Ok. This has me thinking as well.
I need to revisit this.
Looking at my Dyno sheet my HP and torque peak at about 5600 rpm.
I shift at 5800.
I'm running a 383 SR with 12:1 compression.
Everything has been ported, polished, extrude honed, etc.
Am I shifting too late?
I always thought to shift just past the HP/TQ peak point.
Matt383

I thought so too! I do not understand why we would shift below peak HP. Plus the slight overrev put the shift point about at peak torque for the next gear. I am sooo confused! The time slip will tell the tale

 

My 91 shifts at about 5400 when left in 3rd. I have tried shifting it at lower rpms (manualy at around 4200 from 2nd to 3rd) and at WOT it doesnt matter if I shift it or not, still runs to 5400 before it shifts.

 

That is what I would have expected......and as I recall 5500 was where my 89 shifted at wot..

 

There was a magazine in the 80's that street race and strip tested all the new toys from Detroit. Some of the most informative, entertaining, and non-pc reading ever. Sadly they're no longer around. They had an 85 and their findings were that shifting the L98 at 4200 produced the best times. they said the Regal GN led most of the 1/4 but they could get by at the top of the track. One of the writers was Tony DeFeo(?) Really miss that magazine-the dry, ad driven drivel we get now just doesn't compare. They had a lot of good info on short shifting the L98 cars-try it!

 

Geofun, matt383...


WHen I ran the 406 SR combo I shifted right at 5100rpms. The motor was done making power there and would slow up if I shifted any higher. The limitation to the combo was the intake, but ETs did not hurt from it with the SR. I did switch to a single plane EFI setup, the one I am running now and the car did require a higher shift, about 5700rpms, but the ETs did not change much. They improved but nothing spectacular.

On the shifts, its a very well know and proven fact that there are several things to must take into account for and also things to do to help your ET. Let me try to share them with you.

(1), with a 3 speed you will always turn a better ET shifting 1-2 about 400rpms SOONer than 2-3rd. I gained nearly .1sec doing this with my 434 setup. It requires the use of two shift lights. One flashes at 6400 and the other at 6800rpms. It works pretty slick once you get used to it, because on the 2-3 shift you get a nice warning that the other is about to go off so you can really nail the exact shot each time.

(2) You have to figure out how much lag time there is before you pull the trigger and the actual shfit takes place. Every trans is going to be different and every person is going to be different. Right now I am about 250rpm off my lights, and you know how much practice I have at it. Average or everyday drive would be probably closer to 500-700rpms in a same setup that climbs the RPMS as mine does. So you have to figure out your "lag time".

(3) You need a shift light to even begin to try to accurately determine your shift points. You need something to gage off of, a playback tach is even better or a datalogger. Either way you can define what you want at the track pretty easily with a few passes. Usually can have it narrowed down within 5-8 runs. Usually just keep the 1-2nd shifts the same at first- then once I get them - I play with 1-2nd targets.

Yes you can use a dyno sheet to narrow this range down even more, but use real world results to find what the car really wants. Start a little low and work your way through where you think it should be at.

** this is probably the #1 thing most guys do wrong with their setups and that is over-revving them. Everyone in the back of their minds wants to spin their setup to the moon - but usually it just hurts ETs and exposes the valve-train and other components to un-needed wear and tear. ***

I loved my 406, man that baby got it done in a hurry and that type motor would last for MANY MANY YEARS.

 

I have noticed one thing with a miniram. I had to considerable over rev my motor on the 1-2 shift due to the massive gear change on a 700r4 3.06-1.62. The old combo was a stock bottom end 350 with a zz9 cam and it liked to be shifted at 6600-6800 rpm. No real time or mph diff. there. I believe the motor made peak hp at 5800-6000.

Had the motor had more torque down low or a higher stall converter I would have shifted at 6000-6400 but doing so always lost a tenth or 2 and usually about 1 mph. The rpms would drop too low to pull effectivly in second with a short shift.

Once I launched and forgot to screw my dash pad back on and it hit me in the neck causing me to short shift second at 5000 (on playback tach). That run was off 3 tenths and 3 mphs of what i ran the rest of the day.

 

People often forget that transmission ratios come into play when determining shift points. I assume your auto ratios are 3.06 in first, 1.63 in second, and 1.00 in third......then

On your 1-2 shift....6800*1.63/3.06=3622 rpm

on your 2-3 shift.....6400*1.00/1.63=3926 rpm

Looks like your dialed in right on your shift points!!!!

 

So u guys are saying to manually shift even with an auto?

 

Kids manually shift their automatic Honda Civic and think its like a manual. I used to do that at one point. When I was called out about it, I stopped.

When I manually shift my Vette, I still feel like a ricer. If only my shift points were optimum, I'd just leave it alone!!

 

The original poster said he has a stock L98.

Leave it in third/D, provided the TV cable is adjusted properly.
If you want a slower ET shift it manually.

 

Thank you Ski,
Hmmmmm. My new 406"/700R makes the 2-3 shift at 5100 automatically, so I guess I will just leave well enough alone! So far the 1-2 shift comes in such a hurry with all the commotion of tire spin, induction and exhaust roar( uh, perhaps I should say, "music" ) I have not had the presence of mind to look at the tach to see where it is at that moment. It is almost orgasmic

 

the shift point dosen't change my 87 shift strong into second gear even manualy or in 3rd and dont forget to put the a/c offffff and go with the temp around 180f if possible

 

First, I have "never" seen an automatic transmission that you can manually shift "before" the governor shift points, at WOT. If the vehicle has been dynoed, and you know the peak HP rpm, you would "always" shift at least (minimum) 5% (in rpm) over the peak HP. In my 39+ years of working with others on this (dynoing, drag racing, etc.), this is a first, but at my age "nothing" should surprise me, so I thought.