how an adjustable cam pulley works?

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how an adjustable cam pulley works?

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tictac	Mar 20 2011, 03:57 PM Return to original view \| Post #1
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	QUOTE(alamdamai1 @ Dec 3 2009, 09:02 AM) planning to do this mod very soon....but before that, need the help of Sifus here... i've noticed the cam timing for our 4G15 is different between a Carbie and EFI models..append below is the spec sheet... hence, can anyone confirm this and if so, would it be worthwhile to change my stock Carbie Cam to the EFI version for better engine efficiency as the exhaust valve timing for the EFI opens later compared to the Carbie model... members advise is highly appreciated...many thanks... that is 16valve 4g15 datasheet... we only have 12 valve 4g15....
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tictac	Mar 21 2011, 11:00 PM Return to original view \| Post #2
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	QUOTE(tictac @ Mar 20 2011, 03:57 PM) that is 16valve 4g15 datasheet... we only have 12 valve 4g15.... 4g15 12valve (fuel injection) stock Camshaft profile - Intake Valve open : 17 degree BTDC - Intake Valve Close : 55 degree ABDC - Exhaust Valve Open : 59 degree BTDC - Exhaust Valve Close : 17 degree ATDC Intake : 252 degree Exhaust : 256 degree This post has been edited by tictac: Mar 22 2011, 06:51 AM
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tictac	Mar 22 2011, 07:57 AM Return to original view \| Post #3
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	Even with Stock camshaft... the adjustable cam can tune Air Fuel Compression efficientcy. This is with Adjustable cam + Stock 4G15 EFI Camshaft : Stock 0 Degree : Air Fuel Compression 69% Efficiency Advanced 2 Degree : Air Fuel Compression 70% Efficiency Advanced 4 Degree : Air Fuel Compression 71% Efficiency Advanced 6 Degree : Air Fuel Compression 72% Efficiency Advanced 8 Degree : Air Fuel Compression 73% Efficiency Advanced 10 Degree : Air Fuel Compression 75% Efficiency
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tictac	Mar 24 2011, 08:18 PM Return to original view \| Post #4
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	QUOTE(drexchan @ Mar 24 2011, 05:55 AM) 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. =] I think i calculate wrongly Added on March 24, 2011, 8:41 pm QUOTE(tictac @ Mar 24 2011, 08:18 PM) I think i calculate wrongly it 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
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tictac	Mar 24 2011, 09:22 PM Return to original view \| Post #5
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	QUOTE(drexchan @ Mar 24 2011, 09:13 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
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tictac	Mar 24 2011, 09:51 PM Return to original view \| Post #6
Member Elite 2,520 posts Joined: Jan 2003 From: Sibu	QUOTE(drexchan @ Mar 24 2011, 09:29 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. thank you
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