Brake issue after cam upgrade???
06-13-2013, 02:15 PM
#1
Burning Brakes
Thread Starter
Brake issue after cam upgrade???
Just testing a suspicion, could be totally psychotic, err, psychological.
Since my cam upgrade I have been destroying rotors and it feels like the brakes just are not as strong (bite and stopping power) as they used to be. Colemans got toasted in 3-4 days. Calipers were AP CP5555 on 14" Colemans. I went to the Hardbar T1 Kit (DSUNO pads) and the rotors is holding up nice but the brakes still don't feel strong.
The cam upgrade was a smaller 573 lift cam with mild ramp. Heads are GMPP (Lingenfelter), Stock LS6 intake with a 90mm throttle body. Idles like crap, but screams on the track. Roughly 440 rwhp after being tuned by a very reputable shop.
Now the question: Is it possible that the ECU is keeping some throttle applied after I come off the gas quickly, inhibiting engine braking or cancelling it all together? Master cylinder is still stock. Pedal is high and firm.
I will do the obvious experiment of clutching under bake to see if there is a perceived improvement in braking power...but that is still 10 days away.
Like I said earlier...this could all be in my head, I understand that kinetic energy varies as v^2, but the delta in braking performance feels larger than it should be. In the passenger seat of student cars (C6Z, etc.) it feels like their brakes are stronger as well.
Since my cam upgrade I have been destroying rotors and it feels like the brakes just are not as strong (bite and stopping power) as they used to be. Colemans got toasted in 3-4 days. Calipers were AP CP5555 on 14" Colemans. I went to the Hardbar T1 Kit (DSUNO pads) and the rotors is holding up nice but the brakes still don't feel strong.
The cam upgrade was a smaller 573 lift cam with mild ramp. Heads are GMPP (Lingenfelter), Stock LS6 intake with a 90mm throttle body. Idles like crap, but screams on the track. Roughly 440 rwhp after being tuned by a very reputable shop.
Now the question: Is it possible that the ECU is keeping some throttle applied after I come off the gas quickly, inhibiting engine braking or cancelling it all together? Master cylinder is still stock. Pedal is high and firm.
I will do the obvious experiment of clutching under bake to see if there is a perceived improvement in braking power...but that is still 10 days away.
Like I said earlier...this could all be in my head, I understand that kinetic energy varies as v^2, but the delta in braking performance feels larger than it should be. In the passenger seat of student cars (C6Z, etc.) it feels like their brakes are stronger as well.
Last edited by kmagvette; 06-13-2013 at 11:50 PM.
06-13-2013, 04:21 PM
#2
big cams can cause some vacuum booster issues. Especially on the road course because their is often not enough vacuum buildup in the booster. However, that is immediately noticable in that the brake pedal will feel less assisted (unusually hard pedal) when there is not enough vacuum.
Otherwise there is no relation to the brakes. Maybe you are just going faster and using them up more.
Otherwise there is no relation to the brakes. Maybe you are just going faster and using them up more.
06-13-2013, 06:12 PM
#3
Team Owner
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big cams can cause some vacuum booster issues. Especially on the road course because their is often not enough vacuum buildup in the booster. However, that is immediately noticable in that the brake pedal will feel less assisted (unusually hard pedal) when there is not enough vacuum.
Otherwise there is no relation to the brakes. Maybe you are just going faster and using them up more.
Otherwise there is no relation to the brakes. Maybe you are just going faster and using them up more.
06-13-2013, 11:50 PM
#4
Burning Brakes
Thread Starter
It is faster into the braking zones. Read some other posts and see that the check valve can be an issue sometimes, so I grabbed a new one. If all works out well I will have some engine data logging on-board for the next event so my tuner can see exactly what is going on, if anything.
06-14-2013, 12:14 AM
#5
If it does turn out to be a lack of vacuum you can add a canister for additional supply. Easily done by adding a tee fitting to the big booster hose. The easy option is to allow the car to decelerate for a moment before you apply the brakes which gives it time to build up some vacuum. I used to do that way back when on my first race car which initially had factory style power brakes. Of course it does give up some lap time so it's not the fastest way around the track.
