Hi guys, I have a 68 coupe with a mid 70's 302 thats been bored 30 over, it has Duraspark 2 ignition and the original Autolite 2100 set up. I would like to switch to a 4 barrel and am leaning towards Edelbrock Performer intake and 600 cfm carb. Anybody that has any feedback on this swap, benefits, problems, details, please reply, thanks.
Carb swap
- Thread starter puron
- Start date
dennis112
15 Year Member
I too recommend the RPM over the standard Performer. It is a decent dual plane intake that will work well with other performance modifications that you might plan in the future.
Your stock pump is plenty. The Holley 2 bbl swap is a bolt on. The only mod is a slight re-route of the fuel line. And don't forget a fuel filter before the carb, that's where 75% of problems with a Holley occur, the other being owners who constantly "fiddle" with em cause the rest of the motor gets out of tune.
Way too much bench racing and hype in picking an oversized intake, carb, and cam out in the world.
Look at the manufacturers specs for the items you're looking at. Bulding a motor? Then spend the $10.00 for a PAW catalog (1-818-678-3000) and get all the technical info that comes with it!
Edlebrock performer is idle to 5000 RPM. Edlebrock Performer RPM is for 1500-6500 RPM. Are you strictly racing racing or on the street? Street - then you don't need the 1500-6500. Unless you have low gears and a higher stall torque converter, you're not running in the 1500-6500 range, you're down in the idle to 5000.
For a carb, CFM=Cu In x RPM ÷ 3456. 302x6000÷3456=524 CFM
302x5000÷3456=436 CFM. And this is assuming 100% efficiency (80-85% is more like the norm) 524x.85=445 CFM
600 CFM Edelbrock will be more than enough. 500 CFM 2 barrel is not a
good idea. Will bog. Stock Autolite 480 4 barrel works great.
Cam -Edlebrock Performer will work perfectly.(Again not the Performer RPM).
These people that run a big oversized lumpy cam, 750 double pumper, and a single plane intake on their 302 on the street may have a bad azz sound cruising by at 5 MPH and it may sound like a killer combo while bench racing, but run them from stoplight to stoplight and I'll guarantee you'll beat them to the next stoplight everytime with a properly sized combo.
Look at the manufacturers specs for the items you're looking at. Bulding a motor? Then spend the $10.00 for a PAW catalog (1-818-678-3000) and get all the technical info that comes with it!
Edlebrock performer is idle to 5000 RPM. Edlebrock Performer RPM is for 1500-6500 RPM. Are you strictly racing racing or on the street? Street - then you don't need the 1500-6500. Unless you have low gears and a higher stall torque converter, you're not running in the 1500-6500 range, you're down in the idle to 5000.
For a carb, CFM=Cu In x RPM ÷ 3456. 302x6000÷3456=524 CFM
302x5000÷3456=436 CFM. And this is assuming 100% efficiency (80-85% is more like the norm) 524x.85=445 CFM
600 CFM Edelbrock will be more than enough. 500 CFM 2 barrel is not a
good idea. Will bog. Stock Autolite 480 4 barrel works great.
Cam -Edlebrock Performer will work perfectly.(Again not the Performer RPM).
These people that run a big oversized lumpy cam, 750 double pumper, and a single plane intake on their 302 on the street may have a bad azz sound cruising by at 5 MPH and it may sound like a killer combo while bench racing, but run them from stoplight to stoplight and I'll guarantee you'll beat them to the next stoplight everytime with a properly sized combo.
