god damn shunt is killing me

god damn shunt is killing me

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StuVT

79 posts

110 months

Thursday 8th February 2018
quotequote all
Hopefully this should add clarity.
My findings from todays set up.

Chimaera 4.0HC no cats. 14CUX standard management.
I put my vac gauge on the ported vac pipe. As Chimpongas states no vacuum at idle. Rev it and there is a very short and weak vac signal.
Vac gauge on full vacuum from fuel purge take off at the plenum. A good strong consistent vac signal.

Vac disconnected and static set at 12deg btdc. Rev to 3500 rpm + the advance tops out at 28-30 degrees.
Add full vac signal revs increase from 800 to 1250. Turn base idle down to 800rpm. Full vac added 10 degrees so now idle is at 22 to 24 deg.

Now this next part I'm sure is logical and what i would expect to see at load and cruise conditions. I repeated the test several times as you need to be on the ball.
If I snap the throttle open the initial load shows 30 degrees then as the load diminishes and vac increases on the over run / rev down the mechanical advance is still in effect, 30 deg but it also has full vacuum so I was seeing 40 deg until the revs dropped enough for the mechanical advance to start to diminish back to an idle of 22 deg.

My assumption is when driving under load it will be pulling 30deg mechanical only and at cruise mechanical and vac (+10) 40deg and 22 at idle. Part throttle smaller vac signal they both work together.

I need to make some det cans so I can double check for over advance and pinging.

However, everything I saw and tested agree with ChimpOnGas's theory.

I need to echo what CoG has said. My findings are the work of a man in a garage at the bottom of his garden with self taught mechanic skills. Do not take what I say as scientifically proven fact.

Stu

carsy

3,018 posts

164 months

Thursday 8th February 2018
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I`d say those findings are fine. I dont think you will have a problem with detonation with those figures. As you say at full throttle there wont be any difference as there is no vac advance. And the extra 10 degrees on overrun taking it to 40 will be fine.

I run 45 degrees on light cruise.

ric355

215 posts

148 months

Thursday 8th February 2018
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Been watching this with interest and pleased to see someone was finally able to test the theory. The big question is, how does it drive?

StuVT

79 posts

110 months

Thursday 8th February 2018
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I have only gone up and down my access lane and reversed it back in the garage but it feels happier. I want to do it with det cans to be safe.
Before it was easier to stall getting it in garage which I always thought was odd for big engine.

carsy

3,018 posts

164 months

Thursday 8th February 2018
quotequote all
Yep as COG says they are much happier running high teens to twenty at tick over.

Good work, keep us posted as to how you get on with the det cans.

Classic Chim

12,424 posts

148 months

Thursday 8th February 2018
quotequote all
Yeah, it’s all unravelling.
I’m on after market Ecu
Car pulls away on tickover everywhere with ease and loads of power
Timing has transformed the engines character and feeling of power where you want and need it.
Keep up the good work gents, anything that gets the CUX firing well must be a very good thing.

ChimpOnGas

9,637 posts

178 months

Thursday 8th February 2018
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StuVT said:
I have only gone up and down my access lane and reversed it back in the garage but it feels happier. I want to do it with det cans to be safe.
Before it was easier to stall getting it in garage which I always thought was odd for big engine.
Excellent stuff Stuart, remember all you are doing is getting a little closer to what ultimately anyone with a aftermarket ECU typically ends up with, it's just it's cost you nout wink. Please also note you are sacrificing emissions for drivability which makes you a very bad man, but potentially a happier one yes

What you should find as an absolute minimum is... the car will be easier to maneuver at slow speeds, parking will become a much more relaxed affair, and in the same way, pulling away from junctions will become easier and smoother too.

For the record, 22 degrees at idle is a little too much in my opinion, but I freely admit to running this number myself for a while with no issues whatsoever. If I were you, what I'd be shooting for is a 1050rpm idle at 18 degrees, to achieve this it sounds like you'll need to retard your distributor from 12 degrees to 8 at a lowly 800rpm (with the vac advance disconnected).

