Lurked long enough

[AeroCoupe]

Pretty vague on the intake. Ask for a flow sheet on it at 350 cfm doesn't mean anything without knowing the inches of water column. I am also not a huge fan of just flow rate, what was the port velocity? Slow velocity means lazy down low and high velocity means less lazy. You would need some AFE 205's or 225' or the like to keep up with the intake and at that point you better have some cubic inches and an rpm range from 3500 to 8000 to make it work optimally. Stick with an Explorer upper and lower and if you want to jazz things up send them to TMoss to port the lower and clean up the upper.

 

[VERGAZ2]

A dual pattern cam will help maximize the exhaust side to more closely resemble the intake flow. Right or wrong, here's how I think of it: the intake valve opens a certain distance for a certain amount of time and allows X amount of air/fuel into the cylinder. Then, the compression and power cycle produce X amount of exhaust. Since nothing was added, you still have to expend the same volume of exhaust as you'd want to bring air/fuel into the cylinder for the next intake cycle, so the exhaust valve needs to be the same size and open the same distance and for the same length of time. Since it's almost physically impossible (there are exceptions, of course) to match the valves and ports size for size, the only way to help equalize them is to adjust the amount of lift and length of time that they're open. So a dual pattern cam generally has longer duration and more lift on the exhaust side to help equalize flow.

I've shared this video here before, as I know a couple others have, I think it's a good watch to help get a better handle on cam selection.



He gets into single/dual pattern cams at around the 35 minute mark.

I've seen a rule of thumb that when you divide the exhaust flow by the intake flow, & then every percent less than 75% wants 1.5 degrees of exhaust duration @ .050".

Maybe this gives a decent idea of why split patterns work so well on GT40 style heads. Let's take the GT40X heads, for example. Skip to the second list, at the bottom, on this:

So, at .600, it'd be around 69.8%, which would need about 7.7 degrees. The XE274HR, a pretty good cam that would have manners similar to a B-cam is 224/232 @ .050". 8 degrees!

So voila! And on top of the right split, it has 1 degree more LSA, which I'll bet makes it even more street friendly than the B-cam. The extra lift should help a bit, too.

Now, most that are familiar with nitrous cams know that they generally have even more duration on the exhaust side, and that jibes with the idea that injecting nitrous is equivalent to having an even bigger intake CFM flow.

Just some food for thought for ya.

That dude's video is very informative as were both of your posts. This is the first time I've ever had to consider any of these numbers and calculations so I have just a couple dummy questions.

1. when you don't have an extended exhaust valve opening duration, does the unexpelled exhaust stay in the combustion chamber and block fresh air and fuel from coming in? is that why you want to get the extra time for that valve open so it all can get out before the cylinder is reloaded with explosive stuff? why don't they do that from the get-go? (genuine question not sarcasm)

2. that second cam from comp cams the 224/232 means the exhaust valve puts out even more than what's taken in so there's no lingering fumes for the next intake cycle? so it's bringing in almost as much volume on intake and spitting out a lot more to run smoother but also deliver similar power output at full throttle and at the same time better parking lot manners? I like a lopey cam but I don't think a small block Ford requires it ive just always heard about the "B" cam and it being a Day 2 type of upgrade

thanks to all of you for your answers

 

[VERGAZ2]

Well, you'll likely find if it's a stock head/cam and gearing it will be a dog (with a broke leg) around town, moves the RPM range up and you'll likely lose torque down low, needs different heads and cam (and prolly a gear change) to be useful.
JMO

ok I'll keep on the explorer intake/heads hunt then thank you. it looked cool is the only reason I asked

 

[FastDriver]

You're on the right path with your thinking in #1. Adding duration @ .050 and gives more time to both clear the spent gasses, & adds overlap to scavenge to get the intake charge started. Don't overlook the added lift, which means it's going to flow more during that time, too. Yet, the same adv exh duration means that the comp gets there due to more aggressive lobes. The 274HR is def going to make better power on a GT40 head. All of that on the same LSA.

