The ultimate quick-spooling combination?
 

So, I had a thought. Would combining all of the known 'advancements' to enhance quicker spooling on our cars make a large, single-turbo spool as quick as twins?

Assuming you have all other parameters in spec regarding header primary size/design, timing, proper WG circuit, whatever else/etc., would a ball bearing, twin-scrolled, and billet-wheeled turbo make for a very quick spooling combo?

Meaning, will all of these make a substantial difference/gain or is there a point of diminishing returns?

Probably undefinable since back-to-back test may have not been done but if you have read or witnessed this, I would like to know.

I just keep seeing quick-boosting, large turbo'd 4-cylinders and wondering why we still struggle with making boost on the low-end while producing big hp numbers like they do.

:)

Yes a single turbo can spool just as fast as twins. There is a laundry list of combinations and things that can be done to achieve this goal, most have been discussed in various threads. Ball bearings are not mandatory, nor are billet wheels or twin scrolls. If the system is well thought out those items will have diminishing returns as you state.

Besides you have to realize at some point in the rpm range boost isn't doing much for you. The engine has an effective "working" range. Typically a standard street engine has about 2500-3000rpm of usable power. If your motor makes peak power at 6000rpm then you can assume 3000rpm will be the starting point in your power production. Having the boost come in at 2000rpm won't do much compared to coming in at 2500rpm. My new turbo spools up pretty early in the rev range, but until the engine gets into it's "working" rpm range it doesn't do much. So while I am a huge fan of quick spool up there certainly is a point of diminishing returns

Also those little engines are liquid cooled and knock sensored running 30+psi...

If you saw the boost curve on those 4 cylinders you would not like it.

Fun question.

Sorry, I suspect the answer is yes.

My two cents, it depends!

You should be able to match the flow and response of twin turbos with a well tuned and designed single turbo on a 6 cylinder motor so long as the cam's exhaust duration is less than about 240 degs.

The biggest argument for twin turbos these days on a 4 or 6 is if one's HP is so high there is not a good single turbo available to supply it.

On a V8 I suspect a single turbo would not be able to equal the potential of a twin turbo set up as even a twin scroll set up can not overcome overlapping exhaust events so as to minimize reversion.

Still, we are probably splitting hairs.

Proper turbo sizing and tune probably have a significantly more important impact. With EFI, I would guess a ball bearing and reduced turbo rotating mass might have a 200 to 600rpm impact over an older single turbo.

Is there a thread that covers these things outside of the things I mentioned?

How about this one.


Sounds like you already have it covered pretty well and know your stuff.

Some other little things you probably already know.

Capacity. Going from a 3.2 to a 3.4 adds about 6% to power almost everywhere.

Twin Plugs, increases pre boost and low end TQ about 3%.

Compression. Going from 7/1 to 8/1 adds about 3 - 5% to preboost power. Going up to 9/1 about another 3%.

Better charge side plumbing to keep velocity up and pressure drop at a minimum. Things like bends, runs, end tank design, core type, and sizing. Getting rid of your AFM if you have a blow through and by going to a MAP set up.

Sequential injection. Better atomization for better burn at low rpm with low compression.

Minimizing volume after the throttle body's helps. However, it is probably not worth the expense to go to ITB's for most.

Also, I like the Synapsis BOV. If set up right it can let the turbo freewheel a bit at idle and cruse for faster response. Think of it as the opposite of compressor stall.

Sizing the turbo is probably one of the more important and easy varables to play with. To me the relationship between the hot and cold side is like a transmission that transfers TQ from the drive side to the charge side. I am not a fan of the cold side inducer being larger than the hot sides exducer like some of the hybrid turbo's seem to run. This seems like it would slow progression. As such boost often does come in early but they feel lethargic to me.

Also, going bigger than needed on the turbo seems counter to response. Adds unnecessary rotating mass and has more windage to work against.

Sizing the compressor so its peak efficiency island, after an allowance for intake pressure losses, is at TQ peak probably makes for better response and drivability. Many like to size them to put the island at HP peak. Probably makes more HP but at the expence of TQ.

Sorry, got carried away again.

So you can get twin-turbo spool with a single turbo by using older techniques not from the list I provided? Sorry, I am a newbie to turbos coming from S/C's.

