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Underbody braces, turbos and more!

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Nov 03, 2009 3:56 pm 
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Joined: Sun Feb 23, 2003 4:16 am
Posts: 8013
Location: Ontario, Canada
Gasoline Fumes wrote:
why less lift? Unless the lift has to be reduced in order to get the desired duration.


That's about it.
I work with the profiles I have at my disposal. Ideally, if I could, I would dial in as much lift as possible, and set duration accordingly. There are several reasons why this isn't possible.
Although there are grinders available that accept cnc programs, and grind accordingly, they are out of my reach, so I have to work with the master templates that I have.

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 Post subject: Re: Camshaft tech.
PostPosted: Sun Nov 08, 2009 9:17 am 
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Joined: Tue Mar 16, 2004 6:23 am
Posts: 1733
Location: Washington, DC
Every part of the engine can be tuned to work better at low rpm low air flow operation, or high rpm, wide open throttle operation. The valves and cam are just one part of this very complicated compromise equation. For maximum horsepower, which is achieved at high rpm and wide throttle openings, you want maximum airflow. Large tubes feeding the cylinders, large valves with large openings, large throttle body, large exhaust system diameter. At lower airflow rates, flow velocity is the important thing, not flow quantity. So for good low end torque you want smaller intake tubing, valves, valve opening, and a small diameter exhaust system. Obviously you can't do both so the designer takes a decision what he wants the torque curve to look like, and chooses everything to match. VTEC and other schemes seek to have two different torque curves that can be switched between on the fly. Some, more expensive, cars have a VTEC like system that actually varies the tuning of the intake tract and exhaust system.

The XFI cam has lower lift and lesser duration to keep the flow velocity high at low rpms, making more torque at lower rpms in order to go with the taller final drive ratio. This tuning lost quite a bit of horsepower because it ran out of total flow at a much lower rpm and rpm is a very important component to creating horsepower. Standard G10 makes it's max HP at 5700 rpm, XFI makes it's at 4700 rpm but has a flatter torque curve that delivers power lower down.

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Dec 01, 2009 10:11 pm 
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Joined: Wed Jul 08, 2009 11:31 pm
Posts: 26
Location: Vallejo, CA
FWIW, I measured timing on the #1 lobes of my (worn) stock camshaft. The cam sprocket was advanced 5 degrees (10 at the crankshaft). All timings are after TDC. Am I a tooth late???
Intake:
.005: 2 deg A
.050: 43 deg A
.332: 115 deg A max opening
.050: 189 deg A
.005: 230 deg A

Exhaust:
.005: 151 deg A
.050: 185 deg A
.334: 258 deg A max opening
.050: 335 deg A
.005: 015 deg A

This gives an intake duration of 146 deg at .050, and 228 deg at .005.
exhaust duration of 150 deg at .050, and 224 deg at .005
lobe centerlines are 143 degrees apart.

bob

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 Post subject: Re: Camshaft tech.
PostPosted: Fri Feb 18, 2011 10:13 pm 
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Joined: Fri Feb 04, 2011 1:25 pm
Posts: 88
Location: new york
found this site but im not sure if its applicable, mods can delete this if it is'nt.

Installing a Racing Camshaft

http://www.iskycams.com/camshaft.php


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