Carb Recommendation

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65BCODA

65BCODA

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I'm looking for some informed input from the great FABO brain trust,
The car is a 65 Barracuda that will be a weekend warrior mainly, Just want it to be all that it can be.
8 pt cage, frame connecters, Dana 60 w/alter-k, mini tubbed w/ modified wheel openings. Possible RMS 4-link (if can sneak past wife)
The build:
'74 360 .030 over
4" Scat forged crank
Scat I- beam rods
Diamond forged pistons
RPM AirGap Dual plane
EngineQuest Magnum heads
FBO Racer Brown Magnum rocker set 1.6 /1.5
Comp Cam 20-230-4 solid flat tappet
Lift: 502/511
Duration: 274 / 280
9.7:1 comp
2800 stall w/3.73 or 3.91 gears 28" tires
MSD dist. 6AL, coil and starter
Time for carb selection, BIGS carbs are first choice , what CFM should I go with? I always figured under carburation was better than over.
I figure a 750 would do, or should I step up a bit?
Again mainly weekend driver not daily

Thanks in advance , Roger
 
cubic inch.x.max rpm/3,456 = ideal cfm
what are you spinning it to?? lets say 6,000
408.x.6000/3,456 = 708.3333
now remember a street engine only runs at about 80% efficiency, 750 should be plenty.
 
How much horse do you think you will be pushing?

If your around 400 a 750 would be my choice.

My 360 has between 300-400 hp, so I went with a 670 street avenger.
Looks like you will have a little more horse than that.
 
You have put together a great combination. I really liked the input you got from others too. The formula for carb sizing has been around forever because it works. At wide open throttle, your combination can handle it just fine. Holley carb engineer, Chuck Gullege, taught me a few things back when I raced my S/G Vette about over-carbureting. A larger carb can help to overcome deficiencies in an intake manifold or manifold/ port combination. A good example of a carb that would be too big for the formula is the old venerable 3310 780 vacuum secondary carb. This was the same basic carb used on the Z-28 302s. Your engine should give excellent booster signal in the transition from the idle circuit to the high speed circuit. One thing that I learned from serious racing too was that a vacuum gauge is one of the best tuning tools you can have. A properly sized carb on a race engine will show zero (or close to it) vacuum at WOT. Best of luck to you.
Pat
 
Since he's really looking for a cfm amount to live on the street and has the abilty to run at the track (Or light to light) without giving up alot.........

Yes, a 750 would be a very good choice. IMO, top it with a air cleaner top like the K&N extreme top. The top that doubles as a filter.

Actual maker of carb is your choice. A double pumper is what I would do as well.
 
I would call Bigs and give them the info, they are great to deal with, and will dial you right in.
 
Your not talking about a 360 anymore,you've got a stroker now with 48 more cubic inches and they love fuel..go with a 850 i recommend a Quick Fuel ..
 
Thanks for the input guys, yeah my next step was to make the call to Jesse
just wanted to get the opinion of the masses first.

Thanks again, Roger
 
stroked 340 said:
Your not talking about a 360 anymore,you've got a stroker now with 48 more cubic inches and they love fuel..go with a 850 i recommend a Quick Fuel ..
Click to expand...

I agree.

I also think that your cam is too small. A solid at 236 degrees duration will act like a hydraulic at 228 degrees duration. I would also use H-beams for the build.

Pro Demon is right, a vacuum gauge is an excellent tuning tool.
 
rods.....scat 4340 I beams....almost the same price as the eagle sir...

no grinding needed with the stroker crank either
 
Sorry my bad,...was into the brews a little last night when posted, the rods are the Scat I-beams......The parts listed have already been purchased and applied to the build. Don't really want to back up and punt at this point.
 
ramcharger said:
I agree.

I also think that your cam is too small. A solid at 236 degrees duration will act like a hydraulic at 228 degrees duration.

Ramcharger, Please excuse my ignorance (this my first real build) on the subject,don't quite understand all I know about cam selection, but how do I get 236 dur from 274, am I missing something here or is it due to a loss of duration somewhere that I am not understanding ??
I'm looking for really good street performance / not so much all out race.
Please advise, I'm willing to learn.

Roger
Click to expand...
 
65B,

I never use advertised duration numbers as they can be fudged and the measuring point varies from manufacturer to manufacturer. When comparing and choosing a cam I always use the duration given by the cam manufacturer @ .050 lift which for your cam is 236 degrees.

