Chris 96 WS6

iTrader: (1)

The issue of shift extension was brought up recently on my local club's board (http://www.mtfba.org/forum). The conventional wisdom seems to be that the higher stall converter, in addition to dropping 60ft times due to tq multiplication and allowing you to leave the line at a higher power level, provides for "shift extention", aka less RPM drop between shifts, keeping the car in the meat of the powerband.

Having recently converted from an a4 with 2800 stall Vigilante to an M6, I got to thinking about this "logic."

I'd like to have an honest and open discussion about the realities of high stall converters, with people providing real experience on the track as evidence of the pros and cons. Maybe some sponsors who build converters can chime in too.

My theory:

1. "shift extension" is overrated. IMO it is a code word for converter slippage, which is codeword for wasting horsepower in the form of heat all the way down the track. The ultimate converter would slip off the line then immediately tighten up all the rest of the way down the track.

2. If shift extention really helped then auto cars would trap like M6 cars, but they don't.. Usually the more stall speed you have the more MPH you give up, its just a trade off between acceleration down the track and lowering the 60ft time.

3. I'm not a believer in the giant stall stuff. I know know there are some FAST cars out there with huge stalls, but how many of them have back to back comparos with low stall, high efficiency converters? Of course a car is going to be fast with 500hp but that doesn't mean it wouldn't be faster with LESS slippage. I've also heard of other cars picking up et and MPH by going back to a stock converter... With the right gear and tire maybe you don't need all that stall unless you have so much cam you can't get it to idle on the stock converter.

4. There's no way you give up 30 hp through a converter slipping and then go faster, it is against physics. At some point the loss in power to the wheels due to slippage HAS to overcome the gain in 60ft due to stall speed. Tq multiplication is great but it only really helps you off the line, after that when acceleration of the crank vs. the input shaft of the tranny is closer to 1:1 then there's almost no tq multiplication taking place.

5. It is said that shift extension will increase your acceleration down the track. However, the more power you put to a converter the more it will slip, which is why the same converter will stall higher in a big block car vs a 305 TPI. You stay at a higher RPM but the tradeoff is you slip to do it. I'm not so sure that the tradeoff isn't 1:1...in otherwords, after you factor out the HP wasted in slippage I'm not sure there's any more power going to the wheels than there would be at the lower RPM and no slippage.

6. It is also said that shift extension makes a car faster from a roll. It would only make it faster if it quit slipping after it shifted, which it doesn't. If the shift extention really helped then a high stall car should be the equal of an M6 car from a roll. I think from a roll you'd be better of in a stock stall car, because it would slip less and be more like a 1:1 engine/trans output ratio. There's a reason guys try to lock up their converters going down the track, and if shift extension was really beneficial then nobody would be installing manual lock-up switches on their automatic cars.

7. I think "shift extension" is just a gimmick used to sell tq converters. Let me rephrase that...its a gimmick used to sell INEFFICIENT tq converters, because a good efficient one would actually drop more after the shift rather than slipping.

Please feel free to prove me wrong with comparison data. I'd love to see if my intuitive reasoning is correct or if I'm way off.

josh99ta

iTrader: (1)

Subscribing. Good post Chris. I'm on the other side of the fence after seeing alot of the bigger stalled, high MPH A4 cars, so it'll be an interesting discussion if we get some knowledgeable people chiming in.

blue2000Z28

thats good stuff, I just bought a Vig 4000, so I am very intrested...Let the talking begin!!.....

Roarin_8

iTrader: (5)

I know that the automatic won't trap as high as the M6 because its heavier and there are more moving parts. My car does a hell of a lot better from a roll than with the stock converter. I say in order to see which car does better from a roll, you would have to get 2 cars that trap the same, one being a stalled A4 & stock stall A4 and one being an M6. Then you can see the difference.

I didn't lose any mph with my stall. I trapped 104 in 89 degree heat at Island dragway in Jersey with the stock converter, then went to Raceway park in Jersey, 89 degree weather and still trapped 104 with the new converter.

blkZ28spt

Wanna bet? Happens all the time.

Take this example: A couple years ago I dyno'd 319 rwhp through unlocked stock converter. I then added a TCI SSF3500 and ran 12.6 @ 106.5.

This past winter I added a cam (TSP MS3) and dyno'd 343 rwhp, yet I ran 12.2 @ 111.

Comparing dyno numbers and track times I gained 0.4 and 4.5 mph, with the only additional dyno output being 24 rwhp.



It's basically a fact that if you have an M6 and a stalled A4 that dyno the same and are otherwise equal, the A4 WILL win. Better launch, shift extension and consistency all play a part.


