Cylinder Head Discussion
09-09-2004, 12:35 PM
#1
6600 rpm clutch dump of death Administrator
Thread Starter
Cylinder Head Discussion Since the camshaft thread was fairly popular I thought we might start a discussion on one of the things which folks seem to aks about quite a bit. The subject of this discussion is going to be cylinder heads.
One of the huge issues vendors face is the competetive nature of the business. Everyone wants the best flowing heads possible, and they want them for free.
This creates several problems.
Problem one: Vendors are constantly being forced to improve port designs. That cost is measured both in time and money.
Problem two: The proliferation of low cost CNC heads makes it economically difficult for the shops doing hand porting to be able to devote the man hours necessary to a set of heads that they may need while still remaining profitable.
Problem three: Problem three is a direct result of problem 1 and problem 2. Bench numbers from any vendor often times have to be taken with a grain of salt. No one doubts that big numbers (just like big dyno numbers) sell heads.
So, if a vendor can produce really incredible flow numbers chance are folks will spend money with that vendor. So, sometimes vendors are forced to "cheat" on the bench a bit. This can range from outright cheating (flowing on a 4.125 fixture and calling it a 3.900 , to fudging the test a bit. This can involve introducing a bit of an airleak, moving the head around on the bore fixture, etc... Without getting into a lot of details its just like a dyno. We all know that you can dyno with a 9" with 4.56 gears, a steel driveshaft, and heavy wheels and get one dyno number. You can put a 10 bolt with a 2.73 gear, Al driveshaft, and Super light wheels and get a much higher number. But which one is the way you are going to really race the car?
Anyhow, this isn't a condemnation of any vendor in particualr. It about everything as a whole. It also to make you understand that flow numbers aren't always an absolute, and that what you get from a vendor probably needs to be independantly verified. Alos, if it sounds too good to be true, it probably is...
You may be saying no way, Vendor XYZ would never lie. I'm not saying anone is lying intentionally (although some may). There are lots of reasons for numbers not to jive up that doesn't invlove a shop cheating. Lets look at benches themselves. IF they are propely calibrated benches should all read within 1%. But, they don't. Look at the differences between a SF600 and SF1020. In most cases I see them vary, and they are from the same mfg. Bench output is directly related to the operator. If its not operated correctly, then the data collected is garbage. Here is what Superflow has to say on it:
Anyhow, what follows is an object lesson. This isn't to "out" any vendor. In fact I'm not even posting the vendors name. But, before you go making any assumptions this isn't one of the vendors you see getting bashed every day. Anyhow, here is an example of how much difference there can be going from what the vendor says to what an independant bench says.
info on the flowing differences:
Vendor - sf600 w/o flowcom, 3.90 bore, radius inlet, exhaust w/o pipe
Vendor's head specs (what they claimed):
215cc int
80cc exh
66cc chamber
2.02/1.57 valves
independent shop - sf1020, 3.90 bore, radius inlet, 1 3/4 pipe on exhaust, and ls1 and ls6 intake
head specs (as measured):
223cc int
82cc exh
67cc chamber
2.02/1.57 valves
So, in an independant check they varied from what was recorded.
Intake was 8cc larger,
exhaust was 2cc larger,
chamber was 1cc larger.
Now, you might be saying that I'm splitting hairs. Ok, maybe I am, but if a runner is bigger, then just say its bigger. That is one of the things I see a lot of is folks undersizing the intake runner. 225 is really 235, etc... I don't know about you, but depending on where it is, 10cc matters...
Anyhow, on to the bench.
The heads were flowed by Steve Demirjian of Race Engine Development. I assure you, Steve knows how to run a bench. Again, this isn't an advertisement for any shop or vendor (including Steve). I am simply illustrating the fact that what get sold often times isn't what you are getting.
radius inlet
Ls6 intake
ls1 intake
Ok, these tests weren't limited to just one port. All ports in the head were checked for variations.
radius inlet
exhaust with pipe
ls6 intake
ls1 intake
session1 = radius inlet
session2 = ls1 intake
sesssion3 = ls6 intake
Now, a couple of things I think are important about these flow sheets. One they have the low lift numbers which too often get ignored, but are very important if you want a custom spec'd cam. If you just want a "box" cam then they probably wouldn't matter to you.
