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Great thread! Here is a twin turbo set up for your consideration and feedback


Old 01-16-2010, 12:48 PM
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Wo ist die Rennstrecke?
 
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Originally Posted by RarlyL8 View Post
Nothing was changed but the headers. The existing Euro system was in excellent condition with no leaks. The new ones have all new hardware and I've detected no leakes. There is no O2 sensor or smog equipment of any kind on my engine.
The headers were responsible for the change in idle mixture. Don't know why myself as I did not expect the change to be significant. These headers are obvioulsy vastly different in design than the J-pipe configuration that was replaced, we do know that much. You can hear the pulses hit the turbo at low idle like a cammed engine.
Don I would think you should hear this cammed sound with your headers as well. Have you not experienced this?
No doubt it sounds great and sounds much better than the B&B I had.

I remember when I got my new stainless headers from Marco and how I couldn't wait to replace the short B&B header with my new custom equal length MM header. I spent all night ripping out the B&B and carefully installing the new set. Within a week, I went back to the dyno to see the improvements.

Initially, I found the spool was slower, but from 5000 rpm on, it felt good. When I got to the dyno, it was confirmed. I lost power up to 5000 but from there on, wholly crap it took off, nearly straight up. My problem was that I hardly ever drive at those RPMs on the street. But it sounded mean.

About 6 months later, I was in FL at a builder's dyno where the customer had his 3.3L CIS built and he replaced his B&B header and put 1 3/4 inch equal length pipes. The motor was at the builder not to initially be built, but to find out why the car was not putting out more power (owner spent huge $$). I went back home to GA and I later found out from the builder that they found the problem - the header was too big at 1 3/4in primaries. When they went to 1 1/2 short pipes, the power came up big time and they found they needed a different turbo (turbonetics) to handle the new-found wide power band (2800 to 7000 rpm). They also told me that the back pressure (the pressure between the head and turbo) also increased (sorry, can't remember the pressure they measured, but I think was around 8 psi?????).

So, even though I don't know all the physics and thermal dynamics of building a header, I know what I've seen and learned from my own experiences - short, direct pipes that keep heat and velocity up to a properly chosen turbo works best. I wish I would have kept a record of all those dyno's I did because data is the only way to argue these points.

Last edited by DonE; 01-16-2010 at 01:10 PM..
Old 01-16-2010, 01:08 PM
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Wo ist die Rennstrecke?
 
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Given the course and length of this thread, it looks like it needs to be a business priority.
Great advice. As far as performance goes, I wouldn't buy anything for my car that wasn't tested and proven.
Old 01-16-2010, 01:15 PM
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I knew the answer to that story before you got to the end. 1.75" primaries are WAY too big.
If the pipes aren't the right size for the application they won't work. Sounds like yours were too big as well. Velocity vanishes quickly if the ID is too big.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-16-2010, 01:19 PM
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Is there any resource or rule of thumb for primary and secondary sizes per boosted HP?

Brian, what size secondary size did you choose?

Anyone know a stock 930's secondaries and J pipe ID or OD is?
Old 01-16-2010, 03:59 PM
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Primary and secondary ID are critical to velocity. I use 1.5" primaries and 2" secondaries up to 450WHP and 1.625"/2.25" beyond that. You also have to take a look at the rest of the build and see how/where the power is made to size the headers appropriately.

The stock Euro system is thick walled and I have not cut one of these in two to check the ID. The early Euro/USA system has very tiny secondary pipes.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-16-2010, 04:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #126 (permalink)
 
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Quote:
Originally Posted by RarlyL8 View Post
I knew the answer to that story before you got to the end. 1.75" primaries are WAY too big.
If the pipes aren't the right size for the application they won't work. Sounds like yours were too big as well.
For my 3.3L CIS, yes. For EFI (which was planned within a year) the size is just right for a 3.4L. In fact, I welded on a T4 flange to accept a bigger turbo - GT35.

Still, the problem (for me) is that they are equal length for a mostly street application. But I think this thread is inspiring me to make my own short pipes while the motor is out.
Old 01-16-2010, 05:28 PM
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On a NA motor with SC/Carrera cams above 200whp one starts to benefit with a change to 1 5/8's primary tubes.