If you are looking for good street performance, that solid will do it but I would recommend a hydraulic roller in the 235 range. It will be quieter than the solid and you won't have to adjust it every so often.
 
On a side note watch those racer brown rocker shafts I had issues with mine.

The teflon bushing's galled and melted I was told it was a known issue and was sent aluminum ones. Never could get rid of my lifter noise when I built the 340 I went to use them but the engine shop said the geometry was horrible and they where not the 1.5/1.6 ratio like they where supposed to be but closer to 1.7/1.8
 
Interesting - I checked mine - deadon 1.6/1.5 Xs lobe lift. specific made to measure pushrods are mandatory with such an application.

71Duster said:
On a side note watch those racer brown rocker shafts I had issues with mine.

The teflon bushing's galled and melted I was told it was a known issue and was sent aluminum ones. Never could get rid of my lifter noise when I built the 340 I went to use them but the engine shop said the geometry was horrible and they where not the 1.5/1.6 ratio like they where supposed to be but closer to 1.7/1.8
Click to expand...
 
Thank you Ramcharger for the clarifacation, as far as valve lash adjustment, I don't mind a little tinkering from time to time, as far as cam grind guess I should have spoke up sooner but was a little worried about street manners. Thanks for your time.

71 Duster, these are the magnum stud mount rockers not shaft

yes I will have to have made to measure p-rods, just waiting for my Smith Bros adjusters to show up in the mail to continue on. Trying something different with the EQ magnum heads that I have not seen done before.
 
Leo- the pushrods where Smith brothers checked and ordered by the builder. The rockers just had issues even when the shop measured them, but I tend to be the lucky SOB who'd get the one lemon in a 1000.
 
65BCODA said:
EngineQuest Magnum heads
FBO Racer Brown Magnum rocker set 1.6 /1.5
Comp Cam 20-230-4 solid flat tappet
Lift: 502/511
Duration: 274 / 280
9.7:1 comp
QUOTE]

The street 4" engines I build get the 870 Street Avenger VS carbs. They work very well on them. A 750 will be way too small due to the stroke. the "suck" on a carb is caused by a mix of intake port size and shape, camshaft design, and the biggest thing, piston speed. $" stroker develop a lot more piston speed than a typical 3.58 360 or 3.31 318/340 stroke will. They also tend to get that faster speed further away from TDC, so a msall cam tat closes "early" in relation to the piston's position in the bore can really choke them off. This is why smaller cams will give decent vacuum with a 4" stroke, but tend to have the power fall off dramatically after peak, and they peak early. I would venture to say with a combination of Magnum head ports, 4" arm, and that cam you will make peak power by 5400, with torque peaking around 3K. A more important question... The cam specs I quoted. Those are in 1.5... so the intake lift is going to be .534... Were the heads built to run that much lift? If you have not yet, I would turn the engine by hand and measure for coil bind... It's very close to the limit I think, which is right around .520 IIRC, correct me if I'm wrong guys... But I think it should clear even if you didn't build for that lift.
Click to expand...
 
You have a lot of smart people interested in your car! Congratulations. You are smart yourself to ask for advice because the people that are trying to help you have "been there - done that". I hope you have some buddies that will let you try a variety of the carbs recommended before you buy one. As I said before, an oversized carb can really work because of variable deficiencies they help overcome. The carb that gives you the closest reading to zero on a vacuum gauge at WOT at top end will be the best carb to race with. It will be closest to 100% VE. I am 62 years old and man, I have run a lot of cams. A solid roller is the ultimate and the most expensive. It also makes the most power. Personally, I would never use a hydraulic roller for a serious racing engine because of the inherent upper RPM limitations. They are far better than they used to be! Something else I can tell you and I'm sure the cam manufacturers will back me up is the so called problem of "always having to adjust the valves". If this happens to you, be assured that something is bending or wearing away or something has just come loose. After the initial lash, the entire train will take a set and if no lobe damage has occured at initial startup, you can readjust and it should last. Any variation after this is because something went away that shouldn't. A solid roller cam is the most dependable item you can buy for a serious engine. Also keep in mind that Hughs' Engines has some really great solid lifter grinds that take advantage of the .904 lifter. If you can't afford to go roller, call them and they can put you onto a cam that's right on the money. I truly wish you all the best.
PAt
 
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