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bakerman
06-11-2001, 07:49 PM
hello how are you all doing? my problem is im in utah now and i lost 600 r.p.m due to altitude any ideas as to get some of it back without going more horse power or changing impellers? thanks

timitunnel
06-11-2001, 08:02 PM
check the tune of your motor,ie:jetting, timing, plug temp, and if you do most of your boating at high altitude you might try advancing the cam one tooth. hope this helps.

ponponracing
06-11-2001, 08:19 PM
The only thing that change with altitude is jetting. Since there less oxygen in the air
and that air density change with altitude, you have to adjust carb's jetting.
It is for sure that in high altitude you loose power. That's life, you have to live with it. The only thing you can do is to adjust accordingly to altitude.
Hey Timitunnel, what do you mean by advancing by advancing the cam one tooth?

timitunnel
06-11-2001, 08:58 PM
As you know a motor is just an air pump. By advancing the cam gear one tooth you start to move air sooner hence more air in the cylinder. You can buy timming chain sets where cam gear has multiple timming set ups so you can advance or retard the cam more acccuritly for situation. I live in hailey Id. 5300ft. Hope this makes sence to you.
Tim

Racing Ray
06-12-2001, 01:52 AM
Less air means the engine will want less fuel you will need to jet down a bit . When I race in SLC I jet down 4 jet sizes. But even with this I still lose about 40-50 HP.
Moving the timing chain will not make more HP . What it does is move the peak torque around in the RPM band. Since torque is down as well as HP in some cases it will help to move the peak torque to lower RPMs by advancing the cam timing.

Riley
06-12-2001, 03:44 AM
timitunnel,
I'm not sure I understand the point you made about the advancing for more air theory. It seems to me that with a given stroke and a given duration of valve lift you get the same air in the cylinder. Most cams open the intake slightly before the top of the intake stroke anyways, wouldn't advancing the timing give less duration on the downstroke. Besides if you don't adjust the mixture, any increase in air still has to pass through the carb, so it will be rich or lean like the smaller amount of air you had before. Let me know if I'm wrong.

Racing Ray
06-12-2001, 04:08 AM
Berfore I get chewed out again for making something complex sound to simple a word of caution!
Higher compression ratios (milling heads, piston domes) Longer duration cams, AND cam timing all affect piston to valve clearance and should be approached with caution. Best bet is to consult your engine builder or manufacture and 2-4 degrees advanced or retarded would be a BIG change.

timitunnel
06-12-2001, 08:23 AM
Riley
The way it was explained to me years ago is that most motors are built on the mild side for longgevity. So by advancing the cam one tooth you have the valve open more in a better part of the intake stroke. I don't know if this is realy factual but it has worked for me over the years. I would hope that anyone wanting to use info from this forum would find out what he has in his motor and use the info accordingly. I hope this doesn't make me sound too stupid but I have gotten alot out of a little over the years with keeping to the basics anda few little tricks. It helps when trying to save for the good stuff.
Tim

Riley
06-12-2001, 09:39 AM
Tim,
Yah, I'm all for saving some money with smart tricks. Whatever works, you got to go with it. I typically advance valve timing 1 degree anyway to allow for timing chain stretch.
Riley