Now, the kicker how much did the heads differ from advertised to measured? Quite a bit actually. Now, some of that may be variation from bench to bench. Some of it may be the operator. Sme of it may be a desire to sell heads, and the only way to do it is to make the bench a bit "happy".
Here are the numbers. The first colum is lift, the second is the claimed flow on the SF600, and the second is the measured flow.
.100 71 61.85 -9.15
.200 159 117.5 -41.5
.300 216 177 -39
.400 253 226.87 -26.13
.500 290 250.87 -39.13
.600 303 261.5 -41.5
.100 63 54.75 -8.25
.200 122 106 -16
.300 171 135.25 -35.75
.400 188 159 -29
.500 216 173 -43
.600 227 182.25 -44.75
Again, the point of this thread isn't to come out and label Vendor X, or Vendor Y, or Vendor Z as being crooked. What I'm going to try to do is educate some of you on what makes a good cylinder head.
One of the huge issues vendors face is the competetive nature of the business. Everyone wants the best flowing heads possible, and they want them for free.
This creates several problems. Problem one: Vendors are constantly being forced to improve port designs. That cost is measured both in time and money.
Problem two: The proliferation of low cost CNC heads makes it economically difficult for the shops doing hand porting to be able to devote the man hours necessary to a set of heads that they may need while still remaining profitable.
Problem three: Problem three is a direct result of problem 1 and problem 2. Bench numbers from any vendor often times have to be taken with a grain of salt. No one doubts that big numbers (just like big dyno numbers) sell heads.
So, if a vendor can produce really incredible flow numbers chance are folks will spend money with that vendor. So, sometimes vendors are forced to "cheat" on the bench a bit. This can range from outright cheating (flowing on a 4.125 fixture and calling it a 3.900 , to fudging the test a bit. This can involve introducing a bit of an airleak, moving the head around on the bore fixture, etc... Without getting into a lot of details its just like a dyno. We all know that you can dyno with a 9" with 4.56 gears, a steel driveshaft, and heavy wheels and get one dyno number. You can put a 10 bolt with a 2.73 gear, Al driveshaft, and Super light wheels and get a much higher number. But which one is the way you are going to really race the car?
Anyhow, this isn't a condemnation of any vendor in particualr. It about everything as a whole. It also to make you understand that flow numbers aren't always an absolute, and that what you get from a vendor probably needs to be independantly verified. Alos, if it sounds too good to be true, it probably is...
You may be saying no way, Vendor XYZ would never lie. I'm not saying anone is lying intentionally (although some may). There are lots of reasons for numbers not to jive up that doesn't invlove a shop cheating. Lets look at benches themselves. IF they are propely calibrated benches should all read within 1%. But, they don't. Look at the differences between a SF600 and SF1020. In most cases I see them vary, and they are from the same mfg. Bench output is directly related to the operator. If its not operated correctly, then the data collected is garbage. Here is what Superflow has to say on it:
Three general causes can influence flowbenches to measure
data differently.
1) Flow Separation
Typically occurs at higher test pressures. This
phenomenon usually results in lower indicated airflow
at higher flow rates on SF-1020 flowbenches.
2) Manual Data Collection vs. FlowCom©
Simply stated, the FlowCom© takes all the guesswork out
of collecting flow data without variations in manometer
readings.
3) Method of Calibration and Comparison
The square root of the pressure ratio method (typically
used on 300/600 series benches when operated
manually) vs. the Ideal Gas Law (a novel approach
used by SuperFlow in the calibration of early SF-1020
benches) or operator skill.
SuperFlow Corporation has chosen to standardize the calibration
process by:
1) Calibrate all SF-600, SF-1020, and SF-1200
flowbenches at 25"H2O test pressure.
2) Strongly suggest use of FlowCom© data acquisition
system with motor controller for more precise
measurements.
