Switch to e85 ethanol for similar results or just run pump fuel

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Potato

If this is so why do other cars in categories not 5th Category, still run "av gas" (100 octane race fuel) and this is not policed correctly? And with my involvement in motorsport over the years I have never been asked to produce a "Fuel Passport" or questioned when I have bought fuel at the track!

Also if this is coming from the same scrutineers that were going to book group n minis for not having window winders at Easter last year, this is a joke!!!

It seems to be the blind leading the blind in SA!

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"Ex" is an unknown quantity and a S"pert" is a drip under pressure!

so basically.... don't try to set it up to require avgas, which means stay below 11:1 compression (gurus?)

Have it tuned to run best on a particular brand's 98, and always put that in. Don't ever put in 91 or it'll rattle like all hell

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did I tell you that I won a trophy?

ah,,,well,,, Simon this can be a can of worms this one

comp ratio & fuel octane rating & that`s not all of it really.

there is the camshaft & the ignition & the size of the engine & a whole pile of factors that will make or not make an engine ping

so,,, a general rule of thumb that i use to describe this problem to the average Joe is that small engines (IE: 850-998-1098) would best be kept under 9.5:1 with std-ish cams

the bigger donks (1275 & up) you can squeeze them to 10:1 with std-ish cams & a little more with a wilder cam, (but just a little)

the big donks (1360 & upwards to 1590) well we`ve seen good results with pump fuel & no pinging on 10.5:1 (with hot road/rally cams & shaped & pollished chambers & attention to detail such as cam timing & ign timing & fueling etc)

alloy heads & crossflow alloy heads & 16v alloy crossflow heads """That we have played with""" (Shaped & pollished chambers etc) we`ve had glory (without pinging) with 11:1 & sometimes 11.5:1,,, but there`s not much room for error up there tho--> say a bad batch of fuel combined with a very hot day

so,,, that`s the best "General" description i can muster at this point

but,,, some will argue against those numbers i1`m sure,,, they`re just general & if anyone does argue with me on this one then i reckon they`re silly in the head ,,,or they`re bullsh!tartists

edit--> Oh & just for the record,,, i`m not talking "WILD FULL RACE" cams here,,, you can build em with more comp ratio with wilder cams like race cars ,,, but i`m just talking about the average road mini engine here

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Matt, interesting that the bigger the motor the more compression you can run. Why is that?
Anything to with a comparatively shorter stroke?

more to do with the bore size i believe,,,

V8`s can run way up to 12:1 easilly on pump fuel & yes they have a few more cyls helping keep it rotating too, but they mostly have huge bore size compared to our peeuny little bores (comparatively)

late jap bikes can also run up to around 12 & 13:1 with no dramas on pump fuel & (yet again) they`re way up on bore size compared to us,,,, & of course they have far less weight to lug around, i acknowledge all these helping factors

i`m not too sure on the ducks-guts-intelligence of it all,,,, there are so many governing factors involved--> chamber-fill & swirl-turbulance, squish, flame-front, hot-spots, ignition timing, cam timing, dynamic compression ratio,,, etc etc etc

but i do know what works & what doesn`t in the real world in mini engines on the road

You really do need a little safety margin ... so i always tend to go a tad lower than whats "needed" , just to be on the safe side --> for the sake of a very hot day when someone has bumped the ign a little too advanced & with a poor batch of fuel & up a steep hill in 4th gear etc if you get my drift???,,, i hate pinging, simple as that!!!

if you know what pinging does inside your donk then you`ll be staying well clear of that danger point !!!!!!!!!!!!!!!

comp ratio & cam choice & engine size are all the things to sort when you first start to """design your engine""" & you need to look at it all & """knock""" it all on the head (pun intended ) before you start building the donk ,,, it`s where it all starts... BUT!!! it`s also where it all "may" finish too if it`s not set-up right to suit the fuel you intend to use.

Edit--> I`d bet GR would have some more "hard-core" info/intelligence about this topic than me

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.