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Discussion Starter #1
Hi all,

I had a 302 with a 600cfm carb from edelbrock. In the process of engine swapping to a 351w. In the mean time I bought new heads and a top end kit from edelbrock - I’m wondering if I need to get a different carb ? The person at the machine shop recommended 650/700cfm. Others said the 600cfm would be fine.
I did the online summit racing calculator which said 560cfm for street driving and 730cfm for performance — but this doesn’t take into account the new components and what not.
Any thoughts ?
766519
 

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Nice goodies, and probably the way I'll go, but are you stuck on a carburetor? How about a Sniper?
 

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You already have a 600. Give it a try first.
 
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Your gonna love that setup!!! So here is the scoop on Carbs, for good throttle response you want smaller, for High RPM wide open throttle you go bigger. Your PerfRPM setup already says you want power across the RPM range 2500-5500 so this decision is made, not its time to match the carb to the system. On my motor (same as yours) I run a 650 DP which pulls hard from 2500 to the relatively conservative 6000 RPM chip in the Rev Limiter since I cannot afford to blow this motor and the cam is rolling off by 6k. A lot of folks will SWEAR run big as will bolt on and a dyno run will show good numbers with a big carb because you floor it and the air flows unrestricted and unmodulated through the RPM range. Works great on the drag strip. However, on the street or in an Autocross / race situation, you are modulating the throttle constantly in the mid ranges and a big carb is just not as responsive since the air flow speeds are slower with huge bores. Smaller bores have higher air speeds which keeps the gas atomized in the mid range so a wide open punch is immediately felt due to the speed of the air flow.

Key to all of this is your MAXIMUM RPM, if you plan to be running at 8K, go bigger e.g. 650 to 750. There is a large contingent on this site that will swear a 750 is needed on a 351. I had both and liked the 650 for Autocross. Didn't really notice much difference on the street, but remember, I chip at an admittedly conservative 6k. I would start with the 600 since you have it and during your break-in, it will be just fine. It is possible it will roll off at 6500 but if you don't spend a lot of time there it should give great throttle response. From there, see if you have any Muscle car buddies that have other carbs you can borrow and try. Watch your tailpipes if they get very light in color as it could be running lean which can burn a piston, you may have to rejet. Speaking of which, While you are doing all of this, its a good time to add a Air Fuel mixture gauge which will tell you how your mixture is doing. I wish I had one and folks that have 'em can dial in mixture across the RPM range including the accelerator pump and get it all right on a moving car which you cannot do on a dyno.

On Carbs, Holley is a go to carb for performance but frankly they are a PITA to set up correctly. For instance for years I didn't know the accelerator pump cam could be flipped around and give an more aggressive profile. I couldn't believe the difference, someone at the track mentioned it so we flipped it right there to try it. Because they are made for performance, virtually everything is adjustable and most people do not have the skill or tenacity to set one up correctly. Most of the alternatives are simpler in design and a nice alternative for a street / strip car. As I hear often on this site, just bolted it on and it was great.

Then there is the Vacuum Secondary vs mechanical decision. For an automatic the Vacuum is a go to because it responds to the RPMs and gives you what you need when the motor needs it. People with manuals tend to go with mechanical for better throttle response unless they are building a primarily street machine. Lots of learning to do to make an informed decision.

Good Luck...

ONe last thing, just in case it hasn't been covered, if you got the big 202 valves, it takes special pistons or a fly cut setup for 351s to divot the pistons to clear the big valves. I don't think its as much of an issue with 190s.
 

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Nice top set ! I run a Holley SA 670 on my 351. The mods are in my sig, but pretty much all RPM gear on top. I been learning carb tuning and I have been fiddling with mines. I believe I now have it where I want it, and the performance on it is good. Mind you, I am not really racing anymore, but she is running hard on the street setup I have. As someone else said, you will need to fiddle with the SA's to get it where you want it, but once its dialed in, man oh man it's a good performer. Currently I am running the solid yellow spring in my secondaries.

