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Old 1 Week Ago   #1
Join Date: Jan 2021
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Opening up a 30 mm 1.1 SPI throttle body

Hello fiatforum,

Long time reader, first time poster. Thank you for all the information that's helped me get me going with a fair few things in the last few months!

I picked up a 1989 126 BIS with a 1.1 SPI conversion and have been working of getting it clean and tidy. The conversion was good, just needed some bits finishing off

Along the way I have put a 0.9 cam in and had the exhaust made up to be neat with a slightly higher bore/no cat. It seems that the throttle body is the next step (may be out of logical order) in getting this tiny engine breathing a bit clearer.

I picked up a 1.1 SPI TB from a breaker and set to work on a CNC6040, using a 6 mm single flute long reach endmill. I made some mistakes and I hope to have worked around them, otherwise there will need to be a version 2...

The throat was opened from 30 mm to 35.5 mm. This was the largest I could go before needing to sleeve the body as I would have removed walls. As I understand it this number seems reasonable, maybe even too much for the current modifications?

(Place holder for image - 5 post requirement)
Some sketchy work holding. I'm no machinist.

(Placeholder)
From the underside you can see the wall is about 0.8 mm thick. Didn't fancy going any further.

(Placeholder)
I made a butterfly valve from brass. 1.5 mm thick, ellipse shape 35.5*36.5 mm. This was my major mistake. I should have machined it on a 5 Degree slant as it would be in the TB in the closed position. This would have given me the correct edges of the brass that would lie flat against the throat of the body when closed. Instead I had to work around the valve with a small file, gradually taking off the high points. High points could be seen by holding the body up to the light and seeing where the brass was touching the body, then filing a few strokes off. 20 minutes later and it was reasonable. If the idle can't be controlled I will need to do this properly. Every day is a school day.

Next step is to get the spacer that goes between the intake manifold and the body and match the opening on that to the TB. Then fit and test...
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Old 1 Week Ago   #2
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varesecrazy has donated!
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Re: Opening up a 30 mm 1.1 SPI throttle body

Interesting project

You got a 1108 in the boot??

Shame no images loaded..

Study the instructions at top of newbie section.. it does work ..even I can do it
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Old 1 Week Ago   #3
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Re: Opening up a 30 mm 1.1 SPI throttle body

Cheers varesecrazy! I believe I need to make 5 posts on the forums before I can post pictures. Check my gallery - the pics are there.

The 1108 fits with just enough space to remove the cam belt cover - if the engine was 20 mm longer you'd need to do some mega surgery to get it in and keep the body looking normal.

Took the car out for a drive, pulls great mid/high range (can get to the rev limiter in 3rd quite easily now, may not mean much to you but that's a night and day difference). Low end (pick up at 30 mph in 4th) has suffered, comparable to the setup pre-cam change.

The interim 'adaptor' between the manifold and the TB was cleaned up, gaskets chipped off and machined out to 36 mm (to allow for any error in my centering). This is made out of some kind of resin infused fiber stuff. Really nasty dust, mask on!

I cleaned all sealing faces in the multilayer sandwich and used Hondaseal 4 to seal all joints. Technically this product should be fine for the application (I was very careful to not get any in the suck side) but let me know if this was a huge mistake, please anyone.

This has now amplified my sticky throttle cable which at even 5% open or so is now quite noticeable...

More pics in the gallery (to be inserted here when I graduate beyond 5 posts)

Overall quite impressed, it really pulls through the gears.
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