anyone measure pressure in the headers ?

[louich]

Just wondering if there is a magic number or percent of boost compared to backpressure in the headers.

[Mark55]

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.

[underpsi68]

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.

[domn8rx]

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

[underpsi68]

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.

[domn8rx]

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

[underpsi68]

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. 

[domn8rx]

That makes me feel better cause we have the 1.10ar and 4" dp. Thanks

john

[underpsi68]

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. 

[one eyed willy]

what is needed to measure back pressure?

[louich]

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

[10secgoal]

Subscribing. Will be testing a 480 also with the big AR and wheel

[CW25]

Tested my old very mild motor combo 383" S400sx T6 1.0hsg backpressure was 26 psi at 15 psi boost.

[HOTMOPR]

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.

[Mark55]

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.

[underpsi68]

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. 

[louich]

blew out the header gasket yesterday...the engine made 978 hp and 1300 tq and we only took it to 5000 rpm
heres a video of it

http://videos.streetfire.net/video/496-twin-turbo_639934.htm

[rusted40]

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.

[Wallace]

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?

[1995gtcpe]

It will be the same.

[turboventura]

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

[Supernatural Turbo]

It will be the same.

Can you substantiate that with any data?  How'd you acquire the data?

[10secgoal]

 I could imagine it would be higher possibly in the header than the crossover.
No data.

[rusted40]

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.

[turboventura]

 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.