djm_e22

iTrader: (2)

His peak torque is at 4400rpms and peak horsepower is at 5800rpms

djm_e22

iTrader: (2)

Definantly agree. When I had my m6, my same buddy said to launch at my peak torque. I said no I will bog. Sure enough I did. But when I launched close to my peak horsepower no bog. I tried to tell my buddy that peak horsepower does win in the end. Because your torque may be falling but your rpms our increasing so you are still performing more work every second. Of course your torque will eventually fall to fast that the increase in rpms won't produce more work and that is when the horsepower finally starts to decrease.

OneBadTA

Its not just about a peak number, you gotta look at the entire tq curve. Just because it shows a max at 4400rpm doesnt mean its not making alot already at a lower rpm. You could see 500tq @ 4400rpm and be at 450tq from 2500rpm and up. In that case, you would want the stall being around 2500rpm cause your already seeing majority of the tq.

djm_e22

iTrader: (2)

Yeah but 2500 rpms is alot less rpms compared to 4400 rpms. So if your car can move 600lbs 4400 times every minute you get 2640000/minute. If you do 500lbs 2500 times you get 1250000/minute. In other words the additional rpms with that 600lbs of torque creates more than double the amount of work in the same amount of time.

OneBadTA

So you want to stall the car at 4400rpm at "peak tq" and leave that large area of already made tq behind? If you stall the car too high you will destroy the tq curve by leaving so much of it behind. We all need to see a dyno graph of the engine to make a real assumption on what stall is needed. Were all kinda pissing in a lake here without seeing the real information.

SexyTransAm

iTrader: (6)

his "transmission guy" is a ****** retard

djm_e22

iTrader: (2)

First off I told him 4000. But if he was going for street/strip a 3500 stall should be fine on the street as long as he has a good tranny cooler. By the way horsepower is better than torque like explained above with my 6 speed I would bog at my peak torque but at my peak horsepower bog was completely gone. I will get his dyno sheet I think his peak torque was at 4400 and peak power was 5800. So torque did not drop off to fast since his horsepower kep climbing.

OneBadTA

Heres a graph i found online. Not sure what engine it is but whatever, lets look at it. Where would you place the stall? At 4700rpm where the tq peaks, or more around 3600rpm where the tq begins to make its rise, then plateau, then fall? Maybe im wrong but i wouldnt stall it at peak tq because just after the tq is falling pretty hard. You stall it at 3600rpm and your already seeing alot tq and has a good bit left to keep accelerating. Should launch hard and keep pulling for a while, compared to a hard launch then falling flat on its face from the loss of tq. 4000rpm would probably be even better.

OneBadTA

A stick car launch is totally different. The only way to compare a peak tq launch is by using a 2 step, going full throttle at your peak tq rpm and let out the clutch. I had a turbo car with anti lag and had to do it that way to get it up on boost for a hard launch. Same principles apply to a NA manual car. You only see peak numbers at WOT.

djm_e22

iTrader: (2)

I did use a 2 step and the more horsepower did not bog. But the whole point is I garantee the guy would say the same thing for a small block. He said the same thing to my other buddy that has a small block 400. Which was "a loose converter will help on launch but you will lose at the end of the track because of loss of horsepower. Matter of fact the transmission guy knew nothing of how much torque that this guy made or the torque curve and he still said the same thing. I'm telling you he just thinks plain and simply a tighter converter will win. By the way aren't most races won in the first 330ft?

Wicked94Z

iTrader: (26)

read my post on the 2nd page. Drag racing is about horsepower, rpm and gearing.

OneBadTA

Ah ok i understand it a little better now

1961ba427

iTrader: (26)

I think someone already said it but, without more info about gearing and traction, who could make a real recommendation? I do know that a 58 Chevy truck isn't light by any means. Someone else hear may have a more similar combo to your friends, but this is my convertor experience with my 433/TH400/4.88:1 Twelve bolt combo in a 61 Bel Air.

