BlueAndWhite

HI all,
just got me an old 1988 scarab excel 28 and pretty much everytime i would google for some info i would find links to offshoreonly.com. So here i am hoping to get some tips and advice.
I have a basic non mag carburated 454 thats been rebuilt with stock crank and rods with some domed top pistons 100hrs ago (not forged...). Engine has a edelbrock performer rpm intake and i added some used imco powerflow manifolds.
Has a bravo 1 sterndrive. I got a few props thats i tried out.
23p 3blade mirage plus 4800rpm 57mph
24p 4 blade (not sure about brand) 4450rpm 57.5mph
25p 3 blade (nto sure about brand) 4100rpm 52mph

Obviously the 3 blade 23p prop has the best holeshot but im not sure if this engine should be turning at 4800 rpm.
I was hopping to hit the 60mph but i understand 3mph is allot of $$$$. I was looking at updating or upgrading the ignition setup, is it worth it? maybe it would give my 454 a little nudge with the intake and exhaust manifolds.
Any tips or advice are welcomed.

AllDodge

iTrader: (1)

Assuming your speed is GPS and not the boat speedometer, and the tachometer is accurate

Your WOT rpm is 4800 and you should keep it there as much as possible. Increasing pitch which drops rpm below the 4800 is harder on the motor. The more blades in the water equals more drag, but also can increase efficiency due to less slip.

The slip with the 3-blade is 18% at WOT. If you can decrease slip by 3% bringing it down to 15%, while keeping same rpm, your speed will increase to 59 mph.

Everything has a trade off, decrease slip places more load on the motor so this normally drops rpms.

Rule of thumb going from 3 to 4 blades is drop 2 inches of pitch, might try a 4-blade 21P. Don't think i will do that much better, you need more HP

Being a 1988 have you weighted the hull to see if its heavier then it should be? May have soaked up some water over the years

Tinkerer

Like he said 4800 RPM is perfect for that engine.
Sounds to me like the 23 pitch is perfect also.
Word of advise...
DONT put any more money into that 454.
Find yourself a good 502 MAG carbed engine and sell the 454 if you want to go faster.
You will spend a LOT more $$$ trying to get the boat to go faster with that engine rather than starting with a 502 or bigger cube engine.
I wish someone would have told me that back in 1979.
Steve

BlueAndWhite

thanks for the input. The speed is from the gps, the speedo isnt even pluged. For sure being a 1988 the hull must have soaked up some water over the years, i had it surveyed and nothing was rothed or delamed, the worse reading was some section of the transom was 80% humidity. No Idea wat the weight is at, i have original wellcraft brochure with the boat, it says 4600lbs dry weight. Been reading in the scarab forums the boat out of the factory with 454 mag was doing 60mph.

Yea i have read that many time already about the 454. Stuff like manifolds and ignition systems could be switched over to new engine so thats not so bad.

On the mirage plus prop (23p 3 blade) i have plugs i can take out, how would that affect the prop? ( currently all holes are pluged)

PARASAIL941

If you just want to see 60mph , bump the timing a few degrees , 1/4 tank fuel , take out everything not bolted down , and give it a shot. Your only a few mph below a Mag motor , so it must be pretty healthy.

hogie roll

Pretty good upgrades on the manifold, exhaust and pistons. What cam is in it?

Your next limitation on that motor is the heads.

phragle

iTrader: (3)

A shorty might do it, those old wellcrafts were pretty deep....

BlueAndWhite

I dont see any cam part numbers on the rebuild sheet receipt so the stocker went back in it. will not be doing the heads on this, will keep that money for gas or bigger engine down the line :P

Im guessing you are talking about the lower outdrive part? i did notice its pretty much at the bottom of the ''V''

hogie roll

I don’t know if yours is a roller, but a 500efi or 525 cam (if you can manage the reversion) is probably a nice upgrade to what you have.