ITBs and Tubocharging. Issues?

[RarlyL8]

My car is a '78SC with a 930 engine. I am using the stock SC brake vacuum line to the 930 manifold. There is a check valve in the factory line. The system works perfectly - even on boost. Every now and then when I'm carving the mountain I will hit a corner that may drop me out of boost so I use the brakes to slow the car and the throttle to keep me in boost. Brakes work fine.

The picture of the throttle bodies tied together (thank you) shows what appears to be the brake vac hose between the rear and middle throttle body. That is perfect.

Tim, I don't suppose you'd let me borrow that engine and tranny for a weekend, say November 3-5? HA!

[Eagledriver]

I think there is no reason to use ITB's on a Turbo. Here are some reasons:

1. In a turbo you control the amount of air going into the cylinder by the amount of boost you run. If you have a more restrictive throttle set up you can run more boost. Any pressure drop accross a throttle plate will cool the charge so the there is no down side to raising the boost to compensate for a pressure loss.

2. As far as velocity at the throttle plate, this has no meaning IMO. The velocity at the inlet port at WOT is the only thing that counts. Part throttle power settings are determined by the throttle plate opening. Who cares how much flow you get at part throttle...if it's not enough you open the throttle more.

To summarize: ITB's are great in NA engines because they maximize the pressure available at the intake port at WOT. In a turbo you can set the pressure so you don't care about a small loss in the system. You set the boost to get the power you want (respecting the maximum pressure the engine can handle). If there is a loss in the intake system then you will have a cooling effect due to that loss and can run higher boost to compensate with no danger. (These are small changes we are talking about).

-Andy

[beepbeep]

As you can read in previous post regardning this issue:
http://forums.pelicanparts.com/showthread.php?threadid=295942

...my opinion is that ITB's are not needed on turbocharged engines as eventual advantages of faster throttle responce are miniscule compared to turbo lag. With other words, if you win couple of ms on throttle responce, it won't be felt as it takes turbo 300ms to spool up anyway.

Added costs and complexity just isn't worth it.

But I would still like to point that shape of plenum and runner length is indeed important, even on a turbocharged engine. Engine will still breathe in "gulps" and careful tuning of intake pipes can help you extract more power or (even better) help turbo wake up lower down.

To me, optimal turbo setup are twin turbos with twin plenums and throttle bodies + balancing pipe.

[RarlyL8]

That's one wild looking setup you guys have created Goran, thanks for the link.
I don't disagree that TBIs aren't necessary, just trying to figure out what advantage they have and how it all works. Why do the high end tuners use them? Simply "bling factor" or to add cost and bragging rights?
That plenum design posted by Red9 has to be the worst I've ever seen. I would think the flow from the intercooler should be smooth and equal for all ports. How forgiving is forced induction when it comes to plenum design?

[beepbeep]

Intake setup on picture was created by small shop that is specialized in custom intake/intercooler design, not by me. They also did all the calculations.

Generally, you don't want air to make sharp 90-degree bends. Intake pic posted by Red9 will work but isn't optimal.

Don't get me wrong, ITB probably do provide some improvement in throttle-responce but IMHO those gains just aren't worth the fuss in most street applications. Not even 997 Turbo uses ITB's, but they went extra length and fitted VNT turbochargers (avantgarde technology) to cure turbo lag. Don't you think they would also use ITB's (old & prooven technology) if it could also help?

My personal opinion is that ITB's (and their supposedly better throttle responce) are grossly overrated. We did some calculations on this. We have twin plenums with roughly 3L volume each. 3.6L engine turning @ 3000 RPM will gulp whatever air is trapped between the throttle plate and valves in such a short time that fitting expensive, finicky and hard to adjust ITB mechanism just wasn't worth it. There is also added problem of obtaining quality pressure signal for variety of sensors and devices and crossover pipe (to equalize pressure differencies between turbochargers).

In our case, there are following devices that need pressure signal:

1. MAP sensor (needs even vacuum signal, doesn't need flow)
2. Twin BOV's, quite huge (need vacuum signal and usually flow a little, when pistons start leaking).
3. Bleed solenoid valve ragulating pressure to wastegates (needs vacuum and will induce airflow when it starts bleeding air)

Obtaining all this from a stack of ITB's is a maze of pipes, reservoirs etc. It also raises the chance of one of those pipes rupturing.

It only takes one simple ruptured hose going to MAP to fool ECU into believeing that boost is much lower than it actually is = piston meltdown in matter of seconds when you run 1.4 bar.

Factory team can afford technicians and materials that will make all this reliable, but for semi-professional team the riskts are too high compared to gains.

We connected all signal lines to billet block on crossover-pipe, just to be sure that no crack/leak would ruin the engine. MAP bolted directly to the block so there are no hoses going to it at all.

Good throttle response on turbocharged engine can be obtained by fitting ALS (Anti Lag System) and careful sizing of turbochargers and runner lenghts.

I suppose fitting ITB's is somewhat easier on turbocharged engine that uses Alpha-N + MAP in blended fashion (where pressure signal is obtained from turbocharger north of throttle plate) or Mass Air Sensor.

For N/A engine, no problem. Just fit ITB's with Alpha-N EFI and you are set.

[RarlyL8]

Thanks everyone, quite informative!

[TonyG]

beepbeep

On my 3.6L with the TWM 3003's ITBs using a TEC3r, the signal that is produced via the built in vacuum ports (one on each throttle body) is enough to run straight MAP (with no TPS blend function) and perfect streeet drivability and perfect a/f mapping.

It's also enough, w/o a vacuum resovior, to run my power brakes with no problems thus far.