Is there a way to find out where a turbo will benefit in a jump up from 1.5" primaries?

Any third party expert info on this or rules of thumb?



If not, can we calculate it some way from the NA info above?

My gut tells me that if at 1 bar if we are pushing up to twice the NA air through the intake it might be about about 2 times or 400whp +/- but this may be far from, far from true.

If it is true and a 1 5/8's is about 20% larger that might take us up to about 480whp.

And if 1 3/4 is about 40% larger than 1 1/2 that might be good up to about 560rwhp.

This dose not mean we can not make much more hp, only that there might be some HP to be gained on the top end if there is not something else limiting.


Again, this could be far from true.


Anyone have any data points on primary tube sizes?
Old 01-16-2010, 06:50 PM
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Brian,

Sorry, I did not mean to jump over your reply. Thanks.
Old 01-16-2010, 07:00 PM
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No problem Keith. This is one instance where applying N/A flow theory will hurt you. Size the headers too big and you lose velocity. It's a balancing act (litterally) between back pressure and velocity.
The twin turbo pictured at the top is a nice setup. They could have taken it one step further and terminated the collector at the turbo. You can also eleminate the waste gate plumbing by using internal wastegates like the K16's have.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-16-2010, 09:02 PM
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My 934 style exhaust also has 1.5" primaries and 2" secondaries.. Just installed and not tested yet. But good to hear my numbers are about right..

Those internal wastegates usually dont respond well to higher output tuning..

The new tial MVS 38s probably are the ticket on a fairly high output TT engine.
(new mvs 38right/old tial 38 on left))

2 of these probably weigh less than half of one porsche waste..

Old 01-16-2010, 09:52 PM
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I agree that external WG have advantages but there are packaging considerations as well. Internal waste gates are adjustable which can help offset other weaknesses. The above system has the WG venting back into the muffler so may as well use internal unless just to big/powerful.
I also use dual TiAL 38mm WG on higher HP systems that must have precise WG control. Have made several of these and really like the packaging and control.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-17-2010, 07:11 AM
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[QUOTE=Ringmaster;5129509]Great thread! Here is a twin turbo set up for your consideration and feedback ]

This is beautifully made, and can take advantage of pulse conversion due to being a twin turbo. The problem is that the individual pipes dump into a pretty big collector, which lets the pulses expand before they get to the turbo.

Also, the individual pipes can and should be MUCH shorter and straighter.

Tuning individual pipes to a certain length is done for scavenging effect. For scavenging to work you need to have a fairly large amount of overlap in the valve events. The idea is that a low pressure suction pulse will travel back up the tube and arrive at the exhaust valve just as the piston has gone past TDC and is started on the intake stroke. The low pressure pulse will still let exhaust gas flow out of the engine, even though the piston is now going down. Obviously, such a situation can occur only at a very narrow RPM, and needs a cam with a lot of overlap to work really well. If you are like most, you have the classic turbo cam, which has exceptionally low overlap, so forgetabout scavenging.

The other reason that longer equal length pipes are used is for momentum tuning. In this concept the mass of the exhaust gas gets moving due to the high pressure in the cylinder on the exhaust stroke, and the low atmosphere pressure. Once the exhaust valve closes, the exhaust gas will still keep flowing down the pipe because of its momentum, as long as it doesn't run into any interfering pulses. It will empty out the tube and make the pressure nice and low for the next exhaust event. For us the problem is obvious, we have a turbine in the way, so instead of low atmospheric pressure, it encounters something quite a bit higher, which greatly reduces the momentum effect.

Make the pipes shorter. This will improve your time to make full boost. Since a setup like this can push a lot of air through the engine, the diameter of the pipes is OK, but no bigger. If your goal is in the 450 HP or less, they could be smaller. The diameter balance for you is: 1) too big and the exhaust pressure expands in the tube instead of the turbine at low speeds - no good. 2) too small and your monster motor will have too much backpressure.
Old 01-17-2010, 07:46 AM
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[QUOTE=Speedy Squirrel;5130566]
Quote:
Originally Posted by Ringmaster View Post
Great thread! Here is a twin turbo set up for your consideration and feedback ]

This is beautifully made, and can take advantage of pulse conversion due to being a twin turbo. The problem is that the individual pipes dump into a pretty big collector, which lets the pulses expand before they get to the turbo.

