MuscleHP

Will a high stall converter like a 4000 be okay with 2.73 gears?

I plan to cam as soon as converter is installed.

Personal experience and Input would be great

Thanks

Gabbiani

I haven't run as high as 4k. One of my customers has a 3k with 2.73 gears. Heads/cam car. Cutting 1.60s first time out on motor and low 1.5s on bottle. I think it has more in it with some seat time and maybe some suspension.

Couple times I ran it the converter felt way too tight.

The 6l80 has an awfully short 1st gear so it isn't as bad as some of the old cars.

PRE-Z06

The 6L80 has a 4.02 first gear, making your 2.73 rear equivalent to a 3.36 rear gear with a 4L65. My question to better understand if it'll be ok for you is what is your experience with having a stalled auto?

MuscleHP

I have never had a stalled auto before

Thomasmoto

If this is the case, it will take a little getting used to. It's not a huge deal. I used to daily drive a turbo buick with a 9" converter and it was fine. It will just rpm more than you are used to and you will feel it coast more on decel. When going to a hi stall be sure the tranny cooler is up to the task. You may want to add an additional cooler, maybe. I would call a few of the reputable Vette shops that do these and get their take on it for you. But, to answer your question directly, yes you can use that stall with those gears and once you do the cam I believe you will be pretty happy according on which cam you choose of course.

MuscleHP

Thanks for info! The kind of answer I was looking for

HOXXOH

Two of my racing buddies have a 4000 and 3.42 axle. They cross the stripe toward the high end of 4th. I'm running the 2.56 gear with the 4000 and cross at the end of 3rd. Assuming you run 275/40x17 tires, you'll be on the low end of 4th at the line.

It'll work OK, but it's not the most ideal ratio for the 1/4 mile. If you're not planning on running at the track real often, I'd advise a 3200 or 3600. They're a lot more street friendly. I've had all 3.

MuscleHP

Do y'all know if a 278mm circle d 3000 is a decent stall. Will I notice a big difference by going with that ?

PRE-Z06

With you not ever having an aftermarket converter before I recommend you atleast riding/driving in one before jumping to the far end of the street spectrum with a 4k especially if this is a DD? Circle D makes great converters and a multi-disk unit is recommended for locking at wide open throttle at the track for the fastest acceleration though it won't be cheapest. I would recommend a milder one like mentioned above or the 3k they did and depending on the cam size will do fine just not be max effort for the strip, an better trans cooler is a must with the extra heat from slippage and keep in mind a higher/looser stall will eat up more fuel around town if that is a concern. Them being there in your neck of the woods, I'd stop by and have a conversation with them if I were you.

jpee

When my car had only a "few" mods...(Kooks Headers, Vararam Intake, Ported STOCK LS2 intake, I have an FTI 2800 converter and my "BEST" 60' time in good air on a good track, I had a 1.60 ..60' time but in "average air and track I'm about 1.68 - 1.70

I have not had it to the track with my new set up but it should be well into the 1.5x for a 60' time (I'm using MT 305/35x18" DR...)

My best ET was 11.59 @ 118 mph ...again that was in "Ideal Conditions"

I hope (weather permitting) to go to E Town this Sunday. I won't enter and class races as it's the first time @ the track with the new motor.. I'm going to just Test & Tune.. & see where I'm at before I make any decisions on gear or converter (I'm 3.15 rear end now)

Tommy D

I think that you should be concerned with the STR of the converter. You want the 2.73, converter and cam to be efficient. depending upon where the cam makes power will determine the the best stall to torque ratio.

Below is a post taken from the GTO forum that explains what I have just stated in detail.



Generally, the higher the STR number the more it multiplies torque at the starting line or from a dig at a sacrifice of top end efficiency. The lower the STR, the more it multiplies torque over a longer period of time/longer distance at a sacrifice of short term large torque multiplication. Think of a high STR as a shell of buckshot that hits harder close range/hits all at once off the line and a lower STR like a 9mm that hits decent but effective at a longer range. So if dig racing or strip launching is important to you a higher STR will benefit, if rolls or trap speeds are more important to you than a lower STR will fit. STR range is usually 1.8-2.5.


High STR can also make the car hard to hook up. This is how it works in the first few feet:

Lets say we make 450 ft/lbs of torque at the flywheel @ 4,200 RPM. We add in a 4,200 stall, one with a tight/low 1.8 STR and one with a loose/high 2.5 STR. The STR becomes a mulitplier:

450 x 1.8 = 810 ft/lbs of torque at the trans input shaft when the car flash stalls to 4,200 RPM from a dead stop.

450 x 2.5 = 1,125 ft/lbs of torque at the trans input shaft when the car flash stalls to 4,200 RPM from a dead stop.

See why the higher STR could be harder to hook up consistently? Like stated, the other difference is that the lower STR verter will keep that torque multiplied for a longer time than the big STR. So its all about where you want your power and where you use it the most. If you have trouble hooking up for a reason you cant solve with DRs or suspension, maybe consider a lower STR to get the car off the line.

How about the guy who wants a "driveability" converter in the 3,200-3,600 range that hooks up decent? He may want to still consider a lower STR depending on where his cam makes its power. I.E. lets say we have a 3,400 stall but a big cam that starts the meat of its power band around 4,200-4,400. In that case a lower STR (like 1.8) will still multiply some torque by the time it gets to that engine speed where as a big STR (2.5) combo'd on that same cam will be less efficient and have far less multiplication by the time the car hits that engine speed.

