cam timing mod question

[john22re]

I was reading about some of the new engines that shift the intake cam timing on the fly by as much as 25 degrees by using a helical gear on the end of the camshaft. The recent I-VTEC being one example. I think this is done to advance cam timing at low RPMs and retard at high RPMs for performance as well as gas savings. So I was installing a new cam in my SOHC and learned about how to degree the cam with a degree wheel and dial indicator and adjustable cam gear. I learned that advancing the cam slightly was better for low end and retarding for high. My question is if I were able to adjust my cam timing on the fly similar to the DOHC Honda would it help me out on my SOHC. I can't change it too many degrees with only one cam controlling both intake and exhaust and the fabing up of something to do this would be no small task. I was thinking a helical gear controlled hydralulically by oil. Any thoughts would be most appreciated.

John

 

[enginesrus]

You could use a helical spline arangement. Very similar to what Caterpillar used on their 3406 truck engines to advance the fuel injection pump. It had fly weights that would control the amount of advance. You could use a similar arrangement with electronic control or even manual control if you desired.

 

[zimbali]

Generally speaking you have to advance MORE for high engine speeds. It also depends on the load. there was a SOHC vtec in early honda models (if I remember correctly) that could be useful in your case. you might need to change your ECU as well as it controls the camshaft advance degree.


Cheers


You can live in your car, but you can't drive your House!

 

[overmod]

Take a look at the BMW Valvetronic actuation mechanism. You might, in fact, be able to adapt some of these parts to your specific application.

A shifting-cam approach, although involving much more initial complexity in cam design and grinding, does allow the exhaust-cam optimization to follow a different profile from the intake cam lobes. There is no physical reason you couldn't combine a longitudinally sliding cam with a variable-angle hydraulic advance adjustment, although consequences of mechanical or control failures become more severe.

You might also arrange to shift the followers for one class of valves (intake or exhaust) or for one set of valves in a multivalve engine (e.g., a 'pilot' or smaller intake valve in a 4-valve configuration) which would give you some interesting possibilities. (A shifting cam with mostly 'conventional' lobes would have similar effect...)

There is some interesting work on electronically-valved hydraulic lifter/followers, which effectively modify the cam profile. When these are supplied with high-pressure oil, they can become a method of adjusting duration upward as well as downward, even if they don't become full cam replacements.

Can't you hardly wait for the fully-electronic valve actuation that's just around the corner?

RME

 

[Retracnic]

John,

Before you go to all of the trouble of building your own VVT system from scratch, may I ask you what type of engine you are modifying? If the engine in question is from a Japanese manufacturer, then there is a good possibility that the hardware is already available and can be adapted to your engine with a little fabrication. The Japanese tend to design their engines with a great deal of parts interchangeability.

If you could, let me know what specific engine you're planning on using, then we can tackle this problem with a little bit more specific advice.

Good Luck
Bryan Carter

 

[john22re]

Bryan,
The engine is a Toyota 22re. SOHC, 8 valve, 2.4 litre, EFI. Not too exciting I know, but it does have quite a lot of dedicated owners. If existing hardware could be found for easier modification that would be wonderful. I'm looking.
Just in case there might have been a misunderstanding, when I mentioned the I-VTEC engine, the example I was trying to make was not the "VTEC" portion of that engine, but the "I". This I-VTEC is one of the recent versions by Honda that in addition to the variable cam lobe (VTEC), also includes an intake camshaft that advances or retards in realtion to everything else. I think this is called cam-phasing. Here's a site with a better explanation than mine:

http://asia.vtec.net/article/ivtec/

Zimbali,
Not sure, but don't you mean for IGNITION timing? I was under the impression that advancing the cam more was good for improving low end torque. Maybe I'm wrong.

Overmod,
Wow! Yes the Valvletronic includes the same kind of "shifting" intake camshaft I was thinking about (as well as some other pretty incredible stuff!)
I'd like to keep this as simple as possible possibly some type of bolt on for owners of these engines.

I guess bassically what I'm asking is if this cam-phasing approach would work for an older SOHC engine.

John

 

[htwls]

Gentlemen,
I have already a bit of experimentation on a Ford 2.3l sohc engine with this. Advancing the camshaft will halp with the low end torque to and extent. Retarding the camshaft will shift the power band up higher in the rpm band of the said engine. It will vary from camshaft "size" and a few other details, but fact is you can not advance or retard to much or thew valve timing changes could hurt driveability and mileage on a single cam application. As long as you could limit the total amount of advance or retard you could in a sense, lower the powerband of a given cam and extend/broaden the power band of the engine. I was working with a turbo application that seemed to benefit mostly on the upper rpm ranges and retarding about 8-10 degrees. It is the same as degreeing in a camshaft of a standard single cam racing engine. I used a Holley ignition and used rpm switches to trigger solenoids and oil flow. It isn't simple or inexpensive in the least and most likely not cost effective for "Everyday Joe" that drives older vehicles. That is why I am in the middle of using a DOHC cylinderhead off of a Volvo and retrofitting it to my 2.3l Ford...

 

[bigpaul]

Hi we have played vvt on toyota 20 valve engines we have switch it on at verious rpm it made very little diffreace we we found that you could bring it in at tick over and
it would give good power all the way up, it my opinon that
you would be better off with a low duration quick opening
high lift camshaft, the 22 re does not have the best mid range power this route would greatly help the mid range.