Torque converter

[423dak]

Ok guys and gals. I no everyone has an opinion so let's hear them. My lil Dart is running ok, but I seem to be leaving some on the table in 60'. Car has run the best of an 11.92 @ 112mph but with at 1.68 60'. I feel the car should 60' around a 1.58. Car weight is ball park 3200, 390hp at the crank, 406 torque. 28" tire, 430 gear with a 727. Have thought of the 904 but I still feel the converter is the issue. I bought from a friend that runs SS hemis so it is probably too much. I think it is a 8". Engine is a stock bottom end magnum, shifting at 6000. I also have been leaving at 2200 to 2500 rpm. I would like to know what similar combos are running for converters and what your 60' is.

 

[pettybludart]

You run an 8 inch?What stall?I run a Coan 8 inch 4500 stall,footbraking at 2200rpm my 60fts average 1.44-1.50 with tire pressure at 10psi.You might be best to pull your convertor and take it in to see exactly what you have.When ordering mine I gave cam specs,gear and tire size to match up the convertor.Good Luck.

 

[bOb shingler]

your 60's seem right inline with your et. you might try matting it off an idle to get the vertor to flash stall. which will get the rpm up higher.

 

[423dak]

No I think it should sixty better. A friend's stocker running same et is a full tenth better. It is an 8" ATI converter I think around 4500. Well that is what I was told.

 

[Locomotion]

I've heard several people say that converter flash should be around 1,500 less than what you shift at. There is more to converter science than that (more than I know), but I believe it would be good starting point. Ask your Stock class buddy what his numbers are. That's about what mine is, but I shift at around 67-6,800 and it flashes betwen 5,000 and 5,400, depending on the air temp and humidity.

I also have an Autometer playback tach which has proven VERY useful in learning what the engine and converter are actually doing instead of what one "thinks" the engine and converter are doing. They are not cheap, but it's one of the best "tools" I've bought. But I've seen rpm changes on it through tuning as well as flat spots and missed shift points.

Carb tuning can have a big effect on 60' times. Too little volume and/or duration as well as too much volume and/or duration from the accellerator pump circuit will slow you down. But it takes patience, understanding, a handful of cams & squirters and track time to get it dialed in. Good track conditions and suspension are needed to hook consistently for valid comparisons.

Jet for MPH and change squirters and pump cams for 60'-330' times.

I've had high 1.40 60' times running 11.20's at 3,540+ lbs with a 360. 904 with 2.71 low gear, 4.86 gears and 9"x30" Hoosier radial. But there are Stockers out there that do even better with similar combos. (A radial slick will usually 60' better under good track conditions. But they are more sensitive and will not be as consistent under marginal track conditions.)

A truck can be more difficult to hook because of the typically worse weight distribution compared to a car.

 

[Abodybomber]

I always build my combo one way: peak torque,to peak h.p.Usually a 1500 rpm spread.Works on all big 3 traditional combos.Considering LX guy runs,11.60,11.70s, w/ a trans brake ,with aftermarket heads,consider that.

 

[423dak]

Loco, I was hoping you would chime in here as you are running a stocker too. This is not the truck it is my new ride. Tire hook is not an issue, car is very soft off the hit. Have played with the carb a bit. Put my bothers 750 HP on it with out much change in 60. I do have a new 750 holley for CM stock. Have heard that sometime a smaller carb will help. The verter is 4500 or so but more then likely that was behind a 800 + hp hemi, which would be much different behind a 400hp 5.9l. Right?

 

[moparmanestock]

I'm running similar 360 power level with 904 and 8"ATI converter. 29.5 bias slicks, 4.56 gears in my Demon. 60' is usually 1.55 if track is prepped. I did gain both 60' and 1/8 mile performance changing to this converter. The converter stalls dead on 4600. I leave on the 2step at 2700 and shift at 5800 going through the lights at 6200.

 

[Locomotion]

Loco, I was hoping you would chime in here as you are running a stocker too. This is not the truck it is my new ride. Tire hook is not an issue, car is very soft off the hit. Have played with the carb a bit. Put my bothers 750 HP on it with out much change in 60. I do have a new 750 holley for CM stock. Have heard that sometime a smaller carb will help. The verter is 4500 or so but more then likely that was behind a 800 + hp hemi, which would be much different behind a 400hp 5.9l. Right?

Yes, there will be a big difference in converter "flash" between the engines, even between mild big blocks and small blocks. More torque will flash higher. Slippage is a factor too. But as I mentioned before, there is more to converter science than I know and 2 converterers rated the same can yeild different results.

One reason stockers have good 60' time is that we run more converter, final gear and often more low gear than other racers, sometimes to the point of being overgeared. But with all the rules restricting mods, it's a good way to make up for it as long as the entire package works together.

I've only heard of one or two CM cars running a smaller carb over the years. Not sure if it was for bottom end, to slow it down or because they just had them handy. I believe a 750 is a good size for a 340/360 if you can tune it well. I've only changed jets, pump cams, squirters, throttle blade positions and idle mixture adjustments. No passages, bleeds, etc. But despite playing with them for so long, I'm still tinkering. It seems that getting enough intial volume to squirt without allowing it to squirt longer than needed, and getting both squirters to stop at the same time, is important. Remember that leaving at a higher rpm uses up some of the volume you have available in the primaries. The higher you go, the less gas there is in the pump. But then the primary boosters are starting to flow also! Cam as well as converter changes can affect the carb tune-up so you may have to make more changes. Even a spacer change. Lots going on and each combo can be different.

All 750 carbs aren't the same either. For me, a 4779 DP wants to be run richer than the new Ultra DP carbs. Test, test, test.

 

[KX35]

I would lean more towards converter, Last year I rebuilt my 360 pump gas motor (9:1, .484 purple shaft cam, J heads) and stepped it up considerably. Fresh motor is 11.7:1 ported J heads, with a 2.05 intake valve and more cam (292/299 .508 comp hyd.) used the same converter that I ran with the old combo 10" turbo action that flashed 4200. went from 1.58 60 ft and 11.90s at 110. to 1.62 60 ft and 11.50s at 113 with the new combo flashing at 4500. After trying everything else I finally put an 8" in that is still too tight but it now goes 1.52 60 ft. and 11.20s at 117. Car weighs 3150 with me in it. 4.56 gear and 31 tall tire, I launch at 3000 shift at 6000 and go through the traps at 6200

 

[LXguy]

Having the right converter for your combo is worth a lot.

Our combinations are very similar, horsepower, weight, shift RPM and short block. I run a 3.91 gear and a 26" tire. My car consistently 60's in the low 1.5s on an 8" slick.

I run a 904 with about a 3500 stall, and I have a transbrake just for disclosure. I got my converter from Lenny at Ultimate. I leave between 2700 and 3000. I have launched it higher, but the car didn't pick up.

Given any thought to gearing it up or running a 26" tire? I've never put together a combo that did its best 60' with a 28" tire.

What kind of tire are you running? I have found a lot of Hoosier tires to have too soft a sidewall and eat 60'. However, I am currently running their 8" stiff sidewall slick and it works great.

 

[Locomotion]

LXGuy may be familiar with this, but for others....Running a wheel that is as wide or a little wider than the actual tread width of the slick can allow for using more air pressure while still maintaining a full "footprint". A lot of Stocker racers use 10" rims with 9" slicks. Depending on the car weight, HP, suspension and "hit", I've heard of pressures anywhere from 16 to 30 lbs! That helps stiffen the sidewall and minimize 60' loss from the sidewalls wrinkling too much! I run 21 lbs in my Hoosier lightweight radials.