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Old 05-21-2012, 09:46 PM   #1
headslide
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Default draw threw turbo

who has any experience with this .seams it would be allot easier to just mount the carb on tothe turbo and, not have to worry about boost referencing the fuel system .?
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Old 05-21-2012, 10:25 PM   #2
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Default Re: draw threw turbo

Well it's been tried and should it have been successful, it would be on winning race cars.
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Old 05-21-2012, 10:33 PM   #3
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Default Re: draw threw turbo

VW guys do it all the time............ but whats to big deal with running 1 vacuum line from carb hat to the regulator???
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Old 05-21-2012, 11:21 PM   #4
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Default Re: draw threw turbo

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Originally Posted by headslide View Post
who has any experience with this .seams it would be allot easier to just mount the carb on tothe turbo and, not have to worry about boost referencing the fuel system .?
Who is worried about referencing the fuel system? Fuel system is easy. Carb just requires some simple research. After that research there are several ways to go depending on your abilities and budget.
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Old 05-21-2012, 11:34 PM   #5
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Default Re: draw threw turbo

It works great, is a lot easier to tune than blow-through because the carb can just be a normal carb, it just acts as if it is on a larger engine because of the increased airflow. Introducing the fuel before the compressor lowers the outlet temperature because of the evaporation of the fuel in the compressor and the result can be improved distribution if the ductwork and manifold are correct. There is no need for magic power valves or boost referenced fuel pressure regulators. Connection of the power valve or metering rod piston to the downstream side of the compressor is necessary but the power valve or power piston can be the standard stuff, use regular springs and assemblies.

A problem is sealing the turbo shaft to prevent the high vacuum of closed throttle and coasting from sucking the oil into the compressor. Some people are of the opinion that friction from an oil seal will cause more turbo-lag or slow turbo response to spool up. Other issues are remote mounting of the carb requires a manifold to the turbo intake, supporting the weight and supplying throttle control.
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Old 05-22-2012, 08:51 AM   #6
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Default Re: draw threw turbo

I would think if there was ever any leaks, with or without a cooler, that all that gas and o2 is under pressure and would fill the underhood and be a big bomb, I know it's been done before but still scares me.
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Old 05-22-2012, 02:14 PM   #7
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Default Re: draw threw turbo

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It works great, is a lot easier to tune than blow-through because the carb can just be a normal carb, it just acts as if it is on a larger engine because of the increased airflow. Introducing the fuel before the compressor lowers the outlet temperature because of the evaporation of the fuel in the compressor and the result can be improved distribution if the ductwork and manifold are correct. There is no need for magic power valves or boost referenced fuel pressure regulators. Connection of the power valve or metering rod piston to the downstream side of the compressor is necessary but the power valve or power piston can be the standard stuff, use regular springs and assemblies.

A problem is sealing the turbo shaft to prevent the high vacuum of closed throttle and coasting from sucking the oil into the compressor. Some people are of the opinion that friction from an oil seal will cause more turbo-lag or slow turbo response to spool up. Other issues are remote mounting of the carb requires a manifold to the turbo intake, supporting the weight and supplying throttle control.
Ok, if it works great, show us. Post me some links and video's.


I've got a pretty basic 355 sbc with a borgwarner S480 that has run in the 8's in a 3,6xx lb chevelle with a blowthrough carb and no intercooler. Show me a simple draw through setup running in the 8's. I'm very curious.


I found the Blowthrough very easy, And actually think a drawthrough would be harder to fabricate.
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Old 05-22-2012, 02:22 PM   #8
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Default Re: draw threw turbo

I think it's more about application and packaging. Drag VW's do drawthough because it's easier, more practical, and cheaper than blowthrough IDA's. V8's do blowthrough for the same reasons. My personal VW sandrail had a 1776cc motor with single blowthrough Dellorto. I myself have never liked the issues of getting a 4bbl to work right bouncing around offroad. A good offroad prepped 4bbl is easily $1000-$1500.
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Old 05-22-2012, 02:33 PM   #9
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Default Re: draw threw turbo

On the VW's you can get a lot of fuel to the motor at a decent cost. They have run in the 8"s on draw through with 4 barrel's. I agree that off road blowing through a Weber or Dellorto works much better. I have done both, and had them work good on both. The fast VW's guys are going to injection just like the rest of us. On a V8 application I would not recommend a draw through. The blow throughs work good, injection even better.
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Old 05-22-2012, 02:41 PM   #10
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Default Re: draw threw turbo

Different application for sure, draw through works on a bike too, which is more similar to a VW than an 8 second v8 car.

It is also suggested you use a carbon seal on the turbo instead of the standard oil seals. I don't think they are very common on modern turbo's.
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Old 05-22-2012, 03:29 PM   #11
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Default Re: draw threw turbo

As long as you don't pull a lot of vacuum a carbon seal in not necessary. Plus if you happen to back fire through the carb, you usually take out the carbon seal
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Old 05-22-2012, 04:10 PM   #12
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Default Re: draw threw turbo

"The two types have their own merit. The draw-through system is simpler and, because it is a low-pressure system, no change occurs in air density at the carburetor. Further, no compressor bypass valve is required. That is all that can be said for the draw-through system.


The blow-through system has better throttle response and cold starting, reduced emissions and permits the use of an intercooler. Weighing the merits, there is virtually no reason to build a draw-through system unless one lives in a year-round hot climate and/or never intends to produce serious power."

--- C. Bell
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Old 05-22-2012, 04:45 PM   #13
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Default Re: draw threw turbo

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Originally Posted by Swiftshifter View Post
"The two types have their own merit. The draw-through system is simpler and, because it is a low-pressure system, no change occurs in air density at the carburetor. Further, no compressor bypass valve is required. That is all that can be said for the draw-through system.


The blow-through system has better throttle response and cold starting, reduced emissions and permits the use of an intercooler. Weighing the merits, there is virtually no reason to build a draw-through system unless one lives in a year-round hot climate and/or never intends to produce serious power."

--- C. Bell
Agree with most of that. Accept I have seen power made on a draw through 800 plus on a 4 cylinder
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