Why cant I bust 70mph?
 

OK. I have a 30ft (true :eek: ) Scarab 300. Granted its 1978... but its got two fresh 502s in it. I know its heavy... but:

I can get up to like 69.5 mph... when I run on EMPTY, with NOTHING On the boat... and I strip down to my underwear, toss the extra clothes overboard... and put my tail to the wind, on a perfect 1-2ft chop day and trim it alllllllll the way out, I ONCE got 72mph.

I read about 2002 models that are of equal length, attaining 72-75MPH with a SINGLE 502.

Granted, new hull designs and material make a difference.. but were talking TWO ENGINES here vs ONE.

What gives?!?!?!?

Shouldnt my 78 SCARAB with 502's have MORE than enuf power to bust 70MPH... on a regular basis.

Oh, and by the way... if you aint got nothin nice to say...

and OH YEA... dont be a smart ass.

* all speeds discussed are assumed GPS only, no speedo talk here.

[ 02-03-2002: Message edited by: NICKSLICK ]

How many of you can go past 70mph?

Have you ever taken it to a scale and had it weighed?

PS, 60degrees last weekend and the Busa felt awesome. That thing is even scarrier when youve been off it for awhile. Oh, nice plugs during the game tonight.

Well if you want to break that speed barrier then you will need new props. Plain and simple. :D :D

[ 02-03-2002: Message edited by: Audiofn ]

I've broke 70 a couple of times but not on a regular basis and not with the family aboard.
Oh and mine only has a 350mag in it :D

Those props are not bad!!!

Their mirages! Just had them cleaned, balanced and matched.

After the "incident..."

What props do I need?

How much would they cost?

Can I borrow some? :eek: :D

Boat ways 7800LBS (full tank)

:eek: :eek: :eek:

subtract 120GALS (what ever that ways), empty.

nick have your props labbed for a $100 each. Chad hill is runnging a special deal now.

are you tabs all the way up? maybe you are bringing your drives up to far. Mayeb when you got that 72 you were running with a real strong current and tailwind. Maybe try puting your tabs down a hair. Sometime it helps on my boat. Don't know why but it does.

Read up on hydrodynamics stud!!!!!!!!!!!

I think it is about 7 lbs a gallon. You have the same props that are on my boat. Frankly they suck to todays standards. You need more bow lift on that boat and then you can get more drive from the thing and float the bow some. A pair of props labbed will run ya around 1800+ :eek: :eek: :rolleyes: :rolleyes: :p :p You can find them used from time to time for around 400 each.

Jon

Hey Stinson... where ya been...

Can I borrow those five blade single piece herring props you showed me that day at the shop for a few weeks?

:eek: :eek: :mad: :D :D

I know the bottom has never been waxed.

How does one go about doing such a thing?

Don't ask it wasn't fun and I'm not in a good mood still about that f'ing trip....You can borrow the Herrings as long as you want just leave me a phat check for my account....And tip the boat over to wax the bottom, who know's it might go faster.....I have some killer snake oil down here too, bro

DUDE you are going to let him use the infamous snake oil!!!! What the ..... :rolleyes: :rolleyes:

Nick I think you need to get the boat to start with the key first :p :p :p

Nick, what are your RPMs?

Audio is right. You should try a pair of Cleaver props (pointy ear)and a pair of Chopper props (round ear). You have through the hull exhaust? If so you don't need the big fat hub like a mirage. You want over the hub exhast props.

How about nose cones. At that speed they might get you over the hump. I would think you should be able to tweek it up to 75mph. with a little more $$$$$$$$.

Dude... what trip are you talking about? I must be missing something...

-------

AUDIOFN writes:

"Nick I think you need to get the boat to start with the key first "

HAAAAAAAAAARRRRRRRRRRRRRSHHHHHHHHHHHHH
:mad: :mad:

--------

Im running approx 4700 even on both sides. I am running log exhaust (stock I think), and the exhaust definitly goes thru the hubs at the prop.

I just dont think I have the dough to go thru hull, or to buy new labbed props eithier.

****... it sounds like the bottom waxing and maybe some engine tuning seem the best bang for the buck...

Hey Audio... didnt you say you had some extra center riser exhaust???

Try slipping that thru the metal detector at the airport!!! hehehe... seriously... you have them right?

