Info wanted on ajustable cam gears and cams

[maxhag]

hey guys,

I dont know much at all about aftermarket cams and ajustable cam gears and i just wanted to get some info.

At this stage, i am just building my knowledge and not applying to a motor (yet)....

First of all, What do Ajustable Cam gears do? (i know many will laugh, i dont care, i want to know this stuff)
What and where do you benefit from them? When do you need them?
Do they eliminate the need for aftermarket cams?

any info is greatly appriciated.....


Also, Aftermarket cams. At what point do you need them? If wanting more torque? My 4AGTE could do with some more torque down low, would cams help that? What do i look for when purchasing? I have noticed alot on the market, What do other people use?

thanks

J Riftin

[slide86]

baically you use adjustable cam gears to fine tune the cams.

you can adjust when the cams "come on" in relation to each other and crankshaft position.

they can be used them on stock cams aswell as aftermarket ones.

you have to be careful as to what cams to use in a forced induction application, too much duration will cause problems, as the boosted air goes straight out the exhaust cause the valves are open too long.

i am currently looking into getting some higher lift cams, to open the valve further. this should increase the amount of air going into the cylinder but with the same or similar duratuion time. ie the valve is open for the same length of time. it just opens further....if you can understand that
probably something round the 260 degree and 8.5mm lift

you will need to remember also that when upgrading cams its a good idea to get decent quality valve springs.....coil bind is very very ugly

[maxhag]

<div class='quotetop'>QUOTE (slide86 @ Jan 9 2008, 01:14 AM) </div>
Yeah , i can easily understand that...

If you did what you have said above, where would you notice the effect in performance? (ie more air in cyl but same duration?)

thanks

[slide86]

more boost in cyl + more fuel = bigger bang =

[86adz]

i think he's wanting to know at what rev range will the increase in power from that type of modifcation be most noticable or is it just an all round improvment in the power curve?

[johl]

im no pro but by the sounds of the type of cam gears he was going to use it would be an all round improvement as the cylinder is open for the same amount of time and nothing really has changed. thats my assumption anyway till someone proves me wrong?

[maxhag]

<div class='quotetop'>QUOTE (86adz @ Jan 9 2008, 10:15 AM) </div>
correct

[skit]

Guys,

From what I have read, it would be worthwhile if you all read some textbooks on engine theory. I am not flaming anyone - everyone has to learn from somewhere, but what is written in this thread sounds like a very basic interpretation of heresay.

Maxhag, rather than asking a broad question such as yours on a forum, you may be better consulting known resources (such as in textbooks). On any forum you will get a spectrum of answers ranging from B.S. to facts, and everything in between. There is plenty written on this. Two such books that springs to mind are "Four Stroke Performance Tuning" and "Forced Induction Performance Tuning" both by A. Graham Bell. While different people have different theories on tuning, the basic principles are all covered in such books. There are a million others like these too.

For future reference. Cams do not "come on" and "off". I think someone is confused with the term "coming 'on cam'" which is used to describe when an engine enters the phase where it begins to work most efficiently (i.e. pumps air most efficiently). On a lightly tuned engine this is usually not noticable. The opposite can apply for hard tuned motors.

Adjustable cam gears allow you to change the camshaft timing, relative to the crank, and in the case of a 4a-ge, relative to the opposite camshaft. There are different "types" of cam gears, but the only difference is how accurately they adjust. The function is always the same.

Perhaps the earlier reference to cams coming "on" was describing a valve being lifted off its seat. Of course, the transition of valve closed > open is not a matter of on/off. This is dependant on other factors such as cam lobe angle (i.e. how fast the valve is accelerated off the seat and decelerated to point of maximum lift).

Keeping cam duration constant but changing cam timing will still change the characteristics of the engine. Advancing/retarding the valve opening angle (relative to the camshaft) has pronounced effects, as it is relative to where the piston is, and therefore cylinder pressure is affected. Changing the timing of one cam relative to the other changes the "overlap". Someone refered to too much duration being a problem due to lost charge out the exhaust valve, and therefore lost cylinder pressure. To some extent this is a good thing (referred to as overlap breathing) as it helps flush the combustion chamber of old "burnt charge" from the previous cycle which can linger. This is more of a concern for atmo tuning than turbo, as far as I am aware.

Any engine will only work most efficiently over a certain rpm range. We band aid this using technology such as variable ignition and cam timing to try and maximise the efficiency over the total rpm range. Some engines even have adjustable compression ratios. What you gain somewhere you will usually lose somewhere else, all performance is a compromise.

Anyhow, I don't proclaim to be an expert at all, but there is much that can be understood by turning a page.

[maxhag]

All so very true skit....... They are some wise words.... Obviously i do realise that peoples opinions can either be true, or bullshit...... But, you never know when you might learn something new...

I WILL do some reading, are those books you mentioned Australian? But i just thought that someone else on this forums would be using this equipment and therefore know what it's doing to their engine, and give me a few tips etc.....

thanks

J Riftin

[skit]

<div class='quotetop'>QUOTE (Maxhag @ Jan 9 2008, 10:02 PM) </div>The books are written by an Australian fellow, from Maitland I believe. Thinking back, there is a good chance I bought those books from the Pitstop bookshop online. I really can't recall, it was a long time ago. He also has a good two-stroke book too, if you have even more time on your hands!

I agree with you, you can learn alot here - but it helps to know who is providing the answers. There are some people here with a wealth of knowledge & practical experience to back it up. The more specific your Qn's are, the better your answers will be

Good luck.