When you reconnect your full vacuum signal to the vac advance unit the timing will now be at the optimal 18 degrees and your idle should come up nicely too. There will now be a little bit of juggling required to get everything spot on, balance the base idle timing by rotating the distributor and the idle speed adjustment with the base idle screw, it sounds like you're very close already so everything should come good with minimal fuss. With a bit of tweaking each element you should end up with your tacho needle rock solid and hovering just above the 1,000rpm line (1,050rpm) and your dial back timing light confirming 18 degrees.

Now go for a go for a drive and tell us how the car behaves, you've clearly already found torque at, and just above idle... but with the nasty ported vacuum removed it can no longer violently add and subtract big dollops of timing as the throttle butterfly passes the port, this should translate as a far smoother drive at those small throttle openings around 1,800rpm when your just tricking through town.

In addition to all this, and on a 80mph motorway run, you should pick up roughly 2-3 mpg to deliver 30mpg, because that's what I get on petrol with my light load cruise timing set at 46 degrees, finally you should also enjoy better throttle response pretty much everywhere but this will be most pronounced bellow 2,000rpm as its where the standard enviro friendly ported vacuum retarded timing strategy lets the car down.

Keep us posted as the results come in, you're doing some fantastic work to the benefit of many.

Dave.

StuVT

79 posts

110 months

Friday 9th February 2018
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If I move the idle timing to 18 degrees wont the full mechanical figure go from its current 30 down to 26? With 30 being generally considered a safe figure would 26 not be a touch too retarded?

Steve_D

13,737 posts

257 months

Friday 9th February 2018
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StuVT said:
If I move the idle timing to 18 degrees wont the full mechanical figure go from its current 30 down to 26? With 30 being generally considered a safe figure would 26 not be a touch too retarded?
Other way round. Moving for 10 BTDC to 18 will move your maximum from your stated 30 to 38.

Steve

StuVT

79 posts

110 months

Friday 9th February 2018
quotequote all
My figure of 22 degrees at idle is with FULL vacuum. Its 12 static no vacuum connected.

So surely if its 12 NO VAC CONNECTED and 30 full mechanical at 3500rpm then 22 with vac CONNECTED. Vac has no bearing on load pulls as this is purely mechanical advance so 30deg max. Off throttle high revs or cruise with minimal throttle input vac cames back in and adds 10 deg.

If static is moved to 8deg = 26deg full mechanical. Then the Vac adds 10deg at idle and cruise only. So at idle 18deg and cruise 36deg rather than 40deg as I have now. Load advance (mechanical only) would be 26 where 30 is regarded as a 'safe'

This is theory but I will try and find time to get the car to a steep hill near me soon so I can listen for pinging with my det cans.

ChimpOnGas

9,637 posts

178 months

Saturday 10th February 2018
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I think people are missing the key point here, ie.... Vacuum is not a constant, mechanical advance is... but it has a limit.

If you are idling at 10 degrees with the vacuum advance disconnected, the maximum mechanical advance provided by the distributor when you increase engine speed to 3,250rpm is an additional 18 degrees,,,, so your peak timing number will be 10 + 18 = 28 degrees.

If you are idling at 10 degrees then connect the vacuum advance to full vacuum it will immediately add at least 10 degrees of timing, you are now idling at 10 + 10 = 20 degrees. But this does not mean your peak timing number will be 10 + 10 + 18 = 38 because one of those ten degree additions is coming from vacuum which does not exist to any meaningful degree when you are accelerating under load at wide open throttle.

What you're actually going to get under acceleration at 3,250rpm will be 10 degrees at idle + 18 degrees of mechanical advance plus maybe 3 degrees of vacuum advance if you're lucky!, so 10 + 18 + 3 = 31 degrees when what you really want is 36 degrees. This is a key area where a stand alone engine management system scores, because you can literally choose the optimal timing numbers irrespective of vacuum (load) or engine speed.

Distributors work well enough but they really aren't any more sophisticated than the governor on a steam engine, the faster a distributor spins the more advance you get, up to a limit. Just like a steam engine governor it also works on centrifugal force, the timing it adds can only ever be linear and in direct relation to engine speed, this is a problem as the timing an engine wants can sometimes be very different to the linear and one dimensional way a distributor behaves. A distributor advance curve can be changed easily enough by changing the bob weights and springs, but at the end of the day whatever you settle on will always be compromise, the curve is always going to be wrong in one area or another, indeed the truth is it will be wrong in a number of places.



