UNLEADED FUEL FOR V8 - HC 10:5:1 ENGINE

[lunarboy]

I have a 1970 v8 - don't know if original engine but previous owner fitted electronic ignition and ran on unleaded. It appears to be marked 10:5:1. I have since been told it should have an additive - no pinking that I am aware of. Is it ok to run on unleaded - how do I know if it has ever had unleaded head fitted etc Thanks

 

[JohnGlinn(Cardiff)]

lunarboy,
have a look at Aliatair Morgan's website www.p-six.co.uk where he has a copy of my article on FUELS which was written for our magazine P6 NEWS. All will be revealed!
Regards, John.

 

[Erik The Viking]

I run mine on super unleaded, and Castrol Valve Master Plus, which is an octane booster and lead replacement additive. I've generally found that the car does the same pence per mile as running on straight unleaded, as the higher octane seems to give it more to the gallon. The general advice I have been given to run on unleaded is to retard the ignition to TDC, but mine runs the 9.75:1 V8, and not the earlier 10.5:1.

Hope this helps

 

[The Rovering Member]

I don't use additives in either of our V8's & they seem to run fine. We did put 9.35:1 (is that right?) Range rover pistons in when we restored the P5B as we knew unleaded was on the way. Our P6B is a '75 so won't be the 10.5:1 pistons will they? Both have Lumenition which was already fitted when the cars were bought. Handy! ::

 

[Phil Robson]

Hi,

I've run my '71 V8S (10.5:1) on standard unleaded for 35,000 miles without a hitch. No additives, just a little retarding of the timing.

Phil.

 

[Classicus]

In the more than two years that I have owned my 73 3500s I have often wondered about the compression ratio. The body number prefix stamped on the inner wing is 482. I have looked carefully for the engine number which should be either on the LH cylinder bank near the oil filler or at the rear. despite a carefull search, I cannot find the engine no. or compression ratio. The original certificate of registration in NZ describes the engine as 485. I have referred to Rudiger's helpfull website and I find that the prefix 485 is " V8 manual/ em control 10:1 compression ratio". The 482 body no. is described as "Export RHD". Does this mean that the CR is 10.5:1 ? I doubt that the petrol in NZ at the time would handle it although I had an Australian Holden that had a 9.25:1 CR. Advice sought.

 

[JC.]

I don't use additives in either of our V8's & they seem to run fine. We did put 9.35:1 (is that right?) Range rover pistons in when we restored the P5B as we knew unleaded was on the way. Our P6B is a '75 so won't be the 10.5:1 pistons will they? Both have Lumenition which was already fitted when the cars were bought. Handy! ::

Think you wasted your time doing that.
The only thing that needs changing to make the V8 compliant with unleaded running is the fitment of hardened valve seats. As it is an all alloy engine it should have these fitted anyway!

-JC.

 

[JC.]

In the more than two years that I have owned my 73 3500s I have often wondered about the compression ratio. The body number prefix stamped on the inner wing is 482. I have looked carefully for the engine number which should be either on the LH cylinder bank near the oil filler or at the rear. despite a carefull search, I cannot find the engine no. or compression ratio. The original certificate of registration in NZ describes the engine as 485. I have referred to Rudiger's helpfull website and I find that the prefix 485 is " V8 manual/ em control 10:1 compression ratio". The 482 body no. is described as "Export RHD". Does this mean that the CR is 10.5:1 ? I doubt that the petrol in NZ at the time would handle it although I had an Australian Holden that had a 9.25:1 CR. Advice sought.

Early engines have the number as you say on an ear next to the dipstick or an ear over the bellhousing at the back of the LH head.

Give these areas a scrub, it may be covered in oil and muck. It would not be unusual to find that the numbers have been ground off. This would indicate that you do not have the original engine, but a replacment.

How to tell exactly what engine you have without a number is difficult, but not impossible.
The CR is determined in these mainly by the pistons fitted.
So, unless you feel like taking the thing appart I would just be content that you have a nicely running V8 and leave it there!

 

[The Rovering Member]

I don't use additives in either of our V8's & they seem to run fine. We did put 9.35:1 (is that right?) Range rover pistons in when we restored the P5B as we knew unleaded was on the way. Our P6B is a '75 so won't be the 10.5:1 pistons will they? Both have Lumenition which was already fitted when the cars were bought. Handy! ::

Think you wasted your time doing that.
The only thing that needs changing to make the V8 compliant with unleaded running is the fitment of hardened valve seats. As it is an all alloy engine it should have these fitted anyway!

-JC.

Well! The originals hardly had a complete ring between them so we decided to renew the pistons entirely & the place we went to only had the Rangey pistons which my Mechanic thought would be a good idea anyway. I never noticed any loss of power & I have read since that this is the way to go if you're renewing original pistons. The heads are the unmodified originals.