3) Use the square root of the pressure ratio method for
comparison of flow data.
New CFM = (New test pressure/Current test pressure)
x Current Flow
These procedures and resulting calibration methods are
traceable to the standards of the National Institute of
Science and Technology (NIST). All flowbenches released
after 1/19/2001 have been calibrated using this new
Standard.
Special stainless steel calibration orifices are also available
from SuperFlow to use as standards for those organizations
that may want to apply their own individual calibration
methods. Although the calibration orifices are very
expensive, some flow labs may need and want to use them
as measurement standards.
data differently.
1) Flow Separation
Typically occurs at higher test pressures. This
phenomenon usually results in lower indicated airflow
at higher flow rates on SF-1020 flowbenches.
2) Manual Data Collection vs. FlowCom©
Simply stated, the FlowCom© takes all the guesswork out
of collecting flow data without variations in manometer
readings.
3) Method of Calibration and Comparison
The square root of the pressure ratio method (typically
used on 300/600 series benches when operated
manually) vs. the Ideal Gas Law (a novel approach
used by SuperFlow in the calibration of early SF-1020
benches) or operator skill.
SuperFlow Corporation has chosen to standardize the calibration
process by:
1) Calibrate all SF-600, SF-1020, and SF-1200
flowbenches at 25"H2O test pressure.
2) Strongly suggest use of FlowCom© data acquisition
system with motor controller for more precise
measurements.
3) Use the square root of the pressure ratio method for
comparison of flow data.
New CFM = (New test pressure/Current test pressure)
x Current Flow
These procedures and resulting calibration methods are
traceable to the standards of the National Institute of
Science and Technology (NIST). All flowbenches released
after 1/19/2001 have been calibrated using this new
Standard.
Special stainless steel calibration orifices are also available
from SuperFlow to use as standards for those organizations
that may want to apply their own individual calibration
methods. Although the calibration orifices are very
expensive, some flow labs may need and want to use them
as measurement standards.
info on the flowing differences:
Vendor - sf600 w/o flowcom, 3.90 bore, radius inlet, exhaust w/o pipe
Vendor's head specs (what they claimed):
215cc int
80cc exh
66cc chamber
2.02/1.57 valves
independent shop - sf1020, 3.90 bore, radius inlet, 1 3/4 pipe on exhaust, and ls1 and ls6 intake
head specs (as measured):
223cc int
82cc exh
67cc chamber
2.02/1.57 valves
So, in an independant check they varied from what was recorded.
Intake was 8cc larger,
exhaust was 2cc larger,
chamber was 1cc larger.
Now, you might be saying that I'm splitting hairs. Ok, maybe I am, but if a runner is bigger, then just say its bigger. That is one of the things I see a lot of is folks undersizing the intake runner. 225 is really 235, etc... I don't know about you, but depending on where it is, 10cc matters...
Anyhow, on to the bench.
The heads were flowed by Steve Demirjian of Race Engine Development. I assure you, Steve knows how to run a bench. Again, this isn't an advertisement for any shop or vendor (including Steve). I am simply illustrating the fact that what get sold often times isn't what you are getting.
radius inlet
Ls6 intake
ls1 intake
Ok, these tests weren't limited to just one port. All ports in the head were checked for variations.
radius inlet
exhaust with pipe
ls6 intake
ls1 intake
session1 = radius inlet
session2 = ls1 intake
sesssion3 = ls6 intake
Now, a couple of things I think are important about these flow sheets. One they have the low lift numbers which too often get ignored, but are very important if you want a custom spec'd cam. If you just want a "box" cam then they probably wouldn't matter to you.
Now, the kicker how much did the heads differ from advertised to measured? Quite a bit actually. Now, some of that may be variation from bench to bench. Some of it may be the operator. Sme of it may be a desire to sell heads, and the only way to do it is to make the bench a bit "happy".
Here are the numbers. The first colum is lift, the second is the claimed flow on the SF600, and the second is the measured flow.
