So I am a new member to the forum...referred here from a long time member. I just recently introduced myself in the 4cyl section and put some info on my car in that section...so rather than restating it here, here is the link to my introduction and vehicle info: https://www.theturboforums.com/smf/index.php?topic=120377.0

For those who don't go look at that info I have a turbo 4cyl front drive car with an auto. My issue at the moment is not being able to build much boost at the line before launching.

One major limitation that I have that most others dont have to worry about with automatics is the lack of having a transbrake. Because of the physical size (or lack of size is more like it) of the transaxle layout of the valve body and size of the reverse band the transbrake becomes useless...the car will not hold. With that said...I have been using a line lock on the front wheels to hold the car while at the line. I have made some tweeks to the tune a little bit and have been making a little progress with building boost (3-5psi) at the line while on the line lock and 2 step But am wondering if any of you have some tuning tricks or other thoughts to help the car build boost while at the line AND/OR tricks on trying to get the car to come up on boost harder after launching.

I am fortunate enough to be using BS3 in the car along with the MSD Digital 7+ T box....so tuning is fairly unlimited.

The car is and has been primarily a bracket car...however have run some heads-up stuff as well. the car has been 11.3 @ 132 with a 1.98 60'. 132ci motor with a 60-1 .82a/r
My goal is to be able to get the 60's down to the point where the car will run 10.7 to 10.5 with the combo it has. I know some of you reading this are thinking hit it with some nitrous and be done... but i would rather NOT to that to get the car to the 10.7ish mark due to some of the rules in a few classes i plan on running in '09 (since the sport compact series has died we are getting forced to run some more traditional series with more strick power adder rules etc.) I have already ordered a vacuum pump that I plan on plumbing into the brake booster to allow for maxium vacuum at the booster to allow me to put as much break pressure as possible to be able to hold the car on the line lock with out pushing through as rpm and boost increases.

Any thoughts on some things i can try to help the car build boost and or come up on boost sooner after the car launches????? anything would help!!!! Thanks in advance!

(I'll try to get some in car vids loaded up so you can see what the car does as it comes out of the hole)

 

Re: Starting Line Spooling tips... looking for some of your thoughts on my dilem

pull timing to build the boost then add it back in as it builds it to build torque. more torque=higher stall=more boost. from what i understand anyways. i dontk now much about the bs3 though.

 

Re: Starting Line Spooling tips... looking for some of your thoughts on my dilem

Its an auto. I would play with the timing. Auto's should be anywere from 34-40 deg a the line. The a/f usally end up from 12.5 to 13.5, but work your way up to see what your car likes. BS3 has a chart to add timing only on the trans brake/linelock

 

Almost forgot if your not using the 2step start using it. Will make more boost on it if your brakes will hold.

Nice clean build by the way. 132mph out of a 60mm with it being new and all. Impressive

 

What are you running for a converter?

 

Not 100% I understand why not transbrake. The band is not big enough, or can't operate ? Can you exteranlly engage with a solenoid ?

If none would work, can you stick another caliper on the fronts ? that's a popluar trick around here with the guys running big turbos. They use it to pre build boost before the t-brake, but may work good for you. Smaller bore size in the MC ?

 

Another option besides a vacuum pump is to use a hydraulic booster if you have a PS pump still. GM stuff used em a good bit. Or if you wanted to get into a mess (dunno if you do or not) a power master from an 85.5-87 GN/T-type is electrical.

 

Hydra boost brakes work great until you kill a motor at 140mph. You won't have hardly any brakes.
The 86-87 powermaster's have several times failed on the big and caused some crashes.

If you are pushing the brakes like 10secgoal said duel front calipers would probably be the way to go.

 

Thanks for the feedback everyone. The torque converter that we are using....(get ready for this one) is a modified Daewoo converter from a 2000 Daewoo lanos. These converters were the loosest converters out of the box for our application...i believe a 240k factor....I believe now after being done it is at 260k.

to help clearify the transbrake issue as to why we do not have one is the reverse band is not large enough to hold the vehicle when applied. I would say in comparison to a C4 or a T350 or T400 or Glide the reverse band is probably about 1/4 of the width if not smaller...and it is a 3 peice design...very hard to picture i know but if you looked at one you would think to yourself how the hell do these things go in reverse at all!!! Transbrakes have been used on the larger 4t65 transaxle that is used in the GTP's etc and they had external soleniods to activate however like I said the reverse band in the 4t45 transaxle we use just wont cut it.

