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Discussion Starter · #1 ·
In a recent thread (sorry don't have it), there was talk about running less base timing (such as 8 degrees BTDC) and increasing boost pressure. Is there any data that would suggest less advance, but more boost pressure would result in more power output?
Thanks.
 

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That is how many of the DSM guys are running 25+ PSI on 93 octane or lower fuel, some as high as 35 PSI.

It doesn't net you the smooth power delivery that higher timing advance and lower boost does, but from my experience, if you have a turbocharger that can keep up, it's definitely the way to make more power.

Besides, you NEED less timing advance at higher boost levels anyway.
 

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Joe - did you ever measure the 8*BTDC and higher boost runs or make any comparissons? Since you have 550 injectors, you should be able to really crank up the boost with your turbo and still get plenty of fuel (and of course back timing down).

I have been playing with runnng more boost based on seeing what other communities are doing (EVO and Subie). they almost always seem to be maxing out smaller/mid sized turbos for boost from what I can tell. Then must just be setting timing at the knock threshold for the fuel being used (pumps fuels).

With stock ECU and stock 10*BTDC timing, I am limited on my setup to about 17psi (CT20B) on my crappy 91 octane california gas. AFR was tuned at about 11.8:1 near peak power (SAFCII). With this setup, I dyno'd at 272whp. Any more boost and I got to much knock activity.

I am now experimenting with 19-20psi and backing down base timing as necessary to avoid knock (Still on 91 octane). I am still tuning it now, but it seems to need somewhere between 2 to 4 degrees less base timing to get it to maintain the same knock level. Not sure where power is but it certainly doesn't seem like less power. AFR is getting a little lean at peak power, now at about 12.3-12.5:1.

It drives fine off boost/low boost. I am using the SAFC to make low boost/load correction values that are negative (-15 values for the most part). This leans out already rich areas of the stock maps and also adds back the timing at part throttle and low load situations. Two birds with one stone in this case.

My goal is to max out my HP potential on the 91 octane fuel, since that is all that I have readily available where I am at.
 

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Remember first that the goal is to make safe, smooth, reliable power. Bragging about how much boost you run is a fine endeavor for kids, much like arguing about whose daddy would win in a fight.

There is a price to pay for boost regardless of how much power you are getting from it. More intake manifold pressure means more exhaust manifold pressure. That translates into more reversion, which means higher cylinder temperatures, higher exhaust valve temperatures, and a faster falling torque curve. Producing higher boost involves waiting longer to reach maximum boost pressure (lag), running higher turbocharger shaft speeds and turbine temperatures (leading to damatically shortened turbocharger life), putting more stress on the silicone couplers (higher probability of blown hoses, more expensive, higher quality couplers needed), needing a higher flowing fuel pump to fight against the higher fuel pressure, and needing more intercooling capacity to handle the higher temperatures at the compressor outlet. The last point is particularly important to keep in mind on our mid engine setups, which aren't as easily intercooled as the EVO and DSM setups.

So, the main question is can you safely run four more pounds of boost by running three fewer degrees of timing and make more torque? The answer is often not a whole bunch beyond a certain boost level depending on the octane of the fuel. For 91 octane California fuel, I often see the "breakeven" point at around 17-18psi on most built MR2 setups. That means that I can tune the car to run 22psi safely if I want to, but the timing retard and heat soak will just bring the power back down to about the same level as I can get with 18psi and the little bit more I can get is not worth it to me for all the reasons I stated above. With 100 octane, 22-24psi seems to be the breakeven point. With 110, about 27-28psi. With C16 and even more exotic fuels, the limits are usually dictated more by the turbocharger than the tuning.

On different motors and setup, these values will change due to compression chamber design, compression ratios, intercooling capacity and many other factors.
 

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I'm just curious as to what some of you consider low timing advance. I've seen posts from some of the tuners here saying they were being conservative with timing and were *only* running 20-22 degrees peak with 15+ at peak torque. Would you say that is pretty conserative for a well setup street MR2 on 91 octane, by the communities standards?

Also, this tuning method usually means leaning out the mixture as well. With the high timing agvance, you generally have to feed it a pretty rich mixture to keep things under control. The low timing advance usually lets you lean out the mixture considerably while you crank up the boost. Leaning out the mixture often dramatically improves combustion efficiency, which seems to make up for the lower timing advance all on it's own. For example, tuning a motor at 20 PSI with agressive timing and a rich mixture vs. 20 PSI, a leaner mixture and lower timing advance, I almost always find better power in the leaner mixture. In my opinion, the leaner mixture is actually better, because a higher timing advance is more prone to detonation then the lean mixture with low advance. Keeping the timing low is how I've managed to tune stock bottom end DSMs to 125+ mph traps in 3200 pound cars.

