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Old 07-27-2011, 04:46 AM   #551
Subbie Sleeper
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Hey all,

I am a new member to NASIOC, but I have been reading it for sometime. I can't make a thread yet because I haven't made enough 'legitimate' posts yet, so I am piggy-backing off of this one. Does anyone have any recommendations for a good tuner in the NY/NJ/PA area? I have a 05 Legacy GT with an EJ257 short block. I just finished with the headers, up-pipe, down pipe, exhaust, and intake, and I got the Accessport. I want to get this thing tuned right the first time, and I am just curious if anyone knows someone to trust. Also, any advice on other upgrades I can make at this stage would be welcomed, too. I am not trying to upgrade the turbo or intercooler yet, but again, I would like to get some input from some salty dogs. Also, let me add that the engine is currently out of the car.

Thanks fellas
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Last edited by Subbie Sleeper; 07-27-2011 at 05:11 AM. Reason: Forgot something
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Old 07-27-2011, 11:17 AM   #552
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In my opinion the best tuner on the east coast is Dave Brown from MSPT. He is on long island and is worth the trip. Be carefull of kids with tactrix cables. They do not have the experience needed to get the job done right.
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Old 07-27-2011, 12:17 PM   #553
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Subbie Sleeper - If you don't want to use Dave Brown for some reason, you can also check with Clark Turner on getting a mail-order tune. I'm assuming he didn't offer it because a dyno tune would be better and this isn't the appropriate place for a vendor to market his services. He's got a long running thread on his e-tune service.
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Old 01-08-2012, 10:57 PM   #554
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Time to bump this thread.

This thread has been primarily focused on early model years where we were dealing with a single AVCS cam on the intake side. we saw some interesting graphs compiled but all of them came from a non-stock turbos or non USDM cars, all of which will yield different results. I came across another thread that had very good info on the dual AVCS degrees of advance and retardation (no pun intended ). The info supposedly came from a service manual from Subaru so I think it's safe to assume it is accurate. Take a look at how pre 08 AVCS intake valves worked vs. the 08+ system:

link

The intake and exhaust angles explain the range of adjustment that can be done on a USDM STI. Looking at the stock exhaust map, I can see why Subaru set most of the retardation to 17 degrees in low load situations. 17 is where the exhaust valve opening aligns exactly with the intake valve with no intake advance. Essentially, 17 degrees aligns the exhaust valve with intake side (see below).

Stock '11 USDM exhaust AVCS map:


Stock '11 USDM intake AVCS map:


And there is that odd 30 degree section near peak torque area (see above). Adding up the intake and exhaust, it's quite a lot of overlap, to a point where reversion occurs here. I think this is to control emissions by allowing some exhaust gas to reenter intake side and be reburned. This is probably a new way of exhaust gas recirculation for emissions and cooling the chamber down.

--------------------------------------------------------------------------------------------------------------------------------------------

So, I've been staring at the valve picture and trying to come up with an educated strategy of how to tune AVCS. I believe most people just jump into this and go based on trial and error to see if they can see a pattern. I don't have infinite amount of time and a dyno to do this so I want to start a discussion on sound fundamentals that should dictate the tuning. I have some conversation starters:

- I think we need to focus on the valves opening and closing in relation to the piston.

- I think too much advance hurts efficiency. Why? I think it makes most sense to have intake valve open for as long as possible when the piston is coming down. Intake advance past 5 degrees moves the opening into a phase where piston is still coming up. The more you advance, the less time we have to take in the air when the piston is coming down. Makes sense?

- The exhaust retardation seems tricky. With no retard, we will open the valve sooner which I assume is not optimal because we'll start relieving pressure from the chamber sooner while combustion is still happening. I think this will hurt power.

- Retarding the exhaust valve significantly may help power since we'll keep the chamber closed longer thus allowing for pressure to build up. This will likely produce more heat which is something to note. But, retarding it too much creates a major overlap with the intake side. Also, what should we expect to happen when the exhaust valve is open past TDC? As the piston starts to move down, are we in danger of producing reversion when the exhaust is now potentially moving back into the chamber? Does it make sense to close the exhaust valve right at TDC and have some overlap before TDC?

