Carb cfm with ported heads?

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I live in Texas, most of my driving is 75-80mph, so I'm keeping my "shitty gears".
Actually the car has no trouble lighting up both tires from off idle, it has surprised quite a few people, especially when I tell them what gears are in it.
It's not a race car, it's a really fun street car that I enjoy driving 45 miles to the track, run it four or five times, and drive it home. Some of you might not get it, but half the fun for me is making it run a good number with the 3.23's.


YR- What do you dislike about the Nitto 555R's? I have heard pretty good things about them. What do you prefer instead?
 
IMO tune the 750 you have. Is your fuel system up to the task for a 1/4 mile blast. A 26 or 27" drag radial tire will help the gear you have. Learn to drive (get consistent) with what you have before spending money on hp. Bottom line, get the car to hook with current power.
 
KnuckleDuster said:
I live in Texas, most of my driving is 75-80mph, so I'm keeping my "shitty gears".
Actually the car has no trouble lighting up both tires from off idle, it has surprised quite a few people, especially when I tell them what gears are in it.
It's not a race car, it's a really fun street car that I enjoy driving 45 miles to the track, run it four or five times, and drive it home. Some of you might not get it, but half the fun for me is making it run a good number with the 3.23's.
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Been more helpful of you to title the post
"Help me make the most with these shitty gears"
Joking. But replace shitty with 3.23's and we would at least have a better grasp of the limitation in which we can work.
 
MOPAROFFICIAL said:
Been more helpful of you to title the post
"Help me make the most with these shitty gears"
Joking. But replace shitty with 3.23's and we would at least have a better grasp of the limitation in which we can work.
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No worries, I'm smiling and not getting any hurt feelings over it....but, I did say in post #4 the 3.23's and 2.5" exhaust were staying.
 
My street 4" engines run wet flowed vacuum secondary 870s. These cars also run 3.23 gears and convertors that stall under 2500rpm. They manage high teens in fuel economy in heavier cars (E bodies). The right carb is probably a bit bigger than you think. BUt you can't really go wrong by going bigger. Unless you can't tune. Smaller carbs are easier to get well tuned.
 
I think I've mentioned this before with knuckle. The car is trapping at 103ish which is REALLY soft for a 410 with ede's etc. That's 340 with a mild cam range.

It should be making in excess of 450 FWHP and MPH would be in the high teens at 3300#
 
crackedback said:
I think I've mentioned this before with knuckle. The car is trapping at 103ish which is REALLY soft for a 410 with ede's etc. That's 340 with a mild cam range.

It should be making in excess of 450 FWHP and MPH would be in the high teens at 3300#
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Agree on the mph, that's why I asked if fuel system was up to the task.
 
KnuckleDuster said:
I live in Texas, most of my driving is 75-80mph, so I'm keeping my "shitty gears".
Actually the car has no trouble lighting up both tires from off idle, it has surprised quite a few people, especially when I tell them what gears are in it.
It's not a race car, it's a really fun street car that I enjoy driving 45 miles to the track, run it four or five times, and drive it home. Some of you might not get it, but half the fun for me is making it run a good number with the 3.23's.


YR- What do you dislike about the Nitto 555R's? I have heard pretty good things about them. What do you prefer instead?
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I had customers try them. They have a very narrow tune up window. You can do a lot more with something else.

Also, a bias ply slick is much more forgiving than a radial. Unless you have double adjustable shocks on all 4 corners (and you should) and are willing to spend a bunch of time tuning stay with a bias ply radial.


The Nittos were never "happy". Very small changes in track temp would affect the tire. Just not worth the effort.
 
KnuckleDuster said:
There are a few other factors at play that make me think I can get there-

Tires - I've only been able to launch at 2500rpm on the Cooper Cobras with 18 lbs in them. Any higher and I spin 'em. I am looking into getting some Nitto drag radials on there.


My driving- on the 12.66 run I hit the rev limiter shifting to third with the factory console shifter, and lost some time. I will be running a B&M Quicksilver this year. I think the car could run better as it was. It has trapped at 107mph on other runs. I have some room to improve my driving, lol...

Then there is the carb...I will make some runs with the 750 and try to dial it in with the AFR meter and see what's up first.

I think it can be done, but only time will tell.

Here's the 12.66 time slip.

