Power Brakes with Choppy Idle Cams??
Chad Davis
not be able to use your power brakes.. I'm assuming it's due to the
choppy idle and inconsistent amount of torque being applied to the
pulley for the power brakes. My question is: Is there any solution?
Will using different pulleys help, and why doesn't this affect the power
steering, or does it..
There has to be someway around it, does anyone have any suggestions..
--
Chad
Gear Head
<77vinf$8...@news.voyager.net>...
Power brakes are vacuum operated, not pulley operated. With a "big" cam,
you lose a lot of manifold vacuum at idle. Stock motors make 15 to 20
inches at idle, but a motor with ~230 degrees duration will make 10 to 13,
depending on the other variables. This is what I run, with constant 12 to
13 inches, and my power brakes still work fine. When the motor is cold,
you have to use a little more pedal pressure, but not much.
With bigger cams, you have to use a separate vacuum canister for your
brakes.
Justin
--
Take me down to the Paradise City
Where the grass is green and the girls are pretty --Guns 'n Roses
Tygress(Emily)
wrote:
>I read that if you use a Cam with a 225 or higher Duration that you will
>not be able to use your power brakes.. I'm assuming it's due to the
>choppy idle and inconsistent amount of torque being applied to the
>pulley for the power brakes. My question is: Is there any solution?
>Will using different pulleys help, and why doesn't this affect the power
>steering, or does it..
First off, power brakes work from vacuum, not a pulley. Also, the
duration isn't the lone factor in deciding how choppy a cam will be.
The Lobe Separation Angle <LSA> also plays an important part. The
wider this angle <more degrees of separation> the less choppy a cam
will seem. Also, the size of the engine the cam is in will effect
it's ability to produce vacuum. For instance, I use a CC280 with 230
deg @ 0.050 and a 110 LSA in my Cutlass with a 383 engine. The cam is
lumpy but works the brakes just fine. It is about as far as you would
want to go on the street with that engine, though. The same cam put
into a 327 or a 302 would seem like a monster because the smaller
engine simply cannot move enough air at low speeds <idle> to produce
the needed vacuum in the intake. The cam basically puts more air than
the engine needs into the manifold, so the engine doesn't suck <make
vacuum> to try and get more. That's a very simplistic explanation,
but it's essentially accurate.
To run a bigger cam, you can use a vacuum canister that stores
vacuum and your brakes should be ok. Remember, once the engine is
spinning at cruise rpm, it should be making plenty of vacuum, and it
definately will when you snap the throttles shut at 30 or so and hit
the brakes. The lack of vacuum is only a real problem at idle. If
you have a lot of stop and go freeway crawling it might be a concern,
but otherwise I'd say not. I'd also recommend the book How to Build
HorsePower by David Vizard for you. There are other problems with a
big cam, like auto transmissions, fouling the ignition, misapplication
with other parts, and being wrong for the end use all together.
---
'69 Camaro w/Edelbrock manifold and fancy plug wires
'85 Cutlass w/airfilter upgrades w/tricked spark plugs
There's maybe something else on those that I forgot, but
it probably doesn't matter as much. ;) Probably.
Chad Davis
>
> Chad Davis <cda...@awcnet.com> wrote in article
> <77vinf$8...@news.voyager.net>...
> > not be able to use your power brakes.. I'm assuming it's due to the
> > choppy idle and inconsistent amount of torque being applied to the
> > pulley for the power brakes. My question is: Is there any solution?
> > Will using different pulleys help, and why doesn't this affect the power
> > steering, or does it..
> >
> > --
> > Chad
>
> Power brakes are vacuum operated, not pulley operated. With a "big" cam,
> you lose a lot of manifold vacuum at idle. Stock motors make 15 to 20
> inches at idle, but a motor with ~230 degrees duration will make 10 to 13,
> depending on the other variables. This is what I run, with constant 12 to
> 13 inches, and my power brakes still work fine. When the motor is cold,
> you have to use a little more pedal pressure, but not much.
> With bigger cams, you have to use a separate vacuum canister for your
> brakes.
>
> Justin
> --
> Take me down to the Paradise City
> Where the grass is green and the girls are pretty --Guns 'n Roses
I guess that would explain why it doesn't effect the power steering
ha.. lol, man don't I feel stupid. I'm curious, I'm putting a big cam
with the duration you were mentioning in my 96 Z28 with the M6
Transmission. Aside from the work that needs to be done to the heads,
fuel system, and exhaust is there anything that most people don't think
about that I should be looking for.. I know I'm going to have to do
something with the computer, I was hoping that hypertech could sell me
something that would work with what I want to do. Any advice or
suggestions.
