Lock up vs. Non l/u efficiency when unlocked

[turbo nasty]

All the trans pros please chime in. Need a lil more info and have a small grasp on why I think.

With a higher stall convertor of a smaller size vs the D5 I have experienced my car slowing down when not locking the convertor at WOT.
Did some research when I first purchased the convertor and the smaller l/u convertor in the 3k rpm range I thought would be a plus but it seems to nose over in 3rd and lay on the convertor.

Is this the case since the larger convertor has larger vanes that allow better fluid coupling at higher rpms vs a smaller L/U of a higher stall due to the smaller conv having space restriction due to the L/U components.

Or is it true that a smaller L/U convertor vs a bigger convertor (D5) at say 3k stall the smaller convertor "should" do better as far as TQ multiplier, etc.

Honestly my car slowed when I put in the 3k stall vs the D5 both unlocked. I know I can lock the TCC but prefer to have the most efficiency prefer to stayed unlocked at WOT due to parts wear and tear.

This is L/u convertors only .....just to recap a L/U convertor has a a limit to its efficiency due to the L/U components...Is this correct

 

[Dusty Bradford]

All the trans pros please chime in. Need a lil more info and have a small grasp on why I think.

With a higher stall convertor of a smaller size vs the D5 I have experienced my car slowing down when not locking the convertor at WOT.
Did some research when I first purchased the convertor and the smaller l/u convertor in the 3k rpm range I thought would be a plus but it seems to nose over in 3rd and lay on the convertor.

Is this the case since the larger convertor has larger vanes that allow better fluid coupling at higher rpms vs a smaller L/U of a higher stall due to the smaller conv having space restriction due to the L/U components.

Or is it true that a smaller L/U convertor vs a bigger convertor (D5) at say 3k stall the smaller convertor "should" do better as far as TQ multiplier, etc.

Honestly my car slowed when I put in the 3k stall vs the D5 both unlocked. I know I can lock the TCC but prefer to have the most efficiency prefer to stayed unlocked at WOT due to parts wear and tear.

This is L/u convertors only .....just to recap a L/U convertor has a a limit to its efficiency due to the L/U components...Is this correct

If your converter is going into 3rd and laying on the converter, it's too loose.

A 12" OEM converter can mph better because it's maybe a 2000-2400 stall compared to your 3000. What you gained down low to increase spool up, you gave up in efficiency up top. This is the balancing act you have with converters. Technically the larger converter should always be more efficient up top due to it's size but that isn't the case. The design of the core and internals plays a large role in coupling efficiency, not just the size.

The D5 should never be made into a 3k stall. It requires some major "tweaking" to the internals and it's just not ideal. I can't say that a D5 could truely stall to 3k at 0# boost.

 

[turbo nasty]

So its a double edge sword and if you want a good high rpm and low you need to go non L/U?

 

[Dusty Bradford]

So its a double edge sword and if you want a good high rpm and low you need to go non L/U?

That's exactly what it is. Which is also why over-turboing a motor for it's rpm range will kill a combo faster than anything.

It's a balancing act. The engine rpm range, turbo and converter have to match for the et goal.

 

[turbo nasty]

Thanx for the info...
Ive heard 2-3 mpg loss with a no L/U is this true.
The others being more heat and possible cruise control surging if you live in hilly areas.
So for someone that drives their car daily and MPG is important I guess the best thing if one wants to stay with l/u and have good coupling up top is get the trans and a convertor that can handle the abuse and lock it at WOT?

 

[WSLN 6]

For what it's worth, Dusty pointed me toward a 9.5" N/L PTC that I wished I would have gone too a long time ago.... idles up the driveway into the garage no problem, couples great at WOT, and only raised cruise rpm by 200. And it stalls at 3400 rpm at 0 psi boost......:smile:

 

[turbo nasty]

Is yours a DD though? How much MPG did you lose?

 

[Dusty Bradford]

Thanx for the info...
Ive heard 2-3 mpg loss with a no L/U is this true.
The others being more heat and possible cruise control surging if you live in hilly areas.
So for someone that drives their car daily and MPG is important I guess the best thing if one wants to stay with l/u and have good coupling up top is get the trans and a convertor that can handle the abuse and lock it at WOT?

