Homework for those w/ 3" exhaust

[Joel]

I would do this, but I don't have a 3" exhaust to complement the MPI yet. Likewise, I'm only running 7.5lbs of boost due to this.

 

Instead of "Guessing" that the exhaust housing is to restrictive, we need to find out for real. This will be likely be easier for those who already have an EGT mounted in the exhaust manifold, as it's rather easy to remove the probe temporarily and hook up a fitting and 18" long or so steel tubing for a boost gauge.

 

Go to a brake line place (place that does the Steel braided and hard lines, every city should have at least 1, if not 4 or 5 places... Usually Napa's main outlet can do it). Take them your probe and have them make you a line w/fitting out of steel tubing like that used in brake lines/PS lines about 12-18" long. It of coarse needs to fit under the hood, so a 90-degree bend to the driver’s side might be one option depending on the mount location of your probe. Bend up a coat hanger as a template for them.

 

Install the tube/fitting, at the end of the steel line; hook up your rubber hose to a boost gauge that you can run out the hood temporarily (or if you worried about pinching the line, run it through the passenger side floorboard grommet where the A/C drain is located). Make a few passes, and it is VERY important that you note both the Intake boost pressure and the exhaust pressure (both boost gauges), write them down. If you can, adjust your boost from low to high on your setup, and report what the findings where for each boost level on both sides of the head (intake and exhaust pressures).

 

Please respond back with the information, and include information on the extent of the headwork you have done, which cam, which turbocharger, and how big your exhaust is (2.5" or 3" or larger etc). Stock exhaust reports will not help.

 

This will not only save us money, but cut to the chase on that situation. We can't even begin to figure out the exhaust half requirements if we don't have proof that it’s inadequate.

 

Joel

[BMWTech]

Joel since i plan in doing the TD-06 upgrade soon ill try to get some time and set it up and see what the differences are  before and after the change.

 

-Neil

[Joel]

Well, I'm more interested in knowing the numbers more than anything.

 

However,

 

The TD06 Exhaust wheel would be larger wouldn't it? If thats all your going to change, and you have it in an 8cm2 housing, you would actually be lowering the A/R (reducing total flow cross section). I haven't quite got what you were planning on completely, so correct me if I'm wrong.

 

The idea would be to use either a smaller wheel in the same housing, or a bigger housing with the same wheel to increase A/R (or flow section). What turbo do you have now?

 

Joel

[Boosted_One]

Great idea Joel.

 

 

This is my view on the subject:

 

It's not directly that the 8cm2 exhaust housing is too restrictive it's the 20G turbo combo.

 

If you disect the compressor side and exhaust side you get this:

 

A large compressor wheel

a .60 A/R on the compressor side

 

A small exhaust wheel

~.48 A/R on the hot side

restrictive stock exhaust manifold

 

That combo in itself can not flow optimal up top and lends itself to an increase of backpressure.

 

Mismatched turbo IMHO.

 

Then you take me, I had A 20G hybrid with a VERY large compressor side trim, the TO4E 60, and a TDO6H exhaust trim and 8cm2 turbine housing.

 

At 10 psi the power curve was smooth. At 12 psi the power curve was smooth. At 15 psi the curve just died after 4K and never resembled the 3 psi less run.

 

I think the 8cm2 housing is very good with the TDO5 compressor housing. But once you start really pushing some CFMS the bottleneck rears itself.

 

This is my experience with it and this is what I spec'd differently this time around on my TO4B.

 

I'm thinking the 2V large displacement needs a little different attention than what we have been accustomed to.

[Joel]

Ok, you've got me lost a little Mike.

 

If the exhaust housing is not restrictive, and the "exhaust wheel" on the 20G is "small", then the A/R is larger than that of a turbo with a larger exhaust wheel in the same housing.

 

The closer the edge of the wheel is to the housing ID, the smaller the A/R. So a larger wheel + same housing you have now = smaller A/R. Likewise, it becomes more restrictive as such because a larger wheel closer to the housing ID means less air around the wheel. Ideally this would increase spoolup times due to torque at the wheel (move leverage to the center).

