Fiat Uno Turbo intake manifold mods

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Acki

Fiat Uno Turbo intake manifold mods

Post by Acki »

What do you think about this intake for a Fiat uno turbo?
Throttle body is 52mm.
Image

Quick'n'dirty:
Image

Stock is a 42mm throttle body:
Image

But I drive a 48mm throttle body (1.5 MPI) and with a 5th injector I have 108kW...
Guy Croft
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Post by Guy Croft »

Hello Acki!

Thanks for posting the pictures. I'll preface this by saying there are things I am weak on, and in this case - unlike you - I don't have any actual experience of changing throttle bodies like this. However I am asked from time to time whether bigger is better.

Here is my view:
A throttle body is an item that really needs testing on a flowbench before changing. I haven't been asked yet, but I have put a lot of carbs on the flowbench. Any air intake including a single throttle in this application only needs to flow enough air to satisfy the demand of one cylinder, since only one cylinder is inducing at any given time. As a comparative example one barrel of a 44mm Weber idf carb flows 158 cfm at 10" depression with the throttle wide open and no chokes fitted.
That's not far off same flow as one inlet port of a 2 liter 16v Fiat Tipo head at more-or-less fully flowed spec with standard valves. That head will give well over 600bhp if you wind up the boost high enough, wait for the post by Greg from ACE Motorsport in Piraeus, who's 16v Fiat head (I overhauled it and tested it) flows 170cfm at 10" on the Superflow rig.

Does the throttle body need to flow more air than a single port? Why should it? Everyone uses big intake ducts to feed twin carbs and that's fine, because the smaller the pipe especially if it's quite long, the higher the viscous (drag) loss. The throttle body hose/pipework either side is usually big for the same reason, runs right down to the front spoiler on some cars, whereas the throttle body itself is short (and smooth) it's viscous loss is tiny, as the idf carb flow figure shows (and that's about 6" long and pretty bumpy inside).

Now, on a turbo unit a 44mm dia is going to flow a lot more air on a turbocharged engine before it gets anywhere the 'choked' state ie: trans-sonic - won't flow any more. A 42mm throttle body will flow less than a 44mm by ratio of diameters (42/44) squared, that is to say 0.911 x 158 = 144cfm. A full spec 1600 normally aspirated That is more than enough, bearing in mind it's boosted to satisfy the air demand on a 1300cc unit.

In summary - beyond that which I have said above I am not aware of any benefit to going bigger per-se. What I have written may conflict with your experience or the knowledge of somebody else with actual interchange and test experience of these throttle bodies. I'm always happy to learn.

GC
Attachments
I don't have a photo of the bare carb on test, but during prep of Achy Leousis 124 CSA 1800 'works replica' big valve head I tested almost every bit of the intake system
I don't have a photo of the bare carb on test, but during prep of Achy Leousis 124 CSA 1800 'works replica' big valve head I tested almost every bit of the intake system
AL carb & man flowtest on head.jpg (70.01 KiB) Viewed 10459 times
Acki

Post by Acki »

The idea of this is from a guy from swissland, he had built this intake first, a second he built for me.
He testet on the street different throttle body's and he said 52mm was the best. Other guys says the delta turbo's have this, it must be good...

I have spoken with a guy in germany who has a flow bench firm. He said I should built a intake for 2 cylinders with a VW G60 register throttle body (one small and later one msall and a big throttle body is open) and both intakes are connected to have the same pressure on both.

Maybe I will build this with a bicameral intake... because of my study I can use the dyno withput costs so I have only to built, to sell the fuel and to bring the car ;)

I have found some hints for building a flow bench for home use, maybe I will try this and check the things the dyno says and to be sure I let this intakes check by a flow bench firm... we will see...
Attachments
blokopbouw17.jpg
blokopbouw17.jpg (87.8 KiB) Viewed 10450 times
from a opel calibra turbo engine!
from a opel calibra turbo engine!
kelkjes3.jpg (115.14 KiB) Viewed 10450 times
1.500 euro intake - autocross
1.500 euro intake - autocross
inlaatrally2.jpg (41.61 KiB) Viewed 10450 times
kelkjes2.jpg
kelkjes2.jpg (104.23 KiB) Viewed 10449 times
Julian
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Post by Julian »

We're undergoing similar development for the engine in my race car. The mkI Uno Turbo plenum chamber was used in preference to the mkII/GT equivalent simply because of the removable tracts making it possible to shape and match the ports end-to-end while the mkII plenum would need to be cut open to achieve the same.

The throttle body on the plenum was simply enlarged as far as it would go. The engine does respond to the aperture enlargement from stock but as the lowly "customer" I do not have figures of just how good that response is or how effective the "maximum" size is by comparison.

I would certainly like to see the extent of the benefits of this last part and any losses that exist from over-specifying the plate size.
Acki

Post by Acki »

Hmm the last setence I don't understand.

The response of the engine is a little problem at low revs with a big throttle body. But some days you can handle it withput problems (drive in 5h gear at 1.500rpm etc.).

The mk2 plenum chamber is other formed than the mk1 plenum chamber, look at the injectors! At a ported head it's no problem.

The problem at a turbo is the flow speed, when you drive a small throttle body the flow speed raises and so the flow resistance raises, you loses power.

You see this at my dyno results in my other thread.
Julian
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Joined: June 22nd, 2006, 6:45 pm
Location: Manchester, UK
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Post by Julian »

I will rephrase that then - i would like to see "quantative" results of increasing the aperture/plate size.

What concerns me is that changing the plate size is altering the flow patterns inside the plenum chamber. Not all of the intake runners will be receiving the same airflow leading to small differences in performance between each cylinder. From personal experience I've seen this balanced by use of different trumpets for each runner - not really a possibility on any of the Uno Turbo plenums due to the chamber being effectively sealed.

In theory at least the larger throttle plate should lead to lower flow rates and hence more stable and even flow in addition to removing limitations on flow - I don't believe we are not anywhere near approaching the limits of flow.

At the moment my hands are tied in terms of experimentation along these lines due to the fact that I'm having real trouble getting my hands on a spare plenum. The only one I have left is the one waiting to go in my car so not something I would be willing to sacrifice. Not to mention the costs of repeatedly machining the throttle aperture and refitting.
Acki

Post by Acki »

Ahhh understand :)

Maybe I find time to prepare a stock intake with a 5th injector to run a dyno with them.
At higher boost the bigger throttle will show his advantages.

I think it's not important where the throttle body is because the boost is air which stands before the valves. The injectors are deep in the plenum... the air fuel is ok.

Next fact is, that the intake sound raises like a 2l or 3l turbo.
I had run the intake as a pacer to test the sound (AFM direct before the throttle body) it was like this cars which runs a hill up! He runs with very low opened throttle very fast to the rev limiter!

The guy of the flow bench says the stock intake is better designed but the most cars have a intakte like I will use. VW 1.8T, Nissan Turbo's and often I wouldn't say it's because there isn't enough room in the front section...
MR2 Turbo is the only car I know which has such intake like the uno/punto turbo...

I will try the other intake and then we well see.
On the prototype of the intake you can fit other thottle body's, maybe the guy will test then a 52mm against a 60mm oder a 42mm throttle body...
But you need the boost to see differences (like stock filter against high flow filter).
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