Twin turbo configuration questions: Theory & Application

[RickM]

Juan, thanks for the pics. Wish I lived closer to get more detail. If you have a "look down at engine shot" I'd surely appreciate it. Thanks again!

[RickM]

Yerman, Are you taking pics of your build? I'm sure many of us would be very interested in the approach.

[RarlyL8]

Did anyone answer the question of what turbos to use for a tt application?

Are there any out there that are:
- The apropriate size to use in a twin turbo application of 3.2/3.3L
- Oil cooled only
- Found in a stock application (read cheap)
- Configured in such a way that lends itself to the use of stock 930 ancillary equipment (such as oil lines)

A turbo tuner told me that 993tt units would work. I know nothing about them other than water cooling is not an issue and 3.6L is close in displacement to a 930. Anyone have experience with this?

[Natchamp]

Hey Rarly, I'm actually working on that right now. Currently I am using k16/24 hybrids but am not entirely happy with them. I think the k24 compressor is a little aggresive for my 3.2L displacement and 993SS cam. I'm not getting boost as early in the rpm range as I would like. I'm mapping out the different Garrett compressor maps for my motor and am narrowing in on the T04E Super 50 trim. The newer GT32 is also a reasonable fit but not quite as good as the T04E, per my "current" calculations. I am told that its possible to put some Garrett compressor housings and wheels on the kkk center sections so if that's true it would make mine basically a bolt in. Other wise I would have to change the flanges on my headers unless I went with a Garrett T3 turbine housing. Is there a TT in your future?

[WydRyd]

Well, if I were to consider that route, I'd use a pair of hybrid Garrett T3/T4's, spec'd to flow ~300-350HP each.

Or if you want to stick to 3K, go K24's, however, these aren't cheap at all. The T3/4's could be had relatively cheap off EBay. Just ask Mike the mechanic, that's where he got his pair from REALLY cheap

[WydRyd]

BTW, try this URL as a guide for Turbo sizing:

http://www.turbofast.com.au/TFmatch.html

Juan, you car is no longer a 3.2L, right? It's in actual fact, a 3.3L with Flame Ringed Cylinder-heads?

[juan ruiz]

Juan, you car is no longer a 3.2L, right? It's in actual fact, a 3.3L
with Flame Ringed Cylinder-heads?


Still a 3.2 with 3.3 P&C with Flame Ringed Cylinder-heads

[WydRyd]

That's some SERIOUS HP for a 3.3L man! Well done!

I'm going down that route too, however, it looks like I'll be shipping my engine to Protomotive to get all the internals done

[RarlyL8]

Yes Mark, I've been looking into twin turbos for some time now.

I've lusted after the look from the first time setting eyes on the rear end of Porsche race cars in my youth. It is only now that the dream could actually become reality.
It's very impractical in a lot of ways. The advantage that I'm looking for is quick or nearly instant spool up. The tried-and-true system that I currently have sees boost kicking in somewhere around 2800rpm with full boost in before 3200rpm. That's not bad but my driving habbits don't see the engine in that range all of the time. It is interresting how a partial throttle or gradual footfeed will show no signs of lag - none, but tromp it at 2000rpm and all hell brakes loose at 3000rpm. My tires are nearly bald from this form of entertainment.
I plan to leave the entire engine just the way it is and simply add the twins. I asume that the torque curve will really flatten out. What about horsepower? How much of an increase would properly sized twins be over a single K27-7200?

Merv - the T3/4s you speak of, what is the price range and application for these units? Are they oil cooled only?

[Natchamp]

Rarly, I know exactly what you mean, you sound to have a similar driving style to mine. I too, after the lowest boost threshold. That's the basis for my whole setup, short and relatively small primaries, twins, etc. Currently, with my K24's I'm not seeing full boost until @ 4k which is much too high for my liking. There is still tuning left to do, primarily on the ignition, which plays a huge role in things such as when the turbos light up. And it ain't all just about advancement either. Unfortunately, I have some mechanical limitations that aren't as easy to address. I have a short stroke for a turbo motor and I'm learning that turbo motors really like longer versus shorter strokes. I think I might also be giving some up with the overlap on my particular cams. All of this and only 3.2L are contributing to my boost not coming on as soon as possible.

