Please bear with me. I'm new to carburation, and high performance sbc's. I'm looking to install an edelbrock rpm air gap, because I recently sold my dual plane, mad in china, intake. I was running a 600 holley with vacuum secondaries on it. I bought a 700 double pumper, but I read the intake will only bolt up on heads '86 and down, no later than '86. The bolt holes look the same as my old intake. How do I find out what year heads I have, they are world sportsman II. It's an '86 and up block. Here's a pic of the old intake, the center 4 bolts were straight down like the air gap. But I wanted to be sure, thank you.

 

Post a pic of your Sportsman II heads.. As far as I know Sportman II heads all have the 55- 85 intake bolt angle.

Should have bought a 750DP not a 700.

 

I will post pics when I find the damn camera, what's wrong with the 700, I could return it, I haven't even received it in the mail yet. thanks

 

I thought a 750 would be too much, i'm jumping from a 600 to a 700. It needs it though, I have a pretty high lift cam, and it was definetely under carbed.

 

The 700 that I bought is a double pumper also. 4 got

 

A lot if mis information and confusion floating around about proper carb size selection.

I hear a lot of " a 750 is too big for my 350" all the time.

For a "performance oriented 350" you want to buy a 750cfm carb if you want a double pumper. it is the "right carb" 99.9% of the time. All the local drive in folklore and "expert advice" is bull. Unless you have a very mild combination a 750 is not too big. Especially for a dual plane manifold.
Holleys size recomendations are very, very misleading.

the popular math calculation for selecting a carb based on published cfm ratings is also missleading.

When an engine is at max rpm and horsepower output the intake manifold is not at 1.5" of vacuum. More like .75 to 1" manifold vacuum. Convertt he rated arflow of a 750 @1.5" to .75" or 1" test vacuum and you'll see that it is just right for a 350ci motor from 350 to 450hp.

If, you want to go fast sell the 700 and get a 750 or replace the main body with a holley or proform HP style main body.

I bought a used 700DP very cheap with exactly this plan.

 

thanks, you 've helped me before. The seller wont take refunds, and he doesn't have any 750s. But it's got to be a hell of a lot better that a 600 with vacuum secondaries. I can't see spending money on a main body, after I just spent 240 on the carb. Maybe in the summer when I have more money. Even if I did it now, it would probably cause more harm, because I don't know that much about carburation. later

 

My 383 makes better power with a 650.

 

I'm guessing you've tried bigger carbs with your setup. I can't believe a 650 is enough for a 383, but I guess it's all about how you set it up.

 

Put a 750 on it while the engine was on the dyno and tuned it to the same a/f ratio and EGT's and while it made 7 more PEAK HP, it was a much shorter curve and it took 3 seconds more to make the pull. The engine accelerated much slower with the big carb. That's why I said the 650 makes better power, not necessarily more power. I'll sacrifice 7 peak HP for better throttle response, more torque and a wider power curve any day.

 

I'll bet there is a lot more to the story than you're letting on or you're ignoreing a lot of factors.

Have to see the dyno test. For there to be that much difference in a dyno accleleration test between two carbs that ar supposable tuned in correctly one of the carbs muct have something seroiusly wrong with it, or some other factor is affecting the test in a serious manor. 3seconds is a lot on a dyno test.

 

It just shows that the 750 was too much for my particular setup, that's all I'm trying to say. I don't know why you insist on chiming in a thread every time I mention that.

The test was done on the same day using SAE correction factors, identical oil and water temperatures, same settings on the dyno (sweep rate and amount of water entering the absorber, pressure of water and the temperature of the water). Average EGT's differed by <100* throughout the pull and the a/f differed by a max of .2. Data points were averaged from 4000 to 6300 RPM on both tests. Timing wasn't touched either. All done on a Hoffman dyno with Stuska absorber and Depac data system.

 

It shows me that something is fishy. there is not that much difference in ET between a 600 650 700 750 800 850 carb on a typical 350 to 450ci motor in a typical car over a quarter mile, even if the jetting was off on one of the carbs.

In such a comparison of all the sizes of holley DP carbs on such a typical motor I'll bet there would be less than .75 of a sec from best to worst. Your statement is highly suspect.

Sorry, not buying it.

 

Buying it or not, I'm not here to impress the internet gods. My car makes good power, runs consistent and I go rounds every weekend. Have fun in your world.