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Exhaust Manifold Pressures


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Hey all,

I working on a project and I need to know what sort pressures you get in an exhaust manifold (on a turbo car)??

No its not a typo, I do mean the exhaust manifold before the turbo...I realize there is no great need to measure this and it would hard measure because of the high temperature but I am asking anyway just in case someone has done it before...

I am assuming it would be at least 3-4 bar and would increase according to boost (which is good for my project). I know that pressures after the turbo are around 0.5 to 1.0 bar depending exhaust restriction. So ex manifold pressure would be this pressure plus the pressure drop across turbine...which should be greater than compressor boost pressure taking into consideration rotational and other losses in the turbo itself etc..

anyway any info would be great appreciated...

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for a well modified engine running 20~ pound boost. 1.5 times boost is common. only really big turbos can achieve a 1:1 ratio or better.

it can be seen when its building up.. simply the engine will stop making power with more boost if its backing up.

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I wouldn't think anything production based'd get anything like lower than inlet manifold pressure under boost .

The closer you can get exhaust manifold pressure down to inlet manifold pressure the better , looking past boost pressure is a mindset . It's hard to convince people that big gains are to be made in reducing hot side restrictions because its effectively the same thing in reverse . The things that do this don't look bling and don't win points in bonnet up tinnie sessions . They are expensive because you are then trying to undo characteristics the manufacturers build into production cars .

Get it righ and its possible to make killer mid range torque and that feels like big NA engine squirt .

A .

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Thanks for the info...

This is what I was considering...For a couple of years I have been contemplating different ways of doing water injection....I have been trying think of alternatives to the electric pump and controller etc. I admit there is nothing wrong these systems. they are good ..they have come along way etc ...especially in price...(very high!!)

Anyway I am fan of passive systems...in reality they can be much more reliable if the design is right.

Something I came up with the other day is using exhaust gas pressure to pressurize a sealed water tank that feeds water back into the inlet side of the engine. The fact exhaust gas pressure increases with engine load is great because then with a correctly designed nozzle etc your water addition will be proportioned by the engine load.

Obviously there are things to consider....

1. Exhaust gas is very hot.. The heat would need to be pulled out of it before it gets to the tank...I have an idea regarding this though...

2. If water ended up getting drawn back into the exhaust manifold this would be catastrophic. With a good tank design and the right check valve this could be overcome...

3. Water would get contaminated by exhaust gas...I don't think this would be an issue...Your not going to drink it...your engine is...

BUT from what you guys are saying the exhaust manifold pressure are typically a bit lower than what I thought...1.5 -2 times boost pressure is probably not enough to get good atomization though a nozzle. I know the proprietary water injection systems run a lot higher pressure..

The alternative is to run water to the inlet side of the compressor but I know if the droplet size is to big its goodbye compressor wheel....I also came up with the idea of steam injection....yes water in a gas....this would not harm the compressor wheel but you are in effect adding heat to your inlet air...The benefit of having water in the inlet stream may out-weigh the loss through due to extra heat but my guess is you may just break even... BTW the water would be turned into steam via a heat exchanger on the exhaust manifold...

Anyway thanks for your help....cheers

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The alternative is to run water to the inlet side of the compressor but I know if the droplet size is to big its goodbye compressor wheel....I also came up with the idea of steam injection....yes water in a gas....this would not harm the compressor wheel but you are in effect adding heat to your inlet air...The benefit of having water in the inlet stream may out-weigh the loss through due to extra heat but my guess is you may just break even... BTW the water would be turned into steam via a heat exchanger on the exhaust manifold...

A bloke here in SA runs Water injection pre turbo and was pushing close to 500rwkw on a standard rod and cast piston RB30ET + cams and springs.

Motor was fine until the alternator decided to let go causing a lean out and broken ring lands. Prior to that it was solid for quite some time.

Without the water injection the power made on pump fuel simply would not be possible.

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A bloke here in SA runs Water injection pre turbo and was pushing close to 500rwkw on a standard rod and cast piston RB30ET + cams and springs.

Motor was fine until the alternator decided to let go causing a lean out and broken ring lands. Prior to that it was solid for quite some time.

Without the water injection the power made on pump fuel simply would not be possible.

Yep..there is no doubt water injection is awesome...

I know that after the 2nd world war some imported cars such as Alfas etc came over with higher comp ratios (8-9 :1) and wouldn't run on aussie fuel which was below 75RON or something ridiculous like that..Anyway they used to fit water injection..otherwise they had to pull nearly all of the ignition advance out of the tuning...I think they used a small mechanical water pump driven off the crankshaft...similar principle to injector pump on a diesel..

