Swapped out my 727 and 4500 flash convertor for a 904 and looser 5200 flash convertor in the offseason..... took awhile with rain to finally get out.........

First a little history........ car ran anywhere from generally high 11.40’s to high 11.50’s last summer. High 50’s were at Norwalk, probably worst air i had the car in last year..... first season on the combo..... ran more like 11.45-11.50 as it cooled off late last summer and into early fall. Only got out a very few times last year.....
Late last fall i had a mineshaft air type night to cap off the year. I had swapped to a radial so this was first time to try them..... i figured they would be a plus
Anyhow, car ran 11.40 off the trailer at 117.80 or so..... then 11.36, then 11.33, then capped off with personal best 11.26 at 118.40..... per my signature...... most mph’s were 116.50 to 117 and change in the summer
60 foots 1.61-1.63..... only single exception ever..... 1.58 on that last pass where it went 11.26

So i show up last night in what i suspected was probably 11.50-11.52 air going by last years results..... figured the tranny and vert were about a 3/10’s upgrade and figured on running high teens or low 20’s.

Well, night started with a ran out of gas, gurgling 11.71 pass........ added gas to tank to fix that..... lol.... stupid, not first time i have done that
Next pass car goes 11.46, missing in high gear( old plugs i figured) which i should have changed.....i look closer at the time slip...... 111.52 mph. Thats alarming, wasnt missing THAT much........1.55 60 foot though... best ever
Cool down a minute, make another lap.......11.39 at 113.55...... same 1.55 60 foot, same 1/8 mile times. Car pulls strong, no missing, runs fine.
Buddy says.... maybe it doesnt like those new mufflers you just put on it( raced with open headers every outling last year)....... so off they come( kooks units, like dynomax bullets)
Get in the lanes again.... 11.40 at 114.30....... nope, that wasnt it.....
At this point i am about done, little brother insisted i make one more pass...... so i go up with the intent to try something different.... all last year, and previously the passes earlier last night i launched the car at 2k off the foot. With the old convertor it pushed too much to leave any higher, and as i am generally racing, i am looking for consistency, and locking on that 2k mark on the tach is easy and repeatable.....
So with this new looser convertor i got it to 3k pretty easy and bumped in...... 11.374..... same exact 1.55 60 foot as all the others...... but 116.94 mph.... wow, welcome back, thats almost “ normal”

I look at the 60 foot, 1/8 mile mph and ET, this is a car to go to war with..... 7.20 or 7.21 on every pass, 94mph and change.
Top end mph is all over the place, even though times are quite consistent. I bought this Cope built 904 used, never even pulled the pan off. Its a 3,000 super pro unit with A&A brake, billet drum, yada, yada. Convertor is a PTC i gave good detail to them on what i had combo wise and what i wanted, and it got built and works seemingly exactly how i wanted it.
After talking to a good Moparts buddy this morning who has forgotten more than i know, among other things ge told me i should have checked( like taking the pan off the used tranny) he thinks the adj for for the 2/3 shift is way out of adjustment..... i thought going down track the 2/3 shift was ultra mushy and linear........ so...... ideas? Thoughts?
Would slipping on 2/3 shift account 100% for what i was seeing on the time slips..... sure seems to..........and be leaving mph and ET on the table

What's the rpm at the stripe compared to before? Converter is looser and possibly less efficient up top. If the high gear clutch is slipping enough to kill that much mph it would be toast pretty quick

Doug

It's weird that leaving at 3k vs. 2k rpm resulted in the same 60 foot, but so much more trap speed and slightly better ET.

2/3 shift is well before the 1/8 mile mark, so if it were effecting anything it should have shown up in the 660 times/mph, not just the 1320.

A detail i forgot that might be important. I shifted this thing at 6,000 or 6100 ish all last year with the 4500 convertor.
As this convertor is looser, i shifted it at 6500 last night to try and open up the spread some.
It trapped last night right at 6500 on the last pass( frankly the only pass i watched it closely)
Thats about 200 rpm higher than i am used to seeing with the old tranny/ convertor.

Car ran 37, 39, 40 over a period of probably 2 hours. Pretty consistent considering the mph was all over the place, and i am shifting by just watching the tach....
Air density might have moved around couple hundred feet in that time.....

I've never personally done the 727 to 904 swap, but know of few guys that have and they seem to pick up about 2 tenths. You picked up a few numbers in 60, but I'm suspecting your convertor for the 904 may be a tad on the looser side and is slipping more than before. What was your rpm at the strip before vs now?

This convertor slippage calculator seems to be pretty accurate:

http://www.tciauto.com/tc/racing-calculators/

Picked up 6-8 numbers in the 60 foot. Thats a bunch

If its hooking jump that stall up some more. Matt is at 5600 with his 727 and I'm at 5800 with my powerglide. Everytime I send my convertors in I go higher and it goes faster.

are you running a sealed to the carb air scoop

How many rpm does the tach drop at shift change? Any idea of peak power rpm? I would also calculate vert slippage as someone else has suggested. Wallace has one too. I always shifted my sb at peak power rpm as 200 above or below made little difference. My vert had a 6% slippage and would drop 600rpm on shift.

No hood scoop. Just factory 69 Dart flat hood

Shifted it at 6500 last night. That cant be too awfully far off from peak power on a 360 with a fairly big camshaft.
Unfortunately i didnt watch to see rpm drop last night

Sounds about right. I would check your vert slippage. My bet is thats where your lose is at.

Buddy of mine had a 8" in his 65 Belvedere. Mid 1.40 60ft, 12.07@107. He put a real converter in it. Mid 1.50 60ft, 11.70@115. Not all about 60ft.
Doug

Agreed. But in my case the 1/8 mile numbers were stellar as well, not just the 60 foot.

5 passes off the foot just shifting by the tach needle and either 7.20 or 21 all 5 passes, and 94.xx mph on all 5 as well.
Cant beat that for consistency.
Actually the 3 of those 5 passes where i got a clean complete lap on the car were 40,39, and 37. Even that isnt hateful. Just the mph numbers in the 1/4 were all over the place

Interesting... my 6200 8” pretty much set a pattern of going 1.34 60’s wherever we went. Made the car incredibly predictable, but did slow it some. It also removed a small dip in driveshaft speed leaving the line. Pile of 6.13 slips with this one.

My 5800 8” has gone 1.28 (1.30-32 the norm), but is more finicky of track temps etc... “when” it hooks I’ll see my best times with this piece. Two 5.94’s and lots of 6.0’s

Guess I could go back and compare converter slip numbers, but it’s all out the window now as I’m putting our old 904 in to play with