I doubt you'd see 2-3 mpg loss with a good non lock. Maybe in the old days of 3400-3600 stalls but not with the new stuff.

Yes, you'll see more temp with a non lock at hwy speeds but nothing a good external cooler won't handle with ease. Every GN needs a good external cooler anyway.

Never heard of the surging. The locking and unlocking around 40-45 mph in hilly areas is a different story.

Locking at WOT is not a necessity. Choosing the right combo is. The new 61 and 62mm turbo's spool very quickly with a 2800 stall l/u and have 10 second potential. The 2800 works well with a 5400-5600 rpm shift point.

I do feel on the stock cam cars with larger than a 61mm DBB turbo the WOT lock-up is needed. They only rev to 5200 or so and the converter can't fully couple with that low of a shift point.

The other thing is expectations. Just a few years ago 12% slip was considered acceptable for a non lock. Now we have easily cut it in half so the bar has been raised. This makes the L/U's look like 12% is horrible.

 

[bison]

Thanx for the info...
Ive heard 2-3 mpg loss with a no L/U is this true.
The others being more heat and possible cruise control surging if you live in hilly areas.
So for someone that drives their car daily and MPG is important I guess the best thing if one wants to stay with l/u and have good coupling up top is get the trans and a convertor that can handle the abuse and lock it at WOT?

If your driving the car alot and e.t.'s are not that important then you should build around a LU. If you want to go fast and and can stand to have 1-2 mpg loss at most then the PTC 9.5 in certain configurations will be the best answer. If you think your saving $ by getting a couple extra mpg then you arent very serious about performance. If you used 600 gallons a year typical you would only save a couple hundred on fuel if you used 70-80 gallons less in a worst case scenario with a good NL. I noticed you have TA headers in your sig. I doubt they are worth anything in your combo at all. Think of how much gas could be bought with the $. It would take 4-5 years of driving a NL daily to add up to the cost of those. Not knocking just making the point about cost to gain with regard to added expense for extra fuel consumption

 

[turbo nasty]

Good points, looking at the total package.

Whats the best % slip on the "good" l/u's when not locked?

 

[BMF_Racing]

I do feel on the stock cam cars with larger than a 61mm DBB turbo the WOT lock-up is needed. They only rev to 5200 or so and the converter can't fully couple with that low of a shift point.

I can back this comment up, even running it out to 5600 (max RPM for my combo), it was laying way over, but I did so just to see if it would help any with the coupling and did reduce slippage from 19% to 17.7% (compared to 5400 shifting).

 

[Dusty Bradford]

Good points, looking at the total package.

Whats the best % slip on the "good" l/u's when not locked?

Too many variables to say. Most of them are all using similiar internals when looking at the $500 range converters. Some may use a billet cover which raises the price to over $600 but internally, very similiar.

A "good" lock-up unlocked on a mis matched combo may slip 20%

A "good" lock-up unlocked on a matching combo may slip 8-12%

Where you get in trouble is by running too large of a turbo for the rpm range of the motor. You need rpm to spool a turbo. If your turbo is too large you have to run a looser converter to get it going. This also raises the coupling point of the converter so it doesn't have enough time to couple before the gear changes.

 

[Dusty Bradford]

I can back this comment up, even running it out to 5600 (max RPM for my combo), it was laying way over, but I did so just to see if it would help any with the coupling and did reduce slippage from 19% to 17.7% (compared to 5400 shifting).

Something still seems off here. With a converter that stalls 2400 rpm, slip should be better than 17%. It's also wierd that you can spool that 67 so easily with a 2400 stall. Looking at the info, you could tighten the converter another 400 rpm.

Is this rpm data from a power logger or what are you using to read rpm?

 

[turbo nasty]

Guess its either too much stall for my combo or the slip sux on it unlocked. I was hoping that 3k would be more than enough for me now and it would cover future mods/cam/heads/turbo/etc.

