Octane reducer..

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Steptoe
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Octane reducer..

Post by Steptoe » Thu Oct 11, 2007 2:39 am

At car club last night and guest speaker was a competitor in the 2007 Peking to Paris race...
Very interesting...when theu hit Russia in the old 1930 car, they filled with 80 octane...the car ran faster, smoother and increased tank milage from 270 km to 360km.

Ok what has this to do with alternative fuels?
I also run a Bradford van that was designed to run on British pool fuel circa 1938 to 1954
long stroke low compression no overlap..
Appling what I know re difference between hi octane alternatve fuels and lower octane petrol engines and unless an engine has the right fuel for what it is built for...it just doesnt reach anyware its full potentual.

There for our old vinage cars just are not as fast, smooth or economic as when designed...they are not the old slugs that they are credited for in the last 40yrs.

What I want to know is how and what is best to reduce the octane of modern 91 down to somewhere in the 70 to 80 octane range.

kerosine has be suggested but I have also been told long term use is not good because it can wash the oil off cylinder walls??? and messes up the oils???
some stuff called n-heptane added to fuel at about 10 to 12% ???
But what is it used for...what sort of place ould one purchase this stuff from?

Help, ideas comments?
Steps
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Mattelderca
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Post by Mattelderca » Thu Oct 11, 2007 9:48 am

Steps,
It is not the octane rating itself that is to blame for this. Which is quite a debate by the way! Alot of old bike guys talk about this fuel issue as well. Seems the newer petrol formulations are really different in many aspects from fuel some 30, 40 50, years ago. Viscosity comes into play as well as alcohol content. I remember 25 years ago, when I dealt with fuel on a daily basis, the colouring was an amber to dark gold, now it is more clear or even green. Anicdotal I know. There are a few reputable articles out there that adress modern fuel versus old. I find it very interesting but don't have the patience to really grasp the chemistry. Maybe we can throw this over to Franz, our resident expert so to speak. He does live in Texas!

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Steptoe
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Post by Steptoe » Thu Oct 11, 2007 3:06 pm

I have been doing the calc, cc ing swept vollmes and heads of the Bradford engine....working out how the best way to get compression up..
Be deck, plane heads , redisgn combustion chamfers etc etc
By planing the heads, the fillng reshaping the combustion chamber I can get the dynamic comptession up to 7.2 ...which is in the ball park of a modern low performance car on 91.
Which is fine
(have a stronger nichrome steel crank cast and machined to.)
But before getting into machning heads thought it may be worth looking at running a low compression/octane fuel...to learn more frther info for future reference...
These are 2 cylinder 1000 cc horozonally opposed side valve engines.

the main issues with old low compression engines is not the octane but the speed of burn...higher the octane the slower the burn...
Basically there is very little or no overlap on the valve timimh of the old engines...therefore the inlet closes. the hi octane fires, and is still brning when the piston gets to the bottom of the stroke.
besdides valve stuff which im not realy concerned about...this late burn doesnt make for a very efficient engine.

I was talking to a old guy yesterday...he mentioned something about 80 octane aviation fuel???
May get time for a trip out to the local airport? find and talk to some guys out there.
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Steptoe
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Post by Steptoe » Tue Oct 16, 2007 6:33 pm

Bump
Anyone have anything to add...comments thoughts?
Unfortunately my $1,000,000 varable compression octane engine has got lost in the post :shock:
The back shed I was going to put it in ...burnt down, along with my can of n-heptane. :cry:
And my son;s m8, a boy racer sighted the can of octance we resuced and put it in his Wankel engine :idea:

Cheers
Steps
:D :D :D
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