any downside to mixing in some 100 octane fuel into the tank??any
real advantage?–
Peter Willetts 62 OTS
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In reply to a message from PeteWilletts sent Mon 25 Mar 2013:
The only downside is cost. There is no upside, unless you’re
having problems with pinging. Of course, you can also just
tune that out with your EDIS system… :-)–
Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Ray Livingston sent Mon 25 Mar 2013:
In Europe the highest octane fuels/petrol tend to have 100%
gasoline, whereas the lower octane fuels have 5-10% ethanol which
is very detrimental to the fuel system. Some even claim to give
more performance MPG wise. I always keep my old cars with their
tanks full of the highest octane fuel available.–
peder
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In reply to a message from peder sent Tue 26 Mar 2013:
Same down here in Aus or at least state of NSW. 91 octane
is typically 5 to 10% ethanol but the 95 and 98 octane is
up posed to be straight petrol. I have actually found the
E and my old motorcycles tend to run better n the 95. It
has been suggested the 98 is formulated specifically for
very modern FI induction and that it does not work so well
with carbs and my experience mirrors that. Plugs in my '74
Ducati fouled up in 100 miles to the extent the engine
started misfiring on Shell 98 octane.–
The original message included these comments:
In Europe the highest octane fuels/petrol tend to have 100%
gasoline, whereas the lower octane fuels have 5-10% ethanol which
–
Chris , 69 FHC , Ducati, Moto Guzzi , Aston DB7
Sydney, NSW, Australia
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In reply to a message from db7gtgrigio sent Tue 26 Mar 2013:
I believe the E-Type was designed to take advantage of 5-star
petrol in the UK (around 100 Octane).
No longer available sadly.
Here is what Wikipedia says, ‘’ 5-Star = 100 octane, 4-Star = 98
octane, 3-Star = 93 octane, 2-Star = 87 octane … The 5-Star
rating was the motor equivalent of avgas and was only used in high-
performance cars with high compression-ratio engines, such as
Jaguars, etc. It was also used for racing engines.’’.
Seems accurate as far as I remember.–
Neville - http://www.XJ13.eu, XJ13 in-progress.
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In reply to a message from V12 Racer sent Tue 26 Mar 2013:
Neville, Are you sure about the XK engine being designed
with 100 octane in mind ? I personally have no info on this.
However, I don’t understand why that might be so, because
AFAIK higher octane just permits the use of higher
compression ratios, so the XK might be expected to run on
much lower octane fuel? In terms of modern fuels the lower
octanes do not have the more sophisticated additive
packages, so with modern cars we are advised to use the
higher octane grades, not for the octane per se, but for the
better additive packages that they contain, which are better
suited to the fuel injection systems etc. Just musing…not
an expert!–
The original message included these comments:
I believe the E-Type was designed to take advantage of 5-star
petrol in the UK (around 100 Octane).
Neville - http://www.XJ13.eu, XJ13 in-progress.
–
John M Holmes 1973 E Type SIII Supra 5Sp, 70 SII OTS 05XJ8L
Ontario, Canada
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On occasion I have used some 100LL stuff from the local
airport…no question the car runs better/smoother.On Tue, Mar 26, 2013 at 1:11 AM, PeteWilletts pjwilletts@hotmail.com wrote:
any downside to mixing in some 100 octane fuel into the tank??any
real advantage?Peter Willetts 62 OTS
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–
Les…'68 S1.5 2+2
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In reply to a message from John M Holmes sent Tue 26 Mar 2013:
John,
The XK engine was designed in 1948 to run on 72 MON pool
petrol. There is a factory bulletin from Feb 1953
describing the benefits of the new 80 MON (90 RON) higher
octane fuel. Fuels continued to improve and Jaguar raised
compression and ignition timing to take advantage of it.
Most of the then current road tests for the E specified 97
or 100 RON fuel. This would be roughly equivalent to the
modern 94 CLC octane fuel, but it is not the same for tuning
purposes and some cars that run hot or burn oil will ping on
it. Most 9:1 3.8’s I’ve taken apart show some piston crown
erosion from this effect. Octane requirement varies with
many factors and the XK with 100 cc combustion chambers,
wide VIA, high domed pistons and marginal cooling is a knock
limited design. It is not comparable to modern 4 valve pent
roof designs with shallow, fast burn chambers and better
cooling. The factory knew this and chose to use 8:1 pistons
in racing, and give up a little performance for reliability.
