Just researching some heads for a future endeavor...Looking at the ARF 215RRs and Brodix 18*. The brodix heads say they are great for engines that spend time above 4500rpms. Now obviously this doesnt sound like a great head for a street car. But what happens below 4500. Say you were to run a solid roller cam with a reasonably mild demeanor, say ~250 @ .050, and ~.650 or so lift. Is this thing just going to fall on its face if you try to run it at a lower rpm like 1500-3000? And where would the rpm range extend to, if your shortblock requires you to stay below 7500 is it totally pointless to run that big of a head since you only have say 2-3000 worth of rpms for street driving?

All this is very rough and havent put a lot of thought into it. Just want something that will make 600+ at the flywheel but remain relatively streetable (relatively streetable to me means it can be driven on the street, doesnt have to be grandma friendly or anything close).

Im sure I will come up with other questions and all, but Im just playing things out through my head way before I start the project.

 

Well, nobody wants to answer that question for now, heres another.

In very very basic language for lack of a better way to ask the question. How do you figure out how much head is needed to fill up a given amount of cylinder volume?

I know this is a very complicated discussion im sure, but is there kind of a rough way to figure it out, or in the opposite direction, how many cu.in. are needed to suck up the amount of head flow you have.

The way I am looking at it now is the biggest variable is the cam, but well worry about that later, just assume when youre explaining that the cam is designed correctly for the head flow/cu.in. to simplify it for now.

I tried going through it in my limited fluidynamics brain and all I came up with was converting CFM down to cu.in per second and got something crazy like 9200 cu.in.per sec for a 320cfm head. Which if a 430cu in cylinder is only 54 cu in, doesnt make sense.

 

The cubic inches of the engine will also be a factor. If you had a 400 small block than that head is not so big anymore. On a 350 you would have to wind it up to take advantage. So if you want 600HP on the street I would look into one of the bigger small blocks such as a 427. All it takes is money. Allen

 

Well I've never been afraid to make a fool of myself. So here's my attempt at an explanation.

So in generally, if you think about the dyno graphs you've seen and the curves on them. With these heads your peak hp is going to be way up in the 5500 to 7000 rpm range. Idle speed will probably be 1200 to 1500. And your torque curve is also going to be pushed toward the high end, and may be quite steep instead of flat. This doesn't mean that the car wont run at low rpm's, it just may not be comfortable.
Unfortunately I don't think any of this is set in stone. Rear end gearing alone can change this dramatically.

 

Im kindof looking more for a mathematical explanation of how it all works. I understand that big heads and big cams raise rpm ranges, but i would like to know how to figure out the CI required for a certain head, or the head required for a certain CI, and how changing one of the other affects rpms and driveability.

 

There is a lot that goes into this....

There are some basic formulas that if you do a search on Mindgame you might find. It gets a little hairier than that because you can go by the physical measurements or by the actual area that the port actually flows air in......

RPM on a set of heads depends on the cubes..... more cubes less rpm.

Bret

 

this is rough but may help http://www.bgsoflex.com/flowcalc1.html this say's you'll need close to 300 cfm to make 600hp the engine size determines the rpm the power is made and the combo determines is the power capabilities of the heads will be met. good luck

 

Ok, so say for example I build a 434, lightweight valves (TI or hollow), lightweight springs, TI retainers, and lightweight pushrods rolling on a solid cam. If I want to keep my max rpm around 7500 and want to make as close to 700fwhp as possible, would you choose an 18* head with ~250cc port volume flowing 350cfm, or a 23* ~23xcc port volume flowing ~320cfm?
Edit: Both making max compression on pump gas.

 

I don't think you'll need 434 AND 7500 r's to get 700 fwhp on pump gas.

If Joe Sherman's 600 hp @6500 366 pump gas Engine Masters engine did it with about 300 cfm 23 degree heads, 350 cfm 18* should be enough for 700 with a lot less than 7500. My guess is 6500 or so should suffice, and I think maybe a 406 would be enough. It certainly should be cheaper than a 7500 rpm 434.

Look at the 2004 410 cube Engine Masters pump gas small blocks for some ideas. Remember the Chevys were restricted to 23* heads and 6500.

 

If I were to want an aftermarket block, dart or motown, since I remember reading Joe Sherman saying that an aftermarket block is worth ~20hp in some situations. Wouldnt you rather build a 434 or larger, since it would cost almost identical? Dont know whether a 4" crank fits in a standard SBC block, but If I had to pick up the widened pan rail version I can make my own pan no big deal, so thats not a worry.

A 434 over a closer to 400 inch would just make it more streetable, right?

And if you think it wouldnt be that hard to make that power, I could probably stick with some Pro 1s ported very well to keep the runner size and RPMs down right?

Just out of curiosity, how much power do you think the combination I mentioned above would be worth with a super victor or comparable single plane converted over to EFI with FAST?

 

It's not the port volume as much as the size. You can have one head that is 250CC's and one with 225CC's and the 225 have the larger port. High ports have longer runner's=more CC's.

 

read close on the engine masters engines the cranks are all ground down as small as possible. small journal rods and every kind of coating possible to keep friction down. they also mostly have roller cambearings, and more $ in custom machine work than most people can afford so they are not going to make that kind of power for the lay man but it is a good place to learn engine dynamics. most chevy heads have the same length runners so the cc's is a good place to start but keep that in mind. it is the avg. runner diamater that is the biggest affect on low end tq. also you can keep the tq in the same place with a larger runner as long as the air that is capable of flowing through them keeps the same or greater velocity. the 18deg heads have a more direct shot to the cylinder so one vs a 23 deg head with the same runner size and flow numbers should make a little better low end because the airflow is more lienier and should keep turbulance down and produce more tq and hp.

your engine combo with the correct cam and combo shoudn't have a problem making close to 700hp on pump. but you have to have a very well sorted out long block and take advantage of every last little hp. if you want it to keep good vacume and be streetable

just my opinion