Boy, talk about pot calling the kettle blackKK6695GT said:Way too much bench racing and hype in picking an oversized intake, carb, and cam out in the world.
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.
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KK6695GT said: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.........
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: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.......
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: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.
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