- Is there value to opening an intake valve before TDC since the piston will push against the incoming charge? There seems to be value to this but why? Is it because there is still room in the chamber to come in even though the piston is at TDC?

- Assuming keeping exhaust valve closed as long as possible is optimal (more retard), where is the limit to that since more retard keeps the valve open longer past TDC and increases the overlap to a point where it hurts? Does it make more sense to optimize the exhaust valve such that we get a better intake draw and take a hit on the combustion side of the cycle?

- I think there is consensus that on a setup with a small hot side of the turbo (stock), there is no value in valve overlap past 4500RPMs with moderate or high loads. I think this is where the back pressure on the exhaust side starts to exceed the pressure on the intake side. That means 17 degrees of retardation on the exhaust side with 0 degrees of advance on the intake side. Or, if we want to close the exhaust side at TDC, that is 12 degrees exhaust and 5 degrees of advancement on the intake. Make sense?

- I think there are some gains to be had on Stage2+ cars than what we've been lead to believe. Why? By improving the flow on the exhaust side, we can push the reversion point further up the RPM range which allows us to take advantage of valve overlap longer. If you know what is going on, I think there's power to be made with AVCS alone.

OK, I think I blabbed enough. Let me know what you think and if it makes sense.
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Old 02-11-2012, 09:24 PM   #555
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Curious what if you max avcs at idle?
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Old 02-12-2012, 11:31 AM   #556
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Originally Posted by 07wrx84 View Post
Curious what if you max avcs at idle?
Not a good idea. Doing that is an equivalent of running an aggressive cam profile to promote high overlap. Good for top end power but poor idle and stalling issues. The stock programming may not even engage AVCS at idle even if you put overlap in lowest RPM cells.
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Old 02-12-2012, 12:39 PM   #557
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Quote:
Originally Posted by Ziggyrama

Not a good idea. Doing that is an equivalent of running an aggressive cam profile to promote high overlap. Good for top end power but poor idle and stalling issues. The stock programming may not even engage AVCS at idle even if you put overlap in lowest RPM cells.
Sounds bout right just wondering!!
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Old 02-12-2012, 12:46 PM   #558
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Fail. AVCS advance is not goog for Top end power.

You can run AVCS at idle. But you cant get max. There is not enough oil pressure at idle to engage max avcs.

C
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Old 02-12-2012, 12:48 PM   #559
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Quote:
Originally Posted by Clark Turner
Fail. AVCS advance is not goog for Top end power.

You can run AVCS at idle. But you cant get max. There is not enough oil pressure at idle to engage max avcs.

C
I thought avcs is good mid range and gettin into boost!
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Old 02-19-2012, 12:42 AM   #560
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This is an interesting read and is something that interests me, sadly my 04 Sti only has the intake cam that can be played with....

Ziggyrama,

- I think we need to focus on the valves opening and closing in relation to the piston.

--- I agree the position of the valve event in relation to the position of the piston is key in developing maximum dynamic compression, for both intake closing and exhaust opening.

- I think too much advance hurts efficiency. Why? I think it makes most sense to have intake valve open for as long as possible when the piston is coming down. Intake advance past 5 degrees moves the opening into a phase where piston is still coming up. The more you advance, the less time we have to take in the air when the piston is coming down. Makes sense?

---Here I'm having an issue just with the use of the term "advance." Where exactly is the intake valve closing? Most of the fixed cam center line stuff I have played with the intake valve is closing 20-30 degrees after bottom dead center, meaning the vale is closing in the compression stroke. My reasoning for this is that the intake valve closing time is proportional to the point where the velocity of the the intake charge equals zero. That being said, the beauty of adjustable cam timing is that the closing of the valve can be moved closer to bottom dead center when the charge velocity is low and take full advantage of the swept compression stroke. This would also feed into the reason why as the charge velocity goes up you would want to hang that valve open longer to take full advantage of the charge being supplied.


