carb size, 750 or 600??

[no1udknow]

Hey guys, I have a 350 that has been bored .080 over, and has a cam in it ( i can get the specs later) running 202 heads with a torker intake, headers, and 26" glass packs. It came with a edlebrock 750 on it and I was told that the motor was built with the intention of running wither 2 4bbl on a tunnel ram, or 3 dueces. I have an extra edlebrock performer 600 at the house and I am wondering if it will be too small? I feel like the 750 is gonna rape my gas milage. Your thoughts?

[R.L.]

If your worried about gas millage I'm assuming your not racing it just a daily driver if so I would think the 600 would be fine for that.

[no1udknow]

Correct, I just dont want to under carb the engine either

[hugger6933]

The only time I have felt the 750 was right for a small block was on on of those under hood blower motors. I have run a lot of motor with 600's in the past and they all stayed happy. Now if you change the conversation to big block then that is another story I had a dominator on a big block believe or not I could pump twice and crank and walk away from the car and let it warm for minutes without loading up. it was crazy hardly anyone would believe it was a 1050 on it.
In your case the 600 is gonna be the best option hands down. Jim

[bigmac73]

650??

[Stocker]

Back in the late '60s I had a '65 Corvette with 327/365hp engine, same internally as fuel injected but carbed instead. Very strong engine with 11:1 compression, solid lifters, lumpy idle, & 6500 rpm redline. It came with 202 heads and a single-inlet Holley which (here's where my memory gets a bit fuzzy) may have been 650cfm, but I'm pretty sure it was 600cfm. All factory equipment and worked very well together. I bet that 600cfm will be just fine on your 350.

[GASoline71]

.080 over? Sure about that?

Almost any 350 on the road that is not being spun over 6,000 RPM's and is just a little hotter than stock only needs a 600cfm carb.

Gary

[hugger6933]

With a overbore of .80 keep close watch on the cooling system it may be overworked unless it is super big for the 350. Just a thought. Jim

[Prescott]

My opinion is this: If you get good at tuning carbs, either of these can be made to work. Edelbrock says that their 600 cfm carb works on a 454, and it's true. The 600 will be easier to tune and run. The 750 will give you a higher rpm range. So lets look at it mathematically.

Your 350 bored .080 over is now a 364 inch engine. Use the basic formula (not counting volumetric efficiency, which will make it smaller) for cfm:

Cubic inches X RPM / 3456

364 @ 5000 rpm is 526 cfm
364 @ 6000 rpm is 632 cfm
364 @ 7000 rpm is 737 cfm

So you can see that it all depends on the rpm you are aiming for. Don't let any of us tell you which one to use. Please do this instead: Buy the metering rod kits, learn how to calibrate these carbs, and try them both. Here's the best part. We get to read about what happened. How about it?

[no1udknow]

Originally Posted by GASoline71

.080 over? Sure about that?

Almost any 350 on the road that is not being spun over 6,000 RPM's and is just a little hotter than stock only needs a 600cfm carb.

Gary

Im sure about the .080 over, I saw the receipt from the machine shop. And yes, I was a little concerned about cooling issues, could be why they are running a 3 core radiator, I also have the cam box with a bunch of info written on it by the machinist,

the cam is a modified, Elgin Pro Stock E921P. Cam lift is .320 in n ex, valve lift is .480 in n ex, lobe centers are 107 in 111 ex,

Aparently when my friend bought the truck, the previous owner put in a hv oil pump and nothing else and it resulted in some spun bearings so they had it line bored, bored the cylind ed rs, and built for the ground up

[streetstar]

You have the wrong cam if you are concerned one iota about gas mileage

If the PO had a tunnel ram in mind, he was only thinking about straight line performance at high rpm's -- its gonna pass a lot of un burned or poorly burned fuel through at lower rpm's (anything below 3500)

I'd pull it, install an "rv" type cam, then go with the 600 . A Lunati Voodoo cam is a much nicer general purpose bumpstick as well

[sixtyeightC10]

Originally Posted by no1udknow

Hey guys, I have a 350 that has been bored .080 over, and has a cam in it ( i can get the specs later) running 202 heads with a torker intake, headers, and 26" glass packs. It came with a edlebrock 750 on it and I was told that the motor was built with the intention of running wither 2 4bbl on a tunnel ram, or 3 dueces. I have an extra edlebrock performer 600 at the house and I am wondering if it will be too small? I feel like the 750 is gonna rape my gas milage. Your thoughts?

With all of those engine upgrades and you're concerned with fuel mileage? I didn't buy my truck (or Jeep) for fuel mileage, I bought them to use.

