Does torque converter need to be below cruising RPM?

[chapel40]

Building a stroked 400 to 512. Block is ready and about to assemble it. Bought a 2800-6800 RPM cam and wondered which torque converter to use. Any suggestions? Want it streetable.

[Challenger340]

Building a stroked 400 to 512. Block is ready and about to assemble it. Bought a 2800-6800 RPM cam and wondered which torque converter to use. Any suggestions? Want it streetable.

Quick answer is a buy a good quality 11" Torque Converter, and NO... the rated stall speed does NOT have to be below the cruise rpm, because as you increase rear wheel speed the stall capability is lost.

More long winded but still simplified explanation is this:
Within any Torque Converter there are 2 types of fluid Flow... 1.) Axial Flow 2.) Radial Flow
When the car is idling in gear, or at FULL stall with the brake applied WOT, Axial Flow is 100% and Radial Flow is at 0%
As the vehicle begins to move and output speed increases, this reverses as wheel speed increases until eventually maximum efficiency of the Converter is reached at 3-4% Axial Flow and 96-97% Radial Flow (rear wheel speed).
This change in Flow ratio between Axial & Radial within the converter is dependent upon power/loads applied, but generally once highway wheel speeds are reached under cruise/light throttle the convertor is exhibited high or as high as it can deliver Radial Flow with negligible Axial Flow.

Bottom line with a well built 11" Converter is you should be able to idle in gear, remove your foot from the brake and the car will roll ahead, and accelerate quite normally under light throttle.
MAXIMUM stall speed should only be available off the line from a dead stop when the throttle trounced,(or if you hold the brake), and as soon as rear wheel speed increases "Stall" begins to REDUCE accordingly.

[John_Kunkel]

Axle ratio plays a part.

[Kern Dog]

Years back I asked this same question and got a range of answers. I went with my own opinion based on common sense and it worked out well.
I had a 9 3/4" converter that was described as being a 2500-3000 stall in my 440/493 Charger. It was a great converter for WOT action but it felt lazy at part throttle. I installed a Gear Vendors overdrive to take the 3.91 axle ratio to a more freeway friendly 3.05. At freeway speeds, it had the throttle response of a boat on the lake...very lazy unless I floored it, anything part throttle was just a sloppy response.
I pulled the converter and GV unit and went with an 11" Converter built by Lenny at Ultimate Converter Concepts. Afterwards, the car felt responsive like it should.

[BSB67]

Need a bit more info.  Start with cam specs, compression ratio, heads, car weight, gear, and the planned use for the car.  There is a big range on what people will call streetable.

[chapel40]

Thanks guys, its helpful.
Don't know what rear end gears to use. Going to have a dana 60 built. Car came with an 8 1/4
Don't mind if it lopes, shifts hard, etc. Wonder what RPM should be for cruise, I plan on adding a gear vendor OD later.
Rear tires are P255/60 R15
Howards hydraulic roller cam 296/300    600"/600"  108deg   2800 to 6800rpm
Trickflow 240 heads
Performer RPM intake, dual plane
Guessing 4200 lbs car

[chapel40]

I just want to haul butt when I hit the gas. No course racing etc, just a straight line. Rest will be normal driving, maybe a cruise every now and then.

[c00nhunterjoe]

Not to change the subject- but have you already purchased the cam? Thats alot of cam for a hydraulic roller in a mopar block unless you plan on bushing the lifter bores.

[c00nhunterjoe]

On the converter subject- ed at select converters for me. Builds a great bullet proof product that performs perfect in race and street operations. As stated, quality is the key when you are looking for a "loose" converter that is still streetable. I have an 8" select behind the 426 max, and the 440 in my charger. Both idle fine in gear and will take off with no throttle needed. Cruise and normal accel it will act like a traditional converter. However, i can footbrake the 426 to 5000 and the 440 will flash over 6 if i force it to get violent.

[chapel40]

Yeah, I believe you told me about having to bushing the lifters one time. Do you think Ill have a problem if I keep it at 6000 rpm or lower?

[c00nhunterjoe]

To do it "right" they should probably be bushed. To live on the street and run "ok", it will probably be fine.

[Challenger340]

Yeah, I believe you told me about having to bushing the lifters one time. Do you think Ill have a problem if I keep it at 6000 rpm or lower?

Depending upon Lifter Bore leakage it may not make power past even 5,000 rpm ?

My apologies here, but Engine Dyno'ing as many BB Mopar builds as we have, that's one of my pet peeves being what people think a Cam will.... or should rpm to ? Especially Hydraulic Rollers !
"Rear Wheel" Dyno's being the WORST on Automatic Cars for hiding/covering up of the upper rpm Engine power losses associated with HR's as the Torque Converter goes back into Rotary Flow/Torque Multiplication at higher rpm's to keep showing a false curve.

1.) Just because some upper rpm "number" gets posted by the manufacturer, it is only a THEORETICAL parameter that assumes an rpm "potential" based in a perfect world scenario(unlikely)
2.) A Hydraulic Roller Cam's rpm potential is entirely based in how well the Lifters can maintain pump up/transfer of the Cam profile events to the pushrod/Rocker Arm & Valve.
3.) BB Mopar Engine Blocks were never designed for Hydraulic Roller Lifters.... FULL STOP !
And no amount of "retro-fit" anything Lifter is going to A.) lengthen the Lifter Bore itself for sealing distance, nor B. Move the Oil Gallery intersection point itself within the too short Lifter Bore.
BUSHING the short Lifter Bore being the only "fix"... albeit being an extremely expensive procedure on a factory Block....
and begging the question:
WHY NOT just run a "Tight Lash" STREET Mechanical Roller type Cam instead of the HR Cam ?
They make MORE power than the HR's....
They do NOT rely on Lifter Bore seal for stability...
and,
They can be made to run pretty much dead nuts quiet ?

Anyone don't believe me... go look at the differences between factory HR Blocks vrs their NON HR Block brethren in other Engine brands, and SEE the Lifter Bore differences for yourselves.

You want to make power ?... then skip the entire "DUD" HR Propaganda and go get a tight lash street Mechanical Roller Profile.

[Challenger340]

Building a stroked 400 to 512. Block is ready and about to assemble it. Bought a 2800-6800 RPM cam and wondered which torque converter to use. Any suggestions? Want it streetable.

Howards are full of sh*t.... and you can tell them I said so !!

Ain't NO such thing as a 6,600 or 6,800 upper rpm Hydraulic Roller profile for an un-bushed Lifter Bore BB Mopar.... let be most other brands as well, ain't happen'in !
And any dork thinks he's seen one.... it was probably on a "rear wheel" Dyno !

.600" Lift on a 243* @ .050 / 296*  MY REAR !

[c00nhunterjoe]

Fwiw, my stock 440 block is bushed, i run a huge SOLID roller, on the street, with crazy spring pressures, with no problems and it makes power well past 7k. I had problems in my 302 mustang with upper rpm stability and they are factory hydraulic roller motors. She was done by 6k. I swapped to a comparable solid roller and changed nothing else and picked up 30 hp and it now made power to 7. Ets went from 11.40s to 11.0s.

[chapel40]

Well heck, I already own this whole setup. Maybe I should go down a notch on the cam like on this build. Maybe I can use the rest of the parts. Not high RPM but lot of torque down low.
http://www.dodgecharger.com/forum/index.php/topic,124503.0.html

[c00nhunterjoe]

You clearly are not listening..... best of luck with your hydraulic roller. Im out until the post build topic is written about performance issues.

[chapel40]