: shift points???



Randy_W
03-28-04, 02:47 PM
Hi guys, I have a '96 SLS and whether I shift into 1st or leave it in drive, it shifts at about 6000rpm! If I shift to 1st it will shift to 2nd at 6000 rpm even if I don't move the lever, however it shifts much firmer this way. Is there any way to override this feature that won't cause some other problem?:hmm:

BeelzeBob
03-29-04, 02:42 PM
Hi guys, I have a '96 SLS and whether I shift into 1st or leave it in drive, it shifts at about 6000rpm! If I shift to 1st it will shift to 2nd at 6000 rpm even if I don't move the lever, however it shifts much firmer this way. Is there any way to override this feature that won't cause some other problem?:hmm:

What do you want to over-ride?? Do you want to shift at a higher RPM???

Not really a good idea as the engine is shifting at the correct point (6000) for performance and power and shifting it any higher won't really make the car faster. Also, the valve springs in the SLS are only good for 6500 until a no follow condition develops and you really really don't want to run the engine into no follow. The over head cam, direct acting tappets will not last long in a no follow condition. They will crack the face of the tappet if subjected to a no follow condition for even a short period of time and the cracked lifter face will rapidly develop into a shattered tappet.

Aurora40
03-29-04, 03:00 PM
What do you want to over-ride?? Do you want to shift at a higher RPM???

Not really a good idea as the engine is shifting at the correct point (6000) for performance and power and shifting it any higher won't really make the car faster. Also, the valve springs in the SLS are only good for 6500 until a no follow condition develops and you really really don't want to run the engine into no follow. The over head cam, direct acting tappets will not last long in a no follow condition. They will crack the face of the tappet if subjected to a no follow condition for even a short period of time and the cracked lifter face will rapidly develop into a shattered tappet.Um, once my car is warmed up nicely, it will routinely shift at 6400 rpm when floored from a stop (if it downshifts, i.e. rolling already when I punch it, it doesn't seem to hold it as long and shifts anywhere from 5800 to 6200). In fact, the other day with it in 2nd and TC off, weather about mid 40's F, I swear the needle just about touched the red mark at 6500.

I noticed that after getting the Corsa, the highest shifts went up by about 200 rpms. Where the car used to shift at a max of 6200, it started running to 6400 instead. I've only seen the 6500 thing that once, but man was the car feeling extra strong that day. (Though, maybe it was 6400 as usual and I just didn't get the best look at it, but I sure thought it ran to 6500 that time.)

Is this something I should be concerned about? I have not changed anything on the car except using a K&N air filter and a Corsa exhaust. :hmm: Also, the fuel shutoff is listed as being 6500 rpm, so wouldn't damage to the engine come at some point higher than that? Thanks! :)

BeelzeBob
03-29-04, 03:24 PM
Shift points for the 4T80E are different for different model years......the original post/answer referenced a 96 SLS which would have the LD8 engine....the shift points were designed to be at 6000. The STS engine in 96, for example, would shift at 6500 RPM....it was programmed to shift higher due to the more radical inlet cams and it had stronger valve springs to enable the increased RPM upshifts.


The valve springs between the LD8 and the L37 engine were commonized in mid 97 I think (to the stiffer L37 springs) and later model year Northstars shifted slightly higher.

Most things like this changed slightly with 2000 model and later as the Northstar/Aurora engine was significantly redesigned with the roller follower valve train in specific. The roller valve train used the same springs for all applications and the LD8 shifts were bumped up slightly and the L37 and Aurora engines from 2000 on shifted at 6500.

Aurora40
03-29-04, 03:58 PM
Thanks for taking the time to explain it! :)

Is it normal for the shift point to rise as the car breaks-in or something? I'm absolutely positive that my car used to shift at 6200 rpm even when fully warmed, shifter in 2nd, and TC off. But now it definitely runs higher (it seemed to coincide with the Corsa install, but I don't floor it like that every day or anything). Thanks again, you (and this board) are a fountain of info! :)

Olds3.5
03-29-04, 05:07 PM
Randy_W, are you saying that you don't want the car to override your choice of D1 and go into second or you don't want any possible problem from the hard shifts?



