7 replies to this topic

[edi57]

Hi All,

In the MiniMag (Issue 152, Page 137) it has an article about an MPi Mini.

A part of it reads "The throttle butterflies [surely there is only one butterfly??] are actually restricted so they cannot open a full 90 degrees. Remove the L-shaped restrictor stops and you'll suddenly find that your engine is more lively and you thought. The ECU compensates the fuelling to match the extra airflow, so don't worry about running lean".

Does the Spi have these restrictor stops too? If so, has anyone done this mod? Any pics and thoughts also helpful.

Many thanks,

Ed

[Lund]

Hi All,

In the MiniMag (Issue 152, Page 137) it has an article about an MPi Mini.

A part of it reads "The throttle butterflies [surely there is only one butterfly??] are actually restricted so they cannot open a full 90 degrees. Remove the L-shaped restrictor stops and you'll suddenly find that your engine is more lively and you thought. The ECU compensates the fuelling to match the extra airflow, so don't worry about running lean".

Does the Spi have these restrictor stops too? If so, has anyone done this mod? Any pics and thoughts also helpful.

Many thanks,

Ed

As far as Im aware, the SPi has a single butterfly, and I noticed it opening the full 90 degrees on full throttle today.

[miniman retford]

That was my MPI in the mag & after reading that i took mine off, it was an l shaped bracket on the side of the throttle body that the throttle cable went to, It does feel like it has made a difference but not sure if it is the same on the SPI

Oh & yes there is only one butterfly !

Edited by miniman retford, 20 November 2008 - 05:22 PM.

[Sprocket]

Tell me this

If the pedal reaches the floor WITH that plastic L shaped bit.

How will that make the throttle open more if you then remove it?

Do you also have to cut a hole in the floor?

[miniman retford]

Mine was a metal bracket held on the body with two screws, removed this & then adjusted the cable on the bracket to get full opening.

Edited by miniman retford, 21 November 2008 - 11:12 AM.

[SMP]

Sorry for a late reply - only just spotted this one.

When I had my SPI throttle apart earlier this year I took a good look at the opening range - it was definitely not going full open when it hit the L shaped bracket - it was probably about 5 degrees short. So I cut the l shaped bracket off - not a good idea!! I then found that when you moved the linkage to full open it sort of went over centre on the linkage quadrant (that the cable attaches to) and locked the throttle at full open So I quickly welded a bracket back on!

I got round this by extending the linkage that runs from the quadrant by a few mm. This took out play in the system that is either there by design or due to wear and tear.

Whilst it was all in bits I also took the opportunity to slim down the throttle spindle and knife edge the butterfly plate. Read about this when modifying SU's years ago in the Vizard bible. Before anybody leaps in and points out that all this work is useless unless the engine is so highly tuned that the throttle is on it's limit and causing a restriction - I KNOW. But it made me feel better and I sure the car felt more responsive afterwards.

Cheers
Steve

[Sprocket]

Standard 41mm SPi throttle will happily provide enough air for 100bhp without the slightest hint of restricting airflow.

[KLAS]

Standard 41mm SPi throttle will happily provide enough air for 100bhp without the slightest hint of restricting airflow.

i slightly dissagree. we tested a 1380ccm SPi engine over here and with the 41mm disc the manifold pressure dropped from 100kPa, wide open throttle and 4500RPM, to 85kPa and less whenn going over 5000RPM.
after modifying to 44mm the pressure drop was much less, we were getting 95kPa at 5500 RPM and staying there. no other changes.

and a bone stock K-Series engine with SPi, using the same throttlebody as the Mini SPi, giving 90HP stock, gained 10% power using a 44mm throttle disc