Cam experts... (Why does the car push through the brakes with a cam in an auto)
06-25-2010, 05:24 PM
#1
Cam experts... (Why does the car push through the brakes with a cam in an auto) Hey guys, Just installed a 228R with 114LSA in my car equiped with a 4L60E. We tuned the car so it has no problem idling in gear or park, no problems starting the car (hot or cold), changing gears from park to reverse or drive is perfect too.
The idle in gear is set for 650 so only 100 more RPM than stock. The reason we set the idle so low is because I am on the stock stall converter for now. I have read about people having to push the brakes to the floor to stay stopped at a light with a cam and stock stall but I always thought that was because they had to set their idle high.
So my question is why with my idle set so low does it still want to push through my brakes when I am in gear and stopped.
Thank you,
Jason
The idle in gear is set for 650 so only 100 more RPM than stock. The reason we set the idle so low is because I am on the stock stall converter for now. I have read about people having to push the brakes to the floor to stay stopped at a light with a cam and stock stall but I always thought that was because they had to set their idle high.
So my question is why with my idle set so low does it still want to push through my brakes when I am in gear and stopped.
Thank you,
Jason
Last edited by NTIMD8; 06-25-2010 at 05:45 PM.
06-25-2010, 05:30 PM
#2
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I would say reduced idle vacuum causing the power brakes to offer less assist at idle. Combined with a stock converter which is tighter at idle than a stalled one.
When i installed my Torquer V.2 it was hell coming to a stop. My was untuned and had mine idling at about the same rpm's and mine would almost surge into the car in front of me when coming to a stop. I hear that after a stall converter it's much easier to hold it stopped at idle in drive. But i just ordered my stall so i can't say for sure so anyone is welcome to correct me.
When i installed my Torquer V.2 it was hell coming to a stop. My was untuned and had mine idling at about the same rpm's and mine would almost surge into the car in front of me when coming to a stop. I hear that after a stall converter it's much easier to hold it stopped at idle in drive. But i just ordered my stall so i can't say for sure so anyone is welcome to correct me.
06-25-2010, 05:39 PM
#3
Surging is can be related to a bad tune. But it alos is brought on by less than optimal valve events. You get exhaust reversion, and charge contamination which cause low speed drivablity issues like surging.
Here is something from the camshaft thread:
Simply put, on an N/A motor the intake aircharge is not assisted. (leaving wave dynamics of the aircharge out for a moment).
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia. Typically this is overcome before peak torque however. So only low-speed issues are present. At the track these motors are always above 4500rpm so this does not affect track times too much. Stilll....there is significant power lost by allowing reversion. So it makes sense to open the exhaust valve a little later increase the overlap a bit. By adding advance into the camshaft this makes the problem even worse as now you're opening the exhaust a few more degrees earlier..... shortening the effectiveness of the intake unless you have significant overlap flow to over come this.
Simply put, advancing a cam makes it more exhaust bias relative to TDC. Retarding a cam makes it more intake bias relative to TDC.
Here is something from the camshaft thread:
Simply put, on an N/A motor the intake aircharge is not assisted. (leaving wave dynamics of the aircharge out for a moment).
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia. Typically this is overcome before peak torque however. So only low-speed issues are present. At the track these motors are always above 4500rpm so this does not affect track times too much. Stilll....there is significant power lost by allowing reversion. So it makes sense to open the exhaust valve a little later increase the overlap a bit. By adding advance into the camshaft this makes the problem even worse as now you're opening the exhaust a few more degrees earlier..... shortening the effectiveness of the intake unless you have significant overlap flow to over come this.
Simply put, advancing a cam makes it more exhaust bias relative to TDC. Retarding a cam makes it more intake bias relative to TDC.
06-25-2010, 08:03 PM
#4
Surge is a fluctuation of RPM right? I should mention that I no longer have this after it was tuned. Basically I put it in gear and it drops to the tuned 650RPM and stays there (no surging) but still wants to pull forward pretty damn hard. The pull is a constant one and not on off/on one (Surge).
