700R4 Build, tough enough?

[Steve Chryssos]

Right then, baby's asleep. More on efficiency:
At a red light with foot on brake, the engine is spinning, but the trans is not. Difference in rpm is about a thousand. Converters are designed to be inefficient at idle--otherwise the car would surge. So the earlier question about a 2000 stall converter combined with a big cam? Not advisable as it might cause surging.
Other extreme: The top end of a 1/4 mile run should see engine rpm and transmission input shaft rpm at about equal--not quite, but close. Pro Torque has more than a few savvy drag race customers with data logging capability showing 96, 97, or even 98 percent efficiency and that's without lock-up! These days, if a drag car is showing 85% at the top end, the chosen converter is too loose.
The difference in percentage is known as slippage. 85% efficiency is 15% slippage.
What about in between? As your street car accelerates away from an intersection, the output side (turbine) lags in rpm behind the input side (impeller). As load decreases by way of inertia, the two elements (input and output) approach the same speed. So load is inversely proportional to efficiency. And it can be said that a tighter converter is more efficient than a loose converter, all other variables being equal.

So that 2500 stall converter doesn't suddenly come alive at 2500 rpm. It has efficiency while accelerating from, say, 1200, 1500, 1800 rpm to 2500 rpm. Efficiency is present and increasing as the vehicle accelerates because load is decreasing. How much efficiency is present at a given rpm might vary from one converter manufacturer to the next. Good companies maintain a wide range of impeller/turbine/stator combinations and utilize more costly but more efficient CFD designed late model cores.

And of course, efficiency can be maximized when a converter is locked up where a mechanical clutch locks both sides of the converter together.

But there are circumstances during the acceleration phase where lock up is not desirable. It's called torque multiplication.

[critter]

So, locking up the converter in a drag racing application or in a spirited driving situation seems like a bad idea. We not only strain the clutches in the converter but we also deny the possible benefit of torque multiplication under high load situations?

[Steve Chryssos]

Like everything else in a hydraulic coupling, the answer is not cut and dry. But you stated the key word: Load. Lock up is most desirable when load is low. And as stated above, load is lowest when efficiency is peaking.
Torque multiplication occurs whenever engine speed exceeds transmission input speed. The engine side of the torque converter is called the impeller. The transmission side of the torque converter is called the turbine. So whenever the impeller is spinning faster than the turbine, torque multiplication can occur. A greater differential means greater multiplication. A torque converter has three elements: Impeller, turbine and stator. Fluid returning from the turbine is passed thru the stator which changes the fluid flow's direction and sends it back to the impeller. That returning fluid is added to the fluid coming from the impeller. That fluid plus scenario is torque multiplication. It provides an advantage when compared to a mechanical clutch. Torque can be multiplied 1.8-2.5 times.

So now the optimists might think "Great! I'll run a 5500 stall converter to create lots of speed differential between the engine and trans. That'll give me crazy torque multiplication" An the pessimists are thinking "Wait a minute! In an earlier post that dude just told me that speed differential is slippage, so I want a 1500 stall converter--and I want it locked up as early as possible."

We're using fluid to couple the engine and trans. And where there is fluid, there is the potential for turbulence. Turbulence disrupts that vortex loop of fluid in the converter. And where there's turbulence there is slippage without torque multiplication.

So there is a juggling act between stall, efficiency, torque multiplication and finally, lock up.

-At a stop light we want low efficiency, so that the car doesn't move or stall. Slippage is desirable.
-When the light turns green, we want low efficiency off idle so that the car doesn't stall. Again slippage is desirable.
-As we accelerate at part throttle, we want efficiency to increase as rapidly as possible but with as little sacrifice to torque multiplication as possible. Load decreases as vehicle speed increases.
-When we stomp on the throttle from a roll, we want torque multiplication.
-When we drive banzai at a steady 140 mph, we want efficiency. Lock up is very useful here because overdrive causes a negative speed differential. The trans (and converter turbine) is turning faster than the engine and converter (impeller).
-Same holds true at a 70 mph highway cruise, plus we want the added benefit of fuel economy. (at 140mph you have other things to worry about)
-When we decelerate for a turn on the road course, we want and can use lock up here to keep engine and trans coupled.
-When we power out of that turn, we want torque multiplication. And there's no need for rev matching. A fluid coupling takes care of that.
-When we stage at the drags, we want stall. Engine turning at stall rpm with trans at zero rpm.
-Upon launch, we want torque multiplication. High Load.
-Top end--thru the lights, we want efficiency. Low Load. Lock up at the drags is useful only if data logging confirms that it's usage is not negating torque multiplication.

