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Old 10-25-2010, 01:06 PM
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Blow through fuel system.

So after some motivation.....http://www.theturboforums.com/smf/in...?topic=61219.1

I am trying something of this of my own.

I am thinking stock block 305 268H cam and performer rpm intake with 650 holley 4150. I was looking for any suggestion on fuel pump and regulator. This is going in a strict drag vehicle. I have the 305 long block an intake and carb. Also with having to enclose the whole carb wouldn't i need to keep the total fuel pressure above the boost level i am gonna run? thanks
This is what im thinking for fuel pump....http://www.summitracing.com/parts/AEI-11203/?rtype=1
and for a regulator I wasn't sure if i needed a regulator with a boost reference port or not. Can anyone help Also can maybe someone give me some good reading material on blow through carbs. Thanks


Also please note......I know this is a risk...chance are it will come apart but look how much money im gonna have into it barely any. Im not gonna spin the motor over 5000 to help save the internals some and run it on the rich side to try to save the stock cast pistons. and if it blows go get another 305 that no one wants.

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Last edited by zildjian4life218; 10-25-2010 at 01:31 PM.
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Old 10-25-2010, 02:06 PM
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Quote:
Originally Posted by zildjian4life218
...for a regulator I wasn't sure if i needed a regulator with a boost reference port or not.......
What is that? I think you're confused about boost referencing and carb requirements. That has nothing to do with the fuel pressure regulator.

Building a boosted motor on the cheap is never good, especially a race only setup.

I'm thinking how much track owners/operators love oil down's...
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Old 10-25-2010, 02:14 PM
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Quote:
Originally Posted by 68NovaSS
What is that? I think you're confused about boost referencing and carb requirements. That has nothing to do with the fuel pressure regulator.

Building a boosted motor on the cheap is never good, especially a race only setup.

I'm thinking how much track owners/operators love oil down's...
It increase fuel pressure and boost increases. Usually 1:1. They are available.
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Old 10-25-2010, 02:24 PM
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Not doubting you, and would like to read up on them. Can you put up a link?

Also, what do you mean "usually 1:1"?

Boost referencing the carb/power valve is a whole different way to richen it under boost, and the only way I've seen to effectively do that. Live and learn I suppose...

Edit: I came across the Race Pump regulator setup and read up on it. Thanks.

Last edited by 68NovaSS; 10-25-2010 at 02:32 PM.
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Old 10-25-2010, 02:30 PM
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Quote:
Originally Posted by 68NovaSS
Not doubting you, and would like to read up on them. Can you put up a link?

Also, what do you mean "usually 1:1"?

Boost referencing the carb/power valve is a whole different way to richen it under boost, and the only way I've seen to effectively do that. Live and learn I suppose...
Something like this. As boost increase it raises the fuel pressure to help meet the fuel requirements.
http://www.summitracing.com/parts/MAA-4309/

This is an article about opening up the two holes under the power valve to allow extra fuel under WOT.
http://www.hangar18fabrication.com/blowthru.html
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Old 10-25-2010, 02:40 PM
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I see where you mean richening things. The pump itself only creates more fuel pressure, the holes drilled actually provide the richening, similar to boost referencing the carb(s), but requiring carb modification. I'm curious how you lean it for idle when the PV block has been drilled out. Doesn't seem dropping fuel pressure would do it.

Not a cheap alternative to boost referencing the PV, if that's possible in a blow through configuration. Good luck.
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Old 10-25-2010, 02:42 PM
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Quote:
Originally Posted by 68NovaSS
I see where you mean richening things. The pump itself only creates more fuel pressure, the holes drilled actually provide the richening, similar to boost referencing the carb(s), but requiring carb modification. I'm curious how you lean it for idle when the PV block has been drilled out. Doesn't seem dropping fuel pressure would do it.

