Whats for Launch?

[0966Sy]

I'd like to bring up a few thoughts about launching our trucks at the track to determine a combination that results in the best 60ft's and ET's at the track. As there are so many determining factor's i'd like to gather info regarding Footbrake vs Transbrake, 2-step's and Torque converter stall speed efficiancy. Selecting the right TC. I dont want to discuss suspension, tires just a discussion of the above. There are alot of guy's going fast on a FB (footbrake) spooling the turbo against a high stall speed converter. Anyone going fast on a TB (transbrake) with a lower stall speed?

I think our turbocharged V6's with a low rpm redline are overestimated on stall speed when selecting stall speed of a torque converter. Seems to be that everyone thinks the bigger the turbo the faster the ET. So when choosing a big turbo, automatically one is to assume they need a high stall speed to spool there large turbo.

Most of us judge our stall speed based on brake stall when boost launching. When our actual stall speed would be higher at flash stall, when at WOT against the brake. Both situations cause wheel spin limiting your stall flash. So accuratly testing stall would be against a TB, not allowing the TC to hold back engine peak torque.

When selecting a stall speed you want to select based on your engines peak torque RPM, no more. If anything 500rpm less.

So wouldnt we want to select our stall speed based on our engines ability to make max torque and launch at that RPM to gain the best 60ft and ET? So many fast trucks come off the line spinning becuase they are launching at such a high RPM? Lowering launch RPM closer to stall speed would result in better traction and using the engines ability to ceate torque throughout more of the rpm range of the engine.

What data do we have from a stock SyTy Dyno with factory TC/turbo?

 

[0966Sy]

Re: Whats for Launch?

For example someone choose's a 2800 stall speed convertor for there combination and can not build boost untill 3200rpm. They would consider that a "loose" TC, when thats realy not the case. A turbo I have read can actually increase stall speed 500-700rpm depending on the engines peak torque curve.

My syclone ran .50 second slower using a PTE52/2800TC than it did with the PTE52 and stock TC. So the larger the turbo actually will increase a TC's stall speed?

So if you could leave the line at 3200-3500rpm with the same amount of boost as another truck leaving at 2200-2500rpm same engine performance, wouldnt the truck leaving at the lower RPM utilize more of the engine's torque curve than the truck leaving at the higher RPM?

 

[0966Sy]

Re: Whats for Launch?

So here is a good example I dug up in a search, everyone remember's this im sure. So at 3000rpm making 750ftlbs of torque why would you select anything more than a 2500stall TC. Im not sure on the status of this truck but i would bet it would beat out alot of the bigger turbo trucks on this forum given the combination and power level. The ultimate launch RPM of this truck at the track would be 3000RPM, correct?

Just finished engine dyno testing a customer's combo that was an interesting build, with a little different combo than the "norm"". The details:

4 Bolt Mains
Cryoed Crank
Short Block Fill
Eagle Rods
Diamond Pistons
Custom Cam
Ported L35 Heads
Stock Intake / Exhaust Manifolds
Modded 20g turbo with 14cm exhaust housing and a 61mm Compressor wheel


Dyno results:

91 Octane pump gas/ 15 psi - 438HP / 560 Ft.Lbs

109 Octane Unleaded - 23 psi 560HP / 760 Ft.Lbs

C16 Race Gas - 24-25 psi 593HP / 791 Ft.Lbs

With 109 and C16 the engine made 750 Ft.Lbs at 3000 rpm and usually power peaked (with any fuel) in the 4800-5000 rpm range.

 

[Aeroking]

Re: Whats for Launch?

I would set aside wheelspin, that can be solved with better traction (tires, weight transfer)

Say make peak torque near 3000, however like mentioned the larger turbos need a higher stall for initial spoolup. This can be alleviated with an aid such as a 2step, or some kind of anti-lag device. Which would allow you to spool at a lower speed, and hold the engine at a set rpm near peak torque. This can only be achieved if your set launch rpm is below the stall, you would get better torque multiplication.

Also to stay consistant, you should use a multistage boost controller. This coupled with the antli-lag would allow you to find and adjust peak torque output for launching.

in my unprofessional opinion.

