How Fast?
 

I have recently purchased a 1989 Scarab III 340 and was wondering what I should expect for top end speed. It is mostly a stock boat with few modifications if any. With half a tank of gas and three on board, the dual 454 magnums turn about 4300 RPM with a top speed of about 48 on the GPS. They run strong, do not burn any oil and I assume they are stock but recently freshened since the hour meter says 1000 hours. The only thing I have done is have the props lab finished and worked over at Houston Prop. My experience is limited with the boat but I was hoping I could get some feedback on what others were seeing with stock power.

Re: How Fast?
 

Gee, just a guess, but it seems you could turn those Mag's to about 5200rpm if you wanted to. Depends on what speed you want to cruise at I suppose.

Re: How Fast?
 

Thanks for the input. I do not know much about what to expect from the boat, which may seem obvious, and would really like to talk to an operator who has some history with this type and size of boat.

Once I get it to 5200 RPM what should I expect for top end speed? I was not sure how hard people were pushing these engines. What power do you set for cruise? What speed do you normally cruise? I just had the props lab finished but sounds as if I may have too much prop for the power at our altitude. I will talk with Houston Prop and see if they can adjust them and / or I will check to see if there is a pair in the classifieds.

Thanks for the information thus far.

Re: How Fast?
 

Scarab3MDC on the board would be a better one to ask.
Just defected from Cig'ville. Scarab3MDC has a similar model as yours that is pretty hot. Will have to see if we can flush him out. :eek: :drink:

Gotta believe you could get 60 mph or so out of that combo.

Re: How Fast?
 

A friend of mine has a 34 with 370s in it, turns 62mph at ~4800 rpm on lake ontario, about 250' above sea level. What altitude are you running yours at?

Re: How Fast?
 

I'm in Idaho at 4800 ft. Is there a rule of thumb for performance / horse power loss at altitude? I would like to talk modifications and performance strategies with those who know so I do not have to reinvent the wheel each time. Can you email direct to other members with a gold or platinum membership? What are the benefits to those levels of membership?

Thanks for your help.

Re: How Fast?
 

Thank Ernie, for the kind words...High desert...I answered your e-mail... call anytime... I'd keep those rpm's around 5k.. you should see low 60's....heres mine...

Re: How Fast?
 

High Desert, I have an '86 with 496's doing about 525hp each. I can get up around 70 in Long Island Sound. I usually cruise easy. Around 3000RPM's the boat hits a sweet spot and just crusies great at about 42mph. Then when I want to push it I crank 'em. I used to have 454's and was doing about 62 with 3 blade 23Pitch Props. I now have Hydromotive Quad IV's 4 blade 26" Pitch props that are made for a deep V hull like yours. The boat feels great with them on there. Gets out of the hole a little quicker too. I would say you could hit high 50's low 60's, depending on a bunch of other variables.

Re: How Fast?
 

I am looking for cruise and top end performance without trashing the engines. Since I am running a max of 4200 rpm @ w.o.t. I need to increase 800 RPM to get up around 5K. Can I and would I be better off to rework three blade props or go the four blades? It sounds like your happy with the four bladed props. What sold you on them?

What did you see going from three blades to four in mid / top end performance?

Re: How Fast?
 

quad 4's work the best on mine too..hi-desert..sorry I missed yuor call... try again tomorrow..Dave

Re: How Fast?
 

Congrats on the boat, you'll love it!! Are you running TRS' or Bravo's? That was about the time they were switching over to Bravo's, which is what are on mine. The 454 Magnums should top out at 5000 rpms.

Stock with 454 Magnums and Gil Offshore Exhaust, 3 blade Mirage props, I could get 63MPH with fumes in the tank, tail wind, running with the tide in a 2 foot chop. :) 60 was consistent and relatively easy. If you're running TRS drives, not sure what you can expect.

I completely agree with Gotime34, the boat's sweet spot/mid-range is about 42-44MPH at 3200-3300 rpms, where I cruise most often as well. The boat rides real nice in the rough stuff, guests don't get thrown around or think of those 5 scary words . . . . Oh My God, We're Going To Die!!!

I'm running a 4-blade 24p Bravo One prop now with a set of 502's.

Good luck with the boat.

Re: How Fast?
 

Thanks for the information. It sounds like I should switch to the quad 4's instead of trying to re-pitch my 3 blades. What is the best way to figure out the needed pitch? I have the Bravo drives and stock 454 magnums. After having the props tweaked at Houston Prop I am not sure how to compare them to stock and truthfully I am not sure what was done to them prior to my buying the boat.

I have the stock exhaust as well. Is there any secret to upgrades? I currently have the system that joins both sides of the engine into one 5 inch exit through the transom. With all the bends it looks very restrictive. What do you recommend for an upgrade and after looking at the costs of upgrades is it worth the $5K?

Thanks for the help.

Re: How Fast?
 

Test out different props, probably 22p and 24p 4-blades, and 23p 3-blade double cupped to start. You want to the engines to top out at 5000 rpms. Prop shops (i.e., Curtis Prop, Throttleup, Houston prop) might be able to do some math, best to work with them if you want to avoid the trial and error method.

I chose Gil Offshore Wet Exhaust and paid a bloody fortune for them, but that was almost 10 years ago. They still looked like day one inside when we bolted them to the 502's about 7 years later. Great quality & performance to go with a high price tag. They're not very internet savvy, dont respond to emails for tech support or help. Must call.

Up to you how much you want to spend, but there are some other good Gil type systems out there made by others for less (EMI, CMI, SS, etc.). If you plan to keep the boat a long time, get a new exhaust system like one of those.

Re: How Fast?
 

My 502's with the Gil's purchased back in 1996. Pulled them off the 454 Magnums when I upgraded the power package.

Re: How Fast?
 

Hello Neighbor I think, Are you on the Palmdale side
or the Victorville side of thr Hi-Desert???
I bought a place in Victorville area, A second home
and a fixerupper.
Perhaps we can plan a chat some time up there, I worked
at Team Scarab of and on for over 15 years.
I left them in 2000 and have been involved in other
brand Off-Shore race boats for the past years.
Mike J.

Re: How Fast?
 

I would love to set up a time to get together however.... I am in Boise, Idaho. High Desert is part of the brand of a company I own and the boat's name is High Desert Solutions. However, I frequent CA often and would love to meet others with knowledge of this type of boat regardless of make or model.

I am starving for information on this used boat I bought. Being in Idaho it has been difficult / imposable to get hooked up with a marina or knowledgeable local parts distributor. I am slowly learning, thanks to the help of many on this site, about the boat I purchased and any help is greatly appreciated.

I am also planning to attend some poker runs once the tow vehicle is completed. I bought a Freightliner, cut it in half, stretched it 13 feet and built a toterhome out of it. Once it is done the family and I will be able to get to some of these events. I just upgraded my membership so that should help with communicating feel free to email me directly.

Thanks

Re: How Fast?
 

I know the feeling, When I left Scarab I said I was
going to drive till no one could say the Name.
:) Mike J.