GT6 Mk3 only runs well with VERY advanced timing. Any ideas why?

[Iain T]

13 minutes ago, Firefly said:

Well I live in my world, and listen and feel to what the engine is telling me, and if its happy at 17 Deg BTDC who needs Google??🙃😀

I agree you know when something is right or wrong. I can feel if my modern cars tyres are 2-3psi down on pressure. My Vitesse engine did feel fine at around 20 BTDC. 

Iain 

[johny]

Now I think I'll be progressively advancing my timing in search of those extra 10 horses😁

[nicrguy1966]

4 minutes ago, johny said:

Now I think I'll be progressively advancing my timing in search of those extra 10 horses😁

That's what I'm currently doing.

[Firefly]

     Iain,

           My blasted modern starts ring bells and sending all sorts of silly messages when it "thinks" my tyre pressure needs attention.    

           Seriously tho` our findings on how much advance our engines need without doing serious damage, warrants some "scientific" analysis.    

[Wagger]

This thread is going on and on. The most sensible suggestions have come from PeteL and JohnD who has raced his Vitesse.

I am repeating myself now.

Run the engine at 2500 to 3000 rpm. Adjust the advance or rotate the dizzy (after slackening the clamp just enough) for max rpm and back it off a tad.

I have used this method since the 1970's and never suffered pinking, burned out valves, melted pistons or burned spark plugs.

You can play all you like and never better this method. A pal raced Minis using this method and wasted less time than others in the pits. He won most of the time too.

 

 

[Pete Lewis]

well said  

Pete

[Iain T]

I'm disagree I'm finding this a very interesting subject. I found a MG  article which may give a clue as to why our engines running on modern fuel might run better with significantly more advance than standard. I'll try and download but Upshot was they achieved lower exhaust temperature and better timed run by advancing around 13 degrees more than standard and primarily caused by the slower burn rate of modern fuels. At standard timing the fuel is still burning when the exhaust is opening hence higher head, valve and exhaust temperatures. 

Iain 

 

[Iain T]

Link to article 

https://ttypes.org/modern-fuel-on-trial/

Iain 

[johny]

Wow that is interesting! Also I see from the manual the mk1 engine design has a static timing of 13º BTDC while the mk 2 is 10º (or even less in the case of Mk3 GT6) so the problem might be more pronounced in the later cars...

[Steve P]

I had my 2.5 Vitesse setup for optimum performance on a rolling road, much easier. It returned 172BHP.

That`s why it snapped a driveshaft.

S 

[Iain T]

25 minutes ago, johny said:

Wow that is interesting!

I agree, I'll do more digging but it does seem to vindicate DD advice not to be obsessed by standard settings. The variable is the modern fuels. I'll do more digging but after the Christmas festivities and I'm alcohol free I will be trialing advancing my timing as my engine is not in a happy place with standard 13 degrees BTDC. 

Iain 

[johny]

I like the idea of using exhaust temperature to indicate combustion timing but as the article says got to be careful not to suffer pinking...

[Iain T]

As Mac said pre ignition and the resultant stress on bearings etc is the hidden horror. You can hear pinking. 

Iain 

[johny]

well Id argue that pinking at high speed is not so easy to detect and as the article says if your dizzy springs are weak this is a possibility😲 

[Firefly]

       Thank you Iain & Jonny, found that very interesting and have learn something. Think you will find those extra 10 horses, I`m off now, would hate bore anyone any further.  

 

[Wagger]

Octane ratings are very interesting. Slow revving high compression engines run better on high octane fuel. Low compression can use low octane. Low octane burns more quickly. Early Honda motorcycles revved like crazy so used low octane due to the short burn time.

Whatever the fuel, the 'Peaking' method still works. Unless you fit a modern management system that uses sensors everywhere to set the timing, you won't better it.

Nobody to my knowledge made a dizzy with different advance angles. Playing with springs can make differences but you will spend more time playing than driving the car.

I wasted may hours changing camshafts on motorcycles. Race cams were no good for riding to work.

