spills

iTrader: (9)

On my 89 RS, Ive been going on the assumption that Im just going to reuse the stoc in-tank electric puel pump and get a 3 port bypass regulator. Im not sure what the LO3 pushed out as far as puel pressure, but Im sure its much more than 5-7psi Im gonna need for my 750 DP.

That being said, someone one at my work said that I would run a higher risk of vapor lock, saying that with most of the fuel running under the hood, getting hot, and getting returned through the regulator. That heat in the fuel would slowly heat up the fuel in the tank, and result in vapor lock. Can anyone else shine some light on this? Ive read many posts on here about re-using the stock elec FP, but I dont remember seeing anything related to vapor locking due to it.

five7kid

iTrader: (14)

Eventually, perhaps.

The chance of vapor lock without a return is much more likely.

spills

iTrader: (9)

well, vapor lock is when the fuel in the tank/lines gets so hot it actually evaporates and cannot ignite in the chamber, correct? I just wanna make sure I got the right definition of it.

So your saying that using a pump, like a mech., would vapor lock easier than en electric in tank?

BT283

iTrader: (3)

If your going to run a bypass regulator you can run a return line and pretty much not ever have a problem with vapor lock. As for the stock pump i ran mine (also LO3) in my car for a while, but if i was you i would change it in the future because there is no volume. If you build a wild engine and take it to the drag strip or where ever you will probably find the car is going to seem to have a flat spot but it is just the car is running out of fuel, the stock pump just cant pump it fast enought. But i have a friend running a stock pump out of a V6 car and he has a raddicale engine and his does fine.

five7kid

iTrader: (14)

Not exactly. From http://www.misterfixit.com/vaprlock.htm :
"Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older engines with "sucking" fuel pumps at the engine the pressure in the fuel line to the tank was reduced by the sucking action of the fuel pump drawing fuel from a fuel tank nearly twenty feet away, and when heated, the gasoline actually boiled creating a vapor of gasoline which the fuel pump could not handle, thus the name "vapor lock".

"Today's fuel pumps are in the fuel tank where they push the fuel under pressure to the engine systems. Excessive fuel which is not used is sent back to the fuel tank. This causes a constant flow of pressurized, cool fuel in the lines to the engine system, be it fuel injection or carburetor. As a result you would have to heat the fuel line with a propane torch to get the fuel to boil and even then it would be cooled by the flowing fuel circulating from the tank to the engine and back again to the tank. Vapor lock as we once knew it is a thing of the past."

Does that help explain why? You'd be bringing the past back to the present.

five7kid

iTrader: (14)

There is another condition that will cause a carbureted engine to not run properly when hot. It is also mis-labeled "vapor lock".

From http://autorepair.about.com/cs/gener.../bldef_856.htm :
"When gasoline overheats and boils inside the carburetor bowl or fuel pump of a hot engine, it ceases to flow. This can cause stalling or hard starting. This is called vapor lock, and it usually happens during hot weather. If a hot engine won't start, all you can do is let it sit and cool off. You should check the cooling system to see if anything is causing the engine to run unusually hot (a bad thermostat or cooling fan, for example). Switching brands of gasoline may also help."

That should be called "fuel boiling", which will act very similar to vapor lock, but really isn't the same thing.

FWIW, high capacity engine mounted fuel pumps can actually make vapor lock worse, by sucking harder on the fuel line - this reduces the pressure in the line even more, making the fuel boil more easily under otherwise equal temperature conditions.