NordicVenture

Just came across this part of the forum and thought I might have better luck obtaining some answers. I had posted a couple of threads previously but had supplied some info that wasn't extremely accurate due to previous owner info and a very inaccurate speedo. I have 93' Venture w/ a 502 mag (only modifications are a set of EMI Thunder manifolds). My speedo is reading 74mph @ 5200 rpm w/ a 21p Mirage Plus. I just recently GPS'd the boat and found it to be running 65.6 mph @ the above mentioned rpm. Anybody w/ previous experience w/ this hull? I have talked w/ Matt @ Throttle-Up and he thinks the boat should at least be runnig a 23P Mirage. I am really new to the prop game and would appreciate anyone's input/experience. Anybody out there have any past/current experience w/ this particular boat model? Thanks in advance.

Steve Zuckerman

NV,
If you're talking to Matt, you're talking to one of the best prop guys in the country, particularly on Nordics. He's helped several of us (myself included) get our boats propped correctly.
Running your #s through a prop calculator (I am using 1.5 ratio for your gears as that would be standard, and you didn't give us that), says you have the most efficient Nordic in the world @ .048% slip. Normal would be mid teens (.15).
Your tach may be off (reading low), your gear ratio may be lower (1.3ish?), or your propeller may have been pitched up to a 22".
I would:
check the tach against a shop tach. as you see from your speedometer, they can be "happy".
find out what gear ratio you have. get the serial # off your drive and let a merc dealer run it for you.
test a stock prop of known pitch.
BTW, all my friends with 502 Mags in the larger heavier 28' Heat are using 24" Bravo 1 4 blades with excellent results.
Based on that, you are WAY underpropped, and Matt is correct as usual.
Steve

NordicVenture

Thanks for the response Steve.

I also ran the #'s through a prop calculator and came up w/ the same slip. I am pretty sure you are correct on the gears as the outdrive is stamped 1.5. That only leaves me to assume that the prop has been reworked to justify the the mph. Any idea where I can get a hold of a shop tach cheap?

Thanks

Ken

Steve Zuckerman

Ken,
Most Merc dealers, and most high perf shops can check this for you. Even if you don't replace your tach immediately, you can just add or subtract RPMs to get the corrects #s.
If we knew where you lived/boated, I'm sure one of the guys on the board could recommend somebody to help you out.
Since we've confirmed your gear ratio (1.5), I think you'll find your tach is reading low (or your prop has been repitched up). For instance if you are really turning 5500, your slip would be a more realistic 10%.
I have a recall on my GPS speedo and tachometer so I can compare them when I'm tuning or prop testing. It makes testing much easier.
Regards,
Steve
PS, if you decide to replace your speedo, tach or other instruments, I recommend Livorsis from Trick Marine.
Fred's a straight shooter and he's got excellent pricing
www.trickmarine.net

NordicVenture

Steve,

I'm in Phoenix, AZ. I have heard of a couple of shops (AZ Speed & Marine & DryDoc Marine) but haven't checked them out as of yet due to lack of time. I'm really interested to find out the tach accuracy though. I could stand to benefit (mph increase ) if it is reading low and the boat is under propped. Thanks for the line on Trick Marine.

Ken

P.S. You mentioned that alot of the guys you know are running the Bravo 1's. Are they running the newer stepped hull? I thought this boat might benefit from a 4 blade but wasn't sure since it doesn't have the benefit of 'steps'.(something else to tinker on).

Steve Zuckerman

Ken,
All the Heats I'm referring to are pad vees. Pretty much everyone who's running big blocks with bravo drives, whether
single engine or twins, straight vee or step vee, is running Bravo 1 4 blades. Several of us are running 5 blades with great success. 3 blades are really old hat technology.
A friend of mine bought a used Heat/502MagEFI out of Havasu City last year. It had a 23" Mirage 3 blade. It was all over the limiter, and slow out of the hole, due to excessive slippage. He put a 24" B1 on it and it picked up everywhere.
I would verify my instrumentation and test some B1s, in your case both 24" and 26". I think you'll be pleased.
BTW, I think AZSM is on top of their game. They are one of the best ECU reprogrammers in the game.
My best freind and I are both using their 575 boost kits on our boats with good results.
Regards,
Steve

NordicVenture

Steve,

Input is much appreciated. I'll keep you posted.

All the best,

Ken

NordicVenture

Hello all,

Update on previous post:

Had a chance yesterday to test a box stock 23p Miarage+ with some good results. Per the GPS the boat ran 69.7 (up from 65.6) w/nearly identical conditions as before. RPM's dropped to about 5000 (5075 according to shop tach). Seem to have more bow lift and definitely seem to be getting more hull out of the water(slight chine walk). The one thing that still baffles me is the prop slip #'s (6%). I love the improvements in ride and the way the boat handles the water now. I am considering labbing the 23 to get RPM back to 52-5300. Is this hull really that efficient or are there other factors I'm missing here? As a sidenote does anybody have experience w/ hatch rebuild info? I am going to build/rebuild a new hatch cover due to hinge damage fom running one ram. Are there any options/resources other than plywood?

Regards,

Ken

Steve Zuckerman

Ken,
Sounds like you're making progress. I would also try a 24" Bravo 1 4 blade. Same actual pitch as the 23" Mirage, but more blade area. Should handle, lift, acellerate better. Top end will probably be close, but definitely worth the test.
I did modify my hatch for intercooler clearance, but I am not familiar with yours. You may want to give Lonnie a call, or speak with a custom uphoulstery shop. Some of these guys do their own seat framing and hatch building/customizing.
I would go with marine plywood, coated with 'glass.
You can use your current one for a template. I would incorporate some air intakes as the engine compartments on these boats are very restrictive.
There is also a plastic sheet material called Starboard that is easily cut and worked, and will not rot. I think it's pretty heavy though.
Regards,
Steve