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hood vents

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i have 2 78 280s and a 76 280 the 78s have vents but the 76 does not. did vents come on them or are they aftermarket and what purpose are they

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Hood vents were standard on the 77-78 280Z. Those hoods will fit the earlier S30s.

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they let the hot air out from under the hood.

Do the hood vents really work?

I only ask because on my old MGA, high pressure developed by air piling-up on the windshield actually forced air "into" the cowl vents instead of air flowing out of the engine compartment.

I realize the Z's aerodynamics are certainly different than the MG's.

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i thought it had something to do with vapor lock!

EFI cars don't vapor lock.

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Since carbureted engines usually use a mechanical fuel pump located on the engine, they need to suck the fuel from the gas tank, and a bubble of vaporized gas can develop, which doesn't liked to be sucked through, and just gets bigger. This is 'vapor lock.' So you let things cool so the bubble disappears and you can suck gas again.

Since fuel injected engines use a fuel pump near the gas tank to push the gas to the engine using much higher pressure, you pretty much eliminate any vapor bubbles in the fuel line. You'd need a really REALLY hot day for conditions to vaporize fuel in the lines under the car, but it might just be possible, like if a fuel line was too close to an exhaust tube or muffler.

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If that were the case, the ~37psi would push the air bubbles through and at worst, if everything else is working properly, you'd feel a couple of 'hiccups' and keep on going.

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In addition to hood vents, some people here have mentioned that having a splash pan on the car helps even more to improve the airflow in the engine bay.

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thanks, with that being said i should be able to replace the vented hood with a solid one with no problems, or very little , correct

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Yes, the hoods are interchangable. I've seen many 77-78s that have swapped on the solid hood.

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Do the hood vents really work?

I only ask because on my old MGA, high pressure developed by air piling-up on the windshield actually forced air "into" the cowl vents instead of air flowing out of the engine compartment.

I realize the Z's aerodynamics are certainly different than the MG's.

The hood vents are a long way forward of the cowl vents. The cowl on the 240z is where the fan blower gets its fresh air from.

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Stephen is right. 'Vapor lock' is basic chemistry (the gasoline gets too hot and boils in the fuel system, essentially, changing state from a liquid to a vapor). Nothing to do with the fuel pump.

Do the hood vents have anything to do with aerodynamics (reducing lift)?

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I personally think that Nissan was just trying to add something different to their last go rouund of the S30. JMO. Look how fancy they got with hood vents on the ZXs. Are those things even open? Sorry Zx people, but I really don't know.

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If that were the case, the ~37psi would push the air bubbles through and at worst, if everything else is working properly, you'd feel a couple of 'hiccups' and keep on going.

I have what seems like to be a vapor lock issue with my 75 280z. I'm not sure what it is exactly. But i've read many thoughts on this issue and being a newb at S30 i'm pretty confused.

If I drive for 30 mins or more and then stop my car and let it sit for 10-15 minutes it will sputter real bad for a little while. I've read about Vapor Lock, Cold Start Valve, Thermotime switch... I've asked a mechanic that works on a lot of Z's and says that its Vapor Lock and hood vents would help.

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Don't know if I'd agree with that, in fact I know I don't. My Z has hood vents but my 810 doesn't. I've had the two cars a combined total of 17 years and the only times I've ever experienced any thing like that, it turned out to be electrical or component related.

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If that were the case, the ~37psi would push the air bubbles through and at worst, if everything else is working properly, you'd feel a couple of 'hiccups' and keep on going.

Not true. Look up "air lock" on Google. What basically happnes is an air bubble gets trapped between the gas. Air is highly compressible and when the pump tries to push the air, it simply compresses it.

I ran into this issue a few times with my car due to a low spot in my return line. I would lose pressure when the car was off and an air pocket would form in my line. I could not build up fuel pressure until I purged my return line of any gas.

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Are you talking about an EFI car? If so, then you had a component related problem. Remember, I did say "if everything else is working properly".

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I think part of my problem is my car doesn't have a heat sheild between the Exhaust and the Intake. Could be getting hot enough to boil the fuel in the fuel rail?

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If I drive for 30 mins or more and then stop my car and let it sit for 10-15 minutes it will sputter real bad for a little while.
Does it starts okay if the engine is cold? But under those conditions it's hard to start and takes a while to smooth out? That sounds like the fuel pump check valve isn't holding and the pressure drops. Then the pressure has to build up when you start it before it will the engine will smooth out.

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A quick test to confirm Stephen's theory is to cycle the ignition on and off (do not start the car, simply let the pump energize for 2 seconds) a few times. Fuel pressure will build up in the line. On the 3rd or 4th time, start the car.

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