Changed gears poor track results

[1980RS]

I had to change out my 4.10's as I broke some parts with the car last outing. Now most of this year and years past with the 8" TCI converter the car hit the stripe at like 61-6200 so I thought the 4.88's would be like 6800, nope the car now goes through at 7400 all else the same, but I changed exhaust form the rear axle system to my Walker Bullets which I have always used like forever. I was mighty surprised by this result. I lost MPH as a result of this even spinning the engine a lot tighter. I did have some problems earlier in the day but it turned out to be a bad set of spark plugs brand new same as the old ones. Put them back in and the 406 would spin to the moon. Is the stator going bad in the converter?

[steve cowan]

Does it feel like converter slip?
Did you keep shift points the same?
Maybe MPH down cause it's out of breath,was there incremental changes on entire pass going to lower gear ?
It probably at 6200 rpm now at 800ft

[Monza355]

Did you take notice of the shift drop between gears during these runs ?

[SupStk]

Wondering if your 406 is out of breath? Although it's spinning 7400, it's maybe not making any power there?

If the shift points are the same check out the increamental times, if slower than before could be a converter or some other issue.

[F-BIRD'88]

The simple math shows the rpm in the traps whill change from 6200 rpm (4.10). to now 7400 rpm (4.88).
Whats to problem? Hydraulic lifters....

[PRH]

The difference between a 4.10 and a 4.88 is 19%.

6200 x 1.19 = 7378

[1980RS]

Wondering if your 406 is out of breath? Although it's spinning 7400, it's maybe not making any power there?

If the shift points are the same check out the increamental times, if slower than before could be a converter or some other issue.

I think it is the converter as the shift recovery is pretty poor, less than 600 RPM on some runs. Will need to look in that for sure. Just watched the in car vids and after figuring out the duck shooting contest I was on the last two runs were wheels up and it was pulling very well but I am puzzled by this not making as much MPH or ET. Maybe the air was that bad, I didn't have time to check yesterday.

[F-BIRD'88]

Whats it doing in the 1/8th and 1000 ft from time slips?

[F-BIRD'88]

With the gear change the 8" torque converter should show increased efficiency "lockup". Unless it is broken (stator).

Could be valvetrain. Probabily still an ignition issue.

First places to look.

[rfoll]

I have a similar experience, I didn't see the improvement I expected. I shift/go through the lights at about 6300. I made a 10 percent gear change and gained about a half tenth et. I don't remember mph. The car launched much cleaner, but it spent the last 1/8 in high gear winding to 6900 through the lights. My suspicion is that although winding easily to the higher rpm, there wasn't enough power above 6300 to take advantage of the lower gear. The restriction could be cam, carb, header, size or all of them. Big inch motors consume a lot of air.

[1980RS]

I have a similar experience, I didn't see the improvement I expected. I shift/go through the lights at about 6300. I made a 10 percent gear change and gained about a half tenth et. I don't remember mph. The car launched much cleaner, but it spent the last 1/8 in high gear winding to 6900 through the lights. My suspicion is that although winding easily to the higher rpm, there wasn't enough power above 6300 to take advantage of the lower gear. The restriction could be cam, carb, header, size or all of them. Big inch motors consume a lot of air.

That was my thinking with putting on my Super Victor II intake but I didn't have enough time to change it out to test along with one of my other Dominators. Guess I will have to wait until next year got a ton of other stuff to do before winter.

