Factory High Stall Converters
And the original post was .....
In a recent post Duster Daddy mentioned a Factory High Stall used on the 1974 Duster 360 can anyone give me any info on this? Also was there a high stall available for the 340 and if so what was the stall??
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A street high stall will be something like a 2400 to 2800.
Depending on the size of your engine, the performance you are looking for, the weight of the vehicle, rear gearing, and hiway cruising speed with or without a Lock-Up; something in that range will usually be just fine.
However small, low-compression engines with big cams that have a very late intake valve closing angle, will have so little torque at zero mph, that sometimes even the 2800 is too low of a stall.
Stall speed is the quickest easiest, and cheapest way for a streeter to blast off the line.
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For example;
lets say you have a stock shortblock Smoggerteen with 340 heads and cam. Your compression ratio comes in at say 7.5, and with the cam installed at split overlap, the Ica is 66*.
At 900ft elevation, your Dcr is gonna come in at around 6/1 and CCP is predicted to be 105psi.
This is a very sick combo. And I'm trying to prove a point here.
This will take off like a slanty.
>Now suppose this combo makes a measly
51hp/150tq at WOT at 1700 rpm. Lets use a 904, and 26" tires, and 2.76 gears. And finally, at zero mph this TC at this stall, at 1700rpm, might have a TM ratio of 1.5.
So then; At zero mph; to the road, this will put;
150 x 1.5 x 2.45 x 2.76 x 24/26 = 1352 ftlbs into two tires (Sure-Grip), so not a snowball's chance in hell it will spin the tires.
>Some to most guys will immediately swap out the 2.76s for lets say 3.91s for a City car. The new numbers are;
150 x 1.5 x 2.45 x 3.91 x 24/26 = 1990 ftlbs, still no chance.....
>Now lets get rid of that 1700TC and install a 2800.
Lets say the power at 2800 has risen to
140hp/260 ftlbs. and at this power level, let's say the convertor ratio is up to 1.6. The new numbers are;
260 x 1.6 x 2.45 x 3.91 x 24/26= 3680, so now we got a good amount of tire-smoke.
>We could actually give some up in order to reduce hi-way rpm. Lets try 20% or so less gear; say 3.23s, the new numbers are
260 x 1.6 x 2.45 x 3.23 x 24/26 = 3040 just about right for 245/60-14s .
>But what this combo really needs is waaaaaaaay more CCP. Lets bump it up to 150psi, keep the 2800 and go back to the 2.76s
Lets suppose the power jumps to
180hp/338Tq, and the TC jumps to 1.7 ratio; the new numbers are;
338 x 1.7 x 2.45 x 2.76 x 24/26 = 3587 ftlbs
And that friends is why I never recommend to install stock 340 heads and cam into a stock shortblock smoggerteen. 3587 annihilates 1352
>Lets give up some stall, to reduce tirespin, lets go to 2600. Lets say the hi-compression 318 now makes
165hp/333tq, and the TC ratio falls to 1.65; so ;
333 x 1.65 x 2.45 x 2.76 x 24/26 = 3430 Very good.
So what I did here is show you how to take a POS combo, and make ripper out of it, either with stall or with gears and or with proper cylinder pressure.
Lets go back to the first combo, but keep the 150 CCP. This would be
180hp/338tq/1700tc, and 2.76s
Ok but at the new Compression level the stall becomes say 2200 with a ratio of 1.55. At 2200 this 318HO makes say
120hp/286tq, so
286 x 1.55 x 2.45 x 2.76 x 24/26 = 2767 It will bust the 245s loose, but don't back out of it! lol. Compare this to the first combo, namely;
150 x 1.50 x 2.45 x 2.76 x 24/26 = 1352 ftlbs into two tires (Sure-Grip), so not a snowball's chance in hell it will spin the tires.
The only difference is the CCP going from 105psi to 150 psi, which pushed the stall up, and the TM ratio with it.
Now,
I made all the numbers up for illustrative purposes, and I cannot say how accurate the power progression might be. But, IMO, the exercise ends up saying the same things, namely;
CCP is King.
then stall
then gears
some combos are just not a good idea.
Yeah yeah, 20 guys will crawl out of the woodwork and brag on their low-compression 318s being the bees knees with the 340 top end. But they are invariably not telling you the whole story.
Ask them about the Stall and gearing, the vehicle weight, cam-timing and valve lash, and at what roadspeed it finally wakes up.
Even if somebody gave me a nice set of prepped 340 heads and a brand new 340 cam kit, I still would not install that on a low-C 318..... cuz
Bin there done that, and more than once too, so
IMO
some combos are just not a good idea..
BTW; at 105psi such a combo will NOT be fuel friendly either.
There has to be at least a thousand better 318 combos. Maybe 10,000..
BTW-2
the stock smogger teen makes about 135psi at 900ft @8.0Scr, and if you put a 2800 and 3.91s on that you will have a better First gear ripper, and probably to 50 mph; than the 318/340 top-end/lo-stall combo, with the typical 3.23s. And with 3.55s the stock teener/2800 still makes great fuel economy for the ripper that it is.
I know, off track again.........
