Took 1st in NASA TT1 - Electric Vacuum Pump question
Jun 13, 2018, 11:52 AM
#31
If I'm understanding right, he's letting off the gas and the RPM are staying up, not allowing engine braking. Air has to be getting in, somehow, to keep the engine going so basically the same affect as the car still being on the gas as the engine is still firing. I didn't know of another way to explain it LOL. He may not have the pedal down, but the car does 
After reading Dallas' experience with the TB seals, that's kinda what I picture happening.
Unrelated, but I had something like this happen, once: I had my throttle cable too tight after putting the engine back in. I forget to set it. LOL. I was going down the street and the car would cruise at 3k RPM without my touching anything. I was like, "WWWWTTTFFF???!!" HAHA.
Depending on the RPM, this throttle hang may keep enough vacuum from building. I know my stock turbo keeps my car at or near zero psi/in.hg when I just look at it. If you are at crazy full boost, then the car is hanging the revs, I could definitely see the brakes acting up.
After reading Dallas' experience with the TB seals, that's kinda what I picture happening.
Unrelated, but I had something like this happen, once: I had my throttle cable too tight after putting the engine back in. I forget to set it. LOL. I was going down the street and the car would cruise at 3k RPM without my touching anything. I was like, "WWWWTTTFFF???!!" HAHA.
Depending on the RPM, this throttle hang may keep enough vacuum from building. I know my stock turbo keeps my car at or near zero psi/in.hg when I just look at it. If you are at crazy full boost, then the car is hanging the revs, I could definitely see the brakes acting up.
Jun 13, 2018, 05:44 PM
#34
Doesn't matter which foot, you'll get rock and "then" it'll fall and the brakes will come to life. Again it only happens when you're moving uber fast from gas to brake that you fall into this scenario, and most drivers don't do that lap for lap either because of traffic or any number of things. RPM hang was a separate issue. No it's not accelerating per say, but it's not engine braking either. Just slowing down....very slowly for a second or two and then it'd drop normally. Only ever did it in 5th, after a long *** straight. I've replaced about every part in the car 20 times. Maybe razor can comment on what per say is tunable in there.
Some of you may not remember him but Nate, aka Boom tried the vac canister route. I think it was a summit racing part or something but no it didn't help at all. The only REAL fix for this is dry sump where you're mechanically putting a ton of vacuum in there off boost - which ironically - fixes a slew of issues at this level.
However - now I'm curious because if we get back to the OP he just went through this massive dry sumping effort and still has the same problem. My ausi friends all swear that dry sumping fixed the issue. So several questions:
1. What is your measured vacuum during the lap, were you in the 10's or not at all? (is there a design issue in the sump install)
2. How much vac do you pull at idle?
Some of you may not remember him but Nate, aka Boom tried the vac canister route. I think it was a summit racing part or something but no it didn't help at all. The only REAL fix for this is dry sump where you're mechanically putting a ton of vacuum in there off boost - which ironically - fixes a slew of issues at this level.
However - now I'm curious because if we get back to the OP he just went through this massive dry sumping effort and still has the same problem. My ausi friends all swear that dry sumping fixed the issue. So several questions:
1. What is your measured vacuum during the lap, were you in the 10's or not at all? (is there a design issue in the sump install)
2. How much vac do you pull at idle?
Jun 15, 2018, 05:29 PM
#35
Doesn't matter which foot, you'll get rock and "then" it'll fall and the brakes will come to life. Again it only happens when you're moving uber fast from gas to brake that you fall into this scenario, and most drivers don't do that lap for lap either because of traffic or any number of things. RPM hang was a separate issue. No it's not accelerating per say, but it's not engine braking either. Just slowing down....very slowly for a second or two and then it'd drop normally. Only ever did it in 5th, after a long *** straight. I've replaced about every part in the car 20 times. Maybe razor can comment on what per say is tunable in there.
Some of you may not remember him but Nate, aka Boom tried the vac canister route. I think it was a summit racing part or something but no it didn't help at all. The only REAL fix for this is dry sump where you're mechanically putting a ton of vacuum in there off boost - which ironically - fixes a slew of issues at this level.
However - now I'm curious because if we get back to the OP he just went through this massive dry sumping effort and still has the same problem. My ausi friends all swear that dry sumping fixed the issue. So several questions:
1. What is your measured vacuum during the lap, were you in the 10's or not at all? (is there a design issue in the sump install)
2. How much vac do you pull at idle?
Some of you may not remember him but Nate, aka Boom tried the vac canister route. I think it was a summit racing part or something but no it didn't help at all. The only REAL fix for this is dry sump where you're mechanically putting a ton of vacuum in there off boost - which ironically - fixes a slew of issues at this level.
However - now I'm curious because if we get back to the OP he just went through this massive dry sumping effort and still has the same problem. My ausi friends all swear that dry sumping fixed the issue. So several questions:
1. What is your measured vacuum during the lap, were you in the 10's or not at all? (is there a design issue in the sump install)
2. How much vac do you pull at idle?
* Not on the NASA TT Evo thread, but will be now.
* Have Comp Catch can for inline install. Will try.