Now for the size...I believe the 670 gives a 351 a good fit for a street setup. If your racing, you may need more. That would be the 770. But again you have jet sizes and myriad of other things, so for that, someone more knowledgeable may want to step into this thread.
 

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When I bought this setup for my 351w I talked to Edelbrock to see what the recommended they said to big of a Carb is a common mistake and compromises street driving under 6000 rpm (the majority of your driving). I went with a 650 CFM AVS2 Edelbrock Carburetor, best Advice I've gotten
 

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Summit M2008VS600.
You know, I really like my Summit carb. But I'm seeing the rebuild kits are missing a lot of pieces and it appears those pieces are not available from Summit or anyone else. My carb isn't ready for a rebuild, but it does need new gaskets for the float adjusters. Those are available from Summit, but it was while I was searching for those parts I learned about rebuild kit issues.
 

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I've always been a fan of Holley carbs and have always used their carb selector page on their site to determine the approximate size of carburetor I'll need. I've got a 351w in my 65 fastback with over 400hp and run a 650 Holley Ultra Double Pumper carburetor. It's worked quite well for me and went with a mechanical secondary carburetor at their suggestion and also because I have a T-5 transmission. I guess they recommend a mechanical secondary carb for a manual transmission and being under a certain weight and a vacuum secondary carburetor when having an automatic. I also took my engine to a guy and put it on an engine dyno and it didn't even max out my 650cfm carb when on the dyno. Not sure if you have an automatic or manual transmission but the Holley 670 Street Avenger would be a nice choice if you have an automatic, and the Holley 650 Ultra Double Pumper I'd recommend if you have a manual transmission.

 

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I have had multiple people swear to me that a custom carb build is the only way to go. I thought no way am I paying for that, but then started looking and many of the good shops sell carbs for the same price as an out of the box unit and they are calibrated already... I was going to go that route but already have a carb and have constantly been telling myself "I'm just one more tweak away from perfection"... AED (higher volume) and lightning racing carbs (more boutique but have won lots of competitions) were the top two custom ones I was looking at. There are plenty out there if you search.
 

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Discussion Starter #13
Thank you all for the recommendations! I called Edelbrock too, and they recommended 650cfm for regular driving, closer to 800 for street racing.

I may try the 600 first, then upgrade. Or just bite the bullet and go for 650cfm or so. Appreciate all the help! Holley seems great but a bit more involved, so I may go for Edelbrock.

Appreciate you all!
 

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Discussion Starter #14
Your gonna love that setup!!! So here is the scoop on Carbs, for good throttle response you want smaller, for High RPM wide open throttle you go bigger. Your PerfRPM setup already says you want power across the RPM range 2500-5500 so this decision is made, not its time to match the carb to the system. On my motor (same as yours) I run a 650 DP which pulls hard from 2500 to the relatively conservative 6000 RPM chip in the Rev Limiter since I cannot afford to blow this motor and the cam is rolling off by 6k. A lot of folks will SWEAR run big as will bolt on and a dyno run will show good numbers with a big carb because you floor it and the air flows unrestricted and unmodulated through the RPM range. Works great on the drag strip. However, on the street or in an Autocross / race situation, you are modulating the throttle constantly in the mid ranges and a big carb is just not as responsive since the air flow speeds are slower with huge bores. Smaller bores have higher air speeds which keeps the gas atomized in the mid range so a wide open punch is immediately felt due to the speed of the air flow.

