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Quote:
Originally Posted by RarlyL8 View Post
There are many turbos with a lower threshold than your 7200, but not many that will support 500HP. I've got a bolt-on you may be interested in AND you can trade in your 7200.
What turbo? Would it be appropriate for CIS too? I am running a K27S now, Garretson IC and Fabspeed exhaust.
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Old 12-22-2009, 09:06 AM
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Troy, shoot me an e-mail or phone call for info. I don't want to hijack this thread.
Thanks -
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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 12-22-2009, 09:58 AM
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My two cents:

I accept the thought that the current newer ball bearing single turbos are a match to twin turbos in most cases. They are a lot easier to package and simpler.

It is just a guess but I suspect twin's on Porsche's are as much about marketing and packaging the cats & mufflers as performance. May also have to do with what was available from there turbo supplyer.

Check out DonE's car. I think it has a GT35 and has ton's of low end and still makes more than 500rwhp. I do not recall but he might be at .8 bar by well under 3000rpm.

As noted, a lot of low end is in the tuning. Also, proper hot side ratios, just the right size compressor wheels, minimum volume header manfold, making sure you have efficient Wast Gate capacity, AFR's, and ignition. Turbos thrive on low resistance before the compressor intake and as little as possible after the turbine exhaust. Add in 1.5" Synapse Synchronic BOV for a bit of anti lag to keep the turbo spinning at idle and cruse and you have most the pices to work with.

If you want single sexy, Tial makes hot housings out of stainless steel for the GT turbos that are lighter.

If one just has to have the ultimate I suspect is would included a "sequential turbo" system (remember the 959?). Maybe put the turbos to the rear, plumb a cross over tube between the secondaries and put a clipped exhaust butterfly valve just after the tee and before one of the turbos. This should get you full boost by 2k if that is your dream.

Last edited by 911st; 12-22-2009 at 12:00 PM..
Old 12-22-2009, 11:54 AM
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personally I think it cost more for Porsche to twin turbo the 911 vs single so cost wasn't the issue, and I don't believe they were going after the "boy racer" by using twin turbos as a lure so i don't feel thats the reason. So aside from emmisions, which I do feel had a large hand in the decision, I think "turbo lag" is on the top 5 list of reasons to twin turbo the 911. Twins respond quicker than a like sized (power wise) single and people want instant gratification. Look at every other manufacturer that has a performance turbocharged vehicle, they have gone twins or sequential to make the power band seemless and instant.

But ultimately the reason I am going with twins is "because".
Old 12-22-2009, 02:50 PM
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Mostly agreed.

After the want for power, turbo lag has probably sold more add on parts than anything for a CIS turbo.

When many of the writers were first talking up the 993TT back in 95 or so they almost alwas talked up TT's as haveing a response advantage... That was mostly the truth per what was available and reliable enough for a production car.

After all, the 993 was on the drawing board some 18 years ago. Also back then probably the only turbo mfg Porsche probably felt comfortable with for duty on there air cooled motors was KKK.

Flat 6 lends its self very well to a twin turbo lay out (look at the HE's of a TT compaired to the 3.6T's). Then there was the big success of the RUF Yellow Bird and all stars lined up for a TT. The market wanted it and it was a better set up.

On a side note, I belive if twin plugs were a clear advantage for an EFI Turbo of Porsche design, Porsche and RUF would have included it. It probably would not have added to direct labor and materal costs on there $100k+ car more than about $250.

One another side note, Porsche pretty much deemed the base 993 & 996 turbos (K16?) as limited to about 400hp before there effecency was starting to be questioned. Of cource tuners were happy to push them well beond that.

From my limited study it seems motor lay out and the design enviornment tends to be more the deciding factor these days as long as cost not an issue. A V6 or flat 6 is going to usally get a TT set up, a straight 4 or straight 6 a single turbo, a V8 twin turbos... Then there will be those companies that see a marketing advantage to a given lay out.

These days differance in performance between a single turbo and a twin turbo has more narrowed. Things like ball bearing center section; lighter impellers from different casting tech, materials, & machining; varable vein; and other tech improvements are part of this.

There can be single's that out performs TT's and there will alwas be TT's that out perform singles. I just do not see such a significant differance as there once was. Depending on the HP goal. Of course, there are those single turbo drag cars that sport single turbos making 1000 HP a such.

There is probably more of a differance with picking the right single or twin turbo to fit the application and or getting the tuning right when it comes to performance.

Not an expert, I could be off base, this is just my humble thoughts to date.

