CFM question
09-14-2006, 10:49 PM
#1
CFM question
On the stealthram.com mainpage it says that the HSR flows 275cfm per runner assembled. Does this mean that if you use heads that flow over 275cfm that the HSR becomes a bottleneck in you system? I believed that to be true but now people tell me that CFM as it pertains to carbs and intakes is not the same as CFM when it comes to head flow. In other words, you can't compare the numbers you get for heads off a flow bench to what the intake manifold is rated at. I'm already using a Stealth Ram from the first batch back in '03 but I now have a set of heads that peak at 311cfm @ .600". I've read that the newer castings can easily be ported out to a Fel Pro 1205 (which is what my heads were ported to). If I need to upgrade my intake then I will purchase one of these newer castings (assuming summit would automatically send me one of the '06 castings, since they have it cheaper than anyone else) and get it ported to support over 300cfm and to match the Fel Pro 1205. So I guess I just want to know if I will definitely have to upgrade to a newer HSR for my the heads I plan on using.
09-14-2006, 11:09 PM
#2
I got my HSR a few years ago from Summit and it takes a 1205 gasket.
I'd think a 311 head would need a 1206 gasket. So that 311 might be a little optimistic. You might want to spend $20 and have those heads independently flowed. But I've yet to run a cam big enough to use a 311 23* head so what do I know.
The best way to tell if the intake is a restriction is to flow the head before and after the intake is installed. But not all flow benches are big enough to do it at 28". So they do it at a different pressure and convert the numbers to 28". And true there is some difference in how carbs are flowed.
If you don't know the method used, then you have to do a little research on the carb. ie a 950HP Holley only flows about 820cfm. Why, because all the competition was flowing them the other way and advertising big numbers. So Holley had to follow suit. But the dyno doesn't lie and a 1050 Dominator compared the same (difference) to an List# 4781 850 and the 950HP on a 468 bbc. So people started digging.
I'd think a 311 head would need a 1206 gasket. So that 311 might be a little optimistic. You might want to spend $20 and have those heads independently flowed. But I've yet to run a cam big enough to use a 311 23* head so what do I know.
The best way to tell if the intake is a restriction is to flow the head before and after the intake is installed. But not all flow benches are big enough to do it at 28". So they do it at a different pressure and convert the numbers to 28". And true there is some difference in how carbs are flowed.
If you don't know the method used, then you have to do a little research on the carb. ie a 950HP Holley only flows about 820cfm. Why, because all the competition was flowing them the other way and advertising big numbers. So Holley had to follow suit. But the dyno doesn't lie and a 1050 Dominator compared the same (difference) to an List# 4781 850 and the 950HP on a 468 bbc. So people started digging.
09-15-2006, 07:27 PM
#3
I got my HSR a few years ago from Summit and it takes a 1205 gasket.
I'd think a 311 head would need a 1206 gasket. So that 311 might be a little optimistic. You might want to spend $20 and have those heads independently flowed. But I've yet to run a cam big enough to use a 311 23* head so what do I know.
The best way to tell if the intake is a restriction is to flow the head before and after the intake is installed. But not all flow benches are big enough to do it at 28". So they do it at a different pressure and convert the numbers to 28". And true there is some difference in how carbs are flowed.
If you don't know the method used, then you have to do a little research on the carb. ie a 950HP Holley only flows about 820cfm. Why, because all the competition was flowing them the other way and advertising big numbers. So Holley had to follow suit. But the dyno doesn't lie and a 1050 Dominator compared the same (difference) to an List# 4781 850 and the 950HP on a 468 bbc. So people started digging.
I'd think a 311 head would need a 1206 gasket. So that 311 might be a little optimistic. You might want to spend $20 and have those heads independently flowed. But I've yet to run a cam big enough to use a 311 23* head so what do I know.
The best way to tell if the intake is a restriction is to flow the head before and after the intake is installed. But not all flow benches are big enough to do it at 28". So they do it at a different pressure and convert the numbers to 28". And true there is some difference in how carbs are flowed.
If you don't know the method used, then you have to do a little research on the carb. ie a 950HP Holley only flows about 820cfm. Why, because all the competition was flowing them the other way and advertising big numbers. So Holley had to follow suit. But the dyno doesn't lie and a 1050 Dominator compared the same (difference) to an List# 4781 850 and the 950HP on a 468 bbc. So people started digging.
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