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.