Fuel rail and radiating heat from the engine block..

[Dadsun]

Anyone come up with a halfway elegant solution to separate the fuel rail from getting the transfer of heat from where it's bolted into the engine block? (5 places)

I have a 1973 240z that has the Paltech refurbished SU carbs (not the stock flat tops) and when I take it on a 5 or 10 minute drive the fuel rail is hot to touch. Not burn my fingers hot but definitely uncomfortable. 

Am curious if anyone has built aluminum "stilts" or used the same kind of material that is used as a heat block between the carbs and intake manifold. (See where my finger points in the pic)

 

 

[Mark Maras]

I don't remember anyone trying it but I think it's a great idea.

[siteunseen]

In my opinion if the fuel return is working properly, the fuel will not get hot. The rail is  bolted to the cylinder head on my '72.

I think an electric pump that pushes fuel constantly through the carbs and then back to the tank via the return line would keep it from getting too hot.

My 2 cents only. I'm no mechanic just an observant knuckle buster.

 

 

[Jeff G 78]

I ditched the rail completely and went all rubber.  It was a game changer.  I wanted to do a trial as you suggested in order to keep the steel rail isolated from the head, but I never took the time since the all rubber method worked so well.  My plan was to isolate the brackets from the head with a good isolating material.  The material used for carb spacers should work well if you can find something similar.  You need to make sure the bolt is also isolated.  3D printed isolators would be a good proof of concept if you have any access to a printer.  The spacers would be super simple to design.

Edited July 25, 2023 by Jeff G 78
Added missing words

[Jeff G 78]

5 minutes ago, siteunseen said:

In my opinion if the fuel return is working properly, the fuel will not get hot. The rail is  bolted to the cylinder head on my '72.

I think an electric pump that pushes fuel constantly through the carbs and then back to the tank via the return line would keep it from getting too hot.

My 2 cents only. I'm no mechanic just an observant knuckle buster.

 

 

My race car proved otherwise.  I tried EVERYTHING to avoid vapor lock with minimal success.  The heat was all coming through the rail brackets.  The more you insulate the rail, the worse the problem becomes since the heat generated by the head is then trapped by the insulation on the rail.

I spent many hours adding various heat shields and other strategies to keep the temps down, but all failed miserably.  The 5 minute rubber hose trial fixed the issue.

[AK260]

I was told by an old racer that they used tap fibre washers to good effect. Having said that, you have to be careful they don’t deteriorate over time and cause vacuum leaks. I tried this and it made little difference.

The real problem as you said is the radiated heat from the air chairs manifold directly below it. Mine sits at a reasonable temp when driving or with the engine running - but turn the engine off for 5 mins to fill up and the rails become BURNING hot to the touch!! I imagine the fuel is beyond vaporised in there!!

Great to hear the rubber solution worked well - any pictures? Did you route round the back of the engine or the same routing as stock config?

[Jeff G 78]

2 minutes ago, AK260 said:

Great to hear the rubber solution worked well - any pictures? Did you route round the back of the engine or the same routing as stock config?

I was mid-race when I tried the rubber solution, so I simply removed the short rubber inlet hose between the chassis supply pipe and the fuel rail and replaced it with a longer hose that went from the chassis pipe to the front carb area.  I put a T fitting in the hose and ran a short hose from the T to each carb.  I clamped the return hose off with a pair of small needle nose Vice Grips to keep any fuel from dripping out of the rail.  I was able to run the next 10 hours of the race with no vapor lock in 85° ambient conditions.  Prior to the rail change, it would lose power at high RPM after less than 20 minutes.  The misfire would continue to get worse until it had no power.  

I had previously tried different fuel pumps (mechanical and electric), deadheading the fuel system, adding LOTS of various heat shields including bowl shields, swapping carbs, and propping the hood open to increase airflow.  Surprisingly, deadheading the fuel helped a bit compared to keeping the fuel return.  I can't explain why it helped.  It wasn't a cure by any means, but it did allow us to race longer before we got vapor lock.  It was only the rail delete that fixed it completely.

I don't know if I have any pics.  It was never pretty since it was a race car and not a street car.  I'll look.

[Dadsun]

26 minutes ago, Jeff G 78 said:

I ditched the rail completely and went all rubber.  It was a game changer.  I wanted to do a trial as you suggested in order to keep the steel rail, but I never took the time since the all rubber method worked so well.  My plan was to isolate the brackets from the head with a good isolating material.  The material used for carb spacers should work well if you can find something similar.  You need to make sure the bolt is also isolated.  3D printed isolators would be a good proof of concept if you have any access to a printer.  The spacers would be super simple to design.

My question is the same as @AK260's... when you say you went all rubber, did you contrive a return to the hard vent line as well?

[Jeff G 78]

1 minute ago, Dadsun said:

My question is the same as @AK260's... when you say you went all rubber, did you contrive a return to the hard vent line as well?

It's in my other reply.  I did not use a return when I went all rubber.  I wanted to do exactly what you are suggesting in order to keep the rail and the fuel return, but it wasn't needed in the end.  I never even unbolted the rail.  I simply abandoned it in place.

[Tirnipgreen]

I have a carbon copy of Dadsun's '73. I hate to abandon the metal rail, but without another option, I will. Why does this scenario play out for some and not others...?

[Jeff G 78]

I've mentioned this in quite a few threads on the topic.  Before you do anything, run a simple trial and see if the results work for your car in your weather conditions.  The swap takes less than 5 minutes to do and is completely reversible.  Swap the rail for rubber as I described above and repeat the conditions that cause heat soak issues.  If the issues go away, you know where to start.  If they persist, you have a different issue that needs attention either as a fix, or as a step in the right direction.

[AK260]

Thanks for that detailed reply Jeff - much appreciated.

My vapour lock issues were mainly due to idling on hot days or stopping for fuel.

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.

Here’s a pic of my homemade heat-shield (those trumpets were experimental at the time and totally rubbish)! I guess the key thing is to find a way to ensure the rubber line isn’t vibrating / fouling against things that vibrate.