Re: Type 1 twin screw supercharger build / 9 yrs later I'm back at it

[Chip Birks]

Can't give any scientific advise on the return, I put mine in the bottom of my stock tank. Never had any fueling issues.

[turbobaja]

I've got my return just pooring into the top of my tank. I've learned since then that doing this can create problems with fuel evaporation, etc. A better way would be to have the fuel returning near the bottom of the tank so it's not falling and splashing as much. I'll have to add a tube to reach the bottom of my tank. So I'd say just mount the return in the bottom of the tank if you can, or mount up top and hardline/hose it to the bottom for less "emissions" (wasted fuel ).

[Alexander_Monday]

Return in bottom of tank it is then.

[Humpty]

Return in bottom of tank it is then.

I've been doing a little research on this very idea..... Mine is currently fitted to the top, and I have heard 'from those that know more than I' that this method can aerate the fuel, which apparently is a bad thing..... I have also been looking at cleaner options, as the return line entering the top of the tank does not look good to me, and is actually yet another cause for the local plod to harass me...

The general consensus in the local performance world is thus...

For a clean install, fit the return into the bottom of the tank..... But.... It is best to fabricate an suitable return tube inside the tank so the fuel drops into open atmosphere (above the fuel level).... Most suggest a upside down "J" shaped inlet pipe.... The reason being that the curved top portion of the tube acts like a tap outlet, streaming the flow of fuel back in the tank and limited the aeration of the fuel, and also limiting the possibility of the fuel working its way back up the line whilst the car is stationary.... That last point is only view of one person I spoke too, but the tube idea seems solid.... Apparently it's pretty common practice in OEM fuel return applications.

[turbobaja]

For a clean install, fit the return into the bottom of the tank..... But.... It is best to fabricate an suitable return tube inside the tank so the fuel drops into open atmosphere (above the fuel level).... Most suggest a upside down "J" shaped inlet pipe.... The reason being that the curved top portion of the tube acts like a tap outlet, streaming the flow of fuel back in the tank and limited the aeration of the fuel, and also limiting the possibility of the fuel working its way back up the line whilst the car is stationary.... That last point is only view of one person I spoke too, but the tube idea seems solid.... Apparently it's pretty common practice in OEM fuel return applications.

Humpty this sounds a bit confusing to me. I can understand the advantages of having your fittings on the bottom of the tank, but it seems silly to then route the returning fuel back up to the top of the tank so it can fountain out and splash down to wherever the fuel level is at that time. Wouldn't that cause the same kind of fuel aeration problem we both just mentioned? The OEMs generally use some type of fuel tank "module" that drops into the tank from the top and has the returning fuel routed back into a small housing where the fuel pump lives. Avoiding evaporative emissions is very high priority with most OEMs, especially these days. Maybe I'm misunderstanding the "J" tube configuration?

I would think a better way to return fuel would be laterally from the end or side of the tank near the bottom, so the fuel can just swirl around the bottom of the tank and not be shot up or splash back down to the surface of the fuel level at all.

[Humpty]

Apparently the upside down 'J' idea stops the splashing/spraying phenomenon from happening.... But the idea of the excess fuel entering a 'small housing' seems very logical to me.... I was also thinking of fitting a swirl pot too.... Like my bro did with his WRX powered Notchback... But with my car I'll make it internal..... So the idea of the excess fuel dropping into that could work well...... I guess the proof is in the pudding though.... Chip has run his to the bottom of the tank without a need for anything else.... Maybe I'm just over thinking it....

[Buggin_74]

Simon, have you run yours for any length of time with the return in the top of the tank?

I've heard all the aeration theories floating around the interwebz too, dunno how much to believe of it.
I've got my return into the top of my fuel filler neck so unless my tank is full its always filling above the fuel level.
My black bug was setup the same since 1989 and never had a drama either.

any air bubbles would rise to the top of the fuel in tank and stay there, you would have to be almost out of fuel for it to be an issue

[OwenMM]

I ended up returning mine straight into the bottom of the tank because it was easiest, we'll see if there's any issues soon enough.
I think the whole issue of aeration etc only really becomes an issue in endurance racing etc, not really a concern for most of us.

[miniman82]

Agreed, I've been returning to the top of the tank since day 1, never any issues.

[Humpty]

Simon, have you run yours for any length of time with the return in the top of the tank?

Been running mine in the top of the tank since early last year.... Never had a problem.

[turbobaja]

The issue is not air bubbles contaminating the fuel delivery, its fuel evaporating out of your tank breather, as I understand it at least. Evaporative emissions = wasted gas, that's all.

[Alexander_Monday]

Well, I have not had a lot of time to work on it.

I have got the new fittings welded to the stainless tank.
A custom fuel level sender has been ordered.
Also ordered the fittings to convert the Autorotor from internal oil to pressure feed oil,
and a black magic clutch disk to soften the blow to the transaxle.

Next on the adjenda is to finish up this end of the intake plumbing:

655845.jpg

[Alexander_Monday]

Figuring out fuel, intercooler water, and oil systems.

Can the fuel regulator (EFI) go back up by the tank, or does it need to be close to the fuel rail?

Running out of room in back.

[Steve Arndt]

A lot of new cars have the regulator near the pump and fuel tank. You can put it there I believe.

Are you planning on running a vacuum/boost referenced regulator? That is a long vacuum run, but no different than running a boost gauge up front.

I have my regulator mounted above my transaxle to the bottom of the package tray.

[Alexander_Monday]

Yes it will be referenced, so that is one more line to run if I put it up front.

I didn't want to crawl under to adjust it, and the gauge is mounted to it.

I have a flip front end, so it would be simple access up there.