Another thing I like to point out is that comparing trap speeds doesn't tell the entire horsepower story. Last night I ran 11.95 @ 112.7. There was an M6 LS1 running ~12.8 @ 114.X. So, the M6 trapped roughly 1.5-2 mph higher while being way off on ET. If I were to continue accelerating past the end of the 1/4, by the time he crossed the line going 114.X I would be going even faster than that. Just because a car traps higher that doesn't necessarily mean it has more horsepower.

MNR-0

Converters are all about torque, not horsepower. Peak dyno numbers are irrelevant when discussing high stalls. Simple fact is when comparing two equally setup cars, 1 M6 and 1 A4 with a 3500 stally, if both take off the line at 3500RPM the A4 will win over the 1/8 due to increased torque multiplication and the fact the gear changes are instantaneous. Now over the remainder of the track the M6 will start pulling in the A4, but has to work harder to do it, as the A4 already has the jump. It takes 1.5x more HP to rein in at the top of the track than it does to gain it in the 60'. My bet is the A4 would still win, trapping a few tenths less and with less MPH.

Then there's shift extension. An A4 only uses 3 gears. An M6 uses 4. So the A4 wants to maintain RPMs in the peak power band. Aside from diff gears, shift extension will keep the TQ up, but you will lose HP due to slip. Still, the TQ gains outweigh the loss of HP, as at the shift extension RPM, you are pulling more horsepower but less efficiently - BUT ITS STILL MORE.

A4 racers know this well.

Chris 96 WS6

iTrader: (1)

That's apples and oranges. Show me two cars that put out the same CRANK HP, one m6 and one a4 with high stall, and the M6 car will trap higher. It might or might not be quicker because of 60ft.

Either you didn't read my post or you just totally missed my point. if you hold 60ft equal, going from a 2800 for example to a 4400 I bet a car would be slower because more HP is lost to slippage....IF 60ft were held constant.

blkZ28spt

Look again. I was replying to a direct quote that was part of your post, and I believe what I said was relevant.

You offer to pay to have the engine pulled from two cars, dyno'd, and reinstalled (making sure they are the same horsepower and torque with the same curves) and then we'll talk. Easier said than done, in other words.

You are correct, the M6 will likely trap higher and the A4 will likely be quicker. What's your point? It's about who gets their first, not who can go hit the highest speed in a given distance.

Saying "if you hold the 60 ft equal" is a pretty big if. I know you are aware of that, but that is a BIG if.



Is your main beef with the "shift extension"? I think you got a little busy in your first post. If so, some of what you are saying does make more sense that way....

Oh yeah, anyone who thinks a stock stall is better from a roll obviously hasn't driven or ridden in a stalled auto.

Chris 96 WS6

iTrader: (1)

Not all A4 racers apparently. Remember I used to be an A4 racer myself. I know that is what we are TOLD about converters, but I'm not sure I buy it. if you could 60ft the same with tire and gear w/o the big stall I believe a car would be faster with a stock or near stock stall than with a super high stall converter.

I just don't see how shift extension helps. Sure you're in a higher power band but you're slipping more, I think it equals out at best.

And I think my argument is taking the 60ft out of the discussion.Of course A4s 60 better due to tq multiplication, that's why they can out ET M6 cars. But my entire point here is that perhaps the super high stall is costing guys more accerlation down the track than they gain in the 60ft. At what point does the scale tip for that equation? Is there a point where there is too much stall speed and the slippage down the track outweighs the 60ft gain?

And its not all about TQ. TQ is work. HP is work over time. More HP to the wheels means you theoretically can do the same amt of work (1/4 mil) in less time. Only in the 60ft can an A4 gain on the M6 car,assuming the M6 driver can shift quickly.

I suggest that if you had two equal crank HP cars, one M6 and one A4, and both had the same effective final drive ratio, that the M6 car will always have greater acceleration due to the direct 1:1 linkage from the clutch. The A4 slippage will cause the A4 car to lose acceleration because HP is bled off through heat (which is why you need a tranny cooler with high stall converters). The more stall speed the worse this gets.

Show me two equal crank hp cars, one A4 and one M6 where the A4 out accelerates the M6 from a roll.

blkZ28spt

The M6 will lose more RPM between shifts, and the available power will therefore be lower than the A4 when it shifts. It is interesting to try and figure out where the extra slipping losing some of the power offsets the fact that you are at a higher RPM.

Chris 96 WS6

iTrader: (1)

No crap dude...I'm aware what a "win" constitutes in drag racing.

My entire point here, which I apologize for not making more clear, is: Are A4 guys giving up ET and not realizing it because they are going with huge stalls to maximize 60ft, when they might be able to 60ft almost or just as well with the right gear, tire and a smaller converter and then pick up ET with better down-track acceleration.

