Intake Cam Theory
Sep 1, 2005, 09:01 AM
#1
Intake Cam Theory
The stock Evo Intake Cam has a longer duration than the stock Exhaust Cam. They both have the same amount of lift.
Vishnu (fidanza) gears applied to the stock Evo cams at a -5/-5 setting seem to maximize the performance of the stock cams (probably because the offset remains in the duration among the intake and exhast cam).
People who use 272 intake and 272 exhaust cams get a "lopey" idle. Their low end torque seems to suffer aswell where thers not longer is an offset among the cams in terms of duration. However adjustable cams gears set to -4/-1 make a difference where again (this seems to return an "offset setting" to the 272/272 cams).
So here's my question:
On stock cam gears, would it be beneficial to increase the duration of only the Intake cam (leaving the stock Exhaust cam alone)?
Many thanks in advance...
Vishnu (fidanza) gears applied to the stock Evo cams at a -5/-5 setting seem to maximize the performance of the stock cams (probably because the offset remains in the duration among the intake and exhast cam).
People who use 272 intake and 272 exhaust cams get a "lopey" idle. Their low end torque seems to suffer aswell where thers not longer is an offset among the cams in terms of duration. However adjustable cams gears set to -4/-1 make a difference where again (this seems to return an "offset setting" to the 272/272 cams).
So here's my question:
On stock cam gears, would it be beneficial to increase the duration of only the Intake cam (leaving the stock Exhaust cam alone)?
Many thanks in advance...
Sep 2, 2005, 10:08 AM
#2
The factory cams make for clean emissions, but don't have enough duration for best power. The short duration means the intake valve closes too early, which is why they respond somewhat favorably to retarded timing.
With a longer duration cam, less retard is needed to maximize peak power. The -4/-1 setting for the HKS 272s makes good power, but the reduced overlap from this setting (which gives a smooth idle) increases lag.
If you increase the duration of the intake stock cam only, that will increase power, but the reduced exhaust scavenging will not be of benefit.
With a longer duration cam, less retard is needed to maximize peak power. The -4/-1 setting for the HKS 272s makes good power, but the reduced overlap from this setting (which gives a smooth idle) increases lag.
If you increase the duration of the intake stock cam only, that will increase power, but the reduced exhaust scavenging will not be of benefit.
Sep 2, 2005, 05:55 PM
#4
Originally Posted by Ted B
The factory cams make for clean emissions, but don't have enough duration for best power. The short duration means the intake valve closes too early, which is why they respond somewhat favorably to retarded timing.
With a longer duration cam, less retard is needed to maximize peak power. The -4/-1 setting for the HKS 272s makes good power, but the reduced overlap from this setting (which gives a smooth idle) increases lag.
If you increase the duration of the intake stock cam only, that will increase power, but the reduced exhaust scavenging will not be of benefit.
With a longer duration cam, less retard is needed to maximize peak power. The -4/-1 setting for the HKS 272s makes good power, but the reduced overlap from this setting (which gives a smooth idle) increases lag.
If you increase the duration of the intake stock cam only, that will increase power, but the reduced exhaust scavenging will not be of benefit.
What would you recommend on the stock cams in terms of gear settings. The stockers are offset (Intake longer duration than Exhaust). Shiv says -5/-5 for the Fidanza Gears and -2/-2 or -3/-3 for the HKS Gears. Many thanks for your wisdom
Sep 4, 2005, 08:12 AM
#5
Originally Posted by atlvalet
So Ted B, I don't know if you've seen the thread from SilverSurfer on 272s, but he experienced the best results with a -4/-1.5 setting on his cam gears. Vishnu recommends -3/-3. What are your thoughts and preferable settings?
Sep 4, 2005, 08:21 AM
#6
Originally Posted by 4-BNGR
What would you recommend on the stock cams in terms of gear settings. The stockers are offset (Intake longer duration than Exhaust). Shiv says -5/-5 for the Fidanza Gears and -2/-2 or -3/-3 for the HKS Gears. Many thanks for your wisdom
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Sep 6, 2005, 02:37 PM
#12
I would be very careful about using any advanced setting and/or a setting that tightens the LSA with 91 oct fuel. These settings increase low speed and midrange cylinder pressure, which quickly exposes the limits of the fuel, especially if the car is weighted down and under load.
Sep 6, 2005, 02:48 PM
#14
LSA= Lobe Separation Angle - Decreased LSA is what you get when you retard the exhaust cam with respect to the intake, and/or advance the intake cam with respect to the exhaust. Tightening the LSA increases overlap and affects cylinder pressure, but makes the engine more detonation prone.
Post Katrina leaves me with a flooded home and gone are most of my personal possessions. Of course, since I cannot even get to my home (flood water), I can only imagine the status of things at this point in time.
Post Katrina leaves me with a flooded home and gone are most of my personal possessions. Of course, since I cannot even get to my home (flood water), I can only imagine the status of things at this point in time.
Sep 8, 2005, 01:56 AM
#15
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I have already tried a -4 on the 272 intake cam alone on my Evo 6 with a TD-0625G turbo kit. No doubt it picked up 10 WHP at the top but the sacrifice in spool up and how hard the midrange hits at zero position is not worth it. I'd be inclined to stick to -2 or 0.
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