Thread: Rover V8 advance maps

Originally Posted by pibby

in melbourne at the moment and picked up my dizzy after getting it regraphed for lpg. thought while i'm here in melb i'll get a baseline for a correctly setup dizzy and see how that compares to my edis setup so pulled the edis off my motor to do this. anyway, was chatting to the bloke at performance ignitions (they're the people who do the scorcher). that's their trade(dizzys) so they've got some skin in the game and know their stuff rather than a hell of a lot of theory some have which is not worth the hot air it was delivered on! once i put the dizzy back on the car and put my gun on it i'll know what they consider the appropriate curve for lpg. in the conversation i said i had total advance of 25 for lpg on my edis setup which he said was about right then he added total for petrol should be 28. can't recall exactly the reasoning but vaguely remember him saying you end up creating more heat if you advance it more. one of the guys who is part of the megasquirt juggernaut has done his rover motor (i think he was the guy from extraefi who was one of the code cutters). i recall him saying he's car would ping at 36 degrees but generated it's max power on a dyno at 30 degrees. so it says two things - debunks a bit of the theory that says the best timing point is just before the motor pings and also gives credence to the 28 degrees total timing the bloke at performance ignitions mentioned today.

hope this helps in some way?

All motors are different, what suits one doesn't really match up with another with a diffrent tune / head design/ piston crown / rod / etc


What did the guru say about vac advance?

The Total advance for a Rover V8 according to "How to Power Tune Rover V8s" is
3.5 = 36 degrees
3.9= 34 degrees
4.2= 30 degrees
4.5 or more =28 degrees

Mine is now about 32 so I feel safe and haven't heard a ping yet, but it's cold and early days.

Grimace, the lumpiness of the advance curve by Ward at GC was commented on by the other guy who smoothed it out.
I reckon the only way you could get it correct on light throttle would be with an engine dyno and lots of time. That's why it costs car companies a lot.
Regards Philip A

in relation to the vacuum advance didn't go into it in detail but said around 95% of the dizzys they get in for rebuild ( don't know whether was just for rover) have faulty/leaky/not working vacuum cans. and this included mine! it had a leak.

28 degrees - were talking about my motor which is a 4.6 and looking at philip's post it does also show the 28 degrees. will have to look up the book he mentions "How to Power Tune Rover V8s". sounds like an authoritative publication.

I found this article on the subject - thought it was worth a read.


http://autospeed.com.au/cms/title_Ge...2/article.html

As I run STRAIGHT LPG engines way beyond your power outputs I find it Laughable that thers is Specific LPG advance Curves or LPG Cams .LPG may indeed like a Greater initial advance but after idle its got nothing to do with it , For instance my 400HP straight gas engine at 11.9:1 runs initial 16 degress then all in to 28 degress by 3000 RPM

Originally Posted by 400HPONGAS

As I run STRAIGHT LPG engines way beyond your power outputs I find it Laughable that thers is Specific LPG advance Curves or LPG Cams .LPG may indeed like a Greater initial advance but after idle its got nothing to do with it , For instance my 400HP straight gas engine at 11.9:1 runs initial 16 degress then all in to 28 degress by 3000 RPM

Forgive me... why is it laughable? ..it's late BUT...


Surely then one of the determining factors for correct mapping is the octane rating of the specific fuel being used ...hence the expected differences between LP gas (butane /propane mix) and the relative percentages of longer chain hydrocarbons (HC) (pentane/hexane/heptane/octane) etc constituting liquid petroleum products sold as ULP and PULP etc...



The predetonation/pinging factor is obviously going to be different for LPG /LNG/ULP/PULP/winter formulation/summer formulation etc because testing has shown they all have different "octane" ratings...so the mapping for an engine is always a compromise ... unless you can rely on the octane rating being exact and consistent (like the special batches of fuel fractionated each year by "?Shell" for the super V8s...

Hence also the advent of adaptive mapping by the ECUs in later models which also rely on pre/post cat O2 sensors and knock sensors/ping detectors... to try and optimise performance for a given fuel mix.

Developing optimal maps is a complex business ... maps are just not to do with timing and air/fuel mix... valve timing, engine loads etc etc are all variables which need to be considered.

So it's quite reasonable to expect dedicated LPG engines to be fitted with different cams and timing curves to accommodate specific air/fuel mixes under different loads at different points on the rev range ...

running dual fuel is always going to be a compromise unless you have a VVT engine plus all the other sensors which help to address the different fuel burning characteristics under widely varying conditions

In short...there's no absolute correct answer re. timing maps for non EFI / dizzy controlled timing engines with no O2 sensors ,,,,just a "that's close enough" range...it's always a compromise...

here endeth the lesson....

What a fasinating topic.

I suspect that smooth maps are not making the most of the ems ability. Smooth transitions are probably what you would get from centrifugal advance for spark timing and venturis and jet size for fuel maps.

With the normal camshaft arrangements I can't see that you will be able to do much about valve timing other than change your cam. Given fixed valve timing you are just fixing one of the variables and not getting the most out of the engine across the whole rev range.

I think it comes down to knowing what your VE is across the rev range then you have an idea of how much fuel you can put in. A wideband sensor should be useful to determine how much fuel you can feed the cylinders. Close to stoichiometric or lambda greater than or equal to one for cruise and idle and richer than stoichiometric under load.

EGT should help with spark timing.

And we have not introduced the issue of pollutant levels.

Grimace,

Are the maps you have for fuel for a tbi or do you have a means by which to alter the tpi pulse timing/duration for each cylinder?

Heres a proper engine Dyno sheet of one of Holden 308/355 strokers I have built Have a look at the VE % (Dont worry about the fact that its developed 3 times the horsepower and 3 times the torque of usual Rover V8 and is less than twice the displacement.(5.7 Ltrs) This is achieved with early Non-assymetrics cast heads . Wonder what the advance curve was for that ? By the way , it happily Revs to 7000 rpm but I limit it to 6000.