Blow Through CIS

[911st]

When reading about anti-lag strategies on Rally cars they mentioned that the restrictors placed in front of the turbo significantly reduced the turbo's responsiveness.

I am wondering if restriction on the in-side of a turbo is more of an issue than on the compressed side?

Wonder if it would make much of a difference if we converted a 930 to blow thought.

It would not be do difficult to do. Just put an air filter on the turbo intake and plumb the compressed air into the top of the metering assembly. Then the out exit side would supply the inter-cooler and the inter-cooler would still hook to the throttle valve.

Just another crazy thought.

[Turbology]

Back from the grave as I'm also curious if anyone is running a blow-through MAF set-up. These rigs are very popular with the big-turbo DSM crowd as the factory blow-off valves are easily overcome at high boost but the MAF can't account for the lost air from venting-to-atmosphere.

I'm hoping to run a TiAL Q BOV on our 930 build, but we're still trying to decide where to mount it along the turbo plumbing. I've got a Kokeln that had an HKS SSQV welded to the end-tank, so we could just weld the TiAL flange on the end-tank in place of the HKS flage. We shall see...

[sjf911]

I am in the process of adding a blow through MAF right now. I am going to use a current generation Ford blade style MAF. I am having the mounting bung welded on today on the outlet pipe from the IC. I have a straight section of pipe of almost 8" which is supposed to be ideal for MAF placement. The only issue that I have is to relocate my meth/water injection nozzle downstream of the MAF.

[RarlyL8]

Any restriction on the cold side is not an issue with conventional CIS engines that are modded up to 450WHP. Beyond that EFI is used which eleminates all the hardware up stream.
One concern I would have is forcing hot air through the CIS air meter assembly as it is not designed for that.

[Turbology]

Interesting feedback and observations guys, thank you!

Brian,

Does CIS use a vane-type assembly versus a hot-wire or cold-wire? Trying to determine exactly how CIS recognizes airflow to get this BOV mounted properly.

[RarlyL8]

No electronics are involved. This is a mechanical system. Vacuum from the engine pulls the air metering plate open which moves a piston in the mechanical fuel head to feed the engine more fuel.
Ideally the BOV is plumbed between the air metering assembly and right before the throttle body. Air is recirculated when the valve is open so that air is seen by the system.

[Thierry25]

Originally Posted by 911st

When reading about anti-lag strategies on Rally cars they mentioned that the restrictors placed in front of the turbo significantly reduced the turbo's responsiveness.

I am wondering if restriction on the in-side of a turbo is more of an issue than on the compressed side?

Wonder if it would make much of a difference if we converted a 930 to blow thought.

It would not be do difficult to do. Just put an air filter on the turbo intake and plumb the compressed air into the top of the metering assembly. Then the out exit side would supply the inter-cooler and the inter-cooler would still hook to the throttle valve.

Just another crazy thought.

Personnally, I think that wherever you place the restrictions , they will act as same power loss.

As we speak about the restritive path. The most restritiv tube (plastic) is the one whch is located just behind the rubber hose which is fixed on the compressor input. I know there is no big space avalaible arround it.....but maybe we could design new on with few extra mm size.....

[boosted 89]

IMO any restriction on the compressed side of the plumbing to the throttle body is going to create turbulence and more heat going into the engine and running compressed air through the CIS meter is only going to create undesireable tuning issues. From what I've seen, most turbo systems work better using speed density(MAP) systems than MAF systems with EFI...but that is just an opinion!

Chris

[Turbology]

Originally Posted by RarlyL8

No electronics are involved. This is a mechanical system. Vacuum from the engine pulls the air metering plate open which moves a piston in the mechanical fuel head to feed the engine more fuel.
Ideally the BOV is plumbed between the air metering assembly and right before the throttle body. Air is recirculated when the valve is open so that air is seen by the system.

Great info, many thanks for posting. So what, then, are the concerns of running a blow-through set-up with CIS, as you mentioned in your first post?

Being that it's a purely mechanical system, is air temperature a relevant variable? Is there a back-stopper to prevent the plate from moving past closed?

