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> What is Mild CAM?
keenlui79
post Jul 19 2006, 02:30 PM
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Dear Sifus,

Sorry to be ignorant, but what is mild cam? what is the different from our
stock cams? Is it good to change a mild cam for NA car? If upgrade to BOT,
the mild cam still usable?

I saw an article as below:-
"Despite the above facts, milder cam lobes on blown engines is not always
best. Boost pressure will be maximised but this wont necessarily mean more
power.
When a blower is driven at high engine rpms its efficiency quickly drops
off. It starts to put a lot more heat into the air. More heat means more
boost pressure, but it also means less air density (less oxygen in the
air). With a mild cam, the inlet valve closes early so the air being
forced out of the cylinder has nowhere to go. It gets forced back towards
the blower and therefore registers a high boost value, despite the fact
that its not contributing to higher power. This lobe design reduces blower
efficiency, pushes up temperature, and increases the risk of detonation."
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maddriver
post Jul 19 2006, 08:28 PM
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it all depends on the lift & duration of the cam. there are cam specs
for turbos, there are cam specs for na. unless u are planning for some
serious boosting action, a mild cam should be ok for low boost pressures
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keenlui79
post Jul 20 2006, 02:24 PM
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do you mean it's a longer or shorter valve lifted duration / valve lifting
height by using the mild cam? so if I upgrade with BOT is it necessary to
change the stock cam into the cam for turbo? Thanks Maddriver sifu.
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maddriver
post Jul 20 2006, 11:28 PM
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like i said earlier, if it's a low boost turbo, then no problems running
the standard cam. btw, what car?
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keenlui79
post Jul 21 2006, 01:40 PM
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Proton Waja 4G18 stock. I'm planning to get a BOT, boosting around 0.5-
0.6barg. Is it suitable?
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maddriver
post Jul 21 2006, 07:06 PM
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stock? max boost should be at 0.4bar as the engine compression is high.
ok to use fast road spec cam, but are u going to do the cam first or the
bot first? if bot first, better get a cam that suits your application
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seantang
post Jul 23 2006, 03:21 PM
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The article doesn't make much sense to me. All engines have valves that
need to close at some point in time. The positive manifold pressure
generated by the turbine is there all the time while you're pressing on the
gas pedal.

So, considering that engine rpms are thousands per minute and the valves
open and close once per revolution, there is bound to be times when the
intake air has nowhere to go, no matter the valve timing. So, what's too
early and what's just right on time?

Anyway, it generally doesn't matter what cams a turbo or force inducted
engine has. Of course there are some cam profiles that are optimised for
the turbo size, rpm, power band and boost ranges of each engine, but
generally a turbo simply maximises the amount of air going into the engine
with whatever cams it has.

One caveat is actually going too hot with the cams and producing a lot of
intake/exhaust overlap. But that's not going to be your problem with stock
cams, stock timing or mild cams.
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speedchasr
post Jul 23 2006, 08:57 PM
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Yep, the articles doesn't make much sense because they present it in a
half-baked way or the full article is not pasted in.

It DOES matter what cam profiles to put in a turbo or a NA and it's not
only because of power band, turbo size and etc...

Generally, cams that had a higher degree of overlap will not be conducive
for a turbo application because at higher RPM ranges the degree of overlap
will cost reversion on a turbo engine. Overlap means at higher RPM ranges
the intake and exhaust could open nearly at same time. In N/A application
it's essential for high RPM power because there's no pressure involve which
could push the exhaust gas back into the intake.

On the contrary, with force induction, exhaust manifold pressure could be
double that of the intake manifold depending on your manifold design. That
in a way will force exhaust gas back into the intake valve with high
overlap cams. That's what reversion is.

Turbo application could benefit more from cams that has more lift compare
to more overlap. Again the design of the exhaust manifold is critical.
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keenlui79
post Jul 23 2006, 11:43 PM
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dear sifus,

if i'm going for BOT, I need to find a suitable cam profile / high lift
cam, right? usually what pricing will it be for such cams?

with the cam change, do i need to go for adjustable cam pulley and better
timing belt as well? how about the crank pulley? because i think that with
the force induction system, all the mechanical parts especially pulleys
and belt havta lighten / stronger as well.

i'm not going for a high power car but i preferable my Waja to have around
160bhp to run about.
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jeff82
post Sep 8 2006, 12:33 AM
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so,if change mild cam will + more power or?
how about enjin life spam?
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