Whew!

[BRIAN]

Torque converters are one of those black magic deals to me. I think the most important decision is to go straight to the manufacturer and buy the best converter you can afford. Do not buy from a retailer.
There are several co's that offer a free re-stall of the converter if you feel it is off or change your combo. i know it sucks to pull out a converter but it suck even more to pay $800 more while you are doing it.
I think the problem is the lack of 99% of the Co's ability to test effeciency or dyno their product before delivery. Most are using factory numbers and applying them loosely to their product. Some just mix and match OEM parts to obtain a stall rating and others mfg their own parts and are willing to show you the difference. This might work on track only cars but in a street car that is cycling in and out of OD it doesn't work.

Then there is the problem with one or 2 Co's actually building just about every converter out there are selling them under different names. So before you say one is better than the other you might want to check who is actually building them. Don't want to pay $400 for a $139 converter.

I have used Precision Industries and can say the converter was like bolting in a NOS kit compared to another well known Co's product. They asked tons of questions and got it right. Not cheap at about $800 but the car was an animal when I smashed it and drove like a stocker.

[Steve Chryssos]

I guess I'm a retailer, so I should take offense to that. Fortunately, I'm also a paid employee of Pro Torque. Our companies are closely affiliated, so I'm cool with that. Fill out a comprehensive torque converter analysis form HERE and the design process starts at my desk.

I think the problem is the lack of 99% of the Co's ability to test effeciency or dyno their product before delivery.

There's only one aftermarket company devoting R&D time to pro-touring cars--CFD, dyno and track. That's us. The rest are focused on drag cars and new car/truck upgrades. Our R&D can be seen
HERE:

and HERE:

and HERE:

and HERE (This one's a 700R4):

and HERE:

oh, and HERE:


The only other company investing any time in thsi stuff is Bowler transmissions.
As for mixing and matching parts, ALL torque converter manufacturers rely on "cores". Junkyard torque converters supply turbine and impellers. They are simply too complex for the aftermarket too produce. A significant amount of finish work is invested in these cores. Stators are the only critical parts that can be custom made within the scope of the aftermarket's CNC manufacturing capabilities and CFD design. And even then, many OE stators can be used as they are simply defined by the number of blades, angle and shape of blades, and open area. Again, finish work, kinda like porting and polishing a cylinder head, separates the best from the rest. Mixing and matching IS the name of the game. The only new turbine and impeller components are for 8" drag race powerglide converters based on near obsolete but desirable sixties and early seventies compacts. Obviously these turbines and impellers are irrelevant to our needs.
The difference is that cheapie converters use available cores from 40 plus years of manufacture. Stuff that was designed with slide rules. the supply side economics of 40 year availability make them cheap. Advanced manufacturers, including PI, use late model cores that are expensive but worthwhile due to their advanced CFD design. Since they are pulling from a supply side that is only 10 to 15 years old. Unfortunately, most of these converters are still out there driving around. Lower availability means that these newer cores cost significantly more. But, matched correctly, they yield that part throttle efficiency with wide open throttle torque multiplication plus an expensive price tag that you have experienced.

PI rocks. Pro Torque and PI are closely allied friendly competitors.

[Steve Chryssos]

So before you say one is better than the other you might want to check who is actually building them. Don't want to pay $400 for a $139 converter.

A few companies are buying off-shore converters. Not as many as you think. Most converter companies have two sides their business: An OE rebuild side that supplies local transmission shops and a High Performance side. The same holds true for trans shops. Very few shops are exclusive to high performance work. They make a living off of daily driver rebuilt work. Unfortunately, some transmission shops will order up a basic rebuild intended to fix a disabled Blazer (maybe as cheap as $70) and then pawn it off as a high performance piece. The converter manufacturer has no way of knowing that the trans shop did a bait and switch. As far as the converter shop knew the rebuilt converter was destined to sit in front of a rebuilt trans. If that's a concern, buy straight from the converter manufacturer and hand deliver it to your trans shop.

[Steve Chryssos]

Here's an exploded view of a MuscleDrive converter. Prices start at around $659 for a 9.5" Most of the goodies are inside the welded case, but there are still ways to tell if you are getting a serious piece. For that much money or more, your converter will have a billet front cover with integral mounting lugs shown at far left. On the other end, an anti-balloon plate has been welded into the center of the impeller cover--around the splines. The anti-balloon plate makes the surface relatively flat. The pump cover itself is a new replacement piece. The splines are billet and the machine welding is flawless. Machine welding is pretty commonplace though. The billet front cover and anti-balloon plate should be confirmed.