I am really not sure about the pre turbo injection...it would be good to know if the bloke in SA had noticed any erosion on the edge of the comp wheel blades...if the water droplets are too big, its a known fact that when the comp wheel blades collide with water it is like concrete...thats why I thought of using steam...I know this is putting heat into inlet air but depending on your turbo set up the air temp out of the turbo may be close to 100degC anywayso the amount of extra heat input from steam is only a very small percentage of that added by the compressor itself??

the region in front of the compressor wheel runs at a slighty negative pressure so water will vapourise easier so whatever the droplet size at the injection nozzle, it they will be smaller at the compressor wheel. The question is, how much smaller and are they small enough not to do any damage...Once the water goes through the compressor and is pressurised it will have tendancy to condense again..especially after the intercooler because the temp is a lot lower. I keen to try pre turbo injection but the risk is a turbo rebuild if it goes wrong....

You can use ultrasonic energy as well...If you have small plate vibrating at ultrasonic freq, when a drop water hits it, the water is atomised very well...Thats how those humidifier machines work...Incorporating this in the intake pipe work would be pretty tricky though...In the airbox would good but still tricky...

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Yep..there is no doubt water injection is awesome...

I know that after the 2nd world war some imported cars such as Alfas etc came over with higher comp ratios (8-9 :1) and wouldn't run on aussie fuel which was below 75RON or something ridiculous like that..Anyway they used to fit water injection..otherwise they had to pull nearly all of the ignition advance out of the tuning...I think they used a small mechanical water pump driven off the crankshaft...similar principle to injector pump on a diesel..

I am really not sure about the pre turbo injection...it would be good to know if the bloke in SA had noticed any erosion on the edge of the comp wheel blades...if the water droplets are too big, its a known fact that when the comp wheel blades collide with water it is like concrete...thats why I thought of using steam...I know this is putting heat into inlet air but depending on your turbo set up the air temp out of the turbo may be close to 100degC anywayso the amount of extra heat input from steam is only a very small percentage of that added by the compressor itself??

the region in front of the compressor wheel runs at a slighty negative pressure so water will vapourise easier so whatever the droplet size at the injection nozzle, it they will be smaller at the compressor wheel. The question is, how much smaller and are they small enough not to do any damage...Once the water goes through the compressor and is pressurised it will have tendancy to condense again..especially after the intercooler because the temp is a lot lower. I keen to try pre turbo injection but the risk is a turbo rebuild if it goes wrong....

You can use ultrasonic energy as well...If you have small plate vibrating at ultrasonic freq, when a drop water hits it, the water is atomised very well...Thats how those humidifier machines work...Incorporating this in the intake pipe work would be pretty tricky though...In the airbox would good but still tricky...

I don't see the need to inject pre turbo, and definitely not pre intercooler. Pre inlet does exactly the right job why muck around? plus if you are injecting 100% meth, it seems to me to be more risky to inject a flammable substance just inches from something that is glowing possibly red hot (the exhaust side of the turbo).

actually the best system is to MIX the water/meth with the fuel and let the injectors do the job! there is a patent out on that, a system to mix before the injectors always in the correct ratio.

The next best thing is to have the type of controller that can atomize based on injector duty cycle. Then there is no more mucking around with maf or psi triggered injection - you are basically guaranteed the right mix all the time, no matter the engine load.. (key it to only cut in with duty cycle over 20% so you don't use it on cruise). Then you are running around with the functional equivalent of C16 racing fuel. You can buy VP Coogee 20L for $60, so in the correct proportion, that is only adding at most 60 cents per liter cost when the sprayer is on, and perhaps as low as 30 cents per liter. If servos sold 110 octane fuel for $1.70 you'd all be buying that all day every day! And of course if you can handle a 200L tank safely, the math is even better.

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Dude the whole point of this topic is about coming up with an alternative to buying an off the shelf system (that cost about $1000)...Injecting water pre turbo is easier in this regard as you dont need to overcome boost pressure for a start...

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back in the day.(20 years ago) my father built a steam injection setup for his Fj40 v8 land cruiser.

i think he made up a water jacket around 1 of the extractors. i can't remember exactly how it worked. but it used to form ice all over the carby's. i'll try to remember to ask him and take a photo of his set up as its sitting in a cupboard in the shed. (the old boy struggles to throw any thing away)

its preety crude and ghetto looking but it obviously worked.

regards

chris

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The water injection kit was a home made kit.

No damage to the turbo was visible when it was pulled off.

Unable to provide any further information on parts used etc. :ermm:

Edited by TheRogue
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Dude the whole point of this topic is about coming up with an alternative to buying an off the shelf system (that cost about $1000)...Injecting water pre turbo is easier in this regard as you dont need to overcome boost pressure for a start...

