what carb for a 470?

[cudabob496]

there was an article that I read in one of the mags a few weeks ago discussing why larger carbs often performed better and I have seen quite a few others that actually ran dyno tests.  Of course, a carburetor that has not been set up for a given engine may give varying results.

I base my comments on experience, but a quick google brought forth this article from a few years ago.  Theory provides an excellent starting point, but, theory does not always win races   Understanding that there is more to the process than a simple calculation from a formula probably makes it easier to except

http://www.moparmusclemagazine.com/parts/engine/mopp_0111_demon_carburetor_dyno/viewall.html

OK, your article showed a 5 hp gain with the 950 over the 850, with just a carb swap. Kinda what I have read in other articles.

In my opinion, there are carb manufacturers out there, that suggest you need a bigger carb, to help them sell more carbs!  A guy is happy with an 850, and someone comes along and says you definitely need at least a 950. Holley does not seem to be one of the "you need a bigger carb" guys, at least for a street application. Can you get 10 more hp with a bigger carb? Maybe? But you can get 10 more hp much cheaper.  New plug wires, or a $150 ram cold air box will give 30+ hp! I think I'd be willing to shell out $800 for a nice 950, if I could get an honest 20+ hp gain. Problem with me taking the car above 6000 rpm, on the street, is I'll be trying to post bail money an hour later!! And between 3000 and 6000 rpm, my car will probably be quicker with the smaller 850 carb.

[bb71challenger]

I hope the 950 is not too much carb. I ordered it last night as I found a really good price for a new one. I do have a feeling that for my application an 850 would do pretty much everything I need but I just want to make sure I have enough and I have always heard all else being equal its easier to go down from a larger carb than the other way around. I really do appreciate all the suggestions!

[Strawdawg]

I noticed that the 950 gained hp and torque throughout the entire range tested...not just at 6000 rpm and it was on a slightly smaller engine.

The carb is not too big based upon experience and as you are buying a new carb, you are getting the extra power as a bonus.  It's not like you had a 850 and then spent money for the 950 which would be quite a bit per extra foot-lb of torque.  In recent years, most tests that I have seen published reflect similar gains.

If it makes you feel better, the June Mopar Muscle mag had an intake test on a 440.  They chose a 950 for the carb on that one

[cudabob496]

I noticed that the 950 gained hp and torque throughout the entire range tested...not just at 6000 rpm and it was on a slightly smaller engine.

The carb is not too big based upon experience and as you are buying a new carb, you are getting the extra power as a bonus.  It's not like you had a 850 and then spent money for the 950 which would be quite a bit per extra foot-lb of torque.  In recent years, most tests that I have seen published reflect similar gains.

If it makes you feel better, the June Mopar Muscle mag had an intake test on a 440.  They chose a 950 for the carb on that one

Well then, you gotta wonder why Holley specifies (displacement X max rpm) divided by 3456. Assuming the 470 above winds through the gears, shifting at 6000 on the street, the Holley formula gives an 816 cfm requirement for a carb. So, the 850 would be more than adequate. And the other well known formula, of 2 x displacement minus 150 gives a 790 cfm requirement.  These are the two most common formulas to predict carb cfm, and they aren't getting anywhere 950? But, I hear you, if the dyno results say otherwise. Holley needs to change their formula.

[Chryco Psycho]

I challenged BSCuda on this , he tried the formula & I insisted it would make more power with more carb than the formula states will work & his car significantly gained power with a carb larger than the formula suggests

[cudabob496]

I challenged BSCuda on this , he tried the formula & I insisted it would make more power with more carb than the formula states will work & his car significantly gained power with a carb larger than the formula suggests

how much? on the dyno? loss of throttle response on the street could be a factor to consider. I just read the new PHR.  They built a 400 small block that
made 528 hp on the dyno with an 850. But when they put it in their car for the street, they went with a 750 Holley HP DP, specifically mentioning throttle response.
ie, when you push the pedal, you wanna go fast right away!

