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MG Midget and Sprite Technical - Plug types

I'm trying to decide what plugs to fit to my car.
The Sun Test rolling road report 1987,(attached) listed BP7ES

This was when the car was raced and now it is no longer.
Main use is everyday short town driving, occasional bursts up the motorway here in Mallorca.
Engine Spec:

1430 stage 2 (Minispriint engine)
Lumetition optronic ignition
Head: 35x29 Msr158 025 2100
Oselli pistons
MGOC exhaust system & manifold: (C024)
Kent cam 286 or 256 (not sure!)
Frontline 5 speed box.

What do you reckon guys?
I have trouble getting NGK here in Mallorca, so Champion alternatives if possible too.





Mallorcaben

You don't list the compression ratio, which can have a big influence on the type of spark plug. However, I would say that if the rolling road set-up came up with BP7ES then that is likely to be suitable for the road as well. It is also where I would start if I didn't have the benefit of a rolling road.

Generally, for that state of tune and compression ratios over 10:1 I usually find BP8ES plugs are needed. Between 9.5 and 10.5:1BP7ES does the job (note the overlap there - between 10 and 10.5 it could be either). These may not necessarily be translatable as petrol type can have an effect too, and ours can be a bit rubbishy at times.

If the heat range is too low, the plugs will foul at idle or slow speed driving, in that case go to BP6ES. If it is too high, you will get a missfire under prolonged load - for example climbing a long hill on full throttle. Most commonly under these conditions, the misfire won't start immediately but when it does it will gradually get worse and you may get to hear some cumbustion grumbles. The plugs will also show signs of being a bit burnt. If this happens, go to BP8ES.

Paul Walbran

Not sure of the c/r offhand, I know its a VERY high compression engine.
I use 98 octane plus octane booster so its pretty much 5 star.
I do get fouled plugs (black) often.
Mallorcaben

In these days of unleaded fuel, black doesn't always mean fouled. If the plug is wet, it's a sure sign of it being fouled and misfiring. If it is a very high compression engine, I would avoid going to BP6ES at all costs, especially after looking at your pics on the other thread and the inviting looking hills you have!
Paul Walbran

Id do the BP8ES plugs for the reasons Paul outlined above....Just because you got a hotter plug dosnt mean you have to drive it that hard, but being you have that kind of engine, I think it would be harder on the engine to go the other way. Sort a like going to reg. unleaded of 83 octane from 95 just because your not racing it anymore

Prop
Prop

This thread was discussed on 01/08/2009

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