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Topic: anyone measure pressure in the headers ? (Read 1302 times)
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louich
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Just wondering if there is a magic number or percent of boost compared to backpressure in the headers.
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Mark55
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It was suggested to me by a person I feel is an expert to shoot for having the exhaust back pressure equal to the boost pressure or be no more than 15% above the boost pressure.
When I measured it I had 50% more back pressure than boost pressure so I bought new larger turbos.
I've been running 20# boost on E85.
A low boost application would likely be easier to hit the equal point.
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21' Eliminator Daytona V-drive 1800 hp lake boat
540 Arias, Twin turbo S475
FAST XFI fuel injection on E85
FAST XIM/LS2 ignition
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underpsi68
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The lower BP the better of course. I have a 2:1 ratio on my 352 all the way to 16psi where I took it up to. The ratio stays pretty flat from 5psi-16psi.
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domn8rx
teh wikkid chik
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The lower BP the better of course. I have a 2:1 ratio on my 352 all the way to 16psi where I took it up to. The ratio stays pretty flat from 5psi-16psi.
what size turbo?? t4 or t6? john |
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underpsi68
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PT GTS 76mm with a .96 exhaust T4.
My 352 made 787RWHP at 15psi through a non locking AOD on E85 and meth with 30-32psi BP with a 3" DP and tail pipes. The "little" 76 would have done 1000RWHP I'm sure if my injectors were bigger. I had to stop at 15-16 psi.
I would also like to try a 3 1/2" DP. I'm sure that would help it out some and make more HP.
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domn8rx
teh wikkid chik
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I ask cause i have a 363ci and 80mm with a t4. I'm going to tap my header sunday so i can see where i'm at.
john
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underpsi68
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I remember reading your build, very nice. We have similiar setups. I bet you will be close to mine.
I attached a screen shot of my datalogger. The green line is BP and the black is boost (blue rpm). Boost is in KPA with 200 = 14.7psi. BP is 200 = 29.4psi. I have data on 5psi up till 15psi. I was surprised that the BP pretty much stayed the same (a tad over 2:1) from 5psi to 15psi. I guess the DP and such is not being a big restriction so far.
In case anyone is wondering all temps are in Celsius and speed is in KPH.
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« Last Edit: March 08, 2009, 01:40:08 PM by underpsi68 »
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domn8rx
teh wikkid chik
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That makes me feel better cause we have the 1.10ar and 4" dp. Thanks  john |
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underpsi68
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You should be lower. Let us know how much BP you see. I am curious to see if a bigger DP will help me. the larger A/R won't hurt either LOL.
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one eyed willy
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what is needed to measure back pressure?
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07 Mustang GT 4.6
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louich
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we tapped the header 1/8 npt and hooked up sensor lead from dyno....
i know my turbos are too small being t3's but will spool fast on the rpm range i run on the street...1000 ft pounds by 3000 rpm on 14 psi boost
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10secgoal
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Subscribing. Will be testing a 480 also with the big AR and wheel
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CW25
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Tested my old very mild motor combo 383" S400sx T6 1.0hsg backpressure was 26 psi at 15 psi boost.
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Curtis 11.67@118 with 8 psi boost and 2400 DA 79 D100 + 400BB + S400 + MSII + roller cam = supurb drivability and mid 11s on pump gas  2007 Jeep SRT8 CAI and predator. Maybe mid 13s? |
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HOTMOPR
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For max efficiency drive pressure and boost pressure should be equal. Some have put the 1/8 npt fitting in the header with about a foot of coiled copper line then coupled to the plastic boost line. The copper coil will help with the exhaust pulses from destroying the gauge.
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67 Cuda 451 95 Ram diesel twin turbo  |
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Mark55
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Turbo the hell out of it
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To check the back pressure I put a 5' copper line in one pipe where the EGT thermocouple was, about 1 1/2 " away from the head.
I had a check valve in the line so it would hold the highest pressure reading.
I question if the back pressure would have read the same at the collector.
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21' Eliminator Daytona V-drive 1800 hp lake boat
540 Arias, Twin turbo S475
FAST XFI fuel injection on E85
FAST XIM/LS2 ignition
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underpsi68
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I am running a 100psi electric sensor. I modified an 02 sensor plug that I welded a -3AN to 1/8" thread adapter to it. I than took a steel brake line about 4 ft long and coiled it up to dissipate the heat and than screwed the brake line into the sensor.
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rusted40
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Speak softly and carry a big stick. -- Theodore R
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I used two boost gauges with recall for comparing pressure at various places. I used a piece of brake line about 20" and some silicone tubing.
with 2 P-trim T-64s on a 350, backpressure stayed pretty close to 1:1 until 20psi it was about 26 in the exhaust.
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Wallace
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Should the backpressure be measured at the turbine inlet? I see you guys are measuring at the header tube but wouldn't at the turbine be the actual pressure required to drive the compressor?
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Everybody knows you da man
1985 Mustang 3.8L V6 72mm 9.78 @ 133 so far...
1999 F250 PSD
1990 Dodge Caravan 2.5L turbo 5sp
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1995gtcpe
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3.5 in. single exhaust
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It will be the same.
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turboventura
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rusted40 im guessing those were T4 framed turbos? Thats impressive it had that little back pressure compared to the black dodge truck with a single T6. I plan on running a TC78, and see people modifying them to take 3.5 and 4.0in DP, but isnt the biggest restrion the T4 housing? I can understand that a bigger DP flows more, but with a straight DP or straight through muffler i can't see it relieving that much pressure. Interested to see DOMN8RX BP #'s too
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Supernatural Turbo
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It will be the same. Can you substantiate that with any data? How'd you acquire the data? |
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10secgoal
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I could imagine it would be higher possibly in the header than the crossover. No data.  |
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rusted40
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Speak softly and carry a big stick. -- Theodore R
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yes t4 with .81A/R on center housings. 3" downpipes and dynomax bullets. thats also with the wastegates dumping into the downpipe.
I checked backpressure at the primary in the same ports I use for the EGTs. never checked at the collector.
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turboventura
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I could see the primary tubes BP pulsing more, but the pressure can't be that different than at the collector, or at the merge of the turbo.
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