 

In applications that flow more, you would want air to divert around the wheel, as you obviously have more overall flow and heat to spin the exhaust wheel. Likewise A/R on one turbo vs. another is completely different. You can put a .49 A/R on a HUGE exhaust housing and get more flow then a T3 with a .80 A/R.

 

You can match up different housings (say a 14cm2 housing) and use a huge wheel to get the same A/R, and still flow more. Lag still may be a problem more so then a .49 on an 8cm2.

 

The answer to excessive exhaust backpressure is not nessisarily the housing itself, you would be correct, but my interest in this information has little to do with the housings by themselves. I need the data so I can call a few people I know can suggest a decently cheaper alternative then swapping manifolds and going to a garrett. I would love to do that, but I would like to attempt to get the most out of what I have now while I save up the funds for that. I'm sure others are in the same boat.

 

Likewise, as I've stated before, if the turbocharger you have now vs. the one you are looking at both meet the flow requirements at the PR your going to use, the only difference in power will be density, not mass. You get no more air into a motor at 15psi on a 16G than a 20G. The difference is density, and depending on the placement of the compressors effieciency points, the power gain will be minimal. On the other hand, 15psi on a 16G is a hell of alot hotter than a charge from a 20G at 15psi. Hense the power gains noted from density. Changing to another compressor that yeilds less charge peak temps. than a 20G at 15-18psi will be difficult, and the gains will truely be minimal at the compressor side. The exhaust configuration may or may not make the difference there.

 

Above 15psi there could be many other factors that would cause a car to fall on its face aside from the turbocharger itself. Proof of this would be Bill's (now BWMT's) car. 20G pushing close to 400hp at 18psi.

 

Now, since I don't know anymore about that turbo than the compressor type, I suppose that statement is limited on its meaning... What is that thing exactly?

 

Hense the importance of this test vs. changing the turbo config and reporting results. You can extract more power and smoother power if you know whats going in your current configuration, than if you just swapped parts around (and spent tons of money) until you hit the mark,  or more accurately; make a more educated guess.

 

Joel

[Boosted_One]

Ok, you've got me lost a little Mike.

 

If the exhaust housing is not restrictive, and the "exhaust wheel" on the 20G is "small", then the A/R is larger than that of a turbo with a larger exhaust wheel in the same housing.

 

The closer the edge of the wheel is to the housing ID, the smaller the A/R. So a larger wheel + same housing you have now = smaller A/R. Likewise, it becomes more restrictive as such because a larger wheel closer to the housing ID means less air around the wheel. Ideally this would increase spoolup times due to torque at the wheel (move leverage to the center).

 

In applications that flow more, you would want air to divert around the wheel, as you obviously have more overall flow and heat to spin the exhaust wheel. Likewise A/R on one turbo vs. another is completely different. You can put a .49 A/R on a HUGE exhaust housing and get more flow then a T3 with a .80 A/R.

 

You can match up different housings (say a 14cm2 housing) and use a huge wheel to get the same A/R, and still flow more. Lag still may be a problem more so then a .49 on an 8cm2.

 

The answer to excessive exhaust backpressure is not nessisarily the housing itself, you would be correct, but my interest in this information has little to do with the housings by themselves. I need the data so I can call a few people I know can suggest a decently cheaper alternative then swapping manifolds and going to a garrett. I would love to do that, but I would like to attempt to get the most out of what I have now while I save up the funds for that. I'm sure others are in the same boat.

 

Likewise, as I've stated before, if the turbocharger you have now vs. the one you are looking at both meet the flow requirements at the PR your going to use, the only difference in power will be density, not mass. You get no more air into a motor at 15psi on a 16G than a 20G. The difference is density, and depending on the placement of the compressors effieciency points, the power gain will be minimal. On the other hand, 15psi on a 16G is a hell of alot hotter than a charge from a 20G at 15psi. Hense the power gains noted from density. Changing to another compressor that yeilds less charge peak temps. than a 20G at 15-18psi will be difficult, and the gains will truely be minimal at the compressor side. The exhaust configuration may or may not make the difference there.

 

Above 15psi there could be many other factors that would cause a car to fall on its face aside from the turbocharger itself. Proof of this would be Bill's (now BWMT's) car. 20G pushing close to 400hp at 18psi.

