My understanding of it is that it increases the compression a little before detonation. More compression = more performance. Thats why you get pinging when you advance your engines timing too far... which can lead to premeture ejacu-explosions (detonation)kevmif wrote:Hrrrm... was really hoping it would lead to a slight improvement in both! Especially with the higher octane fuel.
Can anyone fill me in on the technical side of how an advance in timing actually improves performance with higher octane fuel?
Performance Options for Older Subarus: *Read before Posting*
- discopotato03
- Senior Member
- Posts: 2134
- Joined: Sun Mar 18, 2007 9:29 am
- Location: Sydney
Advanced ignition timing is about lighting the fire (sparking the plugs) when the rising pistons are further away (before) top dead centre on the compression strokes .
There is a slight time lag between the spark plugs firing and burning enough of the fuel/air mixture to get a pressure rise above the pistons .
With most production engines you want the peak pressure to be with the crank ~ 15 degrees past top dead centre on the power stroke .
Production/emission engines being what they are often want to detonate if you light the fire at the optimal time for BMT or best mean torque ignition timing and the answer is to retard the timing (meaning fire the plugs when the pistons are closer to top dead centre (TDC) on the compression stroke . By retarding the timing the combustion pressure peak is later in the cycle meaning a lower peak and less agressive detonation conditions with low octane fuel .
I should add at this point that high octane fuel does zip for you if you can't take advantage of things like advanced ignition timing/higher compression ratios etc . All high octane PULP has is additives to make it MORE difficult to ignite and less likely to do so when not intended . You can actually go backwards using it in an engine not intended for it because the effort to intentionally light it is more difficult - results - more performance through lighter wallet ...
Anyway advanced ign timing is about increasing combustion pressure rather than compression pressure , how much will depend on how conservative the ign timing was to start with compared to best meant torque timing and the engines detonation threshold .
Things that can help are optimum water and oil temps - and making sure that the airbox/inlet system is doing it's best to find the coolest air available .
Cheers A .
I liked the point about older engines with less ring sealing handling a bit more advanced ign timing - 24 for a high mileage 82T , must try that since mine's doddering up to 290K . I think it clicked over 250 approaching Sydney from where I bought it in Melbourne and when checked its lowest pot showed 80-85 psi compression pressure . It aint strong any more so any help on it's last legs would be most welcome !
There is a slight time lag between the spark plugs firing and burning enough of the fuel/air mixture to get a pressure rise above the pistons .
With most production engines you want the peak pressure to be with the crank ~ 15 degrees past top dead centre on the power stroke .
Production/emission engines being what they are often want to detonate if you light the fire at the optimal time for BMT or best mean torque ignition timing and the answer is to retard the timing (meaning fire the plugs when the pistons are closer to top dead centre (TDC) on the compression stroke . By retarding the timing the combustion pressure peak is later in the cycle meaning a lower peak and less agressive detonation conditions with low octane fuel .
I should add at this point that high octane fuel does zip for you if you can't take advantage of things like advanced ignition timing/higher compression ratios etc . All high octane PULP has is additives to make it MORE difficult to ignite and less likely to do so when not intended . You can actually go backwards using it in an engine not intended for it because the effort to intentionally light it is more difficult - results - more performance through lighter wallet ...
Anyway advanced ign timing is about increasing combustion pressure rather than compression pressure , how much will depend on how conservative the ign timing was to start with compared to best meant torque timing and the engines detonation threshold .
Things that can help are optimum water and oil temps - and making sure that the airbox/inlet system is doing it's best to find the coolest air available .
Cheers A .
I liked the point about older engines with less ring sealing handling a bit more advanced ign timing - 24 for a high mileage 82T , must try that since mine's doddering up to 290K . I think it clicked over 250 approaching Sydney from where I bought it in Melbourne and when checked its lowest pot showed 80-85 psi compression pressure . It aint strong any more so any help on it's last legs would be most welcome !
Sounds like it could be fuel pump or dirt fuel?
