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Recommended AFR on full boost ?

Good advice. Thanks!
BTW, I noticed on your build thread that your exhaust uses some valves to divert the gases through a cat under normal driving conditions?
Do you have any further details you'd like to share?
I'm almost sure I could pass the emission's test here in France with your setup?
The test is quite basic: first measurement at idle and then they run the engine at 3000 rpm at no load.
Hi [MENTION=19738]CB72[/MENTION], Actually my exhaust is a bit of a personal source of pride for me. I'd hate for it to get copied by a vendor so i've purposefully kept the designs off nsxprime. It took a lot of work and design to get right but it's been perfect for 4yrs so I guess I did it right :)

There are a few really good threads from Mac Attack and me which we discussed these concepts. We can help you design your own if you decide to start an exhaust build thread.
 
Thanks [MENTION=20915]RYU[/MENTION], I fully understand.
In any case my design would have to be different as I should need only one Cat as I have only one turbo.
I'll think it over this winter...
 
Thanks @RYU, I fully understand.
In any case my design would have to be different as I should need only one Cat as I have only one turbo.
I'll think it over this winter...
Here are some thoughts that might be of help.

* Use a vacuum operated valve like the OEMs. Mine would not have lasted this long if I used an electric bypass valve.
* If your factory ECU is still plugged in there is a way to activate the valve at VTEC. My valve is fully open at VTEC but you can configure it different ways.
* I have a new 3" vacuum valve with an electronic controller that I bought but never used. It's perfect for a turbo application with an aftermarket ECU actually. I haven't posted it for sale but PM me if you're interested.
* You can get a vacuum actuated valve or a boost actuated valve. I'm using a vacuum actuated valve because it's easier for my ECU to control when it opens.
* In a turbo application I expect at least a 15-20wHP gain if your turbo exhaust is being restricted by a cat currently. This Supra got 50+
<iframe width="420" height="315" src="https://www.youtube.com/embed/mvCl-v_AzLE" frameborder="0" allowfullscreen></iframe>

Good luck! Enjoy your new project
 
To time the engine, take the vehicle to a dyno. An EGT gauge should be used if possible.

You want to be reducing timing as much as possible, until the EGT begins to climb notably, and the torque drops notably at the same time. Once you find this point, there is a diminishing returns with respect to the rate at which you add back in timing advance, and the EGT will drop/torque will improve. I usually start around 10* of timing for 7-10psi of boost at peak torque region for an engine which was originally turbocharged from the factory (2jz, sr20 for example). If the engine has a falling torque curve due to engine VE you can add a couple of degrees as engine RPM increases; if the torque drop is due to compressor maxing out you do not want to be adding any timing because the air is getting hotter when that happens, so be aware of why torque is falling.

That said, say you start with 10* and notice EGT is very high (1500*F for example in the turbine outlet is too high for 8-10psi of boost. It should be 1000 or 1100*F perhaps). You would want to add a couple of degrees of timing. If the EGT drops significantly in the next run (say from 1500*F to 1250*F) then torque will also improve significantly and you are going in the right direction. If you add a couple more degrees and the EGT stays about the same (it will almost always drop some, don't be fooled: you are looking at diminishing returns, stay out of that region. You want only to see a LARGE change in output/EGT, avoid making timing adjustments more advanced when the return is tiny) then you should be reducing back to where you were before. The engine is 'tuned' when the timing is minimal and results within 5-12% of maximum torque.

Example, pretend scenario
with 10* of timing EGT was 1380*F in the outlet of the turbine and torque is 200
with 13* of timing EGT was 1220*F in the outlet of the turbine and torque is 220
with 16* of timing EGT was 1200*F in the outlet of the turbine and torque is 224
with 19* of timing EGT was 1190*F in the outlet of the turbine and torque is 229

The ideal timing in the above scenario is between 12 and 13* btdc. Notice how more timing always seems to give more torque; if you examine the torque curve carefully you will notice this is often due to tiny spikes or bumps, 'glitches' in the torque graph where it seems to rise suddenly some places. This is a sign that the combustion events are becoming more 'peaky', that is, pressure is rising higher and higher peaks due to increase timing. This is showing up as a slight torque improvement, but it is very very bad for the engine because these pressure spikes are what damages head gaskets and pistons, they will get worse when the engine gets hotter or is run in longer gears for longer loads and something will break or pop. You want the minimal timing number which gives a reasonably low EGT and torque within 5-10% of the maximum possible.