.100 71 61.85 -9.15
.200 159 117.5 -41.5
.300 216 177 -39
.400 253 226.87 -26.13
.500 290 250.87 -39.13
.600 303 261.5 -41.5
.100 63 54.75 -8.25
.200 122 106 -16
.300 171 135.25 -35.75
.400 188 159 -29
.500 216 173 -43
.600 227 182.25 -44.75
Again, the point of this thread isn't to come out and label Vendor X, or Vendor Y, or Vendor Z as being crooked. What I'm going to try to do is educate some of you on what makes a good cylinder head.
Last edited by J-Rod; 09-09-2004 at 12:41 PM.
09-09-2004, 12:36 PM
#2
6600 rpm clutch dump of death Administrator
Thread Starter
Port work unlike most other parts of building an engine isn't always a matter of measuring x number of thousandths and calling it good. Port work is more like art, specifically sculpture. Being able to look into a hole , and determine the best way to make air move through that hole is a gift some folks have, and other don't.
Some folks don't realize it, but something I will try to illustrate is that you can have a head that on the flowbench will flow LESS than another head with similar port volume, and the head flowing LESS CAN still make more power. I'm not saying its always the case. But, it can happen. If the heads are done right (and that is a big IF), more flow should equal more power. The thing about the flowbench is you can take material out of the head that will make it look good on the bench, but in reality will cost HP.
Let me cite another example:
Again, I am not going to name the two heads that were tested, For the purpose of this test I will refer to the vendors a Brand X and Brand Y.
In a test of Brand X heads vs Brand Y heads. Brand Y flows as well on the bench (as good as a Brand X), but don't seem to make the same power on the dyno,etc. From discussing it with the head porter (@ Brand X), he was mentioning that Brand Y removes material in areas that will show a gain on the flow bench, but will not make anymore power on the dyno. He says they are big in the wrong spots and too small in others.
A set of Brand Y stage 2s 5.3l heads on a car that had all the bolt ons and a TR224 cam. It made 379/370 or so before adding the heads. After the heads, the car did 413/385 after tuning.
A week before, Another car had a set of Brand X stage 2 5.3l heads on a car that already had the TR224 cam as well and the IDENTICAL mods as the other Brand Y car (FLPs, LS6 intake, ASP, stock rear/4:10s,etc). Both dynoed the exact same before swapping heads on (the curves practically overlayed oneanother). This car pulled 443/418 with the Brand Xs!
On the flow bench, the Brand Ys actually flowed better from .100-.550, while Brand X flowed slightly better past this. Same thing on the exhaust side. This just goes to show that a flow bench is an excellent tool, but not something that should be used as the determing factor in how a head will perform when put on a motor. The CC volumes were identical on the two heads, so compression difference wasn't an issue.
So, you see, it looked good on the bench, but in reality, the power just wasn't there.
Anyhow, I'm posting this to get the discussion going. Please keep this topic technical, not (whose heads should I buy) this thread isn't promoting one vendor over another, it about posting about heads, and what makes a good head along with how to measure that. One of the other points I will be going into is what does and doesn't make a good port.
Some folks don't realize it, but something I will try to illustrate is that you can have a head that on the flowbench will flow LESS than another head with similar port volume, and the head flowing LESS CAN still make more power. I'm not saying its always the case. But, it can happen. If the heads are done right (and that is a big IF), more flow should equal more power. The thing about the flowbench is you can take material out of the head that will make it look good on the bench, but in reality will cost HP.
Let me cite another example:
Again, I am not going to name the two heads that were tested, For the purpose of this test I will refer to the vendors a Brand X and Brand Y.
In a test of Brand X heads vs Brand Y heads. Brand Y flows as well on the bench (as good as a Brand X), but don't seem to make the same power on the dyno,etc. From discussing it with the head porter (@ Brand X), he was mentioning that Brand Y removes material in areas that will show a gain on the flow bench, but will not make anymore power on the dyno. He says they are big in the wrong spots and too small in others.
A set of Brand Y stage 2s 5.3l heads on a car that had all the bolt ons and a TR224 cam. It made 379/370 or so before adding the heads. After the heads, the car did 413/385 after tuning.