As far as hp, I wouldn’t be looking for enormous gains depending on what your current single is. Typically, a single turbo will make more outright hp than twins. I believe what you get with twins is more torque sooner via the lower boost threshold.

For me, I’m not a believer at all (any more) about the myth of worrying about the water cooling issue. Although I don’t know if it holds true for BB turbos too. A major reason I went with kkk’s (and gave up the better flow patterns of Garrett’s) was because of the water issue. Since then several people have convinced me the water issue is bogus. The fact that you can order the center casings with or without the water ports should have been the first clue.

You may or may not have an issue with the stock turbo scavenging system coping with the doubled oil flow to return. Others are well more versed in this than I. Cheers.

[beepbeep]

Twin Turbo guys:

There are pro and cons with twin setup.
Pros:
- Simpler header routing
- (Eventually) faster spoolup due to lower inertia of smaller turbos
- Bragging rights

Cons:
- Less power than one bigger turbo, due to lower efficiency of smaller ones and inherent parasitic losses tied to two sets of plumbing
- More expensive
- Hard to find small effective turbos that spool up nice.


My personal opinion is that there are many TT guys who start with ambition to shorten lag. Unfortunately, they tend to go out and buy two turbos that are a tad too big (to "grow" in) and forget their short-lag objectives when HP-fever catches.

It inevitably ends with laggy and late boosting engines.

If i was trying to build tractable TT engine i would go for very small turbos. To put this in objective:

SAAB built turbocharged cars for decades. They started with Garrett T3 on 2L engine in 70's and it was pretty laggy even if it flowed lot's of air.
Horsepower: 147hp
Size:2.0L
Boost treshold: ~3200RPM

During next decades, they gradually stepped down in size. 2.3L engines got smaller T25's and produced 200hp out of factory (250hp being maximum when chipped for more boost). They deliberately chose small turbo that was out of it's most effective pump range to boost torque and response.
Horsepower: 200hp
Size:2.3L
Boost treshold: ~2000RPM

See my point? They extract 200hp from 2.3L with excellent driveability with turbo that most 911 TT aspirants deem "too small" for their twin installations. If you want to have tractable engine, go down in size!

In real world it's pretty uninteressting with high max HP peak. You will rev trough particular range and car that has meatier torque curve trough that range will pass mega-HP car with peaky curve, lot's of lag and high boost treshold.

P.S.
Talking about size and tractability...i was co-driver in turbo-converted BMW 325 with one Mitsu TD04 HL-16T "miniturbo". That car left my frineds 996 C2 in dust...both in start and in straight line. Go figure.

[RickM]

Merv,
Curious if you know these guys... http://www.turbofast.com.au/balstd.html

[juan ruiz]

I will like to add........... the choosing of the turbo is a very important part of the set up either single or tt, all the information outthere is very good and very close for guide lines, but it will be the "Entire Combination" that will make all the power.........

As an example not long ago I was with one of my friends with a 3.5 single turbo with about everything you can imagine, because all this "Race Bench Experts" he went with a T 66.............ohhhhh the famous. T66, anyways I was about to DIE when this thing only made 500hp barely.

I have seen the same problem with others 3.3s a 3.4 and even a few tt, so remember that the "Entire combination" is the one that will give you all the juice..

If you want little turbos heres a few choices....

TO4B/.58 or 60-1HI-FI .81 of course the list is endless BUT unless someone has done the R&D and is a proven combination only then we could be 100% sure ......and dont expect the Porsche Experts to disclouse their "Secrets" about turbos

Additional Inf...
The T04B and T04E series are the most versatile turbochargers available to the performance aftermarket. High compressor efficiency, strict quality standards, TURBONETICSÕ exclusive "blueprinted" assembly process and competitive pricing makes the T04B and T04E the obvious choice for many applications.

