Talk me into a transmission change...

[jayb]

I have been giving some consideration to a transmission change in my Shelby clone.  The ATI Powerglide that is in there now was originally purchased for my Galaxie, where I plan to put another SOHC and two turbos to make 1800 HP or so.  The ATI trans is supposed to be good for 2500 horsepower, so it was a good plan for the Galaxie, but is way overkill in the Shelby clone.

When I originally built the Shelby clone, the plan was to go to one of those street Lenco transmissions.  But, at the time they were outlawed at Drag Week in all classes except for Unlimited.  And I had the ATI trans just sitting there, so I bought a converter and put it in the car.  I've been running it there ever since.

In the meantime, I've learned more about Lencos, and have learned to like them a little less.  One thing that I don't like is that I've been told that they use a lot of power.  This makes sense to me because they are a planetary gear setup, and as you go down the track, you are just subtracting more gears.  Its not like a regular manual transmission where you are changing from one gear set to another; each module of a Lenco has a direct drive and an underdrive module, so when you shift the first gear module you might be shifting from a 1.37:1 ratio to a 1:1 ratio.  This means that if you are running a four speed car, at launch you have three gear sets engaged.  When you do the 1-2 shift, you reduce that to two gear sets, the 2-3 shift reduces it one, and the 3-4 shift gives you direct drive.  All the gear sets engaged simultaneously will eat some power.

Yesterday one of the guys who did the machine work on repairing my Shelby block came by for a visit.  He has a 67 Mustang with a 347 Windsor engine that runs mid 10s.  He used to have a G-Force trans in the car, but it kept breaking, so he switched to a Lenco.  (It surprised me that a G-Force trans wouldn't take the power required for a mid 10 second pass).  He said that he didn't see a loss of power when he switched to the Lenco, but he wasn't 100% sure because he didn't have back to back data to say definitively.  I do know that when the Pro-Stock teams switched from Lencos to Libertys they picked up quite a bit, so at least compared to a Liberty the Lenco will eat some power.

He also told me about the issue with Lencos coming out of gear when letting off the throttle, which I didn't know about.  I knew that Libertys did that but I didn't know Lencos did it too.  So, if you are on the track and have to let off for a second your pass is over, driving around the pits and doing the burnout requires some special procedures, etc.  After talking to him about his Lenco for a while, I kind of decided that it was not for me. 

At Drag Week, Joel's trunk monkey Jeff (JericoGTX on the forum) mentioned that Liberty now offers a trans with a synchronized fifth gear, so that in fifth the transmission won't pop out of gear when you let off the throttle.  I haven't been able to find any mention of that on their web site, though.  If that option is available, at least freeway driving would be tolerable with that trans.  But it would still be a pain around town.

A G-Force or a Jerico would be a better solution, but they aren't going to hold up in a 3250 pound, high 8 second car.  I think my only options for a manual trans are the Lenco and the Liberty.  Anybody else know of any other standard transmissions that will take 1000 HP and are streetable?

Next consideration is the clutch.  Mike, the guy from the machine shop who visited yesterday, figures that it takes a whole racing season to really dial in the clutch setup.  You've got preload pressure and centrifugal weights to worry about, you are drilling holes in the scattershield and have the car up in the pits to make adjustments, etc. etc.  This is a problem for me because I just don't know much about modern clutch setups, so I'd be starting at the bottom of the learning curve.  A friend of mine just spent $4K last year trying to figure out the clutch in his stock eliminator car.  Doesn't sound like much fun to me.

As opposed to a manual trans, my ATI trans is trouble free.  I just drive the car, on the street and on the track.  At the track, I'm not constantly shifting gears; one shift at about 400 feet and I'm done.  It is easy, easy, easy, and with so many other things to worry about on the car, its nice to not have to think much about the transmission.

But here's what I don't like about it.  My datalogs from Drag Week say that the engine is turning 7700 RPM through the traps, but at 150 MPH, the driveshaft is only turning 7250 or so.  I am losing 400-500 RPM in the torque converter.  I don't like that one bit   Which is why I'm still thinking about going through the trouble of switching to a manual transmission.

Anybody got any useful suggestions on how to overcome the manual transmission hurdles that I've detailed here?

[My427stang]

I'll be the nay-sayer...

With all the respect in the world, most every race has been last minute with an engine hot off the dyno.  If you continue that trend, that means minimal clutch testing, minimal practice driving the car, not to mention a suspension that will be shocked much differently.

I personally think that researching a more efficient AT would match your needs better, if those needs stay the way it has been.

[jayb]

With all the respect in the world, most every race has been last minute with an engine hot off the dyno.  If you continue that trend, that means minimal clutch testing, minimal practice driving the car, not to mention a suspension that will be shocked much differently.

I personally think that researching a more efficient AT would match your needs better, if those needs stay the way it has been.

That's a fact, Ross; despite my best efforts it seems to be a last minute deal every year.  Point for the automatic, that's for sure.

Maybe I should just be talking to the converter folks...

[whitea62.7t]

Ive seen c4's capable of over 1500 hp
And My427Stang Makes some good points
They make some amazing converters for the pro mod guys

[bluef100fe]

Jay,

Unfortunately, I would stick with the glide if I were you. You start adding more gear reduction to a car that I believe is still somewhat traction limited. Your not gonna go any faster unless you can get the power to the ground. 

I would just pull some more gear out of the car to bring the Rpms down a little. Go to a 4.10 or 3.89 gear or try a different converter/ converter company.  I believe you still have a few tenths to find in current setup. The glide is one of the most efficient transmissions made. I also wondered why run the the gear vendors in a car with that much power. I'm sure it eats some horsepower itself.