A week before, Another car had a set of Brand X stage 2 5.3l heads on a car that already had the TR224 cam as well and the IDENTICAL mods as the other Brand Y car (FLPs, LS6 intake, ASP, stock rear/4:10s,etc). Both dynoed the exact same before swapping heads on (the curves practically overlayed oneanother). This car pulled 443/418 with the Brand Xs!
On the flow bench, the Brand Ys actually flowed better from .100-.550, while Brand X flowed slightly better past this. Same thing on the exhaust side. This just goes to show that a flow bench is an excellent tool, but not something that should be used as the determing factor in how a head will perform when put on a motor. The CC volumes were identical on the two heads, so compression difference wasn't an issue.
So, you see, it looked good on the bench, but in reality, the power just wasn't there.
Anyhow, I'm posting this to get the discussion going. Please keep this topic technical, not (whose heads should I buy) this thread isn't promoting one vendor over another, it about posting about heads, and what makes a good head along with how to measure that. One of the other points I will be going into is what does and doesn't make a good port.
09-09-2004, 02:06 PM
#6
Good topic, a bit long of a intro as normal J-Rod, but then again you must like to type a lot.
Inflated numbers have come about because of the internet, plain and simple. There are so many choices out there now for head porting that guys really do more "bench" racing now than they ever did before. Flow bench racing has become a thing of it's own now, and everyone seems to have a 300+cfm LS1 head to offer. Hey now there are even 300+cfm LT1 castings out there. I've yet to actually see one do that, but flow bench racing is flow bench racing.
On the other hand, dyno racing seems to be pretty big now too. A dyno is great when you get before and after numbers, i.e. I gained 58hp from a cam swap over my full bolt on dyno run. A flow bench is the same way, if on the same bench a cylinder head goes from 215cfm to 280cfm and you can see the whole flow curve and it's improvements then you can actually quantify what happened there.
Some of the more important things that never are talked about on here are things like minimum cross sectional area, port tapper, port sizes relative to cubes, RPM and engine useage. On top of that now we have developments in wet flow which are making huge differences in port shapes and development.
Then again the parts that are on the cylinder head and the shape and size of the chamber also have a lot to do with power production. When you get into economical head wars then you start seeing lower quality parts installed on the heads to keep the prices down. It's a fact of life. If we had higher quality valves, retainers, springs etc.... on the heads you could easily see a huge price jump if they had those types of parts in them.
One of the things I think that is most important in head porting or any engine machine work, either a CNC machine needs to do the work or the guy who owns the company and has his name on the line (and cares) does the work. You can have a large company that does very good work, but the guys working for the shop are getting paid well and so the hourly shop rate is going to be extremly high. A CNC when opperated/programed properly can do a very repeatable job, The problem is that stock OEM casting cores are not accurate and don't mix well with CNC machines. That's where the problem comes in, you either get a highly skilled head porter who works with stock castings which is not cheap or you get a head casting that needs to be finished by a CNC machine. (meaning AFR castings and a CNC porting) either way is not cheap. When things need to go down the econmic scale then you have to comprimise either less labor time spent on the heads by hand or a CNC port that is configured to work with a stock casting and all of it's port core shifts.
Engines and anything that takes machine work is really a "get what you pay for" business. When it comes to competiton and beating the guy in the other lane prices get out of hand in a hurry, but then again results are what matters.
My opinion is that we all focus on flow numbers way too much. A good set of cylinder heads, a properly matched valvetrain and a well built motor are going to go farther than anything else. The combination is the key, you can have the baddest *** heads in the world but if the rest of the motor is junk then you just wasted a lot of money. Next you need the setup, and driving skills to get the car to work with the power that you give it.
Bret
Inflated numbers have come about because of the internet, plain and simple. There are so many choices out there now for head porting that guys really do more "bench" racing now than they ever did before. Flow bench racing has become a thing of it's own now, and everyone seems to have a 300+cfm LS1 head to offer. Hey now there are even 300+cfm LT1 castings out there. I've yet to actually see one do that, but flow bench racing is flow bench racing.