Engines which run more competition states and have more 'toys' to deal with temperature increase, like blankets, methanol, coatings, wraps, shields, higher capacity oil coolers/intercoolers/water systems, can run closer to that bleeding edge to gain that last 5% of torque or so. But this is NOT daily driver territory, it is not good for we who wish to preserve our engines.

And just for reference, I run 9* of timing in sr20det engines at 15-19 psi of boost pressure with 93 octane with great success, through to redline as torque is fairly flat, 20 years of driving and perhaps 30-40 tuned cars with no issues; 1100*F~ in the turbine outlet when EGT is available. This is with a large camshaft, high VE engine (nearly 100% ve across the board). With the 2jz-gte engine and a stock camshaft, they can use slightly more timing around 11-12* of timing through to redline. I have never needed more than 12* in those engines, for 5+ psi of boost situations and 93 octane Florida pump gas with 10% ethanol.

Here is a graph to help illustrate what I just went through above
 
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I have an Angus turbo for about 6 years. 12k miles or so at 7.5 psi. My car runs best when my full throttle AFR is 11.8 or so. I know my tuner made the mid range AFR a little leaner to give me more torque which is apparently acceptable. I run 440 injectors and a AEM FIC and manual boost.

No issues. I think SC medium boost cars can bump the AFR to 12.5 but please don't take my word as gospel. I just have been here for a while and see what others do.
This does not apply if you run 91. CA cars seem to blow up more IMO due to lower rates gas. Find a great tuner and make sure your fuel pump is putting out full power. My stock pump was good but began to weaken and I replace with Walbro.

On the flip side, If you are seeing 10.5 AFR at max rpm you may wash out your cylinders.... and loose power.
 
To time the engine, take the vehicle to a dyno. An EGT gauge should be used if possible.

You want to be reducing timing as much as possible, until the EGT begins to climb notably, and the torque drops notably at the same time. Once you find this point, there is a diminishing returns with respect to the rate at which you add back in timing advance, and the EGT will drop/torque will improve. I usually start around 10* of timing for 7-10psi of boost at peak torque region for an engine which was originally turbocharged from the factory (2jz, sr20 for example). If the engine has a falling torque curve due to engine VE you can add a couple of degrees as engine RPM increases; if the torque drop is due to compressor maxing out you do not want to be adding any timing because the air is getting hotter when that happens, so be aware of why torque is falling.

That said, say you start with 10* and notice EGT is very high (1500*F for example in the turbine outlet is too high for 8-10psi of boost. It should be 1000 or 1100*F perhaps). You would want to add a couple of degrees of timing. If the EGT drops significantly in the next run (say from 1500*F to 1250*F) then torque will also improve significantly and you are going in the right direction. If you add a couple more degrees and the EGT stays about the same (it will almost always drop some, don't be fooled: you are looking at diminishing returns, stay out of that region. You want only to see a LARGE change in output/EGT, avoid making timing adjustments more advanced when the return is tiny) then you should be reducing back to where you were before. The engine is 'tuned' when the timing is minimal and results within 5-12% of maximum torque.

Example, pretend scenario
with 10* of timing EGT was 1380*F in the outlet of the turbine and torque is 200
with 13* of timing EGT was 1220*F in the outlet of the turbine and torque is 220
with 16* of timing EGT was 1200*F in the outlet of the turbine and torque is 224
with 19* of timing EGT was 1190*F in the outlet of the turbine and torque is 229

The ideal timing in the above scenario is between 12 and 13* btdc. Notice how more timing always seems to give more torque; if you examine the torque curve carefully you will notice this is often due to tiny spikes or bumps, 'glitches' in the torque graph where it seems to rise suddenly some places. This is a sign that the combustion events are becoming more 'peaky', that is, pressure is rising higher and higher peaks due to increase timing. This is showing up as a slight torque improvement, but it is very very bad for the engine because these pressure spikes are what damages head gaskets and pistons, they will get worse when the engine gets hotter or is run in longer gears for longer loads and something will break or pop. You want the minimal timing number which gives a reasonably low EGT and torque within 5-10% of the maximum possible.

Engines which run more competition states and have more 'toys' to deal with temperature increase, like blankets, methanol, coatings, wraps, shields, higher capacity oil coolers/intercoolers/water systems, can run closer to that bleeding edge to gain that last 5% of torque or so. But this is NOT daily driver territory, it is not good for we who wish to preserve our engines.

