Carb modification for blower use

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Carb modification for blower use

Post  dfree383 on March 27th 2018, 7:23 pm

I’ve got a 6-71 blower going on a Boss 302 build, just picked up a pair of Quick Fuel HR-650’s with mechanical secondary’s.

What needs to be modified for Blower use?
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Re: Carb modification for blower use

Post  pmrphil on March 27th 2018, 8:25 pm

Quick Fuel uses roller bearings on the throttle shafts to prevent binding, (billet baseplates also) that and making the power valve boost referenced is the other. I imagine you can find some bleed numbers online to get a place to start.

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Blower carbs.

Post  blown473 on March 31st 2018, 3:23 pm

Generally you want larger needles & seats, and your jetting will probably need to go up several sizes, 20% is not uncommon. boost referenced power valves and boost referenced fuel pressure and timing are also good ideas. Conservative timing and a limit on total timing as well. You will love the throttle response it's addictive.

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Re: Carb modification for blower use

Post  dfree383 on April 1st 2018, 8:59 am

Do I need to run power valves at all?
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Boost/power valves

Post  blown473 on April 2nd 2018, 10:48 pm

Power valves account for a big portion of your total fuel flow, if you choose to use power valve plugs then you will need to make big jetting changes to compensate for the lost fuel or your engine will go lean as a cutting torch. You might take a few minutes and call the Holley Tech line and give them your engine specs, they have out of the box blower calibrated carbs,they can give you those as a baseline starting point and they are usually very close. Edelbrock offers the same service too, and their carbs with blower calibration work well too.

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Re: Carb modification for blower use

Post  dfree383 on April 6th 2018, 6:12 am

Other than the tune what physically needs to be modified to run the power valves?

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Re: Carb modification for blower use

Post  supervel45 on April 6th 2018, 7:20 am

http://www.motorsportsvillage.com/modifycarb.html

Back in the day most guys myself included ran Holley's without boost referenced power valves with no problems on 6/71's.

PS: The other two ways I have seen them modified is a port in the main body or a port in the base plate.

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Re: Carb modification for blower use

Post  supervel45 on April 6th 2018, 8:34 am

http://www.quickfueltechnology.com.au/content/Quick%20Fuel%20Carb%20Size%20with%20details-AUST.pdf

Check out page 3. I believe the Q650-B2 is the dual quad blower version and it shows the spec's.

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Re: Carb modification for blower use

Post  torino501 on April 14th 2018, 5:53 pm

i had a holley hp 950 blower carb. boost ref. only doing about 5 lb on a holley 174 roots blower. I pullyed down and got about 11 psi and ping like hell with a 93/116 mix. so I decided to send it off for an E85 conversion. mark sullens is doing the conversion. after a long talk he said trust him on no boost ref power valves. so I don't know what kind of voodoo magic hes doing with the carb. guess well see how it turns out. I told him I really need an emphasis on driveability. that 950 out of the box was awesome once the engine warmed up. not that it was bad cold. just no choke..

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