From my limited experience with MR2s, I've seen similar IATs on an MR2 with a good sized turnk mount to a DSM with a good sized front mount. Large intercoolers probably do 90% of the cooling on a drag pass with just absorbtion of heat into the metal and not from transfering heat to the atmosphere. In road racing, I could see the FMIC performing quite a bit better then a trunk mount. But in a drag style race, I question if it really even matters.
 

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Discussion Starter · #8 ·
Joe - did you ever measure the 8*BTDC and higher boost runs or make any comparissons? Since you have 550 injectors, you should be able to really crank up the boost with your turbo and still get plenty of fuel (and of course back timing down).
At the time I ran those tests I didn't have a wideband connected. I would like to try it again. When I did try 8 degrees instead of 10, the power certainly dropped as well as low end torque. I could run more boost pressure, but I didn't get back (power wise) to where I was at 10 degrees for fear of running too much boost and not knowing the AFR.
99_GS-T makes a good point about being able to run leaner mixtures with less advance. Something to try anyway!

http://www.lovehorsepower.com
 

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Well, to answer my own question:

2.0L, 8000 RPM running 28 PSI at sea level with a VE of 95% on a turbo with 70% efficiency.

Intercooler with ~15 pounds of aluminum mass for heat absorption.

To cool the compressed air back to ambient temperatures would take roughly 45kW of heat rejection. The aluminum intercooler will disipate ~ 6kW of heat per degree celcius. For absorption alone, this would cause ~7 degree celcius raise in the temperautre of the intercooler every second. After a 10 second blast, you'd have a pretty hot intercooler. I'd say my thought of ~90% of the heat is rejected just by warming the intercooler is a ways off. Maybe 30% or so is just from raising the temperature of the intercooler.

These numbers were just real quick, they could be a ways off as well.
 

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RickyB said:
Remember first that the goal is to make safe, smooth, reliable power. Bragging about how much boost you run is a fine endeavor for kids, much like arguing about whose daddy would win in a fight.

There is a price to pay for boost regardless of how much power you are getting from it. More intake manifold pressure means more exhaust manifold pressure. That translates into more reversion, which means higher cylinder temperatures, higher exhaust valve temperatures, and a faster falling torque curve. Producing higher boost involves waiting longer to reach maximum boost pressure (lag), running higher turbocharger shaft speeds and turbine temperatures (leading to damatically shortened turbocharger life), putting more stress on the silicone couplers (higher probability of blown hoses, more expensive, higher quality couplers needed), needing a higher flowing fuel pump to fight against the higher fuel pressure, and needing more intercooling capacity to handle the higher temperatures at the compressor outlet. The last point is particularly important to keep in mind on our mid engine setups, which aren't as easily intercooled as the EVO and DSM setups.

So, the main question is can you safely run four more pounds of boost by running three fewer degrees of timing and make more torque? The answer is often not a whole bunch beyond a certain boost level depending on the octane of the fuel. For 91 octane California fuel, I often see the "breakeven" point at around 17-18psi on most built MR2 setups. That means that I can tune the car to run 22psi safely if I want to, but the timing retard and heat soak will just bring the power back down to about the same level as I can get with 18psi and the little bit more I can get is not worth it to me for all the reasons I stated above. With 100 octane, 22-24psi seems to be the breakeven point. With 110, about 27-28psi. With C16 and even more exotic fuels, the limits are usually dictated more by the turbocharger than the tuning.

On different motors and setup, these values will change due to compression chamber design, compression ratios, intercooling capacity and many other factors.
Ricky - thanks for all the great information. The part about "break even" is especially interesting. That is what I was looking for. I am far from a built motor (begin a stock long block and intake manifold), but I do have an nice St205 A2W setup which is probably what is allowing me to run stock ECU and timing and get away with 17psi on my CT20B on 91 octane.

This is a type of tune I would certainly not think about taking to a road coarse is would be for an occasional street boost or drag runs only.

Have you ever tuned a smaller turbo towards the boost limits (like a Ct20B, GT28RS, etc...)? I am curious if the "break even" is still in the same ball park for the same fuel octane.
 