And just for reference, I run 9* of timing in sr20det engines at 15-19 psi of boost pressure with 93 octane with great success, through to redline as torque is fairly flat, 20 years of driving and perhaps 30-40 tuned cars with no issues; 1100*F~ in the turbine outlet when EGT is available. This is with a large camshaft, high VE engine (nearly 100% ve across the board). With the 2jz-gte engine and a stock camshaft, they can use slightly more timing around 11-12* of timing through to redline. I have never needed more than 12* in those engines, for 5+ psi of boost situations and 93 octane Florida pump gas with 10% ethanol.

Here is a graph to help illustrate what I just went through above

Sorry [MENTION=31132]kingtal0n[/MENTION], I had not seen your reply allthough I had activated the thread tool?
This is really excellent, I need to get myself an EGT meter.
Another question, when on the dyno do you hold the engine at peak torque rpm?
This requires a "brake" dyno and not the rolling bench type I suppose?
One of my friends had his turbocharged NSX dyno tuned and he noticed later on that there was a small hole in one of his headers.
Was that used to insert the EGT probe?

- - - Updated - - -

I have an Angus turbo for about 6 years. 12k miles or so at 7.5 psi. My car runs best when my full throttle AFR is 11.8 or so. I know my tuner made the mid range AFR a little leaner to give me more torque which is apparently acceptable. I run 440 injectors and a AEM FIC and manual boost.

No issues. I think SC medium boost cars can bump the AFR to 12.5 but please don't take my word as gospel. I just have been here for a while and see what others do.
This does not apply if you run 91. CA cars seem to blow up more IMO due to lower rates gas. Find a great tuner and make sure your fuel pump is putting out full power. My stock pump was good but began to weaken and I replace with Walbro.

On the flip side, If you are seeing 10.5 AFR at max rpm you may wash out your cylinders.... and loose power.

Do you know the timing that's used at the 7.5 psi boost level?
My AFR is now in the 11.2 to 11.5 range and the car is really going strong since I fixed the leak between the turbo and the T.B.
 
Sorry @kingtal0n, I had not seen your reply allthough I had activated the thread tool?
This is really excellent, I need to get myself an EGT meter.
Another question, when on the dyno do you hold the engine at peak torque rpm?
This requires a "brake" dyno and not the rolling bench type I suppose?
One of my friends had his turbocharged NSX dyno tuned and he noticed later on that there was a small hole in one of his headers.
Was that used to insert the EGT probe?

- - - Updated - - -



Do you know the timing that's used at the 7.5 psi boost level?
My AFR is now in the 11.2 to 11.5 range and the car is really going strong since I fixed the leak between the turbo and the T.B.


It depends on the engine type whether or not a load dyno is appropriate. Most forced induction engines in vehicles are NOT good load dyno candidates; this is because the vehicle weight becomes obscure when searching for optimal timing. In other words, a load dyno can apply whatever load you seek, so when the vehicle hits the real road and feels it's own weight, the timing can be very far from optimal. Many boat engines, however, will run a constant RPM/LOAD so that type of dyno is more appropriate ( an engine dyno might hold the rpm steady and run it at WOT there, for example)

What a load dyno is good for, is finding steady state conditions. For example, if you had a car you run at WOT or 75% throttle for 30 minutes straight. You could simulate that condition and find out where all the variables wander to, their final resting positions (coolant temp, exhaust temp, cylinder head temp, turbine speed, exhaust pressure, etc) at that load/time. Some engines will never reach a steady state, and instead continue to increase in temp/pressure until they simply explode; this is why it is so important to know what kind of setup you are working with, and what to expect from the parts in use. An engine that has alot of "toys" cooling related accessories and some method for rapidly cooling the combustion temps when they get out of hand (water injection/methanol/other) is more equipped to deal with situations which arise when you put the engine to "full blast" and leave it there for a while.

In any case. The kind of dyno I usually go for is a dynojet. Dynojet will use a roller in the ground with a known weight so that power output graphs are 'standardized'. That is, you put your car on the dyno, and then you get a graph, and this graph will easily compare across the board to any number of thousands of other vehicles run on the same dyno. It cannot be "fooled" or "tricked" into reading higher or lower the way so many other dynos can, so when you compare results you can get an actual feel for where your vehicle lies in the sense of power to the wheels.
The dynojet is a "single blast at a time" style, where you simply accelerate the roller as fast as you can with whatever gear you want. I often start with 3rd to do a quick preview, then use 4th(1:1) gear to make the run last longer. The longer you give the engine (slower rpm/time, aka RATE of CHANGE of RPM) to load up, the more time it will have to reach full boost, making the graph look better if the car is turbo or otherwise difficult to reach a maximum VE for some reason.


