Toymods Car Club Inc: Tech & Conversions => 3SGTE Camshaft Specifications

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Toobs
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I Supported Toymods

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Sydney
Registered:
December 2002

Re: 3SGTE Camshaft Specifications

Wed, 15 June 2005 03:49

Heres some info about degreeing your cams.
Also some reasoning behind the HKS 272 / 264 combo that all the 3S guys in the UK and USA seem to run.

Quote:

Cam timing should never be done according to marks on the cam gears but rather according to the lobe center of the cams in correlation to the cranks position.
Performance cams should always be degreed. Marks on the cam gear is only there to help when degreeing not to use as a standard to set.

Reason being:

What happens if I install a thicker gasket? both cams now advance
What happens if I install a thinner gasket? both cams now retard
What happens when I deck/mill the head ? both cams now retard
What happens if I deck/mill the head , install a thicker or thinner gasket?
What happens when I put a new cam belt on?

Too many variables to mention but I hope the point cam across.No two engines are the same therefore my suggestion too always degree the cams and not work of the marks on
the cam gear. It might bring you close but close in my books is not good enough especially if you spend $800 - $1000 on adjustable gears and cams.

Also remember that the HKS cams available for the 3S-GTE are not designed for the Turbo engines but rather for the 3S normal aspirated engines.It has been standard
practice to make the exhaust duration longer than the intake duration on a normal aspirated engine. This has been done to promote scavenging and increase cylinder pressure
at high RPM because overlap is longer and one can run narrower LSA's (Lobe Separation Angles) Applying the same methods to a turbo charges engine will not have the
desired affect because turbo charged engines does not make use of scavenging and reversion caused by larger overlaps can cause havoc.

Keep in mind that in a turbo charged engine exhaust pressure is almost at all times (99.95%) higher than intake pressure.
Reversion, when air flows the opposite direction than what it is suppose to flow, must at all times be prevented in a turbo charged engine.
If not compressor surge will occur which can result in serious damage.

If we take a set of 264 cams we will see that the inlet opens at 4 BTDC and closes at 43 ABDC for LS of 110 degrees and the exhaust opens at 36 BBDC and
closes at 10 ATDC for a LS of 103. This gives us an overlap of 14 degrees and a total LSA of 7 degrees. Not good for a smooth idle even worse when it comes to reversion

Now let's increase the exhaust cam to 272 degrees. Intake still opens at 4 BTDC and closes at 43 ABDC for a LS of 110 degrees, but exhaust now opens at 45 BBDC and
closes at 9 ATDC for a LS of 108. This now Gives us an overlap of 13 degrees and a LSA of 3 degrees.

Let's now go the opposite way, increase the inlet cam to 272 but change the LS for the 264-exhaust cam to 112. Inlet opens at 8 BTDC and closes at 47 ABDC
for LS of 110 degrees and the exhaust opens at 44 BBDC and closes at 0 ATDC for a LS of 112. This gives us an overlap of 10 degrees and a LSA of 4 degrees.
Less change for reversion and great for cylinder pressures.
A couple of things are achieved: longer fill period for a more powerful combustion which in turn will lead to a higher volume of exhaust gases with a higher initial
pressure, smaller overlap which will prevent reversion, longer effective exhaust duration which will help spool faster and stronger because of the higher cylinder pressures
and larger volume of exhaust gases present when the exhaust valve starts to open.

Test this on the dyno?

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