Petrol Question??

[CaptainCaveman]

I have a Volvo Penta 5.7L V8 (260A) which is a 1984 and ideally it should be run on leaded fuel, but since it is no longer available what fuel do you think would be best suited to run it on? I have been using unleaded of late but should I change to LRP or use some kind of lead additive in the unleaded?

thanks for any feedback
CC

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[tr7v8]

Bearing in mind it's based on a Ford or a Chevy from the US where they went unleaded in 1976ish, then I would suspect it would be fine on unleaded and possibly designed for it! Give VP a ring and they'll confirm.

<hr width=100% size=1>Jim

Draco 2500

 

[Will_M]

Your right the 260A needs a minimum fuel octane of 91, ie good old fashioned leaded.

Unleaded Conversion.

(Q) Why do engines need modification to run unleaded?
(A) Lead that is added during the ‘4 Star’ manufacturing process acts as a high temp lube, and stops the hot exhaust valve ‘micro-welding’ itself to its soft cast iron valve seat. The exhaust valve may operate at over 700 degrees C and 75% of its cooling is by transferred heat to the valve seat. As such the fitting of a hard exhaust valve seat and the use of suitable exhaust valve stops this ‘micro-weld’ process.

(Q) Why is the inlet valve unaffected?
(A) The inlet valve and seat are being constantly cooled by the gases flowing past them.

(Q) Do all cyl heads need to be converted?
(A) Every cast iron cyl head will need to have hard exhaust valves fitted, every alu head already has valve seat inserts fitted, some of which are already suitable to run unleaded petrol fuel.

(Q) Should the ignition timing be altered?
(A) The greater majority of engines will run on their factory settings, very occasionally it is necessary to retard the timing.

(Q) Should the compression ratio need lowering?
(A) Not normally, most engines will run perfectly well. Or though as a very rough rule of thumb is a compression ratio of up to 10.5:1 is ok.

(Q) Is there a performance down-turn using the lower octane unleaded fuel?
(A) No measurable performance down-turn, in fact you may find an increase in performance by virtue of the cyl heads been return to ‘as new’ running order.

(Q) Fuel consumption?
(A) Again, as above, there is the possibility of better/improved consumption by virtue of the cyl heads been return to ‘as new’ running order.

(Q) Cooling temp?
(A) There should be no change from the normal/correct operating temperature.

The process.
Cylinder head would be stripped back to bare casting, checked for cracks, valve guide wear etc. Valve seat inserts would then be removed.

Correct sized valve seat inserts are selected and a counterbore would be machined into the casting in the place of the original seat.

Counterbore checked for corresponding size & depth, high temp sealant applied, hard chrome-steel insert fitted and machined to match combustion chamber in shape.

An angle is machined into the valve seat, checked and then finished ready for valve fitment.

The risks.
Water cooled castings have water jackets around their existing valve seats. Considering the age of the engine and the likely hood of corrosion in and around the water jacket area. If when been counterbored this busts through the casting due to the amount of corrosion behind then it goes with out saying the cyl head is then nothing more than scrap!

Valves.
When new these valves were not expected to have to run with unleaded, although a lot of valves are made from suitable material. But you should really change the valves or have new ones machined in a known material that will be suitable for unleaded.



Most automotive engineering companies would be able to do or at least have this process done. (NB automotive engineering co, not your average spanner monkey set-up)


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[brianrunyard]

Very comprehensive reply, but didn't answer the question:-
Should we use LRP or Unleaded with an additive?
(It wouldn't be cost effective to modify the cylinder head on my my volvo AQ105)

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[Chris_d]

It was good reply but misleading, unleaded is in fact 95 octane so no problems on that score, old 4 star is 98 octane which is the same as super unleaded.
As i understand it most old engines which have had a couple of decades use with leaded petrol, don't need LRP or additives just use unleaded. This is because the lead has already been deposited on the valve seats and will continue to protect them. If your engine is relatively unstressed as most boat engines are, just use unleaded, suing LRP or additives might in fact just make things worse, some of the additives used can be harmful to you and the engine.

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