lavamadness

Here's what I've gathered so far (please correct me where I'm wrong):

The rule of thumb is you need 2cfm of air flow per cylinder for each hp you want to make. So with this, you can look at the flow data for cylinder heads to see if they'll support the power you're looking for.

Chamber size (in part) determines how much static compression the engine will have. (I'm sure I'll have more questions about this later on.)

For the intake runner volume, smaller volumes will cause the incoming air to have a higher velocity, resulting in more low-end torque, but with the downside of restricting flow at higher rpms. Higher intake runner volumes are good for high rpm breathing, but if they are too big, there's a lack of power down low.

1) Is it safe to say that the runner volume moves the powerband of the engine? Or is there more to it than just that?

2) How do you determine what runner volume is best for a certain application? I've had recommendations of 170cc (Vortecs), 180 Pro Toplines, 195 AFRs, and 200 Pro Toplines.

3) Does the runner volume make that much difference (for the sizes I mentioned)? If so, what would the resulting differences be?

4) This is more of me going off my limited knowledge, but would different cams help eliminate some of the differences in runner size?

For the record, I'm consider this for a 450fwhp daily driver.

AJ_92RS

1.) There's more to it than just that. Overall runner design plays a huge role in flowing air.

Some head manufactures would like you to believe that bigger runners flow more air than smaller ones, but that's not always the case. It all depends on the design of the runner.

2.) Again, for the most part, ignore runner volume. It's irrelevant compared to how much air a head will flow.

3.) It can, and should, but doesn't always.

Example...... I design a head with 180 cc intake runners that flow 220 cfm @ .500" lift. Then YOU design a head with 170 cc intake runner that flow 230 cfm @ .500" of lift.

See what I mean? Bigger isn't always better.

4.) Eliminating differences is the wrong approach. You want the cam to match and take advantage of the design and flow capabilities of the heads you are using.

Why buy a head with 220cc intake runners that flows 330 cfm @.700" lift, then choke it with a cam that only has 220* duration @.050", and peak lift is at .500"???

RB83L69

1. For an engine of a given displacement, that is true. However, a port that would drown a 305 until it reaches 7000 RPM might be inadequate for a 400.

2. Be realistic with your HP, and therefore flow, requirements. 450 HP in a daily driver is a tall order. The 2 HP / CFM rule of thumb is accurate enough to use for the case at hand. That would equate to about 225 CFM, or actually just a little more most likely, to make 450 HP. Realistically you'd probably want 235 - 240 CFM.

3. Yes the runner size will make a big difference. However, there's more to it than that; Vortecs will flow better for a given runner volume than heads with the ports in the traditional location. You also need to consider the rest of the motor around the ports; TPI for instance de-tunes flow event above 4500 RPM or so, and runs out of flow completely at about 5000 RPM in a 350, so if you're going to run that, adjust your flow goals to match the characteristics of the intake tract. A mismatch there will slow the car down, compared to using smaller but properly matched parts.

4. There are 2 ways to get more flow through a time-proportioned valve: open it farther, or hold it open longer. Keep in mind, there's no such thing as too much cam, only not enough motor. That being said, you can run into the issue where the cam will produce peak volumetric efficiency due to its valve event timing, at an RPM where the flow requirements are beyond the port's capability. This is commonly referred to as "over-camming". It should be avoided at all costs.

Realism and honesty are the keys here. Thinking that you're going to take a 2.73 geared LG4 or TBI car with the stock converter and sticking a motor in it that doesn't make power until it hits 4500 RPM is a great way to waste lots of gas, and money. If you're using some little motor like a 350, that's what you'll end up with by the time you reach that power level with it.

I don't know what you've got now, or what your goal is, or the rest of your car, or what the most powerful car you've ever driven is; but I'll tell you right now, 450 HP is a bunch of power. Most people have no idea how much power that is. Odds are you would tear up enough stuff often enough that it wouldn't be real fun to own.... you might say high-maintenance. And it requires that the other systems of the vehicle can support it; traction, fuel delivery, etc. Just sticking all that power in an otherwise unprepared car is a recipe for a big tire bill and lots of problems and disappointments.

lavamadness

Right now, what I've got (89 L98) would be the most powerful car I've driven. (Next would probably be a N/A Mk4 Supra.) So honestly, I wouldn't know what 450hp is like. When deciding on a goal, I said I wanted a 12 second daily driver. For a 3600lb car, I figured that would be 400 (high 12s) to 500(low 12s) hp at the crank. I realize that with traction and other mods that you could get 12s with less, so as I'm planning things I've been ball-parking it at about 450. If I don't make 12s (or 400/450hp) but it's still fun to drive, not a problem. I am more interested in the daily driver part. I also realize that other parts of the car (rearend, tranny, intake) need to be upgraded/matched to the engine and its output. The route I've been taking is to plan the engine, then move on down the line.

I do want to upgrade my car. I want to do what I can to minimize any costly mistakes. I'd hate to spend a whack of money and, as you said, it not be enjoyable. There're just so many variables that it's quite overwelming. I'm more than open to any suggestions or advice.

Back to the cylinder heads... for the same head design, and same displacement engine, the size of the runner basically moves the powerband up and down the rpm range? I guess what I'm asking is, what would the difference be between the 180cc and the 200cc Pro Toplines for example? Their design is similar right? Just the runner size differs? So how would choosing one over the other affect things for the rest of the engine?

Thanks again for the replies. They are greatly appreciated.

lavamadness

TTT

What would the difference be between 180cc and 200cc Pro Toplines?

How would choosing one over the other affect an engine, all else with the engine being equal.

What would you change with an engine to take advantage of the difference between the heads, if anything.

formularpm

The 200ccs will probably need more RPMs to make peak hp. Youd need a cam to match the bigger heads, and a bottom end to support the necessary RPMs. You also have to consider the drivetrain, stall, gears, etc...

lavamadness

Okay, that's what I thought. Just wanted to make sure I was on the right track.

I guess the problem I'm having is, when trying to decide on a cylinder head, how do you know if it takes more rpms to get peak hp than you want to rev? It's it trial and error? Check on Desktop Dyno or something? Experience?