How much would you charge me to put em on????

IM SERIOUS...

What pitch props are you running now? good luck with the quest for 70 :cool:

What about the direction the props are spinning. I read a post about spinning in or out. one was faster than the other and it verried on the hull. I would look into that.

Try removing the flame arresters for one speed run and try synthetic oil in the motors and drives. You might just find that last 1-2mph.

Isn’t 4700 below the minimum WOT RPM for a 502? Drop pitch and get those babies turning faster. I’d also say that your exhaust is definitely being restricted going through he hubs but as you mentioned, that is going to cost some bucks to correct.

-Chris

Im running traditional 30 weight.

I notice that after a hard run, Im still dropping below 40psi, unless I bump them up to 1000rpms...

hmmmmmm...

No flame arrestors huh? Is it safe? Im looking for permanent solutions.

If it works then buy K+N air filters. Mobil one at walmart like 21 bucks for 6 quart jug.

25lbs. of oil pressure is more than adequate at idle. Also, I agree with the others. Get rid of the Log exhaust. Going to even stock merc stuff through hull could add 2+ mph. You also need to get your rpms up to about 5000. The through hull will help, and also labbing the props will get it there.

sell it and buy a cat :D

Like Ron said FIRST: What are your RPM's? If you are way low on R's you may need smaller props, if too high and hitting rev limiter then you may need bigger props. Buying labbed props until you find the right pitch and diameter is a waste of money.

Once pitch and diameter are found try using a CLEAVER and mayber 4 or 5 blade props as well. All contribute to over performance and handling. Remember that to gain in one area you may likely lose in another. For example, you may lose dock side handling capabilities. Start with your RPM's and go from there.

Shane

Nickslick this is sience that you are dealing with now. Seriously I am working on a place to stay out there for my next trip. Once I get all that figured out I will let you know when and then let me drive the boat and see what I can tell ya. We will get it out on a calm day or behind the break wall and see what we can do to get ya up were you want it to be. There may be some stuff we can do. First thing I would look at is get rid of the Log exhaust and go through hull. There were a couple of sets on EBAY that are worth a look at. I emailed you some info, and I know that there are lots of guys on the board that have them. I have one set I think that are good. I also have the remote Oil filter set up for the center riser. This you will love as it will get your filter up over the exhaust were it will be a piece of cake to get to. You can put that on your starboard motor so that you do not have to struggle to get the filter off any more. That has a Power steering and much larger oil cooler then you currently have. From there you can start to look at props if that does not help get the RPMS up. You should be looking for about another 200rpms out of that set up. However we have to make sure you are trimming it properly and all that good stuff.

Jon

P.S. we had it going 68mph that day you and I had it out on GPS and I know you were not trimmed out all the way and it felt to me that the boat had a little over 70 in it so ......

Jon

Nick,

Talk to my friend Steve. He has a Scarab 29 with small blocks running in the mid 80's. :D

Here is what his looks like. http://www.gcoffshore.com/gco_files/P29a.htm
I am sure he could point you in the right direction.

Dave

Steve those new engines look great in your boat :D :D WOW what a nice job you did. I am sure you are glad that they are in there :D :D

Nick,
Do not wax the bottom!!! Get some different props and think about getting new exhaust.I lose 200 rpms at top end when I have my silent choice closed.Time to spend more money!!

BOAT=break out another thousand!!

1.Exhaust
2.Props
3.Carbs
The worst prob with the older Scarabs (I had one) is the X dimention.
Wellcraft stuck those props/drives so deep down in the water that the drives create alot of drag. It's a big deal to raise so I suggest steps 1-3. ;)

You have to think up until the mid to late 80's if you had an 80 mile an hour boat you were very very fast. Its not until recently that boats started running the speeds we are now. I wouldnt think a '78 hull has the technology to run that fast. 70mph aint too shabby amungst the general population, you just happen to be surrounded by freaks of physics with some wild ass rides. :eek:

You need a CAT!

NO **** Tantrum! Your right!

Let me tell you, besides when Im running you with rich ass nut baskets... I pretty much dominate everything...

Still... I just cant stand it that my boat runs 69MPH. There is just something WRONG with that... ya know what I mean.