07-18-2013, 01:51 PM
#6
Racing
If it does turn out to be a lack of vacuum you can add a canister for additional supply. Easily done by adding a tee fitting to the big booster hose. The easy option is to allow the car to decelerate for a moment before you apply the brakes which gives it time to build up some vacuum. I used to do that way back when on my first race car which initially had factory style power brakes. Of course it does give up some lap time so it's not the fastest way around the track.
07-18-2013, 02:40 PM
#7
I don't think there is anything wrong with your m/c. If this happened as a result of lower vacuum because of your h/c swap then you may just want to try adding a can for more volume.
07-18-2013, 03:37 PM
#8
Racing
, I'm not very tech savy or familiar with the vacuum system....could you explain what you mean? Do they cyphen air supply or pressurize from the same area?
07-19-2013, 06:09 PM
#10
Burning Brakes
Just testing a suspicion, could be totally psychotic, err, psychological.
Since my cam upgrade I have been destroying rotors and it feels like the brakes just are not as strong (bite and stopping power) as they used to be. Colemans got toasted in 3-4 days. Calipers were AP CP5555 on 14" Colemans. I went to the Hardbar T1 Kit (DSUNO pads) and the rotors is holding up nice but the brakes still don't feel strong.
The cam upgrade was a smaller 573 lift cam with mild ramp. Heads are GMPP (Lingenfelter), Stock LS6 intake with a 90mm throttle body. Idles like crap, but screams on the track. Roughly 440 rwhp after being tuned by a very reputable shop.
Now the question: Is it possible that the ECU is keeping some throttle applied after I come off the gas quickly, inhibiting engine braking or cancelling it all together? Master cylinder is still stock. Pedal is high and firm.
I will do the obvious experiment of clutching under bake to see if there is a perceived improvement in braking power...but that is still 10 days away.
Like I said earlier...this could all be in my head, I understand that kinetic energy varies as v^2, but the delta in braking performance feels larger than it should be. In the passenger seat of student cars (C6Z, etc.) it feels like their brakes are stronger as well.
Since my cam upgrade I have been destroying rotors and it feels like the brakes just are not as strong (bite and stopping power) as they used to be. Colemans got toasted in 3-4 days. Calipers were AP CP5555 on 14" Colemans. I went to the Hardbar T1 Kit (DSUNO pads) and the rotors is holding up nice but the brakes still don't feel strong.
The cam upgrade was a smaller 573 lift cam with mild ramp. Heads are GMPP (Lingenfelter), Stock LS6 intake with a 90mm throttle body. Idles like crap, but screams on the track. Roughly 440 rwhp after being tuned by a very reputable shop.
Now the question: Is it possible that the ECU is keeping some throttle applied after I come off the gas quickly, inhibiting engine braking or cancelling it all together? Master cylinder is still stock. Pedal is high and firm.
I will do the obvious experiment of clutching under bake to see if there is a perceived improvement in braking power...but that is still 10 days away.
Like I said earlier...this could all be in my head, I understand that kinetic energy varies as v^2, but the delta in braking performance feels larger than it should be. In the passenger seat of student cars (C6Z, etc.) it feels like their brakes are stronger as well.
Brakes: From the sounds of it you went from an AP 6 piston to an AP 4 piston caliper? Why? You went backwards. The AP 4 piston for our cars and a fast driver is not enough; you will have a mushy pedal. Let me guess, your brake pad life is non existent?
07-19-2013, 10:39 PM
#11
The brake booster on the corvettes is vacuum assisted. When there is not enough vacuum created by the engine the booster may not be consistant if it does not have enough time to build up to the level it needs.
Some the the larger cams with more overlap may have vacuum issues. It all depends on the combination used.
Some the the larger cams with more overlap may have vacuum issues. It all depends on the combination used.
