Probably 350wtq (Dynojet uncorrected).

I'm up at high altitude, so my power is killed, but I still have about 320whp/360wtq, and it can get hairy sometimes on 285/30-18 V710s. When I hammer it, the acceleration is so violent that I pretty much have to be straight and have to have enough room before the next feature to regain full control of the car. Remember also that I lose about 300-400rpm of spool up here, so when I go to Nats, I'm going to probably turn the boost down some or adjust the timing curve, because
I'll have closer to 400wtq that comes on much earlier than I'm used to...

 

So this is an interesting topic that I've experienced to a lesser degree.

I'm running STU and bouncing around between various tunes and exhaust configurations. I feel like I can handle the car much much better with the lesser tunes; I am in control and don't have to hope my car is pointed straight when the boost comes on. The car induces wheel spin, but fairly linearly, at the lower power levels.

As the power increases and the wheel spin and the peaky power band shows up, is it really going to be faster than a lesser, predictable power level? My power levels are obviously going to be less given the STU rules and the 245mm, 140 treadwear, tires, but I'm still dealing with the same questions. Maybe it is just driver preference.

Perhaps the ultimate goal is not to build a lag-monster with violent boost, but a super linear powerband that comes more from boost tuning that turbo sizing. If you take a Green, for example, and try NOT to hit peak boost at the same spot as stock, it might work out. If I took my most aggressive tune and worked into the power, leaving bulk of the gains at higher rpm, I'd take it.

My car is sitting at 30-50wtq above stock on our Mustang Dyno, which equates to 280wtq.

-Jon

 

Mine is actually tuned to run linear boost. Race gas runs a straight 27lbs to redline. No taper. Feels very linear. Maybe Kevo will chime in here as he got a ride shotgun in my car this past weekend.

 

Sorry to go offtopic, but how in the world do you get that much extra power with an STU legal tune? Are you running 100+octane? A timing/fuel fix is worth a little bit, but that's a LOT of torque with exactly-stock boost.

d

 

Just an FYI, the GSC center does not replace the ACD or VCU (in the TC). It replaces the actual differential in the tranny. They do give you a big hunk of metal to replace the ACD/VCU, but I'm quite sure you wouldn't want it for tarmac duty.

 

Mark, do you have any MAP sensor logs showing this? I can't say I've ever seen a 100% flat boost curve at such a high boost level on a stock turbo. All the big power 20Gs taper like normal on graphs that I've seen.

Anyway, I don't think they are referring to how much the boost tapers or doesn't taper, but rather how quickly it ramps up from nothing to 27psi, which is very upsetting to the car, especially with 400wtq or so. You haven't complained about it, so it doesn't seem to be an issue, but even with my meager power levels, I can rip my 285s off the ground and get some nasty tailwhip if I don't manage my exit throttle properly.

 

Not running the stock turbo.



He's a top driver; I would imagine he could drive around it.

What suprises me Mark, is that you're still running stock diffs I see you are putting a rear diff in... is a front diff on the table?

 

OT: Check the Nasioc thread on BSP to see an nice pic of yourself on course

 

No plans for a front differential yet. I have never felt inside front wheel spin, so I have not felt it is an issue. I have on occasion felt the rear, so it is getting replaced.

In response to the the flat boost control, I am running the evogreen, with an aem, and a tial bov, so it is not an issue. Plus the AMS magic tuning.

 

I know Mark has the 20g-LT, but it's a stock turbo - that's what I'm saying. They still taper, because of the fact they are a modified stock turbo. It's less than the normal stocker, but it still tapers nonetheless, and that includes the ones running high 10s and low 11s on AEM EMS. That's all I was saying - just was hoping to see a MAP sensor log showing a 100% flat boost profile. I've never seen one as high as 27psi (on a stock-based turbo), so it would be very interesting to see.

 

It is very possible when using the EMS to control boost. You take it and set it so is spikes at 30 or 33psi and falls off to 27psi like usual. Then AMS works their magic with the boost control logic and makes it NOT spike initially. It comes up to 27 and stays there.

