Had a new convertor made last season and it isnt quite right. Helped the 60 a ton, but its loose in high gear,, lost a little mph.
Currently have 4.10 gear. Some noise in them, gonna swap to 4.30 when i replace them
Is a bit more gear more likely or less likely to tighten me up in high gear?

It'll tighten up slightly...but dont get too hung up on it.

People LOVE to talk about stall speed and slip % because it's the only two things we can easily measure.

There is just a lot more to a good converter then just those two numbers, so unless it's way off...dont worry too much.

Thanks. The car 60 foots a whole tenth better than it did with the old convertor and the 727
Swap to 904 and new convertor, no better ET in spite of that much better 60’
Seems the vert is off enough to kill any 727 to 904 gains, in spite of 60 foot
All i did was gain rpm at the stripe and lose better than 1mph

I swapped from 3:73 up to 3:91 and then to 4:10 and finally 4:30 and saw very little change in ET and MPH do to having a fuel delivery issue in my old pump gas Duster, that car ran 10:30 at 127.MPH, I fixed the fuel delivery issues and it ran faster and quicker
My message is you may be running out of fuel the last 200 to 300 Ft. in the 1/4 mile so swapping to the 4.30 gears will make it run more RPM quicker making it run out of fuel sooner
Can you jet the carb. up enough to slow the MPH down in the 1/4 mile? If not you have a fuel delivery issue in volume, not fuel pressure

Its certainly possible. Big initial gain, gradually gives it back further down the track i go.
I suspected i would make a nice gain going from the 727 to the 904. Car runs the same, just better 60 and little less mph
That all said the car is completely rewired now, relays on everything, excellent voltage abd grounds now.
Find out how much known good juice helps first time out before i change anything

When is your frist test and tune. May

Who knows. Gotta get about 100 degrees warmer around here
And then whenever i get my hip done......

Don, anytime my car has picked up in 60' it carried at least those numbers down track. Also several years ago I switched from 4.10s to 4.30s and saw no gains.

Yep, deeper gear should make the converter feel tighter.
I went from 4.10 to 3.54 and it was noticeably looser. Getting tightened up now.

Agree
But in this case it didnt

The converter will show more and more slip is the rear gears get taller. Slip at the gear change is the worst, decreases as you approach max rpm. As said, don't get hung up on it unless it is really out of whack. I put a ten inch behind a big stroker that liked 5700 rpm shifts. It was too loose, stayed at almost 6,000 from starting line to finish. I had to shift by guess, since it was already above my shift point. It ran the same ET when i had it tightened up! At least then i could tell when to shift!!

For those wondering about the motor; 535, ported 906 heads, 590 cam.

something is wrong, changing to a 904 from 727 should be a good gain. Anything you pick up in the 60 should be doubled in the 1/4. IF you pick up .10 in the 60' you should be picking up .20 in the 1/4.

As already mentioned, look at the fuel system and other things... but id say its the converter.
you have experience with cars, you know
Something is wrong, id take the converter out and get it to a reputable builder and get it looked at. Your leaving a lot of ET on the table.

Chrysler testing back in the '70's showed about .15 improvement going from 727 to 904. All else being equal. (May vary a bit based on HP, weight, etc.) It could very well be that the 904 converter is not as efficient as the 727 converter. Only other thing might be a mechanical issue in the trans. Fluid pressure difference can also make a little difference and I was told a trans brake valve body may be a bit slower footbraking than a regular valve body. Possibly because of pressure requirements.

2 years ago i had a 727 with a tight 4500 flash convertor
Car went my signature. 11.26
Last year i yanked out the 727, put in a Cope built 904, and had PTC build me a convertor
Best was 11.33..... convertor flashes 5200, right about what i figured was optimal. But i figure 14% slip now
With 727 best 60 foot was 1.62
With 904 best 60 was 1.53
The car did need rewired, lots of questionable stuff going on
Now its all new and up to date with zero issues
Maybe it was electrical related and getting worse, but the car was super consistent,went 6 rounds with it several times. So who knows

MY car ran its best passes in nov, Racepak data showed some slippage in the converter. Sent it to Ultimate , upon cutting it open, fins are loose on the turbine and it needs to be replaced. Long story short the car ran well ,but the converter is coming apart …….
Check that there are no other issues, but it may be possible that PTC missed it on the converter. Call them and or send it back after one test session to make sure no other mechanical issues

Will do

All I can add is that going from a converter that was too loose on the big end to one that reduced the slippage by 3+% improved my 60-ft, ET and MPH.

Both converters flashed to 4200+, but the tighter unit picked up .2 and 2 MPH in the 1/4. I can't recall what the improvement in the 60-ft was, but the car picked up across the entire pass. This was a mid-11-sec car at the time, and the converter is the same one I was using when the same car was going mid-10s later, too.

hi don been awhile,definitely t&t it first could be electrical issue.several years ago i was next out to waterbox and car quit,no fuel pump.i had a relay in the system jumped out and hard wired around it and pump fired up,went out and car picked up .2 in the quarter! i haven't ran a relay since.lol..

The guy who wired my car does it professionally. Retired GM electrical engineer
I showed him some things on the car when i took it to him, and he said only one car he had ever done was worse. Burned wires, jumpers, questionable grounds, too small of one wire alternator wire going to the back, battery cable gets real hot when cranking the car....... you name it.
When i got it back i went to start it and you could hear how much stronger the fuel pump sounded, how the car turned over..... etc
So yea, first time out not making any changes till i get a baseline......
BTW.....good to hear from ya Rob