Datsun-240z Vs Fairlady-z432

[Zed Head]

The problem here is not "vapor lock".  It's percolation.  It's described in the Nissan document.  The solution will come from the fine details, I think.

As far as fuel goes, don't overlook winter blend versus summer blend.  This has nothing to do with ethanol.  It's a formulation change designed to make engines start faster and run better when they are cold, by increasing the volatility of the blend.  For emissions purposes.

[HS30-H]

1 hour ago, hls3073z said:

The other thing is that the Z432A may have ceramic coated exhaust pipes and a very good shield over the exhaust header.  That would be a much better design although more costly for the mass market that the 240z aimed at.

The 432's exhaust manifold is stainless steel. It is not ceramic coated.

You may have missed the point that the inlet side of the S20 engine - being a twin cam 'crossflow' design - is on the opposite side of the cylinder head to the exhaust side, so the exhaust manifold dos not heat up the carburettors or the rest of the fuel system in the way that it does on the L-gata engined versions.

[hls3073z]

On 7/13/2018 at 8:11 AM, kats said:

The Fairlady Z manual says , 

Z432 has a fuel pump ( electrical ) which is located under the floor near the diff . This prevents vapor locking  . The reason why Z432 does not have a fuel return system is , no need to concern vapor locking .

I did not know that , is this true ?

Kats

Here is the interesting thing.  The Z's don't experience vapor locking until the temperature get's over 95.  So if the temp never gets higher than that no problem.  My feeling is that the problem happens in the fuel bowls on the carburetors  and in that small hose going to the jets, however, if the fuel is recirculated back to the tank then the fuel that goes to the carbs  is cooler so it improves the margin.  The other thing is that the Z432A may have ceramic coated exhaust pipes and a very good shield over the exhaust header.  That would be a much better design although more costly for the mass market that the 240z aimed at.

[hls3073z]

You are right Zed hed.  From now on I will refer to solving my fuel percolation problem.  Others comments about fuel mixture variations from summer to winter etc.  That may make some difference but only minor.  And remember  I  started working on this problem long ago  when  you could  buy leaded premium  fuel at the pump so its something fundamental when it gets hot.  As long as its below 90deg no problem.  That was before global warming too, 

[Zed Head]

I agree that it is inherent to the design.  That's why Nissan recognized the problem in 1973.  I would assume that they had professional engineers work on the solutions that they proposed also.  Just saying...they didn't publish that document for amusement.  If those proposed solutions don't work then I think it's reasonable to look changes in fuel formulations.

The fundamental problem is the same as for the EFI engines.  Too much heat for the fuel.  Many possible solutions, some not so pretty.  A fun problem though.

[kats]

Thank you everyone, I am learning,  should not be confused about percolation and vapor lock . I am a student here !

Kats

[Gav240z]

For the record my 72 240z has never had vapour lock issues, driving in 40degree (celsius) + Australian weather along the highway in summer. I was dying because of no air con, but the car was fine. My 72 240z at the time still was running twin SU's with factory airbox, heat shield, return fuel line (with no insulation) etc.. I also didn't have an undertray on the car. Factory style radiator (pretty sure re-cored to 3 core from factory 2 core).

The car did however have a later style fluted/vented factory bonnet (75+), so that may have helped.

[hls3073z]

An AC  would make the problem worse.  I was wondering what year they added those vents to the hood.  A vented hood would certainly help the situation where you park it after driving and it sits there getting a hot soak.  

[kats]

So,  if you have the electical fuel pump near the differential gear on L series engined car like Nissan manual said about Z432 fuel system, it will help for preventing percolation , but I think it will not make a big difference. Like everybody here think SU carbs on the exhaust is the problem.

I think Nissan manual should ammend saying like this , " Z432 has carburators opposite side of the exhaust headers. This prevents vapor locking  / percolation " , not come from fuel pump location .

However our cars are no ploblem under 90 F with a stock fuel configuration as long as cars are cruising .   

Kats  

[hls3073z]

I agree with you.  I suspect that the z432 would run fine without  the electric fuel pump running.  They just wanted to be sure fuel pressure is adequate.

[HS30-H]

4 hours ago, hls3073z said:

I agree with you.  I suspect that the z432 would run fine without  the electric fuel pump running.  They just wanted to be sure fuel pressure is adequate.

The 432 does not have a mechanical fuel pump. It has only the electric pump. How would it "run fine" without the electric fuel pump - its only fuel pump - running?

[hls3073z]

oh, sorry, my bad.  I thought it had both mechanical and electrical fuel pumps.  I need to read and look more carefully.