If an XK engine pings at the factory timing spec, higher
octane fuel is a good thing.
Paul–
The original message included these comments:
Neville, Are you sure about the XK engine being designed
with 100 octane in mind ? I personally have no info on this.
However, I don’t understand why that might be so, because
AFAIK higher octane just permits the use of higher
–
PS
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In reply to a message from PS sent Tue 26 Mar 2013:
I live on an airport and have a 68 9:1 with 3 S/U�s I frequently
use 100LL avgas. Runs fine but cost more I tend to alternate with
the local Chevron station down the road. Be advised that Big
Brother does not like you putting 100LL in anything except an
aircraft; so I get mine after the FBO closes. Had some head work
done (Extrude Honed) for better air flow and the pistons looked
fine. On hot days and you want to do some hard driving I think it
is the way to go.
Dan–
DanS
columbus ga. usa, United States
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In reply to a message from John M Holmes sent Tue 26 Mar 2013:
John - I am certainly no expert either!
However, I didn’t say the XK engine was designed with 100 octane in
mind - I said the E-Type was (with its later straight-port 9:1
development of the 1948 XK engine).–
The original message included these comments:
Neville, Are you sure about the XK engine being designed
with 100 octane in mind ? I personally have no info on this.
–
Neville - http://www.XJ13.eu, XJ13 in-progress.
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In reply to a message from PeteWilletts sent Mon 25 Mar 2013:
You might check with your paint store and get 5 gal drum of
toluene to mix in. It has a RON of 121 and a MON of 107
[114 (R+M)/2 or Anti-Knock Index AKI)]. It is denser and
produces more energy (heat) than gasoline - good for faster
turbocharger boost btw. It has a lower fuel sensitivity
compared to most other oxygenated octane boosters. If you
built plastic models you’ll definitely recall the smell from
the old glue. Toluene is one of the main ingredients of
gasoline, its combustion yields only CO2 & H2O so its safe
for catalyst and O2 sensors. It seems you can use from 5%
Also if you’re looking at an off-the-shelf octane booster
which claims to boost your octane up to ‘‘3 points’’ that’s
0.3 and NOT 3.0 AKI points. Toluene is expensive but is
more cost effective than off the shelf octane booster products.
http://www.best-chemical.com/racing.htm
On the broader topic of Octane, you have at least US,
British and Australians replying. Note that the US and
Canada (& Brazil) now use AKI and not the worse (less
stressful) traditional RON test. The US changed from using
RON to an AKI measure of octane sometime during the '70’s.
RON figures are still used by most of the rest of the world.
RON is usually about 8 - 10 higher than MON for most
gasoline, thus the US AKI which is the average of RON + MON
will be 4 - 5 points lower overall compared to a RON figure
quote by our European friends. So our 93 octane fuel here
in TX probably not far from from 100 octane gas in '60’s
Britain or a gas pump in the US during the mid-60’s to early
70’s muscle car heyday*.
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In reply to a message from PS sent Tue 26 Mar 2013:
Paul
I am not sure what you are saying here. ‘‘some cars run hot’’ on
higher compression gas?
Is today’s 94 octane (availiable here in Canada) to high for some
of our cars?–
The original message included these comments:
or 100 RON fuel. This would be roughly equivalent to the
modern 94 CLC octane fuel, but it is not the same for tuning
purposes and some cars that run hot or burn oil will ping on
it. Most 9:1 3.8’s I’ve taken apart show some piston crown
erosion from this effect. Octane requirement varies with
–
larry 71 sII
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In reply to a message from larry 71 sII sent Tue 26 Mar 2013:
I am not sure what you are saying here. ‘‘some cars run
hot’’ on higher compression gas? Is today’s 94 octane
(availiable here in Canada) to high for some of our cars?
Larry,
No, the higher octane gas does not cause it to run hot. If
the engine runs hot because the block and/or radiator is
silted up, or if oil dilution from the rings and guides
lowers the effective octane, 94 is still not high enough. If
it is 30F out and you are cruising at 3000 rpm, regular fuel
is probably OK. If it is 90F out and the engine is above
90C, and you want to use WOT, you probably can’t get enough
octane in pump gas. My experience is there is a wide
variation in +40 year old engines.
Paul–
The original message included these comments:
I am not sure what you are saying here. ‘‘some cars run hot’’ on
higher compression gas?
–
PS
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