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99_GS-T said:
I'm just curious as to what some of you consider low timing advance. I've seen posts from some of the tuners here saying they were being conservative with timing and were *only* running 20-22 degrees peak with 15+ at peak torque. Would you say that is pretty conserative for a well setup street MR2 on 91 octane, by the communities standards?

Also, this tuning method usually means leaning out the mixture as well. With the high timing agvance, you generally have to feed it a pretty rich mixture to keep things under control. The low timing advance usually lets you lean out the mixture considerably while you crank up the boost. Leaning out the mixture often dramatically improves combustion efficiency, which seems to make up for the lower timing advance all on it's own. For example, tuning a motor at 20 PSI with agressive timing and a rich mixture vs. 20 PSI, a leaner mixture and lower timing advance, I almost always find better power in the leaner mixture. In my opinion, the leaner mixture is actually better, because a higher timing advance is more prone to detonation then the lean mixture with low advance. Keeping the timing low is how I've managed to tune stock bottom end DSMs to 125+ mph traps in 3200 pound cars.

From my limited experience with MR2s, I've seen similar IATs on an MR2 with a good sized turnk mount to a DSM with a good sized front mount. Large intercoolers probably do 90% of the cooling on a drag pass with just absorbtion of heat into the metal and not from transfering heat to the atmosphere. In road racing, I could see the FMIC performing quite a bit better then a trunk mount. But in a drag style race, I question if it really even matters.
I am not sure exactly where the stock ECU puts timing, but according to this:

http://carpron.com/multisite/v/Uplo...ginition+tables.bmp.html?g2_imageViewsIndex=1

It has peak torque (about 4200rpm on a stock motor, quick spooling turbo like mine) at about 22*, rising to 30* by 6600rpm. That's a ton of timing an with would seem beneficial even on a small turbo like mine to be at near 20psi and turning back the timing to keep knock in control. I guess I need to get to a dyno and compare it against my 17psi/stock timing numbers.

good to know about the leaner mixture and less advance. It fits what my car is doing naturally as I run out of injector. At 19-20psi I am seeing 12.3-12.5 AFR near peak airflow. But that is just for a short period and peak torque is more like 11:1, and rising from there to peak flow (stock 440's still in there).

I am still experimenting with adding timing and leaning things out slightly near peak torque, as there are not any signs of knock there. Signs of knock right now are coming in the 5800-6400 as I approach peak airflow and the leaner conditions.

I am not sure of my IAT's, but probably good with the ST205 core with IC water temps not going over 80-85F in the cooler fall weather (ambient of 70F).
 

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joeo said:
At the time I ran those tests I didn't have a wideband connected. I would like to try it again. When I did try 8 degrees instead of 10, the power certainly dropped as well as low end torque. I could run more boost pressure, but I didn't get back (power wise) to where I was at 10 degrees for fear of running too much boost and not knowing the AFR.
99_GS-T makes a good point about being able to run leaner mixtures with less advance. Something to try anyway!

http://www.lovehorsepower.com
You seem to be a prime candidate for this, as your turbo really won't have much issue if you decide to push more like 21-22psi (probably near the limit of your injectors?).

My smaller CT20B is putting alot of hot air at 20psi and at least making good use of my A2W IC :) .

Let me know if you do any comparissons. My Gtech is the old style so I have not been able to get repeatable numbers form the "HP" mode. No space to compare 1/4 miles runs with it, and 0-60 being a launch/traction issue, not really power. That leaves going back to the dyno for me which would be another $60 bucks. Might do it after some more tuning just to see how it all comes out in my case.
 

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califcarm said:
Have you ever tuned a smaller turbo towards the boost limits (like a Ct20B, GT28RS, etc...)? I am curious if the "break even" is still in the same ball park for the same fuel octane.
I get to take small turbos towards their limits on 3S motors much more often than I get to take larger turbos just because so very few MR2 around here come in with large turbos and the supporting mods to take them near their limits. 2JZs are a different story.

I don't recommend folks playing around with leaner mixtures or higher boost unless they have a very robust tuning process in place and enough experience tuning forced induction motors to know how to keep the motor intact while experimenting right at the edge of safety. Detonation will very rarely happen above 6K no matter what you do, but running just a little too lean or a little too much timing there will produce so much heat so quickly that you will burn exhaust valves and holes through piston tops (even forged piston tops). To stay away from danger you have to approach the adjustment from a very conservative position and slowly make incremental adjustments while using a stethoscope to listen for the onset of detonation in the midrange and the torque curve for indications that your are approaching the limits across the RPM band. Remember that you are literally playing with fire.