I will look into the dual front caliper deal... that is actually something i never thought about...any pics of someones dual front setup? I have also thought about the piston sizes on the master to try and add to the brake pressure as well so I will have to start digging for masters. The Vac pump idea has actually be around with some of the other racers we know with similar combo's and that was why we thought hell might as well try it.

I know one of my big limiting factors is probably the converter...however i dont have many options. I have spoken with some of the big name converter company's and most of them have given me prices that would make you fall over gasping for air. I know the sport isnt cheap but I think i would rather exhaust some other options first before making the investment into the converter for now.

Keep all the ideas coming... im open for just about everything. I put this post in here to see if any of you had some tuning tricks etc for the boost building issue so if any of you have any other tuning ideas do share as well! Thanks again everyone in advance

 

A K factor of 240? holy crap that is a loose converter. I think the highest stall GM ever stuck behind a V8 was along the lines of 140.

 

I know... very loose as far as K factors go... i think it would be like an 8,000 rpm stall behind a v8 car Gatta love 4 cyl cars that make no low end torque thats the only way they can get the factory heavy 4cyl cars to feel like they have any balls

 

How much are you able to stall or flash that convertor? That will make a difference. I have tested both a 2step and timing retard on my turbotbird. It is a stickshift so I can't load the motor at the line. With the 2step, I could get around 10psi at the tree. With Megasquirt launch control engaged to pull timing down to -10 degrees, it spools up to 15 psi pretty quick. If I drop the timing down to zero, it builds 22-23psi at the tree! My clutch didn't want any part of the 22-23psi clutch drop, lol....Time for a better clutch!
If you can set it up with a momentary switch to pull 10-15 degrees at the tree, you should be able to get some decent boost at the tree.

 

Re: Starting Line Spooling tips... looking for some of your thoughts on my dilem

here's a bit of info from left field. i have a jatco auto behind my datsun 280zxt. i brake boost mine in second gear then drop it in low to leave. for reference i get a 2.0sec 60ft leaving in low at 3000rpm and 4-5psi. with the drop to low from second i get a 1.6-7sec leaving at 5000rpm and 15-20psi.

question: is your transmission like the saturn auto whereby you can control the line pressure via a pwm controller (think higher stall) and shift gears by enterqizing solenoids?

 

Not a bad idea at all, the thought crossed my mind but kind of ruled it out...but i think i might try that in the driveway at the shop and see what i can get out of her, Thanks!...i'll keep you posted on that. Transmission is like the saturns, luckly i have BS3 and have full trans control along with the msd programmable shift controller so we have full adjustability of the trans. could def try messing with line pressure...altho we run max line pressure to help with trans life...however maybe dropping pressure while staging would help...i'll have to try that as well.

As far as stall... in 1st gear i can get 3,000 out of it...havent tried in any other gear so that might be the ticket...will def give it a shot this week...i'll keep everyone posted

 

If you're pushing through the brakes your problem isn't a tuning one, it's with the brakes.

Don't worry too much about line PSI on the brakes, although it will help as well, you need surface area and leverage. This means bigger pads, or dual calipers as was suggested above, and bigger diameter rotors. To increase the pressure to the caliper you can go to a larger diameter master cylinder, and you'll have to do that if you go to dual calipers.

What about switching to the larger trans to get the brake?

 

Ive definitely been looking into the dual caliper swap and a bigger master... just been searching for the right combo for packaging purposes. Switching to the bigger trans is a bigger option however not one in our future. We have been getting support from Hydra-matic in the form of build transmissions as sort of an r&d exchange so we will be sticking with this trans to provide them the info they are looking for.

Swapping to the bigger trans creates a packaging problems as well as the engine bay in the J-body's are very small.

 

I had another thought, what about a boost side wastegate? That would allow you to get the turbo moving air w/o making a ton of actual torque and pushing through the brakes...

 

Re: Starting Line Spooling tips... looking for some of your thoughts on my dilem

At 12.9 AFR iI have Burnt pistons in an Iron headed pontiac.

So be careful and sneak up on the tune.

 

might be a stupid question but what about holding the E brake at the same time?

 

Clutch cars like timing retarded to build boost , Auto cars like LOTS of timing to build boost.....I would kep adding timing in the low boost/vac areas to help bring it up harder.