ITBs and Tubocharging. Issues?

[Amac]

Here's some pic's.
Some of them are old and have been posted
before.

[TonyG]

Amac

Nice setup.

What throttle bodies are you using?

TonyG

[RarlyL8]

Do you have a picture of the heat exchangers?
How loud is that exhaust "system"? Could you live with it as a daily driver? I take it they don't smog test in Plano. Ha!

[TonyG]

>>>Do you have a picture of the heat exchangers?
How loud is that exhaust "system"? Could you live with it as a daily driver? I take it they don't smog test in Plano. Ha!<<<


I love it. Heat, A/C, but no mufflers! Straight wastetgate and turbo dumps.



TonyG

[beepbeep]

Amac: that's nice and clean setup! I especially like the wastegate arrangment with X-tube and single wastegate. Simple and effective!

[TonyG]

If that's a Turbonetics wastegate, which it looks like it is... you might want to rethink that portion of your setup. I've seen too many of these fail in the past.

We won't use anything other than the 46mm Tial (the gold standard). They are bullet proof...

TonyG

[911-32]

Originally posted by beepbeep


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

Just FYI, Subaru made a 2 litre twin sequentially turbocharged engine for the Legacy GT before reverting to single turbo. It made 275hp and underdelivered IMHO as it really needed the second turbo to be fully working to make any real hp and hence needed 5000rpm. You had to drop down 2 gears to pass anything whereas the WRX and single turbo legacys had lots of midrange torque.

Sorry for the mild hijack.

[Amac]

Sorry for the delayed response.
Tony G. - TPS - 54mm, the wastegate is a 3 bar Racegate, I like
Tial also had a 46mm on my 84 turbo.
Rarly - No good pic's of the heat exchangers, I'll see what I can
do. The cars not that loud, the turbo's knock the noise down. I drive it to the office two or three days a week.
The car has that 935 growl.
Just had an alum. flywheel installed, quicker RPM but takeoff's
are a little tricky.

[RarlyL8]

A 20 year old 750hp daily driver. How cool is that!

I was curious about the heat exchangers for a twin turbo configuration. I don't beleive I have seen any with heat before. Any pictures appreciated.

[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?

Found a better picture, as intercoolers were taken off today:

[RarlyL8]

Goran - What is the purpose of the long intake runners? Someone went to a lot of trouble to fab that design.

[beepbeep]

Originally posted by RarlyL8
Goran - What is the purpose of the long intake runners? Someone went to a lot of trouble to fab that design.

The reason for long runners is to lower the resonant frequency of runners to more sensible revs. We found out that early stubby runners were tuned for 10000 RPM and now they are down in rev rannge where they can offer substantial help, both on- and off boost.

When it comes to plenum, turbocharged car works exactly as N/A one. It openns and closes the valves and breathes in "gulps". If runners are carefully designed (length-wise) to resonate in certain rev-range, they will help fill the cylinders with air to greater degree.

We are talking about volumetric efficiency, VE. VE of 90% means that cylinder fills with 90% of air that could theoretically fit inside. The faster you rev the less time air has to fill the cylinder. Some highly-optimized N/A engines (F1 etc.) can obtain VE of over 100% in certain rev range.
Air accellerates down the runner and is "rammed" into the cylinder just before intake valve closes, thus force-feeding the engine w/o turbo.
This is seen as a "sweet spot" on dyno where torque peaks slightly. If this happends just before turbocharger start spooling, it will shorten the turbo lag and provide more power.
Same thing happends even when on boost, only difference is that air is more dense.
With other words even if you are force-feeding air into cylinders by some type of supercharging, there are still gains to be made by optimizing the runners.
At WOT, throttles are wide open and just in a way for air entering the cylinders. So, my opinion is that there is more to be won by careful intake runner design than by installing ITB's on turbocharged car.

[RarlyL8]

That's waaaaaay beyond my capabilities.
What measuring device would you use to measure VE?

[beepbeep]

Originally posted by RarlyL8
What measuring device would you use to measure VE?

Well it's just a ratio between air inhaled vs. displacement x revs. With other words, if your 3.0L engine turns at 1000 RPM, it will "inhale" 25L of air per second in perfect case (3L x 1000 times a minute / 2).

If you measure the actual flow and it happends to be 23L then your VE is 23/25 = 0.92 = 92%

Now if it inhales more air than it theoretically chould, then you hit the sweet spot. (In reality, you will need hi-end 4-valve engine with straight stacks and evil cams/headers to even try this stunt).

[RarlyL8]

"If you measure the actual flow and it happends to be 23L then your VE is 23/25 = 0.92 = 92%"

That is my question - what device is used to measure actual flow (in order to calculate VE)?

[beepbeep]

Originally posted by RarlyL8
"If you measure the actual flow and it happends to be 23L then your VE is 23/25 = 0.92 = 92%"

That is my question - what device is used to measure actual flow (in order to calculate VE)?

Air flow devices are frequently used in all EFI systems since middle of 80's. In order to calculate flow, you could either use hot wire Air Mass Sensor or MAP (Manifold Pressure Sensor) + temperature sensor.

[RarlyL8]

Guess I was wrong, that's not beyond my capabilities at all. I used to build gas Chromatographs using thermal conductivity detectors, also known as hot wire detectors, so I know them well.

All that aside, it doesn't seem feasible to do all the R&D and manifold design work for a simple street car like I have. That monster you fellas created is a whooooole different ballgame. The mear fact that you didn't use ITBs is significant but may not apply to the useful purpose of my car. Your car is a high strung racer while mine is purely street. My car must operate most of the time on part throttle and off boost in traffic situations. Anything that helps throttle response and reduces the perception of lag is a plus. I was thinking that ITBs would indeed be a benefit for a street turbo. Looks like any benefit may not be that significant.

Thanks all for the info.
It looks like there are many schools of thought when it comes to street turbocharging and the 930. Goran, if you (or anyone else reading this) were to build a 930 strictly as a daily driven street car (with spunk), how would you design the bolt-on portion of the engine? Let's say 400HP was your goal and you have to use the stock compression with SC cams. What style exhaust, turbo(s?), intercooler, intake, etc would you suggest to absolutely optimise that 400HP for street driveability? Was the 993tt the apitome of the perfect 400HP street turbo engine?

[beepbeep]

Please, don't get me wrong. Whole VE discussion was purely theoretical. You don't actually need to measure VE in order to build/tune your engine. You can just watch the dyno graph and see where torque goes up. After all, it's maximized torque troughout the rev range you want. Nobody actually measures VE. VE tables are empirically found out by process of mapping the EFI system.

Perfect daily driven 930? Well what's perfect for one person probably isn't for other. There are many factors here:

1. Cost
2. The fun factor ("does it rev a lot and sound sporty")
3. EFI or not, twin turbocharger or not?
4. Do you have to start with 930 core?

The easiest way to achieve steady 400hp goal with as little money as possible would be by doing EFI-conversion on 930 engine using Carrera intake (Megaquirt & Spark), modern turbocharger (Garrett GT35BB is nice), stock exhaust and good intercooler.

Driveability could be further improved by adding a set of short/hi flowing headers, selecting a smaller turbo that doesn't leave a headroom for gazzillion horsepower but spins up faster (GT30BB).

Boost should be capped relativly low, like @ 0.7-0.8 bar.
Such combo would happilly pump 400hp all day.