On the other hand, dyno racing seems to be pretty big now too. A dyno is great when you get before and after numbers, i.e. I gained 58hp from a cam swap over my full bolt on dyno run. A flow bench is the same way, if on the same bench a cylinder head goes from 215cfm to 280cfm and you can see the whole flow curve and it's improvements then you can actually quantify what happened there.
Some of the more important things that never are talked about on here are things like minimum cross sectional area, port tapper, port sizes relative to cubes, RPM and engine useage. On top of that now we have developments in wet flow which are making huge differences in port shapes and development.
Then again the parts that are on the cylinder head and the shape and size of the chamber also have a lot to do with power production. When you get into economical head wars then you start seeing lower quality parts installed on the heads to keep the prices down. It's a fact of life. If we had higher quality valves, retainers, springs etc.... on the heads you could easily see a huge price jump if they had those types of parts in them.
One of the things I think that is most important in head porting or any engine machine work, either a CNC machine needs to do the work or the guy who owns the company and has his name on the line (and cares) does the work. You can have a large company that does very good work, but the guys working for the shop are getting paid well and so the hourly shop rate is going to be extremly high. A CNC when opperated/programed properly can do a very repeatable job, The problem is that stock OEM casting cores are not accurate and don't mix well with CNC machines. That's where the problem comes in, you either get a highly skilled head porter who works with stock castings which is not cheap or you get a head casting that needs to be finished by a CNC machine. (meaning AFR castings and a CNC porting) either way is not cheap. When things need to go down the econmic scale then you have to comprimise either less labor time spent on the heads by hand or a CNC port that is configured to work with a stock casting and all of it's port core shifts.
Engines and anything that takes machine work is really a "get what you pay for" business. When it comes to competiton and beating the guy in the other lane prices get out of hand in a hurry, but then again results are what matters.
My opinion is that we all focus on flow numbers way too much. A good set of cylinder heads, a properly matched valvetrain and a well built motor are going to go farther than anything else. The combination is the key, you can have the baddest *** heads in the world but if the rest of the motor is junk then you just wasted a lot of money. Next you need the setup, and driving skills to get the car to work with the power that you give it.
Bret
09-09-2004, 02:10 PM
#7
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I will have to say this is all true. The only problem I have with this info is that my home ported heads on the intake flowed on a 1020 bench was anywhere from 267-273 and on the exhaust was 204-207. I am not a professional and I do not think I can port as well as any of the xyz companies. The #'s are a little low on the intake side IMO, not to say they are not true #'s.
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09-09-2004, 02:17 PM
#8
This is excellent information! I'm glad someone finally took the time to explain this in such great detail. I couldn't agree with you more! I have tried to explain this concept to individuals in the past and just didn't have the patience to do it to this level. The best part is that you have the test data to back it up. Great post!
I have a guy in PA that does all of my port work for me. He has been porting all types of cylinder heads for over 35 years and really knows his stuff. He does all of the work himself...no one else works for him. I bring him alot of business, so he gives me an excellent price on his work. He actually asked me to become a sponsor on this site in order to market his porting service to the LS1 crowd, but I have thusfar refused to do so, simply because of these kinds of misunderstanding and misconceptions. He (and I) refuse to fudge flow numbers and reconfigure his flow bench to "optimize" the final numbers on a specific style of heads. Its really hard to market a set of heads that flow 280CFM when others are claiming 300+. Unfortunately, that seems to be the only way to be competitive.
I have a guy in PA that does all of my port work for me. He has been porting all types of cylinder heads for over 35 years and really knows his stuff. He does all of the work himself...no one else works for him. I bring him alot of business, so he gives me an excellent price on his work. He actually asked me to become a sponsor on this site in order to market his porting service to the LS1 crowd, but I have thusfar refused to do so, simply because of these kinds of misunderstanding and misconceptions. He (and I) refuse to fudge flow numbers and reconfigure his flow bench to "optimize" the final numbers on a specific style of heads. Its really hard to market a set of heads that flow 280CFM when others are claiming 300+. Unfortunately, that seems to be the only way to be competitive.