Not a cheap alternative to boost referencing the PV, if that's possible in a blow through configuration. Good luck.
Ive never dealt with it before so I came here looking for possibly some help with figuring out what size fuel pump I am going to need and a regulator and the carb modifications.
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Old 10-25-2010, 07:16 PM
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You guys each jave half the information. You need a "boost referenced" power valve and regulator and drilled pvcr's and a few other things. Btw you do not reference a blow through pv the same as a draw through. Most specialty carb shops fab up their own power valves and metering blocks to do this. Some also rework air passages for this purpose. Its not that complcated but you also cannot just throw a pump and regulator on it and race.
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Old 10-26-2010, 09:17 AM
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Quote:
Originally Posted by ap72
You guys each jave half the information. You need a "boost referenced" power valve and regulator and drilled pvcr's and a few other things. Btw you do not reference a blow through pv the same as a draw through. Most specialty carb shops fab up their own power valves and metering blocks to do this. Some also rework air passages for this purpose. Its not that complcated but you also cannot just throw a pump and regulator on it and race.
I know it takes more than just a fuel pump and regulator. I am gonna get some reading material on how to modify the carb appropriately.

But I read in a turbocharging book I have that with carbs and fuel pressure you need a fuel pump capable of producing at least 4psi higher fuel pressure than your desired boost level.

So If I only run say 10psi would I need a 14psi pump or would you also factor in the base fuel pressure of say 5-6psi for a carb.

This would make sense because If my regulator is set at 6spi and It increases fuel pressure 1 psi for every 1 psi of boost (hence 1:1) that means the pump will have to be making a minimum of 16psi and then I would have to give myself a safety margain on top of that like 5 psi or so which means at like 20psi???

Am i confused or is this right? Thanks I am only shooting for like 500hp or so. They guy in the first article i posted was making like 700 some wheel.

Last edited by zildjian4life218; 10-26-2010 at 09:23 AM.
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Old 10-26-2010, 09:46 AM
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Well you have to have about 5psi more than your boost level, BUT that means you want a pump rated for even more unless you want it to spike up to (and maybe past) max duty when you are under boost. To be honest for a carb application just about any fuel pump from a modern fuel injected car can be made to work. You should try to track down the pump curve of the specific pump you are wishing to use before you just throw it in though. pressure is only one side, the other being flow.

Carb modifications vary according to carb model, but the general idea is to seal them so boost/fuel cannot leak out, alter the powervalve circuit to operate under boost instead of vacuum, and devise a method for adjusting the powervalve jetting.

Most people will go with a double pumper holley with screw in PVCR's, "air sealed" throttle shafts, a carb hat, and the lowest rated power valve they can find. While this is not an optimal approach it does work fairly well and is perhaps the most cost effective. If you get a used core and build your own you can do it for about $150 including the core.

I think powervalve and metering block modification helps as well, but that is more than most people are comfortable with and not truely necessary.
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Old 10-26-2010, 10:39 AM
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Quote:
Originally Posted by turbolover

While this is not an optimal approach it does work fairly well and is perhaps the most cost effective.
Yeah if i could go efi i would but i can't afford it. Can anyone suggest how much flow i should need? Also possibly any donor cars that the efi pumps would work well. thanks
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Old 10-26-2010, 10:47 AM
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10gph for every 100 hp. That is at boost pressure plus 5 psi! So you'll need about 50gph at 20psi.

I would use a 600cfm OR SMALLER 4bbl. a 500cfm 2bbl would work as well.
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Old 10-26-2010, 11:09 AM
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Quote:
Originally Posted by turbolover
10gph for every 100 hp. That is at boost pressure plus 5 psi! So you'll need about 50gph at 20psi.

I would use a 600cfm OR SMALLER 4bbl. a 500cfm 2bbl would work as well.
i have a 650dp kicking around. Eventually I would like to run around 20psi but i figure for getting started ill set it at 10 and go from there.
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Old 10-26-2010, 12:02 PM
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Quote:
Originally Posted by zildjian4life218
i have a 650dp kicking around. Eventually I would like to run around 20psi but i figure for getting started ill set it at 10 and go from there.

With the equipment you're running you don't have to worry about 20psi, you're engine will never make it there.
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Old 10-26-2010, 01:58 PM
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Quote:
Originally Posted by turbolover
With the equipment you're running you don't have to worry about 20psi, you're engine will never make it there.
Yeah So your thinking at least 20 psi and 50lb/hr

This is a good deal.
http://www.racingjunk.com/category/1...ries-pump.html
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