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so if 2" is too big, how about 1 3/4? 1 7/8?
Topic Started: Aug 9 2014, 01:20 PM (1,790 Views)
Justahoby
Unqualified informant

t3ragtop
Aug 10 2014, 05:15 PM


using a smaller diameter pipe as a method for maintaining flow velocity is not the way to go about it.

what you will find is that there is a small increase in engine torque in the low rev range with a smaller pipe and a decrease of power at the upper rev range

the 2" diameter pipe lets the engine run better between 3000 and 6000 rpm.

my suggestion is always to run a short, wide high flow air filter and a 2" exhaust front to rear. then drive the little car like you are racing. :D
:gp I am in agreement there. As was my point at saying it increases velocity at lower speeds... Umm where we drive at part throttle anyway so why go with 1.5" pipe.
I am with you. When I floor ( not part throttle) I downshift everything's above 3000 rpm.. I cruise the texas 75mph posted speed limit... Who gives a shit about low speed velocity , your not running WOT anyway at idle. At least I don't :banana

Edit.. iPad likes to spell for me :banghead
Edited by Justahoby, Aug 10 2014, 09:34 PM.
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perfesser
Member Avatar
Elite Member - Former Metro owner

Robertfrank
Aug 10 2014, 07:31 PM
... I know I can make that up by freeing up some by bumping up the timing. How do i do that on this little guy?
Ignition or cam timing? Ignition timing is easy, you just twist the distributor until your mark is where you want it. Cam timing's a bit trickier, and requires putting a small hole in the right place on the cam sprocket.
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Justahoby
Unqualified informant

I wish I took a picture when I did my cam gear on my mill.
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Robertfrank
Member
[ *  *  * ]
That would help lol. There are a TON of Geo's in yards here. I was looking for anything i can grab.
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t3ragtop
Member Avatar
Turbo3 and Twincam Tweaker

perfesser
Aug 10 2014, 10:46 PM
Robertfrank
Aug 10 2014, 07:31 PM
... I know I can make that up by freeing up some by bumping up the timing. How do i do that on this little guy?
Ignition or cam timing? Ignition timing is easy, you just twist the distributor until your mark is where you want it. Cam timing's a bit trickier, and requires putting a small hole in the right place on the cam sprocket.
Posted Image

you can get easy adjustment of the valve timing by using an adjustable cam gear. the deal is that you have to use a degree wheel for all your baseline work when you set the engine up.

precision measurement is essential to set the valve timing. in the grand scheme of engine management it's a good thing to know exactly when valves are opening and closing. ;)
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econoboxer
Member Avatar
I am the one on the left.

t3ragtop
Aug 11 2014, 11:56 PM
perfesser
Aug 10 2014, 10:46 PM
Robertfrank
Aug 10 2014, 07:31 PM
... I know I can make that up by freeing up some by bumping up the timing. How do i do that on this little guy?
Ignition or cam timing? Ignition timing is easy, you just twist the distributor until your mark is where you want it. Cam timing's a bit trickier, and requires putting a small hole in the right place on the cam sprocket.
Posted Image

you can get easy adjustment of the valve timing by using an adjustable cam gear. the deal is that you have to use a degree wheel for all your baseline work when you set the engine up.

precision measurement is essential to set the valve timing. in the grand scheme of engine management it's a good thing to know exactly when valves are opening and closing. ;)
:coche

that is beautiful.
:cloud9
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mwebb
Member Avatar
FOG

Justahoby
Aug 10 2014, 09:32 PM
t3ragtop
Aug 10 2014, 05:15 PM


using a smaller diameter pipe as a method for maintaining flow velocity is not the way to go about it.

what you will find is that there is a small increase in engine torque in the low rev range with a smaller pipe and a decrease of power at the upper rev range

the 2" diameter pipe lets the engine run better between 3000 and 6000 rpm.

my suggestion is always to run a short, wide high flow air filter and a 2" exhaust front to rear. then drive the little car like you are racing. :D
:gp I am in agreement there. As was my point at saying it increases velocity at lower speeds... Umm where we drive at part throttle anyway so why go with 1.5" pipe.
I am with you. When I floor ( not part throttle) I downshift everything's above 3000 rpm.. I cruise the texas 75mph posted speed limit... Who gives a shit about low speed velocity , your not running WOT anyway at idle. At least I don't :banana

Edit.. iPad likes to spell for me :banghead
WOT = Wide Open Throttle
all flow testing should be done at WOT because volumetric efficiency is always best at
WOT and because WOT is a repeatable condition

internal turbulence in the system is what REDUCES flow when the exhaust diameter is TOO LARGE to maintain around
300 to 350 feet per second
of velocity of the pulse train
in the exhaust

insulate the pipes to maintain temperature so that density is constant

assuming that designed for velocity at the rpm that peak flow is designed for
is around 300 to 350 fps or 238.63636 mph

you would need to increase velocity of the exhaust gases by more than 3x to go "sonic"
( above the designed for rpm )
that is unlikely to happen under any conceivable scenario

remember
i have actually measured peak flow
at WOT with the smaller diameter exhaust pipe


