E85/ Eflex and its affect on avcs

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Re: E85/ Eflex and its affect on avcs

Postby BUDDAH » Sat Oct 19, 2013 7:45 pm

Did you here the joke about the old Fitter , managing director and the corporate banking manager :mrgreen:
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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Thu Jul 17, 2014 8:03 pm

Bump for further discussion

After recommendation I'm going to switch to ulx110 10w40 for my donk and see how it goes

However my findings so far from logging and checking is less advance is required on e85 per rev reach same cylinder pressure, meaning more conservative cam timing can be utilized

I question whether its worth reducing ignition timing advance on boost and bumping boost up even higher though with less overlap at lower revs to promote spool

Probably look to run richer on spool as well (12.5-13.0:1) with less timing

Will be more of a dog if staying in those load ranges (less timing and richer) but quicker to reach boost and thus for someone like me, power.

If stuck cruising in 3rd or 4th at 2500rpm though its gonna be a slug to drive

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Re: E85/ Eflex and its affect on avcs

Postby <GB> » Fri Jul 18, 2014 1:17 pm

Any specs on that oil?

why do you want to change ?
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Re: E85/ Eflex and its affect on avcs

Postby jslayz » Fri Jul 18, 2014 8:49 pm

Hmm I just started running 10w40 Nulon full synthetic.
Seems pretty good so far.
Held up fine to 7 full rpm 3rd gear dyno runs only dropped to 26psi at idle after last run.
As you only need 14, all good.

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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Sat Jul 19, 2014 6:13 am

Yeah but holding too much oil pressure is no good. Higher the pressure generally lower the flow (to a point)

And dual avcs doesn't help as the triggers require higher oil pressure to function

GB - ulx110 is the shiznit if interwebz is anything to go by.

I've looked into the specs and its pretty solid. Better on paper than penrite 10w40 10 tenths racing

Ill give it a go next oil change and see what happens
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Re: E85/ Eflex and its affect on avcs

Postby <GB> » Sat Jul 19, 2014 10:05 pm

Any links to good reading on said oil?
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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Tue Mar 17, 2015 10:06 pm

Bumping this thread.

Avcs tuning has become my little project. And the deeper I delve the more I realize how little we have known and how underutilized avcs tuning really is.

Just queitly, Avcs is awesome.

In brief, here are some of my findings:

I have been experimenting with my dual avcs jdm version10 ej207 motor

One thing that isnt generally discussed is the importance of balancing cam timing with respect to intake : exhaust pressure ratio

With the oem or similar sized turbine and turbine housing, intake to exhaust pressure ratio will be higher than a larger, more efficient turbo hot side

With that said, I run a gtx3076 with a 0.82 housing on a 2.0 litre. I have not measured exhaust pressure between the port and turbo housing, but I think its fair to assume that I would be at or close to 1:1 intake to exhaust pressure until about 20psi, and perhaps up to 1:1.5 ratio from 20-28psi

To understand how this would impact a combustion engine and its volumetric efficiency, we need to understand flow and pressure dynamics. Take a naturally aspirated motor for example. When a piston moved down the bore with the inlet valves open, the general concensus is that air is "sucked" in by the moving piston (think a syringe pulling liquid into the body of the syringe when you pull back).

This is technically not correct, as what is really happening is the higher ambient pressure in the atmosphere is flowing to the lower pressure cylinder to "fill" the void and vacuum that is created with air/ fuel.

With a forced induction engine, again its a misconception that air is "forced" through to the combustion chamber by the turbo or supercharger. Infact the volume of air able to be ingested itself is unchanged for any given motor. Turbo / super charging is merely packing the air more densely and thus allowing more oxygen per particle of air to be ingested, thus creating a bigger bang.

Boost is a measurement of inlet restriction, so the more boost you run, yes the more pressurized the intake will be, but the less efficient your engine is in ingesting this air.

