xr2 rpm

[JamesM]

If you do take the airbox off then either get some stacks or cut the airbox up to make an S2000 style intake plate. Cut the front and sides off just leaving the part that surounds the carb entries. You need this part as it rounds the edges of the carb mouths thus stoping the air from becoming turbulent. Without it it wont be much better than with the airbox on. You may need to jet up one size, two to be on the safe side.

[Carl]

7200

[mike k]

I like the sound of these velocity stacks. Where can you get them and how do they fit ??

[Wayne Kerr]

Originally posted by mike k
I like the sound of these velocity stacks. Where can you get them and how do they fit ??

Mike, Bob's Machine Shop has them, 65 of yer US squids!

[mike k]

Thanks Trev I'll check out their web site and talk to Clive about jets.

[JamesM]

Originally posted by carly baby
7200

Bit more detail would be nice, prop size, gear ratio, speed etc.

[Carl]

man of little words me,but, its a 24" prop 1.87 gears and 72mph,with no lifter or set back

[JamesM]

Thats quick dude is your boat quite light then?

[JamesM]

Velocity stacks

[JamesM]

S2000 intake plate. You can make something very similar to this by cutting up your old airbox!!!

[Wayne Kerr]

Originally posted by Johnny Boat Dude
S2000 intake plate. You can make something very similar to this by cutting up your old airbox!!!

OK, got-ya, looks good (exept the sun down syndome on the wall).
Well done, we'll look into this ,,,,,,,,, Top Stuff !!!!!!!

[JamesM]

The first picture is off scream and fly. The second one I took myself with my rubbish £15 digi camera. Its one of those 0.3 mega pixel no proper lens and no LCD screen jobbies. It takes shockingly bad photos

[JamesM]

Here's another picture of a carb plate

[JamesM]

And here's a cut down airbox I found on S and F!!! In the foreground you can see some v. stacks (red)

[Ciao]

I have never understood the fascination with revs! If you rev 5300 and do 56 mph, is it less exciting to rev at 6000 (with a different prop) and run 55 mph?
Surely an engine has a power band, the plan should be to run at the top of that band.
Certain factors have to be taken into consideration off course, calm sea bigger prop lower revs, rough sea smaller prop higher revs to get you out of the hole.
Going back many years ago with our 21’ cat XR2 we revved 5600 (2.1 ratio) with a worked QSS 26’ which produced 74 mph (Windermere certified)
Going back a couple of years ago with our 17’ cat Yam 90 we revved 5600 (took a long time to get there) (2.1 ratio) with a Cleaver 26’ which produced 81 mph (Windermere certified)

[JamesM]

My motors peak output is at 6K but produces good power all the way into the high 6's. So why prop it to only rev to the power peak. That would mean taller prop that would give less acceleration.

Plus if you gained some revs then you must have gained some power and speed.

[Jon Fuller]

Originally posted by Johnny Boat Dude
Plus if you gained some revs then you must have gained some power and speed.

It aint quite as straight forward as that, is it.

If you gained the revs by a prop change, or by raising the motor, or changing the gear ratio, then no.

[JamesM]

Yeah but I was refuring to changes made to the power head only. Like removing the airbox fitting stacks and jetting up may gain you some RPM.

[Silversurfer]

P20, XR2, 23P Laser II, will rev just over 7K if trimmed right up, Max speed seems to be approx 6.6k - 6.8K Fully fuelled (50 Gallons) top speed with 1 person in the boat was 64 mph. If you remove the front tank it will do closer to 68mph in the flat.

Hope that helps.

After blowing my last engine up I try to keep the revs below 7K now!

[JamesM]

Is that 1.87:1 or 2:1?