Top speed is low
 

Just purchased a 22' 1990 scarab with a 454 (supposed to be 400hp) and a Bravo One. Previous owner said that it ran 72 GPS with a 24pitch 4 blade so I went out and bought a brand new one.

Well took it out today and it only ran 58 (low fuel and only 2 people) on GPS. Also ran that at 4100 RPMS.

Timing is set to 8 degrees, new 750 marine carb, MSD distributor. Runs perfect, no pings misses etc.

Is there something else I should check? It seems even a stock 454 would push that to 65mph?

Any suggestions on what to check would be appreciated. Thanks

Sounds like your low on HP. Meaning, the 400 he told you was off by about 75 or so. How many hours are on the motors ?

That's a big difference, but try fresh fuel

If it helps I have a 97 22 with the 454 injected stock and I have the 24P 4 blade. It is new to me so I maybe low due to inexperience in many areas but for reference I got 58mph GPS with 4 adults, 4 kids (under 12) and 1/2 tank of fuel.

The 454 is a rebuild, with less than 50hrs on it. 750 holley marine carb and a brand new distributor. I mean it runs good, but just not getting the power I expected. And only 4100 rpms at WOT. Is that what you were running pluguglyinhere? Do you know what your timing is set at?

I do run higher octane fuel (always fuel up on land) and always add an additive (octane boost, etc).

Never pings or runs rough. I was just wondering about what kind of power it would need to be up around 65mph. I mean I thought stock 454's in those boats ran around that...

new dist?
timing is probably off, you need to check total timing, most 454s like something like 36deg by 3000rpm

what are you trimming your outdrive to and does the boat have trim tabs

Ive only been able to time it at about 700 rpms, and it's set at 8 degrees. Not sure how to time it that high with just a timing light and the marks on the tab over the damper.

Trim gauge doesnt work but I trim it to the point where the outdrive comes out of the water, then bring it back. I do have trim tabs, boat seems to chime walk just a bit with the 4 blade...but at 58mph it doesnt feel out-of-control.

you need to check it at higher rpm to make sure dist is advancing correctly or you will be down on power.

here is a post on procedure:
http://www.offshoreonly.com/forums/d...procedure.html

Ok thanks. Any suggestions on a timing light for advance? It has no vacuum advance. I've attached a pic!

http://www.firstlooksagency.com/images/scarab.jpg

Your boat will run faster with a 3 blade prop. Also, to post good top speed numbers you need to get the 22s up on the pad and keep them balanced there.

I think I have it trimmed all the way. Has a little chime walk and was adjusting the trim tabs to bring it down.

Previous owner said 4 blade 24 was the prop for the boat. Of course that prop didnt come with it. Tried a 25p 3 blade and it cavitated. Gonna check timing, put a couple of marks and see what runs best?

No prop does everything the best, but without question, the RIGHT 3 blade will be faster on your boat than any 4 blade. What 3 blade did you try? Mirage, Mirage plus, Laser, generic? When did the prop cavitate, and how badly? A little cavitation out of the hole can be expected as well as medium to low cruising speeds during tight turns. If you are getting more than that it may be affected by improper trim settings on possibly both/and/or the tabs.

I have a 1995 scarab 22 with about 600 hp, i do a little over 80 mph gps with a labbed 30 pitch , also have a -1 inch imco on it .

On the other end of the HP spectrum, I have the same boat (90 Scarab 21) with a bone stock 350 Mag. I spin a 21' three blade Mirage at 4700 RPM, 53 mph on GPS.

Sounds to me like you've got too much prop on it. Try a Mirage plus 23 / 25, I've heard they run really well with these hulls.

BTW, love the paint job, looks really good.

-Rob

The couple of things I'm going to try are:

Get an advance timing light and set it to 10 degrees / 34 and
I guess I'm going to try a 23p Mirage plus. Sucks cause i went by what the previous owner told me. He said a 24 4 blade was the prop for the boat. So I went out and bought a new one. But I guess that's why you shouldn't trust anyone...

with a four blade prop the boat will come out of the hole better, and the ride is better , you might get a little more top end with a 3 blade but it will blow out in turns , A 24 IS REALLY A GOOD PITCH FOR IT

Since I'm only turning 4100 rpms at WOT don't you think I should try the 23P Mirage Plus? Going to adjust timing also but I don't think that alone is going to give me another 500+rpms...