--
Chad
finehomes
Chad Davis wrote in message <77vinf$8...@news.voyager.net>...
Bottlebob
finehomes wrote:
>
> What planet are you from?????
finehomes:
Sounds like you've never run a big cam with power brakes. :) Just as
Justin and Emily said a big cam can adversely affect the vacuum needed
for your power brakes. A big cam can also make your engine more
difficult to start if the vacuum signal isn't strong enough. Big cams
are notorious for killing bottom end torque. In fact that is one trick
street racers use to help them hook up on street tires.
--
Bottlebob
--
Bottlebob
Quick305
>you lose a lot of manifold vacuum at idle. Stock motors make 15 to 20
>inches at idle, but a motor with ~230 degrees duration will make 10 to 13,
>depending on the other variables.
the other varibles include altitude and atmosphereic conditions among many
others. Also i belive i remember hearing that the 98 4.6 stang used a power
break system that works off the power stereing pump. but i could be wrong does
any one else know. I had a freind that put a set of cobra brakes on his car and
he said he had to do some thing with the power stering pump. also the brakes
should work fine if you have a vacume canister also while you are decelerating
they should work good even with a big cam but when you are siting there idoling
you might have a problem.
Chad Davis
>
> What planet are you from?????
>
> >I read that if you use a Cam with a 225 or higher Duration that you will
> >not be able to use your power brakes.. I'm assuming it's due to the
> >choppy idle and inconsistent amount of torque being applied to the
> >pulley for the power brakes. My question is: Is there any solution?
> >Will using different pulleys help, and why doesn't this affect the power
> >steering, or does it..
> >
> >There has to be someway around it, does anyone have any suggestions..
> >--
> >Chad
Go screw yourself moron..
Chad Davis
>
> finehomes wrote:
> >
> > What planet are you from?????
>
>
> Sounds like you've never run a big cam with power brakes. :) Just as
> Justin and Emily said a big cam can adversely affect the vacuum needed
> for your power brakes. A big cam can also make your engine more
> difficult to start if the vacuum signal isn't strong enough. Big cams
> are notorious for killing bottom end torque. In fact that is one trick
> street racers use to help them hook up on street tires.
>
> --
> Bottlebob
>
> >
> > >I read that if you use a Cam with a 225 or higher Duration that you will
> > >not be able to use your power brakes.. I'm assuming it's due to the
> > >choppy idle and inconsistent amount of torque being applied to the
> > >pulley for the power brakes. My question is: Is there any solution?
> > >Will using different pulleys help, and why doesn't this affect the power
> > >steering, or does it..
> > >
> > >There has to be someway around it, does anyone have any suggestions..
> > >--
> > >Chad
>
> Bottlebob
Thanks for your input Bob.. that's one thing I was hoping for. With the
stock cam's power range mostly begining at idle and going thru 3,000 I
have a very hard time hooking up.. It either falls on it's face or I
have to feather the throttle until the tires bite..
Thanks again..
--
Chad
Tygress(Emily)
wrote:
>Bottlebob wrote:
Chad, just what kind of engine are you building, and what is it in?
The CC280 in my Cutlass is just on the streetable side of too big, and
I can melt the tires whenever I like. I'm running relatively new
Hoosier GT radials, 275-60/15's. One of the things I like to do is
walk out about a length with a "performance <cough cough> car" then
nail the gas. Not too many cars can go from a rolling start, just off
dead idle and then do a decent wheel. It tends to shut up a lot of
people. The reason I mention this is that it's low end punch that
enables the car to do that; the same low end that gives good throttle
response and generally makes the car enjoyable to drive. A cam that
kills the low end is generally one that is *way* too big for the
engine, like Sherman's 250+ @ 0.050 grinds for the 350. If it's not a
race car, you don't want that! You just have to learn the fine art of
gently hazing the tires to keep the revs up while still getting decent
traction, or do a little suspension work on the car. Remember that
what's good on the strip may suck on the street. And fouling out the
plugs every month isn't so nice, either. That's another problem with
big cams on the street, btw.
cowboyz
vacuums at lower engine speeds. I have just increased the idle in some
applications and the power brake problem went away. It all depends upon
your application, timing, and setup.
have fun
cowboyz
webm...@racingengines.com
www.racingengines.com
Chad Davis <cda...@awcnet.com> wrote in message
news:77vinf$8...@news.voyager.net...