07-20-2013, 01:22 AM
#12
Burning Brakes
Thread Starter
I forgot about this thread...got busy. The experiment at the track (clutching during braking) did not yield any differential in brake behavior. I did grab an engine data logger (HP Tuners) and was able to isolate the frames where I came off the gas at high speed and transitioned to immediate hard braking. The TPS was reading around 6% where I was expecting it to be closed...no idea if that is an issue...but, per the above, clutching during the hard braking did not yield any improvement in braking behavior. I agree that is would not necessarily change vacuum, but the goal here was to isolate the engine from the driven wheels to see if I was getting any "push" in the braking zone...I am not.
I did notice that things got worse later in the session, ~ 20 min, presumably heat related - duh. Brake fluid is Motul RBF600 and the brakes get a two bottle bleed before track time. At the onset of a longer pedal, it only takes a few turns at lower speed before things come back to normal. I did swap the check valve, cheap, but the old one seemed to be working just fine.
As far as the T1 kit goes, the rotors seem to last as do the brake pads, probably get 6 solid WGI days out of the pads (DSUNO). Because I play at WGI most of the time, I agree that a larger set-up in front will have better heat capacity that what I currently run. Eventually I would like to get to the 14" AP rotors up front with my 6 piston fronts ad move the 4 piston T1 kit to the rear...just waiting for the boat to come in with the rotors/hats. The piston area on the 8350's is very close to that of the 6 piston AP's; however the pad area and volume is reduced.
With the T1 kit I do notice substantial radial taper on the pads as well as the longitudinal taper that I always had. The radial taper I grind out on a disk after each event, longitudinal taper takes care of itself by swapping the pads around on a daily basis.
When all the smoke clears I am not ready to dismiss the notion that it is all in my head (except the softer pedal late into a session).
I did notice that things got worse later in the session, ~ 20 min, presumably heat related - duh. Brake fluid is Motul RBF600 and the brakes get a two bottle bleed before track time. At the onset of a longer pedal, it only takes a few turns at lower speed before things come back to normal. I did swap the check valve, cheap, but the old one seemed to be working just fine.
As far as the T1 kit goes, the rotors seem to last as do the brake pads, probably get 6 solid WGI days out of the pads (DSUNO). Because I play at WGI most of the time, I agree that a larger set-up in front will have better heat capacity that what I currently run. Eventually I would like to get to the 14" AP rotors up front with my 6 piston fronts ad move the 4 piston T1 kit to the rear...just waiting for the boat to come in with the rotors/hats. The piston area on the 8350's is very close to that of the 6 piston AP's; however the pad area and volume is reduced.
With the T1 kit I do notice substantial radial taper on the pads as well as the longitudinal taper that I always had. The radial taper I grind out on a disk after each event, longitudinal taper takes care of itself by swapping the pads around on a daily basis.
When all the smoke clears I am not ready to dismiss the notion that it is all in my head (except the softer pedal late into a session).
Last edited by kmagvette; 07-20-2013 at 01:35 AM.
07-22-2013, 07:51 PM
#13
Racing
The brake booster on the corvettes is vacuum assisted. When there is not enough vacuum created by the engine the booster may not be consistant if it does not have enough time to build up to the level it needs.
Some the the larger cams with more overlap may have vacuum issues. It all depends on the combination used.
Some the the larger cams with more overlap may have vacuum issues. It all depends on the combination used.
I'm learning slowly but surely. The vacuum issue sounds like it's the culprit 100%. If anyone has a link to making the vacuum assist that would be great.PS....sorry for the thread jack, but I think this might help you out too
07-24-2013, 11:19 AM
#15
Drifting
If you have the 12.8" kit I think you just have too much power for the smaller brakes. I have the T1 kit also and make 392whp and feel that I'm at the limit of what they can do. I find myself wanting more brakes at Sebring sometimes but in defense of T1 I'm still running the smaller stock rear calipers too. With your power I would be running a 14" kit with a rear upgrade as well.
