Governor spring changes...

[KANE]

Red spring- blue spring...
Old spring- new spring.
Dr Seuss... or setting a 700R4 governor?




With the 2.87, I had the GM purple and a B&M orange spring and that gave me a 1-2 shift at 5,450rpm. When I upgraded to the 3.73, the 1-2 shift was probably over 5,800rpm - way too high and I pulled my foot off at 5,800. I've left the GM purple and have been swapping out the other spring. Yellow was high as well with a 5,800 1-2. I skipped green to see what that would be and went to blue.

Fully warm, blue was 4900rpm.

Going to test the green once the transmission is warm. Yeah... green B&M spring & a purple GM spring on GM weights.

I have a scale, so I might have to remove some material from the inner weights to walk it in if I can't get what I want out of the springs.

 

[toobroketoretire]

I have about 20 springs to pick from and right now I'm using 19 ounces of springs with the stock weights cut down. Gives me a 5500 rpm 1-2 upshift point and a 40 mph 3-4 no-load upshift. I use a dieter's scale and my drill press to measure the spring's forces (I'll take a picture of my setup tomorrow morning).

 

[Peer81]

Interesting topic!

Greetings Peter

 

[SVO]

I've never messed with automatic transmissions except to change the fluid & filter on a regular basis. I thought that the shift point was whatever the governor was set at and wasn't dependent on the rear axle ratio. It was going to shift at whatever RPM it was set at. So I'm curious about what you are up to here and why, if I may ask.

Thanks,

Bob

 

[KANE]

I've never messed with automatic transmissions except to change the fluid & filter on a regular basis. I thought that the shift point was whatever the governor was set at and wasn't dependent on the rear axle ratio. It was going to shift at whatever RPM it was set at. So I'm curious about what you are up to here and why, if I may ask.

SVO- the why is simple: I am adjusting the WOT shift point to occur right after I hit max HP (325hp)... which is at 5,300rpm with the engine I have.
1982 Corvette Crossfire Injection with .465"IN / .488"EX Cam - YouTube


Why mess with springs in the first place? I didn't want to be stuck with the OE shift point. I built this motor two years ago and with the original springs on the governor, the 1-2 shift at WOT at around 5,000. That what wasn't what I wanted. Great for a 200hp OEM crossfire- but not mine. I was losing 400rpm where I was making power.

So that led to the first spring change. With that change (and lots of trial and error for springs and weights with B & M governor kits) I was able to settle on a combo that gave me the 5400rpm 1-2 shift at WOT that I wanted.

Recently... I put a new rear end in. And now on WOT, the 1-2 was now past 5,800rpm and I was bouncing off the rev limiter (which isn't good). I verified this with my laptop connected to the car's EBL ECM and a real tame datalog on a fully warm transmission. Springs were now just a little too loose for the combo of engine/rear end.

That's why I am adjusting the governor- to get the 1-2 to happen just after the HP curve starts to taper off at 5,300rpm again.


I have attached a few screen shots for reference. One shows the 5,400rpm 1-2 with the purple spring (January numbers) with the 2.87. The other two are post 3.73 and you can see one is at 5,625rpm (purple & yellow springs- and you can see the lean spike when I hit the rev limiter on the shift) and the other is at 5,375 (purple and green springs). I have since upped the rev limiter to 5,800 so that while I am adjusting the 1-2 that I don't go to lean.

I'm really close to where I want the shift point.

 

[Tom Bryant]

Cool stuff.

 

[KANE]

Fully warm transmission... 5,375rpm 1-2 shift and 4,925rpm 2-3 shift. It was 82 degrees outside with 30" baro pressure.

When the transmission is still cool, it will run up to about 5,600rpm for the 1-2. I have noticed there is a 200-300rpm difference between "warm" and "cool" for the transmission and that's just the car's nature. I can totally see why the 4L60-E and later transmissions brought consistency to the shift behavior.

 

[SVO]

@ Kane - Thank you for the explanation. I'm picking up what you laying down now

Bob