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What do you guys think it will gain?

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Old 10-08-2012, 05:08 PM
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Default What do you guys think it will gain?

Ok, here's what I have. '91 Formula SR-1 292 with twin 502 mags. Stock. Boat has about 460 hours on it and runs flawlessly and with a light fuel load it runs 72 on GPS with 25 Mirages. I am thinking of yanking my motors in a couple weeks and doing some work over the winter. Here's my plan:

Upgrade to good flowing exhaust
Upgrade heads to bigger HP500 size intake valves, roller rockers, etc.
Upgrade to good HP500 like Bob Madura cams
Upgrade to HP500 style intake and carb
Upgraded ignition if necessary

Will dial motors in on the dyno.

Hoping for somewhere in the 500 - 525hp range depending on what we do for cam/valvetrain combo.

How much do you think I will pick up if I add 125-130hp a side?

Has anyone tried 2" shorty lowers on this boat?

Will definitely be trying 4 blades and whatever else I need but would like to be in the upper 70's on 91 non ethanol pump gas.

Your thoughts? We have long winters so I have the time!!!

Last edited by 1000 islander; 10-08-2012 at 05:11 PM.
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Old 10-08-2012, 07:34 PM
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If your 1991 drives have not yet been upgraded to the 6 rib cone clutches, you will blow them up with the new power. Period. Even with the newer style clutches, your non X (X, XR, XZ) drives will be running at the limit of their capacity with 500+hp. Expect drive problems unless you do some more drive upgrades.

Your valve sizes are likely to be already the same as the HP500. The HP500 (early ones) used Manley inconel (Extreme Duty) 2.18x1.88 valves.

The change to a Dart style intake, CMI headers, larger carb, and well matched cam will give you the 500+hp you seek. Keep the squish height under 0.050" and you'll be able to run the gas you want to run.

Speed? You'll likely see over 80 with a light load.

Shorties and 4 blade props will give you some more top speed as well, although you will need full hydraulic steering (not cheap). Your excellent holeshot will suffer a little bit with the shorties, but a good prop selection will minimize the problems there.

The 292 is more weight sensitive than the 311, and you may have to experiment with moving some weight around. Don't use the forward-mounted freshwater tank as ballast weight unless you fill it completely - partial fills let it get to sloshing around, upsetting the handling when trimmed out and running fast in chop.

Have fun.
MC
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Old 10-19-2012, 09:46 AM
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Are you sure about 80 MPH with 1000 hp in a 292? I've got just under 900 hp in my 292 and I get 69 MPH. I'm a bit low on my RPMs which are 4900 with 25 Hydros. So I'm going to have the blades trimmed to bring the R's closer to 5300. So I'm guessing I'm losing a few MPH there.

Islander- is your speed the speedo or GPS. If GPS what were you using. I noticed last summer when using my phone as a GPS depending on what App I ran the speed difference would vary slightly. What kind of RPMs are you spinning with your stock 502s? If the Mirages are really that much faster than the hydros I may be switching props. As it is, if your spinning 4900 RPMs your slip is 7%, which I didn't think was possible with a 292 hull. Currently I'm at 11% slip.
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Old 10-19-2012, 09:57 AM
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On the speed increase, our boats need about 17.5 hp to gain 1 MPH. So if you're adding 120 hp you'll gain about 7 MPH. Like Mc was saying, you're going to need hydraulic steering at those speeds. My boat needs it at my current speeds.
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Old 10-19-2012, 10:58 AM
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Are the 502's gen V?
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