Heat-shield and spacer

[gr_diver]

Hello friends!

I've seen many mentions about the order that things stack up on the intake manifold. From the bottom up it goes: gasket/heatshield/ gasket/spacer/ gasket/carb. And this is how I currently have them in my car. But...

I really can't see the actual reason why we put the heatshield below the spacer. Putting it in contact with the manifold (well, almost, there is a thin gasket there), it effectively turns into a heatsink, that dissipates heat up towards the carb. On the contrary, if we put the spacer below it, it wouldn't get heated by contact, and its shape would protect the carb from hot air going upwards. Thus it will be both cooler, and protect the carb.

In addition, the stock carb spacer is of the open-plenum type, whereas the heatshiled has two holes. If we put the spacer between the heatshield and the carb, the mixture "coloumn" expands as it exits the carb and enters the spacer, and then collides on the middle part of the heatshiled (between the holes) creating resistance and turbulence to the flow... If the spacer was under the heatshiled, then this wouldn't happen...

On the other hand, I am sure that the 40+ years of Opel experience concentrated in the forum has a good reason for recommending the "standard" order I mentioned at the start, and this is what I am trying to find... I am not trying to be smart... I just need the explanation that I can't think of....

Thank you for you time!

Regards

Antonis

[guyopel]

Why don't you try both ways and scan the heat shield with a temp. sensor to see what is the best way for heat
reduction ( I do not have a stock manifold or carb. ) and post the results. HTH

[gr_diver]

That would be a good way to figure out which configuration is more effective. Unfortunately I do not have a heat scanner... Nor can my digital thermometer be used for such a purpose, it must be contained in the substance that it measures...

I may have found an explanation for the stock configuration. Due to two indentations that the heatshield has at the underside, the spacer cannot fit below it. If I had a spare spacer I would mod it, since it would be an easy task, and judge for effectiveness by the means I have. But without a spare, I cannot risk ruining it in the procedure...

All these thoughts came because, now that summer has arrived, I regularly have an empty fuel bowl due to heat soak. And since the heatshield/spacer combination is in place, and have covered the fuel line in plastic loom, I am trying more ways to further reduce the phenomenon. It is not vapor lock, since the engine starts say half an hour later. But a few hours later, the fuel is almost gone, and I have to keep cranking for a few seconds to fill it up again...

[wrench459]

dude I live in the deep south USA
with no problems with fuel foaming,vapor lock, or what ever you might
call it no heat shield at all
where am I'm going with this
how much alcohol is in your fuel in Greece?

[gr_diver]

I am not familiar with fuel composition, but we use SuperLRP for classic cars. That is premium unleaded, with lead replacement additives. It evaporates easier than the old leaded fuel.

I have been thinking about converting to an electric fuel pump. That would solve it once and for all... But lately there are some facts that suggest that I might part with the Opel during autumn, so I am a bit hesitant about making any investments on it...

Anyway, sorry for filling the thread with irrelevant information...

[tekenaar]

Originally Posted by gr_diver That would be a good way to . . . . . . have found an explanation for the stock configuration. Due to two indentations that the heatshield has at the underside, the spacer cannot fit below it. . . . All these thoughts came because, now that summer has arrived, I regularly have an empty fuel bowl due to heat soak. And since the heatshield/spacer combination is in place, and have covered the fuel line in plastic loom, I am trying more ways to further reduce the phenomenon. It is not vapor lock, since the engine starts say half an hour later. But a few hours later, the fuel is almost gone, and I have to keep cranking for a few seconds to fill it up again...

Yes, the factory probably put them there to force the stacking order to their original design specs . . . actually a pretty clever idea, come to think of it.

I think there's a common misconception regarding the carb heatshield and spacer functions at work here. The heatshield blocks hot air rising from the exhaust manifold while the spacer blocks direct heat conduction from the intake manifold to the carb base . . . I believe that is the original design intent anyway.

If swapped around, you'd actually add some heat to the spacer from the exhaust hot air rising and now blocked by the heat shield placed above it . . . not much difference probably, but negative, if any.

[gr_diver]

tekenaar: thank you for the explanation. It now makes sense...

West Coast GT: This is why I want to add an electric pump. . . . . remainder moved to "gr diver electric FP needs" thread . . .

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