mickeyd2005 Posted February 22, 2008 Share Posted February 22, 2008 Boost threshold and throttle response are two different things. For throttle response, I like to think of this as when you are driving around at vacuum and then suddenly punch it. It takes a small amount of time to fill up (increase the air density) of the piping between the turbo and the intake manifold. For a large FMIC, I believe the theoretical increase was around 1/3 second. For boost threshold, that's the earliest rpm you can get full boost if you start your log at a very low rpm. There's actually plenty of time in terms of milliseconds for the FMIC to fill up. However, the energy in the exhaust must be enough to spool the turbine to get boost. I believe that's why the FMIC with better cooling is helping increase energy at lower rpm thresholds. At higher altitudes, I believe that the lower atmospheric pressure requires a lower boost target. In fact, the ecu will automatically reduce the boost target depending upon Patm. The lower air density probably affects throttle response too. However, I didn't see any difference in boost threshold. Here is an old boost plot of a guy who I helped tune his boost in Colorado. Truth be told, I didn't finish his tune for him but he learned enough to continue with it on his own. I don't know where he is with it anymore but this was one of the last boost plots that I saw from him. As you can see, his boost threshold of about 2800 rpm in 3rd gear is about the same as mine at sealevel except his boost target was automatically reduced by the ecu from 17 psi to 16 psi. The boost threshold for 4th and 5th gear is artificial. He can boost at a lower rpm in 4th and 5th gear but we capped it. http://i141.photobucket.com/albums/r69/mickeyd2005/Legend.jpg Link to comment Share on other sites More sharing options...
mickeyd2005 Posted February 22, 2008 Share Posted February 22, 2008 Here is an old boost plot from Infamous1 (FMIC). I know he is way beyond this now, but it shows that even though his boost threshold is like 2600 rpm in 3rd gear, it takes over 2 seconds to get there. So, any decrease in throttle response due to the additional piping is really moot in regards to boost threshold. The boost threshold in 4th gear was capped due to the resonance in the intake. BTW, he gets full boost in 2nd gear before 3000 rpm!! I was impressed by that. http://i141.photobucket.com/albums/r69/mickeyd2005/infamous1rev009a.jpg http://i141.photobucket.com/albums/r69/mickeyd2005/infamous1rev009b.jpg Link to comment Share on other sites More sharing options...
Infamous1 Posted February 22, 2008 Share Posted February 22, 2008 I've got to learn how to use those plots! Link to comment Share on other sites More sharing options...
Nickz31se-r Posted February 22, 2008 Share Posted February 22, 2008 Well, when your engine is not running boost (depending on where you are in CO) you are about 20% or so down from what you would be at sea level. Once it reaches the boost threshold, you are only about 9-10% or so down. The problem is that the boost threshold (where the manifold pressure starts to become positive) is higher at altitude. This is because it takes a certain mass flow rate (combination of exhaust velocity, density, and area of the uppipe) to reach the boost threshold. Since density is lower at altitude ,(as is pressure) it takes a higher RPM (exhaust velocity) to reach the same mass flow rate. This means you reach boost at a slightly higher RPM than you would at sea level. So, your car will feel like a dog out of boost, and it takes a higher RPM to reach boost... BUT, the actual lag will be the same or lower Turbo lag is how long it takes the turbo to hit boost when you are already cruising above the boost threshold and you slam on the gas. Since the density and pressure are lower at altitude, the air flow has less momentum. This means that the time required to accelerate it through the pipes from low velocities to high velocities is actually lower up here ^^nice info, agree completely...so to answer the original question moving could possibly be the "mod" to less lag. Link to comment Share on other sites More sharing options...
itsme Posted February 22, 2008 Share Posted February 22, 2008 ^^^Did it reduce lag or boost threshold (also known as spool)? I'm sorry I come from a Muscle car from the 60's back round. Big V8 and big carbs and big cams. I don't know all of your cool kid, Hi-tech terms. Ask me the bore spacing of a small block chevy or the valve size of a Ford and I can tell that of the top of my head. I just know. I push pedal. Car make noise. Car go fast sooner. Fire bad. But, I'm learning :lol::lol::lol: Racer X FMIC for '05-'09 LGTs, '08+ WRX and '10+ LGT,'14+ FXT, and '15+ WRX TMIC Racerxengineering.com Link to comment Share on other sites More sharing options...
praedet Posted February 22, 2008 Share Posted February 22, 2008 ^^^ Link to comment Share on other sites More sharing options...
