Wadoka

Hey.

I'm just getting used to my '97 SC400 and I feel like I'm missing a gear.

My car is sitting at 2500 RPM at 70 MPH. Is that what everyone else sees?

The reason I ask is, my last two cars were a '93 Corvette auto and a '99 Corvette manual, and both of them held much lower engine speeds on the highway. Granted, the C5 has two overdrive gears and would cruise in 6th at 1200 RPM...

It just feels funny seeing 2500 on the tach and it's not so good on the fuel economy. Weird that my old C5 got much better highway mpg!

Oh, also - does anyone know what mph the torque converter locks up, and if it's possible to reprogram so that it won't lock up until 50 -55 mph?

Psionic

3000 rpm @ 70 on an SC300. My 99 Expedition does ~2000 rpm at 70. My 66 Mustang does ~3500 rpm at 70.

Torque converters lock up at certain rpms, not mphs. Only reason to go higher stall would be due to larger cam lift, or to get maximum torque possible until your turbo kicked in.

Mwmorph

the cor5vettes are technological/engineering masterpieces. They are Chevy SB Pushrod style and yet they can make 505hp @28mpg highway due to the excellent gearing. The Sc4s get lower mileage because of the limited gears 2500rpm is normal, in fact form ost cars, 2000-2500rpm is fine. My friend's MR2 Spyder cruises at 60mph at a disconcerning ungodly 3500rpm and its normal due to the very cklose gearing and lack of a 6th highway cruising gear.

CyberSC4

Just checked today and mine is at 2250rpm at 70mph. It's a 2000 SC400

Jewcano

iTrader: (4)

My 92 sc400 runs at about 2700RPM at 70MPH....

kylessc400

my 95 sc400 is at 25 also at 70

Wadoka

Not on Chevys, Psionic.

My old '93 C4's torque converter was programmed to lock up at 42 mph - and it was a fairly simple bit of editing to change that to 52 mph.

The reason people do it is to stop the TC from constantly locking and unlocking on secondary roads where your speed stays between 40 and 50 mph. I've noticed my SC doing this.

If you shift the lockup speed to 50+, you lose a little more fuel economy but also lose the lock/unlock hunting of a non-highway commuter drive (mine)

Lots of people go to higher-stall TCs in auto Corvettes. 3500 stall, etc. No turbo, no cam change. Usually just a differential swap and a TC swap. You lose streetability but gain tenths on the dragstrip.

* * *

Thank you, gents. I was just feeling strange, waiting for one more upshift to drop the RPM down to my old idea of "normal".

I like my SC a lot. The door hinge is a work of art, compared to a Corvette. Lots of compromises to make the 'Vette a 3150 - 3250-pound car versus the SC's 3600 pounds. Seats, interior quality, the feel of solidity, etc.

Not saying I don't miss the HP/TQ in the C5, though... Sometimes it's fun to let the monster out.