Boy, talk about pot calling the kettle blackKK6695GT said:
You've also given some incorrect info here. First off , a dual plane carb intake designed for 1500-6500 rpm's is NOT too much for a stock or mild motor to handle. There's been THOUSANDS of these used with great success for forty years now. Myself included. I've used the Ford A321 ( same as the "Cobra" high rise, older Edelbrock F4B, Weiand Stealth, also sold thru Ford parts dealers "back in the day" as the C9OX),and the Edelbrock Performer RPM on small blocks, and presently have a 428PI intake on a mostly stock 390 in my 68 Merc. All have worked great with stock to mild engine builds. Secondly, don't tell someone a Holley 500 will bog on a stock 302, that's BS, plain and simple. Obviously you've never used one. I have, several times on at least 4 different engines, the first of which was a stock 302 in a 69 Ford Club Wagon van. It worked great then. ZERO problems, NEVER bogged it down. And I'm talking about a 6,000 lb pig on wheels here. With an automatic trans.Didnt mean to cause a fracas, I ordered the Holley carb and am going to see what happens, this car is not a drag racer, I just wanted a little more punch in the lower to middle range without going to all the trouble of a intake swap. My 302 is bored out, but has a stock cam, Duraspark, and dual exhaust with the K code manifolds, and im thinking it just needs some more gas, it runs smooth with the 2100 carb but it runs out of steam pretty quick. Im hoping this will work, I will post my findings after it gets here from Jegs.
500 CFM no. But yes I have used an Autolite 1.23 venturi 424 CFM carb on a 302 and it will bog if you nail it too hard at idle. You can attempt to compensate with more accelerator pump but that's not the answer.
A Stock 2100 1.14 Mustang 2 barrel is rated for 300 CFM. The stock 4100 1.08 flows 480 CFM and the HiPo 1.12 flowed 600 CFM. Both the 4 barrels are vacuum operated for a reason - so they don't pull in any more than the engine is asking for.
There's physics involved here, not just bench racing. The large venturies in a 500 CFM 2 barrel or intake runners that are too big don't give you the proper velocities and mixes at low RPMs on the street.
Yes the Performer RPM is a dual plane manifold, but it's recommended range is 1500-6500. If you're not running 6500, you're sacrificing low end performance for a top end you'll never use. All you need is the standard Performer. Last I new, idle on a street motor was 500-750 RPM. With no headers, a stock converter, high gears, etc, (ie a basically stock street car), that's quite a few inefficient feet to cover until your motor finally winds up enough to overcome the low velocity issues (and poor performance) you created because you oversized everything. Until you finally get the RPMs up to where you're efficient, the other guy is pulling ahead...
I've been putting motors together for 27 years. This guys asking about a street driven motor. I'm not gonna get in a pissing match here but I still stand by my original post.........
A Stock 2100 1.14 Mustang 2 barrel is rated for 300 CFM. The stock 4100 1.08 flows 480 CFM and the HiPo 1.12 flowed 600 CFM. Both the 4 barrels are vacuum operated for a reason - so they don't pull in any more than the engine is asking for.
There's physics involved here, not just bench racing. The large venturies in a 500 CFM 2 barrel or intake runners that are too big don't give you the proper velocities and mixes at low RPMs on the street.
Yes the Performer RPM is a dual plane manifold, but it's recommended range is 1500-6500. If you're not running 6500, you're sacrificing low end performance for a top end you'll never use. All you need is the standard Performer. Last I new, idle on a street motor was 500-750 RPM. With no headers, a stock converter, high gears, etc, (ie a basically stock street car), that's quite a few inefficient feet to cover until your motor finally winds up enough to overcome the low velocity issues (and poor performance) you created because you oversized everything. Until you finally get the RPMs up to where you're efficient, the other guy is pulling ahead...
I've been putting motors together for 27 years. This guys asking about a street driven motor. I'm not gonna get in a pissing match here but I still stand by my original post.........
69Rcode_Mach1
Active Member
KK6695GT said:
I disagree with this. This isn't a pissing contest so don't worry. D Hearne is trying to show you his point of view, and he is not getting upset about it hence the smilies. Anyway that carb was not tuned right if it was bogging. You can run a 600cfm Holley on a 302 just fine with no problems if you tune it properly. Although I agree that a 500cfm carb would probably be better. I had the performer manifold and it is a waste of money. The only real difference in it with a stock manifold is the fact that it is aluminum. An RPM will produce more power hands down even from idle than a peformer. The RPM doesn't have huge ports, it will not limit an engine. On top of that 1500 is right around where the stock stall is so there is no way it would hinder it even if it were terrible to 1500rpms, and if it is a manual then there is no problem whatsoever.