In contrast, the budget converter below has a stamped front cover with welded on lugs (on bottom). The dished area on top around the splines means that there is no anti-balloon plate. There's nothing necessarily wrong with budget converters. The good ones still have important internal features like furnace brazed fins and good bearings. Just know what you are getting and make sure it matches your engine's load requirements. From the outside looking in, this appears to be a $350 piece.

[BRIAN]

Steve believe it or not no insult meant to you or PT. My experience with a certain converter Co was more as you explained a problem with a tranny shop that escalated into a bigger problem than it should have. Then again Co's chose their retailers and maybe should chose a little wiser.

Few converter Co's are willing to show and explain their internals. You know as well as I do before you actually made the leap to the other side converters were a hard choice. You have to have complete confidence in the Co that they are delivering what they claim. Your R&D looks impressive and money would be well spent with your set ups. Great info and next automatic built car I will give you a ring as i think others should.

Hard to get buyers to understand the difference between a custom built unit and a Summit special. There is a magazine article???

[critter]

Heh. I was in that traffic jam on Hot Rod Power Tour in 2007 along with you guys. That is where that one image came from, correct?



So can I take this in another direction?

I've never rebuilt a transmission. I've done my own motors and restored cars but have never taken on an auto. I have a 1987 core 700 r4. Would it be possible for me to build it myself without a great deal of fear and trepidation or should I put all the stuff in a box and find a reputable local builder to trust? FYI, I make about 420hp and 500+ ft. lbs. of torque.

[6'9"Witha69]

Heh. I was in that traffic jam on Hot Rod Power Tour in 2007 along with you guys. That is where that one image came from, correct?

So can I take this in another direction?

I've never rebuilt a transmission. I've done my own motors and restored cars but have never taken on an auto. I have a 1987 core 700 r4. Would it be possible for me to build it myself without a great deal of fear and trepidation or should I put all the stuff in a box and find a reputable local builder to trust? FYI, I make about 420hp and 500+ ft. lbs. of torque.

At that level, find a good builder.

[Steve Chryssos]

Steve believe it or not no insult meant to you or PT. My experience with a certain converter Co was more as you explained a problem with a tranny shop that escalated into a bigger problem than it should have. Then again Co's chose their retailers and maybe should chose a little wiser.

Few converter Co's are willing to show and explain their internals. You know as well as I do before you actually made the leap to the other side converters were a hard choice. You have to have complete confidence in the Co that they are delivering what they claim. Your R&D looks impressive and money would be well spent with your set ups. Great info and next automatic built car I will give you a ring as i think others should.

Hard to get buyers to understand the difference between a custom built unit and a Summit special. There is a magazine article???

Thanks. Take a drive out when the roads are free of salt and I'll let you drive these things. Function will not be very different that your PI unit. The application is just more comprehensive. Computer control allows us to do more with these converters.
I think I can write such an article and do it in plain english as above. Being highly technical and potentially critical, it might be a tough sell to our industry's advertorial oriented publishers. If that's the case I'll just upload it to twistmachine.com.

[Steve Chryssos]

Heh. I was in that traffic jam on Hot Rod Power Tour in 2007 along with you guys. That is where that one image came from, correct?

So can I take this in another direction?

I've never rebuilt a transmission. I've done my own motors and restored cars but have never taken on an auto. I have a 1987 core 700 r4. Would it be possible for me to build it myself without a great deal of fear and trepidation or should I put all the stuff in a box and find a reputable local builder to trust? FYI, I make about 420hp and 500+ ft. lbs. of torque.

That pic was sent to us by one of our good friends and customers. Bob Bertelson. Out of necessity, he replaced his big brand name, mass produced transmission and converter with an RR system based around a Bowler engine brake trans and MuscleDrive torque converter.
I sincerely believe that transmission building is best left to professionals. It's an art form. Hard parts are readily available. It's not so hard to make the puzzle pieces fit together, but a true builder has a sixth sense regarding blueprinting and calibration. That's the part that can't be listed in an ad or quantified with an attractive price tag.

[Steelrat]

Wow, starting this inquiry into the 700R4 for my Nova has been an education. I appreciate all the info/advice. I am a big supporter of doing business local when I can. The tranny will be built by a local guy. I was pointed to this local company for a TQ convertor by the builder. http://www.tcsproducts.com/index.html


Advice from you has put me at about a 2500 stall, so I am thinking this is the TQ convertor for me. http://www.tcsproducts.com/details.html?id=533 or should it be this one http://www.tcsproducts.com/details.html?id=534

Cheers,
Shaun