Timing for RON 95 fuel?

Does anyone know the timing for RON 95 fuel for a 1988 5.7l omc cobra, the manual(clymer) that I have states 5 degs BTDC for RON 90 and 10 degs for RON 93, can only seem to get the 95 fuel over here(UK)
Is it ok to run it at 10 degs as per RON 93 or should it be something else?
As regards to my other posts, I've got a rib injury which has stopped me doing any work for a while, but when I can I'll post results
Much appreciated, Nick
PS, has been running fine up til now, got a bit lumpy and was cutting out on low revs, so I've sent the carb for a sonic bath while I'm out of action and it will be refitted this week

We start, idle and warm up our engines on BASE advance.... and that's about it.
Your more important numbers will be your progressive advance, and your Total Advance and the RPM at which it's full in.
(see your OEM specs)

While adjusting BASE does affect your TA to the exact same degree (on the old mechanical systems), you do want to check your TA.
Example:
A 5* change to a BASE of 5*, is a 5* change to TA.
If the TA is now 26*, and you change a BASE of 5* to 10*, your TA is now 31*.
31* TA may be too much for your engine build.

GM in this year range was known to use the full dished pistons with the 64 cc chamber cylinder heads.... so be careful.

.

So what would the BASE timing be with the 95 fuel? would it be the same as 93 fuel? is there that much difference between the two to worry about?
Cheers again, Nick

ANYBODY??? or is this a dumb question?
If this is a "does 2+2=4" type of question then please tell a layman what 4 is
BTW, I fit and repair gas central heating boilers for a living, so dont know a great deal about engines

No, it's not a dumb question, and yes..... 2 + 2 does = 4...., but you are omitting the more important aspect of Ignition Timing.
Perhaps Re-Read my previous post.


The Octane rating of gasoline determines it's ability to resist ignition combustion.
The higher the rating, the greater it resists.
A higher rating does not necessarily render a higher output of energy.

Since the higher octane rated fuel resists greater, we can generally throw more ignition advance at the engine..... and visa-versa.

Technically, we could use slightly more Ignition TA with the 95, than what we could with the 93.
I'm not all that well versed on the RON system, but an increase from 93 to 95 in our system, is not all that great.
We probably would not make an adjustment.



Again, forget BASE (for the most part) and pay greater attention to your TA.
The correct TA should allow for a correct BASE, and visa-versa IF the distributor is doing what it's suppose to be doing.

Since we can account for any wear within the advancing system, Checking TA becomes more important and a No Brainer and a very safe No Brainer.

Cheers Rick, just wanted to know if any adjustments were needed for the different octane that we use, to what the book says
Thanks again