Cylinder Heads - What Matters Most?
05-26-2019, 10:05 AM
#41
TECH Veteran
If a valve is right up against the cylinder wall, do it hurts performance and flow potential ?
05-26-2019, 10:21 AM
#42
Moderator
Thread Starter
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
Originally Posted by KCS
Intended Usage
The first thing in selecting cylinder heads is knowing the intended usage. How many cubic inches are you trying to feed and what RPM range will you want to make power? What you're really trying to do, whether you realize it or not, is to manipulate the torque curve for the application. You want to put the torque curve in the rpm range you need it, and then maximize the torque in that area.
Port Size
The port size, or more specifically the minimum cross sectional area (MCSA), is how you place the torque curve in the RPM range you want. Peak torque generally occurs around 240ft/sec so the MCSA can be sized accordingly using very simple math. Since horsepower is calculated based on torque and RPM, the higher up in the RPM range you make torque, the more horsepower you will make. It's common for people buy heads that will put the torque curve higher than what their valvetrain budget can afford.
Port Shape
When the ports are sized correctly, the shape of the port has a tremendous influence on the area under the curve. The better the shape, the higher airspeeds the port can maintain and the longer spread between peak torque and peak horsepower. The short side radius, which is basically the floor of the port as it turns to the valve job, is normally the hot spot. Too abrupt, and the air can separate off the turn and cause some bad turbulence. Tall ports with more gradual short turns tend to be better for this, which is why raised runner heads are so popular in racing. For lower RPM and lower airspeeds, sometimes a more abrupt turn is better to promote better emissions and idle characteristics.
Valve Size
I like to use as big of a valve as possible. The bigger valve achieves more curtain area at every lift point, similar to using a camshaft with more aggressive lobes that open and close faster. Unfortunately, most cylinder head porters will size the MCSA as a percentage of the valve, so a large valve often means a large MCSA.There really isn't such a thing as too much airflow unless it is because the port is too big. At 28" H2O, which is the depression that most heads are tested on the flowbench, you won't flow more than about 142CFM/sq in of area. Flowbench numbers are almost completely useless IMO so I wouldn't worry too much about it
The first thing in selecting cylinder heads is knowing the intended usage. How many cubic inches are you trying to feed and what RPM range will you want to make power? What you're really trying to do, whether you realize it or not, is to manipulate the torque curve for the application. You want to put the torque curve in the rpm range you need it, and then maximize the torque in that area.
Port Size
The port size, or more specifically the minimum cross sectional area (MCSA), is how you place the torque curve in the RPM range you want. Peak torque generally occurs around 240ft/sec so the MCSA can be sized accordingly using very simple math. Since horsepower is calculated based on torque and RPM, the higher up in the RPM range you make torque, the more horsepower you will make. It's common for people buy heads that will put the torque curve higher than what their valvetrain budget can afford.
Port Shape
When the ports are sized correctly, the shape of the port has a tremendous influence on the area under the curve. The better the shape, the higher airspeeds the port can maintain and the longer spread between peak torque and peak horsepower. The short side radius, which is basically the floor of the port as it turns to the valve job, is normally the hot spot. Too abrupt, and the air can separate off the turn and cause some bad turbulence. Tall ports with more gradual short turns tend to be better for this, which is why raised runner heads are so popular in racing. For lower RPM and lower airspeeds, sometimes a more abrupt turn is better to promote better emissions and idle characteristics.
Valve Size
I like to use as big of a valve as possible. The bigger valve achieves more curtain area at every lift point, similar to using a camshaft with more aggressive lobes that open and close faster. Unfortunately, most cylinder head porters will size the MCSA as a percentage of the valve, so a large valve often means a large MCSA.There really isn't such a thing as too much airflow unless it is because the port is too big. At 28" H2O, which is the depression that most heads are tested on the flowbench, you won't flow more than about 142CFM/sq in of area. Flowbench numbers are almost completely useless IMO so I wouldn't worry too much about it
When you say port shape, you are not talking square oval, cathedral, or dodecahedral right? You are talking more about the path the air follows from the intake to the valve? Things like short side radius? Taper? Necking down?
In the valve size, ideally the valve would be the flow bottleneck not something behind the valve?
Regarding torque production, I do not look at it as losing low end torque to gain high end hp. I look at it as the torque curve shifts to the right or to the left. If it shifts right you make more power due to rpm. If it shifts left it makes less power due to rpm. But as you said intended application. In a truck I want peak torque down low to get a heavy load moving. I figure a certain CID can make a certain amount of torque. Cannot cheat that. Only pick the rpm at which it happens.
05-26-2019, 10:21 AM
#43
Moderator
Thread Starter
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
Originally Posted by Tuskyz28
If a valve is right up against the cylinder wall, do it hurts performance and flow potential ?