I think the rev limiter on a standard stock 330 hp 454 more is set at 4350 , a mag is 4850 , hp 500 5350 . when i had a stock 330 hp , i think did 62 with a 23 mirage plus , rember the blades have to be round ear props to get the bow up ,

i have had both the mirage , mirage + and the laser 2 prop on my prochaged 350 22 and the laser was the fastest hands down as it has more bow lift as it has more rake than the mirage. the mirage did plane off better than the laser though. hope this helps

I have been wondering the same thing..I have a Scarab 22 with 350 mag..Horse power is 400. I am running a Quicksilver 24 p and the most I can get is between 55 to 60 at 4500rpm's

Yea after pestering the old owner (he said it ran 72 on gps with the 24p) I found that it is a stock 454, not the mag. So I guess around 330hp? The boat is def maxed out if that's the case. I think these things are pretty heavy so getting 60mph is about it...

I just picked up a 96 22' with a injected 502. I'm pushing 60 at 4000 rpm with a 24p prop. I run it in Havasu where control is key. Any suggestions on props?

Youravspecialist-definitely sounds like you are overproped. That 502 should be making at least 400hp. I would try a 23P Mirage Plus.

Interesting... I have heard both ways. Try a 23 and a 26p 4 blade. Guess I'll give both a try and see what works better

I wouldnt go any higher. If your only at 4000rpm WOT than it's not making the power it should:

502 MAG MPI Specifications

Propshaft Horsepower: 415 (309 kw)
Displacement (Liter/CID): 8.2/502
Cylinders: V-8
Bore (in/mm): 4.47/114
Stroke (in/mm): 4.00/102
Compression Ratio: 8.75:1
Fuel Requirements: 87 Posted Octane (R+M)/2
Full Throttle RPM Range: 4600-5000

Lower your pitch and get more R's

Well I am going to try a Mirage 21..The problem I have is WOT is 4300 rpm's at 55 mph.. So I think I am a little over propped.

So did you figure anything out? Just wondering because I seem to run 5000 rpm, WOT with my 4 blade 24P which seems not right since the rev limiter should come on. My motor specs say 4800 WOT so I am thinking about going to a 26P so i dont hurt the motor. I dont know because this 24P seems to work nice.

My 90 scarab has stock 454 330 w/nose cone 23 quicksilver prop 4850 rpm perfect chop 63mph. no tabs. here's a video of it running, kinda hard to max out speed while taking video and driving at same time. http://www.youtube.com/watch?feature...&v=xI_BiZgWrdk

Ya it seems most run either a 3 blade 23 or a 4 blade 24. It is so confusing for a first timer. I think my rpm are high, I hit 5000 or a little over like 5200 at wot. It could be off as I have read, and I also would think the rev limiter would shut it down.

I think the rev limiter hit once on me. The last ride of the season I was at wot trying to get some good rpm and gps reads to figure it our over the winter. In a big wide turn wot it shut down and kicked back in when it slowed down.

I would think to bring down the RPM I would have to go up like 26, the 23 wold raise it right?

Found out at the end of the season that a Mirage 23+ was working the best for me. Right around 62mph at 4600rpms. I'm thinking of adding "something" next year to get that up a little. Maybe some IMCO manifolds, or a nose cone or ??? Anybody else find a performance gain without the big $$$?

so am I correct that if my tach is right lowering my pitch from 24 to 23 would raise my RPM?

What is a nose cone and what does it do?

[QUOTE=pluguglyinhere;3555653]so am I correct that if my tach is right lowering my pitch from 24 to 23 would raise my RPM?

We have a winner !!!!!!!!!!!!!!

i ran 63mph on gps with mine (454stock) full tank 3adult 23p 3blade..hit the cut off too