Bad torque converter?
Thread Starter
Pro
Joined: Nov 2017
Posts: 587
Likes: 49
From: Belgium
Bad torque converter?
Hi guys!
I'm a manual guy who has a c3 corvette with a th350. It's a bit of a 2 sided question, what converter would you advise? And is it possible that a cheap converter slips at higher rpm/higher speeds?
My engine spec is as follows:
350 4 bolt main
Lunati barebones cam, equivalent to the compcams 268.
416 heads with 1.94" valves.
Edelbrock intake and short headers into a true dual system.
The transmission is a th350, rebuilt with a hardened sprag race etc, transgo kit into a 3.55 rear end.
The combo works well, especially for a 0-60 pull, I get a consistent 4.9-5s as a 0-60 time. But what annoys me is the high rpm/slippage. At about 90mph I'll be at 5k rpm. Almost as if the converter is too loose at higher speeds. Here is a video of it flaring about 1k rpm :
https://youtu.be/ACZLXKgYaJI
https://www.youtube.com/watch?v=ACZLXKgYaJI
Is it possible for a cheap converter to do that? I bought a 10" jegs converter for a whopping 120$. Stall was advertised at 2.2k rpm. I guess you get what you pay for, but is this a typical thing for cheap converters? Or just bad luck?
Trans should be okay, it's a fresh rebuilt trans. The same happens in 1st and second gear too.
Happy to hear your thoughts!
I'm a manual guy who has a c3 corvette with a th350. It's a bit of a 2 sided question, what converter would you advise? And is it possible that a cheap converter slips at higher rpm/higher speeds?
My engine spec is as follows:
350 4 bolt main
Lunati barebones cam, equivalent to the compcams 268.
416 heads with 1.94" valves.
Edelbrock intake and short headers into a true dual system.
The transmission is a th350, rebuilt with a hardened sprag race etc, transgo kit into a 3.55 rear end.
The combo works well, especially for a 0-60 pull, I get a consistent 4.9-5s as a 0-60 time. But what annoys me is the high rpm/slippage. At about 90mph I'll be at 5k rpm. Almost as if the converter is too loose at higher speeds. Here is a video of it flaring about 1k rpm :
https://youtu.be/ACZLXKgYaJI
https://www.youtube.com/watch?v=ACZLXKgYaJI
Is it possible for a cheap converter to do that? I bought a 10" jegs converter for a whopping 120$. Stall was advertised at 2.2k rpm. I guess you get what you pay for, but is this a typical thing for cheap converters? Or just bad luck?
Trans should be okay, it's a fresh rebuilt trans. The same happens in 1st and second gear too.
Happy to hear your thoughts!
Last edited by Dusky; Oct 21, 2019 at 07:26 AM.
Pro
Joined: Mar 2014
Posts: 529
Likes: 113
From: Texas
I hate to tell you, but does not look like a converter issue. Post a video of the car sitting still and power brake it a few times in a video. Then a few times from an idle through first gear. Come out wider with the camera (still need to see the tach) so we can see how the car is reacting.
Last edited by Gunfighter13; Oct 22, 2019 at 10:08 AM.
Thread Starter
Pro
Joined: Nov 2017
Posts: 587
Likes: 49
From: Belgium
I hate to tell you, but does not look like a converter issue. Post a video of the car sitting still and power brake it a few times in a video. Then a few times from an idle through first gear. Come out wider with the camera (still need to see the tach) so we can see how the car is reacting.
maybe the correct term is flaring? The jump of 1k rpm when just pushing the throttle.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
Which is what its supposed to do. Power is up in the higher RPM ranges and the converter is taking you there instead of the motor trying to pull the car along as it gets there ..
Thread Starter
Pro
Joined: Nov 2017
Posts: 587
Likes: 49
From: Belgium
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
It is working fine , the whole point is to allow the motor to spin up so it can pull the car from its power band. And that same converter will act differently in different cars, Its not an exact science.
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Thread Starter
Pro
Joined: Nov 2017
Posts: 587
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From: Belgium
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
Cant you drive from a stop and drive to 60 mph and hold that speed ? Go here and find out what your rpm should be at 60 mph based on tire and gear ratio i think its 2700 to 3000. But you know the specifics enter them here https://spicerparts.com/calculators/...rpm-calculator .. Also remember when you reduce the converters diameter you increase the number of revolutions you need to do the same task. Just like tire size changes the RPM .. A converter will have a similar affect
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Is it possible that your tach is inaccurate? The sound of the engine doesn’t seem to match the tach rpm in the video.
my th350 with a 3000 stall converter gives 3800 rpm @ 80 mph with a 3.55 rear diff. And 27” tires.
my th350 with a 3000 stall converter gives 3800 rpm @ 80 mph with a 3.55 rear diff. And 27” tires.
Last edited by REELAV8R; Oct 23, 2019 at 03:44 PM.
Thread Starter
Pro
Joined: Nov 2017
Posts: 587
Likes: 49
From: Belgium
Cant you drive from a stop and drive to 60 mph and hold that speed ? Go here and find out what your rpm should be at 60 mph based on tire and gear ratio i think its 2700 to 3000. But you know the specifics enter them here https://spicerparts.com/calculators/...rpm-calculator .. Also remember when you reduce the converters diameter you increase the number of revolutions you need to do the same task. Just like tire size changes the RPM .. A converter will have a similar affect
Drifting
Joined: Nov 2016
Posts: 1,957
Likes: 576
From: Pittsburgh PA
im with the others- questioning the tach. watching your videos when you are in the 55-60 mph range your tach is around 4000-4500 rpm. that would be like 18" tall tires.
also, check the vacuum line to the modulator. I had a similar issue with my 68 recently. i had large flares in RPMs when i was driving and going from coasting to on the gas. the vacuum line had split down at the trans, so while it looked like it was still on it had no vacuum since it was split down 1 side
also, check the vacuum line to the modulator. I had a similar issue with my 68 recently. i had large flares in RPMs when i was driving and going from coasting to on the gas. the vacuum line had split down at the trans, so while it looked like it was still on it had no vacuum since it was split down 1 side