 

[johny]

As the article indicates octane doesnt affect burn speed but the resistance to self ignition (different thing to pre-ignition) of the fuel. The mixture is compressed (more so in an HC engine) and burn initiated by the spark whereby the pressure in the camber starts to rise rapidly. If the octane isnt high enough the mixture then self ignites in other areas of the camber before the flame front reaches it so you get two or more and when they meet the pinging sound is produced.

The options to stop this are increase octane, reduce compression or as a fudge start the burn later by retarding ignition timing. The latter is most commonly used but means the peak pressure generated by the burn comes later in the piston cycle so reducing power and efficiency.

Now throw into this the possibility that todays fuel burn speeds have changed and things get really complicated! Certainly would be interesting to carefully try this peaking method of setting the timing and then see where it ends up and how the engine runs...

 

 

Edited December 13, 2023 by johny

[Iain T]

More Internet searching and it does seem that using E5 fuel in our engines advancing the ignition from standard is required but by how much will vary. Due to the fact E5 burns slower than old neat petrol I can see the logic in having to advance the timing to compensate. The only way to get your engines sweet spot is by ear/vacuum and trial and error. Also due to the chemical composition of ethanol there is more oxygen available and to compensate we need to enrich the mixture. I have 7B needles in so fueling isn't a problem just getting the right quantity in at the right time! 

If the above is correct and I have no reason to doubt it this is the opposite of what I've always believed ie retard ignition using E5 or E10(nasty stuff). 

Iain 

 

[johny]

Im worrying now how Im going to stop the wheels spinning with all the extra power😁

[Wagger]

Back in the later 1960's, Cleveland Discol was a five star high octane fuel using (Alcohol) in their advertising. Most others used Tetra Ethyl Lead.

I noticed that this made my motorcycle with a 9.5:1 compression ratio run quite rough compared with the other 'Super' fuels. Some users complained of burned out valves. I have no idea if it was Lead Free.

I later years, 5 star was phased out, so owners of cars with high compression engines like the Rover 2000TC, Hillman Hunter GLS (Holbay) and BMW 2002tii had to start tinkering or buying Octane Boosters.

Until about 2005, one could still buy Tetra ethyl lead. It was the only one that worked properly. I wasted many hours tinkering trying to obtain the lost performance. Eventually I went for Turbo Diesels with larger engines.

Power with economy was the result and no more tinkering for over 100k miles.

 

[Pete Lewis]

who remembers Shell with  ICA  added  (some sort of ignition control addative) caused a lot of moderns to burn valves 

or Pool Petrol   now that would make it pink well 

Pete

[nicrguy1966]

On 11/12/2023 at 21:23, Wagger said:

This thread is going on and on. The most sensible suggestions have come from PeteL and JohnD who has raced his Vitesse.

I am repeating myself now.

Run the engine at 2500 to 3000 rpm. Adjust the advance or rotate the dizzy (after slackening the clamp just enough) for max rpm and back it off a tad.

I have used this method since the 1970's and never suffered pinking, burned out valves, melted pistons or burned spark plugs.

You can play all you like and never better this method. A pal raced Minis using this method and wasted less time than others in the pits. He won most of the time too.

 

 

I'll be setting my ignition timing at 2500rpm as soon as the weather warms up a little.

One scary thing is how loud the engine sounds at higher revs inside the garage. I know it must be even louder at >4k rpm on the road, but it doesn't sound as scary without all the echo and with (some) sound proofing between engine bay and cabin 

[johny]

Yes ear plugs recommended and might be able to do it without an assistant by using the throttle cable adjustment - screw it out to hold the right revs and then youre sure any increase when moving the dizzy isnt from their foot wobble...

[nicrguy1966]

1 minute ago, johny said:

Yes ear plugs recommended and might be able to do it without an assistant by using the throttle cable adjustment - screw it out to hold the right revs and then youre sure any increase when moving the dizzy isnt from their foot wobble...

I was planning on screwing down the idle adjustment on the carbs. Bad idea?

[Iain T]

1 hour ago, johny said:

Im worrying now how Im going to stop the wheels spinning with all the extra power😁

Dig out those driving gloves with the knuckle holes😄, turn yer flat cap round and hang on! 

Iain