3" to 3.5" or 4" or 5" dp how much gain?

[jgme]

So, as a summary

Race Jace has a nice product.

Vader just states that it's not worth getting for most of the turbo Buick owners.

Using information provided by Race Jace it may be beneficial for cars running better than low 10s in the quarter mile.

By the way, engineers designed the turbo Buicks (along with all the cars on the road today). The cars meet cost, performance, and emissions constraints. People might be amazed but even NASA has quite a few engineers that are major car enthusiasts and know what they are doing. Not all of them are stuck in purely analytical worlds (although, there are many that don't know which end of a screwdriver to hold while using it). Red Armstrong is an engineer by trade also. Just not a mechanical but it does give him the skills to develop/evaluate products in a very systematic way. On the contrary I've run into jokers who pass themselves off as engineers and I watch as they have difficulties with the most basic systems that are covered in first year engineering courses.

 

[VadersV6]

Is the 5" overkill for the TE44 turbo? yes.

there were some design constrainst that dictated that the pipe be 5". One of them was, 5" is the smallest dia you can fit all 4 bolts of the DP inside the pipe.

That sounds perfectly reasonable to me. Wonder why you didnt say all this earlier. Instead of throwing all these theoretical reasons out there, you could have just said that there were design constraints dictated by the type of turbo this DP was for. Could have just said that most cars wont need a DP this big. There is this sherlock holmes book...sherlock says that the strange thing in the night was that the dog did not bark. I didnt see you say this DP wasnt for everyone. It seemed like you were going to try and sell it to anyone with a TR and a checkbook. You make good products and Im not bashing anyone. The argument started because you didnt specify who this was intended for, and no one wants to see some 17 year old kid with a stock 14 sec regal drop 500 bucks on something he couldnt use.

 

[broke1]

Everyone being overly negative on this post remember 1 thing,JASON ISNT MAKING STATEMENTS OF GAINING "x" HP FROM GOING TO HIS PIPE.Just stating its for sale.Any other vendor would tell ya its a sure fire way to pick up 50hp IME.

And as always,if youre not going to buy,have a coke, a smile and STFU and let the money spenders aka "the people that keep this hobby alive" ask relavant ????'s about this pipe.

If ya aint buyin,move on...

 

[scot w.]

Everyone being overly negative on this post remember 1 thing,JASON ISNT MAKING STATEMENTS OF GAINING "x" HP FROM GOING TO HIS PIPE.Just stating its for sale.Any other vendor would tell ya its a sure fire way to pick up 50hp IME.

And as always,if youre not going to buy,have a coke, a smile and STFU and
If ya aint buyin,move on...

.



(let the money spenders aka "the people that keep this hobby alive" ask relavant ????'s about this pipe.) Like me? May I ask again? JASON, Will going with a 3" exhaust and a bigger DP with a TE-45a lower my EGT's ???

 

[Race Jace]

.



(let the money spenders aka "the people that keep this hobby alive" ask relavant ????'s about this pipe.) Like me? May I ask again? JASON, Will going with a 3" exhaust and a bigger DP with a TE-45a lower my EGT's ???

EGT (in the header) is a measurement of air to fuel ratio so i don't think it will significantly affect it. The EGT in the down pipe would be significantly less but this would be a meaningless measurement.

 

[Race Jace]

That sounds perfectly reasonable to me. Wonder why you didnt say all this earlier. Instead of throwing all these theoretical reasons out there, you could have just said that there were design constraints dictated by the type of turbo this DP was for. Could have just said that most cars wont need a DP this big. There is this sherlock holmes book...sherlock says that the strange thing in the night was that the dog did not bark. I didnt see you say this DP wasnt for everyone. It seemed like you were going to try and sell it to anyone with a TR and a checkbook. You make good products and Im not bashing anyone. The argument started because you didnt specify who this was intended for, and no one wants to see some 17 year old kid with a stock 14 sec regal drop 500 bucks on something he couldnt use.

I really did not think that someone with a 14-second car would try and buy one of these. If you knew me you would know i would not sell it to someone like that. I talk people out of girdles, head clamps and 70mm TB’s that don't need them at least once a day. Why do i do this? Because i am in this long term and being honest about what is best for my customers is the best way to keep my customers.

