RPM pull down after launch, question

September 20, 2021, 06:15 PM

Toad1

I have about 100 runs on this converter and the truck has been pretty good but looking to get it better.
At the launch it goes from 4200 to 6150-6200, stays pretty flat, maybe loses 50 rpm, then climbs to shift at 6900 (at about 2.8 seconds) and drops to 6100-6200. Normal for 3200 lb S-10, 4.86 gear and mild 406" with 1000 cfm alky carb?? Running the truck at about 160 degrees, thinking of trying to get it to 170-180 but it has a hard time getting there even with 3/8" vacuum valve open most of the time. Just curious if the converter is hurt but cant get one for about 8 weeks...so that sucks pretty much.

September 20, 2021, 06:36 PM

TOP38

quote:
Originally posted by Toad1:
I have about 100 runs on this converter and the truck has been pretty good but looking to get it better.
At the launch it goes from 4200 to 6150-6200, stays pretty flat, maybe loses 50 rpm, then climbs to shift at 6900 (at about 2.8 seconds) and drops to 6100-6200. Normal for 3200 lb S-10, 4.86 gear and mild 406" with 1000 cfm alky carb?? Running the truck at about 160 degrees, thinking of trying to get it to 170-180 but it has a hard time getting there even with 3/8" vacuum valve open most of the time. Just curious if the converter is hurt but cant get one for about 8 weeks...so that sucks pretty much.

I doubt it. I had one that has about the same drop before it climbed also. Usually if they are hurt you will know!

September 21, 2021, 07:27 AM

Toad1

Appreciate that. I know there is no metal in the pan. Probably the 406 not having too much power , the 4.86 gear and 3200 lbs ;-)

Just curious was all , thanks!

Jok

September 21, 2021, 07:52 AM

DLR

sounds normal to me

September 21, 2021, 09:37 AM

pauley

i had a converter recently that would flash correctly to 6300 then in .5 sec it would drop back to 600/6100 and flat line there for about a second before climbing to the shift point. drop back at shift was about 600. it was consistent, flash was correct, mph was correct but 60' was 4 or 5 slow and it was .10 slow. happened all at once. changed everything except converter. finnaly got my converter guy to look at my graph and he felt like the sprag was slipping as it tried to get the car moving. he made repairs and picked my 60 and tenth back up.

ep

September 21, 2021, 02:22 PM

JAFR

Pauley, who is your converter guy? My graph is very similar to yours and Toad 1. The initial launch is good but then it falls back, locks the converter and slowly climbs in RPM. Car is consistent and runs well but we are always looking to improve.

September 21, 2021, 03:36 PM

Woody B

I think Jok's 50 to 100 rpm drop is normal. Pauleys was dropping 200 to 300. I had one that started dropping 300 rpm and slowed down. After messing with non convertor stuff for a couple weeks the spraq finished breaking. It was an old Coan convertor with a million runs on it. Kenny Ford (PTC) fixed it after I broke it.

September 22, 2021, 10:15 AM

pauley

quote:
Originally posted by JAFR:
Pauley, who is your converter guy? My graph is very similar to yours and Toad 1. The initial launch is good but then it falls back, locks the converter and slowly climbs in RPM. Car is consistent and runs well but we are always looking to improve.

I got Greg Slack to fix mine. he is fairly local to me. Kenny Ford at PTC as Woody B stated is a great guy and would look at it for you. I have run Kenny's stuff for years but I am currently running the one that Greg fixed for me.

ep

September 24, 2021, 08:04 AM

JAFR

quote:
I got Greg Slack to fix mine. he is fairly local to me. Kenny Ford at PTC as Woody B stated is a great guy and would look at it for you. I have run Kenny's stuff for years but I am currently running the one that Greg fixed for me.

Thank you for the information. I have dealt with PTC before, good people for sure.

September 24, 2021, 08:37 AM

Mike Rietow

Small tire Super Pro you want a lot dip after flash stall, all it is, is the driveshaft trying to catch up flexplate, after flash stall.

It's traction control right where you need it for small tire Super Pro racing.

You can tailor the dip using a low (slow) starting line ratio number.

Spragless converters are very smooth in this area on the track.

Methanol consistency seems to like the load.

September 26, 2021, 05:28 AM

Footloose

Fuel tube slosh?

September 26, 2021, 12:07 PM

Goob

My flash and shift fall back are never the same, usually 500 RPM above flash on the shift, about 500-600 RPM under shift. Sprag or spragless.

September 26, 2021, 12:40 PM

Footloose

Goob how many passes since trans and converter freshened ? What about filter?

September 27, 2021, 03:03 PM

Goob

quote:
Originally posted by Footloose:
Goob how many passes since trans and converter freshened ? What about filter?

Countless on the sprag unit, probably 300 or so on the spragless. Spragged unit is an Opel style. Both Coan built. TH-400 with a 2.10/1.40 gear set.
Filter and pan are clean, less a smidge of non-metallic friction materials....

Replay tach in the Mega-200, I do review almost every run.