Spec_Ops2087

I think its actually true now that I think about it. When I had my VAFC2 installed for a little amount of time, it logged the highest rpm attained every time it was turned on. When I did a redline shift bouncing off the limiter it logged in around 8992ish rpms. Never went above 9 grand...

RED MX5

[QUOTE=krazik,Nov 11 2006, 01:39 AM]Red:
The link works fine.



He doesnt' say it cuts at 9000 but between 8900 and 9000.

RED MX5

Yea, it sounds to me as if the fuel cut is just before 9,000 RPM, but the tach (and shift beeper) are both a little optimistic.

Do you know what signal the VAFC2 used to determine engine speed?

RED MX5

It's funny that this came up in a retainer thread, but I'm glad it did. It's always cool to learn something new and get shed of a little ignorance.

RED MX5

That's interesting too. At what engine speed does the tach flash? When I shift at the flash the shift beeper records 8,900 RPM. Isn't that the correct RPM for the tach to start flashing? If so, doesn't that say that the tach and beeper are both showing the same thing (at least at that one engine speed)?

I have the beeper set up for 300 RPM intervals, so I get a beep at what it thinks is 8000, 8300, and 8600, and then a continuous tone at 8900 (which coencides exactly with the tach flashing). Maybe I'm missing something, but it appears that the only time the beeper/memory is in error is when it shows 9100 at fuel cut. That is, unless the tach itself is inaccurate (and Modifry said it was).

Heck, I don't know what to think now. My beeper and tach agree, in that the beeper beeps at the correct intervals and engine speeds as indicated by the tachometer. The only thing it is (apparently) getting wrong is the 9100 RPM memory value that it records when I hit the rev limiter. In any event, shifting using the beeper is just as accurate as shifting using the tach, and since they agree, it seems to be a non-issue (in that it doesn't really matter). If the beeper-memory is off a little at 9k and above it doesn't really matter, because it will still tell on me if I over rev the car enough to do any damage.

I think you're right Mike; Both the tach and the beeper have an accuracy of +/- 100 RPM. They seem to agree all the time, and the beep intervals are constant enough to allow accurate shift timing. Now I'd like to know if the errors come from a common source or if they're just too small to matter. LOL, if my tach and/or shift beeper is going to have an error I'd rather have it reading 100 RPM too high than 100 RPM too low.

mikegarrison

I'm pulling the tach signal off the same wire for the beeper and the datalogger. A different wire feeds the ECU, which drives the tach display. But it's probably the exact same signal.

What happens afterwards, though, depends on the computers using that signal. The accuracy of reading the signal depends on the sampling rate. Let's assume they are all sampling often enough to be reading the signal correctly.

Then what happens? With the datalogger, it feeds the display and also records to a file. I'm not sure what the rate of either of those is. But if the RPM suddenly shot up and back down again faster than the datalogger was recording, you could miss the event. The data logger is logging multiple times per second, though, so RPM isn't going to change that quickly.

The beeper is just watching the RPM and going beep if it hits certain levels. It was never really designed as a datalogger, so the memory of the peak RPM is not necessarily very accurate. I don't know how often it checks to see if the current RPM is higher than the saved RPM.

The ECU is reading the RPM and then doing a lot of things with it. One of those things is the fuel cutoff. Another is deciding how many bars to show on the tach.

All of these probably have some time averaging built in to them, to avoid giving spurious signals.

kentarou

When lot of ppl are talking about broken/cracked retainers result in a dropped valve....

Do they mean the valve is physically sitting lower than it should??

Since cam lobe doesn't change, the valves should be going up and down at a set distance regardless of the valve sitting high or low...which means that if the valve is dropped due to a cracked retainer, you should have a low compression then...
Because now the valve goes down further...but will only come up so high....
the valve will no be sitting tight against the valve seat...
So the engine should have low compression..plus it will not run probably because
the engine is not getting all the air/fuel mixture 100% compressed and the
combustion will not be complete due the that "dropped" valve is always little open

Might not be noticible at higher rpm...but should notice the difference at idle...

This is my knowlege...I could be wrong...

Correct me if I am wrong...

Billman250

You are totally wrong, on everything

When someone says dropped valve, it means the retainer failed completely and the valve dropped into the cylinder. That can happen if they are left unchecked. I think I've done 2 already. One needed new valves, one needed a complete head.

With a broken retainer (and "sunk" valve), the valve is in the same place. The valve clearance does not change either. The retainer is higher up on the keepers. It will not affect the running condition of the engine.

The worst one I found the retainer was so far up it was rubbing on the roller.

kentarou

O...icic...I totally got it screwed up then....

Any picture of that?? between good and bad retainers....or what am i expect to see
on a over-reved engine with the valve cover off?

Billman250

Good one on the left.............................................. .......broken one on the right