Every supercharged car I've owned, the earlier the boost, the more tq the engine produced. I am trying to understand how it will not make more power from what you are saying? I would thin if I can get on boost at 2000 RPM vs 3000 RPM, my car would be way quicker - just like the thread where I talked about the 'quick spool valve'.

I would think to run 30+psi would require large A/R's which conventional wisdom says laggy but that is not the case from what I've seen lately. These tiny motors are running bigger turbos than my T-60 and making quick boost. Unreal. :confused:

Good read :)

I like. :)

The one parameter most influential in a single turbo being as responsive as twin turbos in our application is displacement. At 3.3L you don't get the benefit from twin turbos that you would with larger displacement engines.

Having the absolute lowest boost threshold can be a detriment. One car I had dealings with had a boost threshold of 1800rpm and was at 1bar boost by 2600rpm. This was a single turbo CIS engine that put out 400WHP. The car was very nervous to drive. Every time you moved your big toe it wanted to jump out of its skin and eat the guy in front of you. My car, like most tuned 930's, is a Jeckle/Hyde. Very mild mannered and very enjoyable to drive in town and an absolute animal when you jump on it past 2500rpm.
I quit trying for the lowest boost threshold possible and started using those methods on bigger turbos to make them more driveable.

So this car held 1-bar to rev limit? That would be awesome in my book. If it was, what was the recipe?

Cory,

Your sig says you are making 427 whp on a 3.2. Sounds like a great build already.

Any chance you would share your build configuration, turbo spec's if you have them, and how your motor comes on.

Pictures would be cool.


It is not to hard to get a turbo sized to full boost at 2500rpm. Even talked to one builder of a 92 C2 Turbo EFI conversion that made 2 psi of boost at idle.

However, with that usually comes exhaust back pressure of over 2 times boost. This can create a lot of heat, exhaust reversion, and costs HP. This is ok on a street car and many car makers opt for such a strategy but it is not a great idea if it is going to see sustained duty like on the track.

Here's my thread talking about my combo:

Scrutinize my turbo setup! Don't hold back, I want to know! It's is on my C3.2 BTW. - Pelican Parts Technical BBS

The only thing that may be wrong in the original info is I have the factory C3.2 cams rather than the SC (same profile) and I may have 550cc injectors instead of 380cc.

Brian,

Did that car still have the original compressor bypass valve in place?

It may not be the same thing but may years ago I read about a modified 930 that acted like that.

It was traced back to the bypass valve. They modified the valve with a stronger spring to keep the valve from venting at cruse and then closing and providing instant boost with acceleration.

Just a thought.

Has anyone heard of DPV system? It is a throttling device that's installed on the intake side of the turbo compressor. It was invented and patented by a Renault engineer back in the 1.5L Turbo Formula 1 days, and it continues to be used on World Championship Rally cars today.

It reduces lag significantly, obviously on Rally cars instant throttle response is critical, it must certainly work. A good way to describe how this works is to think about what happens when you put your hand over the suction tube of a vacuum cleaner, you will hear the motor speed up. The same thing will occur if you throttle the air going into the turbo. I think there are various technical reasons for this system not being used on street cars, but I thought I'd throw this out there, it's great food for thought.

Google it, there's lots of information out there.

Cory,

Do you know the compressor inducer size (60mm?) and the turbine exducer size of your turbo(guessing about 62-4mm) ?

I am not an expert but here is my opinion for what it is worth.

You have a great build, no glaring mistakes, a better build than most, with no major issues!

Mostly, I suspect a different turbo will transform your car.

A better fit on the sizing, lighter more modern wheels, and ball bearing center section should make a huge change.

Flexability on the hot A/R sizing is somthing to possably look for to fine tune where your boost comes in.

First, a 60mm compressor is a good 425whp turbo but probably at its limit, and on the small side for a T4 based turbo. Your sweet spoot is probably around a 62mm wheel.

If there is a proper sized split scroll turbine available, it would be icing on the cake if you can have a fence welded into your headers to make them a split scroll system. If not, you still have a great system.

I would start by calling Protomotive, Prototech, and or Turbo Kraft and see if they will consult on a Turbo. They know the T4 based turbos for these cars. I would also call Turbonetics and go over what you have going on and get there opinion.

Me, I would be happy it is a T4 turbine set up and work with it.

For reference, you might also check out DonE's build here.

I believe he ran a T4 based GT35 on his 3.45 & 8/1 CR build and had full boost well before 3k rpm with a similar header system and made 500hp to the wheels at .8 bar.