 

Now, since I don't know anymore about that turbo than the compressor type, I suppose that statement is limited on its meaning... What is that thing exactly?

 

Hense the importance of this test vs. changing the turbo config and reporting results. You can extract more power and smoother power if you know whats going in your current configuration, than if you just swapped parts around (and spent tons of money) until you hit the mark,  or more accurately; make a more educated guess.

 

Joel

 

What I was trying to get at in regards to a tdo5 exhaust houing being too restrictive is this. On a 20G the compressor side is flowing alot and on the exhaust side with a tdo5 (small) exhaust trim and 8cm2 exhaust housing it isn't capable of flowing optimally on the cold side.  

 

On my former turbo that was only amplified. I believe with a header the results would have faired much better.

 

 

There's several directions this discussion can head but my primary point was it isn't "cut and dry" making a general statement that a TDO5 exhaust housing is too restrictive. It would depend on what the turbo combo is along with other flow adding modifications.

 

You could literally have a dozen different turbo combos with a TDO5 turbo. Most of those choices differ on the compressor side.

 

The trim doesn't change the A/R that I have ever heard of. I have never heard any turbo shop state running a P trim wheel in a .58 housing will actually be say a .50. If there is a change it is minimal. The trim dictates the flow characteristics and the housing dictates the choke limit. Bigger wheel = more cfm output. Smaller housing = earlier choke limit.

 

 

I picked up quite a good bit of info from several turbo shops and would suggest anyone interested in turbo combos/specs do the same.

[Joel]

What I was trying to get at in regards to a tdo5 exhaust houing being too restrictive is this. On a 20G the compressor side is flowing alot and on the exhaust side with a tdo5 (small) exhaust trim and 8cm2 exhaust housing it isn't capable of flowing optimally on the cold side.  

 

On my former turbo that was only amplified. I believe with a header the results would have faired much better.

 

 

There's several directions this discussion can head but my primary point was it isn't "cut and dry" making a general statement that a TDO5 exhaust housing is too restrictive. It would depend on what the turbo combo is along with other flow adding modifications.

 

Certainly agreed. You can't make a generalized statement like "Restritive exhaust housing"... You CAN make a statement saying there is not enough flow after the head and before the exhaust outlet (muffler/etc). W/ a 3" exhaust and high flow muffler, you can "generally" rule that out. So your down to a few specific components.

 

You could literally have a dozen different turbo combos with a TDO5 turbo. Most of those choices differ on the compressor side.

 

The trim doesn't change the A/R that I have ever heard of. I have never heard any turbo shop state running a P trim wheel in a .58 housing will actually be say a .50. If there is a change it is minimal. The trim dictates the flow characteristics and the housing dictates the choke limit. Bigger wheel = more cfm output. Smaller housing = earlier choke limit.

 

I had my facts wrong here. A/R is dictated by the housing only, not the wheel. Sometimes I read to much into things and over complicate. I enjoy it when someone calls attention to mistakes I make, I learn a little more.

 

This information I mentioned above came from a performance shop I talked to. I didn't read the reference material close enough to prove that wrong. I re-read a couple references (books etc) and realized I was wrong.

 

I picked up quite a good bit of info from several turbo shops and would suggest anyone interested in turbo combos/specs do the same.

 

This is exactly why I wish to collect this information.

[BMWTech]

OK heres the details on my quest (Bill's old car) air flows from the head through a South florida performance header in the turbo. The Turbo: a Mitsu 20G in a TD-06 Compressor housing, mated to a TD-05 exhaust wheel in the stock (TD-05) turbine housing. This flows into a 3' downpipe, exhuast 3' all the way back, uses an external HKS racing wastegate, mounted on a flange on the underside of the exhaust manifold.

 

Now i'd like to point something out.

Likewise, as I've stated before, if the turbocharger you have now vs. the one you are looking at both meet the flow requirements at the PR your going to use, the only difference in power will be density, not mass. You get no more air into a motor at 15psi on a 16G than a 20G. The difference is density, and depending on the placement of the compressors effieciency points, the power gain will be minimal.

 

Joel

 

...the comment about gettin no more air in the motor on a 16g or 20g....I dont agree.

   Look at it like this, at 15psi say the 16g moves 500 CFM, and the 20g 650 CFM.

