Help choosing prop and max RPM?

2258 Views 18 Replies 7 Participants Last post by HTRDLNCN, Jul 11, 2008

Philcat

Discussion Starter · Jun 4, 2008 (Edited)

Hi, I'm a newbie here, but just finished some upgrades to my 1990 Chaparral Villain III.

The engine is now 512 HP at 5400 RPM, and 547 TQ at 4100 RPM. I'm running a stock Bravo I with a 1.50 gear ratio. The motor is balanced and can run in the 6K RPM range, but that is past both the HP and TQ peaks. These HP and TQ numbers are on the dyno with dyno headers and no accessories. In the boat I am running a Stainless Marine exhaust. The engine is a 454 bored and stroked to 489 with 8.7:1 compression ratio burning 89 octane.

We've run the boat with a solid hub 25P 3 blade prop and run 64 MPH at around 5200 RPMs, and a 26P 3 blade prop and run 67 MPH at around 5000 RPMs (before we blew its hub to shreds

). I'm looking for max top speed (hoping for 70 MPH) The 25P will cavitate in a heartbeat out of the hole. A 26P 4 blade was too much prop...

Any suggestions on optimal RPM range or prop brand / size? The Mirage Plus props look nice, but only come in odd pitches (25P and 27P) Should I stay towards the HP or TQ peak?

Thanks in advance....

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1 - 19 of 19 Posts

Super24

· #2 · Jun 4, 2008

You didn't mention what brand of prop the 25 and 26 3 blades where. Your slip is WAY high. A 25P prop at 5200 should be getting you into the low 70's.

If you can turn the 25P to 5200, you should not have trouble turning a 26P 4 blade to close to the same RPMs. Something does not sound right.

What speed, prop, and rpms where you running before the mods?

markt111

· #3 · Jun 4, 2008

you probably want to stay around the 5200 your running with the 25 as your RPM range was probably a little higher with dyno headers! that being said were the 25 and 27 the same type of prop? both in good unmodified condition?

down 200 RPM and 3 mph faster is odd since your motor should like the higher RPM of the 25!

also on s single engine fairly heavy hull you may like a 4 blade to carry the stern more, handling and cruise speeds are usually better too

Philcat

Discussion Starter · #4 · Jun 4, 2008 (Edited)

First let me say thanks for the help!!

Super24

Right now the tach is suspect, I'm going to check things again with another tach either Sunday after the poker run (I'm on someone else's boat all weekend) or next week. I think you are correct, the 25P cavitates in a heartbeat up out of the hole, so I may have some serious slip. Maybe my best bet is a 24 or 26 pitch 4 blade. I need to find one I can borrow for testing

I was running a standard 7.4L Bravo 330HP before with a 23P 3 blade Mirage at 56 mph and 4300 or 4400 rpm.

MarkT111

I haven't run a 27 yet, my engine builder ran the 26 3 blade. I don't know what brands they were. It looks like I need to get back out there and get the prop brand and a good tach on it.

I'll get back out there and get more info soon...

Thanks again!!!

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Philcat

Discussion Starter · #5 · Jun 11, 2008

Finally some solid data:

WOT GPS MPH - 68.7
WOT RPM - 5200
Prop - 25P Mirage (not plus)
Bravo Ratio - 1.50
Engine HP peak - 512 HP @ 5400 RPM

Julie at Throttle Up has been kind enough to help out and suggest a 23P Mirage Plus.

I have a line on a used unit, if that doesn't pan out, I'll be buying one from her. If I save enough money buying a used one, I may look for a 4 blade to run as well.

blackhawk

· #6 · Jun 11, 2008

Philcat said:
Finally some solid data:

WOT GPS MPH - 68.7
WOT RPM - 5200
Prop - 25P Mirage (not plus)
Bravo Ratio - 1.50
Engine HP peak - 512 HP @ 5400 RPM

Julie at Throttle Up has been kind enough to help out and suggest a 23P Mirage Plus.

I have a line on a used unit, if that doesn't pan out, I'll be buying one from her. If I save enough money buying a used one, I may look for a 4 blade to run as well.

Did you verify that your tach was right? That is a lot of slip.

Philcat

Discussion Starter · #7 · Jun 12, 2008 (Edited)

Yep, checked the tach it is 100%. I wonder if the hub on the loaner 25P Mirage I have is slipping?

