L20B Turbo

[MantisX620]

I have an extra L20B laying around that I plan to rebuild myself for my 620. For fun, im thinking of fabricating a draw through turbo setup. I think I get the gist of the mechanics of how it works, but my question is how does fuel get to the cylinders during startup?

 

The carb is a long way from the intake with these setups so how does gas come from the carb, through the turbo and into the engine? This concept makes perfect sense on a running engine, but im a little baffled how it works on startup. Is vacuum that strong on startup to pull gas all that way?

 

Also, how does a weber respond to positive pressure on its vacuum lines?

 

Thanks all

MantisX

[datzenmike]

There is gas and air there from the last time you shut it off just like any other carb motor.

 

 

 For fun, im thinking of fabricating a draw through turbo setup.

Also, how does a weber respond to positive pressure on its vacuum lines?

 

Thanks all

MantisX

 

Not understanding. If a draw through how will it be exposed to positive pressure on it's vacuum lines? Look at it this way...

 

Carb

Turbo

Motor

 

The only difference is that the turbo is doing the work of the motor to suck in gas and air. The carb will work exactly the same and will feel vacuum under it just the same as without the turbo. With a turbo it will have more air sucked through it, is all.

[MantisX620]

Explained beautifully, thank you sir. I figure ill make the intake out of a 4 inch diameter piece of pipe with maybe 2 inch runners and a tubular manifold. Not looking to make holy shit power, 150 or so would tickle me.

 

Thanks again

MantisX

[metalmonkey47]

Why not use L28 EFI? Cut down an L28ET manifold to remove the two center cylinders, and run megasquirt.

 

That's the down the road plan for my LZ22. 3

 

If you're only planning on 150 or so, that's soooo much easier and cost effective N/A. Weber 45's, big bore, ported A87 peanut, etc. 

 

 

Peter Brock made nearly 200 back in the day with an L(16) I think it was?

[MantisX620]

I thought about the route you explained but it seemed the more N/A results I searched, the more money was spent and less hp results. Maybe I was looking at the wrong builds. I like the idea of cutting that manifold though. That may even be a good way to make a good blow through manifold instead.

[Master-O-Turbonics]

4" intake and 2" runners? planning on 600hp?

[Z-train]

Why not use L28 EFI? Cut down an L28ET manifold to remove the two center cylinders, and run megasquirt.

[620Turbo4X4]

I have an extra L20B laying around that I plan to rebuild myself for my 620. For fun, im thinking of fabricating a draw through turbo setup. I think I get the gist of the mechanics of how it works, but my question is how does fuel get to the cylinders during startup?

 

The carb is a long way from the intake with these setups so how does gas come from the carb, through the turbo and into the engine? This concept makes perfect sense on a running engine, but im a little baffled how it works on startup. Is vacuum that strong on startup to pull gas all that way?

 

Also, how does a weber respond to positive pressure on its vacuum lines?

 

Thanks all

MantisX

The only modification that needs to be done to a weber for a draw through setup is isolating the power valve circuit from the suction side of the turbo, and tap it into the pressure side (manifold vacuum) of the turbo so it functions properly. I had a 76 620 with a draw through setup back in the day and it was using a 32/36 Holly/Weber carb from 2.3l turbo 79 Ford Mustang that is already setup up with a remote power valve port.

 

The reason for doing this is power valve normally enriches the fuel mixture as load increases (manifold vacuum decreases). With a carb mounted before the turbo the vacuum will only decrease momentarily under load. Once the turbo catches up, then vacuum at the carb. increases and the enrichment is lost causing a lean condition.

 

There is never positive pressure in the carb in a draw through, only on a blow through... Fuel reaches the cylinders just fine, just takes a split second longer to get there.

 

But….. I totally agree with the others that have responded. If your only going for 150Hp. N/A would be the way to go. Carburetors and turbos just don't work well together. EFI would be the way to go if you really want a turbo.

 

I'm currently building a L20b stroker engine myself and aiming for 250-280Hp. range Will be starting a build thread soon when time permits...

 

I can tell you from experience making a tubular intake is not as easy as it sounds. 

I'm sure I have 60+ hours into this….

 

 

 

 

Starting on a equal length Tri-Y header now. What a pain!!!

 

[Z-train]

What TB are you using?

[620Turbo4X4]

TB was from a '98 Chrysler Sebring... Some thing I found on eBay… I liked that it didn't have tons of vacuum lines, came with connectors, and was cheap!

[Z-train]

Thanks.

[datzenmike]

Tops are S13 KA24E, bottoms S110 200sx

 

 

[Z-train]

Mike-do they both have a idle compensation motor?

[datzenmike]

I don't know.... you mean the air regulator? The thingy that gives it more air when cold so it has a slightly faster idle? Yes.

[Z-train]

Yes-it also kicks the idle up when you turn the A/C on.

[datzenmike]

That I don't know. The air regulator is just like the fast idle on a carb with the choke on. How this is done with EFI I don't know.

[Z-train]

Hmmm,now that I look closer that 3 pin switch is the TPS.I don't see a ICM.

[datzenmike]

Idle Compensator Motor... can't say I've heard of them. Makes sense though.

[Farmer Joe]

they dont have a compensator motor... the KA uses the IACV for the idle control.. 

 

so, idle with a basic TB with no IACV will need an idle adjuster screw.. prolly best to get this running on a MAP sensor and a megasquirt...

[MantisX620]

Has anyone shot a L20B with a methanol kit and turned the timing up to oh shit levels before? I have a meth kit laying around im trying to sell, but im tempted.