Back when we still had lead in standard adding pulp could raise the octane to about 100
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Back when we still had lead in standard adding pulp could raise the octane to about 100
Quote:
Originally Posted by DEFENDERZOOK
Running half ULP and half PULP will give you an octane halfway between the two (ULP is 91 and PULP is 98-100) - so RON would be somewhere in between, octane rating is based on the proportion of aromatics (toluene, etc) and other compact molecules to the ratio of straight chain molecules in the fuel. So a VERY simple calc, would give you - (91+98)/2 = 94.5 +/- a couple of octane points.Quote:
Back when we still had lead in standard adding pulp could raise the octane to about 100
Adding half a tank of LEADED PETROL and half a tank of PULP, would give you a HIGHER octane than the above, but probably wouldn't increase your octane above the PULP octane. This is because tetraethyl lead (TEL), when added at normal concentrations gives about 4 octane (RON) points. If you combine half a tank of leaded, and half a tank of PULP, you get the same RON as above for the base stock, but the half-diluted TEL would probably add a couple of points = 94.5+2 = 97.5 - but notice it still only makes the octane about the same as the PULP!!!
Note that the above doesn't work with l;ead replacement fuels, as valvemaster (1 of the 2 additives) doesn't increase octane, and MMT (the other additive) only adds 1 point.
Compression ratio (CR) doesn't always determine the octane rating required, I have had cars running 9.8:1 CR and happily running on 91RON ULP, it will depend on Cam and Valve timing, head and combustion chamber design and fuel and spark delivery.Quote:
Originally Posted by PhilipA
Do another search on Google and see what Octane rating Holden recommends for that engine, Regards Frank.
Tank, it pings on 91.
A 202 was designed to run on 96 Octane "Super". Holden offered a low comp engine which would run on "standard" 91?, but few bought it. Ford also offered a low comp 3.3 back in XD days.
There is now no 96 "Super"( there is 95 which he could try)
There is a world of difference between a 202 designed in about 1956? , when the first red Chev 250 engines were introduced, and injected alloy head engines from the 80's onwards which can run high comps and low octane fuel.
Regards Philip A
In my japanese shopping trolley (CR=9.5) it makes absolutely no difference to power or economy swapping from 91 to 95.Quote:
Originally Posted by DEFENDERZOOK
Obvoiusly it doesn't have any detonation issues running ideal timing with 91 so the higher octane of 95 is wasted in that car.
If it was pinging on 91 and retarding timing to compensate, then 95 would certainly help.
Where's your air intake? Getting colder air into the engine should reduce detonation a little.
If it pings on 91 then it needs retarding till it stops pinging on 91, Regards Frank.Quote:
Originally Posted by PhilipA
Its probalby not fitted with knock sensors - without them you dont really get the full benefit of the higher octane fuel unless its specifically tuned for it.Quote:
Originally Posted by Dougal
I know it's fitted with knock sensors and being EFI it tunes itself.Quote:
Originally Posted by mark2
To get the most benefit from high octane you've gotta have detonation issues on low octane.
Just to avoid confusion, I don't have a 202 ;)
It's actualy a 173 from a VB commodore, last of the red engines!
The engine was designed to run on leaded super petrol. The purpose of tetra-ethyl lead was to allow the use of higher compression ratios. Without going into detail, the higher the compression ratio, the higher octane fuel is required. My Chrysler Hemi426 with 12:1 compression ratio was happiest on 115 octane leaded Avgas. My modified EH 179 (10:1) in 1967 needed leaded super petrol with 1:5 of added methyl benzine to prevent ping at normal or slightly advanced settings. Unleaded is generally not good enough to satisfactorily run these older higher compression engines.