Above we can see some typical Bosch curves to demonstrate the very one dimensional linear way a distributor adds timing in response to increasing engine speed. The yellow line delivered by the Bosch 019, is by coincidence, very much like the curve delivered by the Lucas distributor fitted our our cars, but what we could actually do with is something a lot more like the blue line delivered by the Bosch 383 because as we can see it delivers 35 degrees of total timing instead of the 30 degrees served up by the Bosch 019.

Now compare these one dimensional distributor advance curves with my Canems 3D ignition map, the benefits are clearly revealed wink



While we have now established the distributor is a rather crude and dumb device we should now consider the influence the vacuum advance unit has on the one dimensional linear mechanical advance curve, what people often don't realise is the vac advance unit is actually the closest thing to adaptive engine load referenced three dimensional ignition tuning. Anyone running a distributor should make no mistake, the vacuum advance unit is very much their friend, anyone who thinks disconnecting it is a good idea... needs to go back to school.

In the above example, and when accelerating to 3,250rpm, we have 10 degrees at idle + 18 degrees of mechanical advance plus maybe 3 degrees of vacuum advance if you're lucky, but in practice probably 0 degrees! Lets be generous and say 10 + 18 + 3 = 31 degrees which as we've already established is 5 degrees retarded from the optimal 36 degrees we would like when accelerating to 3,225rpm. But things get even worse if we are cruising at the same engine speed rather than accelerating because the engine is under far less load, so even though engine speed is the same we can get away with a leaner AFR to deliver better fuel economy. Leaner AFRs demand we ignite them earlier because lean mixtures take a little longer to burn, although it's really engine speed vs load that's of more influence when cruising on the motorway. When we are low load cruising like this the engine is also far less susceptible to detonation, this combined with the leaner AFRs we run means our 31 degrees is far from optimal... to be efficient we urgently need more timing.

A lot more timing yes

Enter stage left our old friend the vac advance unit, now we all know one of the key things that happens when we start cruising on the motorway is we naturally take our foot off the pedal, and miraculously the same road speed is maintained. The engine is now low load cruising, because we've closed the throttle but the engine (just a big vacuum pump) is still spinning fast at 3,250rpm its now sucking super hard against that almost closed throttle butterfly. The consequence of all this suck against that almost closed throttle butterfly is a huge rise in depression within the inlet manifold & plenum, so we use all this suck to pull on the vacuum advance unit which in turn adds roughly 10-12 degrees of timing as we cruise along at light load on our leaner and slower to burn AFR. What we end up with is not the total mechanical timing figure of 31 degrees under acceleration, but 28 degrees of mechanical timing plus 12 degrees of vacuum generated timing too.

So under cruise conditions we see... 10 idle + 18 additional mechanical at 3,250rpm = 28 degrees + 12 of additional vacuum derived timing = 40 degrees.

The truth is the poor old distributor on a Chimaera is all done adding mechanical advance by 2,800rpm, after that it doesn't have anything else to give which is a bit pants really. In addition the vac advance unit can only really help out to the tune of 12 degrees or so which is also pants because what you really want from the vac advance is 18 degrees to get you to the optimal cruising ignition timing figure of 46 degrees.

This is where the aftermarket ECU scores again because, as already stated, you can dial it whatever number is optimal without being held back by the constraints imposed by engine speed rules that govern a distributor, and the design limitations of the vac advance unit. While a distributor has clear limitations as does the vac advance unit, the two are very much designed to work together, if you disconnect your vac advance unit or make it work with ported vacuum instead of a nice strong and consistent full vacuum signal you will never get the best from what is already a compromised setup.

At this point I'll remind your of this, which hopefully is making even more sense to everyone now?



Remember, while engine speeds will change significantly, even the richest and leanest AFRs burn at a fairly fixed speed, at all times what we are trying to achieve irrespective engine speed is peak cylinder pressure at 15 degrees ATDC, so it stands to reason we need to light the fire earlier and earlier the faster the engine spins.

