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

That prop was on it when I bought the boat this summer. She gets on plane with ease, even with a full tank and 4 persons aboard, and I never use the tabs.

You guys really think I can get away with the 64 cc chamber heads and still run 87 octane? I will be using the stock bottom end and I have not opened it up yet to see whats in there so I have no idea what pistons are in there. I know they say you can run higher comp and avoid detonation with the aluminum heads but I don't want to have to worry. Most marinas on my lake are 87.

With aluminum heads, dialed in quench, CORRECT carb jetting, proper heat range plug, timing, proper oil and water temps, it is no problem. My last alum head 383 was 10.18-1 static and ran all day on 87.

I run 87. Stock 91 5.7 shortblock..no machine work....Brodix 64cc heads, 218/224 .570" HR. I can tune pretty good...I think anyway. LOL.

I'm pretty hard on the throttle.

If the OP runs iron heads and over 10-1 ish compression 87 octane may be an issue. If he runs aluminum there won't be an issue.

I consider myself lucky because we have 91 octane ethanol free available at the pumps.

Jealous. LOL.

http://25.media.tumblr.com/tumblr_m8...hg9bo1_500.gif

If it was in a car I would say sure but in a boat that gets run hard it would scare me but it seems people are doing it and not having problems. I have 11 to 1 and run 93 in mine and have no problems....YET!!!

^^^lmao!!!^^^

alum heads and alum center dump GLM exhausts. they are good for about 350 to 375 hp. enough for all but the really exotic small blocks. also taking 150 lbs outta the back of the boat. then you can carry 1 more size 7 girl, or skank as they seem to be called on this forum...

This might sound like a wierd question but anyone see any possible problems losing too much weight off the back of the boat by going with Aluminum intake, aluminum heads, and aluminum manifolds (GLM's) or headers?

Not usually. If I could lose more weight off the back of mine I'd be psyched. In reality my gas tank needs to be a little more forward.

My Eddie Exhaust was 88lbs lighter than the factory system it replaced. That, of course, was a much bigger weight reduction than the aluminum heads, which i did too.

Placing my batteries a few feet forward of where they where helped tremendously. Again, my little boat doesn't like weight in the rear at all...and yet again, I believe the tank should have been moved more forward. Oh well.

Edit in: My boat will lose 2-3mph (min) for having a passenger.

my buddy used aluminum heads and exhaust in his 28 Cigarette SS, fukked the boat all up, so depends on the boat and how much weight...

Because of the weight balance? I quess where you lighten them up makes a difference. Wellcraft once told me that for every 100 pounds I could remove from the cockpit forward (particularly the forward cabin) would equal roughly 1 mph in top speed. They never mentioned the bulkhead back.

http://www.hotrod.com/how-to/engine/...l-block-chevy/



Mild-412HP 383
This is a simple and relatively inexpensive combination of a one-piece roller cam block with a stroker crank, 9:1 compression with dished pistons, a tame GM Performance Parts hot hydraulic roller cam, 1.6:1 roller rockers, factory roller lifters, a set of modified Vortec iron heads, an Edelbrock Performer RPM Air-Gap intake, a 750-cfm mechanical-secondary carburetor, and a set of 13/4-inch headers. The only upgrade necessary is some machine work and better valvesprings for the Vortec heads to accommodate the additional valve lift. This combo makes excellent torque with 466 lb-ft at 3,500 and 415 at 5,500 rpm. Even with a stock converter, this is a tire shredder.


DESCRIPTION PN SOURCE PRICE
Block, one-piece seal used junkyard ${{{100}}}.00
Scat crank, cast, one-piece seal 910526 {{{Summit}}} Racing 169.95
Stock 5.7-inch rod rebuilt Machine shop 150.00
Piston, Speed-Pro hypereutectic HC860-03 Summit Racing 36.69 each
GMPP Vortec iron head 12558060 Scoggin-Dickey 551.50
GMPP Hot hydraulic roller cam 24502586 Scoggin-Dickey 192.95
GMPP valvespring kit 12495494 Scoggin-Dickey 32.95
Edelbrock RPM Air-Gap 7501 Summit Racing 212.95
Holley 750 mechanical secondary 0-4779C Summit Racing 433.95
Hedman 13/4-inch headers application specific Summit Racing 193.95


Read more: http://www.hotrod.com/how-to/engine/...#ixzz3JSwRKDg3
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Stoker's are very cost effective and look at the torque curve's

all 24-7 boats look like they are gonna sink stern first when anchored or tied to the dock.

Mine sits pretty flat, guess its due to the light weight of the sbc/alpha drive combo!

http://djmikeyc.com/media/1981Panter...llage_dock.jpg

that is one nice looking boat.

Thank you!!!

I concur, sweet ride!!

Thanks!!!

Agree, looks good...what's the sheriff boat behind there doing? Taking a pic so he can look you up later when you show him your wake?
I have the earlier non vortec TBI heads and dish pistons that are more prone to detonation. My 64cc heads are supposed to yield 9.3 to 1 CR. Never saw any detonation with the factory cam at 34* total on a 23 pitch prop and 4400 RPM.
I did a 262H this past spring, because it's the most they recommend with regular exhaust. Also did Comp springs, lifters,keepers etc, with a set of no name aluminum full roller rockers (Pro Comp). I started off with a conservative setup, then kept on using the boat and never got to really maximizing the timing. I ran it all summer at 28* all in. It was really good on fuel and had some snappy mid punch, but same 59 mph top speed at higher rpms with a 21 pitch prop. I didn't have the water conditions to trim it out and try to find every mph. Our lake has speed limit so I have to pick my spots. I finally set the timing ahead when I winterized it.
But fuel. Vortecs are more detonation resistant and lake water is nice and cool, run a 140* thermostat and you won't have any trouble at 9:1. Dynamic compression will be way lower. Vortec heads are supposed to need less timing too, maybe start out with 30 degrees all-in.
Regarding fitting the rockers in the factory valve covers; mine hit some of the internal valve cover structure. I just removed the pieces that were touching rockers. Now the insides of the VCs look like aftermarket ones do.
I'm thinking I should degree the cam in the spring and might retard it for top end if there's some room.
Some of the hot rod guys seem to believe Comp tends to grind advance into their cams. So I am going to check.
Your project looks good, I will be following your thread!

I think I see a cooler on there. Scuba sheriffs goin diving. Muff diving. Lol

Just a comment for the OP.. it seems like you have received a lot of good info here. I've been doing a bunch of research on cams as well and from what you've described I think the 270 may be a little much for your setup.