View attachment 1715141620
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The fact with an automatic you can only launch at 2500 isnt costing you anything.
I play around between 1500-3000 off the foot with different cars and motors over the years and almost never does it make any difference in ET thats noticeable if the combo is halfway sorted out. And this always with tires that stick, so i can try different stuff
My W5 motor ran identical off the foot or the transbrake. Ran it both ways hundreds of times at different type races. 9 sec passes
Current car i leave at 2000 off the foot just because its easier to note the tach, and it isnt wanting to push me at that spot. Car ran the same at 1500, but my lights are better at 2000 launch.
Lots of guys leave off idle. Again, motor goes instantly to the convertor, so it dont matter much ET wise

Hitting the chip second to third is probably couple of hundredths, unless you just left it there forever.

Carb might net you a tenth. Maybe.
If your only going 103, you got something else going on than any of this stuff
My bone stock 360 shortblock except cam with stock eddies went 109 at 3300 pounds first time out with the car last year and i was super disappointed.
Picking away at it has gained me almost 10 mph with it. Same gears, convertor, tranny, carb, headers, launch and shiftpoints.
 
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Ok so your not exactly in race trim but this was from 1986>
340 Cuda, stock heads, solid ft cam, race intake/hdrs, 4200 verter, 4.30's, 10x28's, ran 12.4 with an 850DP, all the guys kept going on at me about my carb being too big including a racer with a 3500cc Cortina, so puts my old 750DP back on and gave it a tune, result 12.6's, told that guy with the buick 215ci/rover V8 engine to try my 850 over his 600 holley and he went 2/10ths quicker, he couldn't believe it............nuff said, all these calculators for what an engine needs are a waste of time, its down to bore size/stroke/head design etc, a stock 340 motor came with an 800cfm factory carb..............go for it with a 950.
 
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Now there’s a thought!!!

THERMOOOOOO QUAAAAAAAAD

LMAO
 
I think a lot of it may be driver error, me figuring out when to shift. My tach is also too low to really look at, I need to move it up into to my sight line.Some of it could be tuning, could be valves not adjusted right, or maybe I got the pushrod length wrong, maybe the cam is not where it should be. If you look at my cam plug thread, it was also pushing head gaskets. I have a lot of things I need to go over. I know nothing is optimal yet, but I still am having a hell of a lot of fun, and always willing to learn.

best trap.jpg
 
107 is better, still 10mph from where I'd think it should be.

Looks like a XE285hl camshaft or similar. I'd set preload on the loose side, maybe a 1/4-1/2 turn. Sometimes very hard to gauge when you start to depress cup. Spinning PR while adjusting help with feel.

Fuel pressure and flow when at high rpm? If it has a mechanical pump, that's one place I would look as a pinch point.

Putting a bigger carb on now is a waste of money IMO. It's too far away from optimized to make a difference.
 
XE285HL
Preload is about 3/4 turns, I had a hard time feeling zero preload. Maybe too tight.
Pump is the Edelbrock Carter, 6.5lbs max.
I had starvation issues with a 6902, then the Edelbrock until I shielded the feed and ran a return. With the return, the guage was useless, all over the place.
 
273 said:
The formula people use ( cid x rpm / 3456 = cfm ) doesn't give carb size but how much volume an engine is at rpm.

If we assume 100% VE an engine only has intake stroke once every other revolution so a 410 would be 205 cubic inches per revolution or 0.119 cubic feet. At 6000 rpm it would be 1,230,000 cubic inches per minute or 714 cubic feet per minute.

Since air is compressible any carb can pass any amount of air, so a 650,750,850 etc.. would all pass the 714 cfm just at different velocity and vacuum (restriction) just like different header sizes.

On a pure race engine you can give up velocity for less restriction, opposite for pure street and street in between.

On your engine your 750 should be slightly under a vacuum level of 1.5 if the formula is correct, which is pretty conservative. But like I said measure the vacuum level and decide from there if its worth going larger and by how much. Or see if you can borrow some larger carbs and try it out.
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To whom it may concern if anyone :) know im beating a dead horse, but I think now I know how to make my position clearer.

The carb rating and the cid x rpm / 3456 = cfm seems like an apples to apples but it isn't.

Take a 440 that turns 6300 that formula says this 440 can pass a displacement of 800 cfm or a 100 cfm per cylinder.

