xr2 rpm

scottyboy · 22-08-2005, 06:47 PM

My xr2 only rev,s to 6400 when jacked level with the bottom of the pad and trimmed Just below level! I was told today that it should rev its nuts off with a 23" prop? Mine dont! Im running a 2:1 ratio box to! Anyone got any ideas?

roofer · 22-08-2005, 06:57 PM

when i had the xr2 fitted it revved to 7300 with a 24 yam drag prop, I also had 2.1 gears. sorry cant help you with the why though only used engine for 1 race then got shut.

Burty · 22-08-2005, 09:07 PM

Quote:

Originally posted by roofer
when i had the xr2 fitted it revved to 7300 with a 24 yam drag prop, I also had 2.1 gears. sorry cant help you with the why though only used engine for 1 race then got shut.

think you'll find you had 1.87:1 gears dude. i know this because i now own that gearbox and its defo a 1.87:1

JamesM · 22-08-2005, 10:19 PM

Scottyboy is that Burty's old prop cus if it is it turned 6600 with 200hp on a 1.87:1. Do I remember you saying your boat was a lightweight because Burty used it on a sharp which would normally be alot loghter than a P21.

Burty · 22-08-2005, 10:20 PM

6800 RPM actually

Matt · 22-08-2005, 10:39 PM

Lighter, maybe, owing to the paper mache construction. More likely to fold in 2 - definately.

Quote:

Originally posted by Johnny Boat Dude
Scottyboy is that Burty's old prop cus if it is it turned 6600 with 200hp on a 1.87:1. Do I remember you saying your boat was a lightweight because Burty used it on a sharp which would normally be alot loghter than a P21.

roofer · 22-08-2005, 10:43 PM

Quote:

Originally posted by Burty
think you'll find you had 1.87:1 gears dude. i know this because i now own that gearbox and its defo a 1.87:1

I think you are mistaken,, when ian blacker sent it up it had damaged 1.87 gears in and hutchy rebuilt it with 2.1,maybe he changed them when you bought it .

Burty · 22-08-2005, 10:45 PM

Quote:

Originally posted by roofer
I think you are mistaken,, when ian blacker sent it up it had damaged 1.87 gears in and hutchy rebuilt it with 2.1,maybe he changed them when you bought it .

JamesM · 22-08-2005, 10:51 PM

Go out to your garage with you permanent marker dude. Mark the drive shat and case and the prop shaft and case. Then turn the drive shaft through two revolutions (with it in gear obviousley) and if the prop shaft ends up where it started its 2:1. Do it now cus you made me go out in the dark and measure my transom!!!

Burty · 22-08-2005, 10:52 PM

ffs

JamesM · 22-08-2005, 11:02 PM

Done it yet!!! Some one might be getting a cheap ET lightning!!!

Burty · 22-08-2005, 11:04 PM

Quote:

Originally posted by Johnny Boat Dude
Done it yet!!! Some one might be getting a cheap ET lightning!!!

O no they won't

Defo 1.87:1 just been and checked

JamesM · 22-08-2005, 11:06 PM

There's a bit of luck then

JamesM · 22-08-2005, 11:15 PM

Quote:

Originally posted by roofer
when i had the xr2 fitted it revved to 7300 with a 24 yam drag prop, I also had 2.1 gears. sorry cant help you with the why though only used engine for 1 race then got shut.

Thats good going!!! Was that a standard XR2

roofer · 22-08-2005, 11:23 PM

Quote:

Originally posted by Johnny Boat Dude
Thats good going!!! Was that a standard XR2

maybe, it had been 1 of a pair on a 4 litre boat so probably standard,I had velocity stacks fitted to carbs.

JamesM · 22-08-2005, 11:36 PM

Yep they add a few hundred RPM over an airbox.

mike k · 23-08-2005, 07:58 AM

Scuse the ignorance but what are velocity stacks ?

Matt · 23-08-2005, 09:45 AM

Basically bell mouths on the end of the carburettors.
They provide a gradual transition for airflow into the carurettor making for increased airflow.
Am sure Burty or JBD will have a phot to hand.

Wayne Kerr · 23-08-2005, 09:58 AM

Quote:

Originally posted by mike k
Scuse the ignorance but what are velocity stacks ?

Oi - Oi. I can see a modification coming on!

scottyboy · 23-08-2005, 01:26 PM

guys weve had 7100 but it was seriously over trimmed ie rooster about 40ft high! Looked superb but speed fell off! are you lot getting above 7000 without over trimming??