Theoretically speaking, if you could create an unrestricted, continuously flowing and efficient engine, then you would never be able to build boost because the engine will use all the available particles of air /oxygen to make power without creating an inlet restriction. However this is an impossibility, as anything with work has inefficiencies and losses. So boost is here to stay.

Why do I mention all this? Because its critical in understanding the role of avcs in assisting an engine's efficiency.

Most people know that the beauty of avcs is the ability to have qualities of larger duration/ more aggressive cams at higher rpm, and lower duration / less aggressive cams at lower rpm. The reson for this is at low rpm, where the flow of air / fuel mixtures and the corresponding spent exhaust gas is slower, requiring less valve opening time to facilitate an efficient burn. However at higher rpm, with faster inlet, combustion and exhaust flow, valve opening needs to be longer/timed differently to foster effiency. Problem is the required timing of these events is different for low, medium and high rpm and load points of an engine's operation.

Thus where avcs comes in. Whilst it would be great to have variable duration also (again to allow lower duration at lower revs and higher duration at higher revs), the ability to vary timing of valve opening and closing is still of great benefit.

Valve overlap is important to understand for this discussion, and overlap is the amount of time, measured in degrees of crankshaft rotation, which both intake and exhaust valves are simultaneously open at the end of the exhaust stroke and beginning of the intake stroke. You're talking milliseconds here. Literally.

For n/a motors, generally for balanced performance you want high lift, medium duration and some valve overlap at high rpm to assist with scavenging. Wont go into scavenging discussion here, but for higher power at higher rpm range, this would need to be longer duration, higher valve lift and more overlap. This has been discussed to no end in engine camshaft and tuning papers for many many years. Difficulty however was that overlap in an n/a motor at low revs hurt dynamic compression, as by opening the exhaust valve later to overlap with the opening of the intake, or advancing the intake valve opening so it happens while exhaust is still in progress, then you're releasing some cylinder pressure which reduces the actual compression of air fuel mixture in the cylinder. Lower compression means a lower bang, and less efficiency. At lower rpm this resulted in sluggish power, and thus why high duration high overlap cams were known to "push the power curve to the right of the rpm band", and result in a sluggish performance at low rpm.

In the pre-variable valve timing world, this was a sacrifice needed to be made to allow higher rpm efficiency and power, as valve opening was static based on what the cam lobes allowed, and there was no way of varying valve timing events to alter this. Once again where avcs comes in.

Historically it was believed that for a turbo motor, the camshaft requirements were the opposite of an n/a motor. That is, the thought was you needed lower duration, less overlap, as valve overlap on a forced induction motor would "blow the compressed mixture out the exhaust valve and waste it" or an even better one was "exhaust chill" which purportedly reduced the exhaust temperature and affected turbo spool.

This is true for a supercharged engine. And the reason relates once again to my earlier point around pressure ratios. A supercharged engine generally has the same exhaust pressure ratio as an n/a motor, as the exhaust system is the same (headers out to exhaust). Obviously the intake is higher pressure though (compressed boosted air). This is pretty static and constant across the entire rev/ load range. So at 2000rpm and say 7psi of boost, the intake pressure is 7psi, and exhaust pressure is at most, 0psi above atmosphere. A pressure ratio of 7:1. If you recall my point earlier around flow dynamics, the flow of air will therefore naturally gravitate toward the lowest pressure area, in this case the exhaust. So overlap here will push boosted air straight out the exhaust without an opportunity for it to be compressed and then ignited in the power stroke. A 7:1 pressure ratio indicates a much lower pressure area in the exhaust and therefore the boosted air is going to face very little resistance in getting to the lower pressure area very quickly.

With a turbo however, the actual turbo hot side housing and turbine wheel create an exhaust restriction all the way back to the exhaust port on the head and the exhaust valve by extension. This restriction increases the amount of exhaust pressure between the exhaust valve and the turbo.

As stated earlier, with smaller turbine and housing like an oem turbo, this restriction is higher and thus creates more pressure. Typically your intake to exhaust pressure ratio on a factory turbo'd EJ engine could be 1:1 at up to 7psi, 1:1.5 at 7-14psi, 1:2 at 14psi-20psi and 1:3 at 20+psi.

