Timing Advance

[gpse3400]

...Anyways I was changing my timing belt, and being an endorser for response I advanced all the cams. I knew the power band was going to shunted down, not only that but upper horsepower completely gone out the window... surprise surprise. I advanced the timing by a tooth at the lower sproket. Hows it run? Idles fine, night and day torque. Its like fresh 2.8/3.1 on steriods, a dream come true for someone who likes to go, will always smoke the tires and for a good length. Definately a difference, giving it all it has to 5000, The sound of the engine also changes to a hard at work sound at like 2500..... Heres the bad part. A huge power fall off after 5000, 6000 there's a wall. But you can accelerate at lower engine speeds like nothing. Like I said kinda like a fresh 2.8/3.1 but more...But upper HP is gone. So....I tried it.I like it, but the upper power thing is not nice. I'm going to mess with it some more, If it don't work out, it's going right back to stock. Also the dynamic compresson is raised, intially heard some pinging, had to get some high test in there. Well I guess that advancing the timing like that kinda defeats the purpose of multivalves to be used for upper end power... The dyno 2000 shows a modest gain on bottom end by doing this...I really have to differ, like I said its that different. Just thought I'd share...

[ryan.hess]

As I learned before, 1 tooth = 24*, which is quite radical. (1 tooth = 12*, but rotates 1/2 as fast as the crank, so it's actually 24*)

[Anonymous]

I cant believe it would idle with that much advance. I heard that advancing the cams a few degrees kills the power and idle.

[SappySE107]

It idled at 6 degrees advanced, but I could tell it wasn't stock. Power sucked, but I wasn't really testing out off the line power, but rather 4k plus, and the RPM point that power really picked up.

[gpse3400]

Yeah the horsepower is not great at all but the torque is definately somthing to be felt. I mean if you live in a constant busy area like me, you'll really apreiciate it. Sure enough it idles without a hitch. The power is before 5000. There is nothing after. The car will get to 60 in an expedidted rate though. Anyways, I'm going to mess with it some more, I'll probably end up putting it back to stock. Yeah this is where I can see variable timing would have its affects, on all things automotive...but if you got a big enough engine or whatnot, then I guess it really doesn't matter...Oh well, sometimes you can't have it all.... Oh the fuel economy would appear to be the same. The sheer amount of torque is not what I expected, nor was I expecting it sound so appealing at lower engine speeds.

[jmgtp]

if you keep it like that, have a chip burned to get the trans to shift sooner and keep it in the powerband. hell 5000 rpm shifts the trans will love compared to what 6500 for autos (iunno im blessed with a stick :P )?

its the low end producing, top end slashing, trans saving mod!

[gpse3400]

If you want to put it like that yeah. Not for nothing, my transmission is not going to die anytime soon. I mean the HP at 5000 is falling off but below there it hauls. It's kinda refreshing to see that engine operate like that...power band of a truck motor. I call it the New York City Edition TDC. Now I can keep up with the taxis on the 59th Street Bridge!

[Norm '88 GT]

The power drop off is probably the knock sensor stepping in and pulling timing. I have run 45 degrees of advance in the colder part of the winter and the torque is really nice but the power falls off on the top end.

[jmgtp]

just goes to show..... imagine the insane power band we would have with variable valve timing.

[SappySE107]

I doubt you are running 45 degree advanced cam timing on a 3.4 DOHC. We aren't talking about spark timing.

[brian89gp]

I wonder how hard it would be to make a belt sprocket (possibly just the main one, to save costs) to have VVT, bore out the insides and put in the VVT components.

[SappySE107]

you design it, ill test it

[chvyrulz350]

since im guessing you have a 3.4 liter
i know how the cam pulls mount on the cams and how you align them wiht the gm tool
they are held on kind of like a drill chuck it has a lock collar with a beveled edge on the outside that fi in the pulley and uses the bolt to tighten it on the shaft clamping it it would be easy to cahnge the timing
the gm tool bolts down to a threaded hole between the cams with a flat edge that holds the cam from moving because they have a flat edge on them as well
you could make you another tool for holding down tha cams that was adjustable so you and change the cam timing before you re tighten the bolt to hold on the pulleys
this would allow you to adlust the intake or the exhaust cam separately
which then you could advance the intake only to gain more bottom end and retain the exhaust side stock to draw out the power
just my $.02

[SappySE107]

You could make a tool like that to speed up the process. I just set the rear exhaust first, then the front intake, front exhaust, then rear intake. This allows me to set the exhausts retarded and the intakes stock. Its easiest to do the rear exhaust first since it is impossible to pull the lock ring out without pulling the cam carrier (unless you have a different puller that is much thinner...I dont have one.

Or get the 94-95 cam gears and lock rings so you can pull the lock rings out without pulling the gears.

[gpse3400]

Well I just tried retarding the exhaust cams one tooth and leaving the intake advanced. The idle is now rough like it has a cam. It doesn't have the best idle sound though, doesn't have that racy note as much anymore at part throttle, but the HP level is bumped up a few hundred RPM. Torque on the bottom is still rather strong, not as strong as before though. I'm not totally wowed by this adjustment, so when I have time again, I guess I'll throw it back to stock or retard the exhaust and put the intake stock. I tried to spread the cams by retarding the exhaust and keeping the intake advanced relative to center and the engine wouldn't run. But at least we know the TDC can have strong bottom end torque.