Also the stock ECU is not a very good tuning platform for working at the limits. Having only the ability to adjust base timing is like bringing a knife to a gun fight.
 

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RickyB said:
I get to take small turbos towards their limits on 3S motors much more often than I get to take larger turbos just because so very few MR2 around here come in with large turbos and the supporting mods to take them near their limits. 2JZs are a different story.

I don't recommend folks playing around with leaner mixtures or higher boost unless they have a very robust tuning process in place and enough experience tuning forced induction motors to know how to keep the motor intact while experimenting right at the edge of safety. Detonation will very rarely happen above 6K no matter what you do, but running just a little too lean or a little too much timing there will produce so much heat so quickly that you will burn exhaust valves and holes through piston tops (even forged piston tops). To stay away from danger you have to approach the adjustment from a very conservative position and slowly make incremental adjustments while using a stethoscope to listen for the onset of detonation in the midrange and the torque curve for indications that your are approaching the limits across the RPM band. Remember that you are literally playing with fire.

Also the stock ECU is not a very good tuning platform for working at the limits. Having only the ability to adjust base timing is like bringing a knife to a gun fight.
Thanks for additional information. I will approach it cautiously. Right now I am sitting at 19-20psi, peak torque AFR of 11 to 11.5:1, peak power AFR at 12.2-12.5:1, with base timing set about about 6-7*. I am thinking that with the "aggressive" stock ignition maps that retarding it 3-4* is probably just putting it more where it should be at increased boost levels anyway (kind of like using positive SAFC values, if using one). Yourself or ATS has surely seen the ignition timing tables and could probably confirm that they are aggressive or not. From the table I listed earlier (from another board, Celica board IIRC), peak torque advance is about 22* rising to a high of 30* by 6600rpm. I have a hard time believing it is that much, but then again, these cars are from a different era compared to the likes of the EVO and STI that seem to run higher boost/less advance from the factory, comparatively speaking. Come to think of it, that advance sounds like the same type of stuff that the early DSM guys were trying to run (99-GST mentioned 20-25* at peak torque from the earlier days).

I will watch the knock situation. I had heard that knock in the upper rpm range was not likely, but I think this is real knock. I will try adding some octane points with the exact same tune and see if it dissapears to verify if it is real knock or some ghost signal being picked up.

The stock ECU is definitely not the tool to be tuning with, but with California smog, I am just going to stick with it for now (car is BAR certified and smog legal if I put the secondary cat back in). It seems to drive just fine off boost retarded about 3-4 degrees, especially when using the SAFC with negative values to add some timing back in in the lower rpm/lower load range.

The only tool that I don't think I have that one should to be doing what I am doing is the EGT gage. As you mention heat causing damage at higher rpm rather than knock in the mid range by tuning the way that I am attempting, I should probably get that gage before proceeding further.
 

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Quick update on my experimentation.

I have noticed a difference in detonation events at the higher boost levels (as would be expected). At previous 17psi, if there is a little to much timing, detonation comes on in a linear fashion. Meaning, the J&S detects knock and retards timing a smaller amount to correct for it. The J&S can pull between 1 and 10 degrees timing, depending on the severity of the event and how many times it has occured (incrementally increasing timing retard until it goes away). At 17psi it seems to just pull between 1-4 degrees to get things in check (almost never more).

Each time I have encountered knock signals with 19-20psi, it seems to pull more timing and do it almost immediately (not incremental like before). This morning it suddenly went from fine to pulling 10* timing immediately. I let off the gas the instant it happed, but of course a few knock events of a major proportion had already occured. I checked the data logs and boost/AFR were in line for other WOT runs I have done with very little sign of knock at all. Seems that when it goes, it might do so in big fashion. Engine seems fine, but I think my experiements with higher boost/low octane have come to an end for now and I will stick with RickyB's suggestion of around 17 psi max for 91 octane California gas.

I think the J&S saved my motor. I would not like to know what would have happened with the stock ECU knock control as the only thing saving me.
 

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With the air being cooler outside I'm hitting higher boost levels too. I've hit 17 psi on occasion last week and felt the ECU retard heavily. I also notice it doing the same at lower psi's like 15 after the Greddy IC gets heat soaked after spirited runs.

I really need a good IC or some water injection like yesterday.
 

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DougyD19 said:
I really need a good IC or some water injection like yesterday.

I have the IC situation covered, but you mention the other way I could probably deal with higher boost levels - water injection.

I might have to look into that and just use it when I want to turn up boost and dont' have octane boost or better quality fuel available.
 
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