Does anyone know what amount of gas in the tank will give the best balanced performance for autocross?

Also, I think I'm going to run my first event next week, looking at my mods, would i be a BSP?

 

As little as you can. We run with a 1/4 tank. We have done runs with the low fuel light on but also sucked air once so to me its not worth the risk to save a few pounds.

 

I run a 1/4 or less as well. The weight savings is worth more than anything else. As far as your mods, everything you've done is perfect for STU except for the flywheel. Get that changed back to stock and you have a decently set-up STU car. If you go to Street Prepared, it would be BSP and you will get killed.

 

I found this old thread and thought I'd revive it, because I'm trying to figure out why my car was so loose at the last autocross I ran, after feeling pretty darn good previously.

The only variables which changed in the last event were tire wear (going over 60 runs now on the V710's) and fuel load. The first couple of events in this car, I ran with close to/over 1/2 tank, simply because I didn't really monitor it going into the weekend. The last event, I made sure to have less than 1/4 tank...closer to 1/8 tank.

Has anyone noticed any real difference in handling balance with as little as 3-4 gallons less/more in the tank? Also, has anyone noticed any difference in front/rear grip levels as the Kumhos start to taper off?

 

I try to run mine as low as possible, and at local events (local to me at least), I get away with running with the light on. However, at Nationals I about shat my pants because the thing cut out twice during my first run...I think during sustained, high g right handers.

I would guess your loose condition is related to something else, but I would defer to others in the know...

 

I got fuel starve at natls with just under a 1/4 tank on the right course, first one we ran, on my first two runs. After the fast long left hand sweeper, which is the direction that gives the road racers problems, I down shifted to 1st for the very tight almost 180 right turn. I got a hick-up in 1st gear coming out of the turn on my first run. I thought maybe that car was cold or I just spun the tires and did not worry about it. On run two it did the same thing so I put an extra gallon of gas in for my 3rd run and the problem went away.

 

I'm going to run this weekend with between 1/4 and 1/2 and see how it goes. I'm just searching, here...can't admit that it was my driving that was loose, not the car

Jason, is there any RV parking at Cal Speedway on weekends when Cal Club does two day events?

 

you'll find that rear camber & toe changes more than you think based on rear weight loading, that's why I recommend a small amount of rear toe-in over zero toe

otherwise go for minimum weight, which WRT the original question is the minimum amount of fuel required to prevent starvation, and balance the car using other available methods

 

And make sure that when you get your alignment done you do it with the fuel level about the same as you are going to race with.

 

People have stayed there but the policy is no overnight parking. Unless you join one of the local cal clubs I doubt you will get in to a practice day, most of them fill up in a day or two.

 

I get real loose when my tire pressures get too low (especially when its cold outside)

 

Oh well, I was thinking about coming down for a weekend in January to run with you guys...but, that's a hike for one day/three runs. Maybe if I ask nice, and solicit the help of some of my friends down there, I can get in to a practice day?
Doesn't San Diego run on Saturdays at Qualcom, btw?

Also, back on topic, I realize now that I did have two changes that would make a difference in rear weight and weigh balance, last event. First, as mentioned, I was somewhere between 28-35lbs lighter on fuel. Second, I also had just done the single exit exhaust, which takes about 25lbs directly off the tail. So, maybe a 50-60lbs reduction in rear weight + having my alignment done with almost a full tank of gas could be something to consider...
When I install the Konis over the holidays and put the car back on the rack, I'll be sure to get my alignment done with about 1/4 tank, just to eliminate any noise from that variable.

 

San Diego is the same way as Cal Club, if you are not in a club you have a hard time getting in. They are not as bad, they take about a week to fill up, so if you send in an entry when they first post it a non member can get a spot. I can't help you, I don't belong to any of our local clubs. I have been lucky and got in to a few events when I wanted, but for the most part I just skip the practice events.

 

yeah Mike, you probably lost enough rear camber to cause an issue, of course you could always put a stiffer front bar on instead ...

 

Are you serious about this camber loss, or trying to get me to buy a Team RX8 sta bar?

Seriously, if you lost camber from, in effect, raising rear ride height, wouldn't you gain toe in? Have you ever plotted the change in camber and toe for a given movement upwards?

 

Going up should go to toe out. So if your car came up you would have lost some camber and toe.

Joe runs very little camber and toe out as well. I think Kieth Casey ran some toe out also.

 

rear toe out on the RX-8 is a mistake IMO, you're not doing something right if you need it

 

Hmm... that might explain why my new car feels a bit twitchier than the car I'd driven for most of last season, despite otherwise similar specs...

 

That was just what I heard.... Only KC and the alignment guy know what he ran for sure. We do know his Natls settings worked well for killing cones.

 

I ran the car today, but with almost 3/4 tank of gas...kind of like adding back the stock muffler and the 3/8-1/2 tank I'd been running with (approx. 60 lbs)...and the car was much more neutral. Of course, we were on a different surface, but the front/rear grip was much more even, in any case. The car still felt a little loose, but the tires are now over 80 runs. I may go to a tiny bit of rear toe in, next alignment.

So, the upshoot is that when I install my shocks, I'm going to be sure to do the alignment with the car as it's going to be run...1/8 tank gas and all items removed (tire kit, floor mats, undercoating...oops, jk!). At least then I'll know exactly what I'm working with.

 

mike, im sure you know that most people think GGF makes cars a lot more loose than monster. doesnt seem to affect me (in any of my cars)- i go loose even in front drivers :P

i was sick as a dog and lying down with my head swimming before my runs, so i hardly remember anything that happened sunday. its so bumpy at monster im not sure its easy to tell much there other than if your car hits rubber or metal when it bottoms.

james