Key word, “SMALLEST ACCEPTABLE.”IMO, the original computation was a good gauge of the smallest acceptable carb for an engine
Key word, “SMALLEST ACCEPTABLE.”IMO, the original computation was a good gauge of the smallest acceptable carb for an engine
What did it go when you tuned it? What's the deal with the electric choke? Just wondering is all
you forgot to mention what gears that car has in it, dam sure aint 3:23 `s.yesterday at Pamona the NHRA stock class winner was a 1969 340 Dart in E/SA = 10.7 seconds with - STOCK : 625 AVS carb, intake, rockers, heads, compression ratio (blueprinted), stock cam lift, weight, 9" slick. I run 11.6 with 360 cubes and 2.5" Edelbrock mufflers. an $ 650. ? carb is worth what, .10 seconds?
the problem w/ this is, there`s an intake stroke every 90 degrees. If u divide by two, my 505" wedge would need a 500 something cfm carb. Everyone knows they require 950 to 1200 cfm. Don't divide by two, and it comes out 1047 . What say you ?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.
So you think now the exhaust will be the choke point?
My exhaust guy won't do 3" over the axles. That and the 3.23's are pretty much non-negotiable. Mainly a street car, but would like to crack 11's at the track.
Will the 750 hold me back with the added flow? I want a bigger carb, but do I really need one?
the problem w/ this is, there`s an intake stroke every 90 degrees. If u divide by two, my 505" wedge would need a 500 something cfm carb. Everyone knows they require 950 to 1200 cfm. Don't divide by two, and it comes out 1047 . What say you ?
You can buy a bolt on over the axle 3"
The 3.23's are real tall for that combo.
When you have better heads the carb cfm becomes less critical to hp production. with better heads on a street car it is advisable to run a slightly smaller carb. If you are looking for all out performance go with the 950. For a primarily street driven car with those 3.23's I'd stick with your with the 750.
I run a 950 proform on my combo. It's a great carb. In contrast my fathers truck makes 500hp with a 750 carb. My circle track car makes 463hp with a 500cfm 2 barrel.
The carb doesn’t become bigger or smaller but the engines demand does. The carb can’t change size. The way it is rated is the given size. What it can flow at different ratings changes. Suggesting the carb will flow what ever the engine needs is misleading because by that singlular sentence, a 600 cfm carb is fine. The vacuum draw is not an issue via that statement. Argue that it is a restriction and you contradict yourself.
You write that often and it is confusing to people.
The carb doesn’t become bigger or smaller but the engines demand does. The carb can’t change size. The way it is rated is the given size. What it can flow at different ratings changes. Suggesting the carb will flow what ever the engine needs is misleading because by that singlular sentence, a 600 cfm carb is fine. The vacuum draw is not an issue via that statement. Argue that it is a restriction and you contradict yourself.
You write that often and it is confusing to people.
What more impressive is the 500 cfm 2 bbl is even smaller than the 500 cfm would lead us to believe because of the 2bbl being rated at 3 in/hg instead of the 4bbl 1.5 in/hg. If rated like 4bbl for a more apple to apple comparison it would be more like 390 cfm @ 1.5 in/hg. Shows an engine will pull most of what needs even through the smallest of carbs but at a big penalty of power cause of the over restriction. I bet if you dyno some 4bbl on your engine, even a 650 would give a huge boost in power than every 100 above would give less and less returns, which if this was a street engine you'd have to decide where to draw line for gains vs sacrifices as an eg. to the OP.
Between the ported head and a larger carb, does anybody see a .66+ drop in et.?
it has around 5.13 gears-are u saying a car with 3.23 gears wants more carb than one with 5.13s?you forgot to mention what gears that car has in it, dam sure aint 3:23 `s.
No i believe he is saying velocity at the carb is what is probably helping his combo run with those shitty gears, the only thing lending to any snap it probably barely has under 3000 rpm...is the tiny carb.it has around 5.13 gears-are u saying a car with 3.23 gears wants more carb than one with 5.13s?
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
last time I had an nhra rule book stockers had to run a stock intake and stock rockers and stock cam lift, are U mixing in super stock or have the rules changed?intake is a LD340....T&D roller rockers... cam lift is .480 with about 260 duration at .050.....aint much stock in a stocker....
and many people are saying go bigger on carb??velocity at the carb is what is probably helping his combo run with those shitty gears, the only thing lending to any snap it probably barely has under 3000 rpm...is the tiny carb.
last time I had an nhra rule book stockers had to run a stock intake and stock rockers and stock cam lift, are U mixing in super stock or have the rules changed?
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