building boost on footbrake?
building boost on footbrake? Struggling to build boost on footbrake and need all suggestions. i know there is tons of threads on what is recomended but would like to hear from real world proof that just plain old works. combo in my signiture. ptc converter speced for my combo seems to flash to 3800 and i can get it up to 3400-3500 on footbrake before it wants to push threw them. can only get 5-5.5 psi and just holds there. 20 degrees base timing and hit 2 step at 3400 rpm and it bounces back and forth from 8 degrees to 20 with a 300 rpm soft cut. this was with 112 octane and water meth and normally i run pump gas with water meth. dont have meth spraying til 14psi. was on 2 step wot for over 5 sec and just seems to hang at 5-5.5 psi. I need like 8-10 and fairly quick not in 8 sec. any help thanks in advance. only change from last time to track is Forced inductions s476r billet etr ho turbo with 92 turbine and 1.10ar t4. last turbo was s476r turbo with 87 wheel and compact housing from APT turbos.
If you can, try pulling timing down to zero once the map stalls out (won't go any higher). My combo was worth 3-4 psi only changing timing on the two step from 10 to 0. Only caveat is that have to wait to pull the timing out. If you drop the timing before it's up on the converter, it might not make enough torque to get you there.
My timing is set at -10*, 2-step at 3400, and if I remember correctly it's a 150 rpm spread. I make 8-9 psi fairly quick. This is with MS3 as well.
Here's an in car video. Skip to 30 seconds.
Here's an in car video. Skip to 30 seconds.
My timing is set at -10*, 2-step at 3400, and if I remember correctly it's a 150 rpm spread. I make 8-9 psi fairly quick. This is with MS3 as well.
Here's an in car video. Skip to 30 seconds.
https://www.youtube.com/watch?v=OdSqiWthdkA
Here's an in car video. Skip to 30 seconds.
https://www.youtube.com/watch?v=OdSqiWthdkA
My timing is set at -10*, 2-step at 3400, and if I remember correctly it's a 150 rpm spread. I make 8-9 psi fairly quick. This is with MS3 as well.
Here's an in car video. Skip to 30 seconds.
https://www.youtube.com/watch?v=OdSqiWthdkA
Here's an in car video. Skip to 30 seconds.
https://www.youtube.com/watch?v=OdSqiWthdkA
Is this done by hitting 2step and mashing gas and brake. Or do you build it up and than pulling timing once revs are up. I'm gonna have to post up my timing table and see what everyone thinks. Tried 34 degrees and pulling 10 out still 4-5 psi. Hoping it is tune related and not because I have bigger turbine wheel. May have to step down to 2" hot side from my 2.5. I have built 7.5 pounds on footbrake before just not with this turbo.
Is this done by hitting 2step and mashing gas and brake. Or do you build it up and than pulling timing once revs are up. I'm gonna have to post up my timing table and see what everyone thinks. Tried 34 degrees and pulling 10 out still 4-5 psi. Hoping it is tune related and not because I have bigger turbine wheel. May have to step down to 2" hot side from my 2.5. I have built 7.5 pounds on footbrake before just not with this turbo.
I hit the 2-step button, pump the brakes a couple of times, and mash the gas to the floor. The timing isn't pulled until it reaches the 3400 limit. It pulls it down to -10*, not just subtracting 10 from where it is. At least that's what I think it is doing, ha. I am by no means an expert with this either, just offering up what seems to work for me with my combo. I'd think you'd be able to get similar results though.
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If your brakes can’t hold more power, that’s all there is to it really.
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
If your brakes can’t hold more power, that’s all there is to it really.
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
If I was pushing through brakes at 5 psi I'd be more worried about brakes. But this issue should be tune related I would hope. I made 7.5 psi with old turbo at 3400 and that's where it starts to push which is fine cuz I can cut a 1.46 60ft with that but 2 psi less and it cuts a 1.75. I should not have an issue making more than 5 psi on a 2 step at 3400-3500 rpm. May just make a trip to kp tuning and throw on dyno and work the bugs out.
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Dual rear calipers are almost a necessity for good foot braking.
We don't use a bump box, or anything like that. Foot brake, leaving all the timing in it till get its to about 1psi of boost, then it starts to pull the timing down to the launch boost/timing setting, then as soon as the button is released.. it ramps it back in.
The slew rate dictates how quick it gets put back in also. I have a data overlay video that I posted in here yesterday, or I have an In-car video that can show how he does it from inside the car, without data.
We don't use a bump box, or anything like that. Foot brake, leaving all the timing in it till get its to about 1psi of boost, then it starts to pull the timing down to the launch boost/timing setting, then as soon as the button is released.. it ramps it back in.
The slew rate dictates how quick it gets put back in also. I have a data overlay video that I posted in here yesterday, or I have an In-car video that can show how he does it from inside the car, without data.
Is the motor making more power at less boost now? What you’re saying isn’t making sense to me. The brakes can only hold “X” amount of power back. Regardless of boost pressure. So the motor must be making more power at less boost if the brakes aren’t holding it to 7lbs anymore.