[RarlyL8]

My concern would be pressurized hot air blowing through the air metering assembly. It is not designed for that so no idea what could happen or what the failure mode would be.
Pressure and heat could conceivably make their way into the fuel head.

[911st]

There was pictures and a magazine write up of an SC turbo kit here somewhere. It was a blow through. No issues were reported in the article at the time. I know that is not conclusive evidence but the SC ended up about as fast as the stock 930 they tested it against and seemed to work well.

I could be wrong but I suspect boost would have to be very, very high to exceed any pressures that exist in the lower part of the fuel distributor.

Further, if the fit about the metering pin it such that it can retain the very high system pressure, I would guess there is little of air bypass possability.


As to blow through with an EFI MAF system I believe that is mostly avoided. I suspect that might be because any oil that escapes the turbo seal would work to foul the MAF sensor.

As to restriction on the in or out side of the compressor. Can not think why it is any different than the turbine.

Any undue restriction on either side reduces the differential pressure and impedes potential. Put Brian's headers on the in side of a turbine and it improves the differential pressure. Put a Zork on the out side of the turbine and it increases the differential pressure's and thus potential.

If we are talking about putting a restriction of a fixed size on the in or out side of the compressor wheel I believe there can be a difference. For example. 944T's use the same AFM as the 3.2 Carrera's. However, they use it as a suck through. From the experts I talked with it is difficult to get past 400hp motor with a suck through AFM. Most go to a larger MAF to get there.

However, Protomotive on its 3.2 Carrera conversions has no issue going way past that in a blow through AFM system.

I doubt the SC's metering assemble is small enough to create a restriction issue no matter if blow through or not.

Still, it is an interesting thought and if I had bought the SC I looked at I would have tried it.

Thus, to each there own I suspect if doing an SC conversion. Most just copy the 930's suck through style. I sure wouldn't cut up a 930 to make such a change.

[ly3d]

This could be interesting:

http://www.928motorsports.com/parts/images/ferrari_308/308CoverPage2.jpg
928 Motorsports - Site Map

Bentley Turbo R:
www.rrab.com/cars10/jch22079e.jpg

Mercedes Mosselman and Turbo Technics conversions:

W201 Mercedes 2.3-16 (3.0-24) twin turbo

Other MB conversion:

Brabus 2.0 turbo - Benzworld.org - Mercedes-Benz Discussion Forum

IMO it's worth to try out. The temperature of the compressed air after the IC should not be the problem because it is less hot than the engine bay itself.
Maybe the metering plate could opens to far under boost conditions... but if you try to pull or push it under full fuel pressure, the resistance is amazing.

[911st]

Your examples all look like blow through systems.

Can not totally see the Bentley plumbing.

Good research if so.

Here is the B T SC Kit:

Originally Posted by gavinc69

Found an old article on turbo charging Bosch K-Jetronic 911's, very simple design.
Note this was done on a 1974 model car so should be better all round on a 3.0 car ;-)
Im torn between turbo charging and supercharging myself, supercharger seems easier but when ever i hear a Zork im left nursing a semi lol.
This type of setup with maybe a few added extras from other peoples turbo conversions maybe the answer...







Two more images to follow

[911st]

Cont.

Originally Posted by gavinc69

[911st]

Last:

Originally Posted by gavinc69

[Turbology]

Many thanks again folks for all the helpful feedback and insights, I truly appreciate it. As we've taken our 930 apart piece by piece, a number of problem areas have appeared that will hopefully all be sorted out by our complete revamping of the turbo system.

We didn't really get a chance to rag on the car prior to disassembly exactly for the concern that there might be some unforeseeable issues that could potentially be disastrous. So, as to not take any chances, the only remaining factory component in the FI set-up will be the turbo (for now).

Here's what's being done:

• Fabspeed BMC filter assembly
• Kokeln half-bay intercooler
• TiAL Q 50mm blow-off valve, 10 psi spring
• TiAL F46 Narrow Body wastegate, 1.0 bar spring(s)
• handmade headers
• handmade Zork tube
• handmade wastegate dump pipe

From what the folks at Kokeln and Andial tell me, the Kokeln "install kit" was merely an aggregate of factory parts and hardware that allowed for flawless fitment, so we should be able to source any of that stuff locally.