So if we apply aggressive avcs timing on such a setup, where we advance the intake cam (and for dual avcs we retard the exhaust cam further), then lets see what we come up with.

You would create more overlap, meaning your compressed air/ fuel intake mixture is being introduced while the exhaust valve is open. Using above example, at up to 0 psi (off boost), your pressure ratio is 1:1 so there is no bias to which direction the flow of compressed air and fuel mixture would go. It would just follow the natural path (ie through to the turbo). The more overlap you run here the more volumetric efficiency you create as you allow the engine to breathe better, but also allow some of that unburnt air:fuel mixture into the hot exhaust which will help spool the turbo more.

At 7psi-14psi, with a more restrictive exhaust and turbo setup, this pressure ratio rises. Lets assume 1:1.5 times. This now means flow will favour the lower pressure of the inlet should there be an opportunity for that to happen. So if we have both inlet and exhaust valves open simultaneously here, what we call reversion can occur, where hot exhaust gas flows back into the chamber and even making its way up past the inlet port and diluting your nice cold air charge. This is obviously counter productive to power, and works as exhaust gas recirculation to assist in pollution control.

The same can be said for remaining boost levels as pressure ratio increases, only that the flow "back" to the inlet will happen alot faster as the pressure ratio rises due once again to the flow characteristics of air/ fluid.

It can be seen that valve overlap here is definitely not of benefit.

Taking this further, it is clear that at higher rpm / load / flow, where exhaust back pressure is highest, then the same applies - ie you don't want much/ any overlap at all. The biggest difference here between a turbo and n/a engine is the backpressure, which is minimal in an n/a engine and results in a pressure ratio of closer to 1:1 than a turbo engine.

This has multiple problems also, in that a more restrictive exhaust pressure doesn't allow as much exhaust flow even after the inlet valve closes, and this limits the efficient of the engine to pump out the burnt exhaust gas. Remember an engine is like a big air pump so the slower this burnt gas is able to be pumped out the lower the power/ torque. It also then slows down your combustion process (killing torque) which reduces your ability to advance timing (further killing torque). See how its spiraling??

However with a setup such as mine with a much freer flowing exhaust, a larger more efficient turbine wheel and turbine housing, then the pressure ratio is maintained at 1:1 for alot longer. This means more aggressive avcs timing to create more overlap and promote volumetric efficiency is actually beneficial to engine efficiency and therefore turbo spool. With e85 burning alot slower and not producing as much energy per gram, this means more avcs is required to achieve the same efficiency.

Thus the beauty of avcs. Variable valve opening and overlap points. The ability to set aggressive overlap and valve opening at lower / mid rpm then closing it back up in higher rpm is a real bonus, and when understood and done right, can reap some massive gains in spool, torque and peak power from an otherwise stock setup.

There is even more to this such as the ideal intake valve opening and closing points relative to crank rotation and piston location in the cylinder, and again for exhaust valve opening and closing.

Generally, opening the inlet valve earlier (relative to piston top dead centre before the inlet stroke) allows for the valve to be out of the way so the air/fuel mixture is causing flame propagation as the piston comes down the bore 15 degrees after top dead centre. This allows a more complete and efficient burn.

Keeping the exhaust valve closed longer allows for higher cylinder pressures and more torque, but at a trade off of high egt and scavenging (if the exhaust pressure is low enough to allow for it).

A complex balance and mix to get right depending on your goals. Gotta love avcs and the possibilities.

