Fuel additives timing and compression ratios

carlssonaero

New Member
I am collecting my 1974 V8 on sunday. I am told it is the newer lower compression engine. How do I check this is correct. I think it was reg'd in March74,

The current owner uses premium unleaded with valvemaster plus or optimax with valvemaster. I intend to do the same unless you should stick to one way or the other? Which is better or no difference? How about optimax plus valvemaster plus! or will that be too much Ron and would it harm the car or just make it go faster?

Re timing: I presume if I follow either or both options depending whether I am near a garage with optimax I will be running 97 or 98 ron and so would not need to alter timing from standard by the book?

As ever any help would be grately appreciated

Regards

Julian
???
 
Hello Julian,
yes, cars from October 1973 had the lower compression ratio suitable for 4 star (98) fuel. You need an additive with unleaded to prevent premature engine wear even if you are near a garage that sells Optimax (98) or super unleaded (97).
Optimax plus has an octane booster also so, by getting the right mix, you need not alter your ignition timing.
As usual, if you send me a private message with your e-mail address contained within I will e-mail you a copy of my article on fuels which was published last year in the P6 NEWS.
Hope this helps. Regards, John.
 
Your V8 should be fine with unleaded as long as the octane rating is high enough. You could retard the ignition a few degrees and run on normal unleaded if you wish. The V8 does not require lead or any other additive as the valves, seats and guides are hard enough.
I would expect Optimax or super unleaded would be fine with the standard timing. If it does pink then reduce it by 1 degree and try again.
I think this has been discussed in this forum before. Try a forum search or more information.
 
If the heads are original they are definately NOT suitable for unleaded without an additive!
The compression ratio is stamped by the engine number (should be located by the dipstick/between the exh. manifold branches and read 9.25:1 for your '74, or 10.5:1 for a pre '73).

You can use unleaded petrol + Additive (Castrol Valvemaster Plus or Millers VSP Plus for example, they have octane boosters).

With the larger compression engine especially, I always used Shell Optimax + Additive with octane boost, theroetically giving 100 octane rating (= 5 Star fuel).
 
Sorry, I have to disagree. The V8 valve guides are the same part number as those fitted to early 70's Range Rovers which were sold in the USA and are perfectly ok with unleaded. You only need an additive if you wish to boost the octane level. It's much easier to retard the ignition.
My '73 V8 has about 40k miles on ordinary unleaded under it's belt with the timing retarded to 0 BTDC.
This really is an old chestnut. ALL Rover engines since WW2 will handle unleaded apart from octane issues. That bit of info from an engineer who worked for the company who has made all the aluminium alloy cylinder heads for Rover.
 
Thanks. Don't mention WW2. WW3 seems to have kicked off here.

Thanks I will use premium unleaded with valvemaster plus or optimax with valvemaster, depending where I fill up. On the basis of what I have heard I intend to keep ignition timing (low comp engine) as standard 6 degrees btdc.

It's bloo*y hard to queeke the valvemaster into its reservoir isn't it!!

Julian
 
Hi Julian, I must admit I am a bit confused on this subject. I think I will stick to the belt and braces approach as well. Might get to see your car this weekend. Cheers Derek.
 
Seemingly, for some cars using just Unleaded fuel works, but for others it does not.
It is not worth taking the risk in my view so I use an additive.

Apart from messing with the heads it is the best solution for piece of mind.

Even some SD1's reportedly have had problems when run soley on unleaded fuel.
The hydraulic tappets can also help diguise problems until its too late.
 
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