BBC intake mods
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BBC intake mods
Hi everyone, i have a pancake, low rise 1971 bbc cast iron intake. Are there any known mods that could be performed other than extrude honing? Plan on running a 3/4” quadrajet spacer. I’m assuming that it is a smog intake but maybe not as smoggy as the later model intakes that have the EGR. This one is devoid of the EGR.
Thanks
Thanks
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Re: BBC intake mods
Other then porting or sending it out to Brezinsky for rework the next best thing to do is to run a large Carb .
The larger then needed Carb will slow down the excessive runner air speed above 4500 rpm and allow rising power numbers to be made and a slower nose over of such numbers.
If your running a Q jet era Manifold then this is where a 1000 cfm Carter themoquad will be the way to go if not restricted by some rules.
The larger then needed Carb will slow down the excessive runner air speed above 4500 rpm and allow rising power numbers to be made and a slower nose over of such numbers.
If your running a Q jet era Manifold then this is where a 1000 cfm Carter themoquad will be the way to go if not restricted by some rules.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
Re: BBC intake mods
Ummm.. I'm sure a big Carter carb will help, but how does a higher-flowing carb slow down runner velocity and why would you want to?mag2555 wrote: ↑Fri Nov 01, 2019 7:35 am Other then porting or sending it out to Brezinsky for rework the next best thing to do is to run a large Carb .
The larger then needed Carb will slow down the excessive runner air speed above 4500 rpm and allow rising power numbers to be made and a slower nose over of such numbers.
If your running a Q jet era Manifold then this is where a 1000 cfm Carter themoquad will be the way to go if not restricted by some rules.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
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Re: BBC intake mods
I say this because back in the late 90s I had a .030" over 455 cid street strip motor of mine one a dyno and the Q jet was giving us issues so we got that worked out and with a 1 inch spacer ended up making 406 hp at only 4400 rpm, this was with a Performer Intake.
Air consumption was only 645 cfm so the 750 Q jet had a good amount of cushion I would say , yet just for S & G we slapped on the a Holley 800 and picked up 12 hp, so draw your conclusions from that.
My money was on better average port air speeds more inline with what that cid motor could tolerate thru those size Intake runners and the fact that the bigger Carb pressurized the Plenum better.
Air consumption was only 645 cfm so the 750 Q jet had a good amount of cushion I would say , yet just for S & G we slapped on the a Holley 800 and picked up 12 hp, so draw your conclusions from that.
My money was on better average port air speeds more inline with what that cid motor could tolerate thru those size Intake runners and the fact that the bigger Carb pressurized the Plenum better.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
Re: BBC intake mods
The bigger carb would indeed pressurise the plenum better, aka reduce manifold vacuum.
The standard CFM rating of American 4 bbl. carbs is at an arbitrary 1.5" Hg. pressure drop; considered in the fifties when 4 bbls. became common, to be typical of then-current passenger car engines and not coincidentally, measurable with the same capacity flow benches that tested 2 bbl. carbs at 3.0" Hg.
The only magic in having a carb whose flow rating matches your engine's peak air consumption on the dyno is that it should in theory result in exactly 1.5" of manifold vacuum at that RPM. Unrestricted race engines commonly use much higher CFM-rated carbs in order to increase the density of the inducted air. For example, as long ago as the late sixties, some Ford factory Trans Am Series Mustangs used a pair of 1,000 CFM plus Dominator carbs on their 305 c.i. engines whose theoretical air consumption at 8,000 RPM would have been ~ 700 CFM. This would have resulted in a manifold vacuum of ~ 0.6"Hg at peak revs. and probably 35 HP more than a single 700 CFM carb.
The standard CFM rating of American 4 bbl. carbs is at an arbitrary 1.5" Hg. pressure drop; considered in the fifties when 4 bbls. became common, to be typical of then-current passenger car engines and not coincidentally, measurable with the same capacity flow benches that tested 2 bbl. carbs at 3.0" Hg.
The only magic in having a carb whose flow rating matches your engine's peak air consumption on the dyno is that it should in theory result in exactly 1.5" of manifold vacuum at that RPM. Unrestricted race engines commonly use much higher CFM-rated carbs in order to increase the density of the inducted air. For example, as long ago as the late sixties, some Ford factory Trans Am Series Mustangs used a pair of 1,000 CFM plus Dominator carbs on their 305 c.i. engines whose theoretical air consumption at 8,000 RPM would have been ~ 700 CFM. This would have resulted in a manifold vacuum of ~ 0.6"Hg at peak revs. and probably 35 HP more than a single 700 CFM carb.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: BBC intake mods
There are several shops that can internally port the intake for some serious power gains. Brzezinski is the most prominent among them. Their full out intake work requires machining 4 holes into the intake and then plugging them after the work has been done. If you want the intake work to be absolutely undetectable, they offer a couple of different options...acid porting being one of them.
There are also shops that specialize in 'prepped' intakes for NHRA Stock Eliminator class that have as much internal work done as the cut apart Brzezinski intake but they don't cut the access holes. All the work is covered up and the internals and externals appear stock. It's time consuming and expensive. But they will pass any NHRA tear down. These guys are true cast iron artists.
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Re: BBC intake mods
Unless you plan on running this in a class where that intake is REQUIRED, your money will better be spent on a newer, better intake. Lots of choices here.....
Mark Goulette
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Owner/Driver of the Livin' The Dream rear engine dragster
Speed kills but it's better than going slow!
http://www.livinthedreamracing.com
Authorized Amsoil Retailer
Re: BBC intake mods
Thanks for the replies. Yes, going to bolt on the performer RPM. So much for trying to make a sleeper out of this. The cam is a solid flat tappet and makes power from 2500-6500. Don’t believe the low rise cast iron is going to cut the mustard.
Thanks again all.
Thanks again all.
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Re: BBC intake mods
Paint everything black and put 'Goodwrench 305' stickers on the valve covers.
DON'T PANIC
Re: BBC intake mods
Bought a performer rpm. Interesting info on the late 60’s trans am era.
I like that goodwrench sticker idea.
I like that goodwrench sticker idea.
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Re: BBC intake mods
In my experience the black paint, stickers, bench seat & column shifter were enough to cancel out any complaint about the single stage of nitrous. "Oh come on, how fast could it really be? Look! It's even still got the EGR valve on it!" <snicker>
(EGR ports went nowhere in the manifold, and the nitrous jet was somewhere north of #100, but hey...)
(EGR ports went nowhere in the manifold, and the nitrous jet was somewhere north of #100, but hey...)
DON'T PANIC