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Discussion Starter · #1 ·
Consider two maps on a 1.8T..................

One running more advanced timing, less boost and less airflow (g/s), the other running less timing but higher boost and 20g/s more airflow.
I don't mean silly high levels as a FMIC is doing an excellent job of keeping AIT's down.
Which should make more power assuming all other variables are equal?

Also, 2 timing figures - 28deg ATDC and 18deg ATDC, which is more adavnced? (figures taken from vagcom block 003)

This is the 18deg ATDC map, the 28deg map is similar, just rises to 28deg instead of 18deg....

Posted Image
 

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I ain't no effin padawan
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2 things gary.

1,) I have my doubts about the scaling of your maf, so ignore your airflow reading,.

2.) 28 BTDC sounds well dodgy. Thats timing out of boost. If they're running that much timing in boost they are running race fuel. 18btdc sounds about right, as does 170g/s with a k03s runnig wastegate shut
 

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Discussion Starter · #3 ·
John, these figures have come from block 003 and is a + figure so arent they ATDC?
If so won't a higher ATDC figure mean a lower BTDC figure?

I logged 18deg ATDC, another car logged 28deg ATDC.
Won't that mean Im running timing further advanced?
For the record, I pull hardly any timing at all.

I log around 188g/s, other car logs 170g/s. I run around 4-5psi more boost and cover 80-100mph around 3 seconds faster yet I see 1whp less??

Also, why would MAF scaling be an issue? Its a standard tube, also I used to run 175-180 with Revo but now run more boost so would probably expect higher figures.
 

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I ain't no effin padawan
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Gary BTDC is before top dead centre. The more BTDC you are the more advance you have ATDC is retarded (very) timing.

I used to log high 7's 60-100, logging 175g/s. Sound familiar?

Your turbo was wastegate shut, and at max compressor volumetric capacity when you ran revo.

If you are running more boost in the midrange, you will cover some increments faster as you'll have more torque.

Get your car to trap 103+ at the pod next weekend, and I'll start to believe your airflow figures are correct. It's just I've seen a few logs recenly of CC cars that have suspect looking airflow values.

At the same manifold boost pressure and same rpm, the airflow will be the same, no matter what the turbo is. I have logs of my motor with 7 different turbos on it at various boost pressures on small port an big port, so I know what this engine will flow and at what boost. At 95% VE at 1.86bar at 6000rpm you'll flow 190g/s. You will not make 95% VE on a smallport on a poxy little turbo at 6K rpm. How do I know you make 1.86 bar at 6000rpm?
 

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Discussion Starter · #5 ·
Gary BTDC is before top dead centre. The more BTDC you are the more advance you have ATDC is retarded (very) timing.
Doesnt block 003 log ATDC after top dead centre? Whats the relationship between ATDC and BTDC?
From what i've been reading, a higher ATDC figure means a lower BTDC figure, or am I seeing this wrong?

I read THIS LINK

Noted this paragraph in particular....

13. In our stock model we had the flame front meeting the piston when the crank
is at 15 degrees ATDC (when the piston is 1.865mm on its downward stroke).
Therefore by advancing the ignition process by 4 degrees the piston receives
the flame front 4 degrees sooner. Ie at 11 degrees ATDC.
The piston is located 1.00753 mm from TDC at 11 degrees ATDC.
 

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Discussion Starter · #7 ·
I've updated my post above with a link from where I took my info.

Is the label wrong on block 003 then? Is it actually BTDC and not ATDC?
 

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I ain't no effin padawan
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Gary

Your EMS fires the spark at a certain position of crank rotation.

It only fires each cylinser once every other crank rotation on a 4 stroke engine.

It will fire anywhere between 35 BTDC and 5-10 ATDC. You should see 8-10 btdc at max torque (max boost) rising to high teens as boost tapers and revs rise. On a big port you see low teen rising to low 20's if you run good fuel. The timing is dictated by the compression ratio (dynamic compression ratio on an FI engine or boost to you and me), and knock limit of the fuel you're using. There is nothing any tuner can do in software to change it.

max BTDC is for max torque (within limits)

ATDC is generally for idle stabilisatiuon. You should not be seeing ATDC with the throtle open.

