Not to change any subjects that have been mentioned, but why would GM install CAGGS? Well we all know for fuel economy reasons and to save us a few bucks with the gas guzzler tax. So when you are forced to shift from 1ST to 4TH, what RPM have you seen? I have to agree that the motor is designed to handle lower RPM with high loads on the internals. Now when I am in 6TH gear cruising down the Freeway I never really have any intension of heavy acceleration. Such a motor I believe is capable of handling it just fine. But of course the rest of the drive train comes into play too. Just $00.02 worth.
:cheers:

 

It depends on the situation but, I used to use 6th all the time at 50 mph if I knew I wouldn't need to accelerate. But, after installing my cam, 6th is useless unless I am at about 63 mph.

 

Was reading some of this to my Father-in-law, he couldn't stop laughing (he's visiting Florida this week). He said he never realized that us 'Vette owners took this stuff so seriously... after 30 years in GM though, he said that some of this stuff is the last thing we should be worried about. He has the motto of "drive it like you stole it" and said that most of us will probably be buying a NEW Corvette before any of this stuff would even matter. Regardless, he said you are right Duke.

 

When I'm on the highway cruising over 65.

 

I am a long time C5 owner and use the highest gear possible. The manual says to be over 900 rpm. Today I was coming home with the Z in 6th at 50 mph and the tach was reading just over a grand.

Been doing it for 7 years and have never seen a problem. Some people have too much time to think.

Bill

 

I use 6th when I am in light traffic, taking it easy, and traveling at highway speeds of 65+. You can't go by RPM, because if you wait to use 6th above 2000 RPM, you will be well in excess of 70MPH and speeding. Even 75, my "normal" cruising speed, is below 2000 RPM. Why waste gas if you are already above the speed limit? If you like the extra "whine" of higher RPM's, go for it, but I'm usually trying to hear my wife talk or listen to music! :D

 

At very low revs it doesn't take much throttle opening to cause manifold vacuum to go to zero, but once you're down below 1000 and try to accelerate there is very little response. Also, about this speed you get a lot of low frequency vibration and gear rattle in the drivetrain if you load the engine. At this point intuition tells you it's time to downshift.

Even my SWC with an AFB, Duntov cam, and 3.08:1 axle will put from 1000 in top gear. In normal cruising I drop it into fourth at about 30 MPH, which is 1200.

Duke

 

I use it whenever I'm at crusing speed, whether that be 40 or 100 :thumbs:

 

:iagree: All the time at around 50 or so.

 

on the freeway

 

Quote:
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So called "dual pattern cams" work on certain engines that have "unbalanced" exhaust/inlet port flow. Equal duration is usually called for if the exhaust/inlet flow ratio is about 0.75. If less (like a vintage SB) longer exhaust than inlet duration will usually broaden torque bandwidth; if greater, less exhaust than inlet duration will broaden torque bandwidth. The increased duration should be at the front end in the form of an early opening exhaust valve, and this is one reason why the '70 LT-1 cam works so well on a vintage SB. It has a very early phased exhaust event with about 16 more degrees duration than on the exhaust side. The modern smallblocks have better balanced flow. Likewise, for a very free flowing exhaust port (relative to the inlet port) the opening of the exhaust valve can be delayed, which effectively retards cam phasing.
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I think that's pretty much what I said. The intake/exhaust ratio you're talking about is affected by the exhaust system, intake system, and other factors...not just the ports in the head, so if your camshaft was selected with the exhaust system in mind, then removing it, without any tuning or cam change, will cause a drop in total performance even if it increases your top end slightly. You can have a head that has a perfect 73% flow differential, and if you stick a cat and a muffler off the exhaust, suddenly it's 60% or whatever...so then you pick a cam that works well with that..more exhaust duration for more exit time, and then if you remove the exhaust restriction then suddenly you're dumping all the exhaust out too quickly and performance suffers unless the cam is changed. The engine is a tuned system, not a port. I think that's where the "Engine needs backpressure" myth came from...it's not all that inacurate, it just should say "Some engines need backpressure", or 'Some engines are tuned for backpressure'. Or actually, "some engine configurations need backpressure to perform acceptable on the street." :)

Quote:
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Bearing designs have a limit on both ends of the rev scale. At the bottom end high engine load (WOT) causes high loads at the bearing, and the bearing is held away from the journal by hydrodynamic pressure, which increases with the square of speed. Thus, any engine designer runs as one of the worst case bearing loads the lugging limit and makes sure the bearing is of sufficient size that available hydrodynamic pressure will prevent bearing/journal contact. For many designs the lugging case defines bearing size rather than high speed loading.
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Very true, and lugging gets you close to that lower tolerance limit. In a perfect world with pure oil and proper temperature, the film is just as simulated during the design. But as the oil gets contaminated and the temp heats up and oils with different compositions are used, the film strength becomes less and the clearance area under the crank becomes less too (between the joural and bearing surface.) Being closer to the limit makes for a greater chance for contact if you get a detontation occurance. Knock can and does happen today, because knock sensors report detonation 'after the fact', the detontation is already happening so the PCM can correct whatever to get it back under control.

Besides, lugging does more than just apply pressure to the bearings. An engine operated in lugging conditions has higher cylinder pressure than an engine operating in non-lugging conditions, and this will push the piston against the cylinder bore harder (as the piston rocks in the bore) and also presses the top compression rings against the cylinder walls harder, which causes accelerated wear as well.


:cheers:

-Dave C. '04 Z06





[Modified by Dave C. '04 Z06, 12:29 PM 3/25/2004]

 

I was told the reason for keeping the RPM's up (except for long trips) was to prevent carbon build-up. Seems logical to me but I don't really know. I do know I don't ping - at all -ever! Also, I am not saying I scream around at 80 in 5th for prolonged periods of time. :thumbs:

 

Is that a Split Window Coupe? Very Nice.

Do you also have a Z06?

 

For steady speed driving, I use the highest gear I can get. If it shows any sign of lugging, I downshift. No point in wearing the engine or wasting gas.

 

I use six when the car is redlined at 5th. Im not sure how fast im going because im to scared to even look down at the hud :yesnod:

 

I know, of course, that this is a jest, but if you shift from 5th to 6th at redline, you'll slow down. You'll drop out of the power band enough that you can't overcome the aerodynamic load. Top speed is reached in 5th, not 6th.

 

After reading how many people use 6th gear at such low rpm's, its know wonder the rings had problems .

 

Only when I run Out of Fifth Or highway Driving :party: :party:

 

i shift to 6th only at 70 or past 70, can't imagine driving in 6th at 55 :leaving:

 

Not so. Part of the ring problem (oil burner 01's) was defined by GM as being caused by people driving under light load conditions at relatively high rpm's. There are a zillion threads here as well as copies of TSB's posted on this forum that state this.

400 lbs. of torque will pull a high gear rather handily.

The only time I use sixth gear is when I drive my car. :D