- The exhaust retardation seems tricky. With no retard, we will open the valve sooner which I assume is not optimal because we'll start relieving pressure from the chamber sooner while combustion is still happening. I think this will hurt power.

---Here I think by opening the valve sooner you may be able to increase the mass exhaust volume aiding spool up. I could be wrong, its most definitely something that could be tested without a dyno by comparing boost curves relative to exhaust valve opening.

- Retarding the exhaust valve significantly may help power since we'll keep the chamber closed longer thus allowing for pressure to build up. This will likely produce more heat which is something to note. But, retarding it too much creates a major overlap with the intake side. Also, what should we expect to happen when the exhaust valve is open past TDC? As the piston starts to move down, are we in danger of producing reversion when the exhaust is now potentially moving back into the chamber? Does it make sense to close the exhaust valve right at TDC and have some overlap before TDC?

----I'm going to take this one bit by bit.
- Retarding the exhaust valve significantly may help power since we'll keep the chamber closed longer thus allowing for pressure to build up.
--- The exhaust valve opens in the power stroke, the piston is traveling away from top dead center. Therefore the volume is increasing, and that means pressure is being lost regardless of what you do with the opening time of that valve. As much as I hate to use this definition here: PV=nRT, while the ideal gas law lives in the vacuum academia, it illustrates the point.
---As for the rest of the statement, in my opinion the exhaust valve event will have an effect on spool up and should be position in a way that gives you the best response. Even overlap has it's place where it can be useful, while it may not be good for power it can be used to create an EGR effect while at cruising speed increasing fuel economy. Again, most of the fixed center line cams I have degreed in close the exhaust valve after top dead center by 7-10 degrees to take advantage of the scavenge effect. With that in mind the relationship between the pressure in the exhaust manifold and the cylinder have to be looked at.

Ziggyrama, have put a degree wheel and a dial indicator on the motor and see where the valve events actual happen? Don't get hung up on just power or torque, the reason Subaru, BMW, Nissan or any auto maker puts this kind of dynamic technology into an engine is because it makes ever aspect of the engines operation better.
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Old 02-19-2012, 10:07 AM   #561
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Quote:
Originally Posted by Clark Turner View Post
Fail. AVCS advance is not goog for Top end power.

You can run AVCS at idle. But you cant get max. There is not enough oil pressure at idle to engage max avcs.

C
I was referring to an aggressive cam profile I agree, in FI applications, valve overlap is not desired in high RPMs.
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Old 02-19-2012, 05:25 PM   #562
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Since my last post, I have spent considerable amount of time reading up on VVT technology and general concepts. I also did some tests to confirm certain assertions and I think I got a good grip on AVCS.

Essentially, dual AVCS is designed to handle several things: improve torque, control emissions and improve gas economy. Yes, it does all of these things When we talk about what is 'optimal' or 'best', it's important to mention the context: cruising situations? high load? High or low RPMs? Different scenarios call for different behavior.

Everything I am saying is in relation to stock turbo. Larger turbo will dictate different AVCS settings.

Quote:
Originally Posted by Kevin VanCleave View Post
This is an interesting read and is something that interests me, sadly my 04 Sti only has the intake cam that can be played with....

Ziggyrama,

- I think we need to focus on the valves opening and closing in relation to the piston.

--- I agree the position of the valve event in relation to the position of the piston is key in developing maximum dynamic compression, for both intake closing and exhaust opening.
Agreed. Position of the piston in relation to a valve event is very important. The further away from TDC an event occurs, the more effect the piston movement will have on flow. However, like all things in cars, it's not that black and white.