There may be more opportunity by making other changes discussed. However, they would probably be small compared to the effort and investment.


You may have seen this but have your read MarkRobinson's turbo progression. See here: http://forums.pelicanparts.com/porsche-944-turbo-turbo-s/505406-hp-limit-stock-afm.html#post5361082

Yeah, I'm leaning towards the GT-35R. Friend I bought the car from says I should get a 1.0X A/R divided scroll. He feels the large A/R will make the same or higher hp but with the ball bearing center, it will still spool quicker than my T-60.

I'm not sure of the mm sizes of my turbo.

Great proven Turbo for your HP range. If you get the A/R wrong it is easy to order a different AR.

1.02 A/R sounds big. Might see if you can find out what DonE ran.

Here you go. http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/471286-garrett-gt35-turbo-sizing-question.html

Went to the Garrett site. TurboByGarrett.com - Catalog The GT is sized for 2.0 to 4.5. It has .63, .82, and 1.06.

I would guess or interpolate that the .63 is best for approaching down to a 2.0, at 1.06 for up to a 4.5, and the .82 should be in the ball park for a 3.2.

I have not done this myself. Still you might check with Turbo Kraft. He contributed here on running a split scroll T4 turbo set up's and appears to have real world info. One if the few turners that seems to try to monitor the boost to exhaust pressure ratios on some of his builds.

Also note that Garrette is coming out with a new X wheel. Might want to check on the GTX35 over the GT35.

Thanks! I've got some reading to do.

I want to add; I will be dividing the header even if I use the old (undivided) Turbonetics. My plan was to use the flange I have now but fabbing up a divider piece and then notching between the secondaries and welding in. Finish up by milling flat the mating surface and call it done.

That's pretty much what we do on our split plenum headers. The only remaining area of concern is your waste gate pipes. Using smoother WG pipe transitions and completely divided banks as shown below should correct your overboost issues.

http://forums.pelicanparts.com/uploa...1293166598.jpg

Yep, your the one I got the idea from. I remember you mentioning dividing the headers even if you use an undivided scroll. Made sense to me so that will be the minimum.

Brian,

Wow, I sure like that header set. Best of the best.

And what a clean work bench.


Wondering if that turbo that was so jumpy in traffic you described above was still using the stock compressor bypass valve?

Thx.

Keith,
I use cardboard to cover my work bench so I can just throw it away when it gets dirty, ha!

The above headers were built for a 550+WHP engine. Primaries are 1.625" with the gasket protectors deleted so the flanges could be port-matched.

The "jumpy" 930 used a K27HFS turbo and 965BOV. It went from just spooling quick to jumpy after the fuel and ignition curves were customized and dialed in perfect.

IMO forget ball bearing as anything much else than a sales argument. 100rpm at it max on a 3.3L and short life time (see why does honeywell/Garrett have the same programe with 360 trust bearings..). And billet or cast is not related to spoolup time. It is has to do with reliability (cast, forced, machined). When talking about the wheels vs. spoolup it is mostly a matter of effencency (wheel pattern/flow pr. rotation)...and weight.

Look instead on puls physics....THINK and if not -> look at what the industry with same issues (diesel industry, early formula 1, etc) has done....

NO 6 cylinder engine fires ALL 6 cylinders or even two cylinder at the same time = try to think what happens with each puls ...

Why is it TWIN SCROLL gives up to 1500-1700rpm earlier spoolup than compaired to a single scroll.....on a 3.3L..??

Ballbearing vs. Twin Scroll (BLING BLING vs. physics)

1) PULS ENERGY - Look at your 4 stroke 3.3L engine. Each cylinder fires individual after each other. Start and look at cylinder #1 - What do you think happens when this puls is correct paired with two "neighbor" cylinders closest on 360 degree apart compression stroke (cam/door clost) AND entering a "half size width" turbine wheel and half sized A/R on a Twin Scroll turbine??

Now take the same scenario on single scroll turbine ... why do you then think the puls energy and thereby the ROTATION DIES completely when sharing volume of 5 header pipings, many of them with "cam-leaks" (see stroke/cam overlab) before entering the turbine wheel - wich again is twize as big on width size and A/R surrounding volume???

Which application do you think have +1500rpm earlier spoolup....Single scroll + bling bling Ballbearing < OR > any other Twin Scroll 360 degree trust bearing turbo.....!?!

