There are a lot of cars here in DFW w/ the X/cat set up and not one has said they didn't feel a difference. In fact, everyone can't believe the increase in performance.

I don't see why it would be a big deal to get to 100 mph on a large A/X course, how long does it take us to get to 100? Not very long at all.

 

By the PCA safety rules an autocross course should be set up so it is limited to a maximum of 100mph for the fastest car. I have in the past done parking lot autocrosses where my 944 turbo was able to get up to 105 in 3rd gear before braking for the chicane. However, a typical SCCA autocross course does not have anything straight for long enough to get over 70mph. When doing those events in my 944 Turbo I never got higher than 2nd gear which topped out at 65. Didn't do many SCCA events before I stopped going to them.

And, Okay so I went from slippery four year old 255 Michelin Pilot Sports with LOTS of tread to brand new sticky 285 Pilot Sports. The x-pipe added enough power to make the brand new PS 285 to feel just like the old old slippery 225s.

 

What PCA region are you in? W/ a course like that I might transfer

 

It takes a 1/4 mile min in a straight line in a bout 13.3s in a stock GTS assuming gear changes etc are convenient to the course. Add turns cones etc and you don't get there unless you have more room. So you are saying you have runs at your AX events that are more than a 1/4 mile or so without any turns? I wouldn't call it an AX event without some obstacle, gate, slalom, Chicago box or something within 500 ft of the obstacle before. Most of our events are set up by long time SCCA guys and even at the most open forum we have some trick and highly technical bump to make it a challenge.

IMO all the fun of AX is finding the fastest way through the obstacles in the shortest time. Most of our runs are .8 miles long and take between 45 and 65s with a min of 30 obstacles. Pocono is 1.35 miles long and takes an average of 70s and there is no way you will get further than midway through 3rd gear. We usually get about 8 runs in a day. If I am going to go faster than that I might as well be on the track. Makes no sense to me to exceed 80 mph in an AX event the skill is in the turns and if you have long open straights it gives the high HP cars all the advantage. We usually don't see more than 10 s difference

 

Cobalt, not singling you out. Your post is just convenient.

RDK describes a 1.2 mile course. Lime Rock is about 1 mile IIRC. Hell, it is practically an auto-cross course. You can hit 100 easy on the front straight if you carry your speed through the downhill. I _think_ you can hit 100 or close to it on the back straight before the uphill too. Maybe. Never was looking at the speedo there. But...

Point is: it isn't all about the straights or how fast you can do a quarter mile from a standing start. It IS all about carrying speed through the corner and 928s are slow pigs - comparatively - from 0 - ~20 anyway.

Since RDK has twice(? IIRC) described getting FTD (or very close to it) in the GTS, I think doubters should give him the benefit of the doubt.

I think he'll be even faster once the PSD is working.

 

I am aware. I'm interested in the dynamics on the SC'd cars and the extent to which the cat/x-pipe might required significantly different maps for best use.

 

Just flush and fill with a high temp brake fluid like ATE Blue or AP Racing 600.

 

Richard, I know someone that can help with that.

 

We are dealing with different locals here guys. Texas and New Jersey. BIG difference. Texas would be the right place to run an autocross that is bigger than an actual track in New Jersey.

 

I know LRP well at least the old configuration it is more than 1 mile. You should easily exceed 100+ on the front straight and should be carrying at least 60 downhill if not more. I spun out in my old 911 going into the climbing hill turn doing close to 95mph. Even at that it took a 2390 pound 911 with 275 HP to reach 95mph traveling nearly half the course through the S's to achieve 95mph. Even the S's are tight enough to slow down and prevent a car from accelerating as though it were a straight line.

The course we use at Pocono is not unlike LRP although if it is a challenging course the front straight or any opportunity to run up speed should be full of slaloms, or tight boxes to slow down the run and give the lower powered cars a chance to compete. Otherwise it is like being at a DE and not an AX event. If he says he hits 100mph so be it but out of the numerous events and locations I have been to and there are many trophies all over my walls to prove it, I still highly doubt it. Even my turbo would be hard pressed to pull 100 MPH at an event like this. 80 I can see but 100 is what makes it difficult to believe.