I don't have a N* engine but I have the 3.5L shortstar and I read that the maximum rpm that the computer will allow for my engine is 6500, 6200, 6000 and 6000, respectively, from first to fourth. My engine will routinely shift out at 6500 in first but not always. It's just the electronic rpm ceiling. Other conditions, such as the ambient conditions or external mods, also come into play.

Personally, I don't like hard shifts. My car has the 4T65E tranny (with a starter in the correct location) and I read about people with Grand Prixes (?) who buy the aftermarket mods to get a race hard shift. They say that the clutch plates will last longer but they end up damaging the tranny hard parts.

I am suprised that my engine goes to 6500 in first virtually all the time and the N*s don't. After all, the 3.5L is rated at 215 hp at a lower rpm (5600) and the stroke of the 3.5L is longer than the other N* engines, which translates into greater piston speed. Many, if not most of the upgrades that appeared in the 2000 4.6L and the 2001 4.0L (no 2000 Aurora) first appeared in the 1999 3.5L. And I don't understand why the N* blocks sometimes develop oil leaks when the 3.5L doesn't.

Aurora40
03-29-04, 05:24 PM
Hey Olds3.5, according to the specs I saw, the 3.5L Twin Cam has a fuel cutoff at 6700 rpm, as opposed to the 6500 rpm of the 4.0L and 275hp 4.6. Looks like your cutoff is more like the 300hp 4.6L which is also at 6700 rpm.

It sounds like Bbob is saying the earlier Premium V8 had a lower shift point (and presumably fuel cutoff) than this, which would explain why Randy's 4.6 doesn't shift as high.

Aurora40
03-29-04, 05:33 PM
Hmm, maybe the fuel cutoff and the shift point are not exactly similar for all of the engines. While perusing the GM Powertrain part of media.gm.com, under the "what's new, changed L37/LD8" document, this is in the overview:


OVERVIEW
When it was launched in the 1993 Cadillac Allante, the 90-degree Northstar was the first all-American dual-overhead cam aluminum V-8 engine. Sixteen patents protected its advanced technologies; seven more have been granted since. In 1994, the original Northstar (RPO L37) was joined by a second version (LD8). Different camshafts and cam lobe profiles provided different power curves and very different driving characteristics. The L37 is more responsive, higher revving, with more peak horsepower and a higher redline (6500 rpm vs. 6000 rpm). The LD8 puts more emphasis on quick launch and part-throttle response, with greater peak torque. The Northstar V-8 was the basis for a technological renaissance at Cadillac, lending its name to an entire automotive system that includes the most advanced traction-enhancement, suspension and anti-skid electronics in the world. Since the engine’s introduction, GM Powertrain has steadily improved this premium V-8 and continued to push its technological envelope.


Perhaps the LD8 drops power enough to make further revving useless? Or perhaps this part of the document is really really old and didn't get updated when the engine was revised?

If that's right, it seems:
L37 shift: 6500 cutoff: 6700
LD8 shift: 6000 cutoff: 6500
L47 shift: 6400? cutoff: 6500
LX5 shift: 6500 cutoff: 6700

I dunno...

Randy_W
03-29-04, 09:30 PM
I don't really want to buzz the engine, I just like the idea of being able to shift if I want to without being told when! When I put the lever in 1st myself I get a much firmer shift, I like that, I just don't like it shifting for me when I don't ask it to! I don't have this with my '67 Impala with the '96 LT-1/4L60E and I like being able to control it manually, thats all.

BeelzeBob
03-29-04, 10:19 PM
There are many many factors governing the shift points. You guys are trying to read too much into them...LOL

There is a tremendous amount of analysis and testing that goes into optimizing the shift points for performance.

There can by physical limitations, like the valve springs and the valve no-follow limiting speeds, the speed of the accessories, the spin energy capability of the trans, etc....

The trans has to overcome two things at the shift, the torque of the engine and the spin energy of inertia of the trans rotating parts and the engine rotating parts. The torque of the engine can be instantaneously modulated via torque management to help the shift but the spin energy is there and the trans just has to deal with it. So the spin energy can govern the shift point.