When designing things i think things through very thoroughly. I don't just slap things together and call it a masterpiece. there is a reason for how and why i make things the way i do I just don't think to mention all of them unless asked.


I just wanted to build the biggest baddest DP that would fit in a buick. (and i wanted one for my own car. )

 

[JDEstill]

Whew, just started wading through all this, and I'm not sure I can go much further! But in the interest of the general education...

No matter what DP you have on there, the pressure, pre turbine will not change. On the post side of the turbine, the lowest pressure you can hope to achieve is ambient. This will give you the greatest acceleration of the wheel. Quick spool, but not more flow into the motor, unless you can keep the pressure diff significant at a high rpm to get more rpms out of the turbine.

I hate to disagree, but I guess I'm going to have to. The preturbine pressure *does* depend on what downpipe you have. If it didn't, why would a better DP make more power? Or better tailpipes and mufflers, or ditching the cat? If those changes don't affect the engine in any way, then why would the engine respond with more power?

The fact of the matter is: better DP/exhaust/no cat = lower post turbine pressure = lower pre turbine pressure = less backpressure on the engine = more hp due to better cylinder filling (ie improved volumetric efficiency) = more air flow into engine

And it's not the difference in pressure that is important, it's the ratio of pre and post turbine pressures that is important. Consider the turbine to be similar to a backwards compressor. Notice how a compressor map has one axis as P2/P1, *not* as P2-P1? Same thing with a turbine. The important thing is not P1-P2, it is P1/P2.

Example (and just making up numbers to illustrate): small, bad flowing downpipe with old cat converter and stock exhaust system gives 7 psig at the turbine outlet at full boogie. You measure the preturbine pressure and it is 33 psig. The turbine ratio required to supply the hp needed to drive the compressor is then (33+14.7)/(7+14.7) = 2.2.

Now we hollow out the cat, put on a new exhaust system, and upgrade to a THDP. Post turbine pressure drops to 3 psig because everything after the turbo flows so well now. What is the new preturbine pressure? We still need the same 2.2 ratio to provide the compressor hp required. 2.2 x (3+14.7) = 38.9 psia -14.7 = 24.2 psig.

In our example, dropping the post turbine pressure by 4 psig in turn dropped the preturbine pressure by 8.8 psig. And that is what's important, that lower backpressure that the engine sees, that's what gives the extra power.

Now sure, a street car with a 3" THDP might only see a miniscule change in post turbine pressure if that was changed to a 5". And a miniscule change there isn't going to make any extra power. But an all out race car that might see a 1 or 2 psi change at the turbine outlet should then see a real drop in preturbine pressure, and get a little more power as a result. It all boils down to what the post turbine pressure is right now and how much room for improvement there is.

A race car like that is undoubtedly running an aftermarket EFI system, and any improvements would likely show up as needing a slight bump in the VE table at those rpms and boost levels where the bigger DP would make a difference.

John

 

[JDEstill]

I hate to do this, but again...

Lets say you have the 100 gallon tank at 100psi, (simulating exhaust pressure in the headers, pre turbine) and it has a fixed diameter pipe coming out of it, (say 2") going to a flow control of some type (which will simulate the turbine restriction), and from there it exits into the atmosphere via a 3" pipe. The biggest restriction in this is the flow control, or simulated turbine. Lets pop open the valve and dump the air. Now lets replace the 3" pipe with a 5" pipe after the flow control. Refill the tank to 100psi. Now open the valve and dump the air out of the tank. Would the 5" pipe have dumped it faster? Not necessarily.

Actually, the 5" tail pipe probably would depressure the system faster, depending.

Lets start by working backwards from the end of the tail pipe. For a given flow rate, the 5" has a lower pressure drop than the 3", agreed? So if both are ending up at atmospheric pressure, and you head upstream through the pipe to the "flow restriction" (valve, turbine, orifice, whatever - I'll call it the restriction), you will have a lower pressure at the restriction outlet with the 5" than with the 3", right?

Upstream of the restriction you essentially have a constant pressure, 100 psi less some pressure drop in the 2" pipe.

So now we have the situation where we have a given pressure upstream of our restriction, and two different pressures downstream. Which system will flow more? Our 5" tail pipe system has a bigger pressure difference across the restriction, same upstream pressure and lower downstream pressure. More pressure difference, more driving force, it will flow more than the 3" tail pipe system.

