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Discussion Starter · #1 ·
HEY GUYS!!!!!! its been a long while since ive been on. my computer was down but im up and running now. Well, its been about 2 months since ive been up here. in that time ive got my exhaust done, put in my 3.42 gears, and upgraded my wheels (pics coming soon). im ALOT happier with the new gears but now...i turn to my carburetor. it is functioning properly but...its an edelbrock performer 850cfm and its kinda just too much. it was on my elky when i got it (idk why because the engine was stock when i got it). i was looking to move down to maybe a 600cfm. ive read that decreasing to a 600cfm would increase my throttle response, and lower end. apparently, the 850cfm is for larger motors and higher power bands. my motor-rear is all built for IDLE-5500 so my carb doesn't fit my setup at all. the 850 is a quadrajet (spreadbore) by the way. all the 600's ive seen were squarebore. i know quadrajet is suppose to be more fuel efficient but it cant be much more efficient than a 600 squarebore, by it being an 850cfm, correct? PLEASE HELP A LOST SOUL :???:
 

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VINTAGE MOTORHEAD
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The optimum size for a 350 motor (dkn't know what you have) us 650cfm for motors turning up go 6500 rpm. According to Holley. 850 is for a big big block.
 

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Discussion Starter · #3 ·
The optimum size for a 350 motor (dkn't know what you have) us 650cfm for motors turning up go 6500 rpm. According to Holley. 850 is for a big big block.
I have a 350 good sir, and thank you for your response. I figured that 850 was for something BIG. Do you know if the 600 would provide more throttle response and lower end over the 850? I think it said something about velocity. I can't find the site I was on.
 

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Discussion Starter · #5 ·
THAT THING IS CLEAN!!!!!! whats the difference between that, and the edelbrock or holley 600's?
 

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It's a Quadrajet ! Great for MPG's & When you want to open up those big ones !
Paid around $260. shipped ! It's Been on a year without one problem & RUNS GREAT !!
 

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VINTAGE MOTORHEAD
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Sure! A 600/650/670 will outperform the 850 in every way. It us way too much. The q-jet is also a great way to go.
 

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Discussion Starter · #9 ·
I dont know HOW i didnt notice the quadrajet bottom of that carb lol but yes, i agree that the quadrajet is better. Im not in any way disputing that. Ive been through the forums where theres pages and pages of back and forth. Just wanted to know would i benefit more with a smaller carb. And yes, i have an edelbrock performer intake. Takes spread and square carbs. And that $260 is steep for what im looking. I was going to buy one from craigslist or ebay and rebuild if needed. Found one a guy was selling for $40. Says it works fine but i'd rebuild it anyway. But, if i decide not, would i go Edelbrock or Holley? both have a mixed rep but holley...for some reason, people HATE them
 

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Everyone has the preferences.But for me,the change to a holley 600,from a quadrajet,was one of the best things i have done.Im not disputing they(rochester) are a good carb,as they were used,across the board,back in the day,with great success,,,,,but i had endless,idle,and general running issues with mine,probably more due to not knowing anyone familiar enough to fine tune it...But the holley,was a bolt on and go thing,with maybe a couple of adjustments needed........Prior to buying the holley,when i discussed problems i had with the Quad...90% of the replies from friends and people in the know was....chuck it,and Get a holley....
 

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Discussion Starter · #11 · (Edited)
Everyone has the preferences.But for me,the change to a holley 600,from a quadrajet,was one of the best things i have done.Im not disputing they(rochester) are a good carb,as they were used,across the board,back in the day,with great success,,,,,but i had endless,idle,and general running issues with mine,probably more due to not knowing anyone familiar enough to fine tune it...But the holley,was a bolt on and go thing,with maybe a couple of adjustments needed........Prior to buying the holley,when i discussed problems i had with the Quad...90% of the replies from friends and people in the know was....chuck it,and Get a holley....
wow! well sounds like you had some positive results. power difference?? i thought that quadrajets were easier to work on?? ive never been a carb guy but i DO have someone that can setup and tune it.
 

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Power difference for sure,probably no HP difference,but,the Quad used to bog down on heavy excelleration,and you had to get right into it to get the thing moving, when you wanted to get going in a hurry(as most of us do from time to time:twisted:)where as the holley has a very consistant smooth excelleration...And WAY better economy !......A friend of mine lent me a holley he had,so i could try it,before i bought one,But the carb had been sitting around for some time,prior,and wasnt a Huge improvement........,but ended up buying one anyway,and havent looked back..Good luck and,..Keep us posted .......In my opinion,holleys are way less complicated than a Quad,but sure,with the right tuner,they(rochester) would be a different carb.......to what i had!!
 

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Discussion Starter · #13 ·
Well sir, holley is sounding good to me right about now. I will be getting one or the other in about a week so updates will follow. Thanks for the info thus far guys!
 

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I subscribe to the old "Offy" rule of thumb...

600 CFM Stock...Double that if you can flow..Heads, Headers etc. and really run the upper end of the RPM's...

I ran 3310 Holleys on my 302's, but they had a real Wall to climb over till about 3,500 RPM...I say go Q-Jet for the best of both.

I have a 9:1 350, dual 2 1/2" stainless exhaust, and a 600 Holley in my 84...Still to full throttle the new engine...I just walked away from a Banks Turbo Ram PU...
 

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a good q jet will preform as well as a holley but give you better fuel milage.i have both on different toys.shy away from the edlebrock carbs they are the most expensive to tune.the newer holley is better than the older ones because of the power valve circuit improvments.but for a basically stock setup car i would stick with a q jet.they will give the best milage and good power and great throttlee responce if set up correctly.the 850 you have now is way too much for what you have,the smaller carb will help you all around which ever one you choose. the biggest mistake people make is too much carb or too much cam. so you are on the right track to go smaller
 

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If the carb you use is not set up for your engine it won't matter what you get you won't be satisfied. Buying one off craigslist or privately is a scary thing in that you really don't have any idea what it is. The numbers might say it is a so and so but you will won't know what tuning has been done to it.
On a stock SBC the proper q-jet is hard to beat for all around performance and mileage.
The 850 q-jet you have must be aftermarket because the biggest Rochester or Carter ever built was 800 for the big block Buicks, caddys and Pontiacs and not even all of them got the 800.
Your engine will never use that much CFM and the q-jet will only supply what the engine can use so it really doesn't matter what the total CFM is that it is capable of. If it is set up properly it will give you the mileage and the throttle response you are looking for.
 

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Neil his carb is the same one I had on my engine. Sold (not anymore) by Edelbrock, made by Magni Marteil or something like that. They must have bought rights from Rochester to copy the Qjet. The one for the big block is rated at 850 cfm and has adjustable primary main metering.
The primary bore size may be the same as the smaller model and like Neil said, the secondary will only flow as much as the engine can use. Both carbs set up properly, you may see little difference between that carb and a smaller Qjet.
 
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