Right, after hearing that I can boost the power by changing the CR, Ive been thinking:

A. Raising the CR means charge temp is going to be higher so it will inevitably preignite - but this can be solved so is no major deal.

B. The raised temperature means a higher likelyhood of melting pistons etc...

So with this in mind, whats the highest CR I could use without making engine conditions too warm? Is 11:1 too high? I suppose If I burretted the head I could actually calculate that...or, has anyone already done it?

Do you plan to cure the pre ignition by retardign the timing?

Liam

Nope...using a higher octane fuel.

at £4.00 per litre!!, you are completely barking

Cheers

D

He probably means optimax.

Yeah...Optimax /98 RON fuel is something like that...

Wasnt thinking 110RON racing fuel... Cant source that easily let alone afford it!!

Digging up an old thread, but....

Doing the head gasket on my cinq 1.1 this week. Getting the head skimmed.

Question is - how much is enough to take off and how much *can* i take off in respect to raising the CR?

Played with the CR and squish bands in bike engines, but these car things are new...

the head has a marking on it for the max skimming allowed if thats any help

is a bit more complicated then just asking what cr you can run on an engine, there is alot more that come into play eg cam for a start, the only real way of finding out is to find out what they use on say race engine, but most the time there are rules in racing that dont allow a lot of stuff or try it and see, you can always put lots of octane booster in if it does pink which it prod will. or use avgas but your not allowed to us that on the road

custard said:

the head has a marking on it for the max skimming allowed if thats any help

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You can go over this mark by at least 0.25mm. Also you can take about 0.5mm off the block or alternatively use the new metal gasket Fiat supplies now using the 886 cam.

If you are willing to pocket the pistons a bit deeper than standard you can skim even more off the head.

Only drawback is if you go over the maximum skimming marks you will get into problems with the standard belt tensioner and it would be advisable to use a vernier pulley.

also isnt the max marking the point at which the non interfierence charecteristic of the FIRE engine is at risk? as if you skim past this that could be a risk? (in theory, i dont know for sure)

GhostWKD said:

also isnt the max marking the point at which the non interfierence charecteristic of the FIRE engine is at risk? as if you skim past this that could be a risk? (in theory, i dont know for sure)

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Most probably. It'd seem to be the most sensible explanation IMO

DO NOT AND I MEAN DO NOT skim the head. Use the 0.6mm metal gasket from the new Grande Punto instead...

Asteris said:

DO NOT AND I MEAN DO NOT skim the head. Use the 0.6mm metal gasket from the new Grande Punto instead...

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Why not?

Because metal headgasket is thinner and more durable. Fat headgaskets are more prone to failure...

Agreed. I put an RS Turbo metal multi-leaf HG's on my XR3i... made the world of difference.

BTW, the XR3i head can't be skimmed, and apparently, using the RST HG negated the warp to a certain degree.

Just finished pulling it all off. The old one was shot on number1, with a 4 looking iffy and 2&3 looking good.

Already go the new HG kit and having pulled the rest of the stuff out of the engine i've realised that the gains from increasing the compression would be low as there's soo many other restrictions in the design.

Just got to find someone local to skim it.

By raising CR up to 11:1 and altering ignition maps, you can gain upto 7-8Hp in a cento, which is definetely not low...

That's the way rally centos get to 83-85Hp... (including cam, remap and full exhaust system...)

Hello,

I got round to skimming my Seicento Abarth head to maximum which is just past the max skim marks on the head around 3 months ago, and have no problem with early detonation, although I am using V-Power and have used optimax ever since I got the car, also there appears to be no sign of interfierence within the engine although more time will tell.

I would have to say that 7 - 8 BHP is a tad bit unrealistic for just the head skim, more like 4 - 6 but thats just a personal opinion.

My Seicento was rolling roaded around 1-2 month ago and she was running a tidy 77 BHP although I used performance octane booster in the fuel before the rolling road which made the fuel ontop of V-Power around 109 octane rating. Without the fuel she is running around 72-3 BHP and very nippy and the head skim definatly made a huge difference!

The head skim cost me around £50 at Senars Precision Engineering, was reasonably costly due to the amount I wanted taken off and the fact it needed to be 100% accurate but they did a superb job!! But £50 for 4 - 6 BHP increase is good money spent in my eyes...

Recommended to anyone!

Adam

I got round to skimming my Seicento Abarth head to maximum which is just past the max skim marks on the head around 3 months ago, and have no problem with early detonation,

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Not read the whole of the thread, but someone must have pointed out that the MPI has a knock sensor -- so, if detonation would occur on ordinary gas, a higher octane fuel should prevent the knock sensor kicking in. In any event, it would prevent detonation. Of course, on an SPI motor there's nothing to stop it aside from a remap.

Agree that 50 quid is cheap for 4 - 6 bhp, but not if you have to continue to use an octane booster to get it!