My main "beef" with shift extension is I'm not sure it actually does anything except prove you're slipping more down the track than with a tighter converter, and all that tells me is that you are wasting HP that could be used to accelerate the car and pick up ET.

THink about all the M6 cars you've ever raced. I've raced tons of them. I'd kill them out of the hole and then on the top end they start reeling me in. Well imagine if you could 60ft just as well with less stall, but then since you're not slipping so dang much they don't reel you in quite as fast.

My question I put forward for debate (which again, I seem to have failed to communicate in plain english) is simply I wonder if there are significant top end gains to be made by not going so extreme on stall speed.

Maybe there's a rule that could be tested, like perhaps if you get to the point more stall speed doesn't drop your 60 ft, stay with the lowest stall that gets you that 60.

I can't believe a 4400 stall car puting down 1.5 60s would ET better than a 3500 stall car putting down the same 60s (all else being held equal, like car weight and crank HP).

Chris 96 WS6

iTrader: (1)

You guys seem to think I'm trying to flame A4 racers. No. Autos are the better way to go quick at the track. I gave mine up for durability and fun issues, but I gave up quite a bit of ET because I can't drive a manual worth a damn.

I'm just wondering outloud about the true worth of high stalls. If you can get a great 60 out of a smaller stall I would think you'd be quicker because you'd preserve your top end accereration rather than wasting it away on excessive slippage.

blkZ28spt

Assuming I could run a 3000 stall and somehow 60' just as well as I do with the 4000 stall I think I'd still be quicker with the 4000 due to shift extension due to the size of my cam and my relatively high gears. I see your point more clearly now.

How much of the mph difference between an M6 and A4 is due to the fact that the A4 is under acceleration for a shorter amount of time?

Chris 96 WS6

iTrader: (1)

Also keep this in mind. I'm not comparing M6 to A4..that's not the argument here. I'm using M6 trap speeds to illustrate a point, because you could imagine the M6 as the same as an a4 car with a zero stall speed converter.

My real comparo I'm trying to make is a low stall vs. a high stall. The M6 is just to demonstrate a point about the advantages of less slippage meaning more power to the wheels and therefore more acceleration.

blkZ28spt

I don't think the lower stall would do better, even given your conditions. From what I've seen there isn't a big difference in horsepower output between two different aftermarket, high stall converters. If the lower stall is still high enough to sixty very strongly it will probably be eating nearly as much power as the higher stall converter. (given otherwise equal converters)

Yank

iTrader: (181)

there is a dyno from a dead stop to redline of the stock converter and a YANK SY3500 in the same car the SY converter make more power thruout the range so this is why you go faster from a stop or from a roll

Chris 96 WS6

iTrader: (1)

Say again? I'm not sure I understand your point.

The A4 stays in each gear longer since it only uses 3 of them vs 4 for the M6 through the traps. The A4 loses less acceleration between shifts but the M6 in 3rd and 4th gear is the "payoff" where they really accelerate while the A4 is slipping its way to the traps.

I think its a really good question at what point the slippage for shift extension ends up slowing you down because you're putting less Hp to the wheels than you would be at a lower RPM w/less slipping.

blkZ28spt

What I'm saying is look at the MPH in terms of time to speed instead of distance to speed. The A4, or higher stalled A4 in your test case, is accelerating for a shorter period of time, therefore trapping higher when it takes you longer to get there doesnt necessarily show a higher rate of power application (ie horsepower)


The question I pose based on that, is how much of the higher MPH of an M6 (or lower stall speed a4 in your case) is b/c of more time to accelerate?

Chris 96 WS6

iTrader: (1)

Thanks to YANK for some factual data.

I can gaurantee not all companies can produce a more efficient higher stall converter.

My big question is how do you do it? It seems to me knowing the basics of how converters work that you get stall by making the fins shallower and therefore creating more slippage. To make it more efficient and still stall higher seems to go against physics.

I know a smaller diameter converter can stall higher w/o as shallow a fin angle. But there's obviously an upper limit to how small of a housing you can run and still have adequate flywheel effect and clutch surface area.

Chris 96 WS6

iTrader: (1)

Ahhh, yes, I get it now. I see your point, but again it goes back to the 60ft. I still wager most of the gain is in the 60ft from the converter. Yes its the accepted method to get to the traps quicker, but I'd love to measure ET from 61 ft to traps in a huge stall car then the same car with a 2400 or something.

I'm not saying I have the secret to ET or anything, God knows there are no shortcuts to going fast and if everybody's doing it its probably because it works. But I just thought this would make an interesting discussion.