All in all its seems the L/U convertors just cant revival a non L/U's fluid coupling ability. I chose to not lock the convertor at WOT in the chip to keep wear off the trans andthen got a smaller l/u convertor when the trans was built.

Im at the crossroads.
Either stick with L/U and lock it at WFO raise the chance of wear/boom on the input shaft and od planet, etc (forward drum is billet so thats good) or get a non l/u and lose MPG but save the wear on the above mentioned parts but still be sa lil slower than forced l/u

 

[Dusty Bradford]

All in all its seems the L/U convertors just cant revival a non L/U's fluid coupling ability. I chose to not lock the convertor at WOT in the chip to keep wear off the trans andthen got a smaller l/u convertor when the trans was built.

It's just that when retaining lock-up, your hands are tied on what you can do with the design of a converter. Rather than being able to use your own custom pieces, your stuck using some oem pieces for the lock-up portion. Those pieces can't deliver the performance in all cases.

If someone wants good slip #'s with a lock-up converter, unlocked. You really have to build a combination around the converter options.

IMO. If you want something to run 10's. MPG wouldn't be a concern so the non lock is fine. If you want something to run mid 11's. There's no reason for anything larger than a 61-62mm turbo. This will allow you to run a tighter converter that will deliver better efficiency unlocked and have the spool-up we all want.

 

[BMF_Racing]

Something still seems off here. With a converter that stalls 2400 rpm, slip should be better than 17%. It's also wierd that you can spool that 67 so easily with a 2400 stall. Looking at the info, you could tighten the converter another 400 rpm.

Is this rpm data from a power logger or what are you using to read rpm?

Yep, logging with the Laptop/Maft Pro

 

[Dusty Bradford]

Yep, logging with the Laptop/Maft Pro

Basically, with the spool-up as fast as you say it its. You could run a 2000 rpm stall with a 6776

 

[BMF_Racing]

Basically, with the spool-up as fast as you say it its. You could run a 2000 rpm stall with a 6776

There will be some Lag present then, but it may work. Stock D5 will work, but will not handle the power I suppose?

 

[Dusty Bradford]

There will be some Lag present then, but it may work. Stock D5 will work, but will not handle the power I suppose?

If you get the unlocked slippage down you will have some lag. A restalled D5 should take the power but will spool even slower. The tightest your 10" can be made is another 200-300 tighter which would make it a 2100-2200 but 300 rpm would still be right at the edge of you being out of your power range with the stock cam.

To spool the 67 and reduce the slip your down to putting a cam and spring in it to support more rpm or leave the motor alone and go to a 9x11 or multi-disk so you can keep the rpms down to 4800-5200 in the traps. Of course you know what the tranny will need to make sure it takes the abuse of WOT locking.

The only other option is to back down turbo size so you can run a tighter converter and still have good spool-up. This would allow you to continue running unlocked but have better efficiency and still have 10 second capability. Unfortunately, to make it all work together to optimize everything will require some changes.

 

[quickt]

Guess its either too much stall for my combo or the slip sux on it unlocked. I was hoping that 3k would be more than enough for me now and it would cover future mods/cam/heads/turbo/etc.

All in all its seems the L/U convertors just cant revival a non L/U's fluid coupling ability. I chose to not lock the convertor at WOT in the chip to keep wear off the trans andthen got a smaller l/u convertor when the trans was built.

Im at the crossroads.
Either stick with L/U and lock it at WFO raise the chance of wear/boom on the input shaft and od planet, etc (forward drum is billet so thats good) or get a non l/u and lose MPG but save the wear on the above mentioned parts but still be sa lil slower than forced l/u

As much as I hate lock-ups we are testing a new design 9.5 lockup they say will be efficient with an application similar to yours. Should have some good test data in a couple weeks. I do agree with Dusty the stock cam car with large turbo and RPM limit of 5200 is a very hard combo to build an efficient converter for lock-up or non lock and not sure it can be done. There will most always be a trade off spool for efficiency. In most cases the only way is to lock up the converter or re-cam the car.