( and with the stock system )
and flow was significantly
INCREASED
with Smaller that stock diameter pipe i have posted the "after " value with the smaller pipe

i knew there would be an improvement at cruise , but cruise is hard to repeat , it is vague
WOT is WOT and very repeatable

none of you have asked to see a "before" measurement to go with the "after " measurement
why is that ?

for FE the larger pipe flows better theory has been refuted
and for max power with the 3tech economy cam
the larger pipe flows better theory is also refuted
as in
proven to be false

now
that is with a mostly straight "exhaust " pipe
no bends
front to back
therefore , internal turbulence is minimized

your results may vary as may my own if i introduce additional variables
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Justahoby
Unqualified informant

mwebb
Sep 9 2014, 10:42 PM
Justahoby
Aug 10 2014, 09:32 PM
t3ragtop
Aug 10 2014, 05:15 PM


using a smaller diameter pipe as a method for maintaining flow velocity is not the way to go about it.

what you will find is that there is a small increase in engine torque in the low rev range with a smaller pipe and a decrease of power at the upper rev range

the 2" diameter pipe lets the engine run better between 3000 and 6000 rpm.

my suggestion is always to run a short, wide high flow air filter and a 2" exhaust front to rear. then drive the little car like you are racing. :D
:gp I am in agreement there. As was my point at saying it increases velocity at lower speeds... Umm where we drive at part throttle anyway so why go with 1.5" pipe.
I am with you. When I floor ( not part throttle) I downshift everything's above 3000 rpm.. I cruise the texas 75mph posted speed limit... Who gives a shit about low speed velocity , your not running WOT anyway at idle. At least I don't :banana

Edit.. iPad likes to spell for me :banghead
WOT = Wide Open Throttle
all flow testing should be done at WOT because volumetric efficiency is always best at
WOT and because WOT is a repeatable condition

internal turbulence in the system is what REDUCES flow when the exhaust diameter is TOO LARGE to maintain around
300 to 350 feet per second
of velocity of the pulse train
in the exhaust

insulate the pipes to maintain temperature so that density is constant

assuming that designed for velocity at the rpm that peak flow is designed for
is around 300 to 350 fps or 238.63636 mph

you would need to increase velocity of the exhaust gases by more than 3x to go "sonic"
( above the designed for rpm )
that is unlikely to happen under any conceivable scenario

remember
i have actually measured peak flow
at WOT with the smaller diameter exhaust pipe


( and with the stock system )
and flow was significantly
INCREASED
with Smaller that stock diameter pipe i have posted the "after " value with the smaller pipe

i knew there would be an improvement at cruise , but cruise is hard to repeat , it is vague
WOT is WOT and very repeatable

none of you have asked to see a "before" measurement to go with the "after " measurement
why is that ?

for FE the larger pipe flows better theory has been refuted
and for max power with the 3tech economy cam
the larger pipe flows better theory is also refuted
as in
proven to be false

now
that is with a mostly straight "exhaust " pipe
no bends
front to back
therefore , internal turbulence is minimized

your results may vary as may my own if i introduce additional variables
Yea... I run WOT alot.... never saw a mileage loss at cruise... you know you can go further before you loose velocity ;)
I am sure you confuse max velocity with sonic choke.....it appears as such as you seem to tube all the way down to that point.

there is a range where flow is not dead, in a smoothe pipe, but laminar... just saying.... it rarely is turbulent, but goes into choke... if you run say 2.5 in, wll I am sure flow would become dead.. its not an on/off switch.
Seeing as this is why we build engines within a specific range.... I shift my Geo between lowest- 2100, highest 6000 rpm.
At 1 7/8" I do not really use off idle enough to worry about loss I would never notice..
At each pulse and at cruise velocity I am sure is just fine...
Why you think everybody, including Dynos indicate on even a 305 chevy 2.5" dual is ok on the street?

You think as if there is going to be a perfect range which is unrealistic. Hence why some people making power, yet able to exceed 50mpg are doing 1 7/8" -2" ... I am telling you advancing my cam/ignition and free exhaust I cruise up hills that I used to have to downshift for.

