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osubob

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Discussion starter · #1 ·
Ok everyone. Here's another question...

I've been reading these threads for a while and I am seeing people getting in the 60's with a stock 454 carb. I think I may be missing something. I've got a 237 Powerquest with this same engine. At WOT I'm getting around 50-53mph. WOT RPM is about 4600-4700RPM. It seems to me that I should be getting more speed. I'm running a Mirage (not plus) 21P. Any suggestions what I can do to up the speed a little? I'd like to break the 60MPH mark.

Thanks,
Bob
 
Discussion starter · #7 ·
The fastest I've had it is 57 per spedo, not GPS. I will verify with a GPS this weekend. My guess is that it will be around 50-53MPH. I will let you know. Will a Mirage plus give me more top end?
 
Discussion starter · #9 ·
I haven't checked for a hook in the hull. I'll check that out as well. I assume that the drive has a 1.5 ratio. Also, not sure if my engine has a rev limiter. Its a 95, did they exist then? If so, I don't believe I'm hitting it...
 
#10 ·
When comparing with other boats with the 454 mag getting faster or slower speeds you have to compare apples to apples. Things like: Carb or MPI, overall boat weight, placement of load, fuel level, passengers or no passengers, tabs or no tabs, beam width to list a few.
 
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#11 ·
Did not see in the post if you have a Mag or 7.4. My 7.4, cast pistons, peanut port heads, gives me 56.5 on GPS, 25 ft 4400 lb dry hull, full windshield, Bravo III 26p @4400rpms. It's pretty expensive to switch two props on a BIII. My second set of props are 30" and I would need at least 125 hp to turn them. Cheap on eBay. My slip calcs to around 10%. Neighbor does have a set of 24s that I may borrow just to see how it performs.

The peanut port heads do not flow very well. If this is what you have, you will have more hp at 4500 than at 4700. Going to more pitch, lower rpm would probably give you a little more speed. This engine also has an adapter under the carb to get the square bore WFB carb to the low rise spreadbore pattern manifold. I purchased a used high rise spread bore manifold that I was going to open up to square bore but the surfaces that mate to the heads are too rough and I'm not going to use it. May mill out the low rise. Dennis Miller's book talks about a couple of mods that might give 20 hp or so. Probably a couple of MPH in our speed range. Holley makes an aluminum intake that works good with the peanut heads.

You might post a little more info about your engine and hull so "we" can rattle on about what we think you should do.

Personally, I am looking for around 65 with the wife and I on board. Probably swap in a 502.
 
Discussion starter · #12 ·
I've got the 454 (non-mag). Its turning a 21P Mirage (not plus) on a bravo 1. I'm going to head out to the boat this weekend and verify my WOT RPM and MPH. Maybe I have excessive prop slip. I'll update everyone in a few days.

Bob
 
Discussion starter · #13 ·
OK, Here are the numbers. Sorry for the delay, the weather in West Michigan has been terrible. Anyway, I am getting 48MPH at 4600RPM at WOT. Now, I'm using the GPS off my nextel phone. I'm not sure if that makes a difference. It reads the same as the spedo at 30mph, but at WOT, spedo reads 55, GPS reads 48. I believe I have excessive prop slip. Can anyone help?

Bob
 
#15 ·
Hey Bob it would probably be a good thing to hook up a timing light and make sure your tach is accurate also before checking out other props. This will just insure all data is as accurate as possible. Also have you checked out the carb to see if the secondaries ar opening up all the way? Also when was the last time is was cleaned out and rebuilt. This can make a substantial differance in performance.
 
Discussion starter · #16 ·
Well, I was having some problems with the carb. The choke was disconnected this spring. The engine was running rich. I had new spark plugs installed and had the engine tuned up. The engine sounds like it is running great. Also, I have looked at the carb and the secondaries do open up.
 
#19 ·
I have Formula 242LS with 454 magnum. With a 21'P mirage I was running 53-54 mph at 5300 rpms (too much!). So I tried a 23P mirage plus and couldn't turn more than 4300+ and still was around 54 mph. Next I tried a 22 pitch 4 blade bravo I prop. Trimmed out I was at 55mph @ 4800rpm. But it's not all about speed. The hole shot and accelation were much improved as was the ride in rough water. Others with the same boat/motor see 60mph, I'm not sure what the deal is with my boat/motor, but have decided to still with the bravo I four blade prop for now.
 
#20 ·
osubob,

I am glad you went out to test. Your slip numbers are quite high, 27%! The prop has alot of slip. There are a few things you need to check on. I would check your tach, verify your gear ratio, propeller (Make and Pitch) and your X Dimension. If you have a picture of the prop post it. There are also some great recommendations on checking your carb. Feel free to call me.

Julie
Throttle Up Propellers
727-531-2255
 
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