 

[0966Sy]

Re: Whats for Launch?

I completely agree but am trying to help understand the diversity in choosing stall speed when using a TB vs a FB. When your stall is working efficiantly i have been told your FB and TB luanch will yeild same results. Leaving at a higher RPM on the TB while holding your peak torque RPM.

I think many trucks running the popular 2800 stall convertor is overkill for there application. The popular 9/11 TC gets a loose feel for most being that it is to much stall speed for there application.

 

[Beavis]

Re: Whats for Launch?

This is a good thread. Alot can be learned and shared here.

So my question would be, wouldn't the torque multiplication be higher and better with a TC that has a flash point between peak torque and red-line (shift point)?

When ordering my TC, one thing I was asked was what is my shift point, because they said my stall should be approximately 1800-2000 rpm under my shift point........

 

[bezerk]

Re: Whats for Launch?

it all depends if you want to make it a full out racer or be happy to make 1/4 mile numbers at a good time at a DD status.

i rather have a fast truck on the streets than i can do 'on a roll'' kinda stuff. i hate lag!

my old build was vortec heads bla blah. 412 cam with a pt61 and i ran 12.8 first time on the track ontuned. it was quite fast, and spool up wasn't to bad with the vortecs heads |(2800 stall).

but than i build another truck with a pt67DBB vortec heads and 3k Stall and that thing doesn't feel halve as stupid driving around halve throttle. becasue there is no lag and from a roll it's more powerfull. and a did a 12.0 at 16 psi with poor traction..

for track i could have been ****ing around with stall and set happy times, but the last truck makes a shitload of more HP and don't want to change the DD thing against my track times.

 

[0966Sy]

Re: Whats for Launch?

This is a good thread. Alot can be learned and shared here.

So my question would be, wouldn't the torque multiplication be higher and better with a TC that has a flash point between peak torque and red-line (shift point)?

When ordering my TC, one thing I was asked was what is my shift point, because they said my stall should be approximately 1800-2000 rpm under my shift point........

This is another good point to consider is the length of multiplication in 1st. If you look at it this way is the easiest for me to explain. Say you have two identical builds like listed above. One launch's at 3000rpm and the other launch's at 4000rpm, the one launching closest to the max torque would be utilizing more of the power curve at launch making torque multiplication in 1st the longest.

 

[0966Sy]

Re: Whats for Launch?

When ordering my TC, one thing I was asked was what is my shift point, because they said my stall should be approximately 1800-2000 rpm under my shift point........

So if you shift out of first at 5000rpm and select 2000rpm below that puts you at 3000rpm. Ive been told that a turbo can add 500-700rpm to your stall speed selection. So wouldnt selecting your stall at 2500rpm be the best choice and choose a turbo size based on your engine build/stall speed to spool the turbo fast regardless of street or track?

So why would someone choose a 3200-3500 stall speed that with a turbo isnt going to stall untill 3500-4000rpm on an engine with a 5000-5200rpm redline?

 

[Beavis]

Re: Whats for Launch?

One of the other questions they asked was "since its a turbo'd motor, how much torque does it make?" I think they built it based on those 2 items more than anything. If the T C builder knows/understands turbo torque curves, they shouldn't they be able to build it so it won't have that 500-700 rpm variance?

 

[0966Sy]

Re: Whats for Launch?

One of the other questions they asked was "since its a turbo'd motor, how much torque does it make?" I think they built it based on those 2 items more than anything. If the T C builder knows/understands turbo torque curves, they shouldn't they be able to build it so it won't have that 500-700 rpm variance?

As a general rule of thumb …when the turbo just starts to build boost is really what should determine what stall speed that you will need. The converter needs to have a high enough stall to enable the turbo to spool. As the turbo spools, it will build boost and more power. This added power will increase the stall speed and continue the spooling process. It is not uncommon for a turbo to pull the stall speed of the converter up an additional 500 rpm. If the converter is sized properly with a turbo application, you will get the best of both worlds; a low stall speed for good drivability in off-boost conditions as well as a higher stall under boosted conditions that will give you great performance. With a properly sized converter combined with a turbocharger, it is possible to have your cake and eat it too.