-Now you are right that at 15psi neither turbo is producing more air than the other. The difference is the 20g moves the same volume of air as the 16g, but faster.  The 16g  = 500ft3 of air @ a pressure of 15psi

20g  = 650ft3 of air @ a pressure of 15psi

                                             

                                                650ft3          Y

 Now bare with me here          ----------  = --------     so  Y = 130%

                                                500ft3        100%

 

   so the 20 flows 130% better than the 16g. The same amount of air, just at a greater velocity, hence its more efficient.

   There is also the factor of temperature. Temp x pressure = density.  This also factors in the CFM that the turbo flows, but if both car ran side by side with the same ambient temperature and that air was compressed  to 15psi the same amount of heat would be created in both turbos while pressurizing the air. The 20g would move the pressurized air faster, and therefore move more CFM. I dont think a factor of resistance of flow or friction is a big factor since that would cause the psi to increase and the turbos wouldnt be flowing the same pressures and not comparable.

 

  That takes care of the air flowing into the engine, half of the turbocharging system.

One issue I previously stated in another post is on my car, the 20g produces 650 CFM @15 psi, at @18 psi the amount of air the turbo is flowing tops out, The intake flows far better than what the turbo is producing, so there isnt enough restricition to create any more pressure in the intake and boost higher. This is a two-faced issue and that the amount of air going through the compressor housing wont flow through the turbine housing at the same rate, because of the small TD-05 wheel.

By increasing the diameter of the turbine housing so a larger TD-06 wheel will fit that reduces the pressure in the exhaust housing exiting the turbo because a great volume will flow.  This brings up an arguement about what the Turbine housing of a TD-05 , the inlet side from the exhaust manifold. What is the max this will flow before it becomes more a restriction. I think this i what you are trying to figure out Joel. Im quite positive this part of the Turbine housing on my car has been  opened up/ported.

     

   I'm pretty sure I got way off track somewhere and my information may not even be right, this is from what I know and have learned....tryin to put it simply.

 

- Neil

 

  Check out this equation i found while researching online for this post.

 

Important equation:  cfm = (lbs/min x 10.73 x [degrees F + 460])

                                           ---------------------------------------------

                                                (29 x [boost pressure + 14.7])

 

                                                    1 cfm = ~ .063 lbs/min

[Boosted_One]

OK heres the details on my quest (Bill's old car) air flows from the head through a South florida performance header in the turbo. The Turbo: a Mitsu 20G in a TD-06 Compressor housing, mated to a TD-05 exhaust wheel in the stock (TD-05) turbine housing. This flows into a 3' downpipe, exhuast 3' all the way back, uses an external HKS racing wastegate, mounted on a flange on the underside of the exhaust manifold.

 

Now i'd like to point something out.

 

...the comment about gettin no more air in the motor on a 16g or 20g....I dont agree.

   Look at it like this, at 15psi say the 16g moves 500 CFM, and the 20g 650 CFM.

-Now you are right that at 15psi neither turbo is producing more air than the other. The difference is the 20g moves the same volume of air as the 16g, but faster.  The 16g  = 500ft3 of air @ a pressure of 15psi

20g  = 650ft3 of air @ a pressure of 15psi

                                             

                                                 650ft3          Y

 Now bare with me here          ----------  = --------     so  Y = 130%

                                                 500ft3        100%

 

   so the 20 flows 130% better than the 16g. The same amount of air, just at a greater velocity, hence its more efficient.

   There is also the factor of temperature. Temp x pressure = density.  This also factors in the CFM that the turbo flows, but if both car ran side by side with the same ambient temperature and that air was compressed  to 15psi the same amount of heat would be created in both turbos while pressurizing the air. The 20g would move the pressurized air faster, and therefore move more CFM. I dont think a factor of resistance of flow or friction is a big factor since that would cause the psi to increase and the turbos wouldnt be flowing the same pressures and not comparable.

 

  That takes care of the air flowing into the engine, half of the turbocharging system.

One issue I previously stated in another post is on my car, the 20g produces 650 CFM @15 psi, at @18 psi the amount of air the turbo is flowing tops out, The intake flows far better than what the turbo is producing, so there isnt enough restricition to create any more pressure in the intake and boost higher. This is a two-faced issue and that the amount of air going through the compressor housing wont flow through the turbine housing at the same rate, because of the small TD-05 wheel.

