Hello guys... I just bought a 425 cubic inch nailhead (1964) to put in my big heavy Mercury. I am looking at my options and I see a lot of aluminum tri-power setups but will 97s be enough cfm for a large displacement motor like this? Thanks for the help. Hyfire
Can't say for sure yet. I went through this a couple of years ago when deciding on carbs for my 401. It came with a 3x2 intake set up for 3 bolt carbs. I called Jere Jobe who is a pretty knowledgable guy regarding such things and he told me he believed 3 x 97s would be OK on a 401. I opted to go a bit bigger with 3 x 48s but as yet i haven't driven the car. I'd have to say you could do better with 2 x 4s or maybe even a single 4 bbl. Depends what you want. I wanted 3 x 2s. Pete
zman would know best but i have been told that the nailheads like ALOT of carb if your going with the strombergs i say 6 tk
Now if we could convince everyone of that. Yes Nailheads do like a lot of carb. Now to the OG question. It sounds as if you are more worried about a look than actual performance. I'm thinking if it 3x2's you probably have an Offenhauser manifold, there seem to be a lot more of those than anything else. They're not really performance manifolds anyway. If i remember 97's are about 155cfm, 3 of them is 465cfm. In my opinion not enough carb for a 425 especially with anything better than a stock cam. 48's are a little better at about 170cfm but that still doesn't add up to much. Personally if I was doing a 3x2 for a 425 I'd go with Rochester 2GC's. Yeah they're 4 bolt but they perform a lot better.
I've never built a Nailhead, but CUBES, cams and horsepower require lots of carb - regardless of the engine manufacturer. Three 97's is less carb than just a small 4-barrel. I'm sure a performance 425 could use at least 750 CFM for performance . . . more if it is really a hot engine. Given this, having 6 strombergs is a lot better than 3. Or - switch carbs to something larger (as mentioned below), or go for a dual 4-barral setup with some smaller 4 barrels. It all depends on whether you're trying to make horsepower and want to utilize the performance potential of the motor, or are trying for an early 50's look. (Keep in mind - the engines in the early 50's were much closer to 300 cubes than 425!). Heck, a really hot flathead can use three 97's or more!
The cfm guide charts used for carb size suggest 615 CFM for a typical 425 cube engine at 5000 rpm.If you rev it higher a lot,more carb,if you don't rev the snot out of the engine,less carb will be ok. Running 3 three small 2 barrels with the center one being the primary used part throttle might stave a engine a bit and have you pressing on the throttle pedal and opening all three when a little more than sedate acceleration is called for.What size was the stock 4bbl used on a 425? And they did come with dual quads from the factory,probably dual 400 cfm AFB's? Pontiac use three Rochesters on 389's,what size are they,and go from there as a suggestion.
The hot ticket for the 425 for the GS guys is the '66 quadrajet intake and a '71 800cfm quadrajet. I've always run 500cfm carbs on the 4x2 setups. The factory used 500cfm and 625 cfm AFB's. Those so called cfm guides for some reason don't see to work for me as the Nailhead likes a lot of carb. If you talk to any of the Nailhead guys they'll tell you the same thing.
Three 97's are about like the primaries on a good-size 4-bbl. Unless you're really hung up on the "look", go for just about anything else. The expense and h***le of 97's just ain't worth it on an engine that big.
I agree with zman - the late Q-Jet and manifold is excellent, best power and mileage, cheap carb to buy and rebuild.
Thanks guys.... Regarding Zman, I have already stalked the poor guy enough, so I didnt want to pester him anymore... although I see he found me! I dont have a clue if the motor is stock or not, but I am ***uming it is. It is going into a 1949 Mercury, so I wanted more of a 1950's look, but not at the cost of the motor starving at high RMPs. The posts here pretty much confirmed what I thought... I will go with a dual-quad setup. I will try to keep it looking like the early '50's Caddy setup. I will probably use the suggested stock units until I can afford to do the dual-quad right. Thanks guys...
building a hilborn injected nailhead now for a bantam bodied drag car. a low budget to no budget car with a close friend. what year merc? sounds like a cool combination. what trans? my wife's 55 f 100 is buick but is 350 ( looking for 4 barrel man. to run 2 strombergs on). I am the last person to say go conservative because i overdue most stuff such as cams carbs etc. 3 97's is about 350 cfm. i ran your engine setup on a hotrod math deal and: cruise speed 3000 rpm 368 cfm 4000 rpm 490 cfm 5000 rpm 613 cfm guys ran 3 97's on these motors for many years and as usual people try to rewrite history and say its not good. dont listen . carbs are small but probably lots of torque and mileage and no wierd progressive linkage to build. you could run 94's and have 410 cfm. you could also get an adapterfor 2 2's for your stock manifold for strombergs and have 500 cfm. use your money on cam, exhaust. pertronics breakerless inside orig. dist. maybe. redline cams in Albany or. regrinds...good luck oh yes also ran your motor on comp. dyno and the differance wasnt 20 hp between them all because of small valves (nailheads). sure you can get more power w/ lots of $ and sure these programs are not 100% accurate but close enough for engine design ideas. built a lot of motors (real) in the last 60 yrs, mc and hotrod, and like using them for comparison. if you want me to run some ideas let me know. one thing i do know is you are looking at tons of low end tq....
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