Engine "bogs" - Changed to 3.73 Gears

[hott85]

Got my 85 from the shop yesterday after having the gears changed to 3.73. It has an automatic transmission and accelerates with no problem first to second, and second to third with the pedal to the floor.

When the speed reached into triple digits, the rpm's seem to max out and the engine "bogs" and doesn't produce more power.

I kept expermienting with it and learned if I let up off the gas it would "catch" and produce more speed. But if I floored it again she'd downshift and would "bog" out again.

If I gradually depressed the accelerator it would shift into overdrive and keep going without maxing out the rpm's and produce speed much higher into triple digits. The speedometer needs to be recalibrated so can't say exactly how fast I'm travelling.

What's the problem? Is it getting starved for fuel..a rev limiter or what???

 

[Vettelt193]

is your car stock? how bad of a bog? does it just seem to run out of power? if it is stock, you may be just running the engine out of it's powerband. L98's are low RPM torque engines, they don't like high RPM that much

 

[MoeJr]

Normal 85 Vette top speed is 150mph. with 3.73's I would think 140. I am gonna bet your fuel pump is giving up the ghost. I have had my 84 Cross Fire up to 116 and it was begging for more. Just my.02

 

[hott85]

is your car stock? how bad of a bog? does it just seem to run out of power?

My Vette is not stock - headers, cam, ported heads, chip, on and on. It only seems to run out of power when the accelerator is floored and unable to shift into overdrive.

If I let the speed build gradually, shift into overdrive, it does not bog out and keeps building speed.

I should not have to "baby" it...

 

[Vettelt193]

I don't think it is a fuel pump, because fuel usage is not directly related to RPM.

When it bogs, what RPM are you running at? what RPM does your car shift at when run fast?

 

[hott85]

I manually shift it at appx 5000 rpm's and it does not bog from 1st to 2nd nor from 2nd to 3rd. It bogs at appx 5000 rpm's in 3rd when floored and does not shift into overdrive.

I can floor it from 1st to 2nd and 2nd to 3d. But I must get off the gas slightly when it reaches appx 5000 rmp's in 3d gear for it to shift into overdrive. If I keep it floored she'll bog.

 

[Vettelt193]

Sounds like the problem is all transmission based.... When was the last time you changed the fluid? it may be something as simple as a valve sticking in the tranny. I understand (but have not personally used) that synthetic auto tranny fluid is really good, and helps shifting substantially.

 

[hott85]

Sounds like the problem is all transmission based.... When was the last time you changed the fluid?.

The transmission was rebuilt two weeks ago; a shift kit and stall converter were installed. Spoke with the guy moments ago who rebuilt it and he said it should shift without a problem at wide-open throttle. It's the same shop that installed the gears.

He's taking another look at it on Friday - to ensure there's not a problem with the tranny.

Your question about it prompted me to call him and inquire if the problem could be the tranny. Thanks!

 

[MoeJr]

85 was the first year the 700R4 in a Vette was calibrated to shift out of 3rd at WOT. My 84 would not shift out of 3rd unless I lifted off the floor a little I bought the 3-4 upshift sleeve that would allow that and now my car shifts out of 3rd at WOT. Did the car do this before the tranny was rebuilt? If not the the tranny shop may have gotten a standard 700R4 rebuild kit instead of the Corvette calibration. Even Irocs and Z28's didn't shift out of 3rd at WOT in the mid to late 80's. The problem you describe to us sounds like the tranny was rebuilt to standard spec instead of Vette spec.

 

[FX GS]

:cry :cry

 

[hott85]

:cry :cry

That's exactly how I feel....in the words of the first President George Bush this problem "will not stand." I haven't spent all my hard-earned money with modifications to lift off the freakin gas!!!!