What we are trying to achieve when tuning the ignition timing is to start the combustion event at the right time so that maximum cylinder pressure occurs at approximately 15 degrees ATDC - This is called MBT timing which stands for Maximum Brake Torque timing, or Minimum timing for Best Torque.









When you idle Old Rover at 1,000rpm and you light the fire ten degrees before the piston reaches top dead centre (BTDC), you will not achieve maximum cylinder pressure at 15 degrees after top dead centre (ATDC). What you need to do is light the fire earlier between 18-20 degrees before the piston reaches top dead centre, like this peak cylinder pressure will arrive at the magic 15 degrees ATDC just as we want.

This is why StuVT found more torque when he switched from the dreadful retarded timing strategy imposed by the standard emission driven ported vacuum arrangement, to applying a full vacuum signal to his vacuum advance unit to light the fire 12 degrees earlier (22 degrees before top dead centre)

Like this peak cylinder pressure arrives for StuVT at a much better 20 degrees ATDC rather than the highly inefficient 8 degrees imposed by Land Rover's 10 degrees idle timing number. StuVT should have not only found the extra torque he reports, but he should have heard a noticeable improvement in idle quality too. As already stated you can go too far when advancing timing, and now we know why, what StuVT needs to do now is retard his distributor by 2-4 degrees, like this he will find his peak cylinder pressure will now arrive around the optimal 15 degrees ATDC.

Be aware one or two degrees can make a big difference, so if StuVT doesn't have a rolling road to measure exactly where peak torque arrives, which is the same as proof of peak cylinder pressure arriving at 15 degrees ATDC, he needs to uses his ears to identify where the engine is happiest and his bum dyno to determine generally where the car drives best.

While both AFR and timing work hand in hand, the big improvements to be had really don't come from running a bit richer or leaner, they come from perfecting your ignition timing!

Easy innit silly


Edited by ChimpOnGas on Saturday 10th February 08:51

jazzdude

900 posts

151 months

Saturday 10th February 2018
quotequote all
This is great and very very interesting, thanks folks!!

Big question, what about the shunting, has that improved StuVT, and just to clarify, are you running a standard white tune with your ECU and lamdas adjusting the fuelling?

Dave, you have described the effects on emissions, and as my car is fully decatted not an issue, but what will the ECU be doing with the info following the revised burn due to timing changes, will it be also adding more or less fuel to the mix?

The 14 CUX chip modifiers as you have said throw fuel at the shunt point and this also works although as I have found, it at the cost of higher mpg so how would this vacuum strategy fare with the green tune with manually set CO's at the AFM?

It would be interesting, perhaps if another study could be done with perhaps Blitz or Steve having a look at this and how it combines with their fuelling mapping and the resulting tunes that have come out of this.

Am I alone in thinking that potentially we might be finally getting near the ultimate 14 CUX setup?

Edited by jazzdude on Saturday 10th February 09:11

ChimpOnGas

9,637 posts

178 months

Saturday 10th February 2018
quotequote all
blitzracing said:
It will be interesting to see if more idle advance will help smooth this out a bit.
Clearly it will, because I and others with after market engine management systems have proved it will. Indeed I can demonstrate the effects of altering idle ignition timing in seconds. As I dial in the changes in idle timing in real time with a few key strokes on my laptop, even a def man could identify the changes in idle quality... because not only is it audibly much better but vibration is dramatically reduced too.


blitzracing said:
If you want to carefully add a couple of degrees of peak advance you can carefully grind a bit off the bob weight stops and leave the rest of the advance curve as it is.
If done with care, this can work well and is something I've done a few times when curving distributors, however what you really need if you're going to get into safely and properly curving a distributor, is professional distributor curving rig, here's one from Sun:



Keep in mind the current setup only gives 28-30 degrees of peak timing, when 35-36 degrees is what those of us with after market engine management systems have proved (on the dyno) is what the engine really wants. Remember Old Rover is a low compression engine which is why 35-36 degrees has also been proven to be completely detonation safe.

Another area for improvement centres around how steep your ignition curve is, ie how quickly the distributor adds timing and at what rate it adds it. From what I've seen the standard Land Rover distributor used on Chimaeras and Griffs received no modifications by TVR Power, the bog standard Land Rover curve was left untouched. This Land Rover curve is very flat and was clearly designed to work with a soft cam profile, the way it adds timing early on is extremely lethargic which is far from ideal.

