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Discussion Starter #1
I have been using a pair of 750's and am limited to 5lbs of boost.Will the boost level drop when I install larger carbs?Will be buying a pair of SV1's and was curious if a much less restrictive carbs will reduce boost without changing pullys:confused:
 

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Its not the boost level but the drive ratio,I would say the 750s would be good till about 12 to 14% overdrive at 7000 engine RPM,I used 750s up to 23% over with no problem other then a hot discharge temp................Oldhead
 

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Discussion Starter #3
My junk is 13% under at 5lbs.Will not feed anymore than this.540 ci,1071 bds stage 3.Will the boost level stay the same after the carb change to a pair of 1300 cfm carbs??:smt102
 

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I think the boost will go up a little,The reason the boost number is low is your heads flow very good and will make good power...BE SURE TO LET US KNOW HOW YOU DO....Good luck Oldhead....PS:what have you been turning at the drags??????
 

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i ran out of carb at 10% od with 850's and 270*F intake temp.i went to 1250's and 10% UD and went faster but with a colder charge.i measured my iat at 10%OD and it was 130 before the cooler.my engine is a 446 and yours is a 528 no?with a 10-71[mine is 8-71]it will be near the same boost but denser and will give more hp.
 

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Discussion Starter #6
Oldhead,3850 lbs,9.92 @ 133,5 lbs boost.99 jets pri,105 max jets sec and a 10.5 pv:smt033
 

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Discussion Starter #9
Let me ask a different way,would larger carbs reduce some restriction and lower the boost level???
 

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Let me ask a different way,would larger carbs reduce some restriction and lower the boost level???
With a roots blower a bigger carb will reduce restriction and possibly make more boost cuz it can ingest the air easier. If it where a blow thru procharger setup a bigger carb may lower the boost cuz its forcing the air through the carb.
 

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I would want to make the change simply for the power increase you will see with bigger carbs. Boost can be altered so if it makes more or less you can match it with the same given boost you should see much more of a power increase since the engine will breathe alot nicer. 750's are on the small side for what you have. Don;t get me wrong, it is the design of the carb more than rated cfm numbers, but you should still see more power with the change. Let us know how you make out.
 

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Let me ask a different way,would larger carbs reduce some restriction and lower the boost level???
Boost is another word for pressure, and pressure is resistance to flow. The blower produces the flow and the rest of the engine provides the resistance. The boost pressure you see is generated under the blower rotors, into the manifold and into the cylinder, so you won't see a change of pressure from the carbs.

BUT!!! If your carbs are so small as to limit the intake capability of the blower, you might see some more boost with the bigger carbs. With bigger carbs, the blower can suck in more air, and generate more flow than with the small carbs.

Whe you say you are "limited" to 5lbs, what exactly do you mean? Is there a rule you race under that limits boost, or is 5psi all you can get out of the blower?

Keep in mind that it is going to take a shit load of blower flow to fill up a 540inch engine and start to make boost. If you take your same blower set up and stick it on a 400 inch engine, you would see almost twice the boost as your 540 only because there is more restriction in the smaller engine. (smaller bore, stroke, valves, runners, ect.)

Good luck, -Abone.
 

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Boost is another word for pressure, and pressure is resistance to flow. The blower produces the flow and the rest of the engine provides the resistance. The boost pressure you see is generated under the blower rotors, into the manifold and into the cylinder, so you won't see a change of pressure from the carbs.

BUT!!! If your carbs are so small as to limit the intake capability of the blower, you might see some more boost with the bigger carbs. With bigger carbs, the blower can suck in more air, and generate more flow than with the small carbs.

Whe you say you are "limited" to 5lbs, what exactly do you mean? Is there a rule you race under that limits boost, or is 5psi all you can get out of the blower?

Keep in mind that it is going to take a shit load of blower flow to fill up a 540inch engine and start to make boost. If you take your same blower set up and stick it on a 400 inch engine, you would see almost twice the boost as your 540 only because there is more restriction in the smaller engine. (smaller bore, stroke, valves, runners, ect.)

Good luck, -Abone.

Good post Flame--x2
 

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Discussion Starter #14
I am limited because at 5 lbs with jets over 100,it's lean.Alcohol jets and still on gas,,,,need bigger taters:rolleyes:
 

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Oldhead,3850 lbs,9.92 @ 133,5 lbs boost.99 jets pri,105 max jets sec and a 10.5 pv:smt033
Using your numbers on my calculator says you are making 750 HP.............I used holley 3310s on my 871 and went from 10% under to 19% over using 72f 76r jetting with out beening lean,I made 42 pulls on the dyno with NO problem ,Made 748 HP at 6800 on a SBC-400 and 952 HP using nitrous.......Two years later I installed a Vortech YSI and pulled 1004 hp WITH NO CHANGES TO THE ENGINE.The YSI is a small street blower.............I hope you do better GOOD LUCK Oldhead
 

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Oldhead,
Were you on gas or alky? I have a 8-71 on a 400 with 10.8 compression, have pullies that make 8 10.6 12.2 and 19 over. I was wondering what type of power I will be able to make with the AFR227cc and the hat on alky.
 
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