Thread: Brodix IK Heads.

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You have to be careful when comparing heads because you are not, in most cases, told the flow bench protocol that was used to flow the heads. Did the mfg use a 4.00" intake pipe or a 4.060" intake pipe or a 4.125" intake pipe or what? A bigger pipe will allow the heads to flow a higher number. Did the mfg use undercut valve stems or not? Undercut stems will allow the heads to flow a higher number. What depression was used to flow them? The accepted standard is 28" of water on a manometer, but you have no idea if they don't tell you in their literature, although you can call their tech line. Was an exhaust pipe used? A short pipe will allow more flow, rather than no pipe at all. And so on and so on.

If you don't have a lot of time to compare the entire flow regimen of all the heads that you want to look at, or if it is confusing, then concentrate on only one valve lift, 0.400". This is a quick and simple way to compare heads.

A rough rule of thumb is that you would use the cubic inches of the motor and multiply times 0.5 to get the intake runner size for the heads. 355 cubic inches would work well with a ~180cc intake runner head, for instance. A 400 cubic inch motor could use a 200cc intake runner to advantage. A 327 might run well with a ~165cc intake runner.

For a 355 Chevy, I would not be interested in any cylinder head that would not flow at least 200 CFM on the exhaust side, at some point in the valve lift and I like to see 260/270 on the intake side. Now, you can get 200 exhaust on most any manufacturers cylinder head, but not with smaller runners such as 180/185cc intake runners or even 190cc's. A 355 needs the smaller runners to keep velocity up in order to pack the cylinders and make horsepower. Larger runners (200, 210, 220, 230 etc.) will flow 200, but the velocity suffers and the motor may actually slow down from the less dense packing of the cylinders. I see that Dean already knows this because he's looking for 180cc heads for a 355, but I'm expounding on the info for the benefit of others reading this who may not understand that when it comes to cylinder heads, bigger is not necessarily better. Matter of fact, if I wanted a daily driver to haul grandma back and forth to bingo that would operate from idle to maybe 4000 rpm's, I would choose an even smaller intake runner, something like 165cc or 170cc, for brute off-idle torque to pull a numerically-low rear gear and generate fuel economy using a stock or very mild aftermarket cam. Combination, combination, combination.

Brodix IK180
0.200" 138/112
0.300" 188/149
0.400" 234/167
0.500" 243/175
0.600" 245/178
Brodix 1021002, Brodix Small Block Chevy IK Series Aluminum Cylinder Heads | Brodix

Pro-Filer 23 degree 185
0.200" 135 110
0.300" 201 145
0.400" 245 180
0.500" 265 206
0.600" 270 213
SBC 23 Degree Cylinder Heads
Under $1100 fully assembled, ready to bolt on
Available in 64, 70 and 72cc chambers

Airflow Research 180
0.200" 138 110
0.300" 198 158
0.400" 240 190
0.500" 260 207
AFR - Airflow Research 0919, AFR Small Block Chevy 180cc Eliminator Street Aluminum Cylinder Heads | AFR - Airflow Research
No 70cc combustion chamber examples are available from AFR in this runner size, only 65 and 75

With either the Pro-Filer or the AFR heads, 10.0:1 static compression ratio, Edelbrock Performer RPM intake manifold #7101 or Weiand #8150, a 220-225 @0.050" cam, 750 carb, 1 5/8" long tube headers, this motor would easily produce 400 hp and 400 ft/lbs of torque. Actually, I would rather use the Edelbrock #7104 and a Quadrajet, but that's just me.

Dean, before you choose or purchase ANY parts, please allow me to school you on squish/quench if you don't know about them. Setting the squish/quench properly will make or break a motor and usually involves cutting the block decks to a new block deck height when using aluminum heads. Iron heads will work fine with steel shim gaskets to effect a tight squish/quench, but aluminum heads need some compliance in the head gasket, so a thicker composition gasket is used. When you combine the stock piston deck height of ~0.025" with a, for instance, Fel-Pro 1003 gasket with a compressed thickness of 0.041", you end up with a squish/quench measurement of ~0.066", which is too thick to offer a tight squish/quench to control detonation on pump gas.

What we would do is to measure the "stack" of parts to be used, then cut the block decks to that figure (called "zero decking" the motor) and use the thickness of the composition gasket for our squish/quench figure. For instance, if you used a piston that has a compression height of 1.560", a rod length of 5.700" and add in the radius of the 350 stroke (1.740"), we find a stack height of 9.000" with a block deck height of ~9.025". This is the blueprint dimension that was used at the factory when the 350 was built and leaves the piston down in the bore by ~0.025" with the piston at top dead center. When combined with the steel shim head gasket thickness of 0.020", this puts the squish/quench at ~0.045", just on the high side of what us hot rodders like at 0.035" to 0.045". With the piston crown flush with the block decks with the piston at top dead center and 0.041" composition gasket thickness, the squish/quench is 0.041", which will work nicely to prevent detonation on pump gas.

As the piston approaches top dead center, the close proximity of the crown to the underside of the cylinder head will "squish" or "jet" the mixture out of that area, toward the spark plug, creating turbulence that will bust up pockets of lean and rich mixture in the chamber, homogenizing the mix for a more complete burn and maximum power, as well as preventing detonation on fuel quality that might be less than what the motor wants. The "quench" part of squish/quench is the transfer of heat from the piston crown to the underside of the cylinder head so that the cooling system can carry the heat to the radiator. The closer we get the piston crown to the underside of the head, the better the quench and the more heat extracted from the piston crown.

Some fellows run into a problem when they begin choosing pistons. As I stated, the design compression height (wrist pin centerline to the crown of the piston) of a 350 is 1.560". Some piston manufacturers also make a piston with a reduced compression height to allow cutting of the block decks to bring the block to flat to prevent blowing a head gasket due to a wavy surface on the block. If a fellow isn't careful, he can choose these ~1.540" pistons and add another 0.020" to the piston deck height, which of course widens the squish/quench by 0.020", not a particularly good thing. There are a few piston manufacturers who make 350 piston with a little taller than stock compression height. Keith Black, for instance, manufactures their 350 hypereutectic pistons at 1.561"and I have seen some others that produce pistons with a 0.006" to 0.007" compression height over stock. The taller the piston, the less you have to cut from the block decks to effect a tight squish.
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Thank you Techinspector. I was looking at these heads mostly do to the 70 cc they offer. that would put my SCR at 9:5-1 and dynamic at 7:8-1. I was going to use a .039 head gasket as my block is decked to .005 I think that will be ok for the street. I am just wondering about flow of the heads I don't know much about flow numbers. I did see the AFR heads had higher numbers and there 75cc heads would bring my SCR to 9:0-1 aprox. I am using a 270 /278 @50 219/228 519/530 cam from Lunati. Edelbrock performer manifold and a holly 650. Block is bored .030.

Thank you for all the info gives me a lot to think about before I screw something up..

Hi Techinspector, thank you for all the information, i had posted you back but for some reason it still has not shown..

My block is decked piston to deck is .005 i was going to use a .039 gasket.

After reading your post i am looking into the pro filer heads, 72 cc, that should put me at around 9.5:1 SCR abd 7.8:1 DCR..Will the 185cc be a little too much for me? 350 bored .040 over.

thank you again I was a little confused with the Quench so let me see if i got it now..
piston to deck height .005 + head gasket .039 = .044 that should be ok ? Need to stay within .035 & .045 right?