The Great American SBC Cylinder Head Debate.

[BigAL]

So here's the question, is there such a thing as to big of an intake runner for a 406 sbc? Or is bigger better?

[SuperBuickGuy]

bigger isn't better because bigger takes more force to move. Of course, with that said, while there are general theories - rules are few and far between.

[Barry Donovan]

intake just changes speed. All engines have a set volume with cams and compression.

the interest in heads, is chamber size, more than valves.

The tighter it is, the faster it is, and more likely to make the tuner an idiot.
406 sbc, I'd be icing it with a quick high vacuum.

Todays injection , way more open with controls, cams with big fat lobes.. and good for everyone, even an aging dodge hemi driver.

Something I have done twice, from foreign and american.. is purchase and drive and maintain the transition engines... old carb, to modern injection.
Not many manufacture have done this. I have a subaru ea82, and the 305 chevy as two examples that have. I learned every lesson. I got the subaru mixed up with very old, and all the way to optical ignition at the same time.

The 1996 chevy seems to have a 1984 H.O. 305 chamber size, in bigger cams and vortec injection.

To maintain draft and thermal, go as big as you can go without spewing a bad firing realm in the rpm range. The 406 should stay fast, appear tight (classic).

[anotheridiot]

well, digging into these 85 heads, the exhaust ports are the size of a quarter, the exhaust valve is about the size of a worn out quarter. The parting lines are many, the gravel texture is noticable, there are pads where the blocks sat at the stem and the bottom of the intake port that definitely do not induce flow. If I were atomized fuel, I would be bouncing around in turbulence. The valves are so shrouded by the casting its almost pure ignorance that there wasnt a change in the molds for the casting fillers. This is all full force emissions technology seemingly making an effort to get that chamber as hot as possible so the fuel mixture just sit there so it could completely burn.

Aluminum heads have become very affordable with CNC machining and I highly doubt these are gonna flow as good as aluminum, but there wont be any hot spots at the tips of the 55 peaks in the combustion chamber either.

[BigAL]

The thing that gets me is the difference in heads between a SBC 400 and a BBC 402, both basically have the same bore and stroke, but when you look at the stock big block head it is bigger than some of the biggest small block heads that are available today. A large oval port big block head has a 253cc intake runner and 2.19 and 1.88 valves, why is that considered acceptable for a big block but not a small block of the same cubic inches??

[Scott Liggett]

It's my theory that you want the smallest sized intake port that moves the most air for a street engine. This increases port velocity and really builds low to midrange horsepower. I also look at flow numbers between .200 and .400 lift because that is where the valve is open the longest. Why would you care what it flows at peak lift height? The valve is at the top of the lobe so little time, how can it be important? I have people telling me what their heads flow at .700 lift, but they only have a .520 lift cam? What difference does that make? But, most of those people have no idea what they are talking about and are only spewing numbers that they think are neato sounding.

On GM's big block heads, the oval ports that were closed chambered shrouded the intake valve nearly half it's circumference. It didn't flow as well as the same size oval port with open chambers where air can get past the valve all the way around. When GM went to the "peanut port" heads, they were going after port velocity for high torque at low rpm. The 454 was only for trucks by then so what it flowed at high lift was irrevelant. The trucks had small cams. They didn't have the magazine selling high horsepower numbers, but they produced fantastic low end torque. GM's rectangular port heads were great for racing, but they suck for mostly street racing. The corners of the ports have very low port velocity at low lift numbers.

I learned this weekend that Pontiac went the other way with their heads on their big inch engines. They had rather small ports compared to the Chevy big blocks, but look at what those engines are known for, big torque numbers.

[BigAL]

So if you looking for torque go with small ports and if your looking for top end HP go with big ports? But what happens when the low lift numbers are better on a bigger port head than on a smaller port head. Are you better off going with the bigger head and getting the best of both worlds?

[Scott Liggett]

So if you looking for torque go with small ports and if your looking for top end HP go with big ports? But what happens when the low lift numbers are better on a bigger port head than on a smaller port head. Are you better off going with the bigger head and getting the best of both worlds?

Like camshaft selection, your cylinder head choice should be what the car and the engine are going to be used for. For me, my cars are strictly street use in heavy cars. I like smaller ports and smaller cams. If you are building a race engine where the engine will be revved over 4000 rpm for the most part, I would be looking for larger ports and good flow near the camshaft lift levels.

Take a look at the Boss 302's heads. They put four barrel 351 Cleveland heads on a tiny engine. With a big cam, that engine would rev to 8000 rpm no problem. It literally sucked to drive on the street at low rpm.

The little 195cc heads BluePrint Engines make will support 500 hp with a 396 sbc and a rather mild hydraulic roller. They shine in the low lift numbers and low rev engines, 6000 rpm or less. AFR has 195cc heads that can support close 550 hp in a small block.

[dieselgeek]

This stuff is all voodoo to me. When I wonder about it, I pick up the phone and call Nick Smithberg or Chad Speier. lol

[yellomalibu]

I've had AFR 195's on my 406 for several years... like 15 years, except for a bit when I had them traded for some bow ties.

I completely agree with what Scott said - that head selection should fit the build.

[Scott Liggett]

Take three sbc 406's. All built differently for different purposes using AFR heads since you are familiar with them.

Street version, 10:1 compression, hydraulic roller cam, @2500 stall converter, 475-525 hp, AFR's 195's.

Weekend warrior, Street/Strip, close to 11:1 compression, but still runs on pump gas, mid level solid roller, 550+ hp, 3000+ stall converter. 210's maybe CNC 210's if using a 150 shot of NOS.

Full Race, 13:1 compression or more, big solid cam, 300 shot of NOS, 4000+ stall converter, CNC 220's or bigger.

[BigAL]

Here are AFR's flow numbers for their 195cc Eliminator heads.

Here is the flow numbers for their new 245cc Eliminator heads.


Now if your only running a cam with .550 lift which head would you rather go for?

[yellomalibu]

Pick a head based only on a lift number?

[Scott Liggett]

Personally, with a smaller cam for a street engine, I would still go with the 195's. Talk to AFR about it. Go to the source for the best recommendation.