I have two different cabs for my car, the one thats on it is a 600cfm edelbrock and the other is a holley 4v rated at a little over 700 cfm. Dose anyone know what kind of performance gains I would have if I were to bolt on the bigger carb. my engine specs: 302 bored out .60 over, stock internals wth an "RV" cam, stock 302 heads, aluminum intake and long tube hedders. * I guy once told me that 289 heads would raise compression, how true is that?.
The 700 cfm carb is too much. You would not get any more performance out of it until you are over 7500 rpm or so. the 600 is just right for a 302ci engine. Larger carb would be harder to tune also with the decreased vacum pressure youd get from it. Some or most 289 heads will increase compression when switching from the 74 heads you probably have now. the 289 heads have a smaller combustion chamber.
*289 heads I was sceptical because the year 302 I have was bulit after the ford stoped building 289's. My 302 is like a late 68 or 69 model. I didnt think there was much difference between 289 and early 302 heads
Youll have to look up your head casting number and wee what size chamber they have, could be little to no difference if they are the early ones. The later emissions cars had larger chambers.
There's some overlap here in talking about 289 and 302 chambers. The C6OE 289 heads had the smaller chambers, the 67 heads had 63 cc chambers, in 68, the 289 2 bbl's got the same heads used on the 302 2 bbl motor (63 cc). The J code 302 heads (4 bbl engine for that year only) had the small 54 cc heads. Starting in 69, some of the 302 heads had 58 cc chambers. Be that as it may, unless you positively know what heads you have now (actually looked at the head numbers on the bottom of the intake runners) there's no telling what heads you have at this point in time as many 302's have been rebuilt over the past 40 years with different parts than they came with. What is the list number on the Holley carb ?
I know for sure that the heads that are on it now are 302 heads. the list number for the carb is 4118
Is the Holley VS or DP? What Trans and rear gears? Some will tell you that the 600 cfm carb is as big or bigger than what your engine can use. Problem is the way carbs are flow rated has almost nothing to do with how they work on a running engine. And not all carbs are created equal. Edelbrock vs. Holley, someone once asked Vic Edelbrock why he runs Holley carbs on his nostalgia race car instead of his own carbs. He simply replied, "The Holleys make more power".
I had the 600 edelbrock and it ran great on my stock motor, with just a touch more cam. When I put in 3.80 gears, headers, gt40 heads, it started to run lean. I swapped out the rods and jets, and got it as rich as it would run, but still too lean. That is when I went to a 750 holley double pump carb. Yes, too big, but my engine likes it off idle. But the edelbrock was great on that mostly stock motor, and really easy to tune.
Not too big if you know how to tune it. I know of a guy that runs a modifed Holley that flows over 900 cfm on a street 289. Car runs crisp and clean, but pulls like a bat out of h&ll.
Thats odd. If tuned right you should have been able to get it not lean with the 600. You can only draw so much air through it, 600 cubic feet per minute, regardless of engine combo. It would just restrict power if the volume required by the engine was greater than it could could flow. That wouldnt happen until about 7000 rpms. When I used to run through emissions testing on my car I was running a 347. I had a Edelbrock 600 that was jetted just right to get it through running clean. But on the 347 the 600 maxxed out the volume requirements at 6000 rpm so I used a 750 for racing purposes because I shifter about 6500. I actually fealt better low end power running the 600 on the stroker. It was just barely not enough carb at top end, where the 750 was a little too much carb on the bottom end (too low vacuum).
The 4118 is a vacuum sec 725 cfm carb. It'll work on even a mild 302. I used a 3310 750 for a time on an Explorer long block with a Ford A321 intake. It worked fine, but I prefer a smaller carb for better throttle response and mixing at lower rpms. You can tune the secondaries to open later on the 725 so in effect, you're only going to use half the cfm capacity for most driving, so you can think of it being a tad less carb as a 500 2 bbl which is exactly half a DP 750
