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| so if 2" is too big, how about 1 3/4? 1 7/8? | |
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| Tweet Topic Started: Aug 9 2014, 01:20 PM (1,790 Views) | |
| Justahoby | Aug 10 2014, 09:32 PM Post #16 |
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Unqualified informant
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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 Edit.. iPad likes to spell for me Edited by Justahoby, Aug 10 2014, 09:34 PM.
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| perfesser | Aug 10 2014, 10:46 PM Post #17 |
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Elite Member - Former Metro owner
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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 | Aug 10 2014, 10:49 PM Post #18 |
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Unqualified informant
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I wish I took a picture when I did my cam gear on my mill. |
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| Robertfrank | Aug 10 2014, 11:26 PM Post #19 |
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Member
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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 | Aug 11 2014, 11:56 PM Post #20 |
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Turbo3 and Twincam Tweaker
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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 | Aug 12 2014, 10:55 AM Post #21 |
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I am the one on the left.
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that is beautiful. |
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| mwebb | Sep 9 2014, 10:42 PM Post #22 |
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FOG
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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 | Sep 10 2014, 10:35 AM Post #23 |
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Unqualified informant
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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 | Sep 11 2014, 12:02 AM Post #24 |
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FOG
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"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 | Sep 11 2014, 12:22 AM Post #25 |
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Unqualified informant
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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 | Sep 11 2014, 12:22 AM Post #26 |
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Unqualified informant
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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 | Sep 12 2014, 06:46 AM Post #27 |
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Member
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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 | Sep 12 2014, 12:44 PM Post #28 |
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Unqualified informant
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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 | Sep 12 2014, 03:06 PM Post #29 |
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Member
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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 | Sep 12 2014, 06:32 PM Post #30 |
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Unqualified informant
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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 did, I plan on going by that for dual look ..
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Welcome to the all new Geo Metro Forum. We hope you enjoy your visit.


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.






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did, I plan on going by that for dual look ..
7:58 PM Jul 10