two newby questions

[hughandjenny]

Sorry but am being a bit thick. I keep reading posts on `shunting' . What the H..l is shunting.

Second question. I bought a 450 Chim three weeks ago and want to learn as much as I can. Am slowly reading through all the post and am up to page 80. is there any way you can so directly to say page 80 without clicking next page 80 times.

Thanks

[Pupp]

Shunting is explained on page 81

[clarkmagpie]

[neal1980]

page 80 of 1209 fair play we will be asking you soon

[Pupp]

hughandjenny said:

What the H..l is shunting.

Some of the Rv8 cars are a bit lurchy on neutral or slightly trailing throttle at about 2k rpm (it varies)... this drives some owners demented in the pursuit of smooth (usually round town) driving. Many potential causes suggested, but plenum effects from cam overlap/duration possibly the favourite although timing and fuel mapping can impact/mask for sure. Has also been attributed to driveline play (cv joints, diff bushes, loose drive shaft flanges etc)

[miniman]

Isn't shunting just the inability to drive smoothly?

[deeen]

If you haven't noticed any shunting in 3 weeks, don't worry about it.

[Chris71]

deeen said:

If you haven't noticed any shunting in 3 weeks, don't worry about it.

If it does it - a sort of hiccup (or even mild kangarooing) on light throttle loads and low-ish rpm - then that's relatively normal. If it doesn't do it noticeably then it's better than normal (and they do vary).

Not wishing to go off topic, but although I'm not too fussed about the shunting itself I can imagine anything that smoothes that out might make the engine braking a bit more progressive. There's really no need for them to be as abrupt as they are.

[Chimpafrolic]

Chris71 said:

deeen said:

If you haven't noticed any shunting in 3 weeks, don't worry about it.

If it does it - a sort of hiccup (or even mild kangarooing) on light throttle loads and low-ish rpm - then that's relatively normal. If it doesn't do it noticeably then it's better than normal (and they do vary).

Not wishing to go off topic, but although I'm not too fussed about the shunting itself I can imagine anything that smoothes that out might make the engine braking a bit more progressive. There's really no need for them to be as abrupt as they are.

Chris, the unusually high levels of engine braking are really down to two things on your 500.

1) 300 ft lbs of torque

2) The very light weight of the car

The solution is not to down shift in the same way as you would have done when blasting around in your 4 cylinder Caterham Roadsport.

Much better to use the brakes, leave it in the higher gear and ride the torque on the way out.

Its just a different way of driving that gives its own unique pleasures, you'll get used to it mate.

To solve my shunting I fitted an SC Power plenum spacer & dropped the trumpets (velocity stacks) slightly.

I believe what I achieved with this was solution was actually to disguise an underlying fuelling characteristic, so I wouldn't call it a definitive fix.

Even so the effects were excellent, the plenum spacer eliminated the shunting gave much better driveability with cleaner on/off fuelling which in turn meant gear changes are much smoother.

All this for a relatively low cost, I still consider it one of the best mods I have done.

Dave.

Edited by Chimpafrolic on Friday 3rd December 13:02

[spend]

500's are far worse than 400hc's in the engine braking stakes IME;)

Contemplate the weight transfer to the rear when lifting, the bedsteads do benefit from more nose down stance and careful selection of spring rates to minimize the fore-aft balance shift which is the most upsetting effect. Many have tired springs & components as well as incorrectly set heights, inappropriate wheel+tyres (axle height) from 'modifications' that all can throw out the chassis ride heights (roll centres / static balance / CoG) as well as its overall performance?

[Chris71]

Chimpafrolic said:

Chris71 said:

deeen said:

If you haven't noticed any shunting in 3 weeks, don't worry about it.

If it does it - a sort of hiccup (or even mild kangarooing) on light throttle loads and low-ish rpm - then that's relatively normal. If it doesn't do it noticeably then it's better than normal (and they do vary).

Not wishing to go off topic, but although I'm not too fussed about the shunting itself I can imagine anything that smoothes that out might make the engine braking a bit more progressive. There's really no need for them to be as abrupt as they are.

Chris, the unusually high levels of engine braking are really down to two things on your 500.

1) 300 ft lbs of torque

2) The very light weight of the car

The solution is not to down shift in the same way as you would have done when blasting around in your 4 cylinder Caterham Roadsport.