On top of that - Try to think what backpressure on cam overlab dos to ignition timing ..... not only in regards to spoolup but also tourge.... Why is it race cars now days on single turbo setup use twin scroll applications and have NO CONCERNS on cam overlab and use high revs NA cams...how can they do that and what is ment by..."forced induction is only NA engine on a different atmospheric pressure" how can that be approached and what advantages dos that have in regards to spoolup...??

2) No "ketchup effekt"....again think why...

3) High backpressure on low revs when you want it (it spoolups turbo) AND LOW backpressure in high revs when you least want it (flow stop) - what benefits dos that have to spoolup and tourge and how do you fit Bling bling ballbearings into this...!?!

4) Twin scroll = Possibility to run higher CR = quicker spoolup + more power + much better fuel economy "off-boost".

Disatvantages when applying Twin Scroll physics to your application:

1) KNOW-HOW ->> You need to identify the firing order to determinate the cylinders that needs to be paired (2 x3) with the closest 360 stroke apart. NOT necessarely JUST the 3 easiest paired on a row!!! Could be, but not necessarely...depends on the firing/stroke order

2) EXTRA WORK - Two seperated WG or ONE BIG wg with DIVIDED wall all the way up under the WG-valve (very important)

3) TIME/WORK = money

IMO Choose GT3582R if you want BLING BLING and a label saying BALLBEARING (juhuu). HOWEVER ANY same sized turbo as a GT3582R with TWIN SCROLL will beat a GT3582R with +1500rpm in spool up and top end power if headers and WG setup are divided correctly. It is pure physics.

Put your money on puls efficiency and correct manifold setup (with "application-tuned" tube primary and secoundary diameters -> secoundary not necessarely bigger than the 3 primary unless very high rpm -> again engine only fires ONE puls at the time). Hereafter choose your correct wheel (and A/R) sized twin scroll turbo for your application.

You go Jakob.


We are lucky with the flat 6 set up. The phasing of each bank is equal with an exhaust event every 240 deg's on each side. Most domestic V8's do not have equal events side to side.

Without a divided exhaust, a stock cam has overlapping exhaust events about 72% of the time and 964's about 92% of the time making for significant exhaust reversion potential.

Split the exhaust and that goes to zero overlap with most the cams we run.

I suspect, go over 240 deg's exhaust duration on a 6 and you start to get back into a potential reversion situation.

On a race motor with a radical cam, twin scroll is probably not as much of an advantage over a single scroll turbo. on a 6. On a 4 it is a different story.

For example, a stock 930 cam has 206 deg's, a 964 has 230 and the 935's had a crazy 324 deg's of duration. Thus, even with twin scroll, go much past about 964 specs and we may start to loose some of the reduction in reversion advantage of twin scroll.


Fun stuff.

911st - interesting stuff you are mentioning with the exhaust duration from 930, 964 and 935...thanks for sharing.

IMO exhaust reversion is only an issue when we are running boost below backpressure...

Duration and overlab...depending on the application...say racing then one of the BIG advantages of Twin Scroll is the possiblity to build low topend backpressure without hurting the spoolup time. Low top end backpressure gives us much more posibility to keep the "balance score-card" still equal (boost vs. backpressure) 1:1 or best 1:0.8 (example) THEN we are still running a "NA engine" and we are much more free to pick the most suitable cam without the normal concerns on backpressure. A "turbo" cam is then "almost" non-existing and we can now have the discussion on "blow through" in regards to valve cooling, cylinder filling etc...

Mount a "10mm brake nipple" just before the turbine inlet and fit a 30cm copper piping in a spiral with say 10 turns. Then fit a silicone vacuum hose to it and place a boost gauge on the other end and place it just near the inlet boost gauge. That will give some fun stuff/thinking in regards to A/R turbine-, exd/ind turbine wheel-, AND cam selection. Or even better log all data within your ecu log file.

Keeping boost over, or equal, to backpressure on high revs and we are in for high effiency build applications. Twin Scroll will do that when build correct AND with not much lost on spoolup (still race application with BIG turbines to hold 1:1 all the way up to say 8.000 rpm). On single scroll setup you would need to run a turbine as big you could stick your arm through it. Seen it. Early cars running 402m did first huge bling bling turbos and had full boost as late as 6.000 rpm running up to 10.000rpm (and empty pockets) and then afterwards building twin scroll (using truck twin scroll turbos) and now having same size turbo (now twin scroll) and now full boost from 4000 rpm and same high end power and rev pattern. Such cases mostly 4 cyl (not porsche) with boost vs. backpressure about 1:0.5-1 at full boost/power and CR 10.5:1 on race fuel (or 9-9.5:1 on normal fuel). In comparison the 993 air cooled, ecu driven, twin turbo runs CR 9:1.