The tach readout can be "slow" and "variable" due to the update rate of the info to the tach over the serial data link from the PCM... Depending on how fast the engine is accelerating this error can be 200 or 300 RPM and can be variable depending on how the update rate coincides with the shift point.

Often the speed of the accessories can govern shifts... if the generator is overdriven so as to keep the sytem alive at idle it will then govern how fast the generator can turn at the shift point ... which will often limit the shift point.

With the LD8 and the L37 and the 3.5 V6 you are comparing different engines in different cars with different trans and final drive ratios and vehicle masses....apples to oranges is the comparison.....

It is true that the roller valve train first went into production on the 3.5 V6 but the system was designed/developed/validated on the Northstar engine several years before the V6... The implementation on the Northstar was delayed to coincide with the 2000 model year to go along with all the other changes to the engine at that time. The roller follower that is used in both of those engine families is actaully a common part for the LD8, L37 and the 3.5 V6...as well as the Vortec inline 6, 5 and 4 cylinder engines and the EcoTec 4 cylinder. The first development of that part took place on the Northstar and the Northstar was used as the genie pig for all of GM Powertrain applications.

The LD8 was orginally released with the softer valve springs so as to improve the fuel economy (less friction). That , and the lower torque peak, is why the LD8 shifts sooner..about 5800-6000 RPM. The L37 can rev higher and make more power at higher speeds due to the revised cam timing...so it got stiffer valve springs to allow the higher RPM operation.... The roller system was developed with "stiffer" springs from the beginning as there is little or no penalty to stiff springs with the rolling element followers so the 3.5 and both the LD8 and L37 can shift at higher speeds from 2000 on....

One obvious tweak to this scenario is the Pontiac Bonneville GXP with the NOrthstar. Even though it is "just" the LD8 it has (for the first time in production ) the 3.71 final drive and a very low restriction exhaust system. The lower final drive lets the engine rev a little easier and the exhaust helps the engine to extend to pull off the higher, 6500, shift points of the GXP.

So, there are no hard and fast rules about the shift points and shift RPM. It depends on the car, the mass, the trans, the spin energy, the final drive, the torque curve, etc...

With the LD8 for example it is quicker in acceleration to shift a 6000 and let the engine work in the next gear due to the greater low end torque characteristics of the LD8 compared to the L37....

Randy, sorry you do not like being forced to shift. You'll have to learn to live with it. It isn't a 67 Impala... The engine and trans and driveline have to be protected so the forced upshifts are there. It is either that or hit the rev limiter which would be lowered. Since it is not any faster to upshift at a higher engine speed just put the selector in 2 , get the firmer shifts and live with it.... As previously mentioned, the direct acting tappets are very sensitive to any engine overspeed conditions and valve train no follow conditions so it has to be protected.

Aurora40
03-29-04, 10:28 PM
One obvious tweak to this scenario is the Pontiac Bonneville GXP with the NOrthstar. Even though it is "just" the LD8 it has (for the first time in production ) the 3.71 final drive and a very low restriction exhaust system. The lower final drive lets the engine rev a little easier and the exhaust helps the engine to extend to pull off the higher, 6500, shift points of the GXP.
So, when is the GM Performance Parts kit coming out to put this in the Aurora? :worship:

Thanks a lot for the thorough explanation. I was a bit surprised to know the tach could be off by as much as 200-300 rpm, though!

BeelzeBob
03-29-04, 10:31 PM
So, when is the GM Performance Parts kit coming out to put this in the Aurora? :worship:

Thanks a lot for the thorough explanation. I was a bit surprised to know the tach could be off by as much as 200-300 rpm, though!


Well the tach won't be off on a steady state sitution...it is just in the transient where the engine is changing speed rapidly where the update rate of the electronic system can be a little behind.