A little offbase in #2. It's not going to bring in "almost as much," it will definitely bring in more. It will expel more, and it will more efficiently make use of the exhaust charge to initiate the intake charge.

For driveability, look at overlap. B cam has 0 at .050" but 60* at .006. 274HR has 4* @ .050" but only 54* at .006, again due to the faster ramp rates. A bit of a conflicting signal. My guess is about the same driveability, or maybe a slight edge to the 274.

B-cam advantages? Softer ramp rates means easier on the valvetrain and more compliant of weaker springs. Cheaper. Can say you have the almighty B! *Might* squeeze out or equal the 274 on the low end.

 

[VERGAZ2]

You're on the right path with your thinking in #1. Adding duration @ .050 and gives more time to both clear the spent gasses, & adds overlap to scavenge to get the intake charge started. Don't overlook the added lift, which means it's going to flow more during that time, too. Yet, the same adv exh duration means that the comp gets there due to more aggressive lobes. The 274HR is def going to make better power on a GT40 head. All of that on the same LSA.

A little offbase in #2. It's not going to bring in "almost as much," it will definitely bring in more. It will expel more, and it will more efficiently make use of the exhaust charge to initiate the intake charge.

For driveability, look at overlap. B cam has 0 at .050" but 60* at .006. 274HR has 4* @ .050" but only 54* at .006, again due to the faster ramp rates. A bit of a conflicting signal. My guess is about the same driveability, or maybe a slight edge to the 274.

B-cam advantages? Softer ramp rates means easier on the valvetrain and more compliant of weaker springs. Cheaper. Can say you have the almighty B! *Might* squeeze out or equal the 274 on the low end.

Much appreciated info..Is the B cam a meme/ joke nowadays or just an actual Meta piece of the 'game' that's since been replaced with more efficient stuff? Almost all of my knowledge comes from 20+ year old forum posts and old 5.0 Fast Fords or whatever magazines I read when I was 9 in 1996 so I don't know if I'm getting goofed on with the B cam talk ie "almighty" or what. normally I'm a smart ass troll online so I know I'm a good mark for a laugh for the old heads right now with all of my rube questions. if this 274hr piece from COMP does most or more of what the B does with better manners then I'm probably into that especially with the nitrous talk.....
I have no idea about any of that but always liked the idea of it just because... is that still a thing people are doing? bottle, tank warmer, lines to intake for a dry shot? not looking to blow my motor up but just the idea of it is appealing and kind of in line with my overall build ethos...bolt-ons that my 9 year old self would have been reading about in the magazines...

found a 1997 v8 explorer locally when I finally got to it..... motor yanked but they're still out there I was only a couple days late on it
going to st Paul summer nationals in a couple weeks maybe I can find someone there with an extra set

 

[FastDriver]

B-cam memes are just for fun. Split pattern is definitely better in this application. Custom from Ed would be better. Xe 274HR is not a bad selection, otherwise, IMO.

 

[VERGAZ2]

B-cam memes are just for fun. Split pattern is definitely better in this application. Custom from Ed would be better. Xe 274HR is not a bad selection, otherwise, IMO.

ok cool. first things first gotta get the intake and heads figured out and go from there. in the meantime I have a paint chip repair kit on the way LOL

 

[General karthief]

Don't forget to measure that back-pressure, very important

 

[Noobz347]

 

[AeroCoupe]

Or...

 

[VERGAZ2]

goddamit

 

[Noobz347]

 

[AeroCoupe]

......

 

[AeroCoupe]

 

[General karthief]

The lowly B cam, it deserves better!
B Cams Matter!!!!

 

[FastDriver]

lmao... Hey man, FWIW, I had in my head you were going with a GT40 style head when I recommended the 274. And, it'll work pretty decently with most inline 302 sbf heads, but let us know what heads you actually decide on.

In general, you pick the hp and RPM you want to make it at, then the displacement/motor right for the application, then heads that will flow enough and provide good velocity, then intake and exhaust with the right flow and runner lengths, and finally the cam.

Nothing is chosen in isolation. There are usually constraints based on the finances and desired platform. So, let us know as the situation develops and we'll try to help with more info.