Much better to use the brakes, leave it in the higher gear and ride the torque on the way out.

Its just a different way of driving that gives its own unique pleasures, you'll get used to it mate.

To solve my shunting I fitted an SC Power plenum spacer & dropped the trumpets (velocity stacks) slightly.

I believe what I achieved with this was solution was actually to disguise an underlying fuelling characteristic, so I wouldn't call it a definitive fix.

Even so the effects were excellent, the plenum spacer eliminated the shunting gave much better driveability with cleaner on/off fuelling which in turn meant gear changes are much smoother.

All this for a relatively low cost, I still consider it one of the best mods I have done.

Dave.

Oh I'm quite happy heel and toeing on the downshifts, it's more backing off the throttle in-gear. It can oscilate if you do that, much like a learner driver kangarooing away from a junction and I can imagine that would upset things if you were near the limit of grip when you did so.

There are things that can be done to control the rate at which the torque drops off though. To be fair I'm used to electronic pedal inputs and torque-based mapping on diesel engines, but there we defined our own ramp rates for tip ins and back outs based on the fuelling. You could give an 1800kg Galaxy pretty vicious engine braking if you didn't specifically engineer it out and I'm sure the Rover V8s responses could be smoothed too.

ETA With references to spend's post above I have noticed that the dive under braking seems to be out of proportion to the relatively small suspension movement in bump and roll. This isn't a problem I hasten to add, it's just an observation...

Edited by Chris71 on Friday 3rd December 14:08

[Chimpafrolic]

Interesting Chris, it sounds like you have some impressive technical knowledge.

Any ideas on a solution?

A couple of years ago I rode a Ducati with a slipper clutch, you could knock it down two cogs right in the middle of a bend without getting spat off.

Took balls to try it the first time though, goes against everything you learn on two wheels.

What I can say is the bike had way more talent than the pilot.

Those of us with motorcycle experience (road riding) will know its about getting all your braking and gear changes done before you enter the bend.

In my experience if I drive my Chim like this it handles very well, still not great in snow & ice though

How about a slipper clutch for the RV8?

[Chris71]

To be fair it may not be possible with a conventional throttle on a petrol engine. The diesel engines I worked on had no physical connection between the pedal and the engine. When you stamped on the throttle or suddenly backed out the software would decide how quickly it would actually alter the fuelling etc.

That wasn't there to act as traction control or anything, it was just put in place to smooth out the torque delivery for drivability (and admittedly to help meet emissions requirements). It may well be on a basic petrol engine there's not a lot you can do to maintain the cylinder pressure when the pedal is released and the throttle snaps shut.

This is obviously separate to the shunt, but my thinking was that if you back off quicker than intended and upset the car that way you could then find the revs dropping into the shunt zone, which would make things even worse. In other words, without the shunt it would be easy to deal with the engine braking perhaps. Just thinking out loud basically.

[Chimpafrolic]

As an old school Luddite I still prefer a physical connection between my foot and the throttle butterfly.

My Toyota Prius has fly by wire everything including the brakes!!!!

You get a tube filled with hydraulic fluid to mimic the feel of a master cylinder, but just two switches at the end of it & no hydraulic connection to the brake calipers?!?

Under certain braking conditions you can find "the computer says no", last time this happened I sailed into the back of the car in front, the brakes simply failed no matter what I did with the brake pedal.

Give me a throttle cable & some brake pipe any day.

Try the plenum spacer if you want to improve the shunting, I will show you when we meet at the Ace.

[hughandjenny]

Thanks for all the feedback. it too used to ride Ducatis, but not with slipper clutches. the engine braking on these bikes was much much more than the four cylinder bikes. When we stopped riding some would comment why I did not have to brake into corners. I have swapped a 911sc porsche for the Chimaera 450 and I agree it takes quite a different driving style with the big V8.
With regard to the shunting mine is not bad at all I must be lucky.
By the way I love the feedback from the non power assisted steering, nearly as much as the 911.

Thanks again

[quattrophenia]

To me it's the same feeling I get in any car if you are in too low a gear and the revs drop, ie the power of the idling engine is trying to pull the car along and because the engine is bigger/torquier and the car lighter than most cars, the first signs of it trying to stall is for it to 'shunt'.