[6.50camaro]

1980RS , you stated in your last post on another thread that you thought the rear diff. went bad . crossed the line at 7100 rpm not your usual 6200-6300 or so . What did the diff. look like when you changed gears ? Maybe the convertors give up the ghost . Only way to tell is try a known good convertor or have that one checked .
I know when I went from 4.56's to 5.13's my 1/8 mile rpm only changed a couple hundred rpms but the calculated slippage at the line went from 20% down to between 10-11% going to try 5.38"s next years to get it under 10% hopefully closer to 7% or under . Coan 8" 5600 -5700 stall with my 422

[steve cowan]

I have a similar experience, I didn't see the improvement I expected. I shift/go through the lights at about 6300. I made a 10 percent gear change and gained about a half tenth et. I don't remember mph. The car launched much cleaner, but it spent the last 1/8 in high gear winding to 6900 through the lights. My suspicion is that although winding easily to the higher rpm, there wasn't enough power above 6300 to take advantage of the lower gear. The restriction could be cam, carb, header, size or all of them. Big inch motors consume a lot of air.

That was my thinking with putting on my Super Victor II intake but I didn't have enough time to change it out to test along with one of my other Dominators. Guess I will have to wait until next year got a ton of other stuff to do before winter.

Maybe stator gone maybe not,
It's a bugger when plans don't come together properly,sounds like a few issue's on the day.
I apologise as I can't remember what heads/ induction you have on 406 at the moment as we have been talking about vortecs, SP2 etc lately.
This is my opinion on what I would do next-
Do another 4.1 rear gear and retest at the track first and see if you are back where you were prior to lower rear gear.
If it repeats previous performance I would do some calculations on Mach index and induction tract sizing as it's possible the engine won't respond to more rpm due to head/ intake / cam size.
Just a thought

[1980RS]

I have a similar experience, I didn't see the improvement I expected. I shift/go through the lights at about 6300. I made a 10 percent gear change and gained about a half tenth et. I don't remember mph. The car launched much cleaner, but it spent the last 1/8 in high gear winding to 6900 through the lights. My suspicion is that although winding easily to the higher rpm, there wasn't enough power above 6300 to take advantage of the lower gear. The restriction could be cam, carb, header, size or all of them. Big inch motors consume a lot of air.

That was my thinking with putting on my Super Victor II intake but I didn't have enough time to change it out to test along with one of my other Dominators. Guess I will have to wait until next year got a ton of other stuff to do before winter.

Maybe stator gone maybe not,
It's a bugger when plans don't come together properly,sounds like a few issue's on the day.
I apologise as I can't remember what heads/ induction you have on 406 at the moment as we have been talking about vortecs, SP2 etc lately.
This is my opinion on what I would do next-
Do another 4.1 rear gear and retest at the track first and see if you are back where you were prior to lower rear gear.
If it repeats previous performance I would do some calculations on Mach index and induction tract sizing as it's possible the engine won't respond to more rpm due to head/ intake / cam size.
Just a thought

The 406 has Dart ported 215's on there now. If I go back to a 4.10 gear it will have to wait for next year as then I will put a 9" in the car for reliability and cost of building an new rear axle assy. Plan is to go with my P/G and a known good A1 converter I have, boaring ride but it should get the job done.

[1980RS]

1980RS , you stated in your last post on another thread that you thought the rear diff. went bad . crossed the line at 7100 rpm not your usual 6200-6300 or so . What did the diff. look like when you changed gears ? Maybe the convertors give up the ghost . Only way to tell is try a known good convertor or have that one checked .
I know when I went from 4.56's to 5.13's my 1/8 mile rpm only changed a couple hundred rpms but the calculated slippage at the line went from 20% down to between 10-11% going to try 5.38"s next years to get it under 10% hopefully closer to 7% or under . Coan 8" 5600 -5700 stall with my 422

The only thing busted were the spider gears but a piece did hit one tooth so rather than take a chance of tossing in parts and have that gear fail I opted for the 4.88's. One thing I noticed with this 406 combo is it get up on the tire real quick and I can cut a great light with them, had a 000 dirty red too boot. I watched all the in car video and the converter flashed to 5200 then I take it up to 6900 or a little higher on the shifts and the last 2 passes looked pretty good. The launch problem I was having is much better since I messed with the shock somewhat, maybe in the future I will swap out that intake and try my 1050 Dommy on it, the one I brought was not right for this engine.