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gdat210

Jetting DHLA Dellortos for Blow thru?

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Has anyone had any success with doing a blow thru turbo on DHLA 40's? Or even weber DCOE? what must be done to jet the carburetor to provide more fuel when boost pressure builds? 

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this stuff is becoming black art these days but you need to google modulator rings and how they work. If you call cb performance you may be able to get some info on blow through dcoe's.

 

 

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12 hours ago, scooter said:

this stuff is becoming black art these days but you need to google modulator rings and how they work. If you call cb performance you may be able to get some info on blow through dcoe's.

 

 

thanks. just debating if it would be better to sell them and do an EFI setup instead. it would definitely look & sound cool.

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efi will work 800000x better when running a turbskie

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Balance pressure for the float bowl is taken right at the inlet flange. I wouldn't think it would be difficult at all. If your float bowl is sealed and you can feed it the same pressure as whats in your manifold and you have infinetly adjustable jets wheres the problem?

 

Kurt

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The amount of air moving through the venturi is what determines how much fuel is required so I would think that all you are doing is forcing more air through. I would think the mixture requirements and therefore the jetting would stay the same.

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Another thing to consider.  Increasing the air pressure all around the carburetor above what is atmospheric pressure increases the density of the air going through the carburetor.  Carburetors do not know the air density, they are designed to have manifold vacuum under the throttle plate, and normal atmospheric pressure on the outside of the carburetor.  

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Daniel, it's all relative. At 14 PSI around the carb, at part throttle there will be less pressure below the throttle plate it will 'feel' like vacuum. Carburetors increase the amount of added fuel in response to increased air flow through it. More air draws in more fuel. Carburetors are damn amazing.

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When you have a turbocharger you are not drawing air in/creating a vacuum except when you let completely off the pedal as the pistons are trying to pull air in thru a closed butterfly valve, you give it full pedal the air is being pushed in via the turbocharger, anything in between will stabilize at the PSI it is happy at, but it will still be under some kind of boost except when you completely let off the pedal, and on gas engines that is what a wastegate/blow off valve is for, to release all that pressure on the turbocharger side of the butterfly valve.

 

This is a complicated subject if you don't know the basics, you have to understand what K Appley is talking about, if you don't know what he is talking about then you really need to learn before you jump into the deep end of the pool.

 

Your better off with a high HP engine without a turbo to start with, something that almost scares you, then with a turbo you will have even more power(scares the shit out of you), and EFI makes it WAY easier, or just buy a HP turbocharged engine to start with, one that had a lot of power off the show room floor, not a turbocharged VW Passat engine or the like, them engines needed a turbocharger just to sell them as without the turbo they were gutless, start with an engine that scares you already.

 

 

 

 

 

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I agree, carbs are amazing.   However, using a turbo to blow air through a carb does put the carb into operating conditions it was not designed for. 

Wayno is also right.  Turbocharging a normally aspirated engine is complicated.   i just went to Amazon and typed "turbocharging books" into the search line.  Several pages of books turned up.

 

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Indeed. A boost of about 7 PSI is like 50% more air going through it. If going 2,000 RPMs the carb is seeing 3,000 RPMs worth of air.  At 6,000 it's expected to mix gas for 9,000 which is unrealistic. The float chamber might even go dry trying. Certainly the carburetor would become a choke point.

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And that is what a boost referenced fuel pressure regulator is for, the higher the boost the higher the fuel pressure.

 

 

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