* Have Dry Sump - definitely still a braking problem
* I do left foot brake - rarely at threshold forces
I think a few of you recognize this is a 10/10ths scenario at top race form going for that best lap time. Pucker Factor is extreme when this delay happens, you are already committed into your “OH S%#*” exit strategy....then suddenly interrupted with working brakes.....but blowing your line. It’s awful. Can’t tuck up under anyone’s bumper into corners.
At less boost, this problem is reduced a lot. It’s only at high boost set up. I will try in-line canister. Then vacuum pump. Hope to find a fix. If I can get immediate full brakes coming off full boost (long straights), I will be setting more track records....without brown stains. 😆
Comforting to see BalRok’s post of “old issue”. Glad I am not alone.
YouTube “EMP EVO” to see in car vids. Look for COTA, Topeka GT3 RS, MSR, TWS videos. You might catch a glimpse of me at full panic end of straights. Camera hides the drama, but you will also see me lift and coast for insurance.
Last edited by Driv200; Jun 16, 2018 at 07:40 AM.
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BillAce (Jun 16, 2018)
Jun 16, 2018, 10:02 AM
#37
curious, what is the rest of your brake setup?
also, when you jump onto the brakes, is it initially hard and then falls? or is it hard all the way unless you release or coast and give it a sec?
would be nice if you could swap evos with another guy at an HPDE in the future and see if you experience the same/vice versa
also, when you jump onto the brakes, is it initially hard and then falls? or is it hard all the way unless you release or coast and give it a sec?
would be nice if you could swap evos with another guy at an HPDE in the future and see if you experience the same/vice versa
Last edited by kyoo; Jun 16, 2018 at 11:33 AM.
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Driv200 (Jul 12, 2018)
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Driv200 (Jul 12, 2018)
Jun 17, 2018, 03:38 AM
#39
I saw an Evo wreck very badly with this issue 10 years ago. While in the midst of troubleshooting the problem, he went over the “jump” on the Summit Point Shenandoah Circuit running 30 psi and race fuel on a 50 trim and had a rock hard pedal when he went for the brakes on the other side of the hill before the bowl turn. You can’t make that turn at triple digit speeds 
Last edited by EVO8LTW; Jun 17, 2018 at 11:10 AM.
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Driv200 (Jul 12, 2018)
Jun 17, 2018, 10:26 AM
#40
Wow! That sucks. This is No joke of an issue. I remembered my dry sump is a 3 stage. The 4th stage would probably help with vacuum, but we don’t have room for it. Ordered a vacuum pump today. Will update the progress pics. Pondering how to connect it and when it should activate?????????
Jun 17, 2018, 12:02 PM
#41
Evolved Member
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Driv200 (Jul 12, 2018)
Jun 17, 2018, 12:59 PM
#42
curious, what is the rest of your brake setup?
also, when you jump onto the brakes, is it initially hard and then falls? or is it hard all the way unless you release or coast and give it a sec?
would be nice if you could swap evos with another guy at an HPDE in the future and see if you experience the same/vice versa
also, when you jump onto the brakes, is it initially hard and then falls? or is it hard all the way unless you release or coast and give it a sec?
would be nice if you could swap evos with another guy at an HPDE in the future and see if you experience the same/vice versa
At the end of long straights, I jump on brakes immediately off full boost, pedal
is initially hard with no travel or action. Then suddenly has travel and starts braking. But there is no time for such a delay and you think your are going to crash or are committed to your exit strategy. When I lift early and coast, I have brakes. Also works better at boost below 26psi.
Jun 18, 2018, 05:00 AM
#43
Evolved Member
AP racing calipers, SS lines, and added ABS.
At the end of long straights, I jump on brakes immediately off full boost, pedal
is initially hard with no travel or action. Then suddenly has travel and starts braking. But there is no time for such a delay and you think your are going to crash or are committed to your exit strategy. When I lift early and coast, I have brakes. Also works better at boost below 26psi.
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Driv200 (Jul 12, 2018)
Jun 18, 2018, 09:53 AM
#44
Is there any other difference in the low boost vs high boost configurations? Do you have datalogging of the manifold pressure between shifts? I'm curious how low the manifold pressure falls in your 4th->5th shift as well as duration under full boost before you get on the brakes.
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Driv200 (Jul 12, 2018)
Jun 18, 2018, 12:44 PM
#45
I've had this happen to me a few times too and luckily I had enough room to not kill anyone. But it is not a good feeling the moment it happens and your heart drops bc you literally have a rock solid pedal and no brakes whatsoever.
Just thinking out loud here...the only difference is when you are on a high boost setting. So in theory it would take longer to evacuate the extra pressure relative to less pressure just like it takes less time to deflate the same tire with less pressure since the volume remains a constant. Now we're talking milliseconds here but I wonder if its as simple as your DV or BOV isnt reacting quickly enough to purge the excess pressure when you lift and the TB closes?
Just thinking out loud here...the only difference is when you are on a high boost setting. So in theory it would take longer to evacuate the extra pressure relative to less pressure just like it takes less time to deflate the same tire with less pressure since the volume remains a constant. Now we're talking milliseconds here but I wonder if its as simple as your DV or BOV isnt reacting quickly enough to purge the excess pressure when you lift and the TB closes?