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blow vs suck

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    Default blow vs suck

    I was just thinking.... On a draw thru setup I would need almost twice the carb as a blow thru...why is that? At the top of the piston you are still using the same amount of air and fuel.

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    gn7
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    Quote Originally Posted by terrible_buddhist View Post
    I was just thinking.... On a draw thru setup I would need almost twice the carb as a blow thru...why is that? At the top of the piston you are still using the same amount of air and fuel.
    Because the carb as to flow air at atmospheric pressure. On a blow thru the air is compressed. More air in the same space. You can get more air thru a 1" hole that's compressed to 15psi than you can at 0 psi. Same amount of air takes up twice the space going thru the carb then at 15psi.

    Also, the fuel being in the air going thru the turbo on a draw thru takes up space that air alone would occupy if it was a blow thru. Doesn't sound like much, but that fuel takes up some space better utilized by air. Also the fuel in the air impinges on the turbo blades and slows it down some compared to dry air.
    You can look at draw thru every way you care to, and they are losers compared to blow thru.



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    I don't know that is the case but one has atmospheric air going through and one boosted air going through. I get by with a single blade 100mm throttlebody.
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    Quote Originally Posted by gn7 View Post
    Because the carb as to flow air at atmospheric pressure. On a blow thru the air is compressed. More air in the same space. You can get more air thru a 1" hole that's compressed to 15psi than you can at 0 psi. Same amount of air takes up twice the space going thru the carb then at 15psi.

    Also, the fuel being in the air going thru the turbo on a draw thru takes up space that air alone would occupy if it was a blow thru. Doesn't sound like much, but that fuel takes up some space better utilized by air. Also the fuel in the air impinges on the turbo blades and slows it down some compared to dry air.
    You can look at draw thru every way you care to, and they are losers compared to blow thru.
    It wasn't a winner/loser thing...I was just going through the new Jegs catelog and they has a new demon blow thru carb for like $650 and I was just thinking to myself...I wonder why I could do blowthru on a single 850, but would need 2 of them to do draw thru.

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    because it takes roughly twice the throttle bore or venture area to pass air at atmospheric pressure, compared to 15 psi.

    Yes it is a winner loser thing. Draw thru is a loser. Unless you like running 2 850s instead of one, and reducing the capacity of the turbo. Those are just 2 issues. There are a few more.



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    Quote Originally Posted by gn7 View Post
    because it takes roughly twice the throttle bore or venture area to pass air at atmospheric pressure, compared to 15 psi.

    Yes it is a winner loser thing. Draw thru is a loser. Unless you like running 2 850s instead of one, and reducing the capacity of the turbo. Those are just 2 issues. There are a few more.
    Yep! Barry grant bt carbs are shit btw.qft bt carbs work with alil work.

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    Quote Originally Posted by IMPATIENT 1 View Post
    Yep! Barry grant bt carbs are shit btw.qft bt carbs work with alil work.
    have you run 'em???

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    Quote Originally Posted by bp298 View Post
    have you run 'em???
    Do alil reading on users and youll see what i mean.ive bolted and ran c&s/qft/csu blowthru carbs but never wanna mess with barry grant bt carbs..never read a good thing about them but have read countless bad threads over the yrs. if terrible wants to really shit or get off the fucking pot now he needs to order a fresh new 850dp holley have it shipped to kevin at csu for conversion and frnt billet brpv and be done be about 800 when said and done with it working tits

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    I was looking at a quick fuel BT for my TT SBC an after some research I decided to call Kevin/CSU very cool guy he said save your self the head ache so I filled out his app he called me we went over it so a 750 holley was built an a week I live about an hour away so picked it up put on was at the dyno it lite up perfect with very little idle adjusting made pulls good AFRs I was very pleased with his work now I did have to Chang jets once it was in the car Ontario to plamdale was enough to get a stumble plus my fuel pressure was I bit high to

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    Quote Originally Posted by IMPATIENT 1 View Post
    Do alil reading on users and youll see what i mean.ive bolted and ran c&s/qft/csu blowthru carbs but never wanna mess with barry grant bt carbs..never read a good thing about them but have read countless bad threads over the yrs. if terrible wants to really shit or get off the fucking pot now he needs to order a fresh new 850dp holley have it shipped to kevin at csu for conversion and frnt billet brpv and be done be about 800 when said and done with it working tits
    I dated a girl who had working tits...best weekend of my life

    Seriously...this wasn't a 'why can't I do draw thru'!?! post...it was a...huh, I wonder why? Post. Just doing a little learnin'

    That said...I have some more time to sit on the pot. I will be ordering the heads and cam soon then after that make the final decision on induction. I am leaning VERY heavily towards blow thru right now. I already have a nice 850 with the choke horn milled off. If I could come up with a slick way to use the PFM intercooler as a hat I think I would be all in. Down the road I still may do FI...but Blow Thru seems the path of least resistance right now.

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    Quote Originally Posted by IMPATIENT 1 View Post
    Do alil reading on users and youll see what i mean.ive bolted and ran c&s/qft/csu blowthru carbs but never wanna mess with barry grant bt carbs..never read a good thing about them but have read countless bad threads over the yrs. if terrible wants to really shit or get off the fucking pot now he needs to order a fresh new 850dp holley have it shipped to kevin at csu for conversion and frnt billet brpv and be done be about 800 when said and done with it working tits
    so what I'm reading here is that no carb will work on a given bt deal without being sent to somebody that actually knows what they're doing with it???
    if I believed every shit story I read about bg carbs, I wouldn't have been running them for the past 12 years, and won numerous races with 'em. initially there -were- issues. not that difficult to figure out if somebody wants to learn...

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    Quote Originally Posted by terrible_buddhist View Post
    I dated a girl who had working tits...best weekend of my life

    Seriously...this wasn't a 'why can't I do draw thru'!?! post...it was a...huh, I wonder why? Post. Just doing a little learnin'

    That said...I have some more time to sit on the pot. I will be ordering the heads and cam soon then after that make the final decision on induction. I am leaning VERY heavily towards blow thru right now. I already have a nice 850 with the choke horn milled off. If I could come up with a slick way to use the PFM intercooler as a hat I think I would be all in. Down the road I still may do FI...but Blow Thru seems the path of least resistance right now.
    Check out this thread
    http://www.performanceboats.com/dyno...questions.html
    Do it like this
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    I was watching that a while ago...looks like he has made progress! I have thought about maybe doing an adapter plate or something...of course, I will need to figure something out on the intake too because I have a dominator intake, 4150 carb, and dominator flange on the intercooler.

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    Quote Originally Posted by terrible_buddhist View Post
    I was watching that a while ago...looks like he has made progress! I have thought about maybe doing an adapter plate or something...of course, I will need to figure something out on the intake too because I have a dominator intake, 4150 carb, and dominator flange on the intercooler.
    Why not just go to a dominator carb? It can be done in a blowthrough also.
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