By increasing the diameter of the turbine housing so a larger TD-06 wheel will fit that reduces the pressure in the exhaust housing exiting the turbo because a great volume will flow.  This brings up an arguement about what the Turbine housing of a TD-05 , the inlet side from the exhaust manifold. What is the max this will flow before it becomes more a restriction. I think this i what you are trying to figure out Joel. Im quite positive this part of the Turbine housing on my car has been  opened up/ported.

     

   I'm pretty sure I got way off track somewhere and my information may not even be right, this is from what I know and have learned....tryin to put it simply.

 

- Neil

 

  Check out this equation i found while researching online for this post.

 

Important equation:  cfm = (lbs/min x 10.73 x [degrees F + 460])

                                           ---------------------------------------------

                                                (29 x [boost pressure + 14.7])

 

                                                    1 cfm = ~ .063 lbs/min

 

One advantage to a larger trim is a better efficiency range. Less heat because of less shaft speeds. Less heat = more power @ the same PSI. It isn't quite that simple as there are other variables.

 

Downside is more lag/less responsiveness.

 

It's all about efficiency and that's the advantage to larger trims, larger A/Rs,  larger IC piping, larger IC, etc, etc.

 

there's tons of variables...

[BMWTech]

Yea the more i read, the more I understand that....its pointless to argue one variable and overlook all the others. Thanks

 

-Neil

[Joel]

Now i'd like to point something out.

 

...the comment about gettin no more air in the motor on a 16g or 20g....I dont agree.

   Look at it like this, at 15psi say the 16g moves 500 CFM, and the 20g 650 CFM.

-Now you are right that at 15psi neither turbo is producing more air than the other. The difference is the 20g moves the same volume of air as the 16g, but faster.  The 16g  = 500ft3 of air @ a pressure of 15psi

20g  = 650ft3 of air @ a pressure of 15psi

                                             

                                                650ft3          Y

 Now bare with me here          ----------  = --------     so  Y = 130%

                                                500ft3        100%

 

   so the 20 flows 130% better than the 16g. The same amount of air, just at a greater velocity, hence its more efficient.

 

That doesn't mean the motor would consume it. The volume of the motor is not dynamic. At 100% efficiency at atmospheric you can't get more than 276CFM at 6000RPM. Why? Well, thats your displacement, we all know that.

 

Now adding boost is no different that calculating it at atmospheric, except that you use PR to multiply the CFM consumption (this is how to properly align a turbocharger and a motor up on a map). Just because a turbocharger produced more CFM (MASS) doesn't mean the motor will eat it without additional pressure. You can view the calculator I made for 100% VE at http://www.tristarion.com/boostcalc.php

 

This isn't something I made up, althought I didn't learn it from this book. You can find these equations on page 26-28 of Maximum Boost by Corky Bell.  

 

   There is also the factor of temperature.

 

Temp x pressure = density.

 

Ideal Gas law. P = nRT. In this case the equation would be n (density) = (PV)/(RT)

P = pressure, V = Volume, R = gas constant (8.314 J K^-1 mol^-1), T = tempurature.

 

Wish it was as easy as stated above.

 

 This also factors in the CFM that the turbo flows, but if both car ran side by side with the same ambient temperature and that air was compressed  to 15psi the same amount of heat would be created in both turbos while pressurizing the air. The 20g would move the pressurized air faster, and therefore move more CFM. I dont think a factor of resistance of flow or friction is a big factor since that would cause the psi to increase and the turbos wouldnt be flowing the same pressures and not comparable.

 

Not true. Efficiency includes heat. 15psi to 15psi 20g vs 16g, the 16g will prove to heat the air more. The compressor maps for both turbos will reflect that.

 

  That takes care of the air flowing into the engine, half of the turbocharging system.

One issue I previously stated in another post is on my car, the 20g produces 650 CFM @15 psi, at @18 psi the amount of air the turbo is flowing tops out, The intake flows far better than what the turbo is producing, so there isnt enough restricition to create any more pressure in the intake and boost higher. This is a two-faced issue and that the amount of air going through the compressor housing wont flow through the turbine housing at the same rate, because of the small TD-05 wheel.

