Unleaded

Zed2k

Well-Known Forum User
Does anyone know how much it costs to convert an early  L24 or L26 engine to run on unleaded fuel, I would like to have my head modified for unleaded, which is off the car and also a friend want's his 260z converted and want's to know an approx cost any help or advice would be great.


Thanks

Nick
 

datty240Z

Well-Known Forum User
I had my head done about 2 yrs ago when I restored my 240Z. &nbsp;It was very expensive if I recall at £50/valve. &nbsp;So I only had my inlet valves done. <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>
 

datty240Z

Well-Known Forum User
The head off the 260Z may not need done. &nbsp;My '78 260Z runs happily on unleaded.

If I recall Mike Feeney's advice correctly, if when the manifolds are attached to the head there are spare bolt holes in the centre of the head then you have a late head which can run unleaded.

Mike can confirm this.
 

Zed2k

Well-Known Forum User
Thanks for the advice.

<img src="http://www.zclub.net/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>
 

Mr.F

Inactive
Late 260Zs were officially on Nissan's list as unleaded compatible when it was first introduced. I think the real criterion is whether the head is an injection head or not - early E88 heads will need converting, but N42 and late E88s with injector cut-outs should be unleaded compatible already.

The 280Z was introduced in the USA in 1974 1/2 and would have been unleaded friendly.
 

ben240z

Club Member
head conversion to run on unleaded consists of replacing the valve seats with a bronze item . if the head material is cast iron then the seat is machined straight into the head materialand you get a problem running on unleaded. if the head is aluminium then there is a seat insert set into the head as the aluminium would not take the pounding of the valve hitting the seat that is why the bronze insert is put in.
now the question is this .
is the bronze insert put into the aluminium head at the time of manufacture any different to the bronze insert put into the head when you have a unleaded head conversion done?<img src="http://www.zclub.net/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>??? I have always run early heads without having the valve seats changed and there is no damage been done to the seats.
Is there any other work that should be done to the head on a unleaded conversion?<img src="http://www.zclub.net/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>??
I know many people running V8 engines on unleaded without changing the valve seats and they have run over 100,000 miles without any trouble from the heads.
this is my opinion and experience of heads and unleaded fuel. if you have an aluminium head then it has bronze valve inserts and they dont need changing
 

Mr.F

Inactive
It is my understanding that the valve seat recession problem applies particularly to the exhaust valves. Valve inserts in the exhaust ports on L-series heads are, to the best of my knowledge, steel, not bronze which would be too soft to cope with the exhaust valve heat and hammering. Inlet valve seats may be sintered iron or bronze, but steel would be recommended for higher power engines(?)

I'm not convinced that the L-series head will suffer from valve seat recession (VSR) when using unleaded petrol and there is seemingly a lack of information about materials used in valve and seat manufacture on earlier engines. The problem of octane requirement remains. Later 260Zs were officially listed by Nissan as suitable for use with premium unleaded (all that was available initially), but 240Zs and early 260Zs were not included on their lists - I would presume for octane reasons rather than VSR problems. In the USA, all L-series engines from approx. 1974 on would have to be unleaded compatible as no leaded was available from this date. This leaves just 240Zs and early 260Zs with a question mark. There is a part number change for exhaust inserts effective from 04/76 in 260Z heads, but what this relates to I am unsure. The valve does not change at this time.......
The safest option would be to use super unleaded or Shell Optimax and at least occasional use of an approved additive (like Millers VSP) or tankfuls of the leaded fuel still available from selected sites.
I have no long term test data relating to the Z engine, but the main problem of VSR seems to affect mainly cast iron heads or heads with sintered iron inserts. The expense of a "conversion" for L-series heads is probably not warranted!
Who out there has had an "unleaded" conversion and what was done?? Any problem side effects, e.g. new valve seats dropping out?
 

Wyn

Club Member
Result, I wondered why them cut outs were there
reading.gif

The 240 engine I just removed from my car has little cut outs at the top of the intake ports.
That engine is unleaded suitable then
14.gif
 
Top