Information needed for Pulse and Glide
 

I've been musing about the benefits and drawbacks of P&G (which I am new to) and it occurred to me that I might not be seeing its full effect, if any, due to the lack of critical information about my car.

As I have understood it, the benefit of P&G is that you maximise the amount of time that the engine is operating in its most fuel efficient "zone" and coast for the rest of the time. I've managed to glean that the engine FE (or Brake Specific Fuel Consumption (BSFC)) is dependent on the engine RPM and output torque as it is related to optimum engine temps and frictions I'm assuming. This gives me only the engine RPM to control the FE from the driver's seat at any given driving speed and condition, hence the "revving up" to desired RPM and then gliding.

So that brings me to the question: Isn't it a prerequisite that I know where my car has its optimum RPM for any given torque load, i.e the BSFC map, and won't I just be winging it without that information? I've found that the i10 has its max torque at 4500 RPM, but this doesn't necessarily mean its peak FE is there right?

Can anyone clarify this? Am I better just going for constant low speed/ high gear instead?

PS: If anyone has a BSFC map for a Hyundai i10 (2011) that would be grand!

https://ecomodder.com/forum/showthre...d-19594-5.html

Old thread on P&G, I doubt you'll want to rev past 2500. And IMO if not willing to go Engine Off in the coast I don't think it will save anything over going a constant average speed of the average P&G.

I only do mini-pulse and glides where downhills allow me to glide for longer than I would on flat, and I just put the clutch in rather than kill the engine. Doesn't really save that much.

Also, if anyone is behind me I don't subject them to inconsistent speed. They will get worse fuel economy because they aren't prepared for the speed changes.

I would shift to neutral and let the clutch out while gliding, otherwise you're subjecting your throwout bearing and spring to far more use than it's designed for.

With such a small engine it only makes sense to P&G at lower speeds.

I used to pulse between 2000 and 3500rpm. And learned over time that it was more important to reach the next coast point at the right speed than to load the engine optimally.

Thanks! They seem to be touching on the point that you need to know the optimum BSFC "island" in order to gain the most from P&G, but it's not stated explicitly. I also agree that the benefits seen in my car will be minimal at most

Yeah I've also started doing that lately since it seems that I'm "driving blind" without knowing my engine's best operating point. Also it can be quite fun to try and hit perfect runs in hills and valleys :)

That's actually related to another worry of mine, namely the downsides of P&G. No matter how smooth I release the clutch there's always that slight "snag" which I don't imagine is good for the mechanics in the long run.

Also, a more serious issue is that my concentration on the road is impacted since I'm having to keep an eye on the speedometer. Not good at all!

Interesting... Once I get my OBDII logger up and running I'm planning on creating my own "MPG map" with logged MPG values plotted against driving speed and engine RPM. Hopefully that will inform me on the optimal RPM at any given speed.

I wouldn't so much worry about wearing out the clutch on your bump restarts, that little bit of slip is no more than you would normally have when shifting gears. It is what the clutch is designed to do afterall.

however the throwout bearing and clutch spring are not designed to be held long term. For that matter why strain your leg constantly when it's a simple matter to put the transmission in neutral.

I shift to neutral for very long coasts, buf for anything 15 seconds or less, I don't bother.

Does going from neutral to a gear cause the syncros to work?

If you were coasting at idle with the clutch engaged in neutral, then the transmission should be all synced up (like double clutching does), so in that case no.

15 seconds shouldn't bother the throwout bearing, I was picturing a 5 minute coast down and beyond a big hill holding the clutch the whole way.

Yes. The few times I have EOC'd the transmission was not happy about going back into gear for the bump start.

The bigger question here: Is the throwout bearing SPINNING when the engine is off, which I think it is not, in which case you can hold it down for as long as you want as long as the engine is off. I would definitely be shifting to neutral for a 5 minute coast though.

I just swapped out the flywheel, clutch and throwout bearing on my M5OD-R1HD in my Explorer, so the mechanical relationships are pretty fresh in mind.

Note: assumes all parts working correctly.

When the clutch is engaged (foot off the clutch pedal), the clutch disc is clamped by the pressure plate and turns at the same speed as the flywheel. This, in turn, means the input shaft to the transmission is turned at the same speed as the flywheel. Niether the pilot bearing nor the throwout bearing is spinning at this time. If the transmission is in neutral, you can turn off the engine and coast with no wear on the pilot or throwout bearings. They'll be stationary.

When the clutch is disengaged (foot on the clutch pedal), the throwout bearing is compressing the springs on the pressure plate, un-clamping it from the clutch disc. The throwout bearing will be rotating at flywheel speed. Any difference in speed between the flywheel and the input shaft of the transmission shows up as rotational speed in the pilot bearing. If you turn off the engine, the throwout bearing stops spinning - no wear. The pilot bearing will still be spinning, though.

In either case, if you put the transmission in neutral, the input and output shafts will soon be rotating at different speeds. Re-sycing them to get into gear will require the syncros to do work matching the speeds, unless you start the engine first and do rev-matching. If you want to bump start, you either need to leave the transmission in gear or use the sycnros.

So, for EOC, you can choose: syncro wear (trans in neutral, clutch engaged) or leg pain and throwout/pilot bearing wear (trans in gear, clutch dis-engaged). You can do leg pain AND syncro wear if you want (trans in neutral, clutch dis-engaged) but why?

If you have a Ford/Mazda M5OD-R1 or R1HD transmission, the extra wear on the pilot/throwout bearing doesn't matter: you'll probably have to tear it all apart to replace the throwout cylinder before either wears out anyway. :(

Good point, I was thinking of engine on idling, such as most people will do at red lights. A lot of folks just hold the clutch in and this causes wear on the throwout bearing and spring.

But even with the engine off you're holding tension on the spring, and your leg, neither of which is necessary.

I've done a fair bit of EOC in the past when I was broke as a joke and running on fumes, and never had issues getting the trans back into gear while rolling with the engine off.

No wear bump starts.

The engine is off so zero rpm. Push the clutch down for ~5seconds and the input shaft will slow to zero rpm too. 0+0= zero wear. That's what I have to do with my non-syncro truck. If you don't wait for the input shaft to stop to it will just crunch.

If you can't wait for 5 seconds before bumping, just barely touching any gear will stop the input shaft immediately. Then select the gear you want, just going into gear immediately causes about twice the wear going by feel.

I usually touch 4th to stop the input shaft, then shift into 5th. If sometimes I need to bump fast I just go straight for 5th. That way I'm spreading any wear over two syncros. While accelerating I often skip 4th so that's my 'sacrificial' syncro.

But where possible, I use the 5 second no wear trick.