Vapor lock questions for the hotter climate guys

[zKars]

I've received the book mentioned about and read that bit too.

First, heat shield added in 73? Every 240 I've ever seen has a heat shield. There are three different ones for heaven's sake. 

How the heck does turning the wheel have to do with the car quitting due to heat soak????? Is there some super shiny spot on the steering shaft that suddenly aligns and reflects a ton of heat from the exhaust at the carb bodies????? 

[Patcon]

2 hours ago, zKars said:

How the heck does turning the wheel have to do with the car quitting due to heat soak?????

I was assuming that the fuel was sloshing up onto hotter parts of the fuel bowls and vaporizing. That seemed like the only effect swerving would have on vapor lock.

[Mark Maras]

 I found a lot of holes in that story too. No percolation or rich mixture issues mentioned?, heat shields added later on? I'm with Patcon about the rapid turning under EXTREME heat conditions although I've never heard of it. I'm surprised they didn't find the problem before going to that extreme. I get the feeling that Nissan never considered it that big of a problem and just tinkered with it rather than an all out attempt to fix it. To cure the problem, one may need to refit the engine with early carbs. and intake components (didn't seem to be a problem early on) or move the fuel line from the wrap-around stock fuel lines to a line that comes from behind the engine to the carbs. Probably a little easier if you don't run a mechanical pump. @Bruce Palmer, got any thoughts about this subject?

[Jeff G 78]

My endurance racer 260Z with round tops was a disaster until I rerouted the fuel line and used all rubber.  We tried an electric pump, return line, no return line, heat shielding everywhere, and even running without the hood.  None of the changes helped under racing conditions.  I even swapped to a different set of carbs mid-race with no improvement.  Finally in one race, I pitted and installed a rubber hose, bypassing the steel rail.  The car ran flawlessly for the next 9 hours of the race.  We fought back from 35th place to 9th place.  I am convinced that the only real fix is eliminating the heat transmitted through the fuel rail mounts.  The heat shielding, electric pump, and hood venting likely help, but only the rubber fuel supply eliminated the issue.  We still run the shielding and the electric pump along with the back of the hood propped up a few inches just to be safe.  My biggest surprise was the lack of improvement with the hood removed.

[Namerow]

Based on Jeff's experiences, it sounds like the ambient air temp in the engine compartment is irrelevant and the real culprit is engine heat conducted through the metal fuel rail mounts.  I wonder if the solution might be as simple as thermally isolating the rail mounting points from the engine by using rubber standoffs? (I'm thinking grommets in the range of 1/4" to 1/2"-thick).  This would seem pretty easy for JAlex to try and probably 100% reversible if it doesn't work out.

[Mark Maras]

 Jeff G 78, What year were your round tops? I'm trying to figure out which changes Datsun made in 73(?) that caused the problem. Heated carbs certainly added to it. Considering fuel lines, I have a couple of sets of the factory engine bay fuel lines. One set is two lines the other is three lines. I think the three line set-up is newer. Is it possible the three line set-up was part of the problem? I don't remember any heat soak problems on my 71 which had two lines and the early 4 screw round tops.

[Captain Obvious]

The change from two lines to three is when they went away from the flow guide valve crankcase venting and adopted the more effective CARB charcoal canister.

Documentation says 74. but from what I've heard, the scale tends to slide a little and not always be a hard cutoff at a year.

Edited October 16, 2016 by Captain Obvious

[Jeff G 78]

52 minutes ago, Namerow said:

Based on Jeff's experiences, it sounds like the ambient air temp in the engine compartment is irrelevant and the real culprit is engine heat conducted through the metal fuel rail mounts.  I wonder if the solution might be as simple as thermally isolating the rail mounting points from the engine by using rubber standoffs? (I'm thinking grommets in the range of 1/4" to 1/2"-thick).  This would seem pretty easy for JAlex to try and probably 100% reversible if it doesn't work out.

I thought about doing that, but the isolators would have to be able to handle very high temps.  The bolts would also have to be isolated, otherwise the heat would still transfer.  I'm sure it could be done, but I decided to just remove the steel rail and keep it all rubber.

[Jeff G 78]

25 minutes ago, Mark Maras said:

 Jeff G 78, What year were your round tops? I'm trying to figure out which changes Datsun made in 73(?) that caused the problem. Heated carbs certainly added to it. Considering fuel lines, I have a couple of sets of the factory engine bay fuel lines. One set is two lines the other is three lines. I think the three line set-up is newer. Is it possible the three line set-up was part of the problem? I don't remember any heat soak problems on my 71 which had two lines and the early 4 screw round tops.

Mark, my carbs are '72 three screw round tops while the intake and fuel rail are/were late '74 and were three-line.  The water lines are gone from the intake.

[Mark Maras]

33 minutes ago, Captain Obvious said:

The change from two lines to three is when they went away from the flow guide valve crankcase venting and adopted the more effective CARB charcoal canister.

Documentation says 74. but from what I've heard, the scale tends to slide a little and not always be a hard cutoff at a year.

 So, It's looking like (at least to me) the three line set-up might be the place to look first to cure heat soak problems. @Jeff G 78, Did you ever try a two line set-up with the manifold water blocked? @jalexquijano, Refresh my memory about your set-up. Number of fuel lines by the valve cover?  Carbs-3 or 4 screw and are they heated? Anyone else have an opinion about the two line versus three line set-up and heat soak?

[Jeff G 78]

No, I never tried a two line setup Mark.  I should have one laying around, but I never really thought about it before you brought it up.  

[Mark Maras]

 Development of the Datsun 240Z. Hitoshi Uemura says that after the initial heat resistance tests at 104`F, "The ambient temperature in the engine room did not become a major problem. All the temperatures for the battery fluid, the electrical, and the rubber parts were within the normal ranges. The fuel temperature was also normal and we saw no hesitation during sudden acceleration. However, the NEXT MODEL, to which the more stringent emission control in North America was applied, would cause a problem in this area later."