Two Streams, Two Questions
for writing tech talk. My boats are away for the winter so its time
for planning and dreaming.
DOO w/70 NISSAN redux.
wrote originally asking about propellers. I thought that I would
need more pitch than I could find. This may be true.
raised to the highest bolt position
rpm max with all conditions
boat runs fastest with neutral trim.
dumbo prop is an old Merc race prop from the early 70's. The ears
are pretty big. It looks more like my Hoss Hyperdrive than a
far as set up goes, I think I'm done. Is there anything else to try?
I ever find a used 60 Merc w/1.64 gears would it push the boat faster?
boat is mostly a cottage ski boat, but I do like to go fast on
occasion. Sometimes we take trips and have to buy 'lake' gas.
Laser is too much pitch for pulling my 200 lb brothers out on slalom skis.
At 175 lb, I pull out OK.
Would a stock 200 Merc be worth the upgrade? If I upgrade I would
have two goals. First, to be able to pull my brothers out and still
see 70 mph with the same prop. Second, to see close to 80 with a
'speed' prop. I think the rev limiter on the new 200 carbs
would limit the flexibility.
How far down in pitch do I need to go to pull out my brother? If I
keep the XR4 I think I'll buy a Trophy.
Would water ski duty (lots of idling and starting) constantly flatten the
battery on a 2.5L?
local engine builder recommended not to 'hot rod' the XR4.
for any suggestions
Voodoo stats: for some reason, I'd look at the pad and hull for soft spots and hooks. Your speed seems about 10 mph off the pace. Should be in the low 60's. The hint is that the 18" chopper goes slower after you raised it up. Also the 70 Nissan has an electronic rev limiter at, guess what, 5800. I'll research for you, but if I'm not mistaken, they have a disconnect wire like Yamaha uses and we just need to find what wire it is. The Dumbo prop is an old Merc "offshore" prop. Good prop for engines, find an old 75 hp short shaft Johnson or Evinrude "E" class motor. They are less than $1000 used around here and with the 18" chopper, we had one running 68 on a Vixen at 7400 rpm. As for the Virage, the best thing you could do is get the larger 1:86 ratio gearcase. The little XR4 1:78 gearcase doesn't carry the boat very well. Next just port the XR4 to 200 spec and you'll have what you desire. You can re-jet the carbs or find a set off a late model 2.4 200 and just bolt them on. Both of your props will be perfect for skiing and the speed runs. But this is with the big gearcase. Sounds like the local builder doesn't quite know how to 200ize the XR4. This would explain his reluctance, as it is a simple operation. If you go the "new" 200 route, the rev limiter is a control box on the powerhead and can be removed. The 2.5 has the 40 amp charge system like your XR4, so no difference.Randy
Please submit whatever questions you have to IHRTechTalk@yahoo.com. All questions and answers selected will be displayed on this page as they come in. Note: though all boaters are welcome, priority may be given to I.H.R. members. Randy can not be held responsible for any advice given. Though his information and expertise is second to none, he has no control over what you do with your boat. It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.
I.H.R. l History
Pictures l Feature
Article l Tech