Nitrous and Boost are also better mated to a lower STR converter. You'll often here people saying not to run too large of an STR with nitrous because it will "blow through" the converter. The big STR verters are simply too loose and nitrous would be wasted through the converters slipping action. I.E your going to become good friends with the rev limiter. As far as boost, you want it to build as much pressure as possible in the shortest amount of time so you dont want the engine to flash up so fast before it has a chance to build boost and boosted cars are usually top end cars and low STR verters are better suited for that (once again because of the torque multiplication over a longer period of time). Also boosted applications make a ton of low end torque and a high STR converter could aggravate a traction issue.

Shift extension is another variable to consider. A higher STR verter will give you a higher shift extension (the point your engine RPMs fall to after a shift). A higher shift extension may be more beneficial to those with a monster cam that builds all of its power up high. Example: My 2.5 verters shift extension right now is 5,000RPM. Meaning, when the car shifts the RPMs only fall to 5k and climb back up. Technically, my car is a good example of a mis-match currently since it has the stock cam. However, I spec'd the converter for a big 240+ duration can and dont expect to have the stocker in there forever.

Another thing to consider is high STR converters get their high multiplication from slippage. Slippage causes heat. Heat causes 90% of automatics to fail. I wouldnt recommend a high STR verter for a DD car. Example: I have a ~2.5 STR loose 4,200 stall in my bolt on Goat. Built trans, Derale deep pan w/ cooling tubes, stainless braided -6AN trans lines going to a top of the line Derale Atomic Cool 400cfm fan equipped trans cooler and DEX VI (better heat tolerance than DEX III). My trans cooler fan is auto on @ 180'F and off @ 170'F and lets just say once the fluid hits 180 (and it will) I never hear the fan turn off. Its not uncommon for me to see 200'F temps cruising around town not even hammering on it. Comparatively, my buddies '00 Camaro that is lighter, has a tight 1.8 STR 3,400 verter with a basic B&M supercooler as his only cooling mod sees 170'-175'F in 100'F ambiant temps all day long.

So after all that how is a high STR even good and why do people use them? Because they simply PUNISH the street/strip in an all motor scenario from a dig. The high STR converters simply out 60ft the tighter converters all day long for N/A all motor setups. Take my car for example. Its just a bolt on car with maybe ~370whp if I'm lucky. 3,770 race weight, 275 DRs on stock 17s and stock suspension and I routienly pound out high 1.6s and low 1.7 60fts. ROUTINELY. Its not a fluke, nor a "great launch I had one day!" or any of that, its pretty much every time I launch track or street, I run record bolt on GTO stock suspension 60fts. When I blow the tires through the entire first gear I still get 1.9 60fts. This is all in +1,500 to +3000 DA, I could only imagine if I had some of that -1,800 DA east coast goodness.....but I digress. Its all due to the brutal torque multiplication off the line, plain and simple. High STR/stall speed cars are also a blast to drive. It will make your car VERY LOUD if you have a loud exhaust as it is going to be slipping all over the place and causing higher RPMs at lower vehicle speeds. I.E. Off the line and all the way till 4th gear lock up, around 20% throttle my car sits at 3K and sounds like one long gear where you cant even hear or tell if it shifted. People love it. Out of all the bad *** cars at shows/meets mine gets noticed all the time as I roll into the parking lot and the car is at 2,500+ RPM but doing 5MPH as I lumber it into place. Like to rev at people but have an auto? Big STR/stall speed is your ticket. I can throttle pop in gear at a stop a good 500-700 RPM with the car barely even budging and cruising at 40MPH unlocked I can usually rev about 1,500-1,600 RPM without the car moving as well (this will vary with gear ratio, vehicle speed and stall speed...etc). Like to do burnouts? Big STR verters will HAMMER the tires. You've never seen the limiter hit so quick. Learning how to launch a big STR car is a feat in itself. But my point is, with a big, loose converter an auto car is anything but boring to drive.

However, if you have a high STR on a low stall speed converter (2,400-3,200) you probably wont notice much "looseness" in it due to the low stall speed. Also, "loose" and "tight" are subjective like driveability. People have different definitions for what is loose, tight, too big, too small...etc. The best thing to do is try and find a friend with a stalled auto and get a ride and experience the differences.

How do the mfgs figure STR? A good converter shop can give you a close estimate of your STR but actual STR is something only very few builders have access too. Precision Industries claims to have the capability. Other than that it takes a machine about the length of a building and other than PI stating they have a machine, I'm pretty sure only the major auto mfgs have the others. The formula for STR is: exact output torque ÷ exact input torque = STR. Like I said, a good shop should be able to ballpark your stall fairly close. Some may even tell you an exact number but I know Circle D doesnt guarantee a number they just give you their closest estimation. Converter mfgs control STR by modifying the geometry of the turbine and stator blades inside the verter.

So there you have it. Lots of stuff to consider when buying a torque converter for your combo. All the good converter shops know this stuff and your going to want to listen to what your converter builder has to say about your setup. At least now you'll be armed with a little more info to ask them about and I hope you have a better understanding of why they are telling you that you need a certain converter or not. Remember not to take any of my info as gospel and to communicate your goals FULLY to your converter builder as far as driveability expectations, 60ft, trap...etc as the good builders know whats best for your combo.