IMO the 935 could run crazy 324degr. exhaust duration only due to a "correct balanced" boost vs. backpressure all the way up the revs. I have had a 935 twin scroll turbo in my hand and the turbine wheel exducer is huge. I will measure that turbo (ind/exd) next time.

I havent had my first porsche yet, but I hope it (930) will come soon. At that time I will build it as a "NA" and choose the turbo with an exducer wheel in a A/R 1.0 hous that will tip the "balance" 1:1 on full boost rpm/power @ 8.00rpm and select a "NA" 8.000rpm read line cam and run TB + ECU. CR 9:1.
Luckely I stock/sell full range of turbos and housings (and ecu's) so I will have fun testing to get the 930 to a "NA" Twin Scroll setup.

Wow, you guys...

I am gone think about this for a while. Then I'll go back and read it again.
Thanks for sharing. Very educational.
Jesper

My 964 Turbo has almost no lag in comparison to my previous 930 (both 3.3) I don't know what the factory did but it worked.
All I've done to it is a 1 bar spring and no muffler or cat.

I have to read this a few times......

Holy crap Jakob, you're giving me a headache! Too much information for my feeble mind to contend with. I would need to be an automotive engineer to digest all this on one sitting.

My advice to you: Get yourself a 930 as soon as possible, and proceed to put your knowledge where it counts....and then share success with us!!!

What you propose for min spool time is to build a N/A engine and turbocharge it. Very effective for that goal but no longer a turbo engine. A true turbo engine must use all the tricks to reduce spool time as that is not the build parameter, but rather top end power through increased boost levels.
Electronics have blurred these lines. Not part of the equasion for the CIS 930.

Ok Jakob, I have read your words twice and I want to summarize.

What I interpret:

1. Ball bearings do nothing for quicker spooling and are also less reliable.
2. Billet wheels do nothing for quicker spooling but usually have more efficient maps.

Correct?

I have two questions then:

1. Why did, say Garrett go to ball bearing if it did nothing for spool time and is less reliable (not to mention cost a lot more to produce than journal bearings/center sections)?
2. If a billet wheel is lighter, wouldn't that translate to quicker spool time (not to mention cost a lot more to produce than cast wheels)?

Jus' trying to understand if this really is marketing BS.....SmileWavy

IMO lighter wheels and BB work better in light load situations like when running in lower gears. When having a lot of load they get balanced out.

Good reading.

That is my goal; get the most boost I can in first gear. I don't have a 930, I have a C3.2 with the G-50 so first is pretty low. If the BB works, I would love to get it.

It will make more power to a point as I said. But the engine makes peak torque at the same RPM regardless of when it makes boost (except if it makes peak boost after torque peak). My comment was more about diminishing returns on your investment to make peak boost come in under peak torque RPM. I would strive to have spool up come as quickly as possible for a street driven car, in fact I run a turbo on my car based on that more than top end power so I'm not against your goal. I would not trade boost at 2500rpm for power at 6000rpm for my street car but I wouldn't spend too much more money trying to get 2000rpm spool up.

did I make any sense? it's still early

There are a lot of varables that effect when, where, and how fast boost comes on.

AR and turbine sizing. Turbine wheel relitive to compressor wheel sizing. Clearances, rotating mass, friction. Exhaust system design, intake system design. Ignition, air fuel optmization...

The best info I have seen of a comparison between normal and ball bearing center section was in there TurboTec section.

From their site:

http://forums.pelicanparts.com/uploa...1293554921.jpg

Tippy, I see full boost by 3800rpm in 1st gear with my little $500 Master Power 60mm. So while 1st gear in a 4 speed is longer you will still notice a huge difference when 1st becomes a usable gear. Compare that to my K27 that didn't reach full boost at all in 1st.

I don't want too much boost in first gear as it only ends up spinning the tires. My current low power turbo spins my 315 tires on first gear and I don't like it as it eats the tires pretty soon.

Maybe with an avcr or similar ebc ot would make sense when you can dial it so its just right in every gear.