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Wrong carb for 454

1218 Views 34 Replies 14 Participants Last post by  Senoth1
I was taking my carb off since its winter and was going to have it rebuilt. However when I took it off I noticed it had the wrong carb on it. The carb number says 7043208 which after research belongs on a 350 truck typically. I know the correct carb is 7041200. How big of a difference is it going to make changing these? Thanks!
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1971 Chevelle SS 454
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Discussion Starter · #3 ·
The engine is a stock cam, the heads have been swapped to a set of 109.4 CC semi open heads with 2.9 valves. Pistons are TRW. The engine is 60 over. he rear in the car is a 3:31.
 

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1971 Chevelle SS 454
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Discussion Starter · #5 ·
It ran ok I suppose, to be honest Its hard for to answer that because I dont know if it would run better with the right one. I think the CFMs are drastically different arent they?
 

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The next time you have the valve covers off for some maintenence there is a number for your cylinder heads that is casted in about the center of the cyl head. Having the casting number will tell you what the valves were when they brand new but if they were modded who knows ???
Typically Big block Chevy heads with 2.19 intake valves would have 1.88 exhaust valves but if the heads were machined for larger valves the exhaust valves could be anywhere from 1.72 to 1.88.
 

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1971 Chevelle SS 454
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Discussion Starter · #15 ·
The next time you have the valve covers off for some maintenence there is a number for your cylinder heads that is casted in about the center of the cyl head. Having the casting number will tell you what the valves were when they brand new but if they were modded who knows ???
Typically Big block Chevy heads with 2.19 intake valves would have 1.88 exhaust valves but if the heads were machined for larger valves the exhaust valves could be anywhere from 1.72 to 1.88.
Probably need it out them off anyway and look.
 

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Carbs are engine specific. There is no way that the Uremco carb will work well out of the box. Carbs need to be calibrated to your specific engine. You can't order one out of a catalog and expect it to run well. It will start and run but you must change jets and metering rods to match the engine. I would contact a specialty carb guy in your area to rebuild yours and tune it to your engine or to tune the Uremco one. The overall CFM for all of them is 750. There are some larger 800 ones but they are rare and they were not for Chevrolet.
 

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The typical factory stock Big Block Chevy 454cid cylinder head valve diameter size is 2.19" for the intake valves, and 1.88" for the exhaust valves. Of course aftermarket hi-perf aluminum heads offer those same size valves, but also a larger intake valve too, (such as 2.25" and even 2.30") for a power increase.

The factory BBC iron cylinder heads And the "conventional" aftermarket replacement cylinder heads from places like Brodix, Dart, AFR, etc. are 24 degree and 26 degree heads. All of which can be used with conventional factory and .off the shelf Big Block Chevy pistons. Then there are the big horsepower and big dollar BBC aftermarket heads that have different (flatter) valve angles such as 20 degree, 15 degree, 12, and even 9 degree intake valve angles, none of which can be used with conventional factory stock, nor off the shelf aftermarket pistons since they're all made for the conventional 24/26 degree BBC heads. Hopefully I haven't confused you.

But unless you have factory heads which have been brought to a machine shop and fitted with larger intake valves by a previous owner, then you have the 2.19" diameter intake valves and 1.88" diameter exhaust valves. And the heads are the typical BBC factory 24 degree intake valve angle design.
That's a very broad and misleading statement. The majority of OEM oval port passenger car BBC heads had 2.06" Intake and 1.72" exhaust valves. Rectangular port iron heads 1969 and earlier (not sure about 1970 and later) generally were 2.19" intake and 1.72" exhaust (My 1969 L72 with 3919840 iron heads had 2.19'/1.72" fwiw). Early 427 L88 Corvette with 3904392 aluminum heads had 2.19"/1.72", 3919842 aluminum heads had 2.19"/1.84" valve sizes and 1969 L88 and ZL1's with 3946074 heads were the first heads to have 2.19"/1.88" valves. What happened to these heads after they left the factory is anybody's guess and aftermarket heads are a totally different ball game. That's my experience.
 

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Honestly, I am really learning. This is what was wrote on the ad when I bought it. Any education you want to give me is much appreciated.
Back to your Qjet. Very likely replaced somewhere along the way with an stock off-the-shelf rebuild, which would likely have truck numbers. That's OK. I know one of the carbs Eric did for me was off a motor home ( from Tom mobely ) and the other maybe a md 70's something or other. The RV one is800+ cfm, while the 70s small block Camaro is a standard 750 cfm version.

You COULD try to find the correct casting #, and again Eric is a restoration pro, so may be able to help you there as well.

PS I decided not to run either, but I really ogth take a shot of the one Eric restored. I don't wear jewlery, but that thing is uber bling! in an OEM way. Just friggin' stellar finish. Reminds me to do that.

If the carb seems to run fine, run it! As long as Qjets dont get too much fuel pressure, once in tune, they do tend to remain that way.
 
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