05-26-2019, 10:35 AM
#44
The details
The test car in the article is a 2001 z28 a4
mods:
l76 intake
fast 90mm tb
stock ls1 block
226/240 588/597 114 cam
mast motorsport 61cc ls3 small bore 12 degree heads
rpm built 4l60
vig3600
9" rear
power 423 whp / 405wtq on a dyno jet. 325/326 before heads/cam
Head flow numbers:
lift Intake Exhaust
.300 208 105
.400 266 217
.500 306 222
.600 335 226
.700 351 234
.750 335 238
Like i said its a old article, 2010 to be exact. Dan, i still dont no real MAGIC even if the car was equipped with a ported fast 102mm etc.
The test car in the article is a 2001 z28 a4
mods:
l76 intake
fast 90mm tb
stock ls1 block
226/240 588/597 114 cam
mast motorsport 61cc ls3 small bore 12 degree heads
rpm built 4l60
vig3600
9" rear
power 423 whp / 405wtq on a dyno jet. 325/326 before heads/cam
Head flow numbers:
lift Intake Exhaust
.300 208 105
.400 266 217
.500 306 222
.600 335 226
.700 351 234
.750 335 238
Like i said its a old article, 2010 to be exact. Dan, i still dont no real MAGIC even if the car was equipped with a ported fast 102mm etc.
05-26-2019, 10:39 AM
#45
TECH Veteran
05-26-2019, 10:46 AM
#46
TECH Fanatic
Join Date: Aug 2009
Location: Coast of San Mateo County Between Pacifica & HMB
Posts: 1,815
Received 215 Likes
on
128 Posts
The details
The test car in the article is a 2001 z28 a4
mods:
l76 intake
fast 90mm tb
stock ls1 block
226/240 588/597 114 cam
mast motorsport 61cc ls3 small bore 12 degree heads
rpm built 4l60
vig3600
9" rear
power 423 whp / 405wtq on a dyno jet. 325/326 before heads/cam
Head flow numbers:
lift Intake Exhaust
.300 208 105
.400 266 217
.500 306 222
.600 335 226
.700 351 234
.750 335 238
Like i said its a old article, 2010 to be exact. Dan, i still dont no real MAGIC even if the car was equipped with a ported fast 102mm etc.
The test car in the article is a 2001 z28 a4
mods:
l76 intake
fast 90mm tb
stock ls1 block
226/240 588/597 114 cam
mast motorsport 61cc ls3 small bore 12 degree heads
rpm built 4l60
vig3600
9" rear
power 423 whp / 405wtq on a dyno jet. 325/326 before heads/cam
Head flow numbers:
lift Intake Exhaust
.300 208 105
.400 266 217
.500 306 222
.600 335 226
.700 351 234
.750 335 238
Like i said its a old article, 2010 to be exact. Dan, i still dont no real MAGIC even if the car was equipped with a ported fast 102mm etc.
Mid-Length Fast or one of the short runner intakes & 7500 RPM.
Between the 3600 stall and L76 intake very small window to perform, better cam maybe 224/232 because of intake limitations.
I think it was vr that did a 383" build with those heads and standard length runner FAST made like ~490 with 235/243 kaotic
cam, left 20+ on table with runner choice on that combo imo.
05-26-2019, 10:54 AM
#47
TECH Fanatic
Join Date: Aug 2009
Location: Coast of San Mateo County Between Pacifica & HMB
Posts: 1,815
Received 215 Likes
on
128 Posts
will not excel like a 4.060"+ Bore and reach full potential on 4.125+ Bore, but then most will want LS7 heads at that point.
05-26-2019, 11:38 AM
#48
Moderator
Thread Starter
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
Originally Posted by Tuskyz28
So we both agree on that. You said earlier in this thread that some believe its MAGIC in the shape of the port... are you one of those people that believe that ?
05-26-2019, 11:40 AM
#49
TECH Veteran
Those Heads with 346" Need RPM! (or piston speed ~ 4.0" stroke) IMO.
Mid-Length Fast or one of the short runner intakes & 7500 RPM.
Between the 3600 stall and L76 intake very small window to perform, better cam maybe 224/232 because of intake limitations.
I think it was vr that did a 383" build with those heads and standard length runner FAST made like ~490 with 235/243 kaotic
cam, left 20+ on table with runner choice on that combo imo.
Mid-Length Fast or one of the short runner intakes & 7500 RPM.
Between the 3600 stall and L76 intake very small window to perform, better cam maybe 224/232 because of intake limitations.
I think it was vr that did a 383" build with those heads and standard length runner FAST made like ~490 with 235/243 kaotic
cam, left 20+ on table with runner choice on that combo imo.
The L76/LS3 intake is better than you think.
Richard Holdener showed where a Fast 102mm with the longer showed this in a article in Hot Rod magazine. Also Richard gave me a Tech book back in September at the LS fest when i met him in person. Anyway the book is full of heads, intakes, headers, etc comparisons.
#foodforthought. The LS3 255 TFS head tested on a stock GM LS3 vs a GM LS3 head... the TFS LS3 head only made 21 hp over the factory head.
