lead additive- Tetraboost

[g5wqian]

hi stephen ;
i used to do drag racing in the 1980s and had various american vehicles chevy and buick , but on the road i had a landrover with a ford v6 engine which i raced up using a 310deg cam , powermax pistons , 4 barrel holley carb and larger valve ported heads , different valve springs and different ignition etc .
the compression ratio was around 12.5-1 and measured 220psi on the compression gauge .
it would rev to 7500rpm and took that old series 2 landrover to 130mph if you dared .
for a couple of years it ran great , but in 1987 i remember the govt dropped the 4 star fuel rating by 25% almost overnight .
well one day after this i was going to work and had the engine pulling hard on the dual carriageway and i heard a rattling sound [pinking] coming from the engine .
it wasnt many seconds after that it started running rough .
i managed to get it started later in day to come home but limped home .
i then stripped the heads off the engine and found a handfull of melted piston tops .
it had detonated and burned the pistons .

was all due to the lowering of octane rating in the current fuel , and no good for 12-1 compression ratio and a lot of ignition advance .

so with this i had to build another engine and took a different approach by using 9-1 pistons and ignition advance much less than previous , i think about 38degs as opposed to 42degs.

once engine was run in i could use it to full potential , and it was fine then on unleaded fuel , no pinking and no detonation occurred at flat out throttle .

so i think if youre up in the double figures of compression ratio then need to keep and ear on the engine noises under WOT especially in higher gear pulling hard and up an incline .

on my AJS twin , i found that just by using thinner copper head gaskets it was enough to give me a bit of pinking when going uphill pulling hard , even at lower revs on 4th gear , but now i use composite head gaskets and it doesnt pink .

there was only about 5-10psi difference between compression ratio pressures between the gaskets used but it was enough to notice the difference .
compression pressure when i put the rings into a newly honed bore was 145psi with thin copper gasket and 135psi with composite gasket .
gasket thickness was 0.93mm copper and 1.7mm composite .

maximum ignition adavance along side compression ratio seems to be the mitigating factor when it comes to how the engine will run with unleaded fuel and so in my own experience if you run 9-1 or lower and under 40degs total ignition advance then it will run fine on unleaded , but if over this then need to be carefull .
the octane boosters that i have used are , silkolene proboost which is what the motocross boys use a lot of , stp , carplan , millers etc.
i used the silkolene proboost in /since the 1980s .
i have also used 100LL avgas mixed or non mixed , i can obtain it from work when we do filter changes etc , but it is potent stuff to the nose and to lawnmowers .
the C16 racing fuel we used in a ford pop in the 80s and 90s that we raced in the "outlaw anglia" series with a 505cu inch chrysler race engine and ran great without problem using high compression pistons .

i would think the easy way to work out if an octane booster works in someones engine would be to run on unleaded first and then find somewhere you can get it to pink , and then do the same again but with octane booster added , then youll know if it works .

good luck with youre G80S , i would like one myself someday .

cheers , ian

[StephenG80]

Hi Ian,

That sounds like a pretty a impressive landi! - I am not playing in that league of compression and timing with my G80s so, as you say, all should be OK. If you are looking for a G80s I presume you have seen this one:

http://www.ebay.co.uk/itm/MATCHLESS-195 ... OSwyYJZyUb~

and just so happens I have a LR Series 3 for sale - if you're looking fr one of those - you might want to upgrade the brakes before you tune her to do a 130mph though!

http://www.ebay.co.uk/itm/1978-Land-Rov ... SwtGNZz6R7

cheers

Stephen