Powerman Posted February 22, 2008 Author Share Posted February 22, 2008 ^^nice info, agree completely...so to answer the original question moving could possibly be the "mod" to less lag. That's a big negative there. Small, small price to pay to live in the best place in the country. I just need more mods. Link to comment Share on other sites More sharing options...
Infamous1 Posted February 22, 2008 Share Posted February 22, 2008 ^^^ If the track isn't open all year around, I can't call it the best place to live in the country Link to comment Share on other sites More sharing options...
Powerman Posted February 22, 2008 Author Share Posted February 22, 2008 ^^^ My track is open year round. It's called the Rocky Mountains;) Link to comment Share on other sites More sharing options...
Richard B. Posted February 23, 2008 Share Posted February 23, 2008 left foot brake Link to comment Share on other sites More sharing options...
KartRacerBoy Posted February 23, 2008 Share Posted February 23, 2008 What can be done about turbo lag? Anticipate. Accelerate harder, sooner. And hold on, bitch! Pappa is spoolin' up! Link to comment Share on other sites More sharing options...
Silverstar Posted February 24, 2008 Share Posted February 24, 2008 Wouldn't an external wastegate improve spool? I've thought I heard that this does...but can't find anywhere explaining how it does it. Wastegates are closed to get the turbo to spool, so why would an external gate spool faster? Can anyone enlighten me? Sorry if it's off topic... And yes I know an external wastegate is foolish on a stock turbo, but I'm an engineer and think of foolish things. Link to comment Share on other sites More sharing options...
mickeyd2005 Posted February 24, 2008 Share Posted February 24, 2008 I don't think an external wastegate improves spool. When the wastegate is closed during spool up, ALL exhaust goes through the turbine. It doesn't matter if you have a IWG or EWG. The EWG helps top end where some of the exahust goes through the wastegate. With an EWG, that portion of the exhaust doesn't have to go through the turbine housing. Link to comment Share on other sites More sharing options...
Infamous1 Posted February 24, 2008 Share Posted February 24, 2008 I think when most refer to an EWG spooling faster, they are saying it will keep the WG close more efficiently. I could see just by design how this could be true especially on high boost applications. Link to comment Share on other sites More sharing options...
mickeyd2005 Posted February 24, 2008 Share Posted February 24, 2008 That would indicate a mechanical problem with the IWG. The exhaust pressure attempting to open the wastegate door is not usually a problem during spool up. At high rpm, the exhaust pressure is very high and may force the door open. The classic example is the 2.5R. That IWG was improperly designed and would open at high rpm. That turbo worked perfectly fine with an EWG. Link to comment Share on other sites More sharing options...
Infamous1 Posted February 24, 2008 Share Posted February 24, 2008 But what about on applications running say 21-22psi down low on a IWG with a 10psi actuator. Most EWG's are rated at about 1 bar. Kind of an unfair comparison but it wouldn't be a lie if marketed that way. Link to comment Share on other sites More sharing options...
mickeyd2005 Posted February 24, 2008 Share Posted February 24, 2008 But what about on applications running say 21-22psi down low on a IWG with a 10psi actuator. Most EWG's are rated at about 1 bar. Kind of an unfair comparison but it wouldn't be a lie if marketed that way. I believe this is actually what BBB is running. He doesn't have a problem keeping the WG door shut because if he did, he wouldn't be able to hold boost at 6000 rpm. How does he do it? 3 port bcs plus large diaphragm wastegate actuator. He could have used a 2 port with a pill but I believe a 3 port is able to dump more boost at 0% WGDC. BTW, I prefer the EWG design. If I had an STi, I would go with a EWG plumbed back. However, I wouldn't expect spool to improve. Link to comment Share on other sites More sharing options...
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