Maybe I'm just reading too much into the total BS line.
I'll try to get back to my original point - a Holley 600 CFM or better yet an Autolite 480 will work much better than a 500 CFM 2 barrel on a street driven daily driver motor. Again, I'm referencing a street driven motor with no gears, cam, heads, or torque converter. A smaller 4 barrel will run more efficiently and give you a better performance then that large of a 2 barrel.
My reason for starting in on this thread - Sticking a large carb on a stock intake will give you drivability issues and will not perform to it's optimal potential on a small stock street motor.
Getting off my original point and trying to give him some insight I went off on intakes and sizing - the Performer looks very simliar to the stock 289 intake but it is definitely larger. The ports and the runners are definitely larger. The runners physically drop lower into the lifter valley, that's maybe why it doesn't seem as obvious up on top. I have one myself and I have pictures of them side by side....
The Performer 289/302 has the same runner configuration as the stock 289/302 intake but has a carb flange height of 3.50/4.75". A performer RPM is still a dual plane but has a different runner configuration and a carb flange height of 4.30/5.50". In other words, still larger runners. Bigger runners at low RPMs = low air velocties and poor mixtures for combustion. My point on intakes was some improvement can be good but too much can also be bad. Yes the Performer RPM is not that much larger than the standard Performer. I was just trying to explain the reason for not going larger if you didn't need it. There are basic laws of physics involved in the operation of a combustion engine. That's why the winning racers are the winners and the guys who don't follow the mathmatics are the ones in 2nd place. To simplify my original 750 double pumper example, go larger. Dual quads on a street motor are a perfect example. Those look cool and sound great bench racing but those are strictly for high RPM use. That's an example of as where I was going with a properly sized vacuum secondary street combo will beat him everytime - on the street.
Efficiency = Power
The point of my original thread was, everything works as a package. Big intake runners, big cams, big carb ventuies, big valves in the head, big ported heads, steep gears, they all work great for high RPM racing and sound cool when you're bench racing. What I was trying to help him understand is going overboard in just one area can be detrimental to overall performance. Choose your parts realistically. Maybe you'll make more improvements later and maybe you'll need a bigger intake later. But everything is only as good as the weakest link.
Lets try another area. An easy example of a single "performance" change would be gears. Yes they're your biggest bang for the buck but again there are limits and everything is relative to the complete car package and how you're actually driving/using the car. The don't fear the gear crowd would make you think the taller the gear, the bigger, badder, faster, and quicker you'll be. 4.10s for racing my be great, but for street driving, they could be your weakest link. Unless your motor and car is set up to support the higher RPMs those gears will require, there are downsides. They may be great for racing, but for the street with a stock motor, you will probably quickly be out of your usefull RPM band. And, without an overdrive transmission, you loose high speed cruising and if you're using a 4 or 5 speed you'll be shifting at much lower speeds sometimes with 1st gear almost useless.
Everything works as a package and you're only as good as your weakest link. You must choose your parts wisely.......
I'll try to get back to my original point - a Holley 600 CFM or better yet an Autolite 480 will work much better than a 500 CFM 2 barrel on a street driven daily driver motor. Again, I'm referencing a street driven motor with no gears, cam, heads, or torque converter. A smaller 4 barrel will run more efficiently and give you a better performance then that large of a 2 barrel.
My reason for starting in on this thread - Sticking a large carb on a stock intake will give you drivability issues and will not perform to it's optimal potential on a small stock street motor.
Getting off my original point and trying to give him some insight I went off on intakes and sizing - the Performer looks very simliar to the stock 289 intake but it is definitely larger. The ports and the runners are definitely larger. The runners physically drop lower into the lifter valley, that's maybe why it doesn't seem as obvious up on top. I have one myself and I have pictures of them side by side....
