Tune ups of older cars

[Talking Hoarse]

Just to pose a question (maybe a discussion) about engine tune ups or tuning of older spec engines.

My car (a 1983 Datsun Bluebird with a bog standard but fit L18S engine) – like all Datsuns I guess – was designed to run on unleaded (2 star) petrol of old. We don’t get that petrol in UK any longer – the nearest is unleaded that is higher octane than 2 star, probably somewhere between 3 & 4 star. I gather modern petrol also has different additives as well as alcohol that may affect running (maybe making engines run hotter?), not to mention damage all sorts of components (http://fbhvc.co.uk/ etc).

According to all the handbooks I have, the suggested settings for my car are (were?) ignition timing of 10° BTDC (at idle or static etc), and idle CO of 2% (the only mixture adjustment I can make on the Nikki twin choke carb). My car runs quite well at these settings, and I reckon deteriorates if I advance the timing by a few (a couple?) of degrees. I haven't heard it pinking though - except when I initially ran it on 5+ year old petrol (my old technique was to advance the timing until pinking under load and retard a couple of degrees).
I know that any factory settings are only a starting point, but indeed these are the only settings that many tuners (even armed with a Crypton etc) will bother with. Even tuners who are sympathetic with classics will likely be used to Ford & BL cars etc that were designed to run on 4 star and might need the ignition retarded for modern unleaded fuel.

Do you think that modern fuel makes any discernable difference?
Is there anything we should do to take advantage of / or to protect our cars from modern petrol?
What sort of settings (ignition timing & CO) would be a likely starting point for me to experiment with on my car?

Thanks in advance for any advice. If you are a member of the Datsun Owners Club forum you will see I have unashamedly posed the same question there.
Ed

[Wicksy]

I always set the ignition on my cars "by ear" as I have found the official settings result in pinking. I have electronic on the Princess and it is more or less permanently set but the MGB does get a check after points change.
I have a favourite test hill and back the ignition off a tad if the engine pinks in top gear - that's the way all the old handbooks used to recommend to do it before the advent of fancy electronic gismography
On the fuel side, luckily the good old SU's mixture strength can be easily be checked at idle using the piston lift method and adjustment is straightforward. Normal mixture seems to be fine for every day running.
You can get stressed by reading all the accounts of the horrendous damage that unleaded will cause to tanks, pipes and sundry parts, not to speak of the increasing percentage of ethanol that is to be stirred in soon - there are aditives available to ease the paranoid amongst us but I can't get very excited about them
IMHO as long as you are not driving at track day speeds every day, an old style engine will cope OK with modern fuels - unleaded is a dream compared with the crap stuff available in the 50's and 60's even, de cokes every 20K miles, burnt valves and gummed up carbs are a thing of the past thank goodness

[Grease Monkey]

The manufacturers settings are not a starting point, they are the figures that give the best economy and performance, having been in the motor trade for over 40 years all the makes and models of cars I've ever worked on have always been set to manufacturers settings with no problems and I continue to do so with modern fuels, all my classics are adjusted to their recommended settings and I've had no problems with 'pinking', I don't agree with all this 'setting by ear and knocking back', the manufacturers spend thousands on finding the best settings what makes you think you can improve on it by guesswork?

Rant over!!


John Simpson.

[Luxobarge]

the manufacturers spend thousands on finding the best settings.

Yes, and they did so with fuels that are significantly different to what we run the cars on today, so they are almost by definition, wrong.

[Wicksy]

I have tried setting the 2200 on my princess at "book" and I do have quite a sophisticated strobe and anaylizer but it just won't run correctly and that is also on super unleaded.
The MG is a bit sweeter but still needs that extra tweak I have found - I aggree with Luxo

PS The only way to settle this would be on a rolling road and ajusting to maximize power but I've heard old motors can react badly to RR's

[JPB]

.......I aggree with Luxo

Me too. We have the facility to view the nature of the flame front and other aspects of the combustion process in one of the student bays at work and although the modern Premium (95RON) fuel has a lower octane rating than the old 4 star, it really loses out when the timing is set "by the book" for cars originally intended for running on octane ratings now found in Super (97-99RON). Even the engine in the Dolomite - originally designed to run on pretty much anything above pool grade because of Sweden's inconsistent fuel quality when the engine was first launched - needs to be set to around 15 degrees BTDC static rather than the 11 degrees specified in Saab/Triumph literature of the period or it'll be flat as a fart. That's for premium fuel, on super fuel, then 17 degrees is considered the ideal these days. Other engines' behaviour varies on an individual basis with some combustion chamber designs offering less need for such experimental deviation from the old figures, but although my own engineering experience only spans the last 30 years and not the 40 that Mr Simpson should be proud to have behind him, I have to admit that some cars need the ostensibly crude approach of advancing until it starts pinking then retarding until it just doesn't.
It's the only way that takes into account unknown variables such as how many times a head has been refaced or, in the case of our Reliant 750 engines, how many times the block too has been shaved back and the liners and piston crowns reworked to suit.