I agree with Prescott, do the math.

[no1udknow]

Originally Posted by sixtyeightC10

With all of those engine upgrades and you're concerned with fuel mileage? I didn't buy my truck (or Jeep) for fuel mileage, I bought them to use.

I agree with Prescott, do the math.

I didnt buy my truck with the intention that it had all the motor upgrades. I bought it 1) in rememberance of my father 2) to build a truck I would love 3) something for me amd the wife to cruise in here and there. I just want to be able to take the wife out on a date ine it amd not have to steal money from my childs piggy bank. Im thinking I will likely change the cam at some point, and drop it down to the 600, followed up by an overdrive tranny and some better gears out back (currently 4:11 with a th350)

[67 cst swb]

Originally Posted by Prescott

My opinion is this: If you get good at tuning carbs, either of these can be made to work.

I totally agree with this statement. The key is getting good at tuning the carb.
If its an edelbrock, they have a specific tuning guide. READ IT!! Edelbrocks can be great carbs... if you learn to tune them.
I would run the 600cfm based on your intended usage.

[sixtyeightC10]

I can understand that you're doing this in memory of your father. Both of my parents have passed on so I can relate.

An overdrive trans will help to increase fuel mileage, but not as much as you would hope. This is what can be expected on drive ratio changes; *Note, this statement below is for an automatic trans only. Manual transmissions may vary (but not by much), but will follow the same principal.

The 700R4, 4L60, and the early and late 4L60E overdrive ratio is .70:1. Your current Axle ratio is 4.11:1. The over drive will make the truck feel like that it has a 2.88:1 final drive ratio (4.11 X .70 = 2.877).

So say that you're getting approximately 10 mpg. With a changed final drive ratio you "could" get up to 14.28 mpg. (10 mpg divided by .70 = 14.2857). Of course all of this is theoretical and can't be expected in the real world, especially with the variables of start-up/warm-up, stop-and-go, hills, driving habits, and so forth.

[gcottingham]

600 will be plenty, just make sure it's jetted right. You'll want to check it on a dyno. People always over-carb engines. After all, when NASCAR was still running carbs, they were only 830 CFM. And that was on an 800 hp engine.

[67 chevelle]

Originally Posted by gcottingham

600 will be plenty, just make sure it's jetted right. You'll want to check it on a dyno. People always over-carb engines. After all, when NASCAR was still running carbs, they were only 830 CFM. And that was on an 800 hp engine.

total agreement , if you are driving on the street this is the carb I would run , if it was a track only , read race truck , it might get better quater mile times with the 750 , might not , the 600 might do better for all out quater mile times

[piecesparts]

Look at the Edelbrock AVS line of carbs. The AVS model is rated at 650 CFM and not the 600 CFM the others are. That is a good sizxe for all around use. A 750 workis great on a smaller sized vehicle, but looses efficiency on a heavier vehicle on daily street driving. This info is not of my dream factory, I got it from all of the different tech gurus from Holley, Edelbrock, Barry Grant, and etc... The heavier the vehicle the more air signal (NOT total air flow capability) is required to make it operate efficiently. That means a small CFM rating will keep the air signal higher and thus make the carb work better moving that larger load. However, this will cut the top end capability to some degree, so get a little and give a little.

[GASoline71]

With an .080 over 350 I'd be more concerend with cracked cylinders. If this was a drag engine... the PO didn't fill the block with hardener did he?

Gary

[truckster]

Originally Posted by sixtyeightC10

I can understand that you're doing this in memory of your father. Both of my parents have passed on so I can relate.

An overdrive trans will help to increase fuel mileage, but not as much as you would hope. This is what can be expected on drive ratio changes; *Note, this statement below is for an automatic trans only. Manual transmissions may vary (but not by much), but will follow the same principal.

The 700R4, 4L60, and the early and late 4L60E overdrive ratio is .70:1. Your current Axle ratio is 4.11:1. The over drive will make the truck feel like that it has a 2.88:1 final drive ratio (4.11 X .70 = 2.877).

So say that you're getting approximately 10 mpg. With a changed final drive ratio you "could" get up to 14.28 mpg. (10 mpg divided by .70 = 14.2857). Of course all of this is theoretical and can't be expected in the real world, especially with the variables of start-up/warm-up, stop-and-go, hills, driving habits, and so forth.

This is correct as far as it goes, but it's missing a couple of the advantages of the 700R4. First, it has a lower first gear, so the launch is easier, which can also improve fuel mileage. Second, it has a lockup torque convertor, which eliminates slippage at highway speed.