Backpressure measurment.
#1
DEYTUKURJERBS
Thread Starter
![Default](https://passionford.com/forum/images/icons/icon1.gif)
How can you (SAFELY!) install a gauge to read exhaust gas pressure in your exhaust manifold?
Bearing in mind EGTs can get to 1000degC i cant imagine the methods used to measure boost is very safe
What about the pressures themselfs?
Is there a backpressure number where its gone into the realms of dangerous for the engine?
Ive heard people say not to let your backpressure exceed 2.5times your boost pressure.
Ive also heard people saw that if your backpressure is double your boost pressure youd get more gains from dropping the boost lower and advancing the ignition?
Is it purely a trial and error thing with regard to gaining power (without going to a larger exhaust housing) or is there some basic guidelines to go for?
Hopefully this might get the forum all techy again as its been nothing like it for months...
Bearing in mind EGTs can get to 1000degC i cant imagine the methods used to measure boost is very safe
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
What about the pressures themselfs?
Is there a backpressure number where its gone into the realms of dangerous for the engine?
Ive heard people say not to let your backpressure exceed 2.5times your boost pressure.
Ive also heard people saw that if your backpressure is double your boost pressure youd get more gains from dropping the boost lower and advancing the ignition?
Is it purely a trial and error thing with regard to gaining power (without going to a larger exhaust housing) or is there some basic guidelines to go for?
Hopefully this might get the forum all techy again as its been nothing like it for months...
#2
Testing the future
![Default](https://passionford.com/forum/images/icons/icon1.gif)
this was discussed slightly before in a thread steve. i think that it was alex with the turbo mini.
we decided that it should be possible to measure it using a normal manometer. the reason being that it won't get hot at the gauge end very quickly because the pipe will be closed so there will be no mass flow of hot gas up to the gauge.
someone pointed out that the pressure suits that pilots wear are directly pressurised by the jet engine gases, and they don't get hot.
don't know what sort of pressure that you'll be looking at though
we decided that it should be possible to measure it using a normal manometer. the reason being that it won't get hot at the gauge end very quickly because the pipe will be closed so there will be no mass flow of hot gas up to the gauge.
someone pointed out that the pressure suits that pilots wear are directly pressurised by the jet engine gases, and they don't get hot.
![Surprised](https://passionford.com/forum/images/smilies/shocked.gif)
don't know what sort of pressure that you'll be looking at though
#3
![Default](https://passionford.com/forum/images/icons/icon1.gif)
If you use an electrical sensor that will get hot and what about the plastic connector? And what kind of hose do you use with a mechanical gauge, it will get hot close to the exhaust.
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
#5
PassionFord Post Troll
Join Date: Jun 2003
Location: Finland
Posts: 2,866
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://passionford.com/forum/images/icons/icon1.gif)
It's ok if the first meter of the whose copes with heat. After that it doesn't really matter anymore as there is no flow.
Some people even think that the backpressure should not exceed the boost pressure.
Some people even think that the backpressure should not exceed the boost pressure.
#7
Norris Motorsport
![Default](https://passionford.com/forum/images/icons/icon1.gif)
Steve,
For EGT's in the exhaust manifold, I drill and tap each header and use a tapered olive boss suitable for a k type thermocouple. These bosses can also be blanked should you chose to remove the thermocouples after by simply using a blanking cap that screws over.
As a ball park figure I aim to keep preturbo manifold EGT's to less than 950DegC but up to 1000 is Deg C is ok. Post turbo temperatures in the down pipe can be as much as 200 DegC cooler and thus cannot be used to accurately determine peak EGT's.
With regard to measuring back pressure this is primariliy of importance post turbo in the exhaust system. The exhaust manifold back pressure pre turbo is something we can do nothing about as it's a function of the turbine specification and boost required and I don't normally measure this as I'm monitoring EGT's anyway. However measuring exhaust system back pressure is of great use, and I normally use a small fitting again screwed into a boss in the exhaust and use steel capiliary tube for the first few feet. Bare in mind the hole size in the exhaust boss only needs to be tiny to get a pressure reading and something less than 0.5mm is suitable.
With exhaust back pressure the rule of thumb is as low as possible, though I'm not going to give you any ball park figures as that would give the game away as to when certain exhaust sizes become restrictive!!
For EGT's in the exhaust manifold, I drill and tap each header and use a tapered olive boss suitable for a k type thermocouple. These bosses can also be blanked should you chose to remove the thermocouples after by simply using a blanking cap that screws over.
As a ball park figure I aim to keep preturbo manifold EGT's to less than 950DegC but up to 1000 is Deg C is ok. Post turbo temperatures in the down pipe can be as much as 200 DegC cooler and thus cannot be used to accurately determine peak EGT's.
With regard to measuring back pressure this is primariliy of importance post turbo in the exhaust system. The exhaust manifold back pressure pre turbo is something we can do nothing about as it's a function of the turbine specification and boost required and I don't normally measure this as I'm monitoring EGT's anyway. However measuring exhaust system back pressure is of great use, and I normally use a small fitting again screwed into a boss in the exhaust and use steel capiliary tube for the first few feet. Bare in mind the hole size in the exhaust boss only needs to be tiny to get a pressure reading and something less than 0.5mm is suitable.
With exhaust back pressure the rule of thumb is as low as possible, though I'm not going to give you any ball park figures as that would give the game away as to when certain exhaust sizes become restrictive!!
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
Trending Topics
#8
10K+ Poster!!
#11
DEYTUKURJERBS
Thread Starter
![Default](https://passionford.com/forum/images/icons/icon1.gif)
Karl etc- Cheers, thats pretty much it
Dave/Vroom- You mean before or after turbo?
Before would need such a big exhaust housing itd never spin up.
After, yes, easy.
![Clap](https://passionford.com/forum/images/smilies/9c-clap.gif)
Dave/Vroom- You mean before or after turbo?
Before would need such a big exhaust housing itd never spin up.
After, yes, easy.
#13
DEYTUKURJERBS
Thread Starter
![Default](https://passionford.com/forum/images/icons/icon1.gif)
Basicly, yea.
Shorter the better.
Ever seen an Indycars exhaust?
After the turbo its just a single lil stub of an exhaust about 6inches long just to get the exhaust gas past the bodywork, seperate exhaust from the wastegate is exactly the same too
Shorter the better.
Ever seen an Indycars exhaust?
After the turbo its just a single lil stub of an exhaust about 6inches long just to get the exhaust gas past the bodywork, seperate exhaust from the wastegate is exactly the same too
![Clap](https://passionford.com/forum/images/smilies/9c-clap.gif)
![Clap](https://passionford.com/forum/images/smilies/9c-clap.gif)
![Clap](https://passionford.com/forum/images/smilies/9c-clap.gif)
![Clap](https://passionford.com/forum/images/smilies/9c-clap.gif)
Thread
Thread Starter
Forum
Replies
Last Post
Big Will_
General Car Related Discussion.
64
12-05-2011 09:27 PM
Stu @ M Developments
Technical essay Archives
31
01-03-2011 06:35 PM