Really stepped in it now

[LVSteve]

Not arguing, trying to learn…

It seems to me given a high back pressure exhaust vs a low back pressure exhaust downstream of the turbo, the low pressure path will give a higher pressure difference across the turbo (assuming no changes to upstream stuff.). Higher pressure differential allows the turbo to do more work.

What am I missing?

In other words, for power, low back pressure is better. I’m not commenting on longevity, warranty, etc.

After a bunch of googling, it seems that the use of the term back pressure doesn't mean the same thing to all men. Back pressure before the turbo usually results in higher exhaust gas velocity impacting the turbo, giving better response. When the turbo is fully up to speed, low back pressure after the turbo maximizes efficiency and prevents boost drop-off at high revs. The most concise explanation I can find is in the lower section of the opening post on this page.

Just a moment...

 

[taz666]

The blow off valve is on the intake side of the turbo ... it limits the boost PSI to a set pressure. Keeps the engine head gaskets intact It is not going to be effected by the change in exhaust.



Anyway, you just changed the muffler right? The exhaust is still going to be restricted by the smallest pipe ID. In order to realize more power, along with a bit more turbo lag, The whole exhaust piping needs to be replaced with a larger ID pipe exhaust system ... right from the turbo's hot side (down pipe all the way back). Sans this, you really haven't change much right now.

 

[LVSteve]

Well I am already at 60K but I did buy the extended warranty. I guess my other concern is do I need to get a new tune for the muffler? My buddy is telling me that with the change in the back pressure the turbo blow off valve may have issues. This is all so stupid. These auto manufactures protect their profits which I can understand but I also think that they do this even though the damage was a defect on their stuff. Can't win!!!

It all depends on how the turbo wastegate is controlled. If it senses the boost pressure only, then I cannot see a problem. If for some reason Ford have decided to sense the exhaust side pressures before and after the turbo impeller, then a lower back pressure exhaust would cause the wastegate to open early. I doubt Ford do this because it means you have to sense pressures in hot components, and the exhaust flow arrives from the motor in pulses, so the signal requires much smoothing.

As for it being stupid, well what can I say. The demands on engine design to meet the requirements of both the EPA and customer performance expectations are extreme. Once the balance has been achieved, monkeying with stuff can, potentially, cause issues.

The need for a catch can I think arises because real world use is never covered thoroughly by the manufacturers. Ford probably do much testing at the outer edges of the envelope to ensure longevity when heavy towing over long distances in a hot and high location. Lots of shorter runs in a damp location probably does not get the same attention, but I know from living in the UK that you can run into major issues with moisture pickup under those circumstances. Killed a BMW auto transmission with British driving rather than the Bavarian expectation of a banzai autobahn run at least once a week to keep H2O out of the transmission fluid.

 

[jeffrefrig]

I had an SS Impala that was pretty quick. I asked about getting a cold air intake to give it a few more HP and they told me NO! Something about the warranty. What the heck??

 

[Oldengineer]

I had an SS Impala that was pretty quick. I asked about getting a cold air intake to give it a few more HP and they told me NO! Something about the warranty. What the heck??

The warranty concern is potential incomplete/inadequate sealing with hardware that has not been design verified (DV’d).

 

[venomballistics]

Reduced exhaust back pressure is a turbochargers friend. I pioneered turbochargers at Ford Motor Company in the early 80’s. Google “Turbocharging the Ford 2.3L OHC”. You will find an SAE paper I published. The key to long life is synthetic engine oil that resists center section coking and subsequent bearing failure.


Tom H.

Castrol Syntech was my go to back in the day on one of those very plants.
Folks get so misguided over the concept of back pressure. the only reason to increase it is in a quest to make a quieter car.
Beyond that one party trick, it never helps.
In a turbo, the compressor is going to act as a dyno anyhow, and is probably the greatest factor in it's rotational speed.

 

[IAM Rand]

Anyone use Amsoil? I have seen people out there (there being the internet) claiming that Amsoil is one of the best oils out there.

 

[arjay]

I used to tinker with my cars in the 70s and 80s. Last time I was in over my head I took it to an old German mechanic. He fixed it and asked me what I did for a living. I told him. He said “ja,stick to that” lol

 

[venomballistics]

Brand is basically irrelevant - as long as it meets or exceeds the manufacturer's spec.

Exactly.... It all comes from the same hole in the ground and passes through the same refineries.
There's no difference until it's blended.

 

[venomballistics]

Anyone use Amsoil? I have seen people out there (there being the internet) claiming that Amsoil is one of the best oils out there.

Yeah, I've met it's acquaintance.
Pretty spendy for the common commuter.
If endurance competition is your jam, it's worth consideration.
Till then, you'll never ask of your engine enough to see any appreciable difference as a rally cross driver would.

 

[glenwolde]

Exactly.... It all comes from the same hole in the ground and passes through the same refineries.
There's no difference until it's blended.

Well, maybe not full synthetic...

 

[venomballistics]

Well, maybe not full synthetic...

Yes ... Full synth too
Synthetic oil is just more refined than the standard issue schmoo.

 

[IAM Rand]

The blow off valve is on the intake side of the turbo ... it limits the boost PSI to a set pressure. Keeps the engine head gaskets intact It is not going to be effected by the change in exhaust.



Anyway, you just changed the muffler right? The exhaust is still going to be restricted by the smallest pipe ID. In order to realize more power, along with a bit more turbo lag, The whole exhaust piping needs to be replaced with a larger ID pipe exhaust system ... right from the turbo's hot side (down pipe all the way back). Sans this, you really haven't change much right now.

Thanks for the info on the blow off valve. According to Banks, even a little at the end translates into some at the turbo. It may just be meet but, I could swear that the turbos are a little snappier.

[ame="https://www.youtube.com/watch?v=2tZYJHtXG9s"]https://www.youtube.com/watch?v=2tZYJHtXG9s[/ame]

I also email Banks to see if the muffler would need a new tune or any issues with the valve. They told me that it wouldn't need a tune and the new blow off valves are electronic so reducing the back pressure even a little would not affect it.

 

[LVSteve]

I hope the difference between a blow-off valve and a turbo wastegate are clear to our viewers. A blowoff valve dumps excess pressure from the intake, and a wastegate allows exhaust gasses to bypass the turbine wheel to prevent overspeed of the turbo.

 

[taz666]

You could also state the WG function as a (computer controlled) boost regulator.

 

[Oldengineer]

You could also state the WG function as a (computer controlled) boost regulator.

Yes. In 1984 with the release of the SVO Mustang, we very “simply” controlled boost with a premium fuel switch on the dash that modulated the signal to the wastegate. There were just two boost levels, with a slow and stupid knock control system —- by today’s standards. I’ve said before that knock control was the keys to the spark ignition engine kingdom.


Tom H.

 

[A10]

Breaks? Come on, from a car guy?

A guy can't get an even brake around here.....