Mick
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Re: E85/ Eflex and its affect on avcs

Postby KiDo_Tuning » Tue Mar 17, 2015 10:40 pm

Just to clarify on the whole 7:1 for a supercharger. Its incorrect. Air pressure is 14.65psi so you have 46% more air volume than ambient roughly for 7psi so the ratio is actually 1.46:1 approximately not 7x more volume of air pressure
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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Wed Mar 18, 2015 6:03 am

KiDo_Tuning wrote:Just to clarify on the whole 7:1 for a supercharger. Its incorrect. Air pressure is 14.65psi so you have 46% more air volume than ambient roughly for 7psi so the ratio is actually 1.46:1 approximately not 7x more volume of air pressure


I see your point. But if you had 7psi inlet restriction *edit*. (Above ambient) vs 1psi (above ambient) exhaust restriction, what does that represent as a ratio? Are you saying it should be (7+14.65): (1+14.65) ? I guess I was referring to pressures relative to ambient.

I know ambient is at 14.65 psi at sea level but here the ratio doesn't change that. I'm not talking volume I'm talking air pressure, and where boost is 7psi and exhaust pressure is 1psi that's a pressure ratio of 7:1.

Perhaps I shouldn't have used 0psi in the above and I should've used 1psi . Also reality is I was exaggerating the above ratios for supercharged engines as they too have greater back pressure than 1psi but my point was at low engine speeds of 2000rpm per the example, exhaust pressure is alot lower than the equivalent turbo setup, and therefore if boost is 7psi at 2000rpm with a 1 psi exhaust back pressure, then its 7:1 at that engine speed / load, so overlap is not going to do anything for power / VE here.
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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Sat Mar 21, 2015 10:17 am

Gotta love 55 degrees of intake advance and 45 degrees exhaust retard on the w20 v10 207 heads

Full boost now at 4000rpm cold in 3rd gear. Warm should be 3800

Just need to tweak my fueling, maf scaling and timing table and ill be set.

Pulled 5.8g/rev by 5200rpm and this is with 4 degrees timing taken out from my previously optimized table

Its a bit jittery on light throttle at cruise which is mostly fueling related but i think i still need to smoothen avcs tables but I'm finding the ve is improving with more overlap above 1800rpm to 3500rpm
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Re: E85/ Eflex and its affect on avcs

Postby bigBADbenny » Mon Mar 23, 2015 8:23 pm

There's a thread on nasioc iirc where inlet avcs was optimised by doing successive dyno runs with inlet advance at progressively fixed points. The resulting graphs were overlayed resulting in optimised power/timing across the whole range.

Could the process be the same on a dual avcs engine, and if so would inlet be optimised first, then exhaust?

I'll dig up a link... :)

Or is the relationship more dynamic?

dr20t wrote:
Benny - yes that's one way to do it but each avcs change results in different VE which needs timing and fuel adjusted accordingly


Looking at a graph of a dyno pull, can you explain the relationship between exhaust avcs and inlet avcs over the rev range?
Or how the relationship changes as the revs rise?

The intent would give clues for optimization.
I'll see if I can dig up the answer for myself ;)
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Re: E85/ Eflex and its affect on avcs

Postby KiDo_Tuning » Mon Mar 23, 2015 10:51 pm

bigBADbenny wrote:There's a thread on nasioc iirc where inlet avcs was optimised by doing successive dyno runs with inlet advance at progressively fixed points. The resulting graphs were overlayed resulting in optimised power/timing across the whole range.

Could the process be the same on a dual avcs engine, and if so would inlet be optimised first, then exhaust?

I'll dig up a link... :)

Or is the relationship more dynamic?



I have live tuning of AVCS available, lets you swing cam timing to find the best VE value. Thats why our most recent tune got better the longer we drove it ;)
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Re: E85/ Eflex and its affect on avcs

Postby dr20t » Tue Mar 24, 2015 6:02 am

Matt - was the live avcs available for my car?
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Re: E85/ Eflex and its affect on avcs

Postby jakey » Tue Mar 24, 2015 5:32 pm

*giggle*
-Jakey-UBARU
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Re: E85/ Eflex and its affect on avcs

Postby KiDo_Tuning » Tue Mar 24, 2015 6:04 pm

dr20t wrote:Matt - was the live avcs available for my car?


All the VE and other patched stuff takes up a lot of room in your ecu. No room to bootload it into RAM and get it to work

Issue with 512kb raises it head again :(
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