Cinquecento 700 heads

[punkydog]

Has anyone actually fitted Cinquecento 700 cylinder heads on a Bis and is the few extra millimetres of valve size a noticeable improvement?
Is it possible to fit the Cinquecento 700 valves in a Bis head as the Cinquecento heads seem quite expensive if you can find them.

[Rusty's Uncle]

I have a feeling that Gadge has fitted one so is best placed to comment. I would imagine that the Bis and the Cinq heads are the same casting but with the bigger valves it would have bigger valve seats and opened up ports. So you could have this work done on a Bis head. Is it worth it? Well as they say in Tesco "every little bit helps" another thing to consider is the 30DGF carb from  Panda 30 as it is not restricted like the Bis version 

[punkydog]

I didn't realise the Bis carbs were restricted what was the reason and how have they done it?
I have one of the Polish carbs on mine.

[Piotross]

Gadge has a head from me cc700 head has bigger inlet valve seats and valves, exhaust valves are the same as in BIS head

[Rusty's Uncle]

If you look on the side of the carb in the middle above the throttle linkage there should be two numbers that tell you the Venturi size. I think it is 19mm on the Bis and it is 23mm on the Panda DGF Carb so quite a difference. When Fiat launched the 126 it was about the same time as the 500R . They both had the same engine but they detuned the 500R by fitting a smaller carb.

[Gadge]

Yes I'm currently running a cinq 700 head. It's a straight swap and is 99% identical except for the slightly bigger inlet valve diameter. I personally havnt noticed any power gains as such but I'm sure that the torque has improved as it seems to pull well at low speeds when in high gears. That said I'm also using lightened H-beam rods, lightened flywheel, free flowing exhaust and I also took 2mms of metal out of the inlet ports and smoothed them down to a matched inlet manifold so this may also have aided to the torque increase. Personally as rusty says "every little helps". The valves are the biggest restrictor of air flow in the induction system so even a valve that's 1mm bigger will let air pass through just that little bit better but don't expect big performace gains from just having slightly larger valves.

[punkydog]

Thanks, I will bear it in mind. I may have to pull the engine out as I suspect the seal on the water pump shaft is failing, which is annoying as it has only done 2k since rebuild. I found yellow gunk around the coolant cap, oil is fine. I will just monitor it for a while.

Carb - surely the choke size would have been chosen for best all round "performance", the engine can only burn so much fuel at a time. However I spend a lot of time checking the accelerator linkage is opening up all the way as it feels there should be more.
My engine runs better with a new Weber Polsky (£18.00 eBay) than the rebuilt Weber but I assume they are as near as damn it the same. Other folks may have different experiences.

[DEYAN IYI]

If I remember well the exhaust valve on the cc700 is 1mm smaller in order to compensate the larger inlet valve.

The camshaft is pretty different as well since the Bis has 47Nm/2000 vs. 52Nm/3000 for CC700. Also 26hp/4500 vs. 30 or 31hp/5000 depending on the carb and cat.

The camshafts are not interchangeable due to many reasons, but the Bis one could still be timed for performance in higher revs.

Bis: 25°/51°- 64*/12° (256°); h=5,868mm

700: 15°/58° - 55°/18° (253°); h=6,1mm

There is one more thing. The CC700 has oil lifters, so the shape of the cam is specific.