06-25-2010, 08:17 PM
#5
The thing is though the car actually wants to pull forward. When I let go of the brakes the car lunges forward as though I was pressing on the gas. The brakes are having trouble holding the car because it is pushing forward not because the brakes are weak.
06-25-2010, 08:55 PM
#8
Now that I have the idle tuned and was able to do it with a low RPM (650) I am simply wondering why it would still want to pull through the brakes in gear at a full stop. I understand a higher stall will fix my problem since it will be loose but am trying to figure out why I would be having this problem with such a low idle. It doesnt make sense to me but I am not an expert.
If I absolutly need a higher stall converter to get rid of this problem then would I need one that is 3000rpm or higher or could I use something in the 2500-2800 range?
06-25-2010, 08:58 PM
#9
Over the years people have been programed that the first mods you make on a car is intkae, exhaust, cam, etc etc. Realistically you need to have a vision of where you are going with the car. The first mod on an A4 is a stall no 2 ways about it and if any one wants to disagree let me know and I let you know why it should be.
Then:
Breaks
suspension
fuel delivery (pump, injectors, fuel rails if needed(N2O) etc
transmission (A4) mainly
exhaust
intake
cam/heads
Why you ask yourself in this order. The stock stall sucks they are so tight that if you look at the gas pedal it locks up. I have seen stock F-bodies and C5 Corvettes get into the low 13s & high 12 with just that mod.
The breaks should be a must unless you are running a Corvette the F-body breaks are not the best and that upgrade alone will help you with your future power plans. Its cool to have a lot of power but my buddy found out that 620/690 WS6 with stock breaks end up wrapped around light posts.
suspension is another mod that will help you with your weight transfer and getting the hp to the ground. Its a lot of fun seeing guys doing 1/8 mile burns outs with a lot of hp and wondering why they are trapping 12's @ 118. Slicks are not the only answer to a high hp engine. You have to have the suspension to put that HP to the ground and keep it there not watch it go up in smoke because you where trying to get into the burnout hall of fame
Fuel Delivery...how many guys do you know that post up that they are @ 112% of duty cycle and they need to know what injectors to use. What is funny is that after 85% of duty cycle the injector looses the capability to meter fuel,(going static) and that if at any time that injector stays open (its a devise not God so it will fail) now you have an injector spewing fuel into your cylinder and a ticking time bomb. Now I am not saying go out and get 72# injectors so you stay at 85% duty cycle. That is stupid if your making 500rwhp because then your tuner is going to have a hell of a time tuning that car if he is even capable of doing so. Look at the plans you have get the correct injectors. You can run up to 36# injectors with stock equipment and you will see very little ill effect. Yet you can run them to 500rwhp with no issues at all. Then comes the pump..."Men I ran out of pump on my run..." You just leaned out the hell out of your engine and are probably on your way to doing some irreversible damage if you didn't do it already. Or I can only run so much boost because I am running out of pump at 12 psi. Yeah that is what I like to call Captain Obvious
I can go on and on but a lot of what I have to say is common sense **** that people take for granted and look over and wonder why when its too late.
Your best bet is see where you want to go, stop thinking so hard about cams and heads and crap that really unless you have supporting modifications will end up killing your engine killing your self or worse killing some one because your car was not set up to handle that type of power.
again my opinion but i comes from years of experience.
Then:
Breaks
suspension
fuel delivery (pump, injectors, fuel rails if needed(N2O) etc
transmission (A4) mainly
exhaust
intake
cam/heads
Why you ask yourself in this order. The stock stall sucks they are so tight that if you look at the gas pedal it locks up. I have seen stock F-bodies and C5 Corvettes get into the low 13s & high 12 with just that mod.