Now with a normal MBC, you set it to hit 27 and you are correct, it will always taper (some setups more than others).

I do think alot of the power-on wheelspin issues have to do with throttle modulation and parital throttle tuning. Many tuners tune to get the boost to come up absolutely as early as possible. This may be why some folks have issues with partial throttle surging. The turbo is trying to make full boost at partial throttle and the engine just can't use that much air. With my silver car I could hit full boost in 5th gear at probably 40% throttle.

Now it is probably possible to learn to modulate this, but with a smaller window of operation it will be difficult. If you have your boost control set up so that partial throttle = partial boost, and full throttle = full boost, and you don't have to worry about driving around partial throttle surge, then you will have a much smoother car and be able to roll on the throttle coming out of corners an apply just as much power as your tires can handle. I think it would feel similar to a NA car, with power proportional to throttle input.

BTW the most torque my silver car made was 330ft# @3000rpms and 390ft# @3300rpms, on a Mustang Dyno. The red car will make more than that, but probably 1000 rpms later in the powerband.

If anyone wants the crazy low end power cams out of the silver car, PM me.

EVOlutionary

 

I didn't really pay attention to the boost gauge on Mark's car so I have no idea if the boost tapper or not. I just want to get a feel of the green turbo. In the passanger seat, I can hardly feel any lag, boost character is very very similar to stock turbo, just with more power...well a lot more. Power delivery is very linear unlike my friends 20g with 2.3 stroker, no need to wait for spool up even in tight turnaround. The green pull strong all the way to redline. I have to say the tuning have a lot to do with it. The only thing is the tires doesn't really like the new found power that much, there are definitely more time on the table with some fresh tires. I'm looking forward to see how the car will run in Devens.

 

You don't have to have "exactly stock boost". Any allowable mods that let the boost go up as a byproduct of their intended use are OK, but no direct control of boost is allowed. For instance, a downpipe and exhaust will increase the boost spike and make it come on a little sooner. Using an EBay O2 housing can sometimes cause some boost creep which may get up to 22-24psi by redline. That, coupled with race gas and aggressive timing can certainly get you 50whp. . .

I know several Subie guys who run crazy up-pipe or downpipe combos that cause a lot of boost creep and let them run considerably more top end power.


EVOlutionary

 

A quick digression, sorry.

I just inspected the various dyno runs I have and I saw +10-15wtq, mostly in boost spiking, and then up to +30whp through timing and fuel tuning; the orignal number I quoted was from memory and incorrect. The boost curve is slightly higher, but follows the original curve fairly closely. Most of the gains were holding power out, not necessarily higher peak numbers.

The boost, if you can spike it or increase it, pays huge dividends around 4000rpm. A downpipe accomplishes this nicely. However, the downside is that when you do spike, you get a surge of torque that requires some quick reaction to keep it in check.

Just recently I tried out a tune with a full exhaust, boost, fuel, and timing tuning, which (back when we did tune almost a year ago) netted +50whp. The car was an animal and really did need to be pointed straight. Boost spiked hard and caused an onslaught of torque. On dusty pavement while trying the tune for the first time, I had a nasty spin at way too fast that unsettled me for the rest of the day. It was quite a relief to go back to my other tune, quite honestly. As I ran the STU tune this weekend, my very thoughts were,"Hey, nice smooth boost onset is so much easier to drive."

The Evo is silly: feed it boost at the right places and you get a lot. Spike 3psi at 4000rpm, and you see 10-20wtq gains.

-Jon

 

thats the beauty of an aem w/ either the aem or gm boost solenoids, you can set it at whatever, and the aem will do its hardest to keep it there, in which most cases it will


for all you guys running 20g's, are you still on stock tranny/t-case? only reason i ask is becuase w/ big slicks, and a good amount of power, launching that thing will take a toll on the drivetrain..i'll be running 275's and w/ somewhere between 380-400whp on pump i'm scared that the stock tranny/t-case will explode, plus i've got my 2 step set at 7600 rpm's, which makes for some fun launches on street tires