What does loose converter versus tight converter mean

[texasterror]

This sounds like a dumb question but i'll take the hit so others who have had this questions can better understand. What does having a loose versus having a tight converter mean can you please list examples of how this relates to low, mid, and high end power and if i had a lose converter with a large turbo versus having a lose converter with a small turbo and vice versa.

 

[Mr.Spool]

This sounds like a dumb question but i'll take the hit so others who have had this questions can better understand.

I think the only way to really understand it is to actually go for a ride in a car with a loose/tight converter and actually feel the difference as this topic has been posted about alot.the converter as discussed is a very important piece of a combo.

 

[Mr.Spool]

What does having a loose versus having a tight converter mean can you please list examples of how this relates to low, mid, and high end power

It's actually how the converter reacts to the power.

 

[Royal-T-Ltd]

Generally a loose converter has more "stall", takes more RPM to get going, and is used to spool larger turbos or for mismatched combos. On the other side, a tight converter has a stall closer to stock, with a lower RPM to get to moving. It is used for smaller turbos or turbos that are specifically matched to a combo.

Hth - aaron


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[texasterror]

Generally a loose converter has more "stall", takes more RPM to get going, and is used to spool larger turbos or for mismatched combos. On the other side, a tight converter has a stall closer to stock, with a lower RPM to get to moving. It is used for smaller turbos or turbos that are specifically matched to a combo.

Hth - aaron


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Thanks for the explanation. I've always wondered what the tight versus loose meant. is anything physically/mechanically loosened on the converter to make it loose and tightened to make it tight or is it more of a term that everyone has generally come to accept?

 

[Royal-T-Ltd]

Thanks for the explanation. I've always wondered what the tight versus loose meant. is anything physically/mechanically loosened on the converter to make it loose and tightened to make it tight or is it more of a term that everyone has generally come to accept?

It's more-so just a term. I think its all in the internals, how the pitch is on the turbine fins and all the other magic inside. I'm not an expert but if you ask Dusty, maybe he will let us know how the different ratios are achieved.

aaron


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[Dusty Bradford]

It can be a complicated answer or a very basic answer.

A loose converter will require more rpm to get the car moving but the most noticeable thing about a loose converter is very little rpm drop (200-400 rpm) on the gear change and a lot of slip % at the finish line. A loose converter is easier to launch and get a good 60' time but after about 200 feet into the run you are wasting a lot of power.

A tight converter will drive like a stocker and have a lot of rpm drop (1400+ rpm). These make building boost harder and are harder to launch but they deliver the max amount of power to the tires. A converter that's to tight will also keep the motor pulled down to far into is power range. Desired rpm range depends on the cam size.

The right converter for a given combo is something in the middle. You want the spool up to be fast yet still slip as little as possible down track. Where it gets complicated is with turbo cars. There is no real stall speed and a converter that's just right at 15psi can be to loose at 25psi. Stall speed changes as the torque of the engine changes. When I spec a converter for a customer who says he wants to run 10.50's but he's running 11.50, the converter will be to tight.

This is a very basic explanation of it. Then you get into turbo size, weight, gearing. I will say the most important thing in the Buick world is to not over turbo the car. If you want to run 11.50, you don't need a 67mm turbo. Keep the turbo size proper and converter selection is easy.


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[Heskahoka]

Not a dumb question. I learned something from this thread.

 

[texasterror]

i figured i'd get beat up for being a member since 2007 and owning two of these cars yet now knowing exactly what that meant. I'm glad other people are finding this info useful.

Not a dumb question. I learned something from this thread.

 

[texasterror]

It can be a complicated answer or a very basic answer.

A loose converter will require more rpm to get the car moving but the most noticeable thing about a loose converter is very little rpm drop (200-400 rpm) on the gear change and a lot of slip % at the finish line. A loose converter is easier to launch and get a good 60' time but after about 200 feet into the run you are wasting a lot of power.

A tight converter will drive like a stocker and have a lot of rpm drop (1400+ rpm). These make building boost harder and are harder to launch but they deliver the max amount of power to the tires. A converter that's to tight will also keep the motor pulled down to far into is power range. Desired rpm range depends on the cam size.

The right converter for a given combo is something in the middle. You want the spool up to be fast yet still slip as little as possible down track. Where it gets complicated is with turbo cars. There is no real stall speed and a converter that's just right at 15psi can be to loose at 25psi. Stall speed changes as the torque of the engine changes. When I spec a converter for a customer who says he wants to run 10.50's but he's running 11.50, the converter will be to tight.

This is a very basic explanation of it. Then you get into turbo size, weight, gearing. I will say the most important thing in the Buick world is to not over turbo the car. If you want to run 11.50, you don't need a 67mm turbo. Keep the turbo size proper and converter selection is easy.


