Looking for some more speed.

[02RedWS6TA]

Hi,

New to Donzi's here and picked up a Classic 18 a month or so ago and have been reading the forums ever since. Finally signed up yesterday and thought I'd ask about my plan. Currently the boat supposedly has a new merc 260 in it with a quicksilver 21p prop. It's running 58 at 4200rpm's full of fuel and two people/gear. I'd like to see 65+... (It actually only went 57 with a half tank with the quicksilver, 58 full with a generic aluminum 3 blade 21p prop) It's an Alpha 1 1.5 gear ratio.

Plan will have to be done in stages but any advice is helpful as I'm new to these. Looking to stay under 1500 in parts other than the prop itself.

Step 1: Turbo TXP or FXP prop in 23p
Step 2: Edelbrock 600CFM Marine carb
Step 3: Vortec heads, performer intake, and an undecided cam choice.

http://www.lstwo.com/images/75841468739080594054.jpg

[biggiefl]

You are going in the wrong direction. 1) your redline is closer to 5k so try a 19 SS prop or see why you are only running 4200(timing, carb setup, etc.) Second a carb is not going to add speed. You match a carb to what the engine requires. 3) This is not a car. You can't just drop automotive parts on it and think it will gain hp or anything else. Marine is a whole different ballgame and the wrong selection of add-ons will only gain you a shattered engine or worse.

[02RedWS6TA]

You are going in the wrong direction. 1) your redline is closer to 5k so try a 19 SS prop or see why you are only running 4200(timing, carb setup, etc.) Second a carb is not going to add speed. You match a carb to what the engine requires. 3) This is not a car. You can't just drop automotive parts on it and think it will gain hp or anything else. Marine is a whole different ballgame and the wrong selection of add-ons will only gain you a shattered engine or worse.

Judging by what I've seen on here the tach is reading low vs speed with the 260 hp motor? I've tried to read as many threads as I could with people running the same set up. It's tough finding a ton of info based on just the 18 with different search terms.

The carb set up is why I went with a different carb, it's the original carb and has a pretty good lag if you hit it hard from mid range (3,000) and gearing up for the Vortec build. I wasn't necessarily adding speed at that step more of a step towards the finished product. Rather than rebuild it and start over with something I'd replace after going to the Vortec/cam set up I figured get it out of the way. It's just a smaller initial investment and the motor doesn't have to come out. Waiting for winter to do heads/cam. A 600cfm Edelbrock should work good with the stock 350 and a Vortec 350 no?

Thank you for the response/help.

[gcarter]

I suspect you'll need 325-350 HP to hit your target.

[duckhunter]

The Vortec heads are the best small block bang-for-the-buck going. Edelbrock or Holley 600 should be more than adequate for a 300-325hp build that lives under 5k rpm.

You definitely want to get your rpm up into the powerband. I have been working on the same thing, swapping props is an expensive hobby... I doubt a SBC with 1.5 gears is going to pull the 23P TXP - that is a lot of prop. I'd get the motor where you want it and then start the prop testing. $1500 is maybe reasonable for the heads, intake, carb, etc, but it will be close... You may want to shop for some "lightly used" stuff to stay within budget. Jegs, Summit Racing, and Pace Performance have upgraded Vortec heads with screw-in studs and beehive springs that will let you run a bigger cam. Stock exhaust? If so the GLM aluminum manifolds will save you 80# and flow a little better than stock. That's another $750 or so... The misc hardware really adds up, stuff like tune-up parts, good gaskets, throttle linkage, bling, etc. I cleaned up a bunch of my stock parts and broke out the spray paint to save some money here.

You'll need to watch hatch clearance with a taller intake and it may limit your flame arrestor choices. Lots of options if you search for other 18 builds.

A good way to do a sanity check on your tach is with a digital timing light with tachometer. Connect it to any plug wire while running and you or a buddy can compare it to the dash tach while running.

[biggiefl]

Not sure but my bud had some new or as-new vortec heads(triple hump) and alum intakes with brass inlays. I used a set of these heads in my vette and they are awesome.

