Slalom4me

As handling improves, I am finding I have to show up at events
with more and more fuel in my '89 to keep from having the engine
stumble in corners, particularly to the left.

I am wondering whether someone can point me in the direction of a
fix. Something such as a drop-in-baffle, swinging pickup or maybe
a fancy sock. A replacement tank is probably more than I want at
the moment but I'd still be interested in hearing about suggestions,
especially if it is about a fuel cell.

Ideally, I'd like to be able to start with 5 gal in the tank instead
of 15 gal.

I've checked past threads and I've only come across suggestions to
raise the fuel level. Had a look at the DRM and EM sites but did
not find anything there.

Thanks,
Ken R.

TrackDayLT4

I have talked with several other C4 drivers at tracks and all of them seem to have it to one degree or another. It does seem to vary in severity from car to car but I am not sure why. On my '96 at the track under very hard cornering along with hard throttle, it will cut out but only in left hand corners and only when there is less than 6 gallons in the tank, (about 4 bars showing) on my car. I have never had it cut out in right hand corners.

I believe that is has to do with fuel pickup location and a lack of baffles in the tank. Interestingly enough the 2 ZR1 drivers that I have talked to say they do not have the problem, maybe they have different pickups or tank design. I have been thinking about going to some junkyards and seeing if I can find a ZR1 that I can look in the tank and compare to a standard c4 'cause one solution might be to swap in a ZR1 tank.

One C4 driver at the track solved his problem by plumbing in about a 1/3 gallon surge tank to the fuel tank outlet. He put it in an open area behind the license plate. It had enough surge capacity to completely eliminate the problem and he could drain the tank dry without starvation. Not sure I would like to get rear ended with a bottle of gas sitting right there in the bumper though.

A couple of c4 owners have had the problem get worse over time, and replacing the fuel pump made it better again.


Cheers,

Lawrence

96GS#007

Mine does it as well. I always fill up at the start of the day and at lunch. I can run it down to about 5 gallons remaining before it starts to happen.

Solofast

C4's need a full tank for autocross anyway. The extra weight helps put power down coming off of corners and this is a good thing...

With a half a tank on really sticky tires you can feel the fuel kick the back end around when it hits the far side of the tank. This can really make the car loose just after turn in as it hits the outside wall of the tank and brings the back end around. This, and the starvation issue is why everybody autocrosses C4's with a full tank.

For track events getting rid of the weight would obviously be an advantage, but you need to address more than the starvation issue, since the slosh induced oversteer would make the car miserable.

For the relative speed gained there are other places to go and less expensive and easier ways to go faster. When those are exhausted then folks go to a fuel cell or a special tank.

Slalom4me

Right now, I am low on power compared to many other C4s so
it would be nice to be able to drop 60-70 lbs by adjusting the
fuel load. I know what you are saying about the fuel slosh, I've
had that happen when I ran slower courses and less fuel - wheee !

Interesting to hear that ZR-1 owners don't report the problem.
Maybe there is a difference. GM reportedly installed baffled tanks in
1LE Camaros, why not in the Z, too? I'll ask my dealer about p/n's.

After posting, I recalled reading about Rock Valley and the custom SS
tanks they make for rods, street machines and vintage tin.
Checked their site and they make a point of mentioning they baffle
their tanks. They do not list one for the C4 but they build tanks to
spec - prices do not look to be unreasonable. Before taking this route,
I would like to explore for other options and learn a bit more about tank
safety for the track.

Thanks for the replies, everyone.

.

Slalom4me

Then maybe the later cars or the GS ones have a different tank.

Prior to my last event, I added 11.5 gal with the gauge at about
1/3rd. It had been damp and cold during my first two runs but
by the third, the sun and breeze had dried/warmed the track and
I felt a small hiccup on this run. Then on the fourth run, the car
had a pronounced stumble at 65-70 mph and perhaps 0.95+ g. I
don't mind a little help when it comes to rotating the car, but that
was above and beyond what was required :>

I cut my pace at the corner for the rest of the runs.

.

c4cruiser

A full tank is the way to go. The weight of the full tank of gas helps to get the front to rear balance a bit better and should not make a big difference in your times. Depending on the number of runs and the speeds you hit and run times time, you should not really burn up a bunch of gas during an event.

And if you drive to and from the event, you don't have to stop for gas for the trip back

froggy47

Everyone I race with (inc. national champs) runs w/ full tank for autox.

Also any of those mods will bump you out of stock class if that's what you run.

Slalom4me

The events are hosted by local chapters of two german marques and
billed as Solo II. Aside from helmet, belt and procedural requirements,
there are no other set-up rules I am aware of.

For me, it is more a matter of stealth than rules requirements. Aside
from a ZR-1 that made an appearance once, mine is the only 'Vette
I've seen running with this group. Improvements are getting me
close to the times of some fairly high dollar cars while retaining an
outwardly stock appearance.

.

