RJones

iTrader: (5)

General rule of thumb is if you're going to be on the limiter for more than ~2sec shift, if you're not, then let it bounce. But I digress...

It's really an interesting discussion because if you're building a STRICTLY autocross car, I can see how it would add more value to tune in 2nd gear. For those of you that don't autocross, you RARELY see anything other than 2nd gear on a course. I've autocrossed seriously for 2 years now, and I've only hit 3rd maybe 3-4 times (and most of those times, my results were actually better keeping it in 2nd)

It's pretty obvious that a 3rd gear tune results in less power/torque and boost (in the case of load based boost control) in 2nd gear. I think that if you're only going to use the car for autocross, then your performance will be increased by optimizing your tune for the loads in second gear. Remember, we're considering an autocross ONLY car in my example... no road course, no drag racing, etc.

mrfred

iTrader: (50)

How important is predictable and linear part throttle response to all you autocrossers?

RJones

iTrader: (5)

I'd say it's pretty important, how would that be affected by tuning 2nd gear? I know that the 2nd gear ratio is pretty far from 1:1, but if you're pretty much only using 2nd gear, how would that affect/relate to throttle response?

I'm actually really curious. I'm just starting to learn about the fundamentals of tuning.

kekek

iTrader: (22)

VERY. The car is typically spending LOTS of time in a transient state and having lots of power come on in the middle of a slalom (for example) sucks.

mrfred

iTrader: (50)

Based on my street driving experience, I suspected that was the case. My stock turbo would spool to nearly full boost at something like 20% throttle, and it would drive me crazy. I think what we really need is good boost vs TPS control to give a more linear power delivery with throttle position. Of course there is spool lag to contend with, but one step at a time.

I've been thinking about how to set up boost vs TPS, and its easy enough to setup in the ECU, but WGAs are not well suited to control boost at part throttle. Basically, a really soft spring is needed to allow good part throttle boost control, but the soft spring will limit the peak boost that can be reached. I've got an idea on an alternate WGA. Guess I might talk to some vendors about having a prototype built.

FJF

iTrader: (18)

Subscribed! I'd be very interested in knowing more about this.

RJones

iTrader: (5)

Now this is getting interesting...

mrfred

iTrader: (50)

My thought was to add a nipple to the other side of the WGA diaphram to allow controlled pressurization of both sides of the diaphram. Seems simple enough that it makes me wonder if it hasn't already been tried and not produced useful boost control.

03whitegsr

iTrader: (8)

I've been contemplating exactly that for a while now. More so with the intention of simply pressurizing it shut to max out the boost pressure at high RPM without having to have a 20psi WGA.

Most WGAs are not sealed at all on the low pressure side of the diaphragm. Even though they have vent holes that look like you could merely weld a nipple on, they are not sealed on the shaft at all.

I thought Tephra V7 had a TPS correction table?

I wonder if the Forge is sealed as it looks like there may be a tapped hole on the low pressure side that you could screw a nipple into.

Either way though, writing some code to allow a two line boost control system would be sweet for the externally wastegated guys. Using a dual line setup gives you a much larger range of allowable boost pressures for a given spring setup.

mrfred

iTrader: (50)

So its not a totally off the wall idea.

Yes, T7 has a TPS correction table, but I would implement it differently, and if two solenoids were needed for the WGA concept, code would need to be added.

EVO8LTW

iTrader: (41)

My solution part throttle smoothness is a Dejon Tool leak stop modded 1G BOV. At part throttle, it isn't shut tight like a Tial, so it bleeds off some of the boost. When you really stomp on it, it seals up tight through the solenoid switch over. I had other BOV's before that built a lot of boost at part throttle, fluttered, etc. The only improvement I'd make to the leak stop kit is to use an electric solenoid rather than a pneumatic one that switched over the BOV based on TPS rather than reaching 18 psi.

XSivPSI

iTrader: (8)

subd

chrisw

iTrader: (2)

absolutely critical...

It's more important than max boost in gear X....

To be honest with you, I prefer the stock boost tables over Tephra's gear based boost when autocrossing. How much boost you run in 2nd gear just isn't that important as how much usable torque I have through the RPM range.

for me, when I am tuning for autocross, I want to make sure that your fuel and timing is perfect since most of the time I am running at high rpm's usually bouncing off the rev limiter. So for me, it's ok to run a little rich on the top end to keep it safe when the rpm's are over 8k.