Last edited by 911st; 12-22-2009 at 04:11 PM..
Old 12-22-2009, 04:04 PM
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very nicely put. I appreciate your thoughtful responses, it's great to hear an actual thought vs the typical response of "my buddy had a twin turbo and it was bad a$$... turbo technology has come light years ahead and that technology has made it posible to run large single turbos on small displacement engines, but generally speaking the small twins will give the quickest response due to the things you mentioned ie: the turbos are small and light, are generally mounted closer to the exhaust port of the head and individually take up less under hood realestate.

Ultimately I am not looking for much more power than my k27 was capable of providing, just broadening the power band and maybe alittle of the "cool" factor thrown in for good measure.
Old 12-22-2009, 08:05 PM
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For those that follow that are trying to decide between two or one I came across this from Garrett about single v double:

Quote:
What are the main differences between a Single and Twin Turbo setup?

Choosing between a single or parallel twin turbo setup is primarily based on packaging constraints in the engine bay, or a personal choice by the tuner. In most cases, for top performance, a single turbo is preferable because larger turbos are generally more efficient than smaller turbos. However, often there is not room for one large single, or the tuner wants the visual impact of twin turbos. The notion that two smaller turbos will build boost faster than one large turbo is not always accurate because even though the turbos are smaller, each one is only getting half of the exhaust flow.
TurboByGarrett.com - FAQ's
Old 01-16-2010, 07:22 PM
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Here's one.. 87 930TT..

3.5 Ltr w/twin Garret T-04b Turbos and waste-gates by Turbonetics
all the usual case work done, Carillo rods, flame ringed.. yadda-yadda etc..

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Old 01-17-2010, 04:56 PM
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Quote:
Originally Posted by motley911 View Post


Richard, lovely set up there, are you planning on running the engine without a muffler with pipes straight out of each turbo is in the photo?

I would be really interested to know how loud it is as I am thinking of running a twin turbo set-up in a mid-engined installation i am working on so I can run the exhaust pipes straight out the sides in front of the rear wheels.
Old 01-20-2010, 01:32 PM
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Seems the turbo acts somewhat as a muffler.

If so, an un-muffled wast gate might add more to noise than the turbo section.

Some day I hope to try a zork with a muffler on the WG and see if I can live with it.

Anyone tried this and comment?
Old 01-20-2010, 05:13 PM
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Capt Ahab - yes I am planning running the exhaust without mufflers. I don't know how loud it will be yet, but if it is too obnoxious, I was thinking of fitting a couple of Supertrapp Disc only mufflers to the end of the pipes. That way I can remove them easily to run wide open or add / remove discs to "tune" the noise.

Summit sell them for about $80 each for a 3" inlet pipe.




Richard.
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Old 01-20-2010, 09:40 PM
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anybody using supertrapps on a turbo car? I was considering the same on my twin build but have no data on how well they work in a turbo application. They do have a unique sound

oh, right now i run a little 90* elbow off my wastegate thats maybe 5" long and my exhaust consists of nothing more than a slightly bent section of 3" tubing, no muffler... and I can hardly hear the wastegate open over the exhaust howl at WOT...
Old 01-21-2010, 08:31 AM
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Straight pipe it - i did on mine and everyone loves it...trust me you don't want to muffle these things unless you're looking to be a sleeper.
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Old 01-21-2010, 08:38 AM
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I would not use ST on a turbo motor except to get through some type of test.

Better to put a choke in the pipe down to 2.5".
Old 01-21-2010, 08:41 AM
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when i put the twins on it i'm going to run 2.50" pipes. I'll see how it sounds and go from there.
Old 01-21-2010, 08:49 AM
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Please don't even consider using a Supertrapp disk style muffler! It's Ugly and it disperses the exhaust radially. Weird design.
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Old 01-21-2010, 09:31 AM
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Have you decided where you will mount them? This will dictate your options, other than straight out.
Old 01-21-2010, 10:15 AM
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the turbos will be in the 993TT "location". We'll be making headers so they may be moved forward as far as possible to gain more area for muffler options. Otherwise i'll criss-cross the pipes behind the motor and mount mufflers in a stacked configuration
Old 01-21-2010, 01:29 PM
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I have a set of nearly new fabspeed 993tt/964tt headers that I would be willing to sell if someone needs them for a TT conversion. They worked great on my previous 993tt. Gained some peak torque but lost the heat from the lack heat exchangers. This may not be an issue to some of you. Thinking $500.00 for the pair.
Old 01-21-2010, 02:38 PM
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I would be very interested..
Old 01-21-2010, 02:52 PM
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