Also, the individual pipes can and should be MUCH shorter and straighter.

Tuning individual pipes to a certain length is done for scavenging effect. For scavenging to work you need to have a fairly large amount of overlap in the valve events. The idea is that a low pressure suction pulse will travel back up the tube and arrive at the exhaust valve just as the piston has gone past TDC and is started on the intake stroke. The low pressure pulse will still let exhaust gas flow out of the engine, even though the piston is now going down. Obviously, such a situation can occur only at a very narrow RPM, and needs a cam with a lot of overlap to work really well. If you are like most, you have the classic turbo cam, which has exceptionally low overlap, so forgetabout scavenging.

The other reason that longer equal length pipes are used is for momentum tuning. In this concept the mass of the exhaust gas gets moving due to the high pressure in the cylinder on the exhaust stroke, and the low atmosphere pressure. Once the exhaust valve closes, the exhaust gas will still keep flowing down the pipe because of its momentum, as long as it doesn't run into any interfering pulses. It will empty out the tube and make the pressure nice and low for the next exhaust event. For us the problem is obvious, we have a turbine in the way, so instead of low atmospheric pressure, it encounters something quite a bit higher, which greatly reduces the momentum effect.

Make the pipes shorter. This will improve your time to make full boost. Since a setup like this can push a lot of air through the engine, the diameter of the pipes is OK, but no bigger. If your goal is in the 450 HP or less, they could be smaller. The diameter balance for you is: 1) too big and the exhaust pressure expands in the tube instead of the turbine at low speeds - no good. 2) too small and your monster motor will have too much backpressure.

Great post and thanks for the feedback. To quickly address a couple of your comments...

-The cams are large Schrick race units with lots of overlap
-The engine package makes over 700hp
-It was built as a semi-race engine designed to operate effectively between 4000-7500rpm

More later when I have some time to type
Old 01-17-2010, 08:06 AM
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re: primary and secondary sizing.

Quote:
Originally Posted by RarlyL8 View Post
...This is one instance where applying N/A flow theory will hurt you. Size the headers too big and you lose velocity. It's a balancing act (litterally) between back pressure and velocity...

(and)

...Primary and secondary ID are critical to velocity. I use 1.5" primaries and 2" secondaries up to 450WHP and 1.625"/2.25" beyond that...

Spit balling again.

I am not suggesting we just use N/A flow quantities for the header sizing directly. That would not make sense. Just that we interpolate from the N/A numbers if we do not have any solid numbers for turbo'd motors.

For example, if we can flow say twice the air through the intake using pressure. Maybe the same applies to the exhaust side as, at least as a starting point.

As a point of reference 450whp might be compared to 225rwhp on a N/A motor. This seems to fit well.

I had no issue making 217whp through the stock 1.5" headers on my 3.2 Carrera and a sport muffler would have put me at near 220whp.

This worked well on my car but testing by SW confirmed that steping up a size would good for about 10 hp.

Not saying the relationship will be as direct but there may be a strong correlation as long as there is not something else that is going to create a restriction like the turbo hot side or compressor moving out of its efficiency range.

Before anyone making near 450whp runs off and buys a set of larger headers they might note that if the motor is still a 3.3 with SC cams how much might this hurt where the achieve full boost.

If one increases the size of the primary tube about 20% and the secondary tube about 28% velocity is going to slow down around 22% or so. Also the volume of the headers will increase about the same 22% or so.

This could push boost response back in as much as 600rpm (using 3000rpm as the starting point).

Now, bump the displacement from 3.3 to 3.5 and boost response should come in sooner by about 200rpm.

Also, I bet that if a 91/2 3.3 turbo comes on full boost by 3000rpm, a 93 3.6 that uses the same turbo will probably come in at about 2750rpm.

