NewCelica.org Forum banner
1 - 5 of 5 Posts

·
Registered
Joined
·
1,678 Posts
Discussion Starter · #1 ·
Is it safe to say that a cam is only capable of providing power to a limited RPM range? Looking around at different cars it seems about 7k RPMs is the max that any single cam is still effective. Any car that revs 7500+ appears to need a second cam to provide the correct intake & exhaust valve timing.

------------------
<FONT size="1">Joe -- <FONT COLOR="#666666">2000 liquid silver Celica GT 5spd</FONT c>
<FONT COLOR="#550055">Best time: 15.07 @ 90.74 mph</FONT c>
Member of dcm<FONT COLOR="red">7</FONT c>gen
<FONT COLOR="red">Injen</FONT c> CAI <FONT COLOR="red">\\</FONT c> TRD exhaust <FONT COLOR="red">\\</FONT c> TRD springs <FONT COLOR="red">\\</FONT c> A'pexi S-AFC <FONT COLOR="red">\\</FONT c> 17" Omni Crescents wrapped in Yokohama Paradas <FONT COLOR="red">\\</FONT c> <FONT COLOR="#4444CC">hyper-whites</FONT c> all around <FONT COLOR="red">\\</FONT c> altezza lights <FONT COLOR="red">\\</FONT c> <FONT COLOR="blue">Indiglo</FONT c> white face gauges <FONT COLOR="red">\\</FONT c> <FONT COLOR="blue">Blue</FONT c> footwell neons <FONT COLOR="red">\\</FONT c> Clear corners <FONT COLOR="red">\\</FONT c> Painted <FONT COLOR="red">calipers</FONT c>, <FONT COLOR="#666666">rotors</FONT c>, <FONT COLOR="red">engine plastics</FONT c>, <FONT COLOR="blue">interior</FONT c> <FONT COLOR="red">\\</FONT c> Momo Combat knob <FONT COLOR="red">\\ </FONT c> etc. </FONT s>
 

·
Registered
Joined
·
2,430 Posts
I agree that a certain cam profile performs best in a certain rpm range.

But there's no need for multiple cam profiles to achieve high-rpm performance. You can achieve almost 300hp/L normally aspirated with a single cam profile (I pretty sure F1 engines use a single cam profile, and they get >800hp from 3.0L).

And for street cars, the new BMW M3 revs to 8000rpm and makes over 100hp/L with a single cam profile (it does use Double-VANOS variable valve timing, which is like VVT-i on both the intake and exhaust cams).

But many high-rpm street cars feel the need for multiple cam profiles is due to the wide operating conditions encountered by street vehicles. We have to get good idle/fuel economy/driveability/etc. as well as high-rpm performance. If you have a single cam profile, you'll have to sacrifice for maximum high-rpm performance (thus the lopey idle was born <IMG SRC="http://www.newcelica.org/ubb/smilies/cwm1.gif" border=0>).

A system with variable cam timing can expand the operating range of a single cam profile (Toyota VVT-i, BMW VANOS, Porsche Variocam, etc.), and a system with muliple cam profiles gives multiple operating ranges to choose from (VTEC), but a system with multiple cam profiles and variable valve timing is the ideal (VVTL-i, iVTEC).

------------------
<IMG SRC="http://wsphotofews.excite.com/020/mb/x9/xq/1y77575.jpg" border=0>
<FONT size="1"><FONT COLOR="GRAY">2000 TOYOTA CELICA GT-S 6 SPEED</FONT c></FONT s>

<FONT COLOR="#0000ff" SIZE="1" FACE="Verdana, Arial">This message has been edited by vvtlikick on November 07, 2001 at 12:12 PM</font>
 

·
Registered
Joined
·
1,678 Posts
Discussion Starter · #3 ·
Originally posted by vvtlikick:
But there's no need for multiple cam profiles to achieve high-rpm performance. You can achieve almost 300hp/L normally aspirated with a single cam profile (I pretty sure F1 engines use a single cam profile, and they get >800hp from 3.0L).

And for street cars, the new BMW M3 revs to 8000rpm and makes over 100hp/L with a single cam profile (it does use Double-VANOS variable valve timing, which is like VVT-i on both the intake and exhaust cams).
Awesome.

With the M3, how the hell is that single cam doing 8k RPM without retarding the timing on the intake valve? I hear this is really inefficient because the timing is more inaccurate. Is this true, or is this somehow possible to keep the intake valve timing accurate? If so how is that designed?? <IMG SRC="http://www.newcelica.org/ubb/smilies/cwm15.gif" border=0>

How the hell do F1 cars get 800hp from 3L!? LOL
 

·
Registered
Joined
·
427 Posts
Originally posted by Maelfyn:
How the hell do F1 cars get 800hp from 3L!? LOL
Can you say 18,000 RPM

Thats done by alot of diff things nematic valves and a bore thats 2x the stoke if i remeber correctly. I got a paper at home that chui gave me it tells all about it.
Where is that guy anyway?
 

·
Registered
Joined
·
2,430 Posts
Originally posted by Maelfyn:
Awesome.

With the M3, how the hell is that single cam doing 8k RPM without retarding the timing on the intake valve? I hear this is really inefficient because the timing is more inaccurate. Is this true, or is this somehow possible to keep the intake valve timing accurate? If so how is that designed?? <IMG SRC="http://www.newcelica.org/ubb/smilies/cwm15.gif" border=0>

How the hell do F1 cars get 800hp from 3L!? LOL
Just to make sure we're on the same page, the new M3 is a 3.2L Inline Six with Dual Overhead Cams. It has variable valve timing on both the intake and exhaust cams (two continously adjustable cam gears).

VVT-i engines have variable valve timing on the intake side only (with the exception of the Dual VVT-i in the Altezza).

And I'm not sure I understand your M3 question about retarding the cams and inaccurate timing.

But I think the M3's camshafts are not as performance-oriented as the big cam portion of VVTL-i and DOHC VTEC engines, but the M3 uses other design features to achieve the desired revs and power, such as 6 electronically-controlled throttles, variable-length intake runners, etc. (I might be wrong about one of these factors, cause I'm going from memory). If the M3 did have a well-designed "big" cam to switch to, I would make even more high-rpm power with more midrange and low-end to (but I don't think it lacks any power).

The next M3 should be more impressive still, because I'd expect it to use BMW's new Valvetronic infinitely variable valve lift system (I'm not sure if Valvetronic incorporates variable valve timing too, but I'd guess it will soon, if it doesn't already). Valvetronic is pretty cool, because it eliminates the need for a throttle valve, the valve lift is adjusted to do the throttling (WOT = big lift, cruise = tiny lift).

As for the F1 cars making >800hp from normally aspirated 3.0L V10 engines, that's what you get when you sink a couple million into the performance of an engine. But the major physical reason is the colossal revs, peaking around 18,000rpm.

------------------
<IMG SRC="http://wsphotofews.excite.com/020/mb/x9/xq/1y77575.jpg" border=0>
<FONT size="1"><FONT COLOR="GRAY">2000 TOYOTA CELICA GT-S 6 SPEED</FONT c></FONT s>
 
1 - 5 of 5 Posts
Top