Quote:
Originally Posted by Kevin VanCleave View Post
- I think too much advance hurts efficiency. Why? I think it makes most sense to have intake valve open for as long as possible when the piston is coming down. Intake advance past 5 degrees moves the opening into a phase where piston is still coming up. The more you advance, the less time we have to take in the air when the piston is coming down. Makes sense?
It seems that way but it's not that simple. Remember that valve opening profile is not linear. At opening and closing, the valve is almost open/close and the first/last few degrees of movement create major restriction in valve flow. Furthermore, if you focus on maximizing intake valve duration, you're ultimately sacrificing scavenging duration because you're reducing the time when both valves are open. So, what is better? cut the overlap and increase duration during piston downstroke or increase overlap and hope that brief upward piston movement does not hurt your flow? Remember, even if the piston is coming up, you still have room in the chamber for the air to flow into. Since the intake valve presents a major restriction in the flow the first few degrees of opening, the piston movement probably does not have as much of an effect on the flow during that time as you'd expect.

Too much advance can hurt you. In fact, if we're considering high loads, you don't want any of it. But, in cruising situations, a lot of advance provides some benefits, for example, combustion cooling and improved gas economy.

Quote:
Originally Posted by Kevin VanCleave View Post
---Here I'm having an issue just with the use of the term "advance." Where exactly is the intake valve closing? Most of the fixed cam center line stuff I have played with the intake valve is closing 20-30 degrees after bottom dead center, meaning the vale is closing in the compression stroke. My reasoning for this is that the intake valve closing time is proportional to the point where the velocity of the the intake charge equals zero. That being said, the beauty of adjustable cam timing is that the closing of the valve can be moved closer to bottom dead center when the charge velocity is low and take full advantage of the swept compression stroke. This would also feed into the reason why as the charge velocity goes up you would want to hang that valve open longer to take full advantage of the charge being supplied.
I don't recall what intake duration. AVCS does not allow us to retard intake opening so the best we can do is 5 degrees ATDC. So, not much we can do here for 'tuning'. In high load situations, it's best to run 0 advance and align exhaust valve in relstion to that (17 degrees of retard).

Quote:
Originally Posted by Kevin VanCleave View Post
- The exhaust retardation seems tricky. With no retard, we will open the valve sooner which I assume is not optimal because we'll start relieving pressure from the chamber sooner while combustion is still happening. I think this will hurt power.
In low and mid RPMs, this is correct. You want more exhaust valve retard to hold pressure longer in the chamber. Also, in those scenarios, most if not all of the exhaust can flow out of the chamber leaving more room for fresh air when intake valve opens. As you climb in RPMs, it is actually better to open the exhaust valve sooner. As RPMs climb, the exhaust flow becomes more inefficient so more and more exhaust remains behind in the chamber which dilutes the intake charge and reduces efficiency. By opening the exhaust sooner, you're helping optimize the intake charge that follows.

Quote:
Originally Posted by Kevin VanCleave View Post
---Here I think by opening the valve sooner you may be able to increase the mass exhaust volume aiding spool up. I could be wrong, its most definitely something that could be tested without a dyno by comparing boost curves relative to exhaust valve opening.
This is actually not that straightforward. In fact, I would not focus on spool as any kind of criteria. People tend to gauge spool based on measured boost pressure vs. RPM. Perceived faster spool may actually give you less torque. I know, it sounds weird but consider what boost is. It's essentially a measure of restriction. The higher the pressure, the less air you're flowing, ALL OTHER THINGS BEING EQUAL. If the turbo 'pushes' the same way and you see more pressure in the intake, that means that you're moving less air into the engine, essentially lowering your VE. So, it's easy to actually to the wrong thing here. You change your AVCS settings, you see faster spool but you're actually making less power because your VE dropped. This is why I would not focus on spool, but rather on VE. If you increase your overlap to increase your EGTs to get more boost sooner, you might be killing your VE because you're blowing perfectly good gas into the exhaust. More boost sooner does not always equal more torque.

