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-   -   Valve timing "experiment" (http://www.fuelly.com/forums/f8/valve-timing-experiment-3775.html)

skewbe 01-29-2007 04:49 PM

Valve timing "experiment"
 
I had to do my timing belt and was intrigued by lots of posts on teamswift.net regarding advancing the cam timing (not the ignition timing).

The concept is real simple (at least on a metro), I took off the cam timing gear, made a radial line 185 degrees away from the centerline of the existing slot in the direction of rotation (just eyeballed the slot center and had a kids protractor that fit in the gear), then made a hole using my cheesey drill press. since I was WAY off on the distance from the gear center :o I carefully elongated the hole towards the center with a dremel and chain saw sharpening stone. This only took a few minutes and I took my time (grind a little, test fit, repeat) and had a nice snug fit when I was done.

Then I put it all back together with the cam gear on 180 degrees out from where I took it off (don't forget the new timing belt), retarded the ignition and viola, 10 degrees cam advanced.

Note, I've changed so many things in so short a time (and still havent found my timing light) that this isn't much of an experiment, but I did have my best commute yet (49.3 indicated) immediately following this mod, and I was "getting on it". It took off faster and climbed hills better, no doubt in my mind.

This is not a high speed mod, as I understand it, advancing the valve timing is supposed to allow the engine to make peak torque sooner, putting more of your around town driving closer to the engines most efficient rpm. Since I'm never on the hiway, this seems to be appropriate for my situation. Your mileage may vary ;)

Standard disclaimers apply, this info is for entertainment purposes only. This isn't for everyone and you risk really screwing up your engine if you do something wrong.

SVOboy 01-29-2007 04:54 PM

Tempts me to get an adjustable cam gear.

Any plans for testing?

skewbe 01-29-2007 05:54 PM

I don't plan on any specific testing. The anecdotal evidence on the teamswift site is all over the place, so it's an unknown quantity but the general rule of thumb is advancing cam timing yields more mid-low range torque and retarding cam timing yields more top-end horsepower. If I didn't have to take so much junk off I might be more tempted (main pulley, water pump pully, right wheel and some plastic to get to the main pulley bolts, timing belt cover).

An adjustable gear with a seperately removable top part of the timing cover would make a nice test apparatus for the die hard experimenter.

I'm happy with it as is, tromp 'n glide :)

CoyoteX 01-29-2007 06:49 PM

I seem to have slightly better mileage at 5 degrees cam advance on mine but I think it is mainly based on type of driving and speed. I have drilled several holes around my pulley and just sort of mix and match the holes and what notch I put the belt on and I can pretty much hit anything from 0-18 degrees advanced or retarded if I keep playing with it.

You need a timing light though to see what you really ended up with. Set your base timing to 0 then set the cam to whatever you are shooting for then check your timing to see how much it actually moved. Timing lights are pretty cheap if you get a basic one. The dial back to 0 ones are really nice and if you are planning a lot of work on a car they are handy to have.

I tried my car at ~ 3,5,10,15,18 and I like the way 5 feels the best and it seems to put the power right where I need it but it really depends on how you drive. One notch on the belt is 18 degrees btw. And I just take the top bolts off the timing cover and use a tie down strap to hold the cover away while I move the cam sprocket around. Takes like 30 seconds to adjust it that way. I will probably just cut the cover in half this summer and not bother with the top of the cover though.

MetroMPG 01-29-2007 06:55 PM

Quote:

Originally Posted by skewbe (Post 39123)
I'm happy with it as is, tromp 'n glide :)

Funny. New technique name.

Good writeup (and links).

Quote:

Originally Posted by Coyote X (Post 39131)
I just take the top bolts off the timing cover and use a tie down strap to hold the cover away while I move the cam sprocket around.

Think I'll be able to get away with doing that for the cam swap? Or will I have to take the whole cover off?

skewbe 01-29-2007 07:53 PM

A non turbo image might give a better picture. The blue line represents a couple degrees of cam advance on a honda s2000 and also represents 7hp for all RPM's below 5000
http://hondaswap.com/~mike/sedan/200..._timing_lg.jpg

from:
http://hondaswap.com/engine-building...e-build-20867/

SVOboy 01-29-2007 08:02 PM

VTEC hates cam advance.

CoyoteX 01-29-2007 08:07 PM

should be able to for the cam swap. just put the crank on 0 degrees on the timing mark before you do anything so it is easier to line the new one back up. It is an easy swap in warm weather :)

I never take the cover completely off unless I need to change the belt. the cover can bend far enough to get a wrench on the cam sprocket easy. It is real easy to hook a strap to it and pull it way. I hook the other end of the strap on to the wheel or anything that it will stay hooked on. I guess you don't really have to use something to tie it up out of the way but it makes it a lot easier.

rh77 01-29-2007 08:42 PM

You've got a point there...
 
Quote:

Originally Posted by SVOboy (Post 39118)
Tempts me to get an adjustable cam gear.

Same here -- I'm not keen on replacing the whole cam just yet, but the cam gear is another story, and intriguing.

For Hondas this is a pretty common go-fast mod, right?

So for us DOHC-ers: intake, exhaust or both gears?

I would give up top end for low RPM response any day (providing the FE gains are there).

Wondering out loud: a VTEC head swap with 2 fuel efficient cam sets. One for in-town, up to 2000-2500 RPM operation, and the second set for cruising on the highway at higher RPMs to maintain power (but would efficiency increase, hmmm...)

RH77

EDIT: BTW, love the "Tromp 'N Glide" nomenclature.

diamondlarry 01-30-2007 01:55 AM

Quote:

So for us DOHC-ers: intake, exhaust or both gears?
Both can be adjusted but I think the intake is the more important one of the two. We cut an elongated slot in my intake gear and moved it almost imperceptively and the difference was amazing. The torque band seemed to have dropped nearly 2K rpm's. Oroginally peak torque was in the 4000-4500 range and it ended up in the 2000-2500 range with noticeable improvement as low as 1500 rpm's.


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