Hi guys, what size carburater do you think I should run on my newly rebuilt 455. It has the C heads exhaust side slight port job, bored to a 468cu. Any help would be great. Thanks in advance.

 

Oh man that's a candidate for the MSD Atomic EFI system. These are the new bye-bye carb setups. I've spotted them on lots of trick cars. Other makers like Edelbrock also offer this EFI technology. You'll need an O2 sensor and electric fuel pump but that's easy stuff. Rocket Time!

 

Or you could just go with a Q-Jet for about an eighth of the price. Most of them are 750 CFM except (IIRC) for the later Pontiac Super Duty ones which go 800 CFM. I don't know the numbers, but you should be able to recognize the 800 CFM by the price. 750 should be plenty if, as you say, your engine's fairly mild.

 

By the numbers, you've got 468ci, so if you divide that by two (four stroke engine has 2 revolutions for each cycle), you get 234ci per revolution, then take 80% of that for the rule-of-thumb efficiency of a "regular" American V8 and you get 187ci of air moved per rev.
Convert 187cci to cubic feet and you get 0.1083 CF per rev.
Multiply that by the maximum RPM you will use (say 5,500) and you get 596CFM at 5,500 RPM, so a 650CFM carb would be fine.

I agree that a QJ would be a great idea.

- Eric

 

Outside of a quadrajet, you will probably need at least a 750 cfm carb to keep your engine happy at the extremes in performance requirements.

 

My 455 has ported and blended exhaust ports, mild cam, bored 30 over w/ aluminum intake ( aftermarket) and dyno was 326 hp/ 450 ft lbs torque at motor. I used 7042251 QJ carb. Mine would not idle steady until I had the idle circuit drilled bigger. I runs great now. If you go QJ and it keeps hunting at idle you may need the same fix. The mech would take the top off with carb on motor, drill in small increments and run motor. Repeated till he got to a size not too big to ruin carb but idle good. My number was 40 thousandths. Your's may run fine stock but if it does hunt and a smoke test rules out vacuum leak as was my case this could help. Good luck with your choice.

 

 

I forgot to mention i have a single plane old shcool intake torker if that make s diff

 

Well the quadrajet is out for that manifold. What carb is on there now? I've had good luck with the inexpensive Holley 3310 vacuum secondary.

 

Run a dual plane with a 780 Holley. Works great for me.

 

I had a great experience with a 670 CFM Holley Street Avenger on a warmed-over smallblock Chevy some years back -- good idle, precise metering, very smooth and linear and the car ran like a scalded cat. My manifold was a Weiand dual plane, though. Maybe try a 770 CFM.

 

AED 750 HO carb. Great carb for the money & so easy to tune.

 

Quick Fuel 850. BBO loves big carbs.

 

The OP build sounds like a 750 is plenty. But 850 might be the ticket at the track.

 

This is a good question. What have you been using, and what were its shortcomings?

 

What cam? compression?, going to race?

 

There isn't a carb on there at all. I just got the motor from a guy. So I need a fly wheel, and a carb for it.

 

Here is the info the guy I bought it from sent me.

 

That cam sounds a little more than "mild". You may do better to go 800 CFM+. Also, what's your rear gear going to be?

 

Nice build platform. From what I've experienced, bigger isn't always better. The total cylinder/head "area" is normally considered when solving for CFM volume. So that puts you in the 650-750 range by charts the manufactures offer. Not exactly an absolute size here. Porting, headers and intakes make more efficient flow but not really considered with CFM sizing. The tricky part is valve size, lift, and duration. If factored, this can add to the optimum CFM required. So, solving for the exact carb on an unknown engine is a bugger. If you purchase something undersized, a Craigslist ad fixes that. An oversized carb can be a fire hose that also goes to ad. Your best bet is find similar builds and document what they ended up with. Guess and experiment.

For a reasonably priced starter (hopefully keeper), Quickfuel has both a 680 and 780 in their Hot Rod series. Great $400 carbs. Basically a well tweaked Holley.