Available in a wide range of compressor and turbine combinations, the T04B and T04E family can support power levels from 300HP to 550HP for single turbo applications and over 1000HP for twin turbo applications on engines from 100CID to 500CID.

[RarlyL8]

You fellas all touched on what I am after - Torque.

The plan is to not touch the engine. The SC cams give great throttle response and the 915 gearing is very quick. The CIS will remain 'cause it works perfect and I don't need over 400HP, nor do I want it. High horsepower = broken stuff = $$$ + down time. I want LOTS OF RELIABLE FUN.
This car as it sits has the gearing and power to wieght ratio to destroy most things on the street. But ONLY if I'm not caught off guard off boost. So I'm after driveability and fun factor. Period.

Little turbos, bring 'em on!

So what about stock 993tt units? Any good for this application?

[BURN-BROS]

Torque is what I am after as well. I had a kneejerk reaction and purchased a couple of used 996 k16s. I have not been able to find parts for them in the states(maybe someone can help me here). I have not been able to find any maps as well. From what I have learned, you size turbos with your displacement and max rpm. At least that is what the turbo calculators out there are looking for. I will be putting the k16s on a 3.3. Ultimately a map of these compressors is what you will need to find out when they will spool up...So does anybody have the maps?.....Anybody?

[RickM]

Did you try Windward, Powerhause (sp) or Turbo City for parts?

[BURN-BROS]

I called TurboCity, they do not service them. I asked where to find parts and they said there might be a guy in florida. I have them at a place that runs in the american lemans series. I have a friend that is in the porsche buisness as well and does not recommend most of the turbo places(too many disappointments). I will try winward and powerhouse though(for parts). Thanks Rick

[beepbeep]

Ultimately a map of these compressors is what you will need to find out when they will spool up...So does anybody have the maps?.....Anybody?

Calculating boost treshold "dry" is The Holy Grail that many turbo tweekers have been searching for ages. Unfortunately nobody has ever found it. It's very hard to calculate boost treshold even if you have maps. Maps are handy when you want to find correct size of of turbo and see what efficiency range you are into, but they won't tell you much about boost treshold.

Problem is that boost treshold depends on so many different factors that are not included in maps, like exhaust backpressure, header design, IC efficiency, IC flow, plenum volume, head flow etc. etc.

With other words, you can not calculate treshold by looking in the maps. On the other hand, some people can guesstimate it pretty accurate thanx to their extensive expirience with different turbochargers, engine volumes etc. Some of them are uncanny accurate...

For laymans like you and me, it's best done by comparing boost treshold for other cars with same turbocharger and compensating for engine volume accordningly.

With other words, if 2.0 SAAB 9-3 has Garret GT17 turbo has boost treshold of 1800 RPM (which it has) then it's pretty accurate to say that two of those would have boost treshold of 2250 RPM if installed on 3.2 engine.

( 2.0 / ( 3.2 / 2 ) ) * 1800 = 2250

Now 2250 is pretty much better than 4000 Natcham gets but GT17's will also flow less air at higher revs and cap max power output to something like 340hp instead of his 400-something. They will spool up near instantly really quick in 3000-6000 range though.

If you are big dog and run aftermarket ECU then you can use anti-lag and have instant boost everywhere...it chews turbos and wastes fuel though.

Here is a dyno movie of friends 900Nm twin turbo converted 3.6L engine:
http://www.itsfun.nu/itsfun.nu_dyno.mov
Movie is 34MB and has lot's of techno babble in Swedish, so download it on your own risk.

Engine sports two GT30BB's and has antilag (seen and heard at the end of the movie) It has over 1 bar of boost off idle...and 900Nm!! Horsepower figure is north of Ruiz car by quite a chunk...

[RickM]

Here's one more possible avenue for parts and info.... Turbojoe6638@aol.com . He's a custom turbo builder. May be worth an Email.

[BURN-BROS]

Beep, I was under the impression that the dashed line on the left of these maps was boost threshold, can you clarify?