05-26-2019, 12:03 PM
#50
TECH Senior Member
Richard has to relearn his basic math! 571-552 = 19, NOT 21. LOL
The following users liked this post:
Z28SteveA4 (07-30-2022)
05-26-2019, 12:49 PM
#52
Moderator
Thread Starter
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
Originally Posted by JakeFusion
Those magazine tests are weird.
Guys are getting 800HP out of LS3 heads on 427s. What the hell is Richard Holdener doing to get 550.
Also--I still don't have my heads. The joy is unspeakable. So I can't test them.
Guys are getting 800HP out of LS3 heads on 427s. What the hell is Richard Holdener doing to get 550.
Also--I still don't have my heads. The joy is unspeakable. So I can't test them.
05-26-2019, 12:50 PM
#53
TECH Fanatic
Join Date: Aug 2009
Location: Coast of San Mateo County Between Pacifica & HMB
Posts: 1,815
Received 215 Likes
on
128 Posts
I understand that completely Dan but let give you something to think about.
The L76/LS3 intake is better than you think.
Richard Holdener showed where a Fast 102mm with the longer showed this in a article in Hot Rod magazine. Also Richard gave me a Tech book back in September at the LS fest when i met him in person. Anyway the book is full of heads, intakes, headers, etc comparisons.
#foodforthought. The LS3 255 TFS head tested on a stock GM LS3 vs a GM LS3 head... the TFS LS3 head only made 21 hp over the factory head.
The L76/LS3 intake is better than you think.
Richard Holdener showed where a Fast 102mm with the longer showed this in a article in Hot Rod magazine. Also Richard gave me a Tech book back in September at the LS fest when i met him in person. Anyway the book is full of heads, intakes, headers, etc comparisons.
#foodforthought. The LS3 255 TFS head tested on a stock GM LS3 vs a GM LS3 head... the TFS LS3 head only made 21 hp over the factory head.
You know I love me some RH tech! Been reading him since ~1990, 5+ years before LS lol.
Bought some CNC Stock Iron 87 5.0 Powerheads back in my Ford days based of his testing
in MMFF they were incredible for what they were in their day. It was apparent what an
efficient Port job could do for a factory head, one of the first CNC Iron performance
heads available to the public. It only increased Port volume from 124-145 CCs
(remember Port is about 1" shorter than LS so CSA closer to ~180 CC LS Port ballpark)
This was before Tony even worked for AFR or I knew who he was.
Your answer is provided by RH under the red box. The Heads are capable of 800+ Flywheel HP
in the right combo, which is the same thing my Engine Builder, Dustin Lee said about my
MAMOFIED TFS LS3 Heads. I have no doubt OE (untouched ) set up for my combo would
be down 35+ RWHP, and on Hammers 388" closer to 50 LESS.
Now I know EXTENSIVELY worked OE LS3 Heads have made 800 Flywheel HP NA , but
with bigger ports,bigger Cams, and more RPM.
05-26-2019, 01:10 PM
#54
You guys on the forums know more than that ****.
05-26-2019, 03:43 PM
#55
You said a lot, and some follow up questions:
When you say port shape, you are not talking square oval, cathedral, or dodecahedral right? You are talking more about the path the air follows from the intake to the valve? Things like short side radius? Taper? Necking down?
In the valve size, ideally the valve would be the flow bottleneck not something behind the valve?
Regarding torque production, I do not look at it as losing low end torque to gain high end hp. I look at it as the torque curve shifts to the right or to the left. If it shifts right you make more power due to rpm. If it shifts left it makes less power due to rpm. But as you said intended application. In a truck I want peak torque down low to get a heavy load moving. I figure a certain CID can make a certain amount of torque. Cannot cheat that. Only pick the rpm at which it happens.
When you say port shape, you are not talking square oval, cathedral, or dodecahedral right? You are talking more about the path the air follows from the intake to the valve? Things like short side radius? Taper? Necking down?
In the valve size, ideally the valve would be the flow bottleneck not something behind the valve?
Regarding torque production, I do not look at it as losing low end torque to gain high end hp. I look at it as the torque curve shifts to the right or to the left. If it shifts right you make more power due to rpm. If it shifts left it makes less power due to rpm. But as you said intended application. In a truck I want peak torque down low to get a heavy load moving. I figure a certain CID can make a certain amount of torque. Cannot cheat that. Only pick the rpm at which it happens.
The valve is the bottleneck up to a certain lift point, usually just a little beyond where curtain area is equal to the MCSA. After that, the port itself largely influences the flow curve since the valve is mostly out of the way. Small valve heads with low lift cams hardly spend anytime there so the valve job makes more difference than the port itself.
I agree with the comments on torque. You have to be honest with yourself on what you want the engine to do. Lots of people want their street car to make big horsepower numbers, so they pick parts that shift the powerband up in an RPM range that the engine rarely sees. Then they wonder why the car isn’t as fun to drive anymore.
Last edited by KCS; 05-27-2019 at 10:28 AM.
05-26-2019, 03:53 PM
#56
ModSquad
iTrader: (6)
05-26-2019, 05:15 PM
#57
TECH Senior Member