www.dodo-upgrades.nl

You do get a lot of turbulence from a bad designed cat.The oem one's are badly designed.A proper designed one has tapers (cones) on both ends.
The entry has have a cone that tapers 5-8° , the exit has to taper 10-12°.

ow thnx for the tip, soon i'm gonna make a new exhaust system, kan look after that.

thnx!

My de-cats are only tapered at the front, the back is straight. Worse?

Yup but those Decat's are small mufflers,i don't think they work the same as a Cat.A race cat has something like 200cels/inch and it has to taper open gently and taper back a little harder at the rear to compress the gasses back in.
But even for mufflers it can help out i think .
If you take a look at most expensive aftermarket mufflers, they all use tapered sections and the beginning and end.The first Foot or so after your header you need to have a straight piece ,or something that doesn't creat turbulence so the gasses can resonate and mix up.So it's more important the closer you are to the merge collector of header and not so much at the center or rear of the exhaust.

Ah I am foolish... now I realize what you mean. Offcourse, my B16B race-cat is double tapered. No idea about the angles, but it looked at least symmetrical to me. Will measure it one time.

Best cam gear timing depends on the tuning parts of your engine and if the car used for daily driven or the track.

If your civic starts making power above 5000rpm then your cam timing is approx 4-5 dgr retarded. Idle is 100rpm under stock

If you have great torque till 5000rpm and no top end then your timing is too advanced. idle is 100rpm over stock.

For DD its good to set timing 1-2dgs Advanded,nice for the consumption too.
For a strong mid to top end set cam timing 1-2 dgrs Retarded.
Dont forget your Ign Timing after playing w your Camgear.

For every 0,8mm shave of your Head go 1 degree Advance at the cam gear to set timing back to zero.

nice nice, i;m gonna remember this post... thnx

79mm wrote:Best cam gear timing depends on the tuning parts of your engine and if the car used for daily driven or the track.

If your civic starts making power above 5000rpm then your cam timing is approx 4-5 dgr retarded. Idle is 100rpm under stock

If you have great torque till 5000rpm and no top end then your timing is too advanced. idle is 100rpm over stock.

For DD its good to set timing 1-2dgs Advanded,nice for the consumption too.
For a strong mid to top end set cam timing 1-2 dgrs Retarded.
Dont forget your Ign Timing after playing w your Camgear.

For every 0,8mm shave of your Head go 1 degree Advance at the cam gear to set timing back to zero.

I took this of D-series.org

Advancing my timing
1) Ignition timing.......advancing the ignition timing beyond 2-3 degress of stock setting may require a higher octane gasoline to prevent pinging/detonation

2) Cam timing...........advancing the cam timing will trap MORE air/fuel mix in the cylinder at low-mid rpms. The result will be higher combustion pressures. This may require a higher octane gas also. You can advanced the cam too far and damage the vales.

3)worst case issue........advancing the cam timing without readjusting the igntion timing afterwards will equal a combo of 1) and 2) and you can hurt parts.

So we are almost always going to retard our cam timing and advance our ignition timing.



I ever post a diagram with something we talking about:
Milling head or decking block would retard your timing.1mm milled of the head retards your cam gear 1 degree.
So you must advance your cam gear.
http://www.d-series.org/forums/attachme ... having.jpg


On a sohc:
-If you advance cam timing, you will have more bottom end power and lose some peak power up top.

-If you retard cam timing, you will lose some bottom end power and gain power up top.

Generally, advancing the timing will give you better throttle response and low end power along with improved fuel economy. Retarding the timing will reduce the chances of detonation and provide a safer condition for boosted motors or N2O motors.

Running a spark advance that is too extreme for a given setup can yield disastrous results. Be sure to consult a professional before attempting to change your ignition timing.

These are timing marks on a OBD1 crank pully


On a D14 they're the same but The timing marks are 10-12-14 ° and they are colored black-Red-black

very useful topic!

Nice! Joris has said that with stock cam you can play with the cam timing (having an aftermarket cam gear) and get some extra power. Is this true?