rod Brgs - 010

So you actually have a 358? CI SBC I believe, that's what the .040 over bore is. I have a thread about re powering a 260hp 350. I picked up a 97 Vortec truck block and heads.....cheap. And I also picked up another set of Vortec heads. I plan on installing a 650 ish carb, a RPM intake and a cam. My machinist did a .030 over bore and I will be installing new pistons, possibly flat tops. This new combo should push my 21 footer along quite well.

Correct 358ci. .010 ground crank and rod journals. Right off the bat, you are not revving your current setup to peak power potential. Stock 260's like 4400-4500rpms. You might be pleasantly surprised just propping the boat correctly.

Your future setup looks good except for the Promaxx heads. I would go with a more reputable Dart, AFR setup in the 180cc range. Do not skimp on the heads. Go with a 64 cc chamber if you are keeping the stock 260 4 valve relief dished piston. This should land you in the low 9-1 region and run easily on 87-89 pump gas with an aluminum head. Check your block deck height and adjust your headgasket thickness accordingly to achieve .039-.042 quench. There are many benefits in maximizing this part of an engine build. More power, reduced detonation, etc..
The XM270 will be a big step above the stock cam and with a good induction and exhaust should pull to 5200 Rpms. You will need to upgrade to a better flowing exhaust setup to take advantage of the new build.

The stock 260 shortblocks are pretty durable at this power level. My stocker went 1100 hrs and the reman Jasper .060 over 360 ci 2 bolt main ran for 369 hrs at 5400rpms before I pulled it for another engine. I still have it in the shop as a spare shortblock.

in my old Chris Craft 245 Limited, had stock 5.7 260hp, went 41 mph....

I went with stock roller shortblock still 350CI, ZZ4 crate engine cam, Edelbrock performer aluminum heads, with Wiend stealth intake and holley 650, no idea power but boat gained 12 mph and ran 53 after I was done, that combo worked great!!

RyanOOTJ - provided spot on info. My answer is the exact same as is.

Pssst: I can't believe the 24 Pantera didn't have planing issues with that prop.

I have the stock Q jet off my old engine. I also have a cast iron intake too.

Here's the link to my thread....

http://www.offshoreonly.com/forums/r...0hp-350-a.html