A pump from shurflo (identical to the ones used in the kits) cost $100 and something and does 150psi.

So boost is not an issue. The rest is tubing, nozzles, fitments, and a controller which could be as simple as a PSI

driven 12v switch (hobbs switch) for $50, and a plastic tank.. so I don't know where $1000 comes from. Even

the entry level off the shelf stuff is only a few hundred.

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A pump from shurflo (identical to the ones used in the kits) cost $100 and something and does 150psi.

So boost is not an issue. The rest is tubing, nozzles, fitments, and a controller which could be as simple as a PSI

driven 12v switch (hobbs switch) for $50, and a plastic tank.. so I don't know where $1000 comes from. Even

the entry level off the shelf stuff is only a few hundred.

Dude I know about the Shurflo pumps. (i thought they around $200 though)...A hobbs switch is a basic switch so the water is either on or off. The good kits have a mapping capability and are much better at controlling the water according to engine load. Control is via pulse width modulated solenoid etc..By the time you add a decent controller and solenoid valve your at least up to $700 (unless your good with Jaycar kits)

My aim is to come up with a passive system not requiring a controller or a pump...There is value in this...Its not just about the cost but reliability etc etc

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has anyone ever done water injection into the ex manifold to aid spool up?

Never heard of this before....I assume that the principle is water enters manifold, flashes to steam expands and helps spool up turbine...Cant see why it wouldn't work....You would have to be careful about how much water you add...obvioulsy....

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When developing a high flow system for a soarer - EGT and Ex. Pressure were very important given the limitation of the turbos and the manifolds. We found that for every PSI we lost in the exhaust pressure - we could increase the boost by the same amount with no detonation and with a power increase.

It was also noted that due to the system that we had on there, an increase in boost above 19.5psi (ie: 22psi) did not increase the power level. The exhaust manifold pressure and EGT were above acceptable limits. I have yet to power port the manifolds but I would suggest that a good level of porting should see the power increase when running 21spi.

In addition, Exhaust Pressure and EGT is a good way to measure the engine health and condition during racing and dyno. If you have leaned it off too much and/or retarded the ignition - the EGT increase is the first parameter to increase.

So - how can you measure the Pressure in your exhaust? - Simply tap into the collector or turbo area a flared fitting with 3-4mm copper tubing and run it into a boost gauge. I recommend winding a spring like coil of around 5 loops about 10-20cm away from the fitting to shed the heat from the exhaust gases that feed in the boost gauge.

On an ECU such as a MoTeC, you can compensate for the exhaust pressure and temp by including it as another parameter in the maps. Short of knock control/compensation from MoTeC - this is a great way to monitor and prevent failure in demanding times on track / dyno.

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i used to inject a fair amount of water into the turbo years ago, the outer blades looked like it was attacked by a big chunk of rocks, but the inner blades were perfect.

The turbo was still working and had no issues.

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this pre turbo injection....was it fed with boost pressure to help atomise the spray? As in a Y junction with both water and air pressure helping squirt into the centre of the compressor wheel, or was it purely relying on high water pressure?

Someone on calais turbo had this setup on his 30. From memory i dont think there was any noticeable wear to the compressor wheel.

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i used to inject a fair amount of water into the turbo years ago, the outer blades looked like it was attacked by a big chunk of rocks, but the inner blades were perfect.

The turbo was still working and had no issues.

Hey Guilt-toy how you doin? I've done a bit of reading the last couple of days and it turns out that methanol can react with and dissolve the oxide layer that forms on high aluminium content alloys. It's this oxide layer that protects the metal underneath from further corrosion...So over time running a mixture of water and methanol onto the compressor wheel will cause a chemical attack on the surface.

It would be a long term thing and highly dependant on what mixture of methanol to water you run. Btw this is not problem in the plenum because it would be hot enough to keep the water /methanol a vapour...Plus there is much more wall thickness to be erroded before there is a problem. Makes you wonder about the I/C though....

The fact that the inner blades were perfect kind goes against the chemical attack theory though not unless they remain dry and its only the outer ones that contact the water...I also thought of using a very directional nozzle directed onto the retaining nut on the comp wheel...But i ended up decideing that the water would end up being flung off the nut only to be drawn in by the blades any way...It wouldn't work and might even be worse for the comp wheel...

A nozzle just off centre would be the best because the velocity of the blades is lowest towards the centre of the comp wheel..The inner (diameter wise) sections also do the least work as well.. if they lose their edge it has less effect on the operation of the compressor than if the whole edge is damaged..my theory anyway..

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