Randy_W
03-29-04, 10:42 PM
"Randy, sorry you do not like being forced to shift. You'll have to learn to live with it. It isn't a 67 Impala... "


My Impala Has a '96 Corvette drivetrain with full OBD II function. It, too, would be damaged by over reving the engine, but I still have the option to shift when I want to. By the way this OHV motor shifts at 5800 in drive, and I shift at about 6200 manually, sound familier? As for learning to live with it, don't count on it! Someone somewhere knows how to program these things!:lildevil:

dloch
03-29-04, 10:51 PM
As for learning to live with it, don't count on it! Someone somewhere knows how to program these things!:lildevil:
By looking at the valve train on one of these motors if you get into any type of valve float you may be sweeping up some expensive parts.

Randy_W
03-29-04, 10:57 PM
You guys have the wrong idea! I don't want to kill my engine or buzz it's brains out, I just want control when I pull the shifter back, that's all!;)

dloch
03-29-04, 11:01 PM
You guys have the wrong idea! I don't want to kill my engine or buzz it's brains out, I just want control when I pull the shifter back, that's all!;)
Got ya...... been there... done that... I've killed a few.:bighead:

BeelzeBob
03-30-04, 12:03 PM
Uhhh.... not to belabor the point , but, if you didn't want to shift it at a higher speed then why would you want to be able to control it yourself or override the factory shift points.....to shift it SOONER.....right.....LOL

The pushrod engines are MUCH more forgiving of an overrev situation. You can routinely run a pushrod, cam-in-block engine into a mild no-follow condition without damaging parts. The large diameter, direct acting tappets in the overhead cam setup are not forgiving AT ALL to an overrev situation. The tappet is basically hollow inside to house the hydraulic element...so that wide, flat face is like the face of a drum....not much structure there. It works fine as long as the cam/spring controls the motion and there is no no-follow involved. As soon as the RPM increases to the point that the cam/spring is not in control and the tappet is launched off the lobe and comes crashing back down the forces involved at the tappet face skyrocket.....and the face cracks since there is no support behind it....and the tappet fails and it takes out the engine as dropping the valve into the cylinder is the next step. You really do not want to go there. That is why there are some fairly stringent RPM limits put on th engine. It is allowed to rev as high as need be to make the power for the application but no more.

Randy_W
03-30-04, 03:25 PM
I guess it's just a control thing, I own it so dammit I want to shift it!!! :lildevil:

BeelzeBob
03-30-04, 04:03 PM
Well....just move the lever when the tach is near 6000 and pretend you are shifting it.....easiest way out..... LOL

bajarails
09-12-09, 11:31 AM
Arrgh!!! I can't even keep my 98 sts in first gear! Select 1st, and I get 1st and 2d. Does anyone know how to shift the darn thing as if they owned it? Or does GM follow us around looking over our shoulder?

Ranger
09-12-09, 12:29 PM
No way around it. It will not allow you to over rev it. It will shift on it's own when it reaches redline.

Submariner409
09-12-09, 03:21 PM
.............and it will NOT downshift until the lower gear engine speed and deceleration loads are within safe limits for the engine and transmission.

Precisely why you do a WOT in 2: The transmission starts in 1, the engine accelerates to redline and shifts to 2. Miss the 2 redline foot-off-the-gas and it will shift to 3.

As far as engine redline and downshift loading, the car is smarter than we are.

Ranger
09-12-09, 04:59 PM
No offense intended, but they made it idiot proof.

97EldoCoupe
09-13-09, 08:49 PM
Olds40, I've done a 300HP VIN 9 4.6 swap into a '97 Aurora. It MOVED.

John (my shop helper) and I built up a 4.6 VIN 9 (L37) for his '97 Aurora. It's going in this week. Did you want to see some videos once it's done? His is the Autobahn car with the 3.71:1 final drive and the 140 MPH limiter.

The fuel trim will adjust itself to compensate for the displacement, and AJ would know the timing tables (I don't). All I can say is that the last one I did, ran perfect, had no problems at all, and it sure was fast.

Most Mustang 5.0's get blown away even with the stock 4.0.

97EldoCoupe
09-13-09, 08:52 PM
For anyone who has a 3.5 LX5 Shortstar, let me know if you ever need a stud kit for these engines, I have done a 3.5 and it worked perfect. I believe that particular engine was only available in 2001+ Auroras and 99+ Intrigues.