512 stroker carb recommendations

[Geoff 2]

The formula in post #17 ignores a basic engine function, volumetric efficiency.
The VE @ 5600 rpm for an engine like this would be lucky to be 85% so the reqd cfm drops to 614 cfm.

 

[68 HEMI GTS]

The formula in post #17 ignores a basic engine function, volumetric efficiency.
The VE @ 5600 rpm for an engine like this would be lucky to be 85% so the reqd cfm drops to 614 cfm.

sweet, we have a 512 down to being carbureted like a 318

 

[Geoff 2]

Go & have a look at the internet, there is a video floating around of a bloke who fitted a lawn mower carb [ 20 cfm? ] to his V8 Ford. It performed surprisingly well....
Not suggesting or recommending a LM carb, but there are certain mathematical relationships in engine building/performance. Carb flow is one of them....

 

[Geoff 2]

Sorry, I based my calculation in post #21, on info in post #17, 446 ci.
For 512 cu, obviously more flow reqd. 705 cfm for 85% VE.

 

[383man]

I’m wondering if we have similar set up- I am building a 383 to 496 stroker w TF 240 heads, 833 trans and 3.23 gears. Web calculator put me at 750/770.
Would the 850 be too much for street only?

My 493 is a .030 over 440 with a 4.15 crank. I use the basic Indy EZ heads as when I built this eng in 2011 there was no TF heads for the BB Mopar. I run a 727 with a Dynamic 9.5 converter and 4.30's with a 30" tall tire. My 850 is about 20 years old so its an older one. Once I jetted it for mph at the track I then worked the IFR and the transfer slots to keep the cruise lean enough for good street cruising. And it works awesome as the car drives great with it and runs good at the track as I dont change anything at the track. It drives and races all on the same setup as I have it at a happy setting that works good for both. But the 850 should not be to much for a 496 as I feel I could go a bit faster with a Dominator but I like how the 850 works for both street & strip so I stay with it. Ron

 

[1STMP]

sweet, we have a 512 down to being carbureted like a 318

That formula equates a carb with 100% EV
and as stated, just gives a starting point.
Altitude, humidity, ambient temps all play a roll.
What works at sea level, is going to choke
and puke at 5000 ft.
It wouldn't surprise me that the OP''S
configuration is nearing 90% + VE given
the optimal conditions. A car is tuned as
to where it will live most of it's useful life.
I'm at 4200' in a dry 35% average humidity
and run a 750 cfm Holley on a 360 V-8
AMC (mild cam with headers, 401 valves
in the heads) and it couldn't be happier.
it will spin all four with a transfer case
and an added differential for a weight
of 6200 lb gvw. What's on paper can't
compare with what's on the street.

 

[Geoff 2]

While it is difficult to accurately estimate VE, 90% at 5600 rpm would be a stretch in my opinion....given the component selection.
A lot of people do not realise that max VE occurs at or very close to the tq peak. From the tq peak to max expected rpm, the VE drops.

 

[68 HEMI GTS]

While it is difficult to accurately estimate VE, 90% at 5600 rpm would be a stretch in my opinion....given the component selection.
A lot of people do not realise that max VE occurs at or very close to the tq peak. From the tq peak to max expected rpm, the VE drops.

I think you could safely bump the rpm range up to about low to mid 6’s. Any 4.10 gear big block is going to trap probably at 6500 range at a min (6500x512x.85= 819). Round that up to 850. I’ll also make sure to have a conversation with both my 512’s in the garage that even though they ET faster with bigger carbs that I have a formula and a guy on the Internet that tells me otherwise…

formula is a tool, not an end to ends gospel on what can work. You’re trying to split hairs in a perfect world when in fact the world is not perfect. Neither are cfm ratings on carbs. I have two different 1050 dominators. A Holley and a QF. The QF even though rated at 1050 has bigger Venturi's. On a 512 we have in a 69 dart one of the carbs is almost 2mph faster. Guess what, it’s not the holley..

Ops car a 850-950 4150 style carb is probably ideal beings it a 4 speed and a single plane. Keep in mind intake selection can also dictate carb size. Dual planes typically handle a bigger cfm carb.

 

[Geoff 2]

I am not trying to split any hairs.
Try reading what the OP wants/has: mild cam [ for 512 cu in ], TF single plane intake, 90% street driven, good throttle response reqd.
I doubt that a 1050 cfm carb is going to have great throttle response on that big SP intake.
The carb formula I provided did not come from the i'net, it came from Holley, the people who make carbs. They should know.....& they knew loooooooooong before the i'net was a twinkle in somebody's eye.....
Agree that there are variables, but better to err on the side of caution. Plenty of carbs gathering dust on shelves because they they didn't perform as expected.

 

[68 HEMI GTS]

I doubt that a 1050 cfm carb is going to have great throttle response on that big SP intake.

If you look I recommended a 850 to 950 cfm range 4150 for the OP. That would perfect for his combo. That being said my pump gas 512 had great off idle throttle response with a 1050/4500. You could drive it anywhere and it had 4150 mileage and drivability. Of course none of that was by accident. Big carbs don’t act so big when they’re on 500+ cube motors if they’re set up right.

 

[beanhead]

In other words,

Honestly I'm kinda confused why the OP didn't want to use the Quick Fuel 950 he put up for sale about the time this thread started ....I'd run it on that combo without a second thought. Excellent choice for a street 505" with the Trick Flow treatment.

 

[RemCharger]

In other words,

View attachment 1273544




Honestly I'm kinda confused why the OP didn't want to use the Quick Fuel 950 he put up for sale about the time this thread started ....I'd run it on that combo without a second thought. Excellent choice for a street 505" with the Trick Flow treatment.

Weird how that's exactly what the trick flow guys used on their dyno mule. Oh, and the hotrod guys used a 1000.
But that was on a 440, maybe 500+ motors are more finicky.

 

[RemCharger]

A 1050 dominator helped me get to 130mph with my 383, but that's not an apples to apples comparison.