[Oldschool]

The double the cu in rule is 2 X cu in minus 150

Not MY "double the cubic inches rule". Maybe yours, but not mine. Following your rule, I would suspect a very under-carbed engine. Your rule AND my rule are both starting points for figuring carb CFM requirements. The closer to stock the engine is, the better that rule works. The rear gearing, vehicle weight, auto or stick, if auto, what converter etc, all play a role in carb selection. There are many variables to consider when selecting a carb size.

For a modded 470CI engine, if it was mine, I would go with the Holley 950 HP or Profrom 950.

My personal car is 528 CI with 1500 cfm. It runs on pump gas, auto, 3800 converter, 4.10 gears, 31" tall tires, and 3500 pounds. Zero issues with throttle response.    It is immediate and harsh. BUT, like I said, it is modded pretty well.

My experience has shown me that modded applications like WAY more carb than the Holley charts, and other rules of thumb suggest....

[Strawdawg]

Well then, you gotta wonder why Holley specifies (displacement X max rpm) divided by 3456. Assuming the 470 above winds through the gears, shifting at 6000 on the street, the Holley formula gives an 816 cfm requirement for a carb. So, the 850 would be more than adequate. And the other well known formula, of 2 x displacement minus 150 gives a 790 cfm requirement.  These are the two most common formulas to predict carb cfm, and they aren't getting anywhere 950? But, I hear you, if the dyno results say otherwise. Holley needs to change their formula.

No, no one needs to wonder why the rule is not always 100% correct.  The article that I provided the link to explained one of the reasons that cause it to be wrong. 

Another reason that causes it to be less than completely true has to do with the velocity of air moving thru the carb and making the turn into the runners which can affect the atomization of the A/F causing leaness and upsetting the evenness of air flow to the cylinders if too fast.

It is not Holley's rule, it is simply a static computation.  It is a guideline rather than a rule.   It is up to the end user to determine what provides the best performance.  If it was as simple as following a formula, there would be a lot of ties at the finish line and the sport would be one great big, boring bracket race

Frankly, I never heard of twice the engine size minus 150 in all the years I have been trying to learn something about cars.  I thought you made that one up

Makes you wonder why GM put 780 carbs on sb chevies all those years, and why we replaced them with 850 dp's and went faster.  Of course, one could wonder why flow thru a four barrel is measured at a pressure drop of 1.5 inches of mercury whereas two barrels are measured at 3.5 inches of mercury.   Mercury is poisonous! 

[cudabob496]

Mercury is a FORD product!

[Strawdawg]

Not any more...it was determined to be hazardous to Ford's health...

[HP_Cuda]

I found it funny this article said the M1 intake was the best flowing intake out there!

 

I noticed that the 950 gained hp and torque throughout the entire range tested...not just at 6000 rpm and it was on a slightly smaller engine.

The carb is not too big based upon experience and as you are buying a new carb, you are getting the extra power as a bonus.  It's not like you had a 850 and then spent money for the 950 which would be quite a bit per extra foot-lb of torque.  In recent years, most tests that I have seen published reflect similar gains.

If it makes you feel better, the June Mopar Muscle mag had an intake test on a 440.  They chose a 950 for the carb on that one

[bb71challenger]

How did the holley street dominator do in the comparison?  that is the intake I am going to run.

[Strawdawg]

How did the holley street dominator do in the comparison?  that is the intake I am going to run.

It was middle of the pack on this test...I am not sure about the test engine they built.  They put a set of 915 heads that had been cleaned up some on the engine and calculated 10.18-1 cr...then they stuck a solid lifter cam with 264 degs of duration at 0.050" lift.  That seems like a mismatch to me but they called it aggressive   Left me wondering how valid they comparison was for anything other than that particular engine...but, I am cynical about most things magazine, I think

[cudabob496]

Over the last 20 years, the M1 single plane has always seemed to finish near the top in comparisons.

[Chryco Psycho]

Most compoarisons I have seen show the Street Dominator as one of the best intakes along with the M1 , typically the Sd doesn't make the best peak power but has the best average over the RPM range with a very strong midrange where the engine spends most of the time .