auto vs manual transmission boosted application

[srixon4406]

Here's my dilemma I converted my 62 valiant from auto to manual trans for my /6 turbo build thinking I could control my boost better but I'm having serious doubts if I made the correct decision what's your opinion on that
This car will be a Street strip running around 15 psi

 

[Bill Dedman]

Here's my dilemma I converted my 62 valiant from auto to manual trans for my /6 turbo build thinking I could control my boost better but I'm having serious doubts if I made the correct decision what's your opinion on that
This car will be a Street strip running around 15 psi

I have not commented on this because it's YOUR car, and YOUR project, and I have a lot of respect for you and your considerable fabrication skills... and having said that, I want to say that the following is JUST MY OPINION, and I have no hard data of any kind to back it up. It's a somewhat educated guess, at best... so, take it for what it's worth.

IN MY OPINION, for the following reasons, I think the slant 6 with a turbo is better off with a torque converter automatic (904) in 99-percent of the cases. If I were building a car for the Bonneville Speed Trials... top speed... it would have a manual transmission, for sure.

I can't imagine, unless your primary concern is fuel economy, why a manual transmission would be the bettter choice. Here's why...

It is obvious to me that there's something a little "different" about how turbocharged /6s make their power. Let me explain that: Both Tom Wolfe and Ryan Peterson (owners of two lightning-quick turbocharged /6s) contend that their cars perform better at the drag strip with final drive ratios in the 2's... like 2.76:1. They say (and who am I to argue?) that the slant 6 with a turbo LIKES to be "held back" and makes more power that way. They contend that testing has proved that out.

An automatic traansmission will be "holding back" the engine 100-pecent of the time, in a drag race. There could be a problem with a 4-speed (manual,) keeping the turbine spooled during shifts (while the clutch is in), even during a power shift, because there's no load on the engine. I think the very last SRT-4 Neons had something in their computer program to deal with that... but, I never learned what it was...

Launching can be a problem for manual transmission cars because it's difficult to load the engine to make sufficient boost for the launch without burning the clutch up. There may be other ways to deal with this that I am not aware of, but the right stall speed converter is a boon to solving that launch problem with an automatic.

Slant 6's with turbos make outrageous amounts of mid-range torque, and I am sure it would not be easy to find a clutch setup that would live, given the drag strip load that a strong, high-boost /6 could generate.

The cams that work well in boosted /6 applications have minimal duration, and therefore, idle smoothly. Because they have gobs of low-end torque, their street manners are impecable. And so, there's no need for a manual tranny's clutch to allow the engine to get up into an rpm range where it makes sufficient torque to pull away from a stoplight on an uphill grade, as happens sometimes, in street driving.

The consistency of an automatic is said to be an advantage in Bracket Racing, which is where these cars (boosted slants) will be racing IF they race. NHRA has no class for them.

It looks to ME, that a turbo /6 motor really NEEDS a 904, to realize its many advantages.

Like I said, that's all just MY opinion; your mileage may vary...:hello2:

 

[srixon4406]

Bill thanks for the great input when i first started this project i had no idea the direction i was going to take but i always wanted a four speed mopar so it was a no brainer when i first started working on the toad i figured i build a nice 12 second street car.Well Bill now that im ALL IN and have plans on installing a full roll cage,turbo header,and my new turbo.

I do have a 904 in the shed and a brand new rev manual vavle body in a box in the garage ill have to dig it out. Maybe ill pull them out and start to clean things up. What sjze torque converter are u running,do u no what Shaker,and Ryan are running? Ryan runs a 727 i can get a cheap /6 727 for next to nothing. I no the 904 is a bit lighter then a 727. Whats your thoughts on that ive always heard the 904 built right is as good if not better then a 727 but honestly ive always had big block cars and only run 727.

Bill i wish u and Freddie lived up north with u two's knowledge and my fab skills we could do some damage and get both our car together. WISHFUL THINKING I GUESS

THANKS AGAIN FOR THE GREAT ADVICE
AARON

 

[dusterdan]

i'm very curious to hear other members' opinions on 727 vs 904 i'm like you srixon4406 i've only driven BB in the past with 727's and while bullet proof, there's a little weight disadvantage!

 

[Bill Dedman]

Bill thanks for the great input when i first started this project i had no idea the direction i was going to take but i always wanted a four speed mopar so it was a no brainer when i first started working on the toad i figured i build a nice 12 second street car.Well Bill now that im ALL IN and have plans on installing a full roll cage,turbo header,and my new turbo.

I do have a 904 in the shed and a brand new rev manual vavle body in a box in the garage ill have to dig it out. Maybe ill pull them out and start to clean things up. What sjze torque converter are u running,do u no what Shaker,and Ryan are running? Ryan runs a 727 i can get a cheap /6 727 for next to nothing. I no the 904 is a bit lighter then a 727. Whats your thoughts on that ive always heard the 904 built right is as good if not better then a 727 but honestly ive always had big block cars and only run 727.

Bill i wish u and Freddie lived up north with u two's knowledge and my fab skills we could do some damage and get both our car together. WISHFUL THINKING I GUESS

THANKS AGAIN FOR THE GREAT ADVICE
AARON

Aaron,

All of that advice I gave you is based on what I've been able to learn from folks with experience; our car is still not quite opertional, yet, so consider that when evaluating what I say... okay? I am, at best, a keyboard jockey/slant 6 dilettante, with only second-hand knowledge to share...

