MikeyZ28SS

iTrader: (2)

I'd like to know more about what are the best shift points for my 98 SS...
1) I understand its better to put it in 4th (OD) instead of 3rd. Yes, I plan on some 1/4 mile use end of next week (Nov.3rd).
2) I do have 3.42's with my 4-spd Auto, and would like to set my shift points for max 1/4 mile performance; stock drivetrain w/free mods (See Signature). Looked and still haven't found the best RPM for 1st to 2nd, and 2nd to 3rd shift points for drag racing. And once I've got them set I'll adjust Rev Limiter from stock 6,200 - currently have it at 6250, just in case.

Thanks!
Mike

mrvedit

I would expect the best times with as high a shift RPM as possible. Even though the stock engine is probably losing torque after 5500 RPM, you are still getting more torque multiplication by the lower transmission gear.
However keep in mind that the trans, especially a stock one with stock tune, takes time to make its shifts and during this time the engine is revving. If you set the shift point at e.g. 6200, you would definitely hit the rev limiter. You might therefore need to set the shift points at 5800 so that you don't hit the rev limited during the shift.

In my (limited) experience, the '98 PCM starts the shift at the exact RPM you tune it. Later PCMs seem to start the shift a few hundred RPM earlier in anticipation of the shifting delay.
IIRC with my '98 PCM I would set the shift RPM at 6800 with a rev limit of 7000; with my performance built and super fast shifting trans this worked perfectly. With my '02 (411) PCM I set the shift RPM at 7200 and the shift completes by 7000 RPM.

MikeyZ28SS

iTrader: (2)

Agree, more RPM, keeps the TQ multiplication higher than upshifting. While keeping under the Rev Limiter...
Stock 98 LS1 Peaks: HP @ 5500 RPM & TQ @ 4500 RPM.
Stock Shift points; 1-2 @ 6000, 2-3 @ 6000, 3-4 @ 5900
And read that Best Shift points are 800 to 1000 RPM above Peak HP with shift to 2nd & 3rd being 200 RPM's Higher than the 1-2 shift. ( 800-1000 seems excessive for a stock Engine, IMO) *Remember the Max ROM of a stock LS1 (6200 - 6300 RPM Range...?)
I think these would be the Drag Race Optimized Shift Points; 1-2 @ 5950, 2-3 @ 6150, 3-4 @ 5900 (Rev Limiter set at 6250 - leaves about 100 RPM Cushion for the 2-3 shift to occur before the rev limiter kicks in. *Already well through the Traps in 3rd, so the 3-4 doesn't come into play.

Thoughts? Agree... Disagree... Personal experience with a 98-02 F-Body w/4A and 3.42's and stock 275/40-17's (25.66 dia)- Please share your thoughts.
Thanks!
Mike

RPM WS6

iTrader: (3)

Just to add some additional data to this, the factory shift points are 6000rpm for 1-2 and 2-3, as posted above by MikeyZ28SS, for all years of A4 LS1 F-body - including '98s. And all of them had a factory rev limit of 6200, so a ~200rpm window should be plenty with a stock trans that's still in good working order. Having said that, I've usually closed that widow to as tight as 100rpm even with a stock trans and not had any rev limiter contact, but that's as tight as I would go. My '98 still has stock internals so I've left the rev limiter at 6200, but have the shifts set to 6100 and the actual shift occurs anywhere between 6000 and 6150rpm (though usually between 6050-6120 IIRC), via my scanner, with a completely stock/original 4L60E. If there is excessive wheel spin at higher rpms, such as a downshift from a roll, then the shift point usually occurs earlier (sometimes as much as 200rpm earlier.)

I had a similar experience with my '00 car when it was stock; shifts always seemed to occur within about a ~100rpm range of the set point, also slightly favoring earlier vs. later just like the '98 PCM. Once I moved to a built trans, it would shift even earlier (faster) and require a higher set point.

I did not spend enough time logging shift activity in my '02 car to give any solid data regarding observations associated with it's more advanced PCM and shift commands/execution.

gesto

Here is an interesting read: http://www.ls1gto.com/forums/showthread.php?t=334833

This might be better: http://glennmessersmith.com/shiftpt.html#data

mrvedit

The 1st thread is EXCELLENT in explaining the theory. You actually need Calculus (integrals of the area under a curve) to properly determine the best shift for an arbitrary car.
The 2nd link is a nice link to calculate all this for you.

With something like an 8 speed close-ratio transmission, it might be best to shift before redline, but with the wide-ratio 4L60E, I'm confident it is best to shift very close to redline.

MikeyZ28SS

iTrader: (2)

Yeah' I stumbled across that 1st (GTO Forum) thread during my initial search about a week ago. Very cool, but not realistic with a stock engine/valvetrain.
So if a stock LS1 is good to 6,200 (Factory Rev Limiter Setting), then assuming (read it) the '98 A4 Shifts pretty much 50-120 RPM's above the Shift Point set > 1>2 should be at 6,075 to 6,100, Same would apply for the 2>3 and 3>4th shift as well = keep that Torque Multiplication up, so each shift drops you right back into the Peak TQ to Peak HP Curve.
Still need to read that second link: Thanks!

As long as I get another shot at the Drag Strip before Thanksgiving, I'll let you know the results of Stock Shift points, versus roughly 6,100 RPM shifts.