The breaks should be a must unless you are running a Corvette the F-body breaks are not the best and that upgrade alone will help you with your future power plans. Its cool to have a lot of power but my buddy found out that 620/690 WS6 with stock breaks end up wrapped around light posts.
suspension is another mod that will help you with your weight transfer and getting the hp to the ground. Its a lot of fun seeing guys doing 1/8 mile burns outs with a lot of hp and wondering why they are trapping 12's @ 118. Slicks are not the only answer to a high hp engine. You have to have the suspension to put that HP to the ground and keep it there not watch it go up in smoke because you where trying to get into the burnout hall of fame
Fuel Delivery...how many guys do you know that post up that they are @ 112% of duty cycle and they need to know what injectors to use. What is funny is that after 85% of duty cycle the injector looses the capability to meter fuel,(going static) and that if at any time that injector stays open (its a devise not God so it will fail) now you have an injector spewing fuel into your cylinder and a ticking time bomb. Now I am not saying go out and get 72# injectors so you stay at 85% duty cycle. That is stupid if your making 500rwhp because then your tuner is going to have a hell of a time tuning that car if he is even capable of doing so. Look at the plans you have get the correct injectors. You can run up to 36# injectors with stock equipment and you will see very little ill effect. Yet you can run them to 500rwhp with no issues at all. Then comes the pump..."Men I ran out of pump on my run..." You just leaned out the hell out of your engine and are probably on your way to doing some irreversible damage if you didn't do it already. Or I can only run so much boost because I am running out of pump at 12 psi. Yeah that is what I like to call Captain Obvious
I can go on and on but a lot of what I have to say is common sense **** that people take for granted and look over and wonder why when its too late.
Your best bet is see where you want to go, stop thinking so hard about cams and heads and crap that really unless you have supporting modifications will end up killing your engine killing your self or worse killing some one because your car was not set up to handle that type of power.
again my opinion but i comes from years of experience.
Last edited by 02*C5; 06-25-2010 at 09:04 PM.
06-25-2010, 09:26 PM
#10
Basically everything you have listed has been done (except for the stall). I guess I know what I am doing next.
Now I just have to figure out what stall speed.
06-25-2010, 09:34 PM
#11
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Being able to afford a stall converter is not the issue. I didn't want a loose converter as the car sees lapping a few times a year. I did a lot of reading and thought I could get away with the stock stall on this cam if the tune was right. I may have been wrong. LOL If I was wrong I will get a stall no problem.
Now that I have the idle tuned and was able to do it with a low RPM (650) I am simply wondering why it would still want to pull through the brakes in gear at a full stop. I understand a higher stall will fix my problem since it will be loose but am trying to figure out why I would be having this problem with such a low idle. It doesnt make sense to me but I am not an expert.
If I absolutly need a higher stall converter to get rid of this problem then would I need one that is 3000rpm or higher or could I use something in the 2500-2800 range?
Now that I have the idle tuned and was able to do it with a low RPM (650) I am simply wondering why it would still want to pull through the brakes in gear at a full stop. I understand a higher stall will fix my problem since it will be loose but am trying to figure out why I would be having this problem with such a low idle. It doesnt make sense to me but I am not an expert.
If I absolutly need a higher stall converter to get rid of this problem then would I need one that is 3000rpm or higher or could I use something in the 2500-2800 range?
I think someone on the board used a vig2600 for roadracing. do a search
06-25-2010, 09:35 PM
#12
LOL Awesome quote. Thank you very much for your input. I should have specified that the LS1 and 4L60E are in my FD RX-7... https://ls1tech.com/forums/conversio...x-7-build.html
Basically everything you have listed has been done (except for the stall). I guess I know what I am doing next. Now I just have to figure out what stall speed.
Basically everything you have listed has been done (except for the stall). I guess I know what I am doing next.
Now I just have to figure out what stall speed.
but yeah the reduced vacume to your brake booster.. 
06-25-2010, 10:12 PM
#18
Reduced vacuum to my brake booster doesn't make sense for my issue. It is not that the brakes are weaker than usual it is that the car is pulling forward so hard. When I let off the brakes the car accelerates much harder than it should without me pressing in the gas.
06-25-2010, 10:13 PM
#19
I think I average 2 gallons per mile in the city 
lol
06-25-2010, 10:17 PM
#20
Yeah if your doing 1/4 mile only I would do a 4K or even a 4.5K depending on how high your spinning that bad boy. I am running a 3400 right now funds are low and I am killing myself but she is also my DD and she doesn't lock out till 55mph so city driving sucks I think I average 2 gallons per mile in the city lol
I think I average 2 gallons per mile in the city lol