Nealio240z Posted July 5, 2006 Share Posted July 5, 2006 I dont know what carb to use... I have a choice between a Rockchester quadrajet (650 cfm) -or- An Edelbrock proformer (750 cfm ) Iv heard that the 750 is to much for a sb 350, that it will flood at an idel. is this true?... what will give me better proformance? Anyone with expeirence in this matter please help... its been holding me back from being finished... I have a proformer manifold, vortec heads and bored 30 over. if that helps... Quote Link to comment Share on other sites More sharing options...
Guest Dyno_Ron Posted July 5, 2006 Share Posted July 5, 2006 The 750 will be a little big. About 600 cfm will be all you will need assuming mild modifications and 6500 rpm max. The 650 cfm will keep you safe without drowning it with a 750 (if you already have the Q jet, you always have the future option of going to a Edelbrock or Holley). Here is the software if you want to try different rpms, ve or cubic inches. http://www.virtualengine2000.com/Calculator2006.htm Quote Link to comment Share on other sites More sharing options...
Michael Posted July 6, 2006 Share Posted July 6, 2006 Calculators can be very useful for giving an initial baseline, but the mere presence of specific numbers should not be conflated with good accuracy. There are simply too many variables to get much beyond just a rule of thumb. As an example, by most calculators my application seems to call for a 750 cfm carb, but with more specific advice this appears to be a huge underestimate. Off to the dyno in a couple of weeks (maybe...) to verify. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted July 6, 2006 Author Share Posted July 6, 2006 So it is to big? what carb will give me the most hp? Will ir still run with the 750 cfm? Will it do any damage if I use it? like wash the cylinders... Quote Link to comment Share on other sites More sharing options...
specialk Posted July 6, 2006 Share Posted July 6, 2006 If it were me (and I knew the qjet was good), that's what I would use. They're a kind of 'magical' carb when working correctly in that they are a 2 bbl when driving nicely and a 4 bbl when you get your foot in it Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted July 7, 2006 Author Share Posted July 7, 2006 Thanks fot the info... I will use the Q-jet and see what I get... Thanks again.... Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 7, 2006 Share Posted July 7, 2006 The Q-jet is most likely a 750cfm. They did make a few 850's but 95% were 750cfm. And since the secondarys only open as needed, GM put those on 283's to 454's. The very small primarys give it very good throttle response, very good mpg with light throttle input, and the very big secondarys sound great when they start to open up (very cool sounding!). Plus the carb is very reliable and is made out of the right material (not aluminum). I hate edlebrock carbs! Throttle sticking, vapor locking, cheaply built carbs. Pure junk! I threw two of those in the trash a few years back. Edelbrock makes great intakes but they should be ashamed of their carb. I perfer the Holley 750cfm, 3310 vacuum secondary carb. It is easy to tune and looks good. The Q-jet sounds better, gets better mpg, and makes great power but doesn't "look as high performace" as the Holley. If it wasn't for the way the Q-jet looks, I would use it on all my V8's. I guess I'm a little vain when it comes to my engine looks. I just like the way Holleys look. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted July 10, 2006 Author Share Posted July 10, 2006 The Q-Jet is too big then? Im having big problems... When i hit the 4-barrel it backfires through the carb.. What is it? Im running an electric fuel pump from the 2.4L... is it starving for fuel? is it timing? Quote Link to comment Share on other sites More sharing options...
veritech-z Posted July 10, 2006 Share Posted July 10, 2006 Carb backfire is usually a timing issue, is it not? Also, if you are talking about the original 2.4 liter beint from a 240z, that should have had a mechanical pump I believe, so you are probably dealing with an aftermarket pump of some type. Do you have a fuel pressure guage to test for pressure? The Z carbs only needed like 6 psi, I don't think that in the absence of forced induction you'd need too much more than that even on a 4 barrell... Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted July 11, 2006 Author Share Posted July 11, 2006 It did have a mechanical fuel pump. Before I bought it it was changed to electric... My distributor was 180 degrees off.( not my fault) Hence the backfire. thanks for the help... Quote Link to comment Share on other sites More sharing options...
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