Quote:
Originally Posted by Kevin VanCleave View Post
- Retarding the exhaust valve significantly may help power since we'll keep the chamber closed longer thus allowing for pressure to build up. This will likely produce more heat which is something to note. But, retarding it too much creates a major overlap with the intake side. Also, what should we expect to happen when the exhaust valve is open past TDC? As the piston starts to move down, are we in danger of producing reversion when the exhaust is now potentially moving back into the chamber? Does it make sense to close the exhaust valve right at TDC and have some overlap before TDC?
Exhaust flow depends on load and RPM. In low and mid RPMs, the exhaust pressure is lower than the intake side. This means that the exhaust will not flow back into the intake. Delaying exhaust valve works well for low a nd mid range. In high loads and higher RPMs, the exhaust back pressure increases dramatically and so if you retard the valve too much, you will get reversion. When piston reaches TDC, there is still considerable amount of pressure in the chamber. So, there is value to delaying opening the intake side past TDC to drop the chamber pressure before you let the fresh air in. Again, letting the pressure out sooner in certain scenarios is an acceptable compromise to optimize the intake side.

Quote:
Originally Posted by Kevin VanCleave View Post
----I'm going to take this one bit by bit.
- Retarding the exhaust valve significantly may help power since we'll keep the chamber closed longer thus allowing for pressure to build up.
--- The exhaust valve opens in the power stroke, the piston is traveling away from top dead center. Therefore the volume is increasing, and that means pressure is being lost regardless of what you do with the opening time of that valve. As much as I hate to use this definition here: PV=nRT, while the ideal gas law lives in the vacuum academia, it illustrates the point.
Again, this is good for low end torque you'll find that holding exhaust valve closed longer in high RPMs will hurt your VE because of the exhaust inefficiency.


Quote:
Originally Posted by Kevin VanCleave View Post
---As for the rest of the statement, in my opinion the exhaust valve event will have an effect on spool up and should be position in a way that gives you the best response. Even overlap has it's place where it can be useful, while it may not be good for power it can be used to create an EGR effect while at cruising speed increasing fuel economy. Again, most of the fixed center line cams I have degreed in close the exhaust valve after top dead center by 7-10 degrees to take advantage of the scavenge effect. With that in mind the relationship between the pressure in the exhaust manifold and the cylinder have to be looked at.
.
Exactly. Internal EGR can be used for improving fuel economy in cruising situations and does play a role in controlling emissions.
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Old 02-19-2012, 07:27 PM   #563
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Great thread on avcs!!!

Last edited by 07wrx84; 03-05-2012 at 04:35 AM.
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Old 03-13-2012, 11:44 PM   #564
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Quote:
Originally Posted by Clark Turner View Post
Fail. AVCS advance is not goog for Top end power.

C
Higher than stock Exhaust AVCS above 4800rpm is actually perfectly fine for keeping torque high with any post-turbo exhaust modifications to let the turbo breath post turbine. VTEC style power delivery to extend peak torque to rev limiter.

It helps evacuate the exhaust charge air and increases turbine input gas velocity

Here is a total camshaft overlap graph in scaled 3D


VF48 MY11 on stock motor doing 115MPH trap speeds...

Same car is getting 6.4L/100Km's fuel economy(No idea on MPG equivalent but thats nearly Prius fuel economy)
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Old 03-14-2012, 12:08 AM   #565
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Also, this is the stock 2010 STi Spec C 2L Dual AVCS cam timing overlap with the stock 20 degree(not 17) for exhaust cam timing removed to give you all an idea

Last edited by throttlehappy; 03-14-2012 at 12:15 AM.
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Old 03-14-2012, 12:17 AM   #566
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You play with graphs. I play with dynos

C
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Old 03-14-2012, 04:54 PM   #567
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Throttlehappy, I am a bit confused.

You speak of "total camshaft overlap", but the both graphs are titled "intake cam advance degrees (non-cruise)".

And I really can't read the values for any given point, and the vertical axis label is obscured on the first graph.

Can you provide any more detail and explain exactly what we are looking at? Can you provide the actual table of non-cruise Intake Advance and Exhaust Retard values? I am most interested in your work.