"Bianca"
'86 Brumby - Dual Port Heads, 5 Speed Dual Range, Custom Cam, Tuned Weber, Tuned Suspension, 2" Body Lift Kit, LSD, 14" rims, 2.25" Exhaust, Snorkel, Dual Batteries, DVD Player, UHF, VHF, etc. Offically now part of the 350, 000 km Club! And still pulling like a freight train.
"Claudia"
82 MY Wagon - EA81T, RS Liberty WIAC, 5 Speed Dual Range, Tuned Suspension, 14" Rims 27" Tyres, 2" Body Lift Kit, Apline Head unit, UHF, Roof Console, L Series seats, Soon to have New Paint, snorkel, Dual batteries, etc
'86 Brumby - Dual Port Heads, 5 Speed Dual Range, Custom Cam, Tuned Weber, Tuned Suspension, 2" Body Lift Kit, LSD, 14" rims, 2.25" Exhaust, Snorkel, Dual Batteries, DVD Player, UHF, VHF, etc. Offically now part of the 350, 000 km Club! And still pulling like a freight train.
"Claudia"
82 MY Wagon - EA81T, RS Liberty WIAC, 5 Speed Dual Range, Tuned Suspension, 14" Rims 27" Tyres, 2" Body Lift Kit, Apline Head unit, UHF, Roof Console, L Series seats, Soon to have New Paint, snorkel, Dual batteries, etc
I notice a lot of people havent taken fuel mixture into consideration when talking about ignition timming vs engine temp. the leaner your engine is running the hotter it operating temp will be. EG. if your running a standard fuel system with 12-16 deg btdc, you may find your running hotter. most larger carbs put on these engines are not jetted exactly right for them and ussually run richer therefore in most cases running cooler. just helps understand why this bloke overheats on sunny days, but the next bloke dosent.
i am halfway through stripping my '92 Brumby before sending it away to be straightened out and painted.
While this is happening I am going to rebuild the ea81 engine and include a few mods while I'm at it (before anyone says anything about an ej conversion please note that I am determined to keep the original engine and am looking forward to the challenge of drawing what grunt I can out of it).
I already have weber ready to go in and will be putting extractors on when the time comes. I will definitely be porting and polishing the heads and possible even shave a little off of them in the process.
I have seen various brief mentions of custom cams for the ea81 on this site and was wondering if anyone can point me in the right direction in order to get my hands on a set. If so can someone also give me a rough indication of price. I am based in Darwin and therefore limited with what I can get up here however i am more than happy to pay the frieght for the right bits
While this is happening I am going to rebuild the ea81 engine and include a few mods while I'm at it (before anyone says anything about an ej conversion please note that I am determined to keep the original engine and am looking forward to the challenge of drawing what grunt I can out of it).
I already have weber ready to go in and will be putting extractors on when the time comes. I will definitely be porting and polishing the heads and possible even shave a little off of them in the process.
I have seen various brief mentions of custom cams for the ea81 on this site and was wondering if anyone can point me in the right direction in order to get my hands on a set. If so can someone also give me a rough indication of price. I am based in Darwin and therefore limited with what I can get up here however i am more than happy to pay the frieght for the right bits
I don't know if Ive mentioned this before or not but I was under the impression tht porting for performance is still IN wheras polishing is now OUT because the attomised fuel tends to stick to the smooth sticky surface but if its rough it creates turbulance and sometimes a vortex.Brumble wrote: I will definitely be porting and polishing the heads and possible even shave a little off of them in the process.
I have seen various brief mentions of custom cams
There used to be lots of places that would be able to machine down a cam (most engine machining shops) But the key issue is to dial in the timing of a cam otherwise you are not getting their full potential.
Hope this helps!
87 targa brumby (Neglected),
92 targa brumby (weekend runabout),
97 Lifted Outback (Dailey drive),
05 outback safety (Too cheap to pass up),
90 model liberty (was to be scrapped instead sold to workmate)
+ others.
92 targa brumby (weekend runabout),
97 Lifted Outback (Dailey drive),
05 outback safety (Too cheap to pass up),
90 model liberty (was to be scrapped instead sold to workmate)
+ others.