The Performer 289/302 has the same runner configuration as the stock 289/302 intake but has a carb flange height of 3.50/4.75". A performer RPM is still a dual plane but has a different runner configuration and a carb flange height of 4.30/5.50". In other words, still larger runners. Bigger runners at low RPMs = low air velocties and poor mixtures for combustion. My point on intakes was some improvement can be good but too much can also be bad. Yes the Performer RPM is not that much larger than the standard Performer. I was just trying to explain the reason for not going larger if you didn't need it. There are basic laws of physics involved in the operation of a combustion engine. That's why the winning racers are the winners and the guys who don't follow the mathmatics are the ones in 2nd place. To simplify my original 750 double pumper example, go larger. Dual quads on a street motor are a perfect example. Those look cool and sound great bench racing but those are strictly for high RPM use. That's an example of as where I was going with a properly sized vacuum secondary street combo will beat him everytime - on the street.
Efficiency = Power
The point of my original thread was, everything works as a package. Big intake runners, big cams, big carb ventuies, big valves in the head, big ported heads, steep gears, they all work great for high RPM racing and sound cool when you're bench racing. What I was trying to help him understand is going overboard in just one area can be detrimental to overall performance. Choose your parts realistically. Maybe you'll make more improvements later and maybe you'll need a bigger intake later. But everything is only as good as the weakest link.
Lets try another area. An easy example of a single "performance" change would be gears. Yes they're your biggest bang for the buck but again there are limits and everything is relative to the complete car package and how you're actually driving/using the car. The don't fear the gear crowd would make you think the taller the gear, the bigger, badder, faster, and quicker you'll be. 4.10s for racing my be great, but for street driving, they could be your weakest link. Unless your motor and car is set up to support the higher RPMs those gears will require, there are downsides. They may be great for racing, but for the street with a stock motor, you will probably quickly be out of your usefull RPM band. And, without an overdrive transmission, you loose high speed cruising and if you're using a 4 or 5 speed you'll be shifting at much lower speeds sometimes with 1st gear almost useless.
Everything works as a package and you're only as good as your weakest link. You must choose your parts wisely.......
69Rcode_Mach1
Active Member
Of course and you bring up a good point. I agree with what you are saying because you are correct. The only thing I am disputing is the intakes. If you are going to spend the money you might as well go performer RPM it is not detrimental in any way, in fact it has gains on the performer even with a bone stock engine. A 4 barrel 600cfm carb would be better than a 2 barrel 500cfm. D. Hearne was just giving him an alternative, if he didn't want to change intake manifolds and still get a little more kick out of the engine. The engine should work fine if he tunes it properly maybe a touch of throttle response would be sacrificed. It is not the best choice though for a street driven car that you are aiming to get the most mpg out of, but I think it can be made to work fine. BTW I don't know if anyone has welcomed you yet, so welcome to stangnet. People are friendly here so don't take anything anyone says offensively. The only way we can all better our knowledge is to take in everybody's experiences.
Thanks for the welcome.
So many times you get on these forums and the "everything should be bigger and badder crowd" just throws stuff out there like if it's good on a a race car, it'll be good on your car. Inexperience combined with whatever seems like the cheapest route combined with too much bench racing hype has a tendency to create problems sometimes down the road because someone didn't plan ahead.
I was just trying to get Puron to think before he jumped at the cheaper 2 barrel carb solution because in the long run it really wasn't going to be his best choice. It's hard to get on here and type and fully describe what you're trying to say sometimes. Performer vs Performer RPM I agree no big difference. I was trying to explain basic intake differences as in not using a single plane or something, didn't mean to attack the RPM, was trying to explain there are downsides to oversizing on the street and it just didn't come out right...
Was just trying to give a suggestion and I probably felt attacked on the "total BS" thing and shouldn't have taken it that way.
Anyhow, thanks for the welcome. So far this StangNet site has been a real nice forum to peruse!
So many times you get on these forums and the "everything should be bigger and badder crowd" just throws stuff out there like if it's good on a a race car, it'll be good on your car. Inexperience combined with whatever seems like the cheapest route combined with too much bench racing hype has a tendency to create problems sometimes down the road because someone didn't plan ahead.
