Stock carb CFM?

[83XLT]

'83 XLT 4.9l and a 4 sp. tranny -

I have the stock YF carb on it and was wondering what the approx (or official?) CFM rating was for it.

I want to go with a 4bbl 390 or 450 but a good friend says I should go bigger as it's technically a 300+ CID engine. I'm not trying to win any awards with either my towing ability or LACK of fuel economy, I am however trying to drag this poor engine (mine specifically) into the realm of the living!

Also, should I be looking for a manual choke or electric choke? I recently DL'ed an old YF manual from Project Old Car and it seems my YF has the electric choke piece, however, I know I have to depress the gas petal on first starts; so I dunno.

Thank you all for your input!

 

[Broncobill78]

'83 XLT 4.9l and a 4 sp. tranny -
I have the stock YF carb on it and was wondering what the approx (or official?) CFM rating was for it.

I want to go with a 4bbl 390 or 450 but a good friend says I should go bigger as it's technically a 300+ CID engine. I'm not trying to win any awards with either my towing ability or LACK of fuel economy, I am however trying to drag this poor engine (mine specifically) into the realm of the living!

Also, should I be looking for a manual choke or electric choke? I recently DL'ed an old YF manual from Project Old Car and it seems my YF has the electric choke piece, however, I know I have to depress the gas petal on first starts; so I dunno.

Thank you all for your input!

The factory carb is pretty small but you have to remember it's sized to the engine/intake/cam combo and going to something like a 450 without changing anything else will probably just make it bog. If you want to run something that large or "wake up" your 300 you should call someone like Clifford performance who specializes in 6-cyl performance. To take advantage of the additional fuel you're going to need a new intake & an exhaust header and should really change the cam as well. You really should get a new intake to do this, you might be able to find an adapter plate but I don't think you'll really be happy with it if that's all you do. Unless you're going to make the other upgrades I'd stick with a 2bbl, a 4bbl will really go thru some gas and you won't see jack as far as improvements go you'll just be buying more gas & getting angry. If you improve the airflow (after all, the engine is just an air pump) you can probably run that 450 and see some improvement but there's usually more to it than just bolting on a larger carb.

As far as your choke goes, yes it's an electric. Hitting the pedal just sets it for the initial start, if it were a manual choke you'd have a push/pull cable running thru the firewall & mounted in or under the dash. I've used both and prefer an electric but there are plenty of guys who get along just dandy with a manual. If you want to adjust your electric just loosen the 3 screws around the round housing on the side of the carb & rotate the housing then snug the screws back down.

 

[Bear76]

I agree with Broncobill78, I would not go much bigger than a 390 cfm 4bbl. I ran a Clifford 4bbl intake with my stock 300, and I bought my carb with some "help" from my buddies, who follow the whole bigger is better rule. I ended up putting on a 500 cfm 4bbl and was very dissapointed right away. I then put on a 2bbl adapter and a 350cfm 2bbl and that worked 100% better. Throttle response was right there and I never had too much trouble with it bogging down the motor with too much fuel ever, and it got right around the same fuel mileage, if not better, than the stock 1bbl. But like always, it is the drivers choice on what he installs and can handle. What one guy thinks is too much motor, is just enough for another. Hope this helps you out some. Just my two cents worth.

 

[83XLT]

Yea, I'm a carb idiot! The last carbed auto I owned was a '66 Mustang with a 200 CID, and that was almost 20 years ago. Man - I could STAND in the engine compartment and change the plugs on that thing!

I certainly do plan on getting an Offenhauser intake and throwing on some I6 EFI manifolds with a new 2.5 or 3 inch exhast system. Again, Im not trying to make some super HP beast, Just trying to open it up a little and expose some more of that precious torque.

On that note, what would be the best cam to buy for the ole 300? I have been told to search RV shops as they sell the Iskendrin brand.

Most of all, I was just wondering what the stock YF carb's CFM was to keep a comparison in the back of my mind. I'm pretty conservative with something like this, relizing I can still adjust the fuel and idle as well. I didn't want to go big and have it run like a dog. First and foremost, I'm working on safety issues first, then I'll be transitioning into engine maintenance/upgrades next. (e.g. new, brighter lights; new tires; replacing all the seat fasteners with new fixtures) I have to say, LMC is mah friend!

Thanks all for the replies, and if anyone knows the YF, please lemme know!

 

[Bear76]

I did some looking, and from what I can tell, the YFA found on the 80's 4.9/300 sixes should have a tag on it and on the tag the correct flow will be indicated. I did find on place that stated the ratings (which were for the YF, which is found on older engines.) claimed to be from 150 to 180 for the 1bbl. Sounds a bit small to me, but it could be right, the six never needed a lot of fuel, it hardly ever sees the high side of 4,000 rpms after all. Dunno. As for the cams, Isky does make a good one, as well as Clifford and a few others. Clifford offers a kit that includes everything from the head to headers to the crank and rod sets. They also offer a kit that has the headers, intake manifold, cam and lifters plus the carb(I think), all for one price. I just looked it up, 706.00 minus a carb. They can be reached at www.cliffordperformance.com Once again, I hope this helps you out some.

 

[Broncobill78]

I did some looking, and from what I can tell, the YFA found on the 80's 4.9/300 sixes should have a tag on it and on the tag the correct flow will be indicated. I did find on place that stated the ratings (which were for the YF, which is found on older engines.) claimed to be from 150 to 180 for the 1bbl. Sounds a bit small to me, but it could be right, the six never needed a lot of fuel, it hardly ever sees the high side of 4,000 rpms after all. Dunno. As for the cams, Isky does make a good one, as well as Clifford and a few others. Clifford offers a kit that includes everything from the head to headers to the crank and rod sets. They also offer a kit that has the headers, intake manifold, cam and lifters plus the carb(I think), all for one price. I just looked it up, 706.00 minus a carb. They can be reached at www.cliffordperformance.com Once again, I hope this helps you out some.

No, that actually sounds about right. I seem to recall the factory 1bbls were something like 2 & some change for CFM (maybe 230) it's always some strange CFM with factory carbs, freaking engineers, go figure.

Isky makes a good cam (I've run 2 or 3 myself & still have the stickers to prove it) but really, any major cam mfg can give you a good grind. ISKY, Erson, Comp Cams, take your pick and that's just off the top of my head. But really, bull$hit aside I'd try to pickup a package deal if I could. The folks at Clifford and places like that have already taken the time & spent the money to come up with packages that work. I think we can all appreciate that you're not looking for a torque-monster and don't have out-of-this-world expectations but yes, you absolutely CAN get probably 30+ more HP out of that 300 with a package like this but doing it yourself a piece at a time, trial & error is not only time-consuming but expensive and frustrating. Take the time to talk to the people who live & breathe 6cyl performance and take their word for it, I sure would and I can't TELL you how much $$$ I've wasted trying to re-invent the wheel when there's already someone out there willing to tell me what I need to know if I'd just put down the wrench & pickup the phone. There are a LOT of people who've already done what you want to do and lucky for you a few of them have started companies. CALL THEM. In the end it will save you time, bull$hit & money.