Engine is 13.5:1 cr, aluminum rods, CC solid roller
278*/282* @ .050" lift - .714"/.680" - 110* LSA - 106* ICL
675 HP @ 7,400 RPM - 550 ft/lb @ 5,600 RPM - flywheel numbers

The car is lightened some and I run on MT 28"x10.5's

When I originally put the motor in, it had stock suspension...which is a three link. The lowers are much like fox mustang lowers where the coil sits on the LCA, then it has one upper offset on the RH and a panhard bar to center. Comp Cams suggested a minimum 5,000 RPM convertor. They said anything else and the car would be a dog and I'd be lucky to get it moving at all.
I had a TIGHT 10" convertor that was built for a big displacement nitrous motor that I installed. I knew it would stall much less than they recommended (ended up being barely over 2,000 on the foot brake) BUT I also knew that the car was at it's limits as far as traction based on my old 468"/2800 stall combo. (a much milder engine to say the least)
I went against what the "experts" recommended because I knew the car would do nothing but blow the tires off if I used the stall they suggested.
With the TIGHT convertor I ran 7.30's @ 96 MPH with only a 1.74 sixty foot hooking good, but lazy for a good 20' out.
The MPH shows enough power to run high 6's at least if I got the sixty foot down in the 1.5X range. If I had installed the 5,000 stall, IF I had even been able to run the same 1.7X sixty foot, the car would have been slip sliding all over the track.

Since then I have re-worked the rear suspension with Meto Billet LCA's, UMI double adj UCA's (two of them now), adj PHR, chunked the original coils, and fabbed up my own design upper shock crossmember that bolts in and allows me to run Chassis Engineering adj aluminum coil-overs. The UCA's also have adj mounts I fabbed that allow changing the instant center. Along with this, I went to an 8" - 5,500 rpm stall. Even with all these changes, the car still runs about the same 60' yet it's spinning a good 30' off the line and breaking lose on the 1-2 shift. Hoping fine tuning pinion angle and instant center will solve some of this.

So many variables in choosing a convertor that someone really needs to know the car (or truck) to pick the right one.

djm_e22

iTrader: (2)

I appreciate your opinion, but I am tired of y'all talking about traction. The transmission guy said "a higher stall will help your take off but you will lose at the end of the track cause of the lost in horsepower. So he expected him to get traction. Plus with nitrous yes you would want a lower stall. In other words if you wanted to have your stall set at 4000 rpm with nitrous you need a converter that stalls at many 2700 NA. So that does not mean you don't have a stall converter of 4000, it just simply means you have a stall converter of 4000 with nitrous.

1961ba427

iTrader: (26)

I said it was a nitrous convertor. I never said I used nitrous. I run NA. I also stated the convertor only stalled to about 2000 rpm on the footbrake.
Anyone who thinks traction isn't a MAJOR concern when choosing a convertor on a 600 lb/ft TQ big block drag application obviously has ZERO experience with it. The transmission guy "expecting" him to get traction is about like Comp Cams expecting my stock suspension 10.5" 61 to get traction with the 5,000 stall they recommended - - ideally it would be nice, but it wasn't going to happen.
YES a loose and inefficient convertor will slip enough to cost you a few MPH (more in the 1/4 than the 1/8th)
But to think a 2500 stall will be better given the dyno numbers and rpm's you stated for his combo (assuming that your trans guy is correct and he has traction) is hilarious. Give us an update if/when he puts a convertor in that actually stalls near 2500 and tell us how he does. Will it be quicker than a low torque small block? Maybe so...but it will still be nowhere near it's potential. If he is planning to run in one of those "real street tire" classes where they don't allow even drag radials like is gaining popularity then a convertor that lets him leave well below where his engine starts working so he doesn't fry the tires would be good, but that is about the only time.

1961ba427

iTrader: (26)

Maybe his transmission guy's only experience with 10" or smaller convertors are the cheap, sorry ones that slip so bad that they soak up a ton of power. Just because two convertor are both stall at 4000 rpm doesn't mean one won't be extremely more efficient.....with an E.T. and MPH much better than the other....as well as slipping much less at part throttle.

djm_e22

iTrader: (2)

Thank you. That was the answer I was looking for. By the way that was 600lbs at the flywheel. By the time it goes through his th400 and 9" it will most likely be mid to upper 400. These numbers plus with a heavy truck and with true slicks I think he should do well with traction. If not hopefully he will setup his suspenion better. My bad about the nitrous I misread it.