Cylinder Head EXPERTS***
02-04-2010, 02:39 PM
#1
Cylinder Head EXPERTS*** I know everybody talks about How much a cylinder head flows at .600 and ofcourse the higher it flows at .400 ofcourse the better the head is as well as the smaller the runner, more velocity, etc, etc... My question is to you guys that know about heads, How big of a role do the exhaust numbers effect the performance of the head?? I mean, does it have to do alot with the cam as far as the bigger the lobe the more exhaust is needed on the cylinder head??
I see all these heads that that have great numbers and then I see the exhaust numbers and those vary greatly between different companies heads. I would really like input from from anyone that designs/helps design heads. Thanks in advance
I see all these heads that that have great numbers and then I see the exhaust numbers and those vary greatly between different companies heads. I would really like input from from anyone that designs/helps design heads. Thanks in advance
02-04-2010, 05:36 PM
#3
I know everybody talks about How much a cylinder head flows at .600 and ofcourse the higher it flows at .400 ofcourse the better the head is as well as the smaller the runner, more velocity, etc, etc... My question is to you guys that know about heads, How big of a role do the exhaust numbers effect the performance of the head?? I mean, does it have to do alot with the cam as far as the bigger the lobe the more exhaust is needed on the cylinder head??
I see all these heads that that have great numbers and then I see the exhaust numbers and those vary greatly between different companies heads. I would really like input from from anyone that designs/helps design heads. Thanks in advance
I see all these heads that that have great numbers and then I see the exhaust numbers and those vary greatly between different companies heads. I would really like input from from anyone that designs/helps design heads. Thanks in advance
I will quickly throw in my two cents here.
IMO, the exhaust port plays a larger role than some give credit for (or pay attention to). Not to mention the strength of the exhaust port also helps dictate camshaft selection and usable RPM range. A strong exhaust can help a curve hang on longer upstairs and a weaker one forcing an earlier (lower) peak and a power curve that drops off more aggressively (not desirable obviously).
Its back to the oversimplification of an engine being described as an air pump, but the reality is that's a very accurate oversimplification. If you cant properly evacuate the burnt gases and spent charge you will never get a complete fill of the next fresh charge ready to enter the cylinder. Once that happens your energy from combustion starts to drop off as well as your total power output. Exhaust flow has a larger impact on high RPM power because the exhaust port has much less time to get the job done.
Also, don't get caught up in comparing "advertised" flow numbers....I could go on for days on this topic (see my Interesting Flow Data thread sticky at the top of this page). Inquire what type of flowbench is being used and even if its the same drawing conclusions is a dicey proposition. Awhile back a different site sponsor claimed our 205 heads flowed 265 CFM while we only advertise 230. They aren't using a SuperFlow style (fixed orifice) type of bench and the type of equipment they use tends to read extremely generous on the exhaust side.
The best test of any products worthy of comparison is on the same bench at the same facility (no different than chassis dynos)....this way, whether that bench reads low, high, or in the middle, all the numbers have the same advantage or disadvantage.
Hope this helps....
-Tony
02-04-2010, 08:17 PM
#4
I'm no expert but I have always heard the majority of the power is made around the valve and the bowl. I guess that's why in the early days guys did so much work with valve angles.
Is this correct Tony?
Is this correct Tony?
Last edited by printmanjackson; 02-04-2010 at 08:23 PM.
02-05-2010, 02:21 AM
#5
Bottom line, port shape, chamber shape, valve job, proper port sizing (CSA), and even the shape of the valve all have a significant impact on flow....its the optimization of all these attributes than can separate an average head from a very good head.
Much like an engine, combination is key....you cant just hit a few of those details and expect a top of the line piece.
-Tony
02-05-2010, 09:36 AM
#6
OK...
I will quickly throw in my two cents here.
IMO, the exhaust port plays a larger role than some give credit for (or pay attention to). Not to mention the strength of the exhaust port also helps dictate camshaft selection and usable RPM range. A strong exhaust can help a curve hang on longer upstairs and a weaker one forcing an earlier (lower) peak and a power curve that drops off more aggressively (not desirable obviously).
Its back to the oversimplification of an engine being described as an air pump, but the reality is that's a very accurate oversimplification. If you cant properly evacuate the burnt gases and spent charge you will never get a complete fill of the next fresh charge ready to enter the cylinder. Once that happens your energy from combustion starts to drop off as well as your total power output. Exhaust flow has a larger impact on high RPM power because the exhaust port has much less time to get the job done.
Also, don't get caught up in comparing "advertised" flow numbers....I could go on for days on this topic (see my Interesting Flow Data thread sticky at the top of this page). Inquire what type of flowbench is being used and even if its the same drawing conclusions is a dicey proposition. Awhile back a different site sponsor claimed our 205 heads flowed 265 CFM while we only advertise 230. They aren't using a SuperFlow style (fixed orifice) type of bench and the type of equipment they use tends to read extremely generous on the exhaust side.
The best test of any products worthy of comparison is on the same bench at the same facility (no different than chassis dynos)....this way, whether that bench reads low, high, or in the middle, all the numbers have the same advantage or disadvantage.
Hope this helps....
-Tony
I will quickly throw in my two cents here.
IMO, the exhaust port plays a larger role than some give credit for (or pay attention to). Not to mention the strength of the exhaust port also helps dictate camshaft selection and usable RPM range. A strong exhaust can help a curve hang on longer upstairs and a weaker one forcing an earlier (lower) peak and a power curve that drops off more aggressively (not desirable obviously).