Last edited by GC99TA; 09-09-2004 at 05:20 PM.
09-09-2004, 03:17 PM
#10
I guess now that I've made my "Great Post!" post, I can hopefully add some technical information to this thread, or at least stir up some further questions. Another thing that always bothers me about cylinder head discussions is the following: People always seem to be afraid of running a set of heads that have been milled, due to the perceived "loss" in piston to valve clearance. That train of thought is understandable, if the heads have only been milled and nothing else was done to them. But, if a set of heads is worked properly, the tips of the valve stems should be put back to the correct height/location in relation to the deck of the head and push rods. This is done to maintain proper valvetrain geometry. Of course, in addition to doing this, you must also run an shim under you rockers that is equivelent to the amount of material removed from the deck of the heads. For example, if a head is milled .030, everything on that head is now .030 lower than it used to be, but the pushrods will still be at the stock height. So, to maintain proper valvetrain geometry, one must sink (or raise) the vavles .030. Doing this puts the tip of the valve stem at the proper height in relation to the pushrod height. Add an equivelent shim under the rocker arm and all is good. What this also does, is gives you back your .030 piston to valve clearance you lost when you milled the heads. Some may say the solution is to run a .030 shorter push rod, but I don't think that is the best solution. So I guess my question/point is: Is everyone thinking they're losing P/V clearance due to a misunderstanding about what is actually being done to their heads, or is it because alot of the porters out there simply are not correcting valve locations when milling their heads?
Last edited by GC99TA; 09-09-2004 at 03:25 PM.
09-09-2004, 04:22 PM
#11
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I'd like to also add something, to expose the smaller displacement truck crowd. Ones who which are not payed attention to as much, especially when it comes to head work.
Over and over I've seen vendors try to sell ported 5.3 heads to us. This would be great if they weren't already worked to fit the LS1. The bore sizes between the 5.3L and 5.7L are different. I guess this is just overlooked.
What gets on my nerves is the valve size they recommend. 2.02intake valves, 1.57exhaust valves. Maybe this is normal on a 346ci motor, but thats just a tad bit big on a 325ci, dont you think? I know some non-vendors who think so, but they don't know anything.
Theres also a guy in the truck crowd with a 5.3 getting his heads worked. He has been told he will achieve 10:9.1 compression. I wish I had more information on this but the buyer isn't even aware how a point and a half in compression is going to be achieved. Something seems fishy about it all.
Send these crooks to Tech jail.
Over and over I've seen vendors try to sell ported 5.3 heads to us. This would be great if they weren't already worked to fit the LS1. The bore sizes between the 5.3L and 5.7L are different. I guess this is just overlooked.
What gets on my nerves is the valve size they recommend. 2.02intake valves, 1.57exhaust valves. Maybe this is normal on a 346ci motor, but thats just a tad bit big on a 325ci, dont you think? I know some non-vendors who think so, but they don't know anything.
Theres also a guy in the truck crowd with a 5.3 getting his heads worked. He has been told he will achieve 10:9.1 compression. I wish I had more information on this but the buyer isn't even aware how a point and a half in compression is going to be achieved. Something seems fishy about it all.
Send these crooks to Tech jail.
09-09-2004, 05:03 PM
#12
Originally Posted by SportSide 5.3
Over and over I've seen vendors try to sell ported 5.3 heads to us. This would be great if they weren't already worked to fit the LS1. The bore sizes between the 5.3L and 5.7L are different. I guess this is just overlooked.
I'm beginning to believe more and more that the best set-up is a ported LS1 head, milled to produce the desired compression ratio. Don't you guys remember when it was popular to put 305 heads on 350s for the same reason? That never worked out that great either.
