LPG (propane) Carb options.

[amichie]

OK here is my dilema.

I have a impco 225 LPG carb on my 7mge. I have found that it is too restrictive and since the air flows through it regardless if its running on LPG or unleaded it affects the performance both on LPG and on unleaded.

The impco 225 is rated to 329cfm. This sounds like enough but if I remove it and put the put the plastic pipe back on I get a noticeable improvement in performance on unleaded above about 4500rpm.

So the question is what is the simplest upgrade option.? I am not considering gas injection as the cost would be too high.

See pic below

 

[CRE]

Speed/Density and a butterfly valve to bypass the impco?

 

[amichie]

Speed/Density and a butterfly valve to bypass the impco?

Yeah. That is what I was leaning towards.

Since my model j converter would also need to be upgraded if I got a bigger carb such as the impco425.

I have a spare throttle body that could be used as a butterfly/by pass as you mentioned.

I will need to fabricate some piping to make it all work. Maybe just out of painted mild steel mandrel bends from the exhaust shop.

 

[CRE]

Just so you understand, I mentioned converting to speed density so that you can avoid having to route everything through the same inlet. In this case the intake would just Y out to two different air filters with no VAF in either. But then again there is the cost of additional hardware.

 

[Poodles]

paging IJ...

 

[CRE]

^^^Heh, I had thought the same thing. Just figured he'd have already replied if he had anything to add.

 

[figgie]

he is still sleeping!

give the man a break!

 

[amichie]

Just so you understand, I mentioned converting to speed density so that you can avoid having to route everything through the same inlet. In this case the intake would just Y out to two different air filters with no VAF in either. But then again there is the cost of additional hardware.

Don't you still need either a VAF or a translated MAF reading when on LPG for the ignition timing control.

 

[CRE]

You do need airflow data, yes. Speed/Density calculates airflow based on manifold pressue and air temp. It'd give you the room you might otherwise not have... but as I said, there is cost to consider.

I run Speed/Density with the MAFT Pro. Not cheap, but it gives me more than just the ability to delete my VAF.

How are you controlling your air to fuel mixtures?



EDIT: See, plenty of room to play now (old pics): http://www.fadingworld.com/Supra/Engine/20080426%20- Engine/



Whatever route you go you may need to build some sort of bypass. I'm not familiar enough with the internals or flow restrictions of that unit to suggest anything more.

 

[amichie]

You do need airflow data, yes. Speed/Density calculates airflow based on manifold pressue and air temp. It'd give you the room you might otherwise not have... but as I said, there is cost to consider.

I run Speed/Density with the MAFT Pro. Not cheap, but it gives me more than just the ability to delete my VAF.

How are you controlling your air to fuel mixtures?



EDIT: See, plenty of room to play now (old pics): http://www.fadingworld.com/Supra/Engine/20080426 - Engine/



Whatever route you go you may need to build some sort of bypass. I'm not familiar enough with the internals or flow restrictions of that unit to suggest anything more.

Thanks for the pics. Looks great. I presume the filter is mounted in front somewhere?

The impco 225 is very restrictive. It is rated at 329cfm at 1.5 inches Hg Vac.

But even that seems optimisitic.

 

[IJ.]

Normal airflow calcs won't work for an LPG vapour system as during phase change the LPG expands 240x and will displace a good percentage of the incoming air.

 

[amichie]

So what do you reckon?

Options
1. Bypass system
2. Impco 425
3. Dual Impco 225s.

 

[IJ.]

This is for an NA correct?

 

[amichie]

This is for an NA correct?

That is correct.

 

[IJ.]

So any of the bigger Impco converters should be well within any realistic HP you'll get?