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| Tweet Topic Started: Nov 22 2013, 12:01 AM (2,630 Views) | |
| mwebb | Mar 2 2014, 11:56 PM Post #16 |
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FOG
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understand that my goal was / is not to reduce back pressure BUT to improve system flow and there fore to improve volumetric efficiency at cruise RPM by fussing with the exhaust an un intended consequence was that exhaust back pressure was reduced so much that the back pressure was insufficient to open the EGR back pressure transducer so EGR no longer functioned i had not considered this possibility prior to my fussing with the exhaust since i have also improved flow at heavy load and hi rpm i suspect that the exhaust pipe id is still too large for optimum flow at cruise more testing is required in the final pipe id that i settle on i can measure back pressure using running compression i measure pressure in the cylinder during EVO which is Exhaust valve open so that there is no restriction between the top of the piston and atmosphere - what ever the pressure is in the cylinder at the time is exhaust back pressure like this this is running compression a mid 1980,s MGB with a bad cat and burnt exhaust valve - pressure in the cylinder measured with a pressure transducer in the spark plug thread the cylinder should NOT be firing as there is no spark plug and no spark the hi peaks happen every 720 degrees , they are right at TDC at about 150 degrees after TDC you have a plateau of pressure a wee bit above ambient barometric pressure which is the white horizontal line that spike upward between about 150 degrees and about 360 degrees ATDC is a back fire , another cylinder has a burnt valve and is firing into the exhaust but the pressure spike shows up in this cylinder between the second pair od TDC pressure peaks you can see the exhaust back pressure the amount that the pressure is above the white line between about 150 and 360 degrees ATDC about 2 psi average , which is very high for that load and rpm the pressure and vacuum in the cylinder gets measured and recorded - the file is saved - so yes i can measure exhaust back pressure but that was not what i was doing Edited by mwebb, Mar 3 2014, 12:18 AM.
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| john. | Jul 20 2014, 04:49 PM Post #17 |
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Elite Member
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any more details from anybody on this? does going smaller exhaust pipe improve mpg? I imagine there would be a loss of top end performance. but for strictly fuel mileage? |
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| dayle1960 | Jul 20 2014, 06:17 PM Post #18 |
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Fastest Hampster EVER
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The only person who I've heard of doing this is mwebb. He jumps on GMF from time to time so be patient and he might reply to your query. Also the style of his writing takes time to get used to. You might want to re-read his thread and see if you can glean some additional nuggets.
Edited by dayle1960, Jul 20 2014, 06:18 PM.
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