Fuel rail and radiating heat from the engine block..

[Jeff G 78]

58 minutes ago, AK260 said:

I found 90% of all issues was fixed by a home made heat shield that protects the carbs and float bowls. In fact my carbs are fridge cool to touch after a run and often have condensation on the domes.

BUT - the super heated fuel rails bother me both from a performance and vapour lock perspective. If going the rubber route, I would suggest running it round the back of the engine and closer to the carbs where the heat shield protects the rubber from the most extreme temps.

I'll have to see if I have any pics of my 5 minute rubber hose fix.  I ran the hose directly over the top of the valve cover, so it wasn't really touching anything.

One thing I did have was a factory asbestos(?) insulation sleeve that covered the fuel rail.  My guess is that it did the exact opposite thing it was designed to do.  If the heat came through the rail mounts, the insulation kept the heat in the rail rather than keeping it away from the fuel.

I tried several different heat shields like yours with no success.  Keep in mind that mine was an endurance racer, so the underhood temps were sky high.  We pitted for fuel every 2 hours and we'd open the hood as soon as the car stopped to keep it from heat soaking.  Races were up to 25-1/2 hours long, so you can imagine the heat we had to deal with.  When we still ran the iron exhaust manifold, it would glow cherry red during night time pit stops.  

Edited July 26, 2023 by Jeff G 78
Fixed typo

[Dadsun]

43 minutes ago, Jeff G 78 said:

One thing I did have was a factory asbestos(?) insulation sleeve that covered the fuel rail. 

 

Yes, same, it came with the flat top original configuration I inherited from the original owner. 

I tried to clean it up, but then realized I was probably given myself cancer and had no chance to actually get that gunk off. It didn't line up with the roundtop carbs anyway.

I bought the fuel rails in my OP pics from someone on this forum. 

Back to topic, I should really get more scientific and measure the fuel rail temps at different times. But, not even sure it's a problem now that I fixed some fuel and fuel filter issues (again). I need to reproduce it. 

 

 

Edited July 26, 2023 by Dadsun

[KenFirch]

Here's another thing that didn't work.  It helped a little, but didn't completely get rid of the stumbling engine problem after idling in traffic in hot weather. 

I wrapped the fuel lines in DEI's Vapor Lock Sleeve hoping to fix the problem.  Not quite the solution, still looking.  And it looks funky!  

[AK260]

I'll have to see if I have any pics of my 5 minute rubber hose fix.  I ran the hose directly over the top of the valve cover, so it wasn't really touching anything.
One thing I did have was a factory asbestos(?) insulation sleeve that covered the fuel rail.  My guess is that it did the exact opposite thing it was designed to do.  If the heat came through the rail mounts, the insulation kept the heat in the rail rather than keeping it away from the fuel.
I tried several different heat shields like yours with no success.  Keep in mind that mine was an endurance racer, so the underhood temps were sky high.  We pitted for fuel every 2 hours and we'd open the hood as soon as the car stopped to keep it from heat soaking.  Races were up to 25-1/2 hours long, so you can imagine the heat we had to deal with.  When we still ran the iron exhaust manifold, it would glow cherry red during night time pit stops.  

Gosh - that really sounds like engine bay hell!!!!! I can only Imagine what all that heat must have done to other rubber hoses / components!

Speaking of glowing manifolds - one dark evening I had the car warming up on the choke at around 2k rpm and came back 3-5 mins later to find this ….



Which is what makes me think whatever fuel line is used above the primaries is going to suffer with that radiated heat - especially when on full chat for prolonged periods as you experienced. The AFR in the photo was around 12.5 - I checked as my instant thought was “it must be super lean to cause that much visible heat”.

I often wonder why the engineers didn’t run the rails on the “cool side” of the engine.

[Yarb]

Might want to consider ceramic coating your manifold/ header to drop the temp. Fairly inexpensive.

[Dadsun]

My exhaust header is ceramic coated. 

[Tirnipgreen]

How about some kind of insulating washer plates for fuel rail mounting...? Two holes...one to bolt plate to intake, one the through bolt rail to plate. Like some kind of Phenolic material...? Just a thought.

[Jeff G 78]

3 hours ago, Tirnipgreen said:

How about some kind of insulating washer plates for fuel rail mounting...? Two holes...one to bolt plate to intake, one the through bolt rail to plate. Like some kind of Phenolic material...? Just a thought.

Yep, that's what the OP proposed.  They would be simple enough to mock up.

[87mj]

The common vapor lock issue on the '73 cars doesnt make sense to me.  If you swap out the carbs and the tank/fuel lines are open, it is just like all other z cars (excluding fuel pumps).  Way off the subject, I often wondered if the fuel rail could be the cause?  On the '73, there is a bend at the return.  On the earlier cars, there is a square block.  Maybe that block helps dissipate heat?

[AK260]

  On the earlier cars, there is a square block.  Maybe that block helps dissipate heat?

Not at all likely!!! As you can see on mine, it bolts up metal on metal to one of the hottest part of the head (cyl5/6) and directly transfers heat into that block thing, nicely heating up the fuel on its way to the rear carb ! :(



And don’t even get me started on the middle one that unlike the others doesn’t have an insulator of any sort.





So not only do you have heat radiated from the manifold below, you also have metal on metal conduction from the head. I don’t wish to upset anyone but I do feel this is a flawed design - probably a common design of the era?

I’ve literally spent the afternoon thinking about this and redesigning mine to go round the other side, behind the engine, then come to the carbs behind the heat-shield and be properly isolated from metal on metal contact. I’m sure it won’t solve heat-soak issues but should alleviate many other heat related problems.

You could of course re-route from behind the engine if you don’t use the mech pump, but I like having a mech pump in the circuit. And my mech fan and my mech water pump. Analogue man in a digital world and all that.

Will definitely share when / if I ever get the time to build an alternative fuel rail. Ordered the parts so no excuses now ;)

[siteunseen]

My '72 has old opaque looking plastic wraps on the lines through the supports.

Maybe the newer zinc plating melted or were lost somehow that away?

[AK260]

My '72 has old opaque looking plastic wraps on the lines through the supports.
Maybe the newer zinc plating melted or were lost somehow that away?

Mine has them too but there are two “hangers” that definitely came out of the factory without them. :(

Obviously my car has been tinkered with by POs, hence it came with round top 3 screws rather than the flat tops (and the most deliciously ported head). So I can’t be sure what year fuel rail I have. Either way, I’m sure as stock they had some issues in hot climates but with the modifications and performance we’re extracting these days, we are just exacerbating any minor / inherent heat issues.