Chad Davis
> The CC280 in my Cutlass is just on the streetable side of too big, and
> I can melt the tires whenever I like. I'm running relatively new
> Hoosier GT radials, 275-60/15's. One of the things I like to do is
> walk out about a length with a "performance <cough cough> car" then
> nail the gas. Not too many cars can go from a rolling start, just off
> dead idle and then do a decent wheel. It tends to shut up a lot of
> people. The reason I mention this is that it's low end punch that
> enables the car to do that; the same low end that gives good throttle
> response and generally makes the car enjoyable to drive. A cam that
> kills the low end is generally one that is *way* too big for the
> engine, like Sherman's 250+ @ 0.050 grinds for the 350. If it's not a
> race car, you don't want that! You just have to learn the fine art of
> gently hazing the tires to keep the revs up while still getting decent
> traction, or do a little suspension work on the car. Remember that
> what's good on the strip may suck on the street. And fouling out the
> plugs every month isn't so nice, either. That's another problem with
> big cams on the street, btw.
>
> ---
> '69 Camaro w/Edelbrock manifold and fancy plug wires
> '85 Cutlass w/airfilter upgrades w/tricked spark plugs
> There's maybe something else on those that I forgot, but
> it probably doesn't matter as much. ;) Probably.
Hi Emily,
You're right I don't want to go with that big of a cam. What I have now
is a 96 Camaro Z28 LT1 with the M6 Trans. I would like to carry around
400-425 horse when I'm done. Back to the cam, from what I understand
the cam in a stock LT1 has a power range starting right from idle. I
would like to put a cam that maybe has a power range starting around
1500-2000. I'm hoping that will help on my starts with street tires. I
agree with you though, that I do need to do some suspension work. Right
now the only mods I have done are a flow master exhaust and K&N filter,
just basic stuff.. I want to port & polish the heads and change the
valve sizes to 2.020 & 1.060, and run with a bigger cam with a good
idle, also of course move up to a 58 throttle body with headers. In
time I wanted to move up to a 3.73 gear also. I'm pretty new to this
game so any suggestions are appreciated.
--
Thanks, Chad
Tygress(Emily)
wrote:
>Hi Emily,
>
>You're right I don't want to go with that big of a cam. What I have now
>is a 96 Camaro Z28 LT1 with the M6 Trans. I would like to carry around
>400-425 horse when I'm done. Back to the cam, from what I understand
>the cam in a stock LT1 has a power range starting right from idle. I
>would like to put a cam that maybe has a power range starting around
>1500-2000. I'm hoping that will help on my starts with street tires.
Don't pick a cam to soften the start on a street car. It's a
racer's trick for track cars that can afford to have a high, narrow
powerband. Also, the term "power band" isn't concrete. For instance,
the Weiand Stealth I use is advertised as being good from idle to 7000
rpm. However, I would hardly consider the 200 ft lbs or so I can make
at 1500 to be in my powerband. That band can be termed the rpm range
from your torque peak to the hp peak. That def is subjective, of
course, but it's what I consider when I refer to a power band. There
is a better term, the ideal operating range, for the rpm spread where
certain components can work well. That could go as low as idle.
> I
>agree with you though, that I do need to do some suspension work.
Try some subframe connectors. They'll help out the car all
around, not just on launches.
>Right
>now the only mods I have done are a flow master exhaust and K&N filter,
>just basic stuff.. I want to port & polish the heads and change the
>valve sizes to 2.020 & 1.060,
You might just want new heads. You'll at least want an valve job
and a pocket port done too, and that could put you up near a new set
of aluminum heads. Especially once you consider that you'll want new
springs for a stronger cam and other incidental stuff, like seals.
Price shop before you decide on what to do. All the little stuff done
to a set of heads adds up fast.
> and run with a bigger cam with a good
>idle, also of course move up to a 58 throttle body with headers. In
>time I wanted to move up to a 3.73 gear also. I'm pretty new to this
>game so any suggestions are appreciated.
Try the gears now. It'll give you a great seat of the pants
feeling and make the car more responsive in every gear. It's also
something you can do quickly and is a stand alone step that won't hurt
the car or need other mods to see good results, and you won't
duplicate your labor or labor costs. For instance, the new headers
have to be removed to do the heads, the cam change is a pain and has a
bunch of incidentals, etc.
You also might want to try and add some smaller things yourself,
like a set of 1.6 roller rockers. It's not that hard to do, and it'll
compliment the new cam and heads later down the road.
bo...@illinoiselectric.com
69 Camaro, Edelbrock manifold with “fancy plug wires” that’s outstanding.