Geoff2 wrote: ↑Tue Jun 26, 2018 6:16 am
Keep going Stat, you are just showing your ignorance....
A DP works on vacuum. If you knew anything about carbs, you would know this....but you obviously don't.
There is no flow from the boosters of a DP [ or any carb for that matter ] until air speed is high enough through the venturiis to create a depression [ vacuum ] & cause fuel to flow from the boosters.
Craig, sorry if I came on a bit strong. Don't think Carter ever got the credit they deserved. Holley had a much better marketing campaign. Pity their carbs didn't match...
Ok. I understand how a carb functions. Keep using smaller than required carbs. Keep using vacuum secondary carbs. I'll keep pulling them off, throwing them in the garbage and going faster with the correct carb.
One more time for the slow folks...THE MATH PUBLISHED SINCE AT LEAST THE 1970'S FOR CARB SELECTION IS WRONG. ALWAYS HAS BEEN, ALWAYS WILL BE.
BTW, I realize it takes air moving through the booster (a pressure difference) to get fuel moving through the booster. That's why I want an accelerator pump on the secondaries. DUUUUH.
statsystems wrote: ↑Tue Jun 26, 2018 1:09 pm
One more time for the slow folks...THE MATH PUBLISHED SINCE AT LEAST THE 1970'S FOR CARB SELECTION IS WRONG. ALWAYS HAS BEEN, ALWAYS WILL BE.
Instead of screaming "YOU'RE WRONG" over and over again, how about enlightening us on the correct way to size a carburetor, since everything published in every carb book (Mike Ulrich, Doug Roe, etc) is apparently incorrect?
Posts like this sure make me miss the speedtalk forum of 10 years ago.... this place is getting worse than Yellowbullet.
I would say:
The conventional math for carb sizing is based on the assumptions that at WOT and peak RPM, the calculated manifold vacuum should be 1.5" Hg., based on the engine having 100% volumetric efficiency.[E.g. 302 c.i. @ 6,000 RPM: (302 x 6,000/2)/1728 = 524 CFM] The resulting CFM target is actually OK for low to moderate performance engines and the relatively strong vacuum signal makes it pretty easy to tune.
However, serious engines need not be saddled with such a restriction and many have (plenum intake) carbs sized for as little as 0.5" Hg. at red line, although the resulting gains come in diminishing steps. Since flow is proportional to the square root of pressure differential, it will obviously take a huge increase in the (rated at 1.5") carb flow to achieve such low restrictions and will result in a very narrow 'tune' window and usually significant loss of low speed manners.
Have to throw in another jab.... Those Super Stock/A Hemi 'Cudas and Darts seem plenty fast with those old junk vac. secondary carbs!
Not to forget the SS/C 427 Fairlane Thunderbolts too!!
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427dart wrote: ↑Tue Jun 26, 2018 1:57 pm
Have to throw in another jab.... Those Super Stock/A Hemi 'Cudas and Darts seem plenty fast with those old junk vac. secondary carbs!
Not to forget the SS/C 427 Fairlane Thunderbolts too!!
How about all those NHRA SS class racers going fast with.... GASP... a Q-JET!
statsystems wrote: ↑Tue Jun 26, 2018 1:09 pm
One more time for the slow folks...THE MATH PUBLISHED SINCE AT LEAST THE 1970'S FOR CARB SELECTION IS WRONG. ALWAYS HAS BEEN, ALWAYS WILL BE.
Instead of screaming "YOU'RE WRONG" over and over again, how about enlightening us on the correct way to size a carburetor, since everything published in every carb book (Mike Ulrich, Doug Roe, etc) is apparently incorrect?
Posts like this sure make me miss the speedtalk forum of 10 years ago.... this place is getting worse than Yellowbullet.
I base carb selection on Venturi size. It ain't that hard. I just get tired of repeating myself.
427dart wrote: ↑Tue Jun 26, 2018 1:57 pm
Have to throw in another jab.... Those Super Stock/A Hemi 'Cudas and Darts seem plenty fast with those old junk vac. secondary carbs!
Not to forget the SS/C 427 Fairlane Thunderbolts too!!
How about all those NHRA SS class racers going fast with.... GASP... a Q-JET!
You make the ASSumption they would be slower with something else. Rediculous.
Guys run carbs like that because of rules. I'll give you the credit you want when I see Pro Stock or any other unlimited class running 2 quadrajet carbs.
MadBill wrote: ↑Tue Jun 26, 2018 1:47 pm
I would say:
The conventional math for carb sizing is based on the assumptions that at WOT and peak RPM, the calculated manifold vacuum should be 1.5" Hg., based on the engine having 100% volumetric efficiency.[E.g. 302 c.i. @ 6,000 RPM: (302 x 6,000/2)/1728 = 524 CFM] The resulting CFM target is actually OK for low to moderate performance engines and the relatively strong vacuum signal makes it pretty easy to tune.
However, serious engines need not be saddled with such a restriction and many have (plenum intake) carbs sized for as little as 0.5" Hg. at red line, although the resulting gains come in diminishing steps. Since flow is proportional to the square root of pressure differential, it will obviously take a huge increase in the (rated at 1.5") carb flow to achieve such low restrictions and will result in a very narrow 'tune' window and usually significant loss of low speed manners.