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I have a much better appreciation for those that know this stuff and can spec a combo for someone. I bought a converter from you in 2007, not sure if you remember me but you where super easy to work with and I appreciate the trust (we exchanged routing and account info and i wired money to you for the converter). I thought that was pretty cool of you since you didnt really know me. I called you from Don Wang's shop while he was building my tranny for me. With regards to slippage, does that literally mean its slipping or losing efficiency and what causes slipage? Does that mean certain metal on metal parts arent 100% contacting eachother so they are sliiping (loosing efficiency)?

 

[Dusty Bradford]

A converter is a fluid coupling so there is no metal to metal contact. In a lock up converter you will have clutch contact just like in a manual trans car. When a lock up converter is unlocked, it functions just like a non lock converter.

Slippage is loss of efficiency. This slippage is caused when the flash stall and the shift rpm are to close to each other. Flash stall is the coupling point of the converter at a given power level. In a turbo car, that number changes with boost. If your flash stall is 5200 and your shift rpm is 5400, you will have high slippage because you don't have enough gap between stall and shift. High slippage IMO is above 12%. Many with high slip will be 16-20% range in a turbo car. The converter is pumping fluid around inside of it. We change the design of the internal pieces to fit a converter to the combo its going behind. These include fin angles in the pump and stator, number of blades in the pump and stator, gap between internal pieces, etc....


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[SCOOBY DOO]

Dusty...if you have the time...could you fully explain flash stall.

 

[Dusty Bradford]

I mentioned it in the previous post.

It's the coupling point of the converter at a given power level. When you launch and the rpm jumps up, then rolls over....where it rolls over is your flash stall. After the gear change, the rpm it drops to is the flash stall. As you increase power that number will rise. If your at 20 psi and the rpm falls to 5000 rpm....5000 is the flash. Then you turn the boost to 30 psi and it drops to 5300....that's your flash stall.


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[SCOOBY DOO]

I mentioned it in the previous post.

It's the coupling point of the converter at a given power level. When you launch and the rpm jumps up, then rolls over....where it rolls over is your flash stall. After the gear change, the rpm it drops to is the flash stall. As you increase power that number will rise. If your at 20 psi and the rpm falls to 5000 rpm....5000 is the flash. Then you turn the boost to 30 psi and it drops to 5300....that's your flash stall.


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Thanks...wasn't sure on the flash stall on the gear change...got it straight now. Once again...thanks.

 

[Dusty Bradford]

The flash stall moves around because of torque and load. Your flash stall in 1st gear will be lower if you aren't at full boost in low gear as well as the 1st gear isn't loading the the converter as hard as 3rd will.


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[bison]

The flash rpm is a very overlooked piece of data. In a drag race car or anything that will go in a straight line quickly it's extremely important. A good converter design can accommodate a high power engine at flash and won't effect spool up and ramp in much. Usually I can tell if a converter is going to work based on the combo with only a couple seconds of WOT in 3rd (1:1). If it's way off there it's not going to improve itself. What I see is race converters dropping flash stall too much and cheaper converters flashing too high. Both slow the car down though the butt dyno may not agree with that especially with the cheap converter.


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[Dusty Bradford]

Yep. A loose converter will make the car feel great for a second or two after WOT but track data and butt dyno data is often off by a good bit.


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[belsie]

WOW, thanks to the learned opinions as this is apparently one of those variable conditions based on personal demands & results...................
Can one assume the stock GN system will take you pretty far? Any combo will have exceptions yet there hopefully is a acceptable consensus on this??

 

[cycletech]

Thanks!! I too have leaned something new about our cars today.

 

[bison]

WOW, thanks to the learned opinions as this is apparently one of those variable conditions based on personal demands & results...................
Can one assume the stock GN system will take you pretty far? Any combo will have exceptions yet there hopefully is a acceptable consensus on this??

There's no need to assume these things. They've been proven. In the 90's and early 2000's many racers went low 11's (a few high 10's) with a TA49 and a stock converter. No internet (good thing) or very little Internet, no wideband, no logging, didn't read plugs, non adjustable chips and worse tires than available today. They also stayed together quite well. Today you will see threads about racers running mid 11's with a billet turbo, aftermarket converter, all kinds of Internet support, logging, better tires and a whole lot more than what was used 20 years ago. There was a lot less garbage available in the 90's and early 2000's. Look at aftermarket down pipes and exhausts. There is more ill fitting and performing crap for sale these days than I have ever seen. The market is flooded with Chinese crap that strokes the buyers when they see it for sale cheap. Yet it causes a lot of problems on install. Plenty of converters are complete crap for these cars and are still readily sold to unsuspecting buyers as a performance part.


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