By increasing the diameter of the turbine housing so a larger TD-06 wheel will fit that reduces the pressure in the exhaust housing exiting the turbo because a great volume will flow.  This brings up an arguement about what the Turbine housing of a TD-05 , the inlet side from the exhaust manifold. What is the max this will flow before it becomes more a restriction. I think this i what you are trying to figure out Joel. Im quite positive this part of the Turbine housing on my car has been  opened up/ported.

 

     

 

You got it, and this is where my lack of experiance and expertise stumps me some, So many choices. So many problems. I want proof this is a problem in the first place, instead of making assumptions. If you get to much at the manifold, then you have only a few choices.

   I'm pretty sure I got way off track somewhere and my information may not even be right, this is from what I know and have learned....tryin to put it simply.

 

- Neil

 

  Check out this equation i found while researching online for this post.

 

Important equation:  cfm = (lbs/min x 10.73 x [degrees F + 460])

                                           ---------------------------------------------

                                                (29 x [boost pressure + 14.7])

 

                                                    1 cfm = ~ .063 lbs/min

 

 

 

CFM consumption of a motor = cid x max rpm x ve

                                               __________________  = total cfm

                                                          1728

 

CFM consumption at Y psi of boost = PR x cfm, PR = 14.7+Y/14.7

 

Joel

[BMWTech]

Joel, Im not doubting your knowledge here at all....

  When i was writing that post and had to keep referencing things to get data, I knew i was going in over my head, well more than i could remember at the time. Now that I have a fierce headache lol, I realize too many variable to argue and I got way off subject. Now to get back on to it, If I can help at all, pls let me know.

 

   I will be upgrading the TD-05 turbine housing to  TD-06 spec, thats it along with turbo rebuild.

 

-Neil

[Joel]

No worries. My head hurts to.

 

Ever thought about getting a big clip done?

 

Joel

[BMWTech]

When i was talking to Mike at M.I.C. about my turbo. I asked him about clipping, he told me he recently had some training on it and said this.

 

-its almost impossible to clip the exact amount on each fin, so over time you a killing your turbo

 

-the difference in weights on the wheel slowing cause it go out of balance, some time in catastrafic failure, he said he stopped doing it since then and doesnt reccomend it anymore. So i wont be doing it =)

 

-Neil

[propeine]

well Im sorry i cant help you with your homework but i must say this has been a most informative post.  Thanks for all the info guys even if that wasnt where it was supposed to be going.  I'm trying to build my engine up based solely on the numbers so the more of this stuff i can get together the better off i am.

Tom

[Eldos1]

What about that fact that a bigger turbo has MORE mass to move; therefore you could hurt performance by having to big of a turbo. It will take more exhaust gas to move the turbo. After all, if that wasn’t true, we would call be raiding turbos off of Peter builts and Freightliners.

 

Steve Gee

[Boosted_One]

There's obviously limitiations to size.

 

With a larger turbo you set it up to minimize the lag.

 

This is why people opt for split tang turbine housing and other bolt ons which signicantly cut down on lag issues.

 

Ya, you take a T-61 and slap it on a stock Starion and it'll be a boat anchor, you slap it on a built motor set up for that turbo and it'll rip.

 

The exhaust side dictates the lag.

[Joel]

Within limits, you can also use smaller A/R's on a bigger housing to help reduce lag.. No a small A/R on a Big diesel turbo would simply not do anything, but on a T3/T4 it certainly could make you or break you depending on choices made.

 

Joel

[Joel]

No one gives a rats a** about why this topic was posted?

 

Seems to have gone everywhere but the original intention...

 

Joel

[dstar26t]

Joel,

I've got the stock fuel injection, adjustable BCFPR, 2 1/2" exhaust, pocket porting in the head (no JV), stock TB, schneider 274 and a TDO5-17C.  I'm curious to see what my exhaust pressure in the manifold is compared the intake pressure.  I'll probably spend some time within the next couple months to check it out after I get the cam degreed and other crap.  I'd be happy to relay the info to you.

Nate

[Joel]

I would really appriciate it!

 

Joel