77 Scarab 300 Prop Selection
 

New to the forums here, and have a really newbie question. I just purchased a 1977 Scarab 300 with rebuilt sbc 350's. Only apparent performance work that's been done to the engines is a high rise intake. The props are both dinged up as well as the lowers on the outdrives. My question is, what kind of props suit these boats? Any and all help is much appreciated.

Need to answer a couple of questions what drive system and what props you already have? They should have part numbers on the inner hub of the propeller or cast into the side of the hub

Drives are the factory merc trs, far as props, I'll get the numbers off them tonight. 3 blade stainless is what I know, but I'll update later. Thanks for the reply.

Props are Mazco 1013 and 1014

Those motors don't sound like they are original to the boat that set up should have had BB chevys Not sure about Mazco props don't know what there part numbers are. That boat from Wellcraft with 330 Hp BB chevys would have come with a 23 Pitch merc 3 blade the 400 HP version came with 25 pitch props.

My understanding of it was that the 77's came with sbc and then in 78' the bbc were swapped in. It's got 3 blade props but I've got no clue on pitch.

Sorry to resurrect an old thread, but I have had a little down time with the boat and pulled a prop off. Ive got a number stamped on the inner hub ring that is 48-74599-21....Prop measures 15" across. They are Mazco Props and when I called them they said they had no way of telling what they were. Any insight or help?

P.S. I looked up a rudimentary way of measuring pitch with a downloaded template and came up with 28"

Pic

the number you give stamped on the hub is a merc part number, I'm not familiar with Mazco. I would think a prop like a mirage would be better than a cleaver on that boat.

http://www.offshoreonly.com/forums/p...5-prop-id.html

Mirage 25p???

Well back in the day I had '76 Scarab along with a good friend of mine. They both came stock with sbc and were called 280TRS. Stock came with 21" cleavers and my friends Scarab had a little work on it but still used the 21" and cupped them a little bit. Of course there were no Hydromotives or Mirage props back then. Since then I had a 9m Mirage SS and tried a half dozen props on it looking for best midrange and top speed and the mirage 3 blade props worked the best. The cleavers slipped a lot midrange but top speed was not too far off.

Thanks for that, mines got the sbc in it, top speed with no trim control was 43mph

Well something is wacked. The boat should run around 57/58 mph with clean hull, straight props, tuned up and trimmed out. If I remember right it was turning around 5200rpm. You'll get there, good luck and enjoy.

Ya, I didn't have my trim pumps wired in, so that was full drag in the water, I'll get it all dialed in this weekend

I would think a 21 mirage plus would be close

21p mirage will be the best prop for your boat with those motors. 23p will be the easiest to find used and will work but the rpms will be a little on the low side for optimum. More important is to get your trim working. you are pushing too much water for any props to make a worthwhile difference.

Agreed, pumps and cylinders are being rebuilt now and will go on, then hopefully I'll have a better idea on what it's doing/needing

As others stated a 21 Mirage would be the best choice for that hull. When I was looking for a Panther I looked at a beautiful 1976 300 with the 260 or 280 package. It ran out at 55mph with 21 cleavers. My TRS Panther is the same hull as yours and I've tried every style of prop out there. A 27 Mirage is the best prop I found. Stick with a plane Mirage.

I've got a pair of 21p mirage props I bought for my 78 Scarab 300 with BBC's but they're too low for me to use so I need to sell them. I only got 55mph out of the boat with them and had plenty of throttle left, but with small blocks I bet they would be perfect

I've got a set of mirage 21p labbed on there now and best i was getting was 53, I'm gonna try a set of 25's and see what they'll do after the performance parts go on.

53mph at what RPM?

No clue, neither tach was working correctly, somewhere around 4800-5000 if I were to guess

i have a pair of 25 mirage plus that i ran on my 30 scarab w/ trs drives
they track straight are balanced, never been welded, have no reconditioning stamps, and are for sale 400 bucks, plus shipping

[ATTACH=CONFIG]558101[/ATTACH][ATTACH=CONFIG]558102[/ATTACH]

Well that's between 17% and 20% slippage if they are a true 21" pitch. A bit too much for a Mirage prop so there must be a problem. Guessing you already checked carbs are wide open at full throttle and timing is on the money (good tune up). Could be the trannies if your props slightly spin in neutral (clutch packs warped) or just tired motors/heavy boat.

His tachs aren't working.

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I could not imagine propping a boat without having working tachs.

I wish you woulda posted that about 4 hours ago, I just gave a guy my word Id spend 500 on his props, same as yours. Thanks for the offer though!

Ive gotten the tach problem figured out, just haven't had it back in the water since the repair.

Ive read several posts on the 30' scarab hull with TRS drives and the consensus was that the 25p was the perfect prop. Props don't spin very much at idle out of the water, trannies seem to be holding up. The three blade 21s that are on there have been labbed, but are in pretty bad shape, looks like the PO used them as a depth finder more than for propulsion. Were gonna try the 25's and see what they do, in the meantime we're gonna send these 21's off the be trued (if that's possible)

I couldnt spin 25s on my magnum sport with the 280 trs which is a more powerful small block, and lighter boat. Again you need to get the necessary items working correctly before i would spend a dime on props. trim-tachs then props

So then let me ask this, mind you I'm undoubtedly the most ignorant person on this forum, but at what rpm do you spin your motors at WOT?

My magnum was a similar hull but lighter-high rev 280 small blocks would turn 5k with 23s. Back in the days of working at a dealer rigging wellcrafts, all the scarab panthers received 23s with the 454 mag and 21s with the 330s. That was through bravo dirves. You are spinning small blocks through transmissions and trs drives. Bullet proof package but not efficient. If memory serves me you loose about 18 percent of your power going though the trans and trs. Your WOT target should be 4700 with light load. This would give you your most efficient cruise speed at 3400. 21 Mirage should put you there.

Is there anything to be gained by spinning the motors at a higher RPM than 4700 under load? Obviously the inherent risk of blowing something up, but if the blocks were built to handle say 6000 RPM for sustained runs, is it advantageous or just a waste of fuel.

I'm sure these questions seem rudimentary, but I do appreciate the time yall are taking to answer.

Generally HP/torque figures rise as RPMs rise. If you can let them spin a little faster, you get into more HP/torque. The hope is the gain in HPTQ will allow the prop to spin faster than the pitch difference, and you gain speed and efficiency, along with acceleration and better "boatability". Example: say you drop two pitches and mechanically that should net you 2-300 RPM. But, because you gained another 30hp, you pick up 600 Rpm. It's a fine line, but you have to remember......NOTHING touches the water to transfer energy but the prop. I see people have props as an afterthought. They will spend $5000 to get 3 mph, when a couple hours at a prop shop with a cupping hammer would have the same result. We used to cup our racing props on the trailer ball!!!! Lab that Mercury! LOL!

So spend some time with them and get them where you want them. Makes a world of difference.

Getting the props I have reworked is on the To-Do list, I will get some pics posted up here in just a few, they are pretty bad as far as edge contour goes. I have called a couple of the local boat places but none of them seem to want to touch props.

Call BBlades.

Are you Stephenville Texas? If yes, call B&B Propeller Service in Ft.Worth.

Ok, I'll give them a call in the morning , thanks CD

You are never going to be able to spin those 25's. A stock big block 330HP scarab with bravo drives came with 23's and ran around 63mph. I have run the 25's to 80mph but I have 550HP/side big blocks. I suggest you fix your 21's and tachs and then baseline from there. You want to spin you engines to peak HP. Lugging the engine in lower RPM's near peak torque is torque loading it. And I personally would not do that. I believe you need to be around 4800 RPM.