312 carb choice

[ReddingScott]

My 57 Fairlane is a .060 bored stock block with AT . I have been using a Holley list 1849 carb which is in need of a rebuild. As it is not the carb that  came stock I am wondering if I should consider another choice. List 1848 (4160,465 com) was stock for 57 and 1849 is a 4160 with 550 com I believe. First question is: Is there such a thing as too much cfm for the 312?second question is can a Holley 1850 new Holley work well? They are affordable and would be a new unit.  So.... rebuild the 1849 or replace it with something else? The 1849 probably was never rebuilt correctly as I am experiencing poor acceleration rough idle and poor top end performance. Any help much appreciated!!

[SkylinerRon]

The stock carb for 57  312 is 1273 which is 410 cfm.
That 1848 is 58 352, the 1849 is 58 383&410, 1850 is for the 430 and 600 cfm.
The smaller carbs will give you crisper low end and the 600 will give you more top end.
I'd rebuild 1849 before buying a bigger carb.
Goodluck,

Ron.

[ReddingScott]

Thanks Skyliner Ron!

A  rebuilder who comes well recommended will charge $350 to rebuild the 1849 that I now have on the car. The lower CFM carb , the 1848 I can buy brand new for $450. I am inclined to buy the brand new unit which has a CFM rating closer to the stock 1273 model. I have not been able to find a new 1273 anywhere. Any other thoughts would be appreciated but I think I Will go the route of a brand new 1848 since the price is not that much more than a rebuild of the larger CFM model. Any other advice is greatly appreciated.

[SkylinerRon]

Wow, $350. Guess I haven't been charging enough for a rebuild. You should check with Holley
they will rebuild and recolor their carbs.
The 1273 has been obsolete for decades. It came with early internal adjusting float bowls.
The 1848 was the recommended carb for edelbrock
crossram for sbc in the 60's&70's. The new ones now have a chev style throttle arm.

Goodluck,

Ron.

[gasman826]

https://www.ebay.com/itm/1957-Ford-Holley-carb-list-1273/332549069005?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

[ReddingScott]

Thanks for the help, guys. I think I am narrowing this thing down at least on paper. Using the Holley selector information and working out some numbers, I am being directed by Holley to the model 0-8007 which is the smaller, 390 com carb. Using a calculator I found on the web I was able to calculate the cubic inch displacement of my engine (312 bored .060" over) to 322 cubic inches. Then using the cfm calculator (cubic inchesx rpm which is listed as 4500 in my manual divided by 3456) I come up with 419 cfm required at 100% efficiency. Most tables I have seen indicate using 85% efficiency for a stock engine. This yields out to 356 cfm which is pretty close to the 390 carb offered by Holley.

Any ideas there? Am I way off base?

[hiball3985]

If you are just using it for a street drive and not a race car the 390cfm works great. I've been running one for 4 years now and I know of two other Y blocks in my area using them, one in a T bird and another in a Fairlane. Mine is on my 292 + .060 and Isky E4 cam, because of the cam I did have to increase the main jet size..

[ReddingScott]

Anyone ever try the Summit M2008 series carbs? I took my car to a recommended carburetor mechanic and he is suggesting one of these. According to him, it is a modern version of the Autolite 4100 carb that gets many rave reviews when used on Yblocks.

[hiball3985]

Anyone ever try the Summit M2008 series carbs? I took my car to a recommended carburetor mechanic and he is suggesting one of these. According to him, it is a modern version of the Autolite 4100 carb that gets many rave reviews when used on Yblocks.

I've only heard good things from people who have used them. I may try one in the future on my 289 Mustang.

[ReddingScott]

Wanted to send out a final update to all who helped on this issue. I found a great carb guy who did a complete check of the engine including valve clearance, timing, vacuum check. He installed a new Summit 600 com carb and boy what a difference! I have acceleration and take off power that I never had before. It idles smooth and with the new electric choke, it starts right away. So I am grateful for the advice to check other parts of the engine before tackling the carb itself. I highly recommend the Summit brand 600 com carb for the 312 yblock with an .060 bore out.

[KULTULZ]

Is there such a thing as too much cfm for the 312?

In short, no (IMO). Carb choice and sizing is dependent on the engine type, modification(s) and how the car will be used. The chosen carb will then have to be calibrated to the engine.

The choice of the SUMMIT 600CFM shows this. The formula(s) used just for engine size is a ball park guesstimate and sales tool (again IMO).

[Ray]

The original 1273 carb was a little over 400 cfm. With the correct original 1957 cam "available from Clay Smith" my convert will absolutely smoke the tires in first gear on an automatic trans. If you have installed a 312 with a generic aftermarket cam, any carb that delivers over 500 cfm is wasting fuel. With the correct stock 1957 cam it will allow you to use an 1859 without to much unburned fuel. The 1860 is a bit much without an advanced cam and other modifications. Smell your exhaust, if you smell unburned fuel you understand your issue. That's my best recommendation. Good luck