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Old 11-07-2001, 01:30 PM   #1
Scooby Newbie
Member#: 10118
Join Date: Sep 2001
1991 Pimpssan

Default please educate me...

I have been searching through here for a while now and would like to know...replacing what parts gives an engine the higher reving ability, and why it does so. I have seen people talking about r/s ratios and changing valves and spings and all those goodies and just want to know some theory and reason behind this. Thanks for the help, and please everyone who knows a great deal about cars, i encourage you to talk as technical as possible so that youngins like myself can ask questions and learn the technical terms for everything. Thanks again.
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Old 11-07-2001, 01:40 PM   #2
Scooby Specialist
Member#: 1994
Join Date: Jul 2000
Location: "Teh Hebro Town"
2013 Impreza WRX


Before this get's moved to the N/A forum, I'll help as best I can.

You run into 3 problems when the motor is spinning fast.
#1, the car can't pull air into the engine fast enough, so it doesn't run well, resulting in no power gains
#2, you risk floating valves or spinning the motor apart.
#3, Friction

Getting the motor to rev higher involves making things stronger, reducing mass, and getting air into the engine. Tougher springs help keep the valves from floating (where they stay open and don't close VERY BAD), lighter valves, cams, and crankshaft reduce rotating mass and make it easier to spin at high speeds. A better camshaft grind, and maybe new heads helps flow air into the engine when it's spinning quickly.

Reducing friction is a matter of lubrication, and proper materials. If you browse the web and look for some tech sites on the S2000 motor (I THINK it's the KA20 or something) you'll find ALOT of info on what they did to give that car a 9000RPM redline.

I'm sure there is MUCH more to be explained, but that's a quick summary.

Oh yea, the bore and stroke of the cylenders does come into play, but sadly I can't remember exactly which is better. Maybe someone else can expand on what I said.
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Old 11-07-2001, 02:11 PM   #3
Frank Army
Member#: 1457
Join Date: May 2000
Chapter/Region: SWIC
Location: Phoenix, AZ
1999 Outback Sport
Steel Blue Mica


a moving we will go....
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Old 11-07-2001, 02:30 PM   #4
Scooby Guru
Member#: 6551
Join Date: May 2001
Chapter/Region: MWSOC
Location: Carol Stream, IL
'01 GC8 Dinged STM
'09 Concours 14 ABS Black


shorter stroke and bigger bore makes a car rev faster...long stroke and small bore doesn't.
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Old 11-07-2001, 03:10 PM   #5
Scooby Specialist
Member#: 1871
Join Date: Jul 2000
Location: Salt Lake City, UT
2000 Impreza 2.5RS
Blue Ridge Pearl


not quite true... shorter stroke allows the engine to rev faster because the pistons move less and slower(relative to the longer stroke) making it easier to throw them back and forth... a bigger bore doesn't help revability, but you will need a bigger bore to provide the same displacement and therefore better torque... actually, all things being equal(but really, when are they ever?) small bore, small stroke would rev highest because pistons would be lighter and more "tossable".
...but in reality, you are always making compromises between cost, horsepower, torque band, and everything...
oh, yeah... one other thing, short stroke is easier on the block as there is less angle at which the piston is being forced into the side of the cylender.... but again... there's always compromises
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Old 11-07-2001, 07:04 PM   #6
Scooby Newbie
Member#: 10118
Join Date: Sep 2001
1991 Pimpssan

Default sorry everyone...

I figured since i heard all of this information in the forced induction forum, figured i should ask about it there. I also figured the fact that adding a turbo in the mix will shake some things up. Please tell me if this makes a difference.
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