I'm looking for a 23P Mirage plus now...

HTRDLNCN

· #8 · Jun 12, 2008 (Edited)

You should have no problem spinning a 26p Bravo especially if its labbed.

I run a 24p Mercury labbed Bravo, 57mph at 4250rpm on a stock 310hp/454 and it pulls it very easily,gets on plane in a heartbeat and my Chappy cruiser is heavier than your sportboat, with your extra 200hp you should have NO problem with a 26p

any more pics of your Villian?

Chapparal 215XLC Merc 454/Alpha

Sherry buys a paper and a cold 6-pack of beer
Headlines read that Sonny's goin' to the chair
She pulls back on Main Street in her new Mercedes Benz
The road goes on forever and the party never ends........

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Philcat

Discussion Starter · #9 · Jun 12, 2008

Pics you say?

I've got a few more

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Philcat

Discussion Starter · #10 · Jun 12, 2008

And another

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Philcat

Discussion Starter · #11 · Jun 12, 2008 (Edited)

And one more... Now I need 29Scarabthunder to email me about his 23P Mirage plus so I can buy it !

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DonMan

· #12 · Jun 12, 2008

My stock 502 spins a 26p Bravo 4 blade to 4900 rpm. Holeshot is great. My boat handles the best with a 4 blade prop.

Super24

· #13 · Jun 12, 2008

Hey Pkilkat,

Where do you usually boat? I'm hoping to be in the Annapolis area tomorrow. Is EGO Alley still under construction?

Philcat

Discussion Starter · #14 · Jun 12, 2008

Hey Super24,

I usually boat anywhere from Deale up to the Magothy. I have a few friends on Round Bay. I keep my boat on Selby Bay.

EGO Alley is OPEN!

I might sneak out tomorrow afternoon if it's smooth...

cfm

· #15 · Jun 12, 2008

Philcat said:
Pics you say?

I've got a few more

Is that a quadrajet ? Was it on the engine for the dyno ? Who built the carb ?

Originally posted by Philcat
The engine is now 512 HP at 5400 RPM, and 547 TQ at 4100 RPM. I'm running a stock Bravo I with a 1.50 gear ratio. The motor is balanced and can run in the 6K RPM range, but that is past both the HP and TQ peaks. These HP and TQ numbers are on the dyno with dyno headers and no accessories. In the boat I am running a Stainless Marine exhaust. The engine is a 454 bored and stroked to 489 with 8.7:1 compression ratio burning 89 octane

Philcat

Discussion Starter · #16 · Jun 13, 2008 (Edited)

That's a SHARP eye you've got there CFM.

We dynoed the motor with a Holley and the rebuilt Q-Jet off of the original 7.4L Bravo. Can you believe the HP was exactly the same? The curve just moved a little in RPM. My engine builder also rebuilt the Q-Jet. We changed a few sets of metering rods on the dyno to tune it up. It may not be as fancy as some of the other carbs out there, but it is simple and reliable, it went 18 years on the old engine without any problems at all.

I haven't heard from 29Scarabthunder about the prop he has for sale in the classifieds. I guess I've got to go buy a new one.

Philcat

Discussion Starter · #17 · Jun 13, 2008

blackhawk said:
Did you verify that your tach was right? That is a lot of slip.

Is it possible that the 25P Mirage RUBBER HUB is slipping? I know I need a solid hub prop for this boat, but this 25P Mirage is all I could borrow at the time.

Philcat

Discussion Starter · #18 · Jul 11, 2008

Just an update for anyone that was interested, I've got the slip down to a reasonable number now.

We are running a 23P Mirage+ at around 5250 RPMs and getting 69.7MPH by GPS.

Still trying to break 70MPH. Maybe once the engine breaks in and I get a good day...

HTRDLNCN

· #19 · Jul 11, 2008 (Edited)

you added 180hp and gained 14mph,
sounds about right. Get some nice choppy water to lift
the boat further out of the water and you will see 70+.
Thats one nice looking Chappy!

Chapparal 215XLC Merc 502/Alpha

Sherry buys a paper and a cold 6-pack of beer
Headlines read that Sonny's goin' to the chair
She pulls back on Main Street in her new Mercedes Benz
The road goes on forever and the party never ends........

See less See more

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