09-09-2004, 05:57 PM
#13
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Originally Posted by GC99TA
I guess now that I've made my "Great Post!" post, I can hopefully add some technical information to this thread, or at least stir up some further questions. Another thing that always bothers me about cylinder head discussions is the following: People always seem to be afraid of running a set of heads that have been milled, due to the perceived "loss" in piston to valve clearance. That train of thought is understandable, if the heads have only been milled and nothing else was done to them. But, if a set of heads is worked properly, the tips of the valve stems should be put back to the correct height/location in relation to the deck of the head and push rods. This is done to maintain proper valvetrain geometry. Of course, in addition to doing this, you must also run an shim under you rockers that is equivelent to the amount of material removed from the deck of the heads. For example, if a head is milled .030, everything on that head is now .030 lower than it used to be, but the pushrods will still be at the stock height. So, to maintain proper valvetrain geometry, one must sink (or raise) the vavles .030. Doing this puts the tip of the valve stem at the proper height in relation to the pushrod height. Add an equivelent shim under the rocker arm and all is good. What this also does, is gives you back your .030 piston to valve clearance you lost when you milled the heads. Some may say the solution is to run a .030 shorter push rod, but I don't think that is the best solution. So I guess my question/point is: Is everyone thinking they're losing P/V clearance due to a misunderstanding about what is actually being done to their heads, or is it because alot of the porters out there simply are not correcting valve locations when milling their heads?
09-09-2004, 07:06 PM
#14
Originally Posted by TD's z
that is a good idea but in sinking the valve job you inlarge the chambers and 90% of the time you you end up hurting the flow unless of coarse if you grind even more material out of the chamber to get it back to the same shape
thing was an attempt to make me look stupid, I can do with out it. I would expect a little more professionalism from someone representing a site sponsor. No hard feelings though, I've got thick skin and this is a tech thread, not preschool. So it sounds like you have some expierience with sinking the valves to regain piston to valve clearance. What is the typical loss in flow that you have seen with this method?
09-09-2004, 08:31 PM
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Actually alot of the marketing of the 5.3 heads is aimed at LS1 (5.7) guys.
09-09-2004, 09:08 PM
#16
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CG99TA,whats the point of milling your heads then sinking the valves?The valve heads make up about 80% of the area in the chamber,besides sinking the valves hurts flow and changes the spring installed height.The correct solution is .030 shorter pushrods.You lose all you gain with the milling process,I mean compression if you sink the valves.
J-ROD,great post AGAIN but 276 on the intake flow??A stock 241 will flow about 250 or so at .500.All I can say is he"s not a good headporter!!Since the other guy ported his own heads and got similar results,what gives?This will be a interesting post no doubt!!
J-ROD,great post AGAIN but 276 on the intake flow??A stock 241 will flow about 250 or so at .500.All I can say is he"s not a good headporter!!Since the other guy ported his own heads and got similar results,what gives?This will be a interesting post no doubt!!
09-09-2004, 10:48 PM
#17
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j-rod i would like to invite you to watch my car get dynoed at H.P.E. in the next couple of weeks.....since i know you are a big fan of the corvette world....it should be pretty impressive,,,,the smallest number my heads flowed was 352 at .650 lift this was a 60cc head with a 2.08 valve i belive on a 4.00 inch bore....
09-09-2004, 10:54 PM
#18
FormerVendor
I've seen ported LS6 heads that only flowed 10-15 cfm more than stock. Fixing them by throwing them away and starting over with new castings and getting them really ported by someone that knew what they were doing netted 14 mph in the 1/4 on that car. Those original heads were done by a former LS1tech sponsor no longer here. After fixing this situation the car ran over 140mph and mid nines. 
09-09-2004, 11:14 PM
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ok, i read everything you have said, but forgive me if you already answered this question. From what you are saying, what can we as the customers/consumers do to make sure we are getting what we want. I mean we can't ask vendor X if we can borrow a set of those heads to flow on our own bench to verify and then dyno to see if we like them or not. I wish I had the resources and the time to do some of my own research. I would love to pull my heads and flow them. As far as dyno numbers go I too have always agreed that dyno numbers don't tell everything. First off their are some FREAK cars out there that just dyno high with whatever you mod them with and of course the dyno tricks.
Thanks for making this post. Maybe see ya around town soon.
Thanks for making this post. Maybe see ya around town soon.