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Highaboosta
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Draw through is old school.
Prone to fuel settling out in the compressor and piping.
Add an intercooler and the problem is compounded.
I did it that way back in the 80's when I was racing sand drags.

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Discussion Starter #3
I meant for efi...I know DT is old school when it comes to carbs...but I have seen it done very successfully.


That boat was turn key for decades. Not saying there wasn't work arounds with it, I know at 20lbs he was using a NOS plate to dump fuel in...but it did work.

My question was more about EFI though...Is it better to locate the throttle body under the innercooler (blow thru) or before the turbos (draw thru)?
 

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Draw through may be old school, but it has been working for many years and generally, it's way cheaper.
There are a couple of limitations to draw through to keep in mind. Generally you may be limited to the cubic inches
that it really works with and not all turbos are compatable with the draw through system.
On the other hand, if money is not an object, blow through is usually better if you know how to operate a computer.

I'm sure others will chime in with more details, both for and against.
Yea, draw through is old school, but we know it works...:D
 

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This is a Gentry/Brummett EFI twin turbo.. The throttle blades are after the turbo before the intercooler. Injectors are in the intake runners under the intercooler..
 

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My Idea for that factory clean Smartcraft gauge dash board
with guardian mode protection features

Use a Mercury Racing 1350 TT PCM EFI/ COP ignition system .
and there oem computer controlled turbos

Hook that up to the BBC of your choice

Mercury makes the harness ,sensors and link gauges
plug and play wiring
 

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Just because I am curious...what is the better way to do EFI...draw thru or blow thru?
Draw through is old school.
Prone to fuel settling out in the compressor and piping.
Add an intercooler and the problem is compounded.
I did it that way back in the 80's when I was racing sand drags.
Draw through may be old school, but it has been working for many years and generally, it's way cheaper.
There are a couple of limitations to draw through to keep in mind. Generally you may be limited to the cubic inches
that it really works with and not all turbos are comparable with the draw through system.
On the other hand, if money is not an object, blow through is usually better if you know how to operate a computer.

I'm sure others will chime in with more details, both for and against.
Yea, draw through is old school, but we know it works...:D
Maybe the rocket scientist here can explain to this dummie how a turbo needs to be something special to deal with draw thru as opposed to blow thru, or how fuel puddles in the cooler, or manifold if the EFI throttle body is before the turbo. Or why you need special computer skills that different for a draw thru than a blow thru

Please use plain English so this dummie can understand your explaination. After all I am just a dumb carb and roots hick.



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Here's a pic of my old Race Aero EFI blow thru, Autronics ignition, 500 ci BBC made 760 hp with 9 lbs of boost. It starts right up every time. Next is a carbed Race Aero blow thru, 468 ci BBC made 850 hp with 15lbs boost. It starts a little harder, but I've had it for nine years View attachment 450089 P1030554.jpg
 

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I DKS about turbos, but I would think the blow thru deal would offer better perf. having positive airflow available at the intake above the tb, as opposed to having the tubo sucking the air through it then sending it down stream to the intake. Like I said I don't know squat, just my thoughts on the way it would work.
 

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I DKS about turbos, but I would think the blow thru deal would offer better perf. having positive airflow available at the intake above the tb, as opposed to having the tubo sucking the air through it then sending it down stream to the intake. Like I said I don't know squat, just my thoughts on the way it would work.
As opposed to a roots sucking thru a hat???



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As opposed to a roots sucking thru a hat???
No plumbing for the roots air to get to the intake, its all right there close together, and no science to back the thought up, just a thought thinking about available air. Kinda like why the car man. have all added big plenums to the engines of modern cars.
 

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No plumbing for the roots air to get to the intake, its all right there close together, and no science to back the thought up, just a thought thinking about available air. Kinda like why the car man. have all added big plenums to the engines of modern cars.
No doubt a blow thru throttle body can be made less complex, simpler and lighter. Plus you can even use fancy dancy inlet bells with trick little inlet guide vane on them. I see no benefits to a draw thru
My original question was how a draw thru efi creates fuel puddling or require different computer skill set.



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No doubt a blow thru throttle body can be made less complex, simpler and lighter. Plus you can even use fancy dancy inlet bells with trick little inlet guide vane on them. I see no benefits to a draw thru
My original question was how a draw thru efi creates fuel puddling or require different computer skill set.
As far as the puddling thing, I thought you were joking. Kinda hard to puddle fuel in the inlet hoses when its being injected in the manifold!
 

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Discussion Starter #15
I think he missed the part about it being EFI at first.

Wouldn't draw thru efi be better though since you can eliminate the BOV and limit air going in rather than blocking air going out?
 

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I think he missed the part about it being EFI at first.

Wouldn't draw thru efi be better though since you can eliminate the BOV and limit air going in rather than blocking air going out?
I would think you would loose alittle throttle response and add alittle lag, not to mention you could get an adjustable bov that could also serve as a max boost control
 

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Highaboosta
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Maybe the rocket scientist here can explain to this dummie how a turbo needs to be something special to deal with draw thru as opposed to blow thru, or how fuel puddles in the cooler, or manifold if the EFI throttle body is before the turbo. .

I know your smarter than this Bob but since you asked.
If the carb or throttle body is ahead of the turbo it pulls manifold vacuum on the compressor housing.
The turbo then needs a carbon seal to on the compressor side or the vacuum will pull oil out of the bearing housing.
Along with this fuel in suspension will settle out in the long path between the carb and the head.
This happens more in cooler weather but the system is prone to this and I've had it happen many times.
It's just old school and undesirable. Kind of like you Bob ;)

I know in the boating world there are many draw through setups left over from the 1970's that everyone thinks have been running just marvy. Well like many other things there has been progress since then. Some will stick with the old school shit and some will adopt newer technology.

In the car world NO ONE would ever run their fuel mixture through their intercooler.
It's just the wrong way to do it.
 

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I know your smarter than this Bob but since you asked.
If the carb or throttle body is ahead of the turbo it pulls manifold vacuum on the compressor housing.
The turbo then needs a carbon seal to on the compressor side or the vacuum will pull oil out of the bearing housing.
Along with this fuel in suspension will settle out in the long path between the carb and the head.
This happens more in cooler weather but the system is prone to this and I've had it happen many times.
It's just old school and undesirable. Kind of like you Bob ;)

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I am aware of the seal issue. I am still hung up on the fuel falling out of suspension due to the throttle body being ahead of the turbo. and intercooler. In fact there has been a couple pics of throttle bodies before the cooler on a couple boat engine in this thread. Do they have fuel puddling issues in the cooler as well?



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I think unchained pretty well described the situation regarding the need for a carbon seal on the draw through system. It's not practical for all turbos to be converted to use a carbon seals.
My statement regarding needing some computer skills was made because many efi systems require a computer to tune the system. If it's carburetor,
the tuning is done either with an o2 meter or checking plugs, generally.

The original poster did ask about efi and not carbs.
 

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On EFI the fuel is introduced at the intake manifold right at the head, so no puddling issues. I think what the OP was trying to ask is why does it matter which side of the turbo the throttle body is on? Blow through or draw through. The main draw back to having it before the turbo is because at idle the turbo will see vacuum and oil could possibly be drawn from the seal and into the intake tract. I would put it after the turbo, and install a BOV. jmo.
 
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