[02RedWS6TA]

Not sure but my bud had some new or as-new vortec heads(triple hump) and alum intakes with brass inlays. I used a set of these heads in my vette and they are awesome.

That he'd like to sell? PM me if you want I could be interested.

[Kirbyvv]

I recommend confirming your RPM's first. My 260 hp SBC turns 5000 rpm, but doesn't quite hit 60 mph. but I'm dragging an older volvo. Check the tach, then work from there.

[MOP]

You say you have a new 260 it should already have vortech heads, count the hold down bolts are they straight down or angled? A fairly simple way to get decent bang is cam and intake, pretty easy to get 350 out of a 350. You can swap in a cam easily by putting a small port into the back seat.

[02RedWS6TA]

You say you have a new 260 it should already have vortech heads, count the hold down bolts are they straight down or angled? A fairly simple way to get decent bang is cam and intake, pretty easy to get 350 out of a 350. You can swap in a cam easily by putting a small port into the back seat.

Ok, I'll check it out. The owner really didn't know much and the receipt wasn't really descriptive. He said they put a new short block in it... The inside of the heads looked new so they were either new or remand. The receipt for the engine was $3,500 for parts and $500 for labor so it could be anything from a new engine, fake work, to...

Thanks for the help.

[Ghost]

If you decide to buy a carb, I have a 600 cfm 4 barrel Holley 4160 for sale. It's basically new (less than one minute running time, then drained and on shelf). Way less than new.

[tiupc]

If you decide to buy a carb, I have a 600 cfm 4 barrel Holley 4160 for sale. It's basically new (less than one minute running time, then drained and on shelf). Way less than new.

I would be interested in the carb Pleases PM me.

Trevor

[biggiefl]

The way to tell a vortec is if the bolts holding the valve covers on are on top or on the bottom lip. Also the intake will only have I think 4 bolts instead of 8.

[smokediver]

There are center bolt valve covers on non vortec heads also. The vortec intake manifold will have 4 bolts on each side running in a straight line.

[biggiefl]

I thought all vortecs were center bolt starting with the later 86 Vettes. Anyways if you don't have center bolts, she is not vortec.

[duckhunter]

All Vortec heads are center bolt, but not all center bolt heads are Vortecs. A lot of the late 80s to mid 90s SBCs (TPI motors in particular in Vettes and Camaros/Firebirds) had non-Vortec center bolt heads. But absolutely, no center bolt valve covers is a good indicator.

Mercruiser started using the Vortec heads in '97; this was a transition year so both styles were available.

As already mentioned, the intake is the best way to tell. Here's a picture of the vortec intake - two bolts per corner straight into the head (8 total). Old style had 12 bolts installed at an angle into the heads.

Good deal that you've got a fresh short block to build!

76716

[02RedWS6TA]

Bad news, parameter valve covers. Good news Thunderbolt IV ignition already on it.

I couldn't even read what the carb was, it either needs to go or be rebuilt.

[duckhunter]

My inclination would be to pick up the Holley from Ghost vs. messing with rebuilding and recalibrating the old one.

On the heads, if you want an improvement you would have a tough time matching box stock new vortecs with any kind of work on your current heads and cost would end up pretty close. Call that a vote for the upgraded Vortecs from Jegs or Pace (with the screw-in studs)...

Lots of great intakes out there, Edelbrock RPM at around $200 and store brands (Jegs, Summit) around 20% less. Stinking gaskets are $30, and you gotta spend the money for good gaskets since the bolts are all at the corners of the manifold. You can cobble up your current linkage to the Holley no problem, lots of pictures floating around for ideas. CP Performance has some decent deals on flame arrestors; I would wait on that until you know how much real estate you'll end up with under the hatch.

TB IV is good to go. No more than 30deg total timing with the Vortecs.

Comp and others have marine-specific cams for small blocks. Watch your valve lift (keep it <.460 if running stock springs). I'll let someone else chime in on advice on the cam.

I've just mentally masturbated your entire budget.... Have some fun with your project. :)

[02RedWS6TA]

Are there any spacers that will allow the Edelbrock carb to bolt on my spreadbore intake and clear the hood? I'm guessing no since there is little clearance as is.

Thanks