Mirror finish polishing does nothing good for a street engine, for a full on drag engine its a different matter cause the idea is to get the fuel into the engine asap and its nearly flooding in anyway.tex wrote:I don't know if Ive mentioned this before or not but I was under the impression tht porting for performance is still IN wheras polishing is now OUT because the atomised fuel tends to stick to the smooth sticky surface but if its rough it creates turbulance and sometimes a vortex.
Rough casting hinders air/fuel movement and can in some cases cause turbulence that negatively impacts on atomisation because the fuel can get caught in the roughs and puddle.
ExtrudeHone or AbrasiveFlow Porting is the new technology that seems to be getting brilliant results. It evens the individual port flows so each port is flowing similar to the others, it takes out rough castings allowing air/fuel to flow unhindered thus stopping puddling, it does not mirror finish the port, and it helps to create a near optimum valve throat profile.
A vortex will never be formed in a square or rectangle port. Vortexes are created in the valve throat and many factors including valve stem thickness, valve seat angles, combustion chamber shape, and the engines compression ratio have an effect on it.
Realistically what is required is a clean port that flows the amount of air the engine requires for the revs it pulls at the highest velocity possible. with everything else even a small port will have a higher velocity but a big port will flow more air. If you have an EA engine that is going to pull over 6000rpm continuously go the biggest port you can muster, if you just want a street engine then port matching, valve throat and bowl cleaning, and a good 3 angle valve seat profile will give you what you need.
my brumby has what you mentioned with a 2 inch pipe but has a 1.75 inch pipe just before the rear muffler and what i'm guessing is a stock oval muffler. Which is better in terms or performance, sound and cost, a 5 inch cannon tip or a straight through/high flow muffler?BaronVonChickenPants wrote:Exhaust upgrades:
Replace everything after the Y pipes with 2-2 1/4 inch pipe, a hotdog and a straight through/high flow muffler.
Cost: hotdog $50, lukey turbo muffler $100, whole setup supplied and fitted $220
thanks
this my freinds is hard to say.Storm wrote: Rough casting hinders air/fuel movement and can in some cases cause turbulence that negatively impacts on atomisation because the fuel can get caught in the roughs and puddle.
.
back in the day you wanted the air going in to have turbulence. apparently this would break large droplets of fuel or somthing.
personally im a fan of mirror finish if your carbies doing it right then it should be ok.
for those looking to get an ea series motor to go hard, start saving me thinks if you buy the car for 1000 at 16 then by the time your 30 still mooching of your parents you can have enough for some power
if im needed for anything spike.pickstock.racing@hotmail.com and ill try and get back to you.
pickstock racing fabrication
pickstock racing photography
GETDIRTYCLOTHING
track day classics and customs
pickstock racing fabrication
pickstock racing photography
GETDIRTYCLOTHING
track day classics and customs
id say for soundkona480 wrote:my brumby has what you mentioned with a 2 inch pipe but has a 1.75 inch pipe just before the rear muffler and what i'm guessing is a stock oval muffler. Which is better in terms or performance, sound and cost, a 5 inch cannon tip or a straight through/high flow muffler?
thanks
cannon i hate them but yeah.
cost probably cannon tip.
performance, probably hard to say as neither of them are my choice but id go with the high flow
if you want to get the most out of the motor you need to start from the top, pulse tested headers are the best, expensive and if your engine has any mods then you have to have them custom, probably a straight throuw from the headers cause there is a special size for your gas movement, cross overs and the like, then bring into a twin barrel muffler where they can cross over and come out again
hard, costly and illegal and only get a few ponies.
for those running an engine in a race car, especially a special then it could be worth it.
an exhaust that is a special lengeth can release almost double the power of the above metioned stuff, as the exhaust blows it almost sucks air though the other end but its not a guess work thing. and impossible to route around a car
if im needed for anything spike.pickstock.racing@hotmail.com and ill try and get back to you.
pickstock racing fabrication
pickstock racing photography
GETDIRTYCLOTHING
track day classics and customs
pickstock racing fabrication
pickstock racing photography
GETDIRTYCLOTHING
track day classics and customs
Carburetor upgrades
The most common upgrade is a weber 32/36 DGV (manual choke), DGEV (electric choke), DGAV (water choke) or a 180 holley, they're all essentially the same carb, you'll need to buy or build an adaptor plate.