Edited by Justahoby, Sep 10 2014, 10:39 AM.
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mwebb
Member Avatar
FOG

"there is a range where flow is not dead, in a smoothe pipe, but laminar... just saying.... it rarely is turbulent, but goes into choke... if you run say 2.5 in, wll I am sure flow would become dead.. its not an on/off switch.
Seeing as this is why we build engines within a specific range.... I shift my Geo between lowest- 2100, highest 6000 rpm.
At 1 7/8" I do not really use off idle enough to worry about loss I would never notice..
At each pulse and at cruise velocity I am sure is just fine...
Why you think everybody, including Dynos indicate on even a 305 chevy 2.5" dual is ok on the street? "


to keep it simple
"everybody " who believes that using exhaust pipes that are too large for the rpm where optimized flow is desired is wrong , they are all mistaken

before you said "sonic " because you did not understand what it meant, now you say "choke" .... and "laminar "
understand
flow will not be laminar if velocity is too low , too low means somewhere below 300 fps depending on many variables
if flow is not laminar there will be turbulence and turbulence restricts / reduces flow , which is bad

many - most of them do not have any idea of how to measure flow or turbulence in the pipe
and so they just
replay myths that originated in the past that have since been DIS proved by actual testing

test - do not guess

if you are happy with what you have , great
if you want to fix it and make it better ,
test it
(you can not test a car with a dyno )
then correct what is broke
Edited by mwebb, Sep 11 2014, 12:05 AM.
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Justahoby
Unqualified informant

mwebb
Sep 11 2014, 12:02 AM
"there is a range where flow is not dead, in a smoothe pipe, but laminar... just saying.... it rarely is turbulent, but goes into choke... if you run say 2.5 in, wll I am sure flow would become dead.. its not an on/off switch.
Seeing as this is why we build engines within a specific range.... I shift my Geo between lowest- 2100, highest 6000 rpm.
At 1 7/8" I do not really use off idle enough to worry about loss I would never notice..
At each pulse and at cruise velocity I am sure is just fine...
Why you think everybody, including Dynos indicate on even a 305 chevy 2.5" dual is ok on the street? "


to keep it simple
"everybody " who believes that using exhaust pipes that are too large for the rpm where optimized flow is desired is wrong , they are all mistaken

before you said "sonic " because you did not understand what it meant, now you say "choke" .... and "laminar "
understand
flow will not be laminar if velocity is too low , too low means somewhere below 300 fps depending on many variables
if flow is not laminar there will be turbulence and turbulence restricts / reduces flow , which is bad

many - most of them do not have any idea of how to measure flow or turbulence in the pipe
and so they just
replay myths that originated in the past that have since been DIS proved by actual testing

test - do not guess

if you are happy with what you have , great
if you want to fix it and make it better ,
test it
(you can not test a car with a dyno )
then correct what is broke
It is not too large... 1 7/8" is perfect, even stock is 1.5". It would have been cheaper to go smaller, but they did not...
I am not arguing with you or your misinformation..
The way you go about it , I would be running 1 7/8 duals on my 454,
I run 3 in duals on that engine, and pull off 24 mpg Carbureted in a pickup with a t56 6 speed at 75 mph!
Right now a new 2 in system is going to go on my car.. This weekend! It's a hair big, but hey.. I never run around in idle....

My friend had a 350 with 1 7/8 dual exhaust and an rv cam... I said " you need to get rid of that drinking straw exhaust..." He asked about 3, I told him that was too big, told him 2 1/2"
At IDLE, the bigger exhaust picked up vacuum from 15" up to 17".
And was hell of a beast through Two pipes of that size.... And pulls trailers like mad off idle..
Since I went bigger on the geo... The power and less shifting on hills is undeniable! Not too big..
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Justahoby
Unqualified informant

Sonic choke is where it reaches Mach .. Mostly on intakes... Vizard taps exhaust to keep just below 2 psi on pulse.. If I remember right...
He is over on pistonheads forum... I haven't seen him there for awhile...

Edit rereading i left out.. i say mostly on intakes, as exhaust acts different.. near the end where its cool is about the same, main reason most later model cars move the muffler to the rear.
Edited by Justahoby, Sep 11 2014, 12:37 AM.
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Robertfrank
Member
[ *  *  * ]
Well I ended up putting a 2 inch xcelerator catback with a dump before the rear tire (i will soon be completing it to goall the way to the rear with a Y into 1 inch duals lol) and I picked up power EVERYWHERE. My mileage has remained basically the same. I will eventually be building my own header for an extra kick.
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Justahoby
Unqualified informant

Robertfrank
Sep 12 2014, 06:46 AM
Well I ended up putting a 2 inch xcelerator catback with a dump before the rear tire (i will soon be completing it to goall the way to the rear with a Y into 1 inch duals lol) and I picked up power EVERYWHERE. My mileage has remained basically the same. I will eventually be building my own header for an extra kick.
Exactly.... i feel 2" is a little big on a 3 cyl, but it doesn't hurt it one bit...still maintains enough velocity throughout the rpm range... Good deal!
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Robertfrank
Member
[ *  *  * ]
Well i figure once I put the 1 inch duals at the rear it might increase velocity a small bit but we'll see. If not I'll go with 7/8 tubing. I have a set of chrome tips I've been dying to put on lol
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Justahoby
Unqualified informant

I wouldn't worry about that... I would just go with it velocity would be after the header colector.. If you go to a split I wouldn't go down.. I'd stay the same will help with the tone ..
I been busy but look what :mullet did, I plan on going by that for dual look ..
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