Basically boost (airflow)will always make more power, untill you reach heavily retarded timing on your chosen fuel. At a certain point, the spark starts combustion so late, that most of the pressure expansion is too late to push the piston down, and goes down the exhaust, losing power. At 25psi plus you might start to approach this on 98ron fuel
 

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Discussion Starter · #9 ·
The 28deg figures taken from block 003 relate to another car run on the same rollers, same day as me. My block 003 figure is the graph above.
As I said, he runs less boost and makes less airflow.
Same AUQ 180bhp smallport heads.

What im getting at is, how can this car make more power?
Is there something else im missing here?
 

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Gary

Combustion is started around 30deg BTDC to achive maximum pressure rise at about 15deg ATDC, in other words just as the piston starts its downward stroke.

If max pressure rise is too close to or BTDC, you get knock/pre ignition.

A higher pressure charge burns faster, so less ignition advance is available before you see knock. The max pressure rise is not much higer than in an atmo engine, but it is sustained for longer. This means that in a heavily boosted engine that the charge cannot fully burn before the exhaust valves open, wasting power, and giving high EGT's
 

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Discussion Starter · #11 ·
I'm think im getting this now but can you clarify if block 003 is showing ATDC or BTDC? The label states ATDC but if thats the case then a rising number (see my graph in the first post) is actually retarding if im seeing this right - combusion is happenning later and later as the piston travels downwards hence losing power.
It would make sense (to me!!) if it was BTDC as that way the spark will be firing further away from TDC as revs rise and boost drops off (on the pistons upstroke) finally combusting as close as possible to ATDC on the pistons downstroke giving it the biggest possible push.

Appreciate your replies John.
 

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Gary

003 shows btdc or atdc.

It shows timing angle, and the lable changes acordingly. If you're reading the label when stationary, it may well be atdc as the ems fires late to reduce torque, and keep egt's up for emission puposes.

On idle, the throttle is closed, so the ems can vary timing angle, to vary torque to control (smooth) idle

Your graph is btdc, and exactly what I would expect from a maxed out ko3s on a small port running 98+millers. It's a good set up.

Was the other car you logged an early ecu. I know that they display timing differently. They show max timimg angle, not the actual timing reduced by boost.

The ems has a base timing map. The timing angle is reduced from the timing map by a certain number of degrees per psi of boost. There is also an adjustment for throttle angle, coolant temp, and rpm. All these things added/subtracted together give actual timing angle.

Early ecu's display base timing in 003 not actual.
 

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Wilko, Gary,

I had to join the fray, it's my car that Gary is talking about and we are trying to get to the bottom of some very strange goings on, basically my car is remapped by A.N Other tuner and the power / torque curves follow Gary's almost to a T bar Gary's brief torque excursion upwards of about 20lbs/ft then settles to the same, however things are not as they seem!

My car is an 03 Octavia HN code ECU, I have attached the RR Logs showing Timing etc this using Millers CVL Turbo, without it the CF Figures are all over the place! (2nd log and I have seen much worse than this)

http://uk.msnusers.com/h3t7qf0gj6vp2is45inte5qge3

From what you say the higher 28 degerees my car is showing will ignite the mixture earlier ( at 28 degrees BTDC) to enable the flame fron t to have travelled far enough so that as the piston has gone over TDC the maximum piston pressure is generated without detonation whereas Gary's map ignites the mixture at 18 BTDC therefore allowing the piston to travel further past TDC until maximum pressure without detonation is achieved.

This is where we thought that my car was making power on timing using low boost whereas Gary's Map ( if what I have said above is correct) would be using lower levels of timing advance but higher boost
 

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Dsrr

cvl turbo will help a little, but 28BTDC is high even for race fuel when in boost. If your CF values are 12, the ecu is retarding as far as it can, and the car is probably detonating.

Timing certainly makes power, upto a point.

I can't see your logs by the way. Host them somewhere else, and I'll take a look at them. Or pm me and I'll send you my email and you can send them there.

Mine runs about 20-22btdc at the top end, but the large port head rund 2-3 degrees more timing than a small port before det, and needs to to make power. In line with garry's.

You've got the general idea though. The charge at a certain density (dynamic comp ratio) burns at a certain rate. Timing for max torque is whatever is needed btdc to give max pressure rise just after tdc. If you're running less boost, I would expect to see a little more timing, but not 10 degrees.

If you think gary is running 1 bar ish and 18btdc, and with no boost you may get 30btdc, you may se a couple of degrees more advance, but not 10 degrees.

Are you sure that you're not running a race fuel map by accident. Mind you even then I'd expect the ems to be pulling timing back a lot due to knock.
 
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