Its back to the oversimplification of an engine being described as an air pump, but the reality is that's a very accurate oversimplification. If you cant properly evacuate the burnt gases and spent charge you will never get a complete fill of the next fresh charge ready to enter the cylinder. Once that happens your energy from combustion starts to drop off as well as your total power output. Exhaust flow has a larger impact on high RPM power because the exhaust port has much less time to get the job done.
Also, don't get caught up in comparing "advertised" flow numbers....I could go on for days on this topic (see my Interesting Flow Data thread sticky at the top of this page). Inquire what type of flowbench is being used and even if its the same drawing conclusions is a dicey proposition. Awhile back a different site sponsor claimed our 205 heads flowed 265 CFM while we only advertise 230. They aren't using a SuperFlow style (fixed orifice) type of bench and the type of equipment they use tends to read extremely generous on the exhaust side.
The best test of any products worthy of comparison is on the same bench at the same facility (no different than chassis dynos)....this way, whether that bench reads low, high, or in the middle, all the numbers have the same advantage or disadvantage.
Hope this helps....
-Tony
Thanks Tony, Its definately useful information. Now,....back to the drawing board again. LOL
02-05-2010, 09:45 AM
#7
When it comes to heads... I'd look at what kind of lift you want to run, then aim to find heads that will flow as much as possible at the lift you want to run and under, if you're looking at heads taht flow 400 at 800 lift, but are only going to open them up to 600, thst head probably won't be the best choice.
Also, fwiw, this is somewhat general, but I find that heads with really good upper lift #'s usually are weaker in the bottom lift areas. Again, more critical if you don't plan on running the lift up to and past the max flow of the head.
Runner size, smaller are generally more street friendly, bigger runners are more of a race thing, as they are usually a higher lift/flowing head. Example, a race car with a set of heads that flow 400 cfm at 800 lift, and has an 820 lift camshaft, that leaves the line at 5000 rpm and never sees anything less then 5000 the whole track pass won't care about the power at anything under that mark.... street car that only sees over 5000 maybe 5% of it's life (if that much) is going to care about the 3000 rpm power alot more, meaning port velocity is going to be more improtant, as well as low lift flow #'s
In the end, what is your use for the car, and then what is the power goal? A car that makes a peak of 500 rwhp but makes 400 rwhp at 3800 rpm is gonna feel a TON faster on the street then a car that makes 550 peak and is only making 300 hp at 3800 rpm.
But, that 550 hp car, if geared right, will be faster at the track.
Make sense?
Also, fwiw, this is somewhat general, but I find that heads with really good upper lift #'s usually are weaker in the bottom lift areas. Again, more critical if you don't plan on running the lift up to and past the max flow of the head.
Runner size, smaller are generally more street friendly, bigger runners are more of a race thing, as they are usually a higher lift/flowing head. Example, a race car with a set of heads that flow 400 cfm at 800 lift, and has an 820 lift camshaft, that leaves the line at 5000 rpm and never sees anything less then 5000 the whole track pass won't care about the power at anything under that mark.... street car that only sees over 5000 maybe 5% of it's life (if that much) is going to care about the 3000 rpm power alot more, meaning port velocity is going to be more improtant, as well as low lift flow #'s
In the end, what is your use for the car, and then what is the power goal? A car that makes a peak of 500 rwhp but makes 400 rwhp at 3800 rpm is gonna feel a TON faster on the street then a car that makes 550 peak and is only making 300 hp at 3800 rpm.
But, that 550 hp car, if geared right, will be faster at the track.
Make sense?
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02-05-2010, 10:59 AM
#8
JL ws-6: Thanks for the input. On that end, I pretty much have it covered. These are new heads that I am upgrading to from my old setup. Its still going to be a street/strip car, but mainly street. So I understand what you are saying about flow numbers. My question was How the EXHAUST flow numbers played a role on the heads as far as performance. (I.E. wider split on the cam=bigger exhaust flow, Higher LSA=smaller exhaust flow, etc, etc.) Tony gave some good advice on Post #3, but I really didnt get the whole picture on how the size differences on the cam effect it.
Tony: So what Im getting out of your post is that regardless of cam, its always better to have a bigger exhaust flow through out the curve? Please correct me if im wrong.
Tony: So what Im getting out of your post is that regardless of cam, its always better to have a bigger exhaust flow through out the curve? Please correct me if im wrong.
02-05-2010, 11:11 AM
#9
Essentially yes, the better exhaust flow is always welcome, the better the exhaust port is the less you need to split the duration on the cam (unless you have a bottleneck in the exhaust, but that's a different topic for the sake of saying)
That being said, if your intake to exhaust ratio is in a good place (say .8 or higher for the sake of saying) you can get away with less of a split then on a car with a worse ratio, of say .6 for the sake of saying.
A head with a .8 ratio, probably needs about 4 to 5 degrees more duration on the exhasut, a head with a .6 ratio will probably need about 10 to 12 degrees more exhaust duration, a head with a .9 would need just about none at all.... for example.
That being said, if your intake to exhaust ratio is in a good place (say .8 or higher for the sake of saying) you can get away with less of a split then on a car with a worse ratio, of say .6 for the sake of saying.
A head with a .8 ratio, probably needs about 4 to 5 degrees more duration on the exhasut, a head with a .6 ratio will probably need about 10 to 12 degrees more exhaust duration, a head with a .9 would need just about none at all.... for example.
02-05-2010, 01:48 PM
#13
How about NEITHER does this. Make sure when you call someone out on something, that you dont have crap in your pants at the same time.
02-06-2010, 04:56 PM
#20
http://autospeed.com/cms/title_Flow-...5/article.html
