Is it worth it to upgrade intake manifold and carb?
 

I have a Scarab 29 with twin SBC 350. I was wondering if it is worth upgrading to better intake manifold and a Holley, Quickfuel, or Eldelbrock 4 barrel carb?

What are you looking for? If its speed the likely answer will be no. An intake and carb can't give you enough to make a worthy difference on a stock engine.

What is on it now, Q-Jets? For all the bad mouthing that some like to do with Q-jets, they are a decent carb when set up properly on a stock engine. IMO, the only thing you will see by switching to the Holley is more fuel consumption, and probably more dicking around with it. Unless you plan to also upgrade exhaust, cam, heads, etc., keep the whole thing stock and enjoy running on the water with your hatch down instead of wrenching on it in the driveway.

+1 on the stock quadrajet. Great carbs.

I don't totally agree with these guy's as far as the intake is concerned.

However, you may already have the good Highrise cast iron intakes on those motors already as many twin engine 350cid powered boats have them. If that's the case, other aftmkt intakes won't gain you anything.

Get a casting # for me or pics of your engines and I'll let you know.

I've seen modest gains on 7.4L's going from the flat, cast-iron truck intakes to an RPM Air-Gap and 4150 Holley. I would assume similar, modest gains would be seen with the small block. Key word here is modest.

Just realized the later 350 mags, could have came with a 2 barrel ''merccarb" or a 4 barrel weber. The older 260's could have the quadrajet.


SB is right, get some pics or better description of what you have there.

I will take pictures this evening and load them. The intake on it now is flat for sure and I am pretty sure its quadrajets but I will also take some pictures of the carbs to.

Yep, that cast iron high rise was essentially the same thing as the "472" intake used on the DZ302's and LT-1's by Chevy back in the day. They are pretty good, and having the cast iron is probably better in a marine application than aluminum.

I went from the "flat" standard intakes on my Chris Craft 260 to the "Z-28" iron high rises. WHAT a difference. I then added the magnum flame arresters which were 2x-3x taller. This actually slowed me down until I called the Carburetor Shope in Ontario California.
They sold me the correct jets and metering rods for my Quadrajet. This is an awesome upgrade. I gained 400 r.p.m.s and much better acceleration. There are probably better intakes now but I was "raw water" cooled at the time and needed to stay with iron.
At the time (late 80s) the iron intakes were about $130 each. The metering rods and jets were about $75 but I could have saved if I went with the Carb Shop's recommendation instead of buying jets larger and smaller. I ended up going one size up on the
primary side for a gain of 50 r.p.m.s. The gain didn't even show up on the boat's tachs but it did on the digital tach we used for tuning.
Good luck!

When using those Cast Iron Bowtie Intakes (awesome btw - as good as Eddy Performer RPM intakes) on stock Merc 350 Mag engines I used DA secondary rods. Cheap, and good tune. Nothing different on primaries.

SB, wish I could remember the exact metering rods... seemed to me there was a "C" somewhere in the sizing. It was the same secondary metering rods from the 350 Magnum which was rated at 270 h.p.
If I remember correctly the Magnum came with the high rise intake, taller flame arrestor and 4" risers instead of the 3" risers from the Merc 260. Those were 10 of the STRONGEST horsepower in
upgrade history! I'm guessing it was at least 30 h.p. stronger. Either the 270 was underrated or the 260 was overrated. Another inexpensive upgrade (if the engine is out) was adding a windage tray in the
oil pan. I don't remember the exact price but I think it was under $50 including the new maincap bolts (4) and the tray fasteners.

if you were to go to performer RPM air gaps, you might see 2 mph increase...hope that answers your question

Wes, maybe CY rods ? In the following chart they look identical to DA's ?
http://www.thirdgen.org/rods

I installed many of these intakes to small lightweight single outdrive Alpha outdrive'd boats.
I would also use Felpro #1204 intake gaskets that blocked off the heat riser / exhaust crossover passages. If carb had typical choke (ie:not electric) I would remove choke plate from carb. If person just had to have choke, I'd drill 1/2" hole in block off plate on the side of the heated choke mechanism. Around here in the summer, you do not need a choke. Merc no longer sells the required longer choke rod for use of these intakes. GM no longer sells these intakes anyway. Bummer ! Probably sold 50+ of them.

Anyway, performance from these small boats would indicate near 15hp and with Felpro#1204 gasket around 18-20hp.

Great mod for small lighterweight boats that respond to most everything.

And the nicest thing about changing secondary jetting in Q-jets is it is literally a 5 minute operation, if that. Single screw to undo the metering rod hanger, pull them out, and change them. Done. You can literally do while the engine is running.

SB, I am remembering using "CP" metering rods in the secondaries when I switched to the Hi rise iron intake manifolds on my CC Stinger. Once I got the taller flame arrestors and the jetting correct I felt it was the best bang for the buck I did on that boat. I went on to try different heads, cams, and roller rockers.
Bottom line for my Stinger was stock it would turn (1:50 Alpha drives) 21" 3 blade clevers to 4200 r.p.m.s. I could then trim it out to reach 4600 r.p.m.s. With the hi rise setup it would hit 4600 r.p.m.s with the drives tucked all the way in. It would trim out to 5,000.

I didn't block the heat risers as I boated year-around in the Pacific Northwest. I had a full top and a Red Dot heater (after I went to fresh water cooling). We even took the Stinger out when it was snowing!

Wish it was as easy to make "mini mods" on the 6.2 MPI s! I'll probably just settle for blueprinting the props! BTW I enjoy your posts.

I would go along with this and add a set of holleys or Barry grants on top. Yrs ago I read an article where they took a stock motor and swapped the intake and carb and gained 22 hp. But I don't know if it would gain u much in speed. I had a 88 260 that I swapped out the junk iron intake and q-jet for a air gap and holley and gained 5 mph on the junk stock speedo!!

Might be, however leaner than what I ended up with. Again, many of the high rise cast iron bowtie intakes I used on stock 260hp motors - and modded of course - had Felpro 1204 intake gaskets, closing off exhaust passage that heated the intakes, choke removed, and many also got a lifter valley tray that kept the hot oil off the intake. So...can't answer for your deal...just mine.

Here's a Merc tidbit i found:

http://www.boatfix.com/merc/bullet/93/93_15.pdf