I was just trying to get Puron to think before he jumped at the cheaper 2 barrel carb solution because in the long run it really wasn't going to be his best choice. It's hard to get on here and type and fully describe what you're trying to say sometimes. Performer vs Performer RPM I agree no big difference. I was trying to explain basic intake differences as in not using a single plane or something, didn't mean to attack the RPM, was trying to explain there are downsides to oversizing on the street and it just didn't come out right...
Was just trying to give a suggestion and I probably felt attacked on the "total BS" thing and shouldn't have taken it that way.
Anyhow, thanks for the welcome. So far this StangNet site has been a real nice forum to peruse!
69Rcode_Mach1
Active Member
dennis112
15 Year Member
Welcome to the site KK6695GT. 
I agree that there is a tendacy for overkill on many of these websites, but there are also those in the know who will call BS should there be something afoul. If someone mentioned a Vic Jr., they certainly would have been shot down.
This is a "performance" website and most of us are looking to get the best bang of the buck now AND in the future.:SNSign: For the money spent and for the possible future gains, at least in this case, a larger dual plane seemed like a wise choice. I supposed that we should have asked Puron what his long term goals were before making recommendations.
Certainly not here to rag on KK6695GT (or anyone else.) We need to remember that a little friendly debate is always good--that is how we learn.
I agree that there is a tendacy for overkill on many of these websites, but there are also those in the know who will call BS should there be something afoul. If someone mentioned a Vic Jr., they certainly would have been shot down.
This is a "performance" website and most of us are looking to get the best bang of the buck now AND in the future.:SNSign: For the money spent and for the possible future gains, at least in this case, a larger dual plane seemed like a wise choice. I supposed that we should have asked Puron what his long term goals were before making recommendations.
Certainly not here to rag on KK6695GT (or anyone else.) We need to remember that a little friendly debate is always good--that is how we learn.
You speak well, like you know your stuff, but the facts are facts, putting a 500 cfm Holley on a stock 2 bbl intake, does not cause driveability issues. I know, I've tried em too many times, on several engines. The last one, it worked better than the Autolite 2100. And a large runner DUAL plane intake also doesn't affect bottom end on a stock motor ( long as you don't plant a too large carb on it, which is likely why some have experienced such: i.e. putting something like a 750 DP Holley on a stock 302 with any intake will do that) You want soggy bottom end ? Use a single plane. Holley used to advertise a 20 hp gain from just a 500 2 bbl, this was way back when (30 years ago) Dollar for dollar, it's the cheapest & easiest hp gain you can get, if you're not mechanically inclined and don't want to swap intakes too.KK6695GT said:
there was a hot rod article on this very thing a few years back. they wondered if over carbing an engine was detrimental to power. turns out on a dyno it wasn't. they ran 1000cfm dominator carbs on exact same engine and it made same power. the article somewhat disproved the urban myth of over carbing.KK6695GT said:
Well, theory aside, I got my carb and installed it today, here is my feedback! The Holley 2300 fit exactly in place of my Autolite 2100, Holley even provides a new base gasket. I had to mess with the fuel line, went to NAPA and got a 90 degree 3/8 fitting to attach new fuel line and an inline filter to. Strange Holley doesnt supply a fuel line connection. The linkage hookup required fabbing up a new retaining clip for the throttle rod, the old one wouldnt fit and the Holley one didnt work either. I noticed my pedal wouldnt open up the carb all the way, found my old pedal linkage had been tromped on so many years the pedal needed to be bent up from the floor a bit. I left the choke wide open and didnt add a choke cable, being in Myrtle Beach SC I dont have warm up problems anyway. The car fired up and idled pretty well right off the bat. I installed a new Holley chrome air cleaner and a vented oil fill cap and took it for a spin, and found at least 30 horsepower has been added. Throttle response is crisp, no bogging at all. It burns rubber from a dead stop, chirps the tire going into second (C4 trans) and has strong punch stomping on it at 60. I ran it up to 100 and it pulled strong all the way. Huge improvement over the old Autolite, and the carb, air cleaner and oil cap cost 280 bucks from Jegs. I dont think id get that much more from a 4 bbl carb in this tune so I am real happy with this set up. Thanks to D Hearne for his advice and everybody else here too.
dennis112
15 Year Member
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