The single canister coil Land Rover based ignition system also isn't the best, on our cars the spark can be even weaker because the wiring and earthing TVR inflicted on us can be a long way off optimal. Now consider what happens when you pull away from a stand still and before you build momentum.

At this moment the engine will immediately go under considerable load, this is because as you pull away you are trying to move a lot of weight that's sat still, think about bump starting a car (we've all done it), the hardest point is getting the damn thing rolling. However once you've gathered a bit of speed it becomes easier and easier to gather speed up to a point, what you're feeling is the same thing the engine must suffer.

Now consider that when a engine is subjected to load the other thing that will increase is cylinder pressures, the thing is making sparks becomes much harder as pressure increases which is why my ancient only Champion spark plug tester had a point where I could attach my airline to raise the pressure in the spark test chamber. My old Champion spark plug tester had a coil and points arrangement and a window into the sealed spark test chamber, you ran the coil then used a knob to slowly increase chamber pressure as you observed the spark. At low pressures the spark may be strong and bright, but add pressure and you can soon find yourself with no spark at all.

Because on our cars the spark is typically weakest at low rpm, and because cylinder pressures rise rapidly as you first pull away, this is the point when the system is most compromised, to help what you could really do with is adding some more advance early on. Inside your distributor it's the strength of those little springs and the mass of the bob weights that govern how quickly timing is added, so there may well also be some benefit in getting the Dremel out to shave a small amount of mass from the bob weights, and or fitting some slightly weaker springs.

As such three ways you can look to tune your ignition timing if you're running a distributor are:

1. As suggested by Blitz, progressively remove some material from the bob weight stops until the stock 28/30 degrees of total timing at 2,800rpm becomes the far more optimal 35/36 degrees at 2,800rpm and beyond

2. Carefully shave a small amount of mass from the bob weights, and or fit some slightly weaker bob weight springs

3. Switch from ported vacuum and apply a full vacuum signal to your vac advance unit

The correct combination of all three are very likely to give some real benefits, benefits close to certain elements(but not all) that are already being enjoyed by those ruining aftermarket engine management systems with 3D mappable ignition.

But caution is required!

While the switch from ported to full vacuum I'm promoting caries little danger, I would express extreme caution to anyone considering grinding away the bob weight stops and playing with how aggressive their curve is by removing mass from the bob weights themselves and or fitting lighter springs. Go just a fraction too far and you could easily end up with too much timing early on or 42 degrees plus of total timing, which is definitely too much, in both cases you'll be running the very real risk of engine damage from the violent effects of detonation.

That's why the only safe way to curve a distributor is to use a professional distributor curving machine, but if you you haven't got one you could always take the figures people with after market engine management systems have proven to be optimum, and get someone like the Distributor Doctor to curve your distributor for you on his rig.

For everyone else who just wants to see some benefits from something easy, safe and free to implement... I recommend experimenting with switching the standard ported vacuum signal applied to their vac advance unit to a nice consistent full vacuum signal.

Another cheap mod is to ditch the dreadfully inappropriate shrouded electrode NGK B7ECS plugs TVR fitted from new and replacing them with the far more suitable extended electrode NGK BPR6ES, or better still a set of BPR6EIX iridium plugs. In many ways because combustion it initiated more effectively the effects of a set BPR6EIX iridium plugs can be very similar to adding a couple of degrees of timing at idle and just as you pull away.... when both the ignition system is at it's weakest and cylinder pressures will monetarily rocket .

Obviously none of this will help much unless your entire ignition system is in tip top condition, which on Chims and Griffs it very often isn't due in part to those dreadful plug extenders failing, burnt HT leads and a poorly earthed coil ect. You are also strongly advised to eliminate every single vacuum leak for which there can be many, to this end I recommend people pay close attention to their crankcase breathing system wink

StuVT

79 posts

110 months

Saturday 10th February 2018
quotequote all
Excellent info again Dave. I'll shy away from bob weight mods.
The book figure states 950rpm. Can I ask the significance of the 1050rpm idle you promote?

