Race Engine Forum UK

Hello Guy,

A friend of mine is building a replica of Fiat 131 Abarth. The car will be equipped with 16v engine and cylinder head comes from original 131 Abarth. Compr. ratio is 11.5, rally cams 280 deg, Kugelfisher mechanical injection will be used. Could you please advise what exhaust specification should be used on that engine?
I suggested following parameters (4-2-1 setup):

- primaries ID 41 mm, length around 500 mm
- secondaries ID 50 mm, length around 300 mm
- tailpipe ID 58-60 mm

What do you think?

Kind regards
Slawo

Your info in blue:

- primaries ID 41 mm, length around 500 mm (19.7")
- secondaries ID 50 mm, length around 300 mm (11.8")
(py-sy above OA length 31.50")
- tailpipe ID 58-60 mm

Py and sy diameters are OK.
Tailpipe can be same bore as sy - 50mm not need to go so big.

Lengths will work as the py is longer than the critical minimum of 17" and the OA length is OK but in view of what I have learned and seen in recent years I would change the ratio of py-sy lengths and go a bit longer:

py length 27" (658mm)
sy length 9" (228mm)
OA pipe length 36"

If space is limited keep the same ratio of lengths and reduce the OA.


It is vital that the py pipes are all the same chord length and the sy too. Pairing should be 1&4, 2&3. The lengths do NOT include py and sy collectors which can be whatever length you like but there will be an ideal length for pipe entry and exit size which will give the required internal taper of 15 deg or less. The py length BTW is from head face to entry of py collector ie: includes flange.

Once the system is in place you can power-tune with various rampipe lengths.

Hope this helps,

G

Thanks a lot Guy! I remember you mentioned some time ago, that in most cases 4-2-1 setup is better than 4-1. So I understand that also in this case we should rather opt for 4-2-1?

If you can fit it in, yes,

G