Race Engine Forum UK

Hello Guy,

I understand that you are a very busy man and so I don't intend to bother you with nonsence questions. If you could find the time to reply to my question I would be extremely grateful, if not don't worry.

Is the Fiat X1/9 1300cc SOHC equipped to run on unleaded fuel?

Thanks for your time,

Adam

This is an old chestnut. In theory, all alloy headed Fiat engines can run unleaded. But for an engine that is getting beyond 20 years old, i would run super unleaded and every other tankful, use a lead substitute, like from Millers Oils.

Andy.

Thanks for the reply Andy,

I was really planning to use super unleaded anyway. I have heard a lot of tales of how 'this guy' ran his Lancia fulvia on unleaded and on a routine re-build he found that valve seats etc had not suffered any wear after 40K miles. But I just need a clear-cut answer which you have given me. If anyone else would like to add to this in any way I would be grateful, if not then i'll take Andy's advice as gospel.

Thanks,

Adam

The main problem with unleaded fuel is the pairing and welding that takes place at elevated temperatures on the exhaust set/valve combination if the components are of like material. Looking up my TRW valve catalogue I see their valves for that engine listed as 21-4n stainless, and since the seats in that head are high grade nodular iron, either chill cast or induction hardened, we have quite a good 'unleaded' combination. This is because the ferrous content of a race material valve like that running against what is, after all, a very hard seat by the standards of the time, is unlikely to give rise to those effects under routine operating temperatures on unleaded fuel over a very protracted period.

If the valve was a cheaper alloy steel, then that might be another matter, but that said stellite is often used as a head coating on lower grade material ex valves to inhibit wear. You can check your valves with a magnet and if the heads are non-magnetic they are going to be that stainless material. They might be bi-metallic, with alloy steel rather than stainless stems but that doesn't matter.

I do not have the OE spec for the X19 ex valve material unfortunately. They, as OE items may also have been stellite coated, but over the years that might well have worn off, or been ground off in a reconditioning op. On older engines like that I'd advise an exploratory check, maybe new valves of known (21-4n) material, or else go with Andy's recommendation on unleaded additive.

It is worth mentioning that the approach by most OEMs to manufacturing heads to run on unleaded fuel, seems to be simply to fit very hard seats (high chrome/nickel content). This seems, long term, to protect the seats but in my experience, having overhauled enough of them, this only leads to embedding damage to the valve contact faces and a very high level of distortion. A better solution would be to combine this with bronze guides to disperse the heat better from the seat region, which few do on normally aspirated engines.

GC

Ive seen some reconditioned heads have the hardened seat inserts fall out in service causing major problems. One was a peugeot head!!

Andy.

A bit off-topic - but if they come out in service the boring op and interference fit has_been_done_wrong.


GC

To give Fiat their due the X1/9 head has been through a good 30 years of unleaded abuse in the USA and is still going (where the rest of the car is looked after). It simply isn't a question there - it is just taken for granted.

Fiat's response to the question in europe was to place a huge caveat on their statement that the head is safe with unleaded fuel. Instead of a straight yes or no they simply stated that it was safe provided you didn't "race" the engine.

Personally I've tried both options and have noticed no difference at all (in terms of damage). Paying a good few hundred pounds for new valve seats (at the time) seems a very poor way of spending the money now.

Hello,

Well it seems to me also that spending that sort of money on just a 'coversion' is a waste. I think it is best for me to keep saving and get the modifications suggested previously done by Guy in the near future. At the same time damage can be assesed and preventative measures put in place. My engine is completely stock, I don't race it on a regular basis and so I feel that Super Unleaded will be fine. I am also aware that this is my choice and if anything were to hapen then I have only myself to blame.

Thank you for your input everyone,

Adam.

Super-unleaded is 97RON octane rating and 'regular' unleaded is 95RON. High octane gasoline is only needed on high compression engines, say 10/1 or higher.

No need to use super on that motor, just costs more and there's no power advantage at all, it's after all, 9.2/1 compression ratio only, and should run fine on regular unleaded. If it exhibits pre-ignition with ignition timing correctly set, it's either running way too hot or in need of a head overhaul to decarbonise it. Carbon deposits on the head and on pistons (glowing hot and setting off the combustion) can cause that phenomenon.

GC