Thread: Advance or Retard?

Originally Posted by DEFENDERZOOK

i have also heard that running half and half.....ulp and pulp.....in your tank
increases the octane rating beyond the pulp 98ron......

i didnt believe it either.......

Back when we still had lead in standard adding pulp could raise the octane to about 100

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.

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.

Originally Posted by PhilipA

According to a Google search I just did, a 202 red for a HJ has a Compression ratio of 9.4:1.
You would almost certainly need 98 octane to run that CR without pinging.
OR You will need so much retard that it will overheat.
Use 98 octane. Simple.
You only have to use it when you are going to have heavy loads like uphill towing .
Regards Philip A

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.
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

Originally Posted by DEFENDERZOOK

some say that the higher octane fuel will give better economy due to it being more efficient.......

in english.....it gives more kms per litre than the standard uleaded does.....
so in the long run......it works out the same dollar wise......



im yet to notice any difference in my old car.......
but when i run it through the handbrakes falcon.......which is EFI......
it does run better.....you can actually feel the difference as the computer will advance the timing......
so it runs better.......

In my japanese shopping trolley (CR=9.5) it makes absolutely no difference to power or economy swapping from 91 to 95.
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.

Originally Posted by PhilipA

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

If it pings on 91 then it needs retarding till it stops pinging on 91, Regards Frank.

Originally Posted by Dougal

In my japanese shopping trolley (CR=9.5) it makes absolutely no difference to power or economy swapping from 91 to 95.
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.

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.

Originally Posted by mark2

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.

I know it's fitted with knock sensors and being EFI it tunes itself.
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!