Anyone catch the latest CHP article on carb sizing? Very little difference in Tq/HP between the 600 through the 950+ (i.e., the 650 to 750 spread was just a couple HP), but lots of difference in idle and throttle response with the smaller carbs performing best. All carbs tested with stock jetting on the same 440hp 383. They also tested a 390 cfm, but that was just too small. :cool:




[Modified by Chris69, 12:11 PM 1/11/2004]

 

Corvette Fever (March 2004) also has a carburator sizing article. The "test" in this case was done on a computer. :rolleyes: I think the "bolt it on an engine, and hook it to a dyno" tests are the only ones with some credibility. Even dyno tests have lots of variables.

What's next: "My video game car is faster than your video game car!" ?

 

i'm getting fed up with chey hi performance mag.

Every issue is full of expensive crate motors. I want to know how to add do it yourself horsepower.

 

I think this has been a resounding issue with SB Chevy's since their conception. most bubba's swap in a 750 double pumper on an otherwise dead stock 350 and think that will get them mass HP gains when in reality they over carbed the poor SB to death. i'm running a 1400 Eldeborck (650cfm) and the 327 likes it alot.

 

Then Car Craft is for you. :yesnod:

 

:iagree:, I can't figure out with CHP anymore where advertising stops in that mag with those buildups.

 

I have to check it out.. I have CHP but haven't read that article yet...

 

I just read that article last night. I thought it was a pretty good objective article with some free advertising for Holley. I came away thinking that their tests still support the notion that smaller carburetors will work better on the street.
There was also a pretty good article about rebuilding quadrajets and another article showing the products of various carburetor manufacturers.

 

Lars recently did some testing with different size carbs and came up with the opposite response- big carbs are OK.
Posted a thread here but I cant find it.
Maybe he will jump in.
:cheers:

 

Is this it:
http://forums.corvetteforum.com/zerothread?id=688640

 

Yes, I read the article and it was all BS!:(

Everyone of the carbs was right on out of the box. Do you want to know why? It's because they were all altered for the test ahead of time. Carbs that have square jetting - That is the same jet size on both primary and secondaires are only made to run at WOT. Those carbs are only good for dyno testing or drag racing where you only concern is wide open throttle plate operation.

 

Whats the point in testing the carbs if you don't tune them?

Of course there will be no difference they are all messed up.

Pure :bs

 

:iagree: That's the biggest problem I have with CHP and the primary reason I stopped buying the mag, they do a very half-azzed job on any project they do. Sometime they print corrections for their fuggups in the next issue, mostly they just let them ride!

 

I haven't seen the article yet, but I'll say it again.....I haven't seen a 350" anything that didn't go faster with AT LEAST a 750 on it. Of course it can't be all goofed up, but compared to a well set up 650, I'll take a well set up 750 any day on the average smallblock.

If it's on a dual plane intake it can take even more. I have had good luck with small 600-650 cfm stuff but they worked best on single plane intakes on small, relatively mild motors. Always double pumpers especially with the little carbs.

Those tests are for the "bolt it on and forget it crowd". Those guys will always be outperformed by the folks who want to spend a little time thinking out their combo and working/tuning it whether its flat out racing or putting around for gas mileage.


JIM

 

:iagree: :iagree:

 

I agree with you George. Any holley out of the box is more then likely screwed up. Out of the last 5 new holleys that I bought I think 4 of them had major problems. I no longer trust holley and any new car is immediately torn down on gone through.
Also talking about carbs the distance between the mounting flange and the intake floor makes a big difference in the size of carb the motor can handle. As the floor to mounting flange becomes smaller the larger the carb is needed. Small carbs have high velocities through the venturi and if the intake floor is too close the fuel seperates from the air stream. In this case a larger carb with slower venturi velocities is better.
While I only use holleys because I know them I don't like them. :) :)

 

Norval - what I'm saying is other than we both know that out of the box brand new from the factory needs tuning and they are sent with a jet spread between the pri and seconds of at least 8 jet sizes.

I imagin that these so called out of the box perfectly metered air fuel ratio carbs probably didn't even have power valves because they were only worried about 12.5 A/F ratio at wide open throttle for the dyno runs.

 

I really think what the test shows is that there really isn't that much difference between the carb sizes. It is more important to have them set up properly. If were are talking about plain Jane grocery getter engines, use the smallest carb. Otherwise, choose based on vehicle weight, gear ratios, rpm range used, and yes even engie size. A well tuned 850 Holley dp on a 302 high output small block in a 69 Camaro with 4.11 gears and four speed is fine, while the same carb on a very mild BB originally fitted with 2 barrel carb found in a Caprice with auto, <3:1 gears would be a less than happy combination.

The differences shown that are plus or minus 10 horsepower can not be honestly felt by the vast majority of us on the forum, or anywhere else for that matter. Tune it if you intend to use it, change only 1 thing at a time, and eventually it will be perfectly dialed in if you have a consistant way to measure the resulting change. The G Tech pro my wife got me for Christmas will be great for this. Roll on in 3rd gear on the same open, deserted road, at the same temperature, wind speed and direction, etc and plot the differences.

Arguing about the correct size for the carb is the same as arguing the best size for a cam. It depends!

Chuck