This is really common thinking but it couldn't be more wrong, especially the comment about larger heads making more tq across the whole rpm range. Quickest way to kill low rpm tq is with intake ports that are too big for the application. A small plenum will also kill low rpm torque compared to a larger one.

 

What do you base your CSA comment on? What is the head's CSA and what does the engine want, and at what RPM? Are you talking about minimum CSA, average CSA, CSA @ the short turn, CSA through the valve...???

 

Max volume of air is secondary to the velocity. An engine is an air pump...it displaces a positive amount of air based on bore, stroke and rpm. This does not change. The cylinder heads and cam regulate that airflow to determine how much power the engine is going to make, and at what rpm. IDEALLY, it is not up to opinion, it's a matter of physics. The debate comes in when we start describing the power and it's characteristics. How much, and at what rpm....what kind of power do you want. That is an entirely subjective discussion with unlimited variables.

 

Minimum csa.

 

Using your own logic, lets look at it as a matter of time. Since you're spending so little time at the low lift numbers, doesn't it make sense that you'd want them as good and as efficient as possible? Isn't the goal to fill the cylinder?
Do you know where the greatest pressure differential occurs during the intake stroke and intake valve event?
If you're ignoring low lift flow and velocity you're leaving power on the table. Again, it's a matter of physics, not an opinion.

 

OK, what is the min. CSA of that port and what does the engine require?

 

I'm asking about the op's 406 cid and the 195 afr head.I personally do not know the csa of that port.But at 195cc shouldn't it be around 2.1 to 2.2.
I agree for what he wants he will be fine I 'm just curious what will happen if he would want more rpm(6500 +).

 

A 406 making peak power at 6000rpm wants a minimum cross section of 1.98" sq in. to maintain (a specific) velocity. If you want to move the peak power number up in the rpm range and maintain that same velocity then you have to increase the area. Same rules apply to the valve size. We need to maintain an "ideal" velocity through the valve opening. Velocity through the min. area and through the valve are directly related.
We can also look at the air demand of that engine. Lets say he uses an intake lobe of 240 @ .05. For 100% volumetric @ 6000rpm, the engine wants 321 cfm. That head will supply that at ~.475 lift. It has plenty of cross sectional area and plenty of airflow.

 

You are right. The AFR 195 is too small above 6000 rpm if the OP was running over 6000 rpm, it will hit a ceiling at some point above that. Point being this build will not be turning 6000 rpm with the cam and dual plane intake he selected. The heads won't be the first thing to limit RPM the cam and intake specs will. That said the 224/230 cam with sub .550 lift and dual plane matches the AFR 195 well with HIS build specs, intended use and combination. This engine will make power off idle to 5500. Over that RPM will be counterproductive for the combination.

 

Kind of contradict yourself here...
The heads have plenty of cross section and airflow to carry past 6000rpm if that's the goal. Where it makes peak power, and where peak rpm is are two different things. I think this combination will carry nicely past 5500.

 

Operating range, peak power and redline are all different things. 6000 RPM shift points will be fine, will be past peak power but keep him in the fat part of the operating range on upshifts. I really think it is a killer street combo.

 

 

OK....you guys got me all f'd-up......i'm going to order a 195 head for the left side along with a 1 3/4" header, and a 210 for the right side along with 1 7/8" header.
Then I'm going to find a mechancal fuel injection setup....choke it down to 1 1/2" on the left side, and run her wide open on the right side.
That should make everyone happy.....
I'll let you know how it works out....

Thanks for the advise

 

LOL...lot of "opinions" out there. Some have been there, done that.

Did you see this?

https://www.corvetteforum.com/forums...ual-plane.html

 

Scott has worked for both Dart and Alan Johnson. Two premier cylinder head mfgs. His math equates to power per application.

Edmonton, Tell my Randy at ProStock I said hello..Good people at that shop.

 

To make a general statement about street and lets use AFR heads. Heads with high peak numbers tend to also have great low lift numbers. I'm not sure why AFR 210 lags so far behind at only the .400 lift number and then exceeds the 195 by such a big margin at .500.

But when you feed input data to an engine simulation program the more info you can input the more accurate it becomes. So if you add up the .100, .200, ..... .500 cfm intake flow rates of the 210 VS the 195 The 195 appears to win by a margin of 5 cfm just using those numbers.

Now look at the roller cam lobe and see how much time is spent at or near max lift like the posters .530 lift. You are spending much more time getting getting 292 cfm vs the 195 heads 275 cfm. That time spent at .500+ lift more than off sets the 5 cfm mathematical lead of the smaller 195

406 is not a small motor and like me and every other hot rodder out there is never happy with the power after awhile and they seek bigger and better. Well if you buy the big heads to begin with you don't have to buy another set for your next project. I bought 227 cc for my 383 because I didn't want to go over board and later on I had to put in a bigger cam because it needed it.

Flow @ .200
AFR 195- Intake 146 Exhaust 119
AFR 210- Intake 145 Exhaust 110

Flow @ .300
AFR 195- Intake 201 Exhaust166
AFR 210- Intake 199 Exhaust 158

Flow @ .400
AFR 195- Intake 274 Exhaust 197
AFR 210- Intake 255 Exhaust 192

Flow @ .500
AFR 195- Intake 275 Exhaust 213
AFR 210- Intake 292 Exhaust 210

 

Dart makes cylinder heads and are premier. I thought only AFR made cylinder heads they have the best advertised airflow numbers.

They have a 220 series that's never advertised on there web site you have to look for it to even find it on there web. fully CNCed problem is its not a smaller head it starts out at 220 and goes up in size from there.

Brodix has some very good heads that are not as cast but again they don't offer the smaller heads that way and there pricing is higher.

 

If you called AFR and gave them the specs and intended use on this build they would recommend the 195. Higher port velocity causes a ram effect not seen in these numbers also, likely the reason for the elevated lower lift flow numbers with a smaller port. Effects performance more than you would think at low end, midrange. You are a guy that runs high rpm and races. If you look at the item descriptions from AFR for the 195 and 210 you will see for your 3000-7000 rpm and racing the 210 is a better option for your intended use, RPM range and CI.

 

there are a lot of premier parts out there....just need to know how to make premier combination. I have 640CID engine here that was $59K. It makes 1200HP. The customers brother has a 532CID engine with good parts but not as nice as the 640....at $31K it makes 1200HP.

 

Mr. Wehunt's engine proves how good the 220's are.