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Old 09-30-2010, 11:49 AM   #1 (permalink)
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DOHC Adjustable Cam Gears

When adjusting the cam gears on an engine its said you you shift the torque band higher or lower in respect to RPM. I often hear about advancing the exhaust, but what about the intake?

Does anyone have experience with dual cam gears? Id like to shift my torque lower down in RPM where I do the majority of driving, but would like to know how it turned out for others, is there a rule of thumb when advancing and retarding cams (advance one, retard the other), did you have positive results?

Are there any other factors that need to be watched for (reduce timing ect)?

If anyone has some experience Id love to read about it.

Thanks very much

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Old 09-30-2010, 02:04 PM   #2 (permalink)
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Quote:
Originally Posted by Meph View Post
When adjusting the cam gears on an engine its said you you shift the torque band higher or lower in respect to RPM. I often hear about advancing the exhaust, but what about the intake?

Does anyone have experience with dual cam gears? Id like to shift my torque lower down in RPM where I do the majority of driving, but would like to know how it turned out for others, is there a rule of thumb when advancing and retarding cams (advance one, retard the other), did you have positive results?

Are there any other factors that need to be watched for (reduce timing ect)?

If anyone has some experience Id love to read about it.

Thanks very much
don't have any specific experience with your engine but this might help .

Think of valve timing events(intake open/closing , exhaust open/closing) as if it was a SOHC (1 cam) , then split it up to what you want on each cam of DOHC .

Generally advancing SOHC (intake + exhaust) tends to optimize in lower rpm ranges .
when it comes to each cam more valve overlap at TDC =better high rpm and less overlap at TDC better at lower rpm ranges .

from my experiences the affects of say 4 deg advance are small affect but this depends on engine for sure .

Be careful with some interference engines on how much you change timing with adjustable gear (make sure you don't make valve to piston clearance to small ). Probably not a issue with small changes .

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Old 09-30-2010, 06:14 PM   #3 (permalink)
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Ive tried out driving with +4 and +4 and did seem to notice a little bit mroe torque down low, nothing very substantial. As I advanced the intake cam, that controls engine timing I will need to recalibrate my ignition timing aswell.

Ive been reading differnt threads on here and opnions seem devided over advancing or retarding cams to get best results. On a stock car with Variable Valve Timing I believe they advance the exhaust cam in low rpm and retard it in high rpm?

Ignoring the intake cam, would and advance solely in the exhaust cam result in more torque and theoretically more MPG in the 1500-2200 rpm range of an engine with a redline of 7000. Later variation of my engine had vvt on the exhaust cam.

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Old 09-30-2010, 08:01 PM   #4 (permalink)
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Quote:
Originally Posted by Meph View Post
Ive tried out driving with +4 and +4 and did seem to notice a little bit mroe torque down low, nothing very substantial. As I advanced the intake cam, that controls engine timing I will need to recalibrate my ignition timing aswell.

Ive been reading differnt threads on here and opnions seem devided over advancing or retarding cams to get best results. On a stock car with Variable Valve Timing I believe they advance the exhaust cam in low rpm and retard it in high rpm?

Ignoring the intake cam, would and advance solely in the exhaust cam result in more torque and theoretically more MPG in the 1500-2200 rpm range of an engine with a redline of 7000. Later variation of my engine had vvt on the exhaust cam.

Thank
here info from Honda K24 doc on VTC operation .
----------------------------------------------------------------

Driving Condition , VTC Control, Description


Light-load = Base Position, For stable combustion the cam angle is retarded, and reduces the entry of exhaust gas into the cylinder.

Medium/high-load = Advance Control, Cam phase angle is controlled to optimize valve timing, improving fuel efficiency and reducing emissions.

High speed = Advance-Base Position, To reduce pumping loss, the intake valve is closed quickly. This gives the air/fuel mixture a charging effect that helps to maximize engine power.

VTC System
The VTC system makes continuous intake valve timing changes based on operating conditions.
Intake valve timing is optimized to allow the engine to produce maximum power.
Cam angle is advanced to obtain the EGR effect and reduce pumping loss. The intake valve is closed quickly to reduce the entry of the air/fuel mixture into the intake
port and improve the charging effect.
The system reduces the cam advance at idle, stabilizes combustion, and reduces engine speed.
If a malfunction occurs, the VTC system control is disabled and the valve timing is fixed at the fully retarded position.
------------------------------------------------------------
when you say you advanced +4, +4 , you mean both cams 4 deg .
I think it depends on the cam timing as to what can be improved when altering just 1 cam .
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Old 09-30-2010, 08:29 PM   #5 (permalink)
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You would be looking to advance the intake and retard the exhaust. Running both at +4 would negate the gains of the one with the losses of the other. When we were doing some work on a motorcycle engine for another application, we pulled a significant amount of overlap out of the engine. Stock was 110 degrees crank. I believe we removed 24 degrees total. Take your +4 on the exhaust and go -4 and tell us how it goes.
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Old 09-30-2010, 10:14 PM   #6 (permalink)
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here some info Google search . This is for DOHC

Cam Gear Tuning | Adjustable Gear Tuning | Cam Wheels

here some info on checking and single cam timing affects.

http://www.enginebasics.com/Engine%2...%20Timing.html

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Old 09-30-2010, 10:44 PM   #7 (permalink)
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Quote:
Originally Posted by autoteach View Post
You would be looking to advance the intake and retard the exhaust. Running both at +4 would negate the gains of the one with the losses of the other. When we were doing some work on a motorcycle engine for another application, we pulled a significant amount of overlap out of the engine. Stock was 110 degrees crank. I believe we removed 24 degrees total. Take your +4 on the exhaust and go -4 and tell us how it goes.

Looking at this picture would indicate that exhaust would need to be advanced and intake retarded to reduced the overlap. is this the goal to low end power gains?

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Old 09-30-2010, 10:51 PM   #8 (permalink)
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overlap increases higher rpm hp, bottom rpm tq not so much.
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Old 09-30-2010, 11:02 PM   #9 (permalink)
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Quote:
Originally Posted by autoteach View Post
overlap increases higher rpm hp, bottom rpm tq not so much.
sorry i think i edited my post as you posted this one, reducing the overlap is the theory behind increasing torque by making better use of the combustion pressures at lower rpm's resulting in greater efficiency/mpg?

meaning Id need to advance exhaust and retard intake?
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Old 09-30-2010, 11:08 PM   #10 (permalink)
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There is definitely a possibility that in my mind, my visual aid was screwed up. Yes, remove overlap. Keep in mind that if you are doing 4 degrees camshaft timing, that would be 8 on the crank.

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