jasenr

I am wondering if some of my Vette's poor performance can be attributed to it having 3.73 rear end gears? It is a fairly stock L98 with 135,000 miles on it. I am going to check fuel pressure, compression and possibly cam lift. I have never had one before, so I don't really know what I should expect. I put in a chip to compensate for the 24# injectors that it came with. It now runs smoother and idles better, but still seems to have no guts. I think my PT Cruiser is faster! It can't break the tires loose if it had to. Any thoughts?

CFI-EFI

Those 3.73 gears are lower than anything GM ever offered on a C4. You should have much greater acceleration with those gears, than stock. Either you have the ratio wrong, or you have other problems.

RACE ON!!!

Z-07 freak

2.73???

jasenr

Nope, they're 3.73's. I thought it should move better. It runs OK, but it just won't "get it" after half throttle. The only way I can spin the tires is on water in a turn! I guess I should add that the previous owner tried to do a few misc. things to the car with what looks like no real plan. Thus, I am considering jumping straight to a 383 project if this engine is in too much trouble. I really need to get the body/paint work done first, though. Nearly forgot to ask. I have a dist that says Hypertech on top of it. It has to places for wires on the side. They say tac and bat. I assume they mean tachometer and battery. The plugs going to them are loose and I think not making a connection. The RPM lead isn't even in. The BAT lead is really really loose. What does this lead do?

scorp508

1. An L98 should roast the tires with stock gears.
2. An L98 w/3.73s should make 1st gear useless.
3. 3.73s will not gain you anything in the 1/4 mile at all.

With that said... something is wrong. Clogged cats? Fuel pump not holding pressure at full throttle? Timing way off? Balancer split? Lots of things to check into.

scorp508

Wow.... sounds like quite the abortion.

The TACH lead is what provides the ECM with the RPM count. The car shouldn't even run with this unplugged. Does your tach work?

The BAT lead is what provides the 12v to the distributor providing power for the ignition system. The car shouldn't even run with this unplugged.

There should be a 3rd larger plug with 3 or 4 wires in it. This is from the spark control module controlling when the spark is fired.

flyersfan1088

No, the car will run fine with the Tach lead disconnected. Mine hasn't been on for the past 3 months. I never bothered hooking it back up since the tach doesn't work anyway.

But the car should melt the tires with 3.73's I would check the catalytic converter first.

scorp508

Then explain to me why disconnecting mine disables the car completly. It will just crank and crank and never fire. I've forgotten to plug it in at home and had the car in a no-start condition and have also had it come out at the track creating a no-start condition. Plug it back in and BOOM car runs smooth as can be. The ECM needs to know how fast the engine is cranking in order to apply fueling/spark variables.

flyersfan1088

The Tach wire has absolutely nothing to do with any no-start condition. The Distributor Reference Pulse Input is the purple/white wire in the 3 wire connector. The Tach lead supplies a signal to the tachometer display, nothing more, nothing less. The BAT lead disconnected would cause a no start, but not the Tach.

jasenr

The car came with the 3.73's. I would rather have 3.07's, but that can wait. The pre cats are gone and it has flo-max ? mufflers on it I am told. Did I mention that it is an auto? The timing is set where GM says to put it. I just checked that. It does run w/o the RPM lead on. The prior owner saw fit to mod all the wires going into the dist, thus nothing is where it should be. The factory end has been cut off and he crimped on ends. He had an MSD ignition module that was disabled. I removed it since it wasn't hooked up. Should I consider replacing the dist? Is there any way to put factory ends back on the wires. Man have they been messed up! What should the spark plugs be torqued down to. My book said 22 lbs., but that seems too high for aluminum heads, but I don't really know...

C10 JDR

Did you disconnect that electrical connector near the battery when you checked the timing?

scorp508

I think my book says 23 ft/lb for my aluminum heads as well. Close enough to be the same. I don't know if any of us actually torque them to spec though.

If you haven't invested in a Helms service manual I would do so immediately. It will come with all the electrical diagrams of your car showing what goes where and what color all the wires should be.

Then you can step back and take a breather while you analyze your situation. The factory ends can be put back on. You will just need the proper tools to re-crimp and re-pin them.

It is too bad the previous owner did not invest in the $15 harness that MSD sells for HEI cars so that you do not have to cut any wires.

jasenr

Yes, I unhooked the connector that the book said to. It was near the battery and the booster. I have a big red book that says corvette service manual 1991 on it. I think it is the one you are talking about, but it didn't come with the electrical diagram supplement. Everything I have came from the previous owner... Can you send me that Unfit for Command picture? I know some guys who would love it! I would like to add that I got the RPM lead to stay in (weakly). I don't know how long it will last, but the car doies run somewhat better now off the line, but seems to lose out in the long run. I hate those 3.73's. On the highway at 65 I am turning 3500 RPM. MPG still shows 25 MPG on the highway, but I will have to confirm. I can't see how...

C10 JDR

1. 3.73

2. 65mph

3. 3500rpm

4. ???????????

CFI-EFI

Like a lot of this thread, there is something VERY wrong, here. After slogging through every post, it appears you have a 1991, L98, automatic. Do you REALLY have 3.73s? You can turn the wheels and count driveline revolutions to determine the actual ratio. Has the speedometer been recalibrated to match the rear end gears? Also, we KNOW you have tach problems. Is your display set for English rather than METRIC for readout? With 26" tires and a 4L60 (700R4) transmission in OD, 3500 rpms equals 104 MPH! Sixty five mph is attained at 2300 rpms. Something(s) are VERY wrong.

RACE ON!!!

C10 JDR

Like he said.

ratortor

I have 3:73s on my 87 Corvette, and it is amazingly fast.
Along with other mods, it produces alot of torque and burns the tires without hesitation.
Rule out the 3:73, it is NOT your problem.

See my 87 at http://members.cardomain.com/bobcorvette

ratortor

I have 3:73s on my 87 Corvette, and it is amazingly fast.
Along with other mods, it produces alot of torque and burns the tires without hesitation.
Rule out the 3:73, it is NOT your problem.

qdawg41

I have a '91 vert auto and I'm having similar performance as stated above. At 65 mph I'm turning 3100 rpms, and at 90 mph I'm turning 4400 rpms. According to the previous owner everything is stock but I'm not so sure. I don't have any 1/4 mile times but the car has great acceleration. Any ideas on why I'm getting those numbers? It almost seems that it's not shifting into overdrive.

aklim

2 things come to mind.

1. Your tach reading is off. Have you verified it against a known good tach? If the tach is right, are you sure you are getting to all the gears and it is not stuck in D and not going into OD and lockup?

2. Are you realy getting 25 mpg on the highway as verified by the gas tank? If so, your tach is probably way off.