But, I have heard several things from a diverse group of people with no axe to grind, and one thing I have learned about Mopar automatic transmissions is this: a 904, built right, will easily handle 500 foot pounds of torque, and live. I do have personal experience with that issue; my Vortech supercharged (10 pounds of boost) 360 Magnum makes over 500, and I have a 904 in it that shifts crisply at full throttle, and never complains. It has a lot of drag racing starts on it, and shows no sign of giving up. Going on 16,000 miles...

WHAT I HAVE HEARD from several sources, is that on a V8 car, a 727 has enough extra rotational inertia that it eats enough horsepower (compared with a 904) to cost you anywhere from a tenth to a tenth and a half. On a /6, that could be two tenths...

Seems to me, there's just no reason to give away that much performance.

My California friend, Len Schneider, who builds converters and transmission for drag racers, (and who built my 904,) contends that the rotating mass in a 727 is so heavy that IT (the rotating mass) is what tears those transmissions up, not the power going through them... The instant starting and stopping (on the gear changes) of the (heavy) drum, damages the clutches and band more than holding the torque... plus there's the 727's problem of the problematic sprag anchor in the back, that, unless modified can cause one to explode... No such issue with a 904.

I am convinced that at least, with these /6s, transmission choice is a no-brainer...

You only live about 100 miles from Tom Wolfe. He has forgotten more about turbo /6's than I, or Freddie, will ever know. His car flies... You two guys should really get together over a hamburger; you'd have a LOT to talk about... Just a 2-hour drive...

I am 72 years old; the Michigan cold would kill me... I lived in Butte, Montana for 3 years, and Des Moines, Iowa for 16... I know what cold is... LOL!

Our torque converter is a stock-diameter 3,000rpm stall unit. I have no idea how that will work with this engine. I asked Tom how much stall speed he was running, and his answer was, "How much do you want it to be??? It keeps increasing the more I push the accellerator down..."

Such is the mid-range torque of these things... LOL!

I don't have any advice for you on that question. I may, once ours is operational with the turbo. But for now, I just don't know.... sorry.

I have noticed, in an Australian video, that turbo slant 6 guru, Cameron Tillley, runs a 4-speed in his /6 turbo car, but his e.t.'s don't look very good, for the mph he turns. Check it out on You Tube, if you haven't, already.

I'll stop beating the 904 drum, now... LOL!

Good luck with your 10-second /6 project. Sounds like it may be a good, close race for your '67 'Cuda once iit's sorted out, if it runs like it should. Take your time!!! And, keep us posted!!!:hello2:

 

[CUUDAK]

My intentions were to go 4 speed..... Well,
That has since changed since Monday.... I went to my buddies house the other day, the one that really wants this 4 speed! He set me up so when I arrived the 727 case with bolt in sprag was sitting near the front door of his shop. Its getting a reverse manual valvebody and a 2800 stall.
He convinced me!!! I am going with the 727 full manual automatic.

I am sure the 4 speed would have been fun on the street but I have a few friends that need their asses cracked by a streetcar! Their S10's and Luv trucks run in the mid to upper 6's in the 8th so I fully intend on ripping them!! LoL!

 

[srixon4406]

Cuudak I went in the shed today and pulled out a 904 I had put up also I dug a new rev manual valve body out of a box I've had put up for over ten years lol final I might put it to the test. So I might just change the toad back to a auto
Aaron

 

[CUUDAK]

Cuudak I went in the shed today and pulled out a 904 I had put up also I dug a new rev manual valve body out of a box I've had put up for over ten years lol final I might put it to the test. So I might just change the toad back to a auto
Aaron

I have heard of those 904's holding up pretty good in drag racing. Never seen them though. I know with the auto I won't be loosing boost when shifting! It should be a nightmare to drive! LoL!

 

[player1up]

Aaron, Remember when I asked what kind of clutch you planned on using for your t/6? I was asking because my 6psi half running t/6 ripped right through the clutch....I've replaced the clutch with a Ram clutches puck style 10" clutch, but have yet to get the turbo back in. I will say that my old clutch had signs of oil contamination, but I'm hoping that the new clutch will handle just the 6-8psi I plan to run. As for lag during shifts, yes it does lag, but with the turbo you wont need to have the thing at full throttle 90% of the time doing speed shifts to keep up with traffic ( it's that much faster )
As for the auto, I'm kinda wishing I had it in there now myself, but I'm committed to the 4 speed...

 

[srixon4406]

Aaron, Remember when I asked what kind of clutch you planned on using for your t/6? I was asking because my 6psi half running t/6 ripped right through the clutch....I've replaced the clutch with a Ram clutches puck style 10" clutch, but have yet to get the turbo back in. I will say that my old clutch had signs of oil contamination, but I'm hoping that the new clutch will handle just the 6-8psi I plan to run. As for lag during shifts, yes it does lag, but with the turbo you wont need to have the thing at full throttle 90% of the time doing speed shifts to keep up with traffic ( it's that much faster )
As for the auto, I'm kinda wishing I had it in there now myself, but I'm committed to the 4 speed...

Player I remember that conversation that's what I assumed u had a problem with a clutch I have decided to convert the TOAD back to a automatic I had a good 904 in storage that I cleaned up and went through also I've been holding on to a rev manual valve body I installed so as for that I just need to pick up a torque convertor and a rev pattern shifter and then FIGURE A WAY TO COVER UP THE DAMN HOLE I PUT IN THE TRANS TUNNEL and ill be in business
the reason I decided to change may setup was a full roll cage kit kind of fell into my lap and the weird vibration in the motor/TRANS not sure which on its coming from but I said f it if I have to pull the motor again I m going to set it up and shoot for ten's
plus I was alittle worried about a 35 plus year old TRANS coming apart or even a new clutch next to my legs
Aaron