Thank-you................ Frank
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Old 03-15-2012, 01:56 AM   #568
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Quote:
Originally Posted by Clark Turner View Post
You play with graphs. I play with dynos

C
I play with dynos as well...
Low 12's @ 115MPH on a VF48 MY11 STi with a TBE speaks louder than dyno figures though.

Don't let only the LSx turbo guys be the only ones able to get decent power and torque with cam overlap

Quote:
Originally Posted by Frank_Zuccarini View Post
Throttlehappy, I am a bit confused.

You speak of "total camshaft overlap", but the both graphs are titled "intake cam advance degrees (non-cruise)".

And I really can't read the values for any given point, and the vertical axis label is obscured on the first graph.

Can you provide any more detail and explain exactly what we are looking at? Can you provide the actual table of non-cruise Intake Advance and Exhaust Retard values? I am most interested in your work.

Thank-you................ Frank
You can see above the graph that it has both Intake & Exhaust, then the formula applied just to the left (Intake + Exhaust minus the 17 in the far right box)

Basically, we all know that camshaft overlap is key to getting good midrange and the 'red' region is what promotes spool but also provides crankshaft torque to remove the 1500 to 3000rpm flat spot. Deriving more crank energy from an extra few degrees of exhaust overlap and then using the turbo compressor side to 'evacuate' the cylinder ensures a complete cylinder fill at high rpm.
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Old 03-15-2012, 08:38 AM   #569
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Thank-you, Throttlehappy.

Only the Intake Cam had a 'check' in the box, and this was confusing for me.

Still, I cannot seem to read the values on the vertical (Y) axis, so I cannot actually tell what the overlap is. The resolution of the graphic is just too low. Can you tell me how much overlap you are actually mapped for at 7k rpm and 3.0 g/rev?

Frank
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Old 03-15-2012, 09:06 AM   #570
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Originally Posted by Frank_Zuccarini View Post
Thank-you, Throttlehappy.

Only the Intake Cam had a 'check' in the box, and this was confusing for me.

Still, I cannot seem to read the values on the vertical (Y) axis, so I cannot actually tell what the overlap is. The resolution of the graphic is just too low. Can you tell me how much overlap you are actually mapped for at 7k rpm and 3.0 g/rev?

Frank
You can choose which box to modify to smooth out the total overlap, so you can use the + or - to change one map and then see the final cam overlap result etc.

Red zone is in the 60 degree overlap region with overlap at 7K 3g/rev being around 4.5 degrees
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Old 03-15-2012, 09:39 AM   #571
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Got it!

Thank-you for sharing................
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Old 03-15-2012, 11:41 AM   #572
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Throttle happy your figure equates to around 36-37miles/gal. What sort of driving gets you that fuel economy? I can achieve in the 30's but it seems to be only around 55-60mph on flat ground. In strictly stop and go driving it's probably about half that. And a mix of stop and go and freeway speeds with cold starts etc gets me around 19mpg which is more or less in line with what Subaru says it will get and what other people seem to be getting. What octane fuel are you using?
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Old 03-17-2012, 01:39 AM   #573
throttlehappy
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Get rid of the EGR 'humps' in both intake tables, which you can see in my above posted screenshot as the near flat dinner table and you can run 48 degrees of total ignition timing advance at cruise loads to improve fuel economy. I set my Intel mode maps up to drive like a V6 Toyota, still has heaps of torque and only runs wastegate boost pressure along with being 10x better than the factory Intel mode


Stock 09 Forester XT with just a tune...

They do better with an exhaust to let them breathe

Last edited by throttlehappy; 03-17-2012 at 01:49 AM.
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Old 03-17-2012, 01:42 AM   #574
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I trap 115 in the half track mark. Save the watches... Its getting deep in here.
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Old 03-17-2012, 01:47 AM   #575
throttlehappy
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The problem with dyno tuning is ramp rates, if the engine wants to accelerate harder than the ramp rate, the loss of airflow inertia results in a loss of torque and then everyone assumes that cam overlap on an STi is not worthwhile.
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