Key to all of this is your MAXIMUM RPM, if you plan to be running at 8K, go bigger e.g. 650 to 750. There is a large contingent on this site that will swear a 750 is needed on a 351. I had both and liked the 650 for Autocross. Didn't really notice much difference on the street, but remember, I chip at an admittedly conservative 6k. I would start with the 600 since you have it and during your break-in, it will be just fine. It is possible it will roll off at 6500 but if you don't spend a lot of time there it should give great throttle response. From there, see if you have any Muscle car buddies that have other carbs you can borrow and try. Watch your tailpipes if they get very light in color as it could be running lean which can burn a piston, you may have to rejet. Speaking of which, While you are doing all of this, its a good time to add a Air Fuel mixture gauge which will tell you how your mixture is doing. I wish I had one and folks that have 'em can dial in mixture across the RPM range including the accelerator pump and get it all right on a moving car which you cannot do on a dyno.

On Carbs, Holley is a go to carb for performance but frankly they are a PITA to set up correctly. For instance for years I didn't know the accelerator pump cam could be flipped around and give an more aggressive profile. I couldn't believe the difference, someone at the track mentioned it so we flipped it right there to try it. Because they are made for performance, virtually everything is adjustable and most people do not have the skill or tenacity to set one up correctly. Most of the alternatives are simpler in design and a nice alternative for a street / strip car. As I hear often on this site, just bolted it on and it was great.

Then there is the Vacuum Secondary vs mechanical decision. For an automatic the Vacuum is a go to because it responds to the RPMs and gives you what you need when the motor needs it. People with manuals tend to go with mechanical for better throttle response unless they are building a primarily street machine. Lots of learning to do to make an informed decision.

Good Luck...

ONe last thing, just in case it hasn't been covered, if you got the big 202 valves, it takes special pistons or a fly cut setup for 351s to divot the pistons to clear the big valves. I don't think its as much of an issue with 190s.
You're amazing! I may be messaging you when I get the 351w installed!
 

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If you go with the Edelbrock carb, I would politely suggest you order a calibration kit for it. It's a collection of jets, metering rods and springs for dialing it in just right. I ran an Edelbrock 600 CFM on a 351W in my '69 Cougar for many years. That carb ran great right out of the box, but some tweaking with the jets and metering rods made it a little better.

The manual that comes with the carb has good instructions for how to change the jets and metering rods to achieve the best air/fuel ratio. And you can do it all with the carb bolted to the engine.

Have fun!
 

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If you go with the Edelbrock carb, I would politely suggest you order a calibration kit for it. It's a collection of jets, metering rods and springs for dialing it in just right. I ran an Edelbrock 600 CFM on a 351W in my '69 Cougar for many years. That carb ran great right out of the box, but some tweaking with the jets and metering rods made it a little better.

The manual that comes with the carb has good instructions for how to change the jets and metering rods to achieve the best air/fuel ratio. And you can do it all with the carb bolted to the engine.

Have fun!
+1 on this. When I put the Edelbrock heads and RPM Air gap and cam on my little 289 I had to richen mine one level up so I think with your 351W if you decide to keep the original carb you will have to richen it up some as well. Good Luck.
 

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Discussion Starter #19
If you go with the Edelbrock carb, I would politely suggest you order a calibration kit for it. It's a collection of jets, metering rods and springs for dialing it in just right. I ran an Edelbrock 600 CFM on a 351W in my '69 Cougar for many years. That carb ran great right out of the box, but some tweaking with the jets and metering rods made it a little better.

The manual that comes with the carb has good instructions for how to change the jets and metering rods to achieve the best air/fuel ratio. And you can do it all with the carb bolted to the engine.

Have fun!
great tip - thanks! Will i need that kit if i go for a 650cfm too?
 

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great tip - thanks! Will i need that kit if i go for a 650cfm too?
Yes. The size of the carb really doesn't matter. While many hot-rodders will simply bolt-and-go with a new carb, it's always best to do some calibration. This is why you see so many classic vehicles spewing black smoke and making your eyes water at intersections. They didn't take the time to dial in the carb and it's running WAY too rich. (Some people mistakenly believe more fuel means more power, but that's not the case. It just makes for a dirty engine and spews unburned gasoline into the atmosphere.)
 
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