I understand what you are saying but we are talking AX here and not track and although they have similarities they differ greatly and unfortunately we have no way of knowing what the configuration or surface conditions of the place they use is like. I can say that at our events there is no way a 928 or most stock 911's could come close to FTD even highly modified 911's are hard pressed to better the modified and AX prepped cars we run with. Most of these guys hold SCCA records and have 20+ years experience, teach AX weekly and they would all agree with what I am saying.

Sorry didn't mean to get off topic but I have a lot of experience AXing my GTS and even with 928 specialist sways and bilstein suspension it does not make for a good AX car, neither does my turbo.

BTW here is a pic of my wife at our 2007 event at Pocono. As you can see we have her in the foreground the car in the mid ground and other cars were on the straight in the far background where it reads Pocono. You could run that as a straight but that is not AX we do an increasing distance slalom and even with the last half of the straight open for acceleration you couldn't get a car above 80mph unless it had over 700 hp.

here is the area we use not much different as you can see.

http://maps.google.com/maps?f=q&hl=e...00957&t=h&z=17

 

I have done events all up and down the east coast including large airport runways and amusement parking lots that hold tens of thousands of cars. Sorry but if it is AX it doesn't sound very challenging to run up to 100 and brake into a turn that is what DE is for.

 

I did say our autocross is more like a time trial and not your parking lot variety event.
And no, we don't just run up to 100 and turn. That's what the local Corvette club does at this facility.
Having never run in any of your events I will not comment, until you participate in one of ours...

We typically leave ONE of the straights open for the guys to get their speed on, AND EVERYONE LIKES THAT! But we do try to limit the length of that one straight with a chicane so the quickest of cars can't get over 100 mph. The rest of the "straight" track sections we use are filled with obstacles (orange cones).

I have been participating in the War Bonnet Region PCA autocrosses for over 10 years now and we have ALWAYS set up our courses with one fast section where; if you have a very quick car, can exit a corner fast, and can brake really late into a chicane, you can get up to 100 mph. Even on small parking lots.

Cobalt - You make the comment that your autocrosses even out the competition between small cars and big heavy horsepower cars, BUT then you say your 928 and even your turbo can't compete at your events because the courses are too tight and twisty. You should try one of our events, we really do even out the competition by balancing the tight twisty bits with some long fast bits.

 

Yup. You got me there. I went and checked at the web site says 1.53 miles. It sure as Hell feels smaller in a 928 though

You have to carry speed onto the front straight. You'll be going a lot slower into BB if you do a standing start at the bottom of the DH. And the more speed you carry onto the straight the more you have at the end. That's it - doesn't matter if you call it an A-X course or a Track - that's all I was trying to get out.

Let's not get off into a debate of what's a Track and what's an AX course. Maybe Okies (I'm assuming RKD's in Oklahoma) have different definitions and their A-X courses are different.

My point was that saying RKD couldn't reach 100 mph when we don't know the configuration of the track is a bit presumptuous.

And of course, this is a diversion from the PSD anyway. If it isn't working at all you've got an open diff and then you'll get wheel spin in lots of places. Who knows what it does and what happens when its only half-way working?

 

Edit:
I agree David is correct and I shouldn't be pushing so hard, (bad day I guess) Best luck at your events and thanks for the input on the X pipe.

I guess we need to go to the AX section and discuss what makes AX competitive without being biased towards high hp or better handling cars.

 

Here is a dyno graph of a GTS with an X pipe.The X pipe is from Roger 928srus (Dave Lomas). The green line is with stock exhaust in 4th gear. The brown line is stock exhaust in 5th gear. You can see that 4 gear has greater loss at lower RPMs than 5th gear, but the tire rolling resistance has greater loss at higher speeds and acts to hold down measured rear wheel power on the top end.

The magenta line is with the X pipe and all runs were done on the same day. No tuning was done. The top end is usually too rich so a few more hp could be gained by leaning some. The most tuning gains are usually found on the lower end below about 3500 where the mixture is usually too lean and not enough spark advance. So fatten the mixture below 3500 and add some spark advance and get more torque there.
https://rennlist.com/forums/attachme...1&d=1229462527