38 replies to this topic

[whistler]

45 years ago, before "Secret black boxes" did things to the engine, we could buy 105 Octane petrol at any garage which could take 11.5:1 in a race engine, but with today's unleaded stuff, 10:1 is pushing it.

I think you are mistaken. 5 star was generally 101 octane on sale to the public. Maybe it was available as a racing octane but unlikely for a garage/petrol station.

Fuel terminals generally stored 2 grades, 2 star and 5 star. 3 star and 4 star were mixed from the 2 and 5 star. We used to mix it on the tanker loading racks.

i remember the Rovers used to have a sticker on the rear window stating only to fill tank with 101 octane 5 star.

[DeadSquare]

 

45 years ago, before "Secret black boxes" did things to the engine, we could buy 105 Octane petrol at any garage which could take 11.5:1 in a race engine, but with today's unleaded stuff, 10:1 is pushing it.

I think you are mistaken. 5 star was generally 101 octane on sale to the public. Maybe it was available as a racing octane but unlikely for a garage/petrol station.

Fuel terminals generally stored 2 grades, 2 star and 5 star. 3 star and 4 star were mixed from the 2 and 5 star. We used to mix it on the tanker loading racks.

i remember the Rovers used to have a sticker on the rear window stating only to fill tank with 101 octane 5 star.

 

Perhaps it was 50 years ago ?

It was before these newfangled stars, when you pulled up at the pump with the Octane you wanted, and the attendant asked how many gallons you required.

 

The Octane rating was not a fixed definition, the formulation being periodically revised as engines developed, but for a few years in the late 60s / early 70s, there was a 105 pump Octane.

[nicklouse]

 

 

45 years ago, before "Secret black boxes" did things to the engine, we could buy 105 Octane petrol at any garage which could take 11.5:1 in a race engine, but with today's unleaded stuff, 10:1 is pushing it.

I think you are mistaken. 5 star was generally 101 octane on sale to the public. Maybe it was available as a racing octane but unlikely for a garage/petrol station.

Fuel terminals generally stored 2 grades, 2 star and 5 star. 3 star and 4 star were mixed from the 2 and 5 star. We used to mix it on the tanker loading racks.

i remember the Rovers used to have a sticker on the rear window stating only to fill tank with 101 octane 5 star.

 

Perhaps it was 50 years ago ?

It was before these newfangled stars, when you pulled up at the pump with the Octane you wanted, and the attendant asked how many gallons you required.

 

The Octane rating was not a fixed definition, the formulation being periodically revised as engines developed, but for a few years in the late 60s / early 70s, there was a 105 pump Octane.

 

Local aerodrome for 105 octane fuel back in the day. I can get 102 from my local petrol station.

[whistler]

The star system was introduced in the 60's.

[DeadSquare]

The star system was introduced in the 60's.

 

Yes, I can remember reading in the motoring press, the fuel companies explaining that they felt that the expanding car ownership were too thick to understand "Octane numbers", so they were moving to "Stars", but so that the thick and the enthusiasts would know how good the fuel was, for a while the pumps were marked with both systems.

[DeadSquare]

 

 

 

On the same assumptions as per my earlier post here, 10.28:1.

I thought you said 9.69 earlier but that was with a 266.

Quick calf then;

Running 8.3cc dished pistons flushed with the deck and allowing 3.3cc for the head gasket, so 11.6cc total.

To get a 10.2:1 ratio; 1330/4 = 332.5cc / (10.2-1) = 36.14cc - 11.6cc = head chamber volume of 24.5cc?

Now, where did my wife put my slide rule ?

All these calculations are all very well, but for most of the time they bear no relation to what is really happening.

Even if there was no valve in the way, yanking a piston rapidly down the bore does mean that the air pressure above the piston is the same as under the bonnet.

For almost 70 years, I have wondered if anyone has ever actually known how much short measure their pint of mixture is in their 568.25cc engine.

In a full race engine, it is believed that like a 2 stroke, the plug of exhaust gas charges off like a sonic piston down the tail pipe, leaving a partial vacuum behind it, and this vacuum effect helps to keep pulling in mixture past the still unclosed exhaust valve as the piston slows down, stops and begins to return to TDC; furthermore, it is hoped that this effect keeps enough mixture rushing in before the inlet closes, so that there is actually more than a pint of mixture in the 568.25cc pint pot when both valves close.

See what I mean ?

Haha yes I do get the gist of what your saying.

I’m very confused as you no doubt can tell!

 

 

In 1957, Sir Stirling Moss drove a special supercharged 1500 cc MG at almost 250 MPH at Bonneville.

 

The twin overhead cams were timed, such that when the exhaust gas had been pushed out by the piston at TDC, the valve was was held open so that some of the incoming mixture was blown down the exhaust, thus making sure that the cylinder was full of useful mixture and not diluted by any remains of the previous Otto Cycle.

 

I doubt if it was running on 4*

[Cooperman]

I run my rally 'S', which has a 286 cam and 1.5 rockers at 11.1:1 CR.

My 'fuel brew' is 98 RON Shell with an octane booster/lead replacement additive. I can run optimum advance with my custom-built Aldo dizzy (I have to run points as it's a '64 'FIA Historic Group 2' car and it does run extremely well on its twin H4's.

I have sometimes used Shell AvGas 100LL as the base petrol plus additive, but my contact for that at a sensible price is rather a long way from where I now live.

[mini13]

yeah, that MG that stirling set the record in definatly wasnt 4 star.... it was actually a specialized mix of methanol, nitrobenzene and sulfuric ether.

 

 

 

[phoenix11]

Whilst on about 1380cc engines I have an old MED one (1989 ) I thought it would be well worn but I was very surprised at the cylinder pressures taken with Snap on meter today they were all a tad over 200 psi . Which I would assume either very little use or a refurb . While I am on what should be a rough guide be to timing advance .I don't have a dial  gauge but it seems to be about 18 to 20 advanced is that about right