My plan for my truck was just to build a stout engine and automatic trans. Run a 3.89-4.10 gear and 30-31 inch tall tire with no O.D. With converter slippage the 70-80 mph cruising rpm should be very tolerable on the street. Less gear reduction should make it a little easier for the chassis setup to get the power to the track. Anyway, just my two cents worth.

After following drag week coverage this year I see I will have to put a roll bar in my truck and run bottom 11's to mid 10's to have a chance at the 32 car field bracket race on the final day. 

[mygasser]

is there not a lockup convertor available for the 'glide to bring the revs down at the top end?

[cammerfe]

First---my 1.5 cents worth. I, too, would look further into the converter situation.

Second, I'd like to know more about the 'popping out of gear' with the Lenco. I don't see that there is anything inherent in a planetary set-up such that a coast situation doesn't work. But maybe I just don't know.

TIA for any further enlightenment.

KS

[jayb]

Ive seen c4's capable of over 1500 hp

Where?  From what I've been told pushing over 900 HP in a C4 is asking for trouble...

[jayb]

is there not a lockup convertor available for the 'glide to bring the revs down at the top end?

The lockup converters that I know about won't take the horsepower.  But maybe there are some I don't know about that would work.  More research, I guess...

[thatdarncat]

I'm no expert on Lenco's, but I do know there is one in Larry Larson's Nova and he's done ok at Dragweek, must be streetable somehow.



Horsepower drag was only one reason NHRA Pro Stockers went away from the Lenco and the resulting ET improvement  - overall weight reduction was one and the desire to keep the engine in a narrower powerband was another.

[bluef100fe]

Jay,

Who is supplying your converters? I use Ultimate Converter Concepts. They have built a lot of converters for the guys on the 460 sites I frequent. A lot of the 460 guys making 1000+ hp are using aftermarket glides and UCC converters. I told UCC what I was trying to do with my truck and I've been very happy with the results. They use something called a mechanical diode in the converter that is supposed to help with lockup on the big end. They are expensive but I believe ya get what ya pay for when it comes to converters. A lot of low nine, eight, and seven second N/A and nitrous drag cars using their converters and glide transmissions.  I've also heard that much past 800 hp the C4 transmission is unreliable.... They need to be freshened often at that power level if they hold up at all, just not enough clutch pack holding power. I don't think that would be a wise move in a drag week environment.

[jayb]

I'm no expert on Lenco's, but I do know there is one in Larry Larson's Nova and he's done ok at Dragweek, must be streetable somehow.

Well, if I wanted to deal with the trans popping out of gear every time I took my foot off the gas while going from one track to another, I could run a Liberty or a Lenco at Drag Week, but I just would rather not.  At that point I'd live with the automatic.

[jayb]

Jay,

Who is supplying your converters? I use Ultimate Converter Concepts. They have built a lot of converters for the guys on the 460 sites I frequent. A lot of the 460 guys making 1000+ hp are using aftermarket glides and UCC converters. I told UCC what I was trying to do with my truck and I've been very happy with the results. They use something called a mechanical diode in the converter that is supposed to help with lockup on the big end. They are expensive but I believe ya get what ya pay for when it comes to converters. A lot of low nine, eight, and seven second N/A and nitrous drag cars using their converters and glide transmissions.  I've also heard that much past 800 hp the C4 transmission is unreliable.... They need to be freshened often at that power level if they hold up at all, just not enough clutch pack holding power. I don't think that would be a wise move in a drag week environment.

I've been using Neal Chance Racing Converters; haven't looked at UCC.  I'll check them out.

[machoneman]

Yikes, a tough question for sure.
-As noted, last minute dyno sessions and little track testing time IMO almost rule out any stick tranny save a Lenco (later). Larry Larson or other high hp Lenco users should be grilled.
-no true stick tranny as stated will survive 1,800 ponies, for sure.
-mechanical diodes could save lots of convertor slippage and they ain't cheap. Yet, no idea on their longevity before replacement and that can't be cheap either.
-Lencos would not, under a high hp engine as planned, require a 'lot' of clutch tuning when compared to a true stick tranny/slipper clutch setup. Yet, it would require some.
-Now, once dyno testing is done, I'm sure you slap the motor in and go with your 'Glide.  Bluntly, no time for clutch testing =no Lenco in my book!   

Maybe......investigate the mechanical diode, add same if warranted, change gearing as noted and keep the 'Glide. I do like the Lenco idea though and with 1,800 hp the hp loss IMO would be negligible. Keep in mind those 1970's 750 hp Pro Stockers of  the era lost only a tenth with a Lenco due to internal power absorption (or gained a tenth when switched back to a stick tranny). With almost 2.5 times the hp, I doubt you'd loose even that tenth. Then again, one never misses a shift with a Lenco and they are easy to repair...although they never break, they just need occasional clutch pack replacement.  One more benefit: changing gear ratios, 1st or high gear or both is a snap. 

They also allow a MN guy to use his fish scale more often!       

Btw, you should peruse the Top Alcohol and Pro Mod sites (no kidding!) for Lenco, Bruno, Coan and other trick tranny setups, opinion, etc. JMO!

http://www.insidetopalcohol.com/showthread.php?17696-Transmission-Bruno-or-lencodrive

[jayb]

Second, I'd like to know more about the 'popping out of gear' with the Lenco. I don't see that there is anything inherent in a planetary set-up such that a coast situation doesn't work. But maybe I just don't know.

TIA for any further enlightenment.

KS

That was a new one on me too, Ken; maybe I just didn't understand what Mike was saying.  I'm going to have to ask him about that to confirm...