popping through the exhaust at 4500 rpm or so.. HELP!

[Mike W]

Zedyone,

I just purchased a wideband from FAST in order to dial in a new set of Webers I am installing. I also purchased the probe adapter that can be used at the exhaust, so I do not have to have an adapter weleded into my header or exhaust. This also makes it portable to other cars. If you would like I would happy to bring this along to the Texas Z Car rally for you to try out if you haven't solved your problem by then.

Just let me know.

Mike.

[Zedyone_kenobi]

how about a link to said FAST wideband!

I will let you know!

[Mike W]

Here you go.

http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=FS&Product_Code=170401&Category_Code=Gas

Mike.

[Jetaway]

Don't know if carb heating could cause the problem, but I'm very sure that lack of carb heating won't cause this problem. The line was clogged when I got the car and I've since bypassed the intake manifold coolant pass through and in a climate slightly cooler (not much!) don't experience these symptoms.

Timing Chain? I don't know what symptoms a tired, stretched, worn timing chain produces, but it would make sense that they are most noticeable at higher RPMs when the timing of events become more critical. Thinking about it, a loose timing chain has a direct effect on ignition timing and have also, in effect, altering the cams lift and duration. By the latter, I mean that, say, the maximum lift is designed to occur when the piston is at position X and if play in the timing chain causes maximum lift to occur at position X + Y, less air will be able to enter (or leave) the cylinder than designed. Altered duration would be even worse -- it couldn't possibly be a good thing if an intake valve hasn't fully closed when ignition occurs or an exhaust valve remaining open longer than designed during the intake stroke.

Chris

[Jetaway]

Oh, and I assume the symptoms of a worn timing chain would become worse with time.

Chris

[LeonV]

All a worn timing chain does is slightly retarding cam timing, which shifts the powerband up. You will have a bit more power up top and a little less down low. It has zero effect on ignition timing. Cam lift and duration are unchanged, just valve timing changes. The intake valve will definitely be closed by the time spark should occur.

[Jetaway]

All a worn timing chain does is slightly retarding cam timing, which shifts the powerband up. You will have a bit more power up top and a little less down low. It has zero effect on ignition timing. Cam lift and duration are unchanged, just valve timing changes. The intake valve will definitely be closed by the time spark should occur.

You're right about ignition timing as even with a worn timing chain the dizzy will match up with the crankshaft. I am aware that the actual physical measurements of lift and duration are unchanged, what I was trying to suggest was that because the cam would become slightly out-of-synch relative to the crankshaft as the engine was designed, the retarding effect on cam timing, minus any jittering caused by wear, would be duplicated by an engine with a unworn timing chain but an altered from stock cam grind. A worn timing chain is somewhat like a mis-installed cam and to take an extreme example, if the cam were installed sufficiently out of phase, the measured lift and duration would have no effect on engine operation as the opening of the intake valve during the power stroke won't cause a fresh air-fuel mixture to enter the cylinder.

Interesting that you say a worn timing chain would produce a bit more power high and less low. I would think the opposite. Why would retarding the cam produce more power at high RPMs?

Chris

[madkaw]

Retarding the cam timing WILL move the power up in the rpm range.

I think we might be overthinking this a bit when we start worrying about cam timing. There are too many basics that are overlooked and mis-diagnosed in these instances. Not saying the OP is not bright enough or anything like that, it is just the way these things turn out. How many posts have we read that the OP says "oops", forgot to check that, or I swore I looked at that.Sometimes I go back over the basics and find a loose wire that I didn't catch the first time.

[LeonV]

Retarding the cam timing WILL move the power up in the rpm range.

I think we might be overthinking this a bit when we start worrying about cam timing. There are too many basics that are overlooked and mis-diagnosed in these instances. Not saying the OP is not bright enough or anything like that, it is just the way these things turn out. How many posts have we read that the OP says "oops", forgot to check that, or I swore I looked at that.Sometimes I go back over the basics and find a loose wire that I didn't catch the first time.

Precisely. A slightly stretched timing chain is not the problem.

[Jetaway]

I suggested timing chain because apparently it hadn't been checked and the problem existed before the recent upgrade / rebuilds.

I believed you when you said a worn timing chain would produce a bit more power at the high end, what I am still curious about is why, or how. Is it because the factory position is a compromise between low and high RPMs? That a slight delay, for example, in the intake valve opening puts the valve opening during a period of higher vacuum created by the intake stroke than the original factory setting? Which would seem to explain variable cam timing found on some newer cars.

So, just for reference, what are the symptoms of a badly worn timing chain or badly worn sprocket teeth? Really poor low-end with a strong high-end?

Chris

[madkaw]

We might be hijacking this thread at this point, so I think we should get back to this issue at hand.

I know your wanting this wideband-which is very useful. I will say that for my engine, that has a lot of performance upgrades(still a L24 though) the SM needles are too much for that engine. I have gone back to stock needles and under WOT the SU's provide plenty of fuel with stock jets--VERIFIED with the wideband. If anything, you might be too rich with your set-up. How are the plugs looking?

Have you tried running without your vacuum advance hooked up? I bet you could run more intial and final without it installed. I would take it out of the system to make sure it's not messing up and then you can hook it back up.

Look at your dizzy cap closely for cracks also!

[Zedyone_kenobi]

Good info on the SM needles.

I will ping Z therapy tom get his recommendation on those needles as well