Is the motor making more power at less boost now? What you’re saying isn’t making sense to me. The brakes can only hold “X” amount of power back. Regardless of boost pressure. So the motor must be making more power at less boost if the brakes aren’t holding it to 7lbs anymore.
My issue is I can't make more than 5 psi on the footbrake. It is not pushing through the brakes at all. Maybe if I was able to build more boost than 5 it may start pushing but that is not the issue I'm having yet. When I push through the brakes I will address that. My whole reason for this post is about changing settings in the tune ( timing , fuel, 2 step, etc. ) to help build more boost on the line. Maybe even do a 2" hotside if needed. So I'm asking what most people are doing to make more boost on line. No doubt I will have to address brake issue when I get to that point but at 5psi on 2 step I can sit there at 3400 rpm for 5 min.
Sorry, this was confusing me.
Most don’t go far enough when adding/pulling timing to help spool. I’ve seen as much at 50* advance in a tune up to get it up on boost and as low as -27*. Neither should hurt the engine as long as there isn’t any real load on it.
When you retard the ignition a ton you are hanging the exh valve open during combustion and leaking little mini explosions out pre-turbo. This works well (better than advancing IMO) but it’s hard on hot parts.
Advancing isn’t as hard on things. So I’d suggest trying that first. Bump it up to 28-40* and see how it acts. As long as this level of timing is only active when the 2-step is active you shouldn’t hurt it.
With advance you want it leanish AFR wise, retarding you want it rich.
ptc converter speced for my combo seems to flash to 3800 and i can get it up to 3400-3500 on footbrake before it wants to push threw them.
When you retard the ignition a ton you are hanging the exh valve open during combustion and leaking little mini explosions out pre-turbo. This works well (better than advancing IMO) but it’s hard on hot parts.
Advancing isn’t as hard on things. So I’d suggest trying that first. Bump it up to 28-40* and see how it acts. As long as this level of timing is only active when the 2-step is active you shouldn’t hurt it.
With advance you want it leanish AFR wise, retarding you want it rich.
Sorry, this was confusing me.
Most don’t go far enough when adding/pulling timing to help spool. I’ve seen as much at 50* advance in a tune up to get it up on boost and as low as -27*. Neither should hurt the engine as long as there isn’t any real load on it.
When you retard the ignition a ton you are hanging the exh valve open during combustion and leaking little mini explosions out pre-turbo. This works well (better than advancing IMO) but it’s hard on hot parts.
Advancing isn’t as hard on things. So I’d suggest trying that first. Bump it up to 28-40* and see how it acts. As long as this level of timing is only active when the 2-step is active you shouldn’t hurt it.
With advance you want it leanish AFR wise, retarding you want it rich.
Most don’t go far enough when adding/pulling timing to help spool. I’ve seen as much at 50* advance in a tune up to get it up on boost and as low as -27*. Neither should hurt the engine as long as there isn’t any real load on it.
When you retard the ignition a ton you are hanging the exh valve open during combustion and leaking little mini explosions out pre-turbo. This works well (better than advancing IMO) but it’s hard on hot parts.
Advancing isn’t as hard on things. So I’d suggest trying that first. Bump it up to 28-40* and see how it acts. As long as this level of timing is only active when the 2-step is active you shouldn’t hurt it.
With advance you want it leanish AFR wise, retarding you want it rich.
For testing purposes you shouldn’t have to fart around with transitioning from high to low timing or vise-versa.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
For testing purposes you shouldn’t have to fart around with transitioning from high to low timing or vise-versa.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
For testing purposes you shouldn’t have to fart around with transitioning from high to low timing or vise-versa.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
Try 42-45* adv on the 2-step and see what it does. Also make sure if you add a bunch of timing that your tune is pulling it out pretty quick once the brake is released.
If that doesn’t do it try -25* on the 2 step. (it’s gonna make some loud noises when you do this) Don’t sit on the 2-step long with it popping and banging. Shouldn’t take much. We were spooling a S484 with a super mild 5.3 in about 1-2 seconds at -25.
Last edited by gsxrred1000; Jul 28, 2017 at 09:24 PM. Reason: /
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Joined: Jul 2015
Posts: 3,012
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If your brakes can’t hold more power, that’s all there is to it really.
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
All you can do is improve your spool up times once the brakes are released… Or beef up your braking system to hold more power.
What pads do you have on the rear? Is your brake system up to snuff? Have decent vacuum?
We would extend the brake pedals 3-4” and stand on the bastard with all we had. Then use a vacuum pump that was wired to the brake switch to provide extra assist. Also cheap soft organic pads have better initial holding power than a nicer semi metallic or race pad. With all that, we could make some serious power on a foot brake car.
Adjustable brake proportioning valve with more rear bias and/or additional caliper on the rear would help a lot too. For the cost and effort a trans brake is the way to go though. I don’t even have rear brakes on one of my cars!
These threads are great...learned a ton of info i honestly had no clue about. Its cool you guys all help each other out like this. Cant wait to get to these problems on my build. Seems so easy for some of ya. Awesum!
Last edited by rkupon1; Jul 30, 2017 at 01:48 PM.