Cost: Carb $50, rebuild kit $50, adaptor plate $50
Can someone tell what the difference is between the manual/electric/water choke? Also i can't seem to find a weber carb for under $500(new)
The most common upgrade is a weber 32/36 DGV (manual choke), DGEV (electric choke), DGAV (water choke) or a 180 holley, they're all essentially the same carb, you'll need to buy or build an adaptor plate.
Cost: Carb $50, rebuild kit $50, adaptor plate $50
Can someone tell what the difference is between the manual/electric/water choke? Also i can't seem to find a weber carb for under $500(new)
More spark:
Use higher powered coil such as the "MSD Blaster 2" and increase the spark plug gap to 1.1-1.2mm.
Cost: MSD Blaster $120
^^^^
I found this on ebay, is this the one that you are talking about?
http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWAX:IT
Use higher powered coil such as the "MSD Blaster 2" and increase the spark plug gap to 1.1-1.2mm.
Cost: MSD Blaster $120
^^^^
I found this on ebay, is this the one that you are talking about?
http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWAX:IT
- TOONGA
- Elder Member
- Posts: 5335
- Joined: Sat May 30, 2009 10:15 am
- Location: Australind closer to where they divided by zero
- Contact:
the manual choke has a wire control that you pull out to set the choke and then push in when the engine is running suitablySubiegirl wrote:Carburetor upgrades
Can someone tell what the difference is between the manual/electric/water choke? Also i can't seem to find a weber carb for under $500(new)
the electric choke has a sensor that recieves a signal from a water temp sender that runs to a solanoid to turn the choke off
the water choke bypasses the electric signal and has a piped setup that runs to a solanoid/thermostat type arangment on the carby that shuts the choke off when the desired water tempreture is reached
TOONGA wrote:the manual choke has a wire control that you pull out to set the choke and then push in when the engine is running suitably
the electric choke has a sensor that recieves a signal from a water temp sender that runs to a solanoid to turn the choke off
the water choke bypasses the electric signal and has a piped setup that runs to a solanoid/thermostat type arangment on the carby that shuts the choke off when the desired water tempreture is reached
ok thanks alot for that, do you know whether a 92 brumby EA81 has an electric/water choke carby, im assuming it wont be manual.
- TOONGA
- Elder Member
- Posts: 5335
- Joined: Sat May 30, 2009 10:15 am
- Location: Australind closer to where they divided by zero
- Contact:
a 92 brumby should have an electric choke
and will look like this
minus the red dust and other muck
the choke solanoid is on the left of this picture there is a blue wire that runs to it from a relay/sensor that has input from the temp sender and when the engine is hot the choke stops and the butterfly valve opens up in theory
my carby is a wreck and needs a rebuild as it has never had one and my brumby is a 1989 model
TOONGA
and will look like this
minus the red dust and other muck
the choke solanoid is on the left of this picture there is a blue wire that runs to it from a relay/sensor that has input from the temp sender and when the engine is hot the choke stops and the butterfly valve opens up in theory
my carby is a wreck and needs a rebuild as it has never had one and my brumby is a 1989 model
TOONGA
- BaronVonChickenPants
- General Member
- Posts: 1187
- Joined: Tue Oct 04, 2005 10:00 am
- Location: Nowra, NSW
Yes that is the correct unit, your distributor should be electronic and not require the ballast resistor.Subiegirl wrote:More spark:
Use higher powered coil such as the "MSD Blaster 2" and increase the spark plug gap to 1.1-1.2mm.
Cost: MSD Blaster $120
^^^^
I found this on ebay, is this the one that you are talking about?
http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWAX:IT
Jordan.
To become old and wise, first you must survive being young and dumb.