While I don't have any experience with turbo charged 911's with respect to using ITB vs common plenumn, I do have that experience with 944 turbos. And with the 944 turbos, the ITB's have a clear advantage with throttle response, which translates into more exhaust gas, which gets the turbine spinning sooner. The difference is quite large actually (on these cars). And even if it works good on my 911, I don't have a direct before-and-after comparision on the 911 setup like I do on the 944 turbo setup. One would think the results would be similar though.

I went to the TWM ITB's for my 3.6 and took off the PMO's so that I can turbo charge it. And while it my be somewhat expensive for the throttle bodies, it's not that bad if you don't have an intake to begin with that can be used for boosted applications and have to start from scratch (as in my case). I think the TWM 3003's, TPS sensor, fuel rails, fuel pressure regulator, and PMO manifolds were about $2000. Compare that to buying a 3.2 manifold, throttle body, TPS, fuel rails, adapters to use a 3.2 manifold on a 3.6, etc... and the cost difference is not that bad.

Besides... having the TWM's will allow a very simple split intercooler setup that will package nicely in the limited space :-)

mu ha ha


TonyG

[Jim2]

Hey Goran, have you got any data you could share with me regarding turbo discharge temps on one of your built up motors.

I'm looking for post turbo, not post I/C.

I want some comparison for 1 bar at 600 CFM with known ambient in temp? Or, anything close.

Jim

[RarlyL8]

Speaking of intercooling twin turbos, the 996tt has two sepparate intercoolers. Are they pressure balanced with a line conecting them?

Tony, how do you plan to plumb the intercoolers? Do you have pictures or a schematic?

Goran, is the intercooler on the ItsFun2 car one large unit or two that are welded up to look like one? Are they balanced/connected?

[David]

One of our fellow pelicans, poorb0yw, is getting close to finishing his twin turbo ITB setup.

http://forums.pelicanparts.com/showthread.php?postid=2756670#post2756670

[Walko]

Keep me in the loop on this one I need to know about twin turbo setups for the next project

Ruf 911(yellowbird) replica.

Michael

[beepbeep]

Originally posted by RarlyL8
Goran, is the intercooler on the ItsFun2 car one large unit or two that are welded up to look like one? Are they balanced/connected?

It's two completly separate units. They are not connected in any way. There is a balancing pipe between plenum chambers that equalizes pressure with billet block in middle with MAP sensor etc.

Originally posted by RarlyL8

Speaking of intercooling twin turbos, the 996tt has two sepparate intercoolers. Are they pressure balanced with a line conecting them?

996tt intake is siamesed and there is only one throttle. Same goes for GT2.

[RarlyL8]

Thanks, that's great!

[DW SD]

Goran,
Are your two turbos identical? I was under the impression some twin turbo setups use two different turbos so they complement each other throughout the engine's powerband.

If they are different units, wouldn't the engine be out of balance in your setup with each bank having significantly different power bands? AND again, still assuming that the turbos are different, would averaging boost pressures in the shared MAP block really be appropriate for determining fueling, spark, etc? Seems like that wouldn't be a good idea, unless the cross over is large enough to truly equalize pressure between the two banks of the engine.

I guess in thikning about this situation and potential issue(s), I'm guessing your two turbos are identical and that you can use smaller mass turbos to limit lag, but also allow high rpm breathability.

Just curious.

Maybe no twin turbo situation actually uses two different units?

Sorry for the dumb question.

Doug

[beepbeep]

You are talking about sequential turbocharging. Completly different thing that requires special tubing arangment and valves to make work.

No car except 959, Toyota Supra MKIV, some obscure Mazda RX7 Turbo and new BMW 3-series use sequential turbocharging.

Yes, IF2 car has two identical turbochargers working in parallel.

[DW SD]

Goran,
Cool - makes sense! Now I know the correct terminology, which is half the battle.

Doug

[beepbeep]

Sequential turbocharging routes exhaust gases trough one small turbo for low RPM boost, then gradually connects the big puffer when revs rise and engine starts gulping more air. It allows very flat torque curve from low revs and almost no turbo-lag.

While it sounds good in theory, it's a quite extensive/expensive and fault-proof system. That's why most manufacturers use single-stage turbo systems.

[DW SD]

Yeah....thank you for the additional informatoin.

As I was alluding to in my original question, I could see where proper control of different turbos and their varying boost maps would be very challenging to manage, especially with safety and reliability as requirements.

What is more practical for one - off custom turbo applications (either DIY or small shops): variable vane turbos or sequential? They seem like similar means to solving the problem of minimizing lag.

OR are these technologies going to remain in the hands of OEMs for a long time come?

Doug

[Amac]

Rarly,
I run a TT throttle body setup.
And yes the high end shops seem
to favor it. The setup can make lots
of HP, but there is a lot fab work and
EFI will be added to the list.
Ask away, I can tell you anything you
want to know!!!

[RarlyL8]

Amac, your car is the only example of ITBs with twin turbos that I have seen in the flesh. Several years ago I visited Plano and stopped by Norwoods. A lot of awsome machinery in there! I blew through 2 rolls of film before I saw your car. As fate would have it I ran out of film on the first shot. Saving grace was the mechanic working on it stopped to chat and told a little history about the conversion. I nearly bought the twin injected Haltech setup sitting on the shelf that had been removed from the car. Good deal but still a lot of money (for me) so I passed.
ANYWAY - The vision of that beautiful engine burned into my brain. I have wanted to do something like that every sense.
Can you post some pictures of your car and engine?

I just read somewhere that a sequentially turbocharged car is in production as we type. Can't remember the manufacturer but they mensioned the 959 design.