If I can get a smooth drive with full vacuum and tinkering with tge distributor with det cans ill be happy. Then will be modern injectors from Injectortune.

ChimpOnGas

9,637 posts

178 months

Saturday 10th February 2018
quotequote all
A 1,050rpm idle is just my personal preference.

By ear, by feel (vibration), and from every other perspective I prefer 1,050rpm, it definitely works well with my 18lb flywheel & V8D Stealth cam. A 950rpm idle will always present additional AFR stability challenges with a batch fired V8 like ours unless you smother the problem in fuel, in my opinion a 950rpm idle just presents the tuner with additional challenges he doesn't really have to put himself through.

Make 1,050 @ 18 degrees your new 950 @ 10 degrees and quite simply a lot of the classic hunting issues just disappear and even at leaner idle AFRs.... so you end up with a lovely smooth idle while also using less fuel to achieve it.

Oddly you'd think 950rpm would be quieter, which I guess it may be (fractionally) if you measured it with a decibel meter, the thing is because 1,050rpm works so much better and the engine is so much smoother and happier it seems, to my ear at least, like the more refined 100rpm faster idle delivers less overall noise.

Actually I view 1,050rpm as my lower idle threshold, I'd be happy with 1,100 but since adding scatter spark closed loop idle speed control the engine sits exactly at 1,050rpm so I'm super happy with it, no more tweaking required.... that's where it is and that's where it'll stay.

Saying all that, as I've already indicated, the other way I can get the same lovely smooth vibration free idle at the lower 950rpm target is throw a bunch of fuel at it..... but that's wasteful inefficient tuning in my book.

The old batch fired Rover V8 will definitely thank you for a bit more airspeed at idle, after all where not trying to create a 950rpm idling Range Rover here are we wink

ChimpOnGas

9,637 posts

178 months

Sunday 11th February 2018
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It probably doesn't come out too well on YouTube but below you'll find a short video of my Dual Fuel Canems ECU equipped Chimaera at it's happy 1,050rpm idle, the car runs the standard TVR central silencer box fitted when the car was built at Bristol Avenue in November 1996, but I've removed all three cats because they restrict performance and are another element that has a negative impact on idle quality, the Y piece is from ACT.

My 4.0HC Chimaera sports a V8 Developments Stealth Cam and a lightened 18lb steel flywheel from TTV Racing, two mods that give the old girl a bit of extra zing but (in theory) do not lend themselves to promoting the best idle. I'm burning LPG here and it's after a good run so the rad fans were running too, which adds an additional amp draw challenge for the ECU to manage.

I have Bosch two wire rotary idle air control valve closed loop idle management, as well as scatter spark closed loop idle management, the target idle is 1,050rpm on both which the ECU holds with devastating efficiency. Scatter spark is allowed to be the dominant idle management strategy because using a processor controlled ignition timing target to control idle speed is better than using even the best processor managed air bleed.... in my experience.

I target 22° of ignition timing at idle on LPG at the target 1,050rpm idle speed as the burn rate of LPG is slower than that of petrol where I target a lower figure of 18°, the wide band lambda closed loop AFR target is Lamda 0.94 which translates to 13.8:1 on petrol on my closed loop AFR table which is shared by both fuels, this means I'm actually idling here at a true 14.57:1 on LPG.

https://www.youtube.com/watch?v=_oUmPOp7xOQ


Classic Chim

12,424 posts

148 months

Sunday 11th February 2018
quotequote all
This is the only bit I don’t get, 1000 revs idle.
Mine idles at 750 with impunity. I can drive it at 800 revs.
My point being into and out of roundabouts my rev counter regularly drops below 1000 revs and I can still pull away without clutch intervention,usually still in Third gear.
If my idle was set to 1050 the engine would be pushing on and I’d not be able enjoy that benefit, I’d have to ride the clutch or change to second!

I was told Dom likes all the Mbe cars to idle around 750 so it’s not just my car.
This does have benifits as I’ve said, I’m surprised you don’t aim for lower Dave.
Each to their own mind wink

ChimpOnGas

9,637 posts

178 months

Sunday 11th February 2018
quotequote all
No question I could idle Ol Gasbag at 700, 750, 800, 850rpm ect ect... I just choose not to.