Its like owning a bike that only does 198 mph... (which btw, I do... :mad: :mad: )

Why the hell do manufacturers build **** that is JUST short of the mark! Arggggggh (banging head on wall)

:D

If it went 72 then your mark would be 75.

It is what it is. Be happy or be prepared to spend at least $1000 per mile per hour that you want to increase.

Hey nick, my dad had a 79 scarab 30 with 454's in it, I dont remember the speeds it did, but I thought it was fast back then, and never liked the slow cruiser scene after he sold it, I have pic's of it and I clearly can see how deep the drives are with his.With that said, I would have to side with DJD, with the x-dimention being about 12 inches below the bottom of the boat, where two inches would be a safe. But that's a big can o worms to change but food for thought. If the 70 barrier is your goal, picking up a set of newer risers and some rubber exhaust hoses, and tips and going thru hull, would probably be the best all around choice and most inexpensive, but have the advantage of a cool sounding boat too for the same price as props. I've done lots of prop testing and I dont think a cleaver would be a good choice due to lack of lifting the bow. A bravo one 4 blade would probably be the best bet, lots of bow lift with it and a big surface for getting up on plane, a hydromotive might work, but more stern lift than bow lift, and a small surfacre and not too great for getting a big heavy boat on plane, see if you can give some test runs with some oso members and try different prop combo's, take em out lobster hunting for thier troubles, Synthetics, would help too, but all depends what direction you want to go with this.

[ 02-04-2002: Message edited by: advantage_ROB ]

Your RPM's are too low. You should be at 5000. 300 RPM up top makes a big difference. Lab your props for $200 at Chad Hill and you will probably see a big difference. Don't you have TRS drives? I may be wrong but don't they eat some HP? Also check your carbs and make sure you are getting WOT. Remember this, once you break 70 you will want 75, then 80 then 85 etc, etc :p It is a vicious cycle.

Good luck

Nick,
I'm no expert here, but I'd suggest a prop change. NOt sure if you're using 4 blade/3, whatever or what pitch, didn't see it. But, I'd shy away from labbed props if I were you. Only reason is you do a lot of diving, right? Those labbed props can get sharp and hate to see you slice your leg or something. You don't have the greatest luck, you know. LOL!

If you're running 24's or something, lets say, try a set of 23 or 22's. (have no idea what you run, but just an example) Might get your RPMs ups and you can test if that is a problem. YOu can maybe borrow some just to test before spending a lot of money. Try to get your RPMS to 4950-5050 somewhere.

You can check that out, and I bet some headers or other exhaust upgrade would help you. But that is pricey.

Like I say, no expert, maybe I'm wrong, tell me if I am anyone....I could stand to learn more too. :)

Mark

[ 02-04-2002: Message edited by: 32fever ]

Have you ever calulated your prop slip or check the bottom for a hook?

HEY NICKSLICK

I ran your boat on my power vs. speed program with 8000 lbs and 380 prop HP. Are you using 25 Mirage props? With your weight and horsepower, that's the pitch I needed to get 67.9 @ 4700 RPM. I plugged in some upgrades to get some idea of what you could achieve. But before I tell you the results, we have to talk.

Why can't you just be happy with your current speed like the rest of us? Beware! This is what will happen to you if you are determined to break 70 mph.

First comes the better exhaust, which will give you about 69.4 @ 4800 RPM. Then working the prop to drop the pitch to 24, which will give you about 69.5 @ 5000 RPM. So close you can taste it. You have to have more! You will try every cheap trick in the book to push that boat over 70 mph. Finally, you realize that you must have more power!!

You will tear into the engines. You will get pissed off and put on a better set of heads to get 73 mph @ 5250 RPM. Broke through 70 big time, but are you happy? NO! By now you're hooked! A big hydraulic roller cam and you're up to 78 @ 5400. Then the blower, and you're up to 88 @ 6000 RPM.

It's no good. You can't stop yourself. You have to go faster! In a few years you will install a pair of 900SC and go 100 mph @ 6000 RPM but it won't be enough. You will have to put in a pair of Vortech supercharged Torque 1500 V-12s and go 128 mph @ 6000 RPM, after installing the 36" pitch five blades on your soon to be scrap VI drives.

STOP NOW WHILE YOU STILL CAN!! ;)