PS The only way to settle this would be on a rolling road and ajusting to maximize power but I've heard old motors can react badly to RR's

Harsh man. Amusing in a Schadenfreude kind of way, but harsh.

[mr rusty]

Old motors do tend to run best at factory settings...but you need the fuel to be as close an approximation as possible to what was available at the time. My Vitesse was designed for 5 star fuel, and at factory settings it runs like a sack'o'sh*te on straight unleaded. If I want it to work at all on straight pump fuel I have to set the timing way off the book figure and it's still not really happy.

However- if I use an octane booster (valvemaster in my case..other boosters are available) I can set it close to factory numbers and it goes like it was meant to, but on straight pump fuel without an octane booster? No chance!

One point though- if factory settings were the be all and end all when my car was built in the sixties, why did Lucas fit vernier adjusters to their distributors? These disappeared by the time the seventies came around and fuel specs became carefully controlled, but I guess that prior to this you were expected to need to have a means of easily and quickly tweaking advance and retard.

[JPB]

The Vernier adjuster was fitted to allow for wear on the heel of the moving contact and its effect on timing advance. The theory was that its limited range would allow just enough adjustment to cater for this. In practice though, it was no more exact a science than adjusting by ear since 23 and 25Ds (among other distributors fitted with one) could be fitted with contacts whose heel was made of anything from Lignum Vitae through phenolic resins to that newfangled, polymer-based plastic stuff so the rate of wear wasn't predictable and some people even cheated and used a dob of grease on the heel to slow down that wear.

[Maaarrghk]

It might be worth checking up on, but I think that many Japanese engines from the mid 70's onwards were designed to run on unleaded because of the US market - they had switched to unleaded way back then. So I would guess just a bit of timing adjustment necessary.

Ethanol is a whole different bag of adders......

[Raymk]

In 1986 I bought a brand new Hyundai Stellar. This had a Mitsubishi engine from the Colt Galant which had been around for a good few years. 4star was rapidly being phased out in 1986 but the Stellar's handbook confidently proclaimed that no adjustments or additives were necessary when using the 'new' unleaded fuels. That proved to be the case, although the car always felt more lively with 4star. It went on to cover well over 100,000 miles without any trouble, mainly on unleaded.

My current Stellar is a 1988 model which had seen light use by a previous elderly owner, only covering 32,000 miles up to the point I bought it two years ago. It's a nice car (if you like Stellars ) but its engine is nowhere near as smooth running as my old Stellar. It seems to require frequent attention to the points, otherwise it goes off tune and acquires annoying flat-spots when accelerating. Aftermarket points are of very variable quality and this is part of the problem. Factory settings are soon lost by quickly wearing heals, indeed my last two sets of NOS points actually failed totally- the spring broke in the same place on each, suggesting incorrect heat treatment during manufacture.

Tuning my much older Reliant Regal MKVI is interesting. Factory settings for the Austin 7 (Ruby) derived sidevalve engine were based on the use of pre-war fuel which was unleaded and about 2star rated if you were lucky. Its compression ratio of 5.8:1 and modest (alright, extremely low) power output of 17.5bhp together with the passage of time/wear and tear etc. make tuning of considerable importance if one wants to actually move You would think that modern unleaded would be better for this ancient engine than 4star, however, as an earlier post pointed out, the engine was only expected to run for a few thousand miles before needing a decoke and having the valves reground when on its low grade fuel. When set up to run on 4star unleaded, the Regal runs more smoothly and does not suffer as much from fuel vapour locking. Unleaded, with its increasing ethanol content is a major headache during summer runs no matter how well I tune by ear or return to factory settings. Currently available fuel, the state of the engine, its fuel and cooling sytems and the type of driving are all variables that original factory settings do not allow for. The designer of my Regal's engine envisaged motoring at a somewhat slower pace but with much more frequent attention for decokes and valve reseating than is necessary now.