Going to a 1 7/5 from a 1.5" on a 3.3 and boost response could move back as much as 1200rpm or so. Great maybe for a race car if it has the heads & turbo to support it.

Thus. it might be better for most of us to stay with a smaller size to keep drive-ability even if 10-20 hp might be had with a larger size.

Just a thought.

Last edited by 911st; 01-17-2010 at 08:32 AM..
Old 01-17-2010, 08:28 AM
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Quote:
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Great thread! Here is a twin turbo set up for your consideration and feedback




Oooh, that looks lovely! I'd love a system like that on mine, although i'd have the wastegate pipes dumping straight out just for the added noise on WOT. Would the muffler part bolt straight onto a stock 993, are the turbos in the same position? Is this a custom job or is it available for sale off the shelf?
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Old 01-17-2010, 09:09 AM
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Quote:
Originally Posted by Speedy Squirrel View Post
For scavenging to work you need to have a fairly large amount of overlap in the valve events. The idea is that a low pressure suction pulse will travel back up the tube and arrive at the exhaust valve just as the piston has gone past TDC and is started on the intake stroke. The low pressure pulse will still let exhaust gas flow out of the engine, even though the piston is now going down. Obviously, such a situation can occur only at a very narrow RPM, and needs a cam with a lot of overlap to work really well. If you are like most, you have the classic turbo cam, which has exceptionally low overlap, so forget about scavenging.
Sounds like all of this back and forth about equal length vs. short path is moot then. It also saves me $2500
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Old 01-17-2010, 10:25 AM
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Scavenging is not the primary function of equal length headers on a 930 engine; having a tuned or tunable system is the point. It's all about efficiency and velocity. There is neither in a short tube or log system, you are just dumping exhaust at the turbo. If a tuned system is not important to the consumer then a short tube or log header is a much less expensive choice. The Chinese e-bay offerings are dirt cheap.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-17-2010, 11:01 AM
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Interesting concepts, one picks and chooses basic engine principles that increase volumetric efficiency once the turbo is bolted on. Why?

Typically, if one is hotrodding an N.A. engine, yes they employ these principles to effectively use the mass of air flowing in both the intake and exhaust system to deliver more than 100% VE. In effect it’s mild supercharging on the intake and extracting on the exhaust. These are the same concept but acting in different areas of the engine system. They are beneficial acting independently, or combined.
The fact they are at their best when combined (tuned) doesn't negate their potential postive effects across the entire power range.

Suction (such a stimulating term!). Just using it regarding your engine compartment can lead you down wrong paths. It’s best to say absolute pressures. When you consider absolute pressures the lure of the word suction goes way and you are only looking at slugs of air, N.A. or turbocharged.

What changes once you place a turbo in the flow path? If you say the turbine represents backpressure then every N.A. street machine hotrodder with mufflers and tailpipes are only kidding themselves?. They should save their money because you can only see benefits when exhausting into open atmosphere? But then open atmosphere is 14.7#, isn’t 14.7# real pressure................

Last edited by copbait73; 01-17-2010 at 01:22 PM..
Old 01-17-2010, 12:43 PM
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Yesterday I was playing on a Turbo calculator website. I put in the factory data for the '77 930 Turbo motor (no guessing the intercooler eff.). I was somewhat surprised to find the assumed VE had to be dropped to only 75% to make all other knowns work.

Obviously this is low for a performance design like the 911. It shows how much was left on the table to meet all other requirements like emissions, fuel economy, noise, etc while still producing more power reliably. In many ways a diamond in the rough compared with say the MFI 2.7RS.

This exercise also shows expensive hardware only marginally improves HP with no changes to improve VE. The best turbo and best intercooler will add little compared with good old basic hot rodder VE improving techniques of intake tune and balance, port/valve sizing (flowing), cam timing/lift and exhaust tune and balance.

This does not say the most efficient compressor and CAC are not extremely important. They are, after the high VE gets that charge in it needs to be cool not simply a high BOOST pressure.
Old 01-17-2010, 01:18 PM
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