924Board.org

[kondzi]

So I need an outsider's fresh look onto that.

Maybe you remember that I started converting my 931 to IC and Turbo with cold side from Audi Quattro and billet compression wheel.

So the journey continues (but had no time to post anything) and I'm in the process of fabricating the induction system now. Or at least made some progress and need to think a bit before I make next moves.

Decided I want ITBs for my 931 after some discussions with a good 911 racing engines builder. ITBs are from Suzuki GSX-R SRAD 750.







I've made Idle Air Rail utilising the OE Suzuki injectorts' ports as I'm using the stock location of injectors where 997TT injectors are placed and to be used in my application.









I was thinking how to make velocity stacks on my own, but ALiExpress was a no briner when it came to cost/time.



I want to built intake manifold, probably dual plenum one, using those stacks somehow.

But anyway it looks for the time being like that in the car:





Now I need to sort out the design of the intake / runner lengths. Wanted to cut out the 924 turbo script from the OE manifold and weld it into the new one.

Anyone has here experience in building such plenum/intake and can share his insight?
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

[Cedric]

Fun project, even though its overkill for that setup . The runners looks quite short though for a std ish engine which wont have a very large rev range.

Here is some old pictures I found on Joakims high HP car for inspiration, this is the last intake.





This is his first bike stuff based intake.



_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[kondzi]

Overkill you say?

Take a look here:
https://www.bufkinengineering.com/intake%20manifolds.htm

Seems the dual plenum idea is sensible.







Audi in their LeMans cars is also using such:


I was trying to sort out all the pros and cons of ITBs in such setup, with a Turbo I mean.

With N/A obviously the TB can be limiting factor at high RPM, Turbo somewhat overcomes that limitation, obviously if everything flows nicely.

The length of the runners again is key with N/A, due to the wave-something what-was-the-guy-name-effect that it reflects from TB and enters cylinder with more density. For high rev screamers short and wide runners, for low RPM tanks long and narrow...

Then there are adjustable ones, like in a Ferrari or other cars...






Not sure though it it would make any difference in such a small 4-cylinder engine.

Here some look at my inspirations:



















As of my understanding of the physics, with ITBs close to the valve the wave-tuned-runner-length is from throttle to the opening to atmospheric pressure (aka plenum in this scenario).

The velocity stacks I showed earlier are just the "tips". I will fabricate the runners later to the length of... Stil not sure. Probably long enough to go around the alternator, or I will need to relocate it.

Also read somewhere that there is no difference if these are same diameter all way long or wider on the entry and narrower close to the head - what matter is the length and diameter (small one).

So as you can picture now a lot in my head is happening around that overkill. And to be honest I want to test that setup / idea in my 931 before I do similar stuff to my 911 Carrera 3.2 which is still years behind.

So...
_________________
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

[Cedric]

The runner length is affecting turbo engines aswell, but how sensitive it is will depend on exhaust, camshaft, ports etc. A highly tuned n/a engine will be more sensitive than one with conservative camshafts etc.

The length is always the whole runner+port, the placement of the throttle plate doesnt matter when its fully open. The shape of the runner is also affecting the functionality, a straight or tapered will not behave exactly the same.

I can strongly recommend "garage 4age" on youtube, theres ton of testing on the subject there, though its n/a testing most of it though, but you should have a look
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1980 924 Turbo
www.instagram.com/garagecedric/

[kondzi]

One wise man said: fit whatever fits under the bonnet and at the end match a cam to that setup. I’ll watch / learn. Thx.
_________________
---
Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)