 

[Beavis]

Re: Whats for Launch?

So if you shift out of first at 5000rpm and select 2000rpm below that puts you at 3000rpm. Ive been told that a turbo can add 500-700rpm to your stall speed selection. So wouldn't selecting your stall at 2500rpm be the best choice and choose a turbo size based on your engine build/stall speed to spool the turbo fast regardless of street or track?

So why would someone choose a 3200-3500 stall speed that with a turbo isn't going to stall until 3500-4000rpm on an engine with a 5000-5200rpm redline?

Somewhere in this equation turbo efficiency and cfm comes into play also. You may not be able to get the turbo/motor combo into proper efficiency (rpm,cfm) by keeping it at a lower stall like 2500 even if it stalls higher than rated. I know alot of guys go with bigger turbos for the cfm, not because they want to run higher boost. Some have actully lowered their boost level with new/bigger turbo because of efficiency/cfm.

Like I said, this thread should be good.

 

[Beavis]

Re: Whats for Launch?

When I changed out my 700/stock TC for my 80E/2800 Precision Ind TC, everything about it felt better. Even with the lower 1st gear, the higher stall took alot of lag out of it even at lower rpm/off idle light driving. It feels a little loose down low, but that could also be because of the gear change. I might of been able to go with a 2600, but am very pleased on how it feels now.

 

[0966Sy]

Re: Whats for Launch?

Somewhere in this equation turbo efficiency and cfm comes into play also. You may not be able to get the turbo/motor combo into proper efficiency (rpm,cfm) by keeping it at a lower stall like 2500 even if it stalls higher than rated. I know alot of guys go with bigger turbos for the cfm, not because they want to run higher boost. Some have actully lowered their boost level with new/bigger turbo because of efficiency/cfm.

Like I said, this thread should be good.

It would be like adding a turbo so large it takes you all of first gear to get it spooled, adding a TC that stalls at 3500-4000rpm just to spool your large turbo is just about eliminating first gear all togather. You are launching at almost redline, even if you have 10psi on hold at 4000rpm with minimal torque curve considering you put it to the ground.

Not to mention how long you spend on the FB to reach 10psi smoking your tranny regardless what trans you run 80e, 60e or 700r

It reminds me of this honda i saw on the dyno that made like 500-600hp with a massive turbo, absolutly no torque and took all the way to redine in fourth to make that power.

I think people tend to choose so large of a turbo for there engine builds and spend less time thinking about spooling it, instead they just opt for a 2800-3500 stall converter to spool it fast, but for what? 1500rpm in first gear. Pretty much creating a fast spooling highway roller and sacrificing torque multiplication off the line which is what these trucks are known for.

Why bother with a product that is usually considered an integral part of the drivetrain not the engine package?
No other component affects the way a motor/vehicle combination makes power like the torque converter. Like every other part of an engine combination the torque converter needs to match the engine curve.

 

[SYCLONE#1531]

Re: Whats for Launch?

Im using a precision 3 (3400) disc with my stock cammed long block. All stock suspension and just ran 11.40s with it. Launching at 3200 spinning. Anything lower and the truck seams to slow down. I just changed from a 2800 10 inch and ran a best of 11.70. The new 3400 seamed to really wake my stocker up. Just needs some caltracs and front drag rads to get it into the low 11s.. Looser was definetely better in my setup. From my experience, the looser convertor allowed my truck to spool and launch alot better than the tighter conv. 16lbs on the line if needed!:rotf: vs the 3.5lbs for the 2800. Also, if you manually lock your conv slippage should not be a issue..in 2nd, 3rd, 4th..

New mods for the new year will be a Caltracs, frnt drag rads and PT6766 turbo!
My pt61mm will be forsale soon! Like new with aprox 500 miles on it!

 

[TYTILIDIE]

Re: Whats for Launch?