My first point is water pumps on cars aren't really pumps in their true positive displacement sense, they are more water stirrers so you've got to spin them at a reasonable lick or you're more relying on the effects of thermosyphon at idle. With Old Rover's issues as they are I'm keen to keep a nice flow of freshly temp lowered coolant moving around the water jacket and across the rad, anything to avoid the remote possibility of micro pockets of super heated steam has to be a good precaution.

My second point is a similar to my first one, that is I just prefer to spin my oil pump a bit faster, and as the wear prone cam and followers are lubricated by splash only, a bit more thrashing through the oil from the crank webs has to be a good thing too.

TBH its horses for courses mate, but for these reasons and the fact it's been my experience Old Rover simply prefers a bit of airflow at idle, I choose 1,050rpm. The bottom line is there's no real right or wrong Alun, so the way I see it, its a case of each of us being happy with what we have thumbup

Edited by ChimpOnGas on Sunday 11th February 20:35

StuVT

79 posts

110 months

Sunday 11th February 2018
quotequote all
Mines a 95 Chimaera, stock but with no cat or pre cats, a freshly cleaned pipercross filter, and a RT Racing exhaust which essentially is half sleeved. All breathers wirh jubilee clips and a pcv valve on the fire trap.Standard 14CUX with full vacuum from the charcoal canister vent pipe take off on the intake. Standard injectors and standard original flexi intake pipe.

Today I carried on experimenting. I had earlier in the week set it at 22deg idle vac connected which gave 30 full mechanical and 40 cruise. As per CoG's evidence of a slightly more retarded idle would give a better cylinder pressure point of 15deg ATDC I set the static to 18 degrees at 800rpm which was 8 degrees with the vacuum off. Max advance at 3500 rpm was 26deg and has made me consider finding an old school place with a distributor machine CoG showed to trim the bob weights for more max advance. Ideally play it safe to 30deg to get back to the cruise figure of 40deg.
Stepper motor unclamped and it settled to about 950 to 970rpm on Rovergauge. I experimented with 1050rpm but it sounded like it was racing on and going up and down my access lane I didnt like it. Revs hanging between 1st and 2nd and not slowing when I came off the throttle. This was in only first and second gear though.
At 950 - 970 rpm its very steady with minimum vibration. It sounds calmer at idle than before at 22deg if that makes sense. Even though the idle rpm range was similar.

So I set out to give it a run. Drove down the lane gently on and off the throttle between 1200 and 1800 rpm. Felt settled and smooth....... then i ran out of petrol. ??£20 used in idling and messing with the timing this week.

Im off tomorrow so hopefully get some fuel and go for a drive.

Edited by StuVT on Sunday 11th February 21:23

Classic Chim

12,424 posts

148 months

Sunday 11th February 2018
quotequote all
I had similar concerns as warm oil pressure at idle is very low but I’m also well aware many Rover engines running carbs look for 600 tickover, as we know these aren’t high pressure engines and oil flow rate is just as important.
If thousands of landies run at that sort of idle and after two years experiencing such a low idle speed myself with what appears to be no downside I’m all for it.

If most mechanical wear is a consequence of cold engines running with cold oil and tolerances being larger than ideal until everything has warmed / expanded which is what most of the noise is imo then a gentle approach to bringing revs upto 12/1500 revs, ( they say these splash fed cams only recieve oil above 1500 revs ) seems a good idea.
The timing you’ve so eloquently described allows me to drive it below 2000 revs until it’s warm enough so I can keep the mechanical wear to a minimal.
I also noted a 4.6 RR 2006 I think at a petrol station, Gems and sounded perfect. He drove off without applying the throttle, awesome sound and all RR go about on tickover or very low revs which goes to show these engines don’t suffer water or oil problems at low revs when oil is warm. Our cooling system is more than upto the job if the engine management system is helping too. As some of your knowledge suggests not only can timing and fuelling give more power or a more complete burn etc it can also smooth the engine to a fine degree and it seems to run cooler as a consequence.

See as a kid I removed all trace of tickover on crossers, fear and old carbs never shutting off properly was the only reason but it did stop better without one biggrin

Old habits and all that, funny as I sometimes think my tickover still seems a bit high, Racing almost hehe