90pololt4

On our 90 C4 we run a full tank for track events and autoX. The car is better balanced. At three quarters or less I begin to feel the effect of the fuel moving from side to side. At autox's, it may be just me, but the car seems to have more power on a full tank as well.
There was a post here some time ago by some one who had gone to the trouble to install a fuel cell. They said the lower weight actually made the handleing of the car get worse. They put the stock tank back in with baffels welded into it. It worked out better for them.

Mr6spd

If you can do without the tank level sensor (moving float) , or install a tube type or electronic level sensor; you can fill your tank with fuel cell foam. It is an open cell foam that is fuel resistant, that is available in brick sized blocks that you can easily compress and fit through the top opening. If you fill the tank, as completely as possible, with the foam blocks, the fuel can not slosh quickly, it can only slowly move through the foam. This should help both the fuel pickup and fuel slosh problems. In fact, it looks like most racing fuel cells don't have any baffles, they just rely on the foam to control fuel slosh.

I haven't personally tried this yet, but would be interested in hearing if others have.

rhneff

I had the same problem with my 96, and can run now with about 5 - 7 gal without a problem. During last off season I drained the tank to make sure there was no debris that might be contributing to the problem - there's actually a very small plastic baffle in center of the bottom of the tank surrounding the pump fuel sock, but not deep enough to help a lot (the reason the ZR1's don't have the problem is because they actually have two pumps, to go along with their dual set of injectors). I found the fuel sock had gotten really hard and was restricting flow. Replaced the sock and also put on a new pump, replaced the fuel filter (which did have slight restriction), sent the injectors out to cleaning/blueprinting, and haven't had a problem since until I get down below about 5 gal.

Sidney004

Full tank for me too! Works every time.

larryfs

I do the morning / lunch time full tank routine. Never have a problem. Next season I will start to carry fuel.

Slalom4me

The comments about balance have thrown me a curve. I've
regularly removed the 45 lb spare/jack for events. This season
I permanently pulled a sub woofer left over from a previous owner
when I discovered it weighed 45+ lbs. I realigned the car minus
these items and feel the reduction has been benefical. I've
contemplated upping the rear spring rate ('89 FE1) a bit because
shocks and sway bars helped but lateral load graphs still make me
think I need more help - reducing the fuel load seemed like an
alternative quick, cheap fix but as mentioned, I am having to add
to keep it from sneezing in the turns.

Clearly, some sharp people here have found there is a point of
diminishing returns to pulling weight off the rear alone. I've
made changes at the front but I haven't looked at the fr/rr %
since. Thanks to everyone who pointed this out for the
reality check.

.

Slalom4me

I'd wondered about foam, too. I wasn't thinking about filling the tank,
just packing the ends but I imagined the foam would dislodge sooner or
later and discarded the thought.

I can't do without a sensor of some kind. Changing over is an
interesting idea but I have a phobia about fire - the alternate sensor
would need to be an approved/proven bolt-in sensor, meaning this one
is probably a non-starter. If it wasn't a dual-purpose car, foam
would be a big help I think.

I created a link to this thread in the C4 Tech forum but a couple
of posts wound up there. Zix mentions his racing bike had foam and
I gather this worked well.

.

Slalom4me

Thanks for the reminder about the fuel pump sock, I now have it on my
list of winter projects. I know what you mean about how the fuel
lacquers up the woven sock, reducing efficiency. The filter was
changed last year. Wouldn't hurt me to service the injectors, though.

Aardwolf mentioned having a yellow baffle (on an '88 Z52) and says he
can run with low fuel. I'm confident my tank hasn't been touched
but I have not checked yet to confirm one is fitted.

Your description leads me to believe the baffle looks ineffectual. Still,
two of you with it in place can run with low fuel. So if it isn't present
on mine and it is a drop-in, I am going to add it when I replace the
sock. (I'm not overlooking what people have said about balance - I'd
just like to have the option of testing for myself.)

Thank you for the information about the ZR-1 configuration

.

froggy47

You best be careful, locally the PCA & BMW clubs don't take well to being beaten by plastic cars. They eventually find a way to "discourage" the participation of said plastic cars. Actually I think PCA (locally) bans any non Porsche from running with them.

I like SCCA events, a class for everyone, bring on the competition

96CollectorSport

I installed the Racetronix kit in my 96 but the big differance was that I bent the tubing for the pump down so that the pump is farther down in the little plastic tub than before. I'm not sure if the racetronics pump made a differance or not but between the two I can get much more performance out of the car.
Before I replaced my pump if I stabbed the throttle with less than a half a tank it would cut out like the ASR kicked in, same thing when taking corners agressively.
I don't autocross much anymore but I do track the car (Road America mainly) and pull about 1.20 g around the carousel without any problems with the gas gauge on reserve. Usually I will go out with about a half a tank and next thing I know my RESERVE light is on, I can usually go 3 laps before I have to head in to avoid any starvation issues.
Bending down the tube worked for me now I can use all the gas in the tank.

vettmike

We keep our tank full and never let it under 3/4, the weight of the fuel helps balance the car.

vettmike