I run a bog stock 3.5 in my Morris, with the usual Weber 500 and Edelbrock manifold, plus block huggers and a split system. I usually run it on basis unleaded economy dinosaur juice. My dizzy has the Real Steel spring conversion in and I modified the internal advance stop so it will give 36 full advance at 4000rpm, whilst still giving 6 degrees at idle, vacuum disconnected.
http://www.seight.com/ignition.html
I currently have little idea what my full timing advance actually is, as it was pinking at 36 so I retarded it by hand just a smidgeon until it didn't pink under full bore acceleration.
So, the question: Would there be any benefits power wise if I used the best possible petrol available (highest octane?) and advanced the timing as much as it would take? I'm just curious if all this high octane fuel stuff works in the real world.
Using what type of fuel?
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Hi Paul
the real answer is to plot the timing curve using a rolling road for maximun power then build a distributor to match. If you cannot get max power because the thing pinks first then up the octain rating (or change plugs) or remove whatever else is causing the pre-ignition.
36 degrees is quite alot of timing, if you need higher octain rating to get more power at this timing (without it pinking) then I would actually suspect you need more compression.
You get people in the american magazines with running late 70's big block pontiac 440's (and others) complaining that with 42 degrees of timing they can't advance ignition any more as they can't "get good gas" then find out they are running 7.8:1 original compression and 225 degrees of cam at .05" off an aftermarkt cam.
What compression are you running?
What are the timing figures for the cam?
Match compression and valve timing to each other and the heads.
Then plot the timing curve on a dyno.
Build the distributer curve to match
if you need to... tweek the octain and plugs to avoid it pinking.
Mike
the real answer is to plot the timing curve using a rolling road for maximun power then build a distributor to match. If you cannot get max power because the thing pinks first then up the octain rating (or change plugs) or remove whatever else is causing the pre-ignition.
36 degrees is quite alot of timing, if you need higher octain rating to get more power at this timing (without it pinking) then I would actually suspect you need more compression.
You get people in the american magazines with running late 70's big block pontiac 440's (and others) complaining that with 42 degrees of timing they can't advance ignition any more as they can't "get good gas" then find out they are running 7.8:1 original compression and 225 degrees of cam at .05" off an aftermarkt cam.
What compression are you running?
What are the timing figures for the cam?
Match compression and valve timing to each other and the heads.
Then plot the timing curve on a dyno.
Build the distributer curve to match
if you need to... tweek the octain and plugs to avoid it pinking.
Mike
poppet valves rule!
Mike,kiwicar wrote:Hi Paul
the real answer is to plot the timing curve using a rolling road for maximun power then build a distributor to match. If you cannot get max power because the thing pinks first then up the octain rating (or change plugs) or remove whatever else is causing the pre-ignition.
36 degrees is quite alot of timing, if you need higher octain rating to get more power at this timing (without it pinking) then I would actually suspect you need more compression.
You get people in the american magazines with running late 70's big block pontiac 440's (and others) complaining that with 42 degrees of timing they can't advance ignition any more as they can't "get good gas" then find out they are running 7.8:1 original compression and 225 degrees of cam at .05" off an aftermarkt cam.
What compression are you running?
What are the timing figures for the cam?
Match compression and valve timing to each other and the heads.
Then plot the timing curve on a dyno.
Build the distributer curve to match
if you need to... tweek the octain and plugs to avoid it pinking.
Mike
I wasn't actually thinking so technically, just curious whether: more octane = more timing advance= more power.
I'm running stock cam and all, and I think CR is 9.35:1, 1984 SD1 motor. It is funny but the stock distributor curve maxes out at about 26 full advance, as mentioned in the link, but I have never understood why it should stop so short of what is supposed to be 'ideal', unless it was an 80's emission thing.
I'd like to get it on a dyno one day just to see whether the fuelling/timing is anywhere near the ideal, rather than to extract the max performance.
It is, afterall, a relic of a car, with an 80 year old suspension design.
hi Paul
higher octain may let you run more advance, but that does not mean it will always give you more power. Higher octain petrol burns in a more stable manner (there is a horribly complicated bit about shock waves and flame fronts at this point
), hence it can resist detonation it does not have a higher calorific value. The upshot is you can get the fuel air mixtuer burning too soon so the pressure on the piston is building too fast while the piston is still rising, end result you loose power.
The advance on a modern design 4/5 valve engine, or even the ls series engines is much less than on the rover as the newer head design gets the mixture burnt much more quickly.
The short period cam and 9.35 compression you shouldn't need huge advance.
Mike
higher octain may let you run more advance, but that does not mean it will always give you more power. Higher octain petrol burns in a more stable manner (there is a horribly complicated bit about shock waves and flame fronts at this point
), hence it can resist detonation it does not have a higher calorific value. The upshot is you can get the fuel air mixtuer burning too soon so the pressure on the piston is building too fast while the piston is still rising, end result you loose power.The advance on a modern design 4/5 valve engine, or even the ls series engines is much less than on the rover as the newer head design gets the mixture burnt much more quickly.
The short period cam and 9.35 compression you shouldn't need huge advance.
Mike
poppet valves rule!
Re: Using what type of fuel?
I am running a 3.5 on dinosaur 95 juice also with the same advance curve ( on advise from my dynojet centre ) without anny problems at all. I am running an intank fuelcat and while most people will tell you it wont work, well untill you found out your self it will work.Paul B wrote:. I usually run it on basis unleaded economy dinosaur juice. My dizzy has the Real Steel spring conversion in and I modified the internal advance stop so it will give 36 full advance at 4000rpm, whilst still giving 6 degrees at idle, vacuum disconnected.
.
Fuelcat raises octane level from 95 till 99 but it supose to make your engine run on unleaded fuel........
Running a Holley 520 ( custom build ) ontop of it.
Your setup drove me for several years before I fitted a blower last year.
I didn't change the ignition advance at all after this, only fitted a boost timing master.