The MAIN THING you watch on the dyno, is the A/F plot given as you run it. The EGT should be recorded by a video or a data-logger. The A/F is the most important thing to watch; cannot stress this enough. Do NOT use the A/F gauge in the car. You can glance once to make sure they are the same reading; but do not trust the in-car Wideband very much until you run the engine very hard and confirm it works at high turbine temps. Many widebands are placed too close to the turbo (it should be around 4+ feet away from the turbine) and will overheat/read incorrect once too hot. I also highly recommend meth/water injection for turbo cars in general, it is an incredible safety feature and helps to clean the carbon from the engine, definitely worth every penny if you can remember to keep it full.
 
It depends on the engine type whether or not a load dyno is appropriate. Most forced induction engines in vehicles are NOT good load dyno candidates; this is because the vehicle weight becomes obscure when searching for optimal timing. In other words, a load dyno can apply whatever load you seek, so when the vehicle hits the real road and feels it's own weight, the timing can be very far from optimal. Many boat engines, however, will run a constant RPM/LOAD so that type of dyno is more appropriate ( an engine dyno might hold the rpm steady and run it at WOT there, for example)

What a load dyno is good for, is finding steady state conditions. For example, if you had a car you run at WOT or 75% throttle for 30 minutes straight. You could simulate that condition and find out where all the variables wander to, their final resting positions (coolant temp, exhaust temp, cylinder head temp, turbine speed, exhaust pressure, etc) at that load/time. Some engines will never reach a steady state, and instead continue to increase in temp/pressure until they simply explode; this is why it is so important to know what kind of setup you are working with, and what to expect from the parts in use. An engine that has alot of "toys" cooling related accessories and some method for rapidly cooling the combustion temps when they get out of hand (water injection/methanol/other) is more equipped to deal with situations which arise when you put the engine to "full blast" and leave it there for a while.

In any case. The kind of dyno I usually go for is a dynojet. Dynojet will use a roller in the ground with a known weight so that power output graphs are 'standardized'. That is, you put your car on the dyno, and then you get a graph, and this graph will easily compare across the board to any number of thousands of other vehicles run on the same dyno. It cannot be "fooled" or "tricked" into reading higher or lower the way so many other dynos can, so when you compare results you can get an actual feel for where your vehicle lies in the sense of power to the wheels.
The dynojet is a "single blast at a time" style, where you simply accelerate the roller as fast as you can with whatever gear you want. I often start with 3rd to do a quick preview, then use 4th(1:1) gear to make the run last longer. The longer you give the engine (slower rpm/time, aka RATE of CHANGE of RPM) to load up, the more time it will have to reach full boost, making the graph look better if the car is turbo or otherwise difficult to reach a maximum VE for some reason.


The MAIN THING you watch on the dyno, is the A/F plot given as you run it. The EGT should be recorded by a video or a data-logger. The A/F is the most important thing to watch; cannot stress this enough. Do NOT use the A/F gauge in the car. You can glance once to make sure they are the same reading; but do not trust the in-car Wideband very much until you run the engine very hard and confirm it works at high turbine temps. Many widebands are placed too close to the turbo (it should be around 4+ feet away from the turbine) and will overheat/read incorrect once too hot. I also highly recommend meth/water injection for turbo cars in general, it is an incredible safety feature and helps to clean the carbon from the engine, definitely worth every penny if you can remember to keep it full.

Hi [MENTION=31132]kingtal0n[/MENTION],

Once again clear and precise indications for the novice I am.
This last week end I had a track outing here in the South West of France and the car was a real blast to drive.
I had taken a small risk by advancing the ignition by 1° or so at my 7.5 psi level.
The only car with number plates on it that managed to pass me was a 911 ( 997) 3.8 L GT3.
He had a big advantage tire wise with Michelin PSS Cup2's and a small advantage power wise (aided by a dual clutch gearbox) as far as I could judge.
A quick glance at my AEM AFR meter (the sensor sits right next to the ECU sensor) in the long straight ( 220 Km/h) showed 11.0 dipping sometimes to 10.8.
The engine is definitely petrol cooled...
I must have been consuming 1L/min!
I'll open another thread with some video footage.
 
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