Now we wouldn't use the formula to pick a cylinder heads even though there both rated in cfm but neither have anything to do with one another. That engine would need over 3 x's the 100 cfm.

As for carbs, lets imagine we cut a 1" hole in a plate of steel. Now that hole can flow zero or 1000's of cfm depending on vacuum source. Same with carb they can flow anything we want. Now lets take a plate and cut a 2" hole. The 2" doesn't automatically flow more cfm then the 1" just needs less vacuum (power) or in the case of an engine pumping loss (hp). The 1" vs 2" both will flow the same air at different vacuums level.

Same with carbs, the vacuum level with determine the cfm of the carb.

So the trick is to figure out where you want the vacuum level to be. Then convert the cfm of carbs to that level then the formula will work.

So say you figure 1.2" hg gives you the best compromise of streetablity to power.
Say the formula says your engine will displace about 500 cfm of air and say a 650 @ 1.5" hg is a 500 cfm @ 1.2" hg then thats your carb or say its more of a strip terror and decide vacuum should be at 0.8" hg that might be a 850 cfm @ 1.5" hg.

Thats why I think carb should be rated at more the one vacuum drop.

Done beatimg the deadhorse.
 
KnuckleDuster said:
410ci with box stock Edelbrock 63cc heads, been running a 750cfm Proform electric choke street carb.
Considering an 850cfm or even 950cfm Proform or Quickfuel RACE carb now that the heads are getting a max port job.
3.23 gears
2.5" exhaust
3500 stall converter
28" tires
241/247 5.45 lift cam.
Thoughts?
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A 410 with box stock Edelbrocks is going to be sub 450HP. Refer to that EngineMasters episode here if you wish. A bigger carb is not the answer here but then again you are not asking the right question. Reading through the thread you would be well served by a 650-not joking. I have flowed them @ 20.4" H20 and they flow right @ 704-708 cfm. You are not pulling NEAR that @ max RPM @ max HP. Considering your gears again I say 650. I'm sure this will ruffle some feathers-J.Rob

IMG_20180209_105221789.jpg
 
The old tried and true Mopar Performance book and it's take on carb sizing, (not the cfm range mentioned but in general) it's but one of many, but it makes sense to me, especially tuning what one has first before thinking of just going bigger.​

IMG_20180216_094612.jpg


IMG_20180216_095238.jpg


IMG_20180216_095314.jpg
 
RAMM said:
A 410 with box stock Edelbrocks is going to be sub 450HP. Refer to that EngineMasters episode here if you wish. A bigger carb is not the answer here but then again you are not asking the right question. Reading through the thread you would be well served by a 650-not joking. I have flowed them @ 20.4" H20 and they flow right @ 704-708 cfm. You are not pulling NEAR that @ max RPM @ max HP. Considering your gears again I say 650. I'm sure this will ruffle some feathers-J.Rob

View attachment 1715142513
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Funny thing is Blueprint built almost exactly my engine. Same heads, cam, intake, SCR (10.1:1), oil pan, etc...except theirs was 10 years later.
Moper was one of the people who helped me spec it out back in 2006.
It was estimated back then that the combo would make about 410-425hp.

Thanks J. Rob!
 
Knuckleduster, a note about the Nitto's. When I had my old 360 (approx. 350 fwhp) in my car with 3:73's and a 3K stall I couldn't get it out of the hole with stock radials so I put on a set of Nitto's. Like night and day. Launched real good. But as soon as I put in the 408 (approx. 475 FWHP) traction went out the window. Tried different pressure levels. Installed full Caltrac rear suspension. Still couldn't get it to hook good and I now had 3:23 gears. Installed a set of MT drag radials and it hooks much better. Their easily worth the money difference IMO. The only drawback to them is their soft so they don't last long if you drive a lot
 
crackedback said:
Stock Elim has the stock lift (laughable) and a ton of duration. Rockers are no longer an issue in Stock either.
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"Stock" cam NHRA says is .465 in & .473 ex any duration, I think.
The 69 intake is the cast iron version that the LD340 was copied from.
Any 1.5 rocker is now allowed.
An the piston rod rings and wrist pin are weighed as an assemble now instead of individually.
And I believe the heads are 2.02 and 1.6 valve with a 64cc combustion chamber.
 
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