And I believe the referenced caclulator is this attachment (RPM/Shift Point Calc): BC_Trans.zip (116.7 KB, 4 views)

RPM WS6

iTrader: (3)

I agree.

Not necessarily. As mentioned above, my observations with my '98 have been that shifts actually occur as much as 100rpm below the set rpm, to as much as 50rpm above, with most shifts slightly favoring the early side - and that's with marginal or no wheel spin. Keep in mind, shifts in the stock PCM are set by both MPH as well as rpm, with priority usually given to MPH, so any traction issues as you near the shift point can lead to even earlier shifts.

Overall, I would not necessarily count on the shift being ~100rpm late unless your trans is in less than optimal condition. The factory setting is 6000rpm for 1-2 & 2-3, but in my logs I rarely (if ever) saw shifts that were anything significantly above 6000rpm with the stock tuning (usually in the ~5950 range).

DANOZ28

iTrader: (1)

maybe im completely missing the OP's point but isnt the real ? where to set the shifts in relation to your cams peak hp?

mrvedit

Yes, the shift points in theory depend upon the cam's torque curve. If the torque at redline had dropped greatly from the max, then a shift well before redline might be best, but would again depend upon how close the gear ratios are.
As another "detail", the after-shift RPM with an automatic trans and a high stall converter is often higher than would be calculated from just the gear ratios. (Due to something called shift extension).

Going back to the OP, according to his signature he has a stock engine with bolt-ons and we are assuming that.

DANOZ28

iTrader: (1)

when mine was stock i typically shifted between 5800 upto 5900 rpm , i had trouble even after tune shifting higher auto. after adding ls6 cam & stall now i shift at 6-6100 rpm. my ls6 cam peak hp is at 5750 not saying i couldn't keep revving higher. stock valve springs are the weak point so you should upgrade those asap if stock ls1. mine stockers fluttered / sputtered / floated at 5700 rpm.

RPM WS6

iTrader: (3)

A bit off topic, but how many miles were on the springs at that point? The stock valve springs are certainly not a tough piece, but they shouldn't have issues with the stock cam at 5700rpm (500rpm below the stock rev limiter) unless significantly worn (which could be a product of mileage, usage conditions, or some combo of the two.)

gesto

IMHO, you need to get an accurate dyno sheet for your car, then calculate your ideal shift points. Perhaps you can get there with dyno sheets from other stock LS1's off this forum or the internet but they won't be exact to your car.

As for the stock LS1 rpm limit, are you sure it can't be wound higher than 6,200? I'm guessing the factory limiter is on the conservative side. If you up your limiter to 6,500 or a little more, you would be able to up your shift points in accordance with the theory in those links. I understand if you want to be conservative and stick to the factory limiter.

As for how long it takes for the computer to command shifts, you should be able to datalog and change as needed.

In for results!

RPM WS6

iTrader: (3)

As touched on above, it's the stock valve springs that become an issue if going beyond the stock rev limit (6200). The rest of the engine can (and does) certainly handle more even with stock internals, though the rod bolts become the next major concern for a '98 specifically - but I wouldn't worry about that until going over 64-6500rpm or so. For later LS1s with spring upgrades, I wouldn't worry about going to 6600 or even 67-6800 if it made sense for the setup.

gesto

Good thoughts.

MikeyZ28SS

iTrader: (2)

I think I'll try a couple tunes for the A4; And make a least one run on each, see which works best (accounting for any DA or other track differences);
1st; 1>2 @ 5900, then 2>3 @ 6100 (an earlier thread which mentioned being 200 rpm lower on the 1>2 shift - figure its worth a try)
2nd; 1>2 @ 6100, then 2>3 @ 6100 (Use logic as gathered above and in reference posts/data/calculators.)
3rd; 1>2 @ 6200, then 2>3 @ 6100 (will have to bump Rev Limiter to 6300 to be safe/ still under valve float, rod bolts or other major concerns.)

Now, If it stops raining on Sat/Sundays, and they add a Test & Tune to one of the 4 or so remaining events... I can put this to the test!

MikeyZ28SS

iTrader: (2)

AGREE!
I'll do a bunch of searching and pull together a few Stock LS1 Dyno Sheets, see where Peak TQ & HP are. I believe mid points of each of those curves is 4,500-4,800rpm TQ, and 5,500-5,800rpm HP. So around 6100 to 6200 should work pretty well, at least better than the stock shift points. Would be great to see pulls through the gears of an A4 with 3.42 rear gears and really nail down those shift points!

Found a couple more dyno sheets, one is for a 02 Camaro
Hypertech Dyno - Yeah' numbers don't look quite right... Seems low.

DANOZ28

iTrader: (1)

milage was only 48k when i bought it. i've heard atleast 2 other stock ls1's on the dyno with the same troubles. ps never happened with my ls6 springs.

MikeyZ28SS

iTrader: (2)

Dang! I'm glad my 98 SS doesn't have that problem, mine is still pulling at 6000 (tach) when it shifts itself into 2nd...

RPM WS6

iTrader: (3)

Perhaps it's more common to happen during a dyno where load isn't quite the same as WOT on a street/track. Can't say that any of mine have ever presented this issue up to the stock rev limiter either.