Interesting... but need some clarification:

1. degrees as in cam or crank degrees?
2. advance as in advancing the cam (clockwise) or the crank (counter clockwise)?
3. what's A/F comp efficiency?
4. where you get the data from.

TQVM. =]

Why did they set stock 0 degree at 69% efficiency?

I think i calculate wrongly

---

Added on March 24, 2011, 8:41 pmit should be like this...

Stock 0 Degree : Air Fuel Compression 69% Efficiency
Advanced Camshaft 2 Degree : Air Fuel Compression 71.6% Efficiency
Advanced Camshaft 4 Degree : Air Fuel Compression 73.8% Efficiency
Advanced Camshaft 6 Degree : Air Fuel Compression 76.1% Efficiency
Advanced Camshaft 8 Degree : Air Fuel Compression 78.3% Efficiency
Advanced Camshaft 10 Degree : Air Fuel Compression 80.5% Efficiency


Explanation........

A compression stroke consist of 180 degree crankshaft rotation (90degree camshaft rotation)

With a stock 4g15 Camshaft , effective compression stroke is 180 degree minus Intake Valve Close (ABDC)

Stock camshaft have a setting of Intake valve close at 55 degree ABDC
The Effective Compression stroke of a 0 degree stock camshaft is : (180 - 55) /180 x 100% = 69 %

By advancing camshaft setting 10 degree (20 degree crankshaft), Intake valve will close at 35 degree ABDC
The Effective Compression stroke of a 10 degree advance camshaft timing is : (180 - 35) /180 x 100% = 80.5 %

The higher compression efficiency. The more air and fuel is compressed for the Power stroke energy extraction...

Thank you

This post has been edited by tictac: Mar 24 2011, 08:49 PM

My brain went wee wang wang reading your explanation but lets assume that you got it right, have you factored in the effect of advances exhaust valve?

The exhaust valve will open early...
Power stroke will be affected also...

0 degree camshaft (stock) : Power Stroke Efficiency 67%
10 degree advance camshaft : Power Stroke Efficiency 56%

This post has been edited by tictac: Mar 24 2011, 09:23 PM

Exactly. It's all about getting a balanced point between the compression efficiency and power efficiency. While calculations may give you a picture of what's happening, the end result is still pretty much depending on OTR and on-dyno tests.

This is the reason why most DOHC tuners advance the intake and retard the exhaust. While the idea of advancing the intake and retarding the exhaust improve both compression and power efficiency, the high overlapping duration also means poor idling quality and narrow powerband at the high range. That's how high duration camshaft works.

The ultimate questions are - at which rev range the tuner intend to squeeze more juice out of the engine, how much advance, how much retard. The answers come with experience of trial and error, with or without dyno (which just makes things simpler).

Oh yes, just want to point out to you that you have neglected the flow efficiency in the intake and exhaust ports.

This post has been edited by drexchan: Mar 24 2011, 09:38 PM

thank you

Setting also depend on driver preference. When I got mine installed, its setting is for low end, which didn't suits my driving style. So I send it to be re-tuned for high end.

Normally how much for adjustable cam pulley for 4G15 EFI?

I'm guessing about RM 150-200 a piece.

I know Works Engineering selling RM220 for 4G15..but I think its not adjustable..

Sure can adjust what, why can't? If can't, why get it? Why they sell it?

The problem is more of a whether an SOHC can benefit from it or not. A quick search on the Internet says in an SOHC you can only advance or retard the power region, but not increase peak power like you can in a DOHC engine!

Increase hp on dohc?

Yeah, why not? Advance intake retard exhaust? Or other way, I don't know, ask other sifu!

---

Added on March 26, 2011, 8:50 pmYour 4g91 GOOD CANDIDATE!

This post has been edited by GEFORCEXTREME: Mar 26 2011, 08:50 PM

Hehehe.
I dont know la. Already think to buy it since last year. No budget. Huhu

Don't say no budjet la, just get Jasma one maybe? Sell your 2 pc rim to me RM 500! Then you take money go buy! kekeke...

Haha. Heavy r 2 pc. Stock rim is better. Hehe

you mean all cam pulley are adjustable cam pulley?

yes, all aftermarket campulley are adjustable ones... if they arent, might as well no need to change since ur original cam pulley is also not adjustable...

Ok