There's the answer. It depends on the owner's priority.
MadBill wrote: ↑Tue Jun 26, 2018 1:47 pm
I would say:
The conventional math for carb sizing is based on the assumptions that at WOT and peak RPM, the calculated manifold vacuum should be 1.5" Hg., based on the engine having 100% volumetric efficiency.[E.g. 302 c.i. @ 6,000 RPM: (302 x 6,000/2)/1728 = 524 CFM] The resulting CFM target is actually OK for low to moderate performance engines and the relatively strong vacuum signal makes it pretty easy to tune.
However, serious engines need not be saddled with such a restriction and many have (plenum intake) carbs sized for as little as 0.5" Hg. at red line, although the resulting gains come in diminishing steps. Since flow is proportional to the square root of pressure differential, it will obviously take a huge increase in the (rated at 1.5") carb flow to achieve such low restrictions and will result in a very narrow 'tune' window and usually significant loss of low speed manners.
There's the answer. It depends on the owner's priority.
Yep. Bill's summation's are usually well thought out and respectfully executed.
The other thing that can easily happen on bigger cid/cammed higher rpm deals running unported as-cast small'ish csa average design intake manifolds.. is where the intake manifold reaches its flow saturation point before a bigger carb can see a bigger gauge depression. Makes the carb seem slightly too big when actually the manifold is slightly too small. Port the manifold add spacer.. then the carb suddenly starts showing up as the slight restriction.
statsystems wrote: ↑Tue Jun 26, 2018 1:09 pm
One more time for the slow folks...THE MATH PUBLISHED SINCE AT LEAST THE 1970'S FOR CARB SELECTION IS WRONG. ALWAYS HAS BEEN, ALWAYS WILL BE.
Instead of screaming "YOU'RE WRONG" over and over again, how about enlightening us on the correct way to size a carburetor, since everything published in every carb book (Mike Ulrich, Doug Roe, etc) is apparently incorrect?
Posts like this sure make me miss the speedtalk forum of 10 years ago.... this place is getting worse than Yellowbullet.
I base carb selection on Venturi size. It ain't that hard. I just get tired of repeating myself.
So there is one correct venturi size that works across a wide range of throttle positions and rpms. Wow. Never knew that.
Those stupid engineers designed carbs like Q-jets with secondaries that effectively functioned as variable venturis to cover a wide range of operating conditions. What a waste. Too bad you were not there to educate them.
427dart wrote: ↑Tue Jun 26, 2018 1:57 pm
Have to throw in another jab.... Those Super Stock/A Hemi 'Cudas and Darts seem plenty fast with those old junk vac. secondary carbs!
Not to forget the SS/C 427 Fairlane Thunderbolts too!!
How about all those NHRA SS class racers going fast with.... GASP... a Q-JET!
You make the ASSumption they would be slower with something else. Rediculous.
Guys run carbs like that because of rules. I'll give you the credit you want when I see Pro Stock or any other unlimited class running 2 quadrajet carbs.
And you make the ASSumption they would be faster with something else. Ridiculous.
Instead of screaming "YOU'RE WRONG" over and over again, how about enlightening us on the correct way to size a carburetor, since everything published in every carb book (Mike Ulrich, Doug Roe, etc) is apparently incorrect?
Posts like this sure make me miss the speedtalk forum of 10 years ago.... this place is getting worse than Yellowbullet.
I base carb selection on Venturi size. It ain't that hard. I just get tired of repeating myself.
So there is one correct venturi size that works across a wide range of throttle positions and rpms. Wow. Never knew that.
Those stupid engineers designed carbs like Q-jets with secondaries that effectively functioned as variable venturis to cover a wide range of operating conditions. What a waste. Too bad you were not there to educate them.
Do you make up everything as you go? It's a compromise. But using incorrect math is a stupid way of selecting a carb.
How about all those NHRA SS class racers going fast with.... GASP... a Q-JET!
You make the ASSumption they would be slower with something else. Rediculous.
Guys run carbs like that because of rules. I'll give you the credit you want when I see Pro Stock or any other unlimited class running 2 quadrajet carbs.
And you make the ASSumption they would be faster with something else. Ridiculous.
It's not an assumption. How many guys running Hemis with two little VS carbs or guys running quadrajets would do it if there wasn't a rule? The answer is ZERO. Nada. Zip. Zilch.
You can't think those guys are so stupid as to believe they aren't under carbureted. Or hamstrung with an emissions designed carb. That's right...the pile of shit you worship is an emissions carb.
Ok. Play time is over. I can't educate total morons. Later dudes.
Ok. Play time is over. I can't educate total morons. Later dudes.
I can't find anywhere in this post when you tried to educate ANYONE. As I see it, you just told everyone how stupid they are for not using a double pumper carb on everything. Oh well... I guess I must be one of the morons.
Those Super Stock/A Hemi 'Cudas and Darts seem plenty fast with those old junk vac. secondary carbs!