Now to qualify that, when the pressure difference across the restriction is small, it won't flow much. Drop the outlet pressure some and it will flow more. Drop the outlet pressure again and it flow even more. As you keep dropping the outlet pressure it will flow more and more, up to some point, at which it becomes choked. At that point dropping the outlet pressure does not result in any more flow, and the piping downstream no longer makes any difference whatsoever in the flow rate through the restriction. With your example (100 psi air tank being let down), this would certainly be the case. But I do not think this is the case we are really interested in here, headers/turbine/downpipe. I think you've got a bad analogy which could lead to an incorrect conclusion about how the system behaves.

John

 

[Henry8298]

A w e s o m e !

 

[SloGN]

volume

it's all about the volume of air being moved.

take a 5 inch pipe and flow air @ say 100 psi and measure how many CFM of air it's discharging. then do the same thing for the 3 inch pipe and you will see the 5 inch pipe will move more air @ the same pressure.

now that being said that 5 inch pipe being connected to the 3 inch pipe. the 5 inch pipe will only be able to flow what the 3 inch pipe will allow it to flow.

if you apply that into fluid dynamics the results will be the same also dude to friction losses.

 

[JDEstill]

SloGN, kinda, but not quite. Sounds like you are applying the principle of "the system can only flow as much as it's smallest point", which is dead wrong (unless the system is choked as I described above). I'd like to strangle the first guy that tossed that out there, because he has mislead a heck of a lot of people.

Granted, by eliminating the smallest point you get the biggest gains, so as a rule of thumb for what to work on when you are modifying things, then yes, it is a very useful idea. But as an engineering concept, it's just wrong. The bottleneck does not act as a flow control, setting a certain flowrate and not letting the flow deviate no matter what you do to anything else. All the parts make up a system, change one part of the system and the other parts are affected too.

Imagine 3 setups -
A. 20 ft of 3" pipe
B. 10 ft of 4" pipe followed by 10 ft of 3" pipe
C. 19 ft of 4" pipe followed by 1 ft of 3" pipe

Will they all flow the same, since they all have 3" pipe in them? No. A will flow the least, and C the most. In the same way a 5" downpipe necking down into a 3" exhaust system will be able to outflow a 3" downpipe into a 3" exhaust system, and give a lower pressure at the turbine outlet. How much different that pressure will be depends on the amount of exhaust being moved of course. 300 hp of exhaust may not see any measureable difference, where 1500 hp of exhaust might see several psi.

John

 

[SloGN]

i understand you john

SloGN, kinda, but not quite. Sounds like you are applying the principle of "the system can only flow as much as it's smallest point", which is dead wrong (unless the system is choked as I described above). I'd like to strangle the first guy that tossed that out there, because he has mislead a heck of a lot of people.

Granted, by eliminating the smallest point you get the biggest gains, so as a rule of thumb for what to work on when you are modifying things, then yes, it is a very useful idea. But as an engineering concept, it's just wrong. The bottleneck does not act as a flow control, setting a certain flowrate and not letting the flow deviate no matter what you do to anything else. All the parts make up a system, change one part of the system and the other parts are affected too.

Imagine 3 setups -
A. 20 ft of 3" pipe
B. 10 ft of 4" pipe followed by 10 ft of 3" pipe
C. 19 ft of 4" pipe followed by 1 ft of 3" pipe

Will they all flow the same, since they all have 3" pipe in them? No. A will flow the least, and C the most. In the same way a 5" downpipe necking down into a 3" exhaust system will be able to outflow a 3" downpipe into a 3" exhaust system, and give a lower pressure at the turbine outlet. How much different that pressure will be depends on the amount of exhaust being moved of course. 300 hp of exhaust may not see any measureable difference, where 1500 hp of exhaust might see several psi.

John

i'm not talking about the downpipe it self necking down to a 3" pipe. I know that a short piece of 3 Inch pipe will flow a large amount.

what i'm referring to is the rest of the exhaust system that is 3" and the fact that it's about say 9 feet long with bends in it. thats gonna be the factor of it.

I know that the large bend in the DP will allow foir the air to get away from the turbine faster witht he most area to have less pressure. but it can only flow the amount of air the rest of the exhaust system can handle.

pxr2

 

[Race Jace]

All i can say is thank you John for taking the time to explain things correctly.