Sizing carburetor

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rymor92

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I’m looking for some help deciding what cfm carb. I’m building a 360 stock stroke bored .030 over, flat top pistons says would be 10:5:1 compression, ported X heads, Schneider cam 480/430 220/210 at .050, eldelbrock rpm air gap intake, Doug’s long tube headers. It will be street driven only but I’m not an easy driver. Coan torque conver 2500 stall, 904 trans with reverse manual valve body. All redone with cope racing internals, 8.75 posi rear with 3:23 gears. Online calculators say 689 cfm.
 
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I'd top it with a 750 cfm carb. Most flow slightly less than advertised unless you make performance improvements. 65'
 
My 68 Dart 340 stock cam (4 spd.) 20. over KB pistons 10:1 maybe less, Eddy heads Air gap runs great with a 750 AVS carb.
 
Related question. How many cfm flowed in say a 71 Demon with a Therma quad? I've been told 800 but IDK.
 
Can you post the cam card? Is that really a reverse split pattern cam? If so I’d think about an upgrade.
 
TT5.9mag said:
Can you post the cam card? Is that really a reverse split pattern cam? If so I’d think about an upgrade.
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TT5.9mag said:
Interesting, Thanks. It is a reverse split, and the lifts don’t match the listed rocker ratio.
I personally would not run that cam as I feel there are more modern/better grinds.
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there’s always newer better things. This is a NOS cam and comp still makes one very similar. I’ll keep it.
 
65TerrorCuda said:
Why would you want a cam with that much more intake lift/dur? Just curious not knocking the cam
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Well the engine builder had it as Nos and only charged $100 for it, great brand, also better option than the purple cam he had. I believe a 509. But ultimately it’s a lot easier for an engine to exhaust the air out than it is for it to suck the air in as to why typically intake valves are larger than exhaust. So more lift on intake than on exhaust same principle.
 
65TerrorCuda said:
Why would you want a cam with that much more intake lift/dur? Just curious not knocking the cam
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You really don’t. There may be some very specific engine combination (4 valve, static rpm, weirdo stuff) where a cam might be spec’d with reverse split durations like that and be optimal, but all the testing I’ve seen just doesn’t show them making more power. In fact they give up a bunch. On a typical street strip small block wedge head the split pattern almost always makes more power. I went with the advise of a well known cam grinder on a big block remote turbo deal I built and he ground me a 224/218 @050 .510/.510 reverse split and i wasn’t happy with it. Had another cam ground 226/231 @050 same lift and made 100 more hp on less boost. So my opinion is slightly viewed one way.
 
TT5.9mag said:
You really don’t. There may be some very specific engine combination (4 valve, static rpm, weirdo stuff) where a cam might be spec’d with reverse split durations like that and be optimal, but all the testing I’ve seen just doesn’t show them making more power. In fact they give up a bunch. On a typical street strip small block wedge head the split pattern almost always makes more power. I went with the advise of a well known cam grinder on a big block remote turbo deal I built and he ground me a 224/218 @050 .510/.510 reverse split and i wasn’t happy with it. Had another cam ground 226/231 @050 same lift and made 100 more hp on less boost. So my opinion is slightly viewed one way.
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Now you’re talking boosted. That is a completely different animal. You wouldn’t need as big intake to get the air into to cylinder as your pushing the air in and your pushing the air out.
 
rymor92 said:
Now you’re talking boosted. That is a completely different animal. You wouldn’t need as big intake to get the air into to cylinder as your pushing the air in and your pushing the air out.
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I’m always talking boosted. Everything I own is turbocharged.
:thumbsup:
But the principals still apply. Watch a bunch of Richard Holdeners videos on YouTube, he’s done the exact test we’re talking about, both NA and on boost. They do the same thing.
 
rymor92 said:
I have been very interested in the avs2 carbs just didn’t know if the 800 was too big. I know the 650 is a little small. Wish they had a 720-750.
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The secondary air door makes it more than adjustable. You could tune it for a slant 6.
 
Just so ya know, mopars 1970 Hustle Catalog recommended the first improvements be 3310/780 Holley, LD-340 manifold, Hooker under chassis headers.
It was my understanding that the bigger intake valve was because, like a piece of wood, after combustion, the residue volume of air/fuel is far less, requiring a smaller valve.
I'm sure there will be differing opinions.
 
Like your old school cam grind numbers.

Here is hands on >

I usually run the Edelbrock 600 1406 on most everything stock build.

Friend had an AVSII 650 cfm for me to test out on the stock fresh build 360 on the engine run stand, with the 340 cam.

Dropped it on, ran perfect right out of the box. Quick starts, great throttle response, nice idle.

Kind of felt like fuel injection. I was running the Mopar HEI distributor that I converted and the basic 60,000 volt E-Coil that I am sure helped with the quick starts and good throttle response, with the hotter spark output.

Oh and 360 has the Weiand 8022 Stealth square bore intake on it also, probably helps too > gasket matched to the stock heads.

Now the 650 AVSII was too much for my friend's 318 so he had me try it.

I felt the AVSII 650 with the Annular Boosters was the perfect match carb for that stock build 360.

It was right for the increased cfm of the 360.

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My experience, I had good results.

Your expectations may be different and may require more fuel.

The jump to 800 AVSII is a pretty big jump.

Have fun experimenting.

☆☆☆☆☆
 
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rymor92 said:
Well the engine builder had it as Nos and only charged $100 for it, great brand, also better option than the purple cam he had. I believe a 509. But ultimately it’s a lot easier for an engine to exhaust the air out than it is for it to suck the air in as to why typically intake valves are larger than exhaust. So more lift on intake than on exhaust same principle.
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That's not true. You do not want the engine pumping out the exhaust. The more you can get out at blowdown without opening the valve too soon and giving up some power is always best.

There is a reason why it's a hundred dollar cam. But if it makes you happy, run it.
 
AVS #1602 650 or a Holley 3310, 3310-1 (so you get vac 2ndaries, metering blocks and 780cfm with dogleg boosters).

i'll also express my concerns about the camshaft with the added note: odd.
 
Going bigger on a carburetor is always, always, ALWAYS easier to tune than one too small.
 
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