Midrange Timing=Faster spool(time based)

[Black Venom]

I've seen this topic arise before. Midrange torque increasing from timing=faster spool of large turbos.

My belief on this topic has always been, yes increasing timing in lower rpm's before boost comes on makes the car faster, and makes the car spool faster (time based, not rpm based)

Now don't tell me that a car that reaches full boost 100rpm quicker than another is faster, If that engine is a dog to go through it's midrange. I believe there could be enough of a difference in power made from timing in some situations that the lower rpm spool turbo would still spool slower because it does not reach it's rpm as fast.


I understand we're not talking about great amounts of power or time. But it is there and it does help. I've seen way to many people say in the past that it doesn't help spool the turbo faster, without taking the time to note that it is spooling faster time based, just in their topic of rpm based spool times it is not relevant.

IE: It has been said an SCM6152sp can reach full spool in 3rd gear by 4300rpm,It has also been said that a GT3561sp can reach full spool in 3rd gear by 4200rpm. Same 2.0L engine used for comparison(no changes except turbo) If the SCM6152sp had more timing in it's midrange than that of the GT3561sp then it could be said that it spools faster (time based) And indeed would be faster, or at least now on a level playing field. ( till the GT3561 adds more midrange timing and has the upper hand again. )


Please discuss, if you have technical data to support or deny this claim of "faster time based spooling of turbos from increased midrange timing" please share.
This has probably been discussed before in great detail, It appears as though everyone has forgotten.
Moderators: I cannot post elsewhere if you feel this would be better suited for another section, and would receive more technical feedback please relocate it. (On second thought, then I wouldn't beable to reply to my own thread)

Please nobody start adding erroneous amounts of timing to your midrange unless you know what you are doing.

Cliff notes: Read full post before posting. Thank you

 

[GVR4592]

I really don't have much to add except this is pretty much what I've seen in my experiences. Decreasing timing will increase egt's and possibly spool the turbo at a lower rpm, but the engine response can be pretty lazy. You can further decrease spool rpm by leaning A/F ratio's drastically in this rpm range, but again this can negatively affect engine response.

It works on some setups but not on others. I can get 20 psi from my GT3561 at 4000 in 3rd gear and 3600 in 5th gear using this method. My tune isn't as aggressive as it could be, but I didn't want to sacrifice too much power for a quick spool. I just chose a happy medium between quick spool and midrange power. I'm going to further test this at the track to see what method is faster with my setup.

This was discussed somewhat in Andy's thread regarding slow spool on his 2.3.

http://www.dsmtuners.com/forums/showthread.php?t=241373

 

[GVR4592]

I should add that tuning on a load holding dyno will take all of the guesswork out of the equation. You can determine what the optimum A/F ratio and ignition timing value is for every load and rpm site to achieve maximum torque.

 

[andymoraitis]

I concur with the theories posted above. While I still haven't seen optimal spool from my setup I can vouch for the fact that taking timing away on the low end and in the midrange made the motor feel like an absolute slug. At the moment I run a more aggressive A/F map from the low end that starts at 14:1 A/F and peaks at 11.5:1 A/F by around 4400-4600 RPM. I also run more timing in the midrange.

While the addition of a leaner A/F and more timing in the midrange certainly helped increase the sensation of torque and got the motor moving the biggest changes I saw came from removing as many choke points as I could. Swapping a 1G TB, porting the elbow and porting the intake to match has lowered my spool to around 4200 or so (27 psi). I'll be taking down a sharp edge inside the compressor inlet sometime today and will see if that helps at all although I would expect that the change in spool will be marginal. I may even try switching to a 4" intake to see if that makes any difference although I would once again predict only a slight change.

But yes, more midrange timing and a more aggressive A/F curve (which was Luke's recommendation) seemed to help bring the power on more quickly even though spool RPM's didn't see a dramatic decrease.

Great thread by the way,

Andy