Morgan +8 Forum

Fuel grades for 3.9 engine

AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

MrToad Chris Coote
Brixham, Devon, UK   GBR
What grade of unleaded fuel have people found best on this relatively low stressed engine? all it says on the car is "unleaded only". Some engine management systems have better anti knock arrangements than others. Do these engines go better on super unleaded (97 octane)?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
davewhite Dave White
The owners manual for my 2003 Plus 8 recommends 95 to 98 octane. I have always run premium.


GR08MOG Geoff Roberts
Lindfield, West Sussex, UK   GBR
In 22 years with a Plus 8 I used both. No knocking but premium 'felt' better, and with a relatively small mileage the cost difference was insignificant.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Morgan13 Timothy Barlow
Vancouver, WA, USA   USA
I have a 4.0 in the +8 and I always use the best premium gas I can find in both my Morgans. Why would you want go cheap?

2013 M3W
Morgan stage ll motor kit

1998 +8
SS sport tuned exhaust

GoMoG Avatar
GoMoG Lorne Goldman
Mont Tremblant, QC, Canada   CAN
1984 Morgan Plus 8 (+8) "The Phoenix"
1990 Morgan Plus 8 (+8)
US pre-1996 Morgan Plus 8s have no knock sensors and have distributors rather than computerized ignition systems, so fuel quality and the timing it allows is VERY important. Though you can get away with kaka petrol on most crs since the early 1990s, don't try it with pre-1996 US +8s (or pre-2000 +8s elsewhere) unless you are into castrating your sports car. I would also examine your timing. People unavoidably and unknowingly adjust to a poorly performing car they happens so incrementally.

Always use the best fuel you can find. I learned that when I opened up a US propane Plus 8. Propane is around 118 Octane. The inside of the engine looked better than new!!! Absolutely clean.

There are different things about octane levels,

1. UK uses the the RON rating system to rate Octane levels, So when the Morgan Manual says 95 to 98 Octane that means 91 to 93 at a US gas pump.

2. USA used the MON rating system to rate Octane levels, it is the average quality of the fuel being pumped

3. I believe Canada uses the MON system but the rating indicates the minimum quality of the fuel being pumped.

But these things change fast..especially with this weird fascination governments seem to have with ethanol in the last decade.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions

Registration is FREE and takes less than a minute!

Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster

Join The Club

Sign in to ask questions, share photos, and access all website features

Your Cars

1986 Morgan Plus 8 8

Text Size

Larger Smaller
Reset Save

Sponsor Links