1608 big valve engine carburetion

[vcg]

Hello Guy,

I just finished a big valve convertion for my 1608 BS1. Compression is 10.5:1, inlet valve 43.5 outlet 38, and the cam is Kent FT10. I am trying to make it work with 40IDFs, but all I get is very torquy curve from 2000-5000rpm and not a very good top end with 4th and 5th gear. I am working the 40IDFs with F11 emultions, is that ok you think? Or would F9 be better?

Could you please suggest a jetting for 40IDFs?

Thanks,

[Guy Croft]

I'd need more data to be able to comment usefully, eg:

- choke size and main/ air corrector jets currently fitted
- mixture (CO or Lambda) thru range 4000+ as it is at present. If you haven't checked this you cannot pin the problem on jetting...
- ex header details (4-2-1/4-1 and dimensions)
- silencer type
- air filter setup
- cam timing
- fuel pump type/pressure
- head state (fully flowed etc)

Obviously things like carb balance and ignition timing have a bearing on this too.

Photos of engine/car would be nice too, adds interest to GC Q&A .. as I keep saying..

GC

[vcg]

Ok, this is the case:

I preperared this head originally for my 124 BC1 Coupe racer. However since the car worked so good, I decided not to touch it, so I fitted it on the Spider.

The Spider set up now is as such:

Fully flowed ported head 43.5 inlet, 38.5 outlet
4-2-1 Header 38-42-50mm respectively, single see through 60mm silencer
Kent FT 10 282deg, 10.35 lift, 70 overlap
40IDF 34 venturi, 60 idle, 160 main, 180 air, F11 emulsion

The car is a TORQUE BEAST up to 6500rpm, and it continues at lesser pace up to 7200rpm. This is different from what I expected. I was expecting a pretty shallow bottom and a unacceptable top up to 8000rpm, but I guess the fact that I used a mild cam is the reason. I was afraid to use higher than 2.8-3.0 mm lift at TDC cam due to the large valve sizes and the small piston diameter (80mm) and the small carb available (40IDF).

There are two issues that puzzle me:

(1) WIll I gain at the top if I increase overlap-TDC lift with present cams and with present carbs? Or is is it a case of undercarbed setup that the top is at it's limit?

(2) This kind of 40IDF jetting (160 main with 34 chokes) I have seen only in VWs, never in a TC before. Is it because of the valve sizes?


PS: photos will follow

Thanks Guy,

[vcg]

Mystery solved!: Sticky pin in one of the floats...

Jetting is as such for big valve 1608cc Fiat TC with a mild cam:

Weber 40IDF 13-15 with 35mm horns & no filters
34 chokes
F11 emulsions
60 idles
145 mains
200 airs
pumps 40

The car works really nice, it pulls strong from 2000rpm up to 8000rpm - no flat spots. Max torque around 5200rpm, max hp around 7300rpm, estimated around 140bhp at the flywheel.

Sorry for the confusion Guy,

[Guy Croft]

Vassilis, hi

that's great! You got the solution before I could even assess the setup. Sorry but I have been pretty tied up at work and a bit slower than usual with a bad back.

Well done and thanks for telling me quickly!

GC