750 cfm secondary vacuum enough for a blown engine? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-15-2004, 04:08 PM
84Z 84Z is offline
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750 cfm secondary vacuum enough for a blown engine?

I have a 144 B&M blower, with a crower supercharger cam 449 or 459 lift and 288 advanced duration 9.5 compression ratio, with 76cc stock heads. I also have a 750 cfm (*secondary vacuum*) carb. Will this carb be enough to support this engine setup? I've been getting a lot of criticism on whether it'll work or not, let me know what you think, thanks.

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Old 09-15-2004, 07:46 PM
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Old 09-16-2004, 09:58 AM
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any1??
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Old 09-16-2004, 10:52 AM
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how about telling us what size motor it is for starters
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Old 09-16-2004, 02:46 PM
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my bad, it's a 350 sbc and i made a mistake it's 8.5 compression, but will a secondary vac carb be enough in either case? thanks.
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Old 09-16-2004, 02:52 PM
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Hmmm, more than likely not, and I really think that's probably the wrong carb to use. You need a blow through type carb-

K
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Old 09-16-2004, 03:17 PM
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He doesn't need a blow through carb for a 144 supercharger...

On a street driven 350 that should be just about the right size of carburetor...The vaccum secondaries will work fine, allowing the engine to decide how much air it needs...The only time it would cause a problem is if you are running a lot of boost and/or high RPM and there is enough vaccum under the carb at WOT to actually close the secondaries or the powervalve...Use a vaccum gauge hooked to the carb base at WOT, run it up to your "redline" and see if you get more than 4" vaccum...If you get 4" or more THEN you should start thinking about a bigger carb...
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Old 09-16-2004, 03:25 PM
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I would be running a larger carb than that. I also have a 350 with a weiand 142 blower, and I am running a 800 cfm Edelbrock 1413 and it is fine. The problem with the Holley is you need one that has a boost referenced power valve circuit or it will not run right. It could run lean and burn things up, or run way to rich. The reason I went with the Edelbrock is because it was way cheaper than a blower series Holley. I had a perfectly good 750 vac sec holley around from my old non-forced induction setup that I had to get rid of. You do not need to run a blow through type carb because the blower is sucking through the carb.

Subman
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Old 09-16-2004, 04:11 PM
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It is a pretty simple matter to convert a standard Holley carb to use on a roots blower. You basically just reference the power valve to a manifold vacuum source (below/after the blower). For best performance, any carb used on a blower should have this done. I think that for that blower and cam, a 750 would work fine.
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Old 09-16-2004, 04:15 PM
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why the heck did I think he was talking about a turbo?

I'm the ******bag here.

K
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Old 09-16-2004, 04:55 PM
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Sorry, but I'm kind of a noob here with carbs. I got a vacuum hose ont he back of the carb which has the electronic choke and a hose from the valve cover there for brakes. There's another very small valve which has a very small red cap on it. Which one if any of those would the power valve be? And where would it need to be connected to?

I'm trying not to spend a lot of money on this, even thought I dumped a couple g's a lready, but if it's possible to convert this carb to work, I'd like to, but if it's a lot safer to just buy a new carb like the edelbrock 1413, let me know, thanks.

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Old 09-16-2004, 04:58 PM
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The power valve references through a small hole in the botom plate of the carb, by the throttle butterflys. You cant just hook a tube up to it. The carbs that are made for blowers can have a tube hooked up to them, but not the standard ones.

Subman
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Old 09-16-2004, 05:00 PM
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My blower has a hole int he very top of it which is plugged right now, is that what you're talking about?
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Old 09-16-2004, 08:43 PM
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Old 09-17-2004, 12:44 PM
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