I'll give my two cents here since it something I have played with quite a bit. I have a big cam, 2.02 Vortecs, 67gtq turbo. When I was running the 700r4, we stalled out at about 3750. With was with foot on the brake and I was launching with about 9psi. I was cutting a 1.78 60' with some wheel spin. (this is on Sumitomo street tires) Now when I went to the 80e, we asked for a 3600 stall but something was wrong with the converter we bought so we threw an actual stock 80e converter in there. Couldn't build ANY boost at all from the line. The top end felt pretty good.

Now when the new TCS converter got here with the 3600 stall, we put it in and it ended up stalling out around 3800. We are launching the truck at 10psi and are cutting a 1.79 60' for some reason with no wheel spin this time.

IMO, if you have a larger turbo, 2500 stall isn't going to get you off the line. FWIW, I didn't lose any top end with the higher stall (at least it didn't feel any less, in fact, it felt a bit better). I also wasn't able to make as much boost on the top end with the lower stall converter. My point is this, if a turbo "requires" you to have XXXX stall to spool, its saying this because they know that the wheel wont spin to the necessary point unless there is X amount of force pushing it, force you're not going to get with a lower stall speed.

We tried a 3000 stall converter in Abe's Ty and it needed to be restalled because it wouldn't make any boost with the Stealth 70. After the re-stall we were launching at 4k with some wheel spin. However, at 3000rpm, we were only at 3psi. 3 psi, at this altitude, doesn't really get you out of the hole very fast.

Bottom line is, you need higher stall with bigger turbos so that the turbo can actually spin faster. I don't think you will utilize the turbos potential with a lower stall. Just my opinion.

 

[0966Sy]

Re: Whats for Launch?

Im using a precision 3 (3400) disc with my stock cammed long block. All stock suspension and just ran 11.40s with it. Launching at 3200 spinning. Anything lower and the truck seams to slow down. I just changed from a 2800 10 inch and ran a best of 11.70. The new 3400 seamed to really wake my stocker up. Just needs some caltracs and front drag rads to get it into the low 11s.. Looser was definetely better in my setup. From my experience, the looser convertor allowed my truck to spool and launch alot better than the tighter conv. 16lbs on the line if needed!:rotf: vs the 3.5lbs for the 2800. [/B]

What rpm did you build 3.5lbs with your 2800? What was your launch boost rpm with the 2800?

What rpm and boost are you launching at with the 3400?

 

[0966Sy]

Re: Whats for Launch?

I'll give my two cents here since it something I have played with quite a bit. I have a big cam, 2.02 Vortecs, 67gtq turbo. When I was running the 700r4, we stalled out at about 3750. With was with foot on the brake and I was launching with about 9psi. I was cutting a 1.78 60' with some wheel spin. (this is on Sumitomo street tires) Now when I went to the 80e, we asked for a 3600 stall but something was wrong with the converter we bought so we threw an actual stock 80e converter in there. Couldn't build ANY boost at all from the line. The top end felt pretty good.

Now when the new TCS converter got here with the 3600 stall, we put it in and it ended up stalling out around 3800. We are launching the truck at 10psi and are cutting a 1.79 60' for some reason with no wheel spin this time.

So what are your times? What do you mean when you say big cam? a 67gtq is quite a large turbo, should make for 10second truck?

I can cut 1.7 60's in my stock Ty all day long on radial tires, and im launching at 5-6psi at roughly 2800-3000 on a stock TC.

 

[SYCLONE#1531]

Re: Whats for Launch?

I was footbreaking 2800+ on the 2800. Just wouldnt spool. This was a cheap generic conv off of ebay. The precision I launch at aprox 3200 and 8 to 10lbs. With the precision, boost comes on pretty fast! Precision says they use a special designed stator for faster spool up for turbo applications.

Launch video
http://www.youtube.com/user/westfabrications?feature=mhee#p/a/u/1/vfWOz6Y4InA

 

[0966Sy]

Re: Whats for Launch?

I want to see what people that are cutting 1.4's and 1.5's are doing for there launchs. A stock truck can cut 1.7 60's. Every tenth counts and it starts at the launch.

I would say using a transbrake, 2 step and a 2 stage boost controller are some of the key factors. How do all of these affect your launch RPM/spool time. What stall speed convertor are you using?