romandian

well, this makes my day, it means i have eaqualized weight distribution by adding a centri blower. no need to get a lighter battery, then?

Juhatee

In C5? No they won't.

Right tank will be emptied first and at that point you'll have the driver side tank half full. The only 3 ways fuel gets to right side tank are:
1. Filling tanks
2. Siphon jet being clogged (in fact that clogging doesn't add fuel to it, it just prevents it being used after 1/2 tank).
3. Car is storaged on it's right side on the paddock

My lap times seem to be holding at the same when I drive by myself and when I get a passenger next to me. When I have company, I drive smoother and do not try more than I'm capable.

Rookieracer

The tanks on both my C5s equalize when the car sits. You can watch it happen very slowly with a Tech II or EFILive and on scales.

The second you start the car, you can also watch the drivers side tank increase and the passenger tank decrease.

Rookieracer

If the budget allows, go with the light battery, then add some weight to the corner that best balances the car.

Juhatee

I'll have to try myself before I believe.. Too bad my tanks are 50 % full both right now so I couldn't check it before draining some fuel out (it's winter here so I can't drive it). Those hoses connecting both tanks route very high above the transmission so the only way they would equalize is by siphon and that would require beginning of the line higher than the end of the line.

romandian

97-03 without ffs system (whatever that is) equalize.

Rookieracer

If your tanks are half full, now is the time to try the experiment.
Observe the gallons in each tank with a Tech II, or EFILive before starting the car, Start the car, you will see the gallon display for the drivers tank increase while the passenger tank decreases until almost all of the fuel is in the drivers side tank.

I discovered this by accident while diagnosing the famous C5 fuel gauge to zero symptom.

Juhatee

Thanks for the tip, I'm starting to believe. I hotwired the fuel pump (car is on stands so the fuel level is not changing for any other reason than the fuel flow).
First I had 1.57 V left and 1.6 V right side (I used HPtuners to observe this). After 30 minutes I had 1.9 V left and 1.3 V right side. I shut down the pump and after 1/2 h I had 1.89 left and 1.32 V right side. I left it as it is overnight and I will look at the voltages tomorrow again.

It already looks like you are absolutely right. If I would have been right in this, the beginning of my test would have shown different voltages between tanks.

The reason I'm so interested in this matter is that last thing I did this season was that I raced one afternoon on race track and on my last laps engine stalled suddenly for few seconds in tight right hand turns. My fuel pressure gauge wasn't working but I thought I had fuel feed problems. I had about 2/5 fuel left. I assumed the siphon orifice got stuck in right hand tank but my today's tests prove that the siphon is working.

Soloontario

This information makes the whole corner balancing thing even more complicated. ALL the tracks I run are clockwise and if it is only the Left side tank that is full as fuel runs low, I need even a higher percentage weight on the R side of the car.

Any suggestions as to what percentage R side weight I should carry?

Juhatee

Now I believe: Tanks will equalize while the car is standing. I checked levels after 24 hours and left one has dropped and the right one has raised. Both read the same now.

Rookieracer

It comes down to the whether or not you can you can improve your overall lap time by sacrificing some grip in the left versus right turns. In a situation where the left turns are very mild and the right turns more aggressive, I would bias the car as much as possible to the right, even to the extent of adding lead bars to the right side.

The idea being, build the car as light as possible and add weight were it will do the most good. Be careful to try and add your weight low and centered between the right side wheels as possible. This will help avoid the pendulum effect.
Of course use scales to determine the best overall weight placement.

Tire temps will also reveal which tires are working hard and which are not. Try to get more weight to the corners that aren't working as hard.

69427

I would have to see some actual lap times to believe that was a wise tuning method. The additional weight slows the acceleration out of the turns (unless the corner exit speed was so slow that wheel spin is an issue, and then additional rear weight might help that situation. Think Porsche 911), hurts the deceleration coming into the turns (weight never helps when trying to stop a vehicle), and given that tires usually only return about a 90% increased grip compared to the added weight/downforce, it all seems to be a losing proposition here.

redtopz

I guess I'm the oddball here, but I'm faster when I remove weight from the car...

SunnydayDILYSI

I'm with you, but an interesting thread. My theory is that if you are a road racer (i.e., running 1.5+ mile tracks with 100+mph straits), the additional weight is a drag on speed and lap times (I see this in my data across hundreds of laps and multiple tracks). However, having grown up in the snowy mid-west where we put sand bags in the trunk/bed of rear wheel drive vehicles in the winter to improve traction on ice, I can see where in lower speed auto-x events with low traction surfaces it could potentially be an advantage if it puts weight on the back wheels. Definitely a drag on higher speed acceleration and cornering though.

Soloontario

I would never plan to add weight to the car as F=MA, (Force =Mass X Acceleration) still holds but our cars can be cornerweighted (not as easily as when using coil overs but still there is individual adjustment at each corner).

If the fuel tanks equalise over a long time, that doesn't help me at the track either.

My point is putting more of the car's weight on the right side for clockwise tracks may be good. Just don't have any idea of how much.

redtopz

When I add 200 lbs of ballast to change classes, it only changes my side to side weight distribution slightly more than 1% and my front to rear distribution by about 0.5%. That's not enough to make much difference IMO. I do agree 180-200 lbs of weight is not as big a deal as it may seem and I have turned single lap times nearly as fast as without the ballast. Tires and track conditions are more important. However, over a 30 minute race the extra weight adds up to slower lap times and more heat in the tires and brakes. I agree in auto-x on cold tires or low grip the extra weight might not hurt at all or even help a little.

I don't know anyone that races with more weight than they have to (at least not a lot more weight). In my experience, +/- 100 lbs doesn't make much difference in a vette. But 200 lbs starts to be a factor that I can feel. I would way rather take out 200 lbs of weight and go from 50/50 side to side to 51/49 even on clockwise tracks.

mountainbiker2

I use to add weight to my Slot Cars. It was the only way to go fast.