If you're looking for an out of the box carb that will work great often without any tuning required, check out Edelbrock Performers 650-750. * Use them and would recommend to friends.

I think anything over 780 might be pushing it without forced air? Really surprised about the big numbers reported. Maybe these bad boys can run dandy fine with lots-O-fuel? Hoo hoo.

 

With that setup, I expect you'll need the ability to rev higher as well, so I would agree you're in 750 territory.

Devil is in the details, eh?

- Eric

 

I'm gonna go back to the Holley Street Avenger 770. Runs great out of the box, easy install, electric choke, vacuum secondaries, very tunable. I loved my 670.

 

My gear ratio is currently the stock 3:91, but i'm thinking about swaping the carrier and putting in 3:23 for so I can comfortably drive 70mph. Where now 60 is about 3100 rpm's with my 29inch tall wheel/tires

 

Yeah, you might want to hold off on that for a bit. With that much cam, 3.91 would be okay -- if anything you'd probably want to go numerically higher. In any case, it probably won't be much of a highway cruiser.


Automatic or manual?

 

My car is acually the rare 70 W-31. Not the original 350 though. It has the automatic 3speed hurst dual gate shifter in it.

 

I think I have it narrowed down to two 750 carbs.What would be a better of the two to go with? Demon 1904 for $346 or Quickfuel Slayer series for $318 not sure why the diff in price though

 

Hmmm, that Demon series have a proprietary height. Guys have had issues fitting air cleaners getting hood clearance. Demon has their own cleaner for these tweaked to go low. I have the problem due to an RPM manifold rise where a standard open element setup only works with a 2" filter instead of the common 3".

My son runs the Quickfuel carb and thought it was easy to dial-in. That Demon series gets good reviews. Hard to say which is "better".

 

Looks to me as though I should be running an 830 cfm. The price is very steep though. Check it out. 800 bucks? Holy Moly!
http://www.summitracing.com/parts/hly-0-80511-1

 

Still a lot cheaper than an EFI conversion.

 

Run a 850 cfm and be done with it. That is what i run. Good luck on what ever you choose.

 

Why do you want to run that style carb?

 

It's just an example of the cost. The combo I am currently running really works well. But, you know car guys, always looking for that last hp. I'm leaving it alone.

 

I honestly, don't know what to run, these are the two that seemed to fit what I was told to look for. My mechinc whose breaking in and Dynoing my motor said go with a 750 for streetable use. Do you have a good carb in mind. I know the demon I will have to get a new bracket kit for $113 more dollars per a friend of mine that runs that demon carb on his 71 skylark. I'm open to advice and opinons

 

Sorry my question was aimed at z11375ss on his choice.

What bracket kit is he talking about? The easiest Holleys for the street are the 3310 and the Street Avenger. The Demons are ok but more complicated and expensive. I was wrong earlier and I believe your manifold will accept both a Rochester and any square bore.
http://www.edelbrock.com/automotive/...orker-bb.shtml

 

Wow, I'm back in for the 830-850 talk. That thing would have to be jetted down or unburned fuel would shoot out the exhaust pipes as flames!

Kidding, just astonished at that size. Wish those EFI setups were reasonably priced.

 

I am not against quick fuel or a proform carb. What i do know from racing a street car at the race track is this. If i had to give up my 750 or my 850 demon for a holly or quadrajet there will be a knock down drag out fight! I will bring a walking tall club i don't want to lose.

 

The brackets he had to get were for his transmisson ATV or kick down. But I will worry about those latter I guess. I ended up ordering the Demon carb because of the large secondaries. I hope it works well. Now I also am concerned about hood clearence. I do have the factory fiberglass induction hood so it should allow for extra clearance.

 

What is more complicated about a Demon carb Eric?I am curious!

 

Drop base or build a custom dropbase would be the way to go.JMOWhich carb did you order/buy?

 

I ended up ordering the Demon 1904 carb. I did some research on the new goggle secondary. seems like a pretty cool deal.