Air flow question
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Air flow question
I been trying to make sense of a couple of things.
I have posted several questions about an L98 engine build that will pass California emissions. I already have a set of AFR 195cc heads with competition porting. Recommendations have been a Superram, Lingenfelter 74219 camshaft (219/219 duration @ .050 .560"/.560" with 1.6 rocker), and a 383. Ok, sounds good.
After looking at all the airflows of everything, I have one question: what is the "choke point" for this engine? Does increasing airflow in any of these components really going to improve performance or is the engine going to get all it needs?
The reason I ask is that I think that my heads are too much for the engine. Even with an extrude honed Superram, one site shows each runner capable of flowing 240cfm, which is what the heads flow at 0.4". I understand that just because the cam lifts 0.56" doesnt mean 280cfm will be flowing through the intake valves.
My goal is to build this engine once and be done with it and not have to play with it trying to tweek it. Thanks for your input.
I have posted several questions about an L98 engine build that will pass California emissions. I already have a set of AFR 195cc heads with competition porting. Recommendations have been a Superram, Lingenfelter 74219 camshaft (219/219 duration @ .050 .560"/.560" with 1.6 rocker), and a 383. Ok, sounds good.
After looking at all the airflows of everything, I have one question: what is the "choke point" for this engine? Does increasing airflow in any of these components really going to improve performance or is the engine going to get all it needs?
The reason I ask is that I think that my heads are too much for the engine. Even with an extrude honed Superram, one site shows each runner capable of flowing 240cfm, which is what the heads flow at 0.4". I understand that just because the cam lifts 0.56" doesnt mean 280cfm will be flowing through the intake valves.
My goal is to build this engine once and be done with it and not have to play with it trying to tweek it. Thanks for your input.
Burning Brakes
Joined: Jun 2003
Posts: 937
Likes: 0
From: Bedford Tx
are there some people on this forum that think
that flow numbers should 'match'?
if so, what would you rather have?
1} three components,
...300 cfm@1 psi, 300cfm@1psi, 300cfm@1psi,
2}different three components,
...300cfm@1psi, 300cfm@0.5psi, 300cfm@0.7psi
? one system flows 300cfm@3psi, the other
flows 300cfm @2.2psi ???
that flow numbers should 'match'?
if so, what would you rather have?
1} three components,
...300 cfm@1 psi, 300cfm@1psi, 300cfm@1psi,
2}different three components,
...300cfm@1psi, 300cfm@0.5psi, 300cfm@0.7psi
? one system flows 300cfm@3psi, the other
flows 300cfm @2.2psi ???
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
As far as whether the components are properly matched, spend a hundred bucks to buy the Engine Analyzer program and run simulations to your heart's content.
When the Mach index gets up to about 0.55 the inlet system is essentially choked, and the engine won't make any more power or revs unless you have higher flowing components.
Anything else is just guessing!
Duke
When the Mach index gets up to about 0.55 the inlet system is essentially choked, and the engine won't make any more power or revs unless you have higher flowing components.
Anything else is just guessing!
Duke
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Originally Posted by Performance nut
I been trying to make sense of a couple of things.
I have posted several questions about an L98 engine build that will pass California emissions. I already have a set of AFR 195cc heads with competition porting. Recommendations have been a Superram, Lingenfelter 74219 camshaft (219/219 duration @ .050 .560"/.560" with 1.6 rocker), and a 383. Ok, sounds good.
After looking at all the airflows of everything, I have one question: what is the "choke point" for this engine? Does increasing airflow in any of these components really going to improve performance or is the engine going to get all it needs?
The reason I ask is that I think that my heads are too much for the engine. Even with an extrude honed Superram, one site shows each runner capable of flowing 240cfm, which is what the heads flow at 0.4". I understand that just because the cam lifts 0.56" doesnt mean 280cfm will be flowing through the intake valves.
My goal is to build this engine once and be done with it and not have to play with it trying to tweek it. Thanks for your input.
I have posted several questions about an L98 engine build that will pass California emissions. I already have a set of AFR 195cc heads with competition porting. Recommendations have been a Superram, Lingenfelter 74219 camshaft (219/219 duration @ .050 .560"/.560" with 1.6 rocker), and a 383. Ok, sounds good.
After looking at all the airflows of everything, I have one question: what is the "choke point" for this engine? Does increasing airflow in any of these components really going to improve performance or is the engine going to get all it needs?
The reason I ask is that I think that my heads are too much for the engine. Even with an extrude honed Superram, one site shows each runner capable of flowing 240cfm, which is what the heads flow at 0.4". I understand that just because the cam lifts 0.56" doesnt mean 280cfm will be flowing through the intake valves.
My goal is to build this engine once and be done with it and not have to play with it trying to tweek it. Thanks for your input.
My build is EO compliant here in California, and just recently dyno'd at 504 torque at the wheels...............you're on the right track with your build!
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Originally Posted by Caboboy
I have this exact same setup on a 421CID. My Superram was hand ported and flows 280 on the bench. Extrude hone claims they can get me 290+ but I don't need that (it was gonna be $650). My heads flow 286 @ .500 and 292 @ .600 with a cam lift of .560, so as you can see, your parts are well matched.
My build is EO compliant here in California, and just recently dyno'd at 504 torque at the wheels...............you're on the right track with your build!
My build is EO compliant here in California, and just recently dyno'd at 504 torque at the wheels...............you're on the right track with your build!
If you dont mind me asking, what cam are you using and what were your last smog numbers?
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Originally Posted by Performance nut
Wow, 421. I assume that is an aftermarket block? Those flow numbers are excellent not to mention the power.
If you dont mind me asking, what cam are you using and what were your last smog numbers?
If you dont mind me asking, what cam are you using and what were your last smog numbers?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by Caboboy
Same cam as you plan.....in fact the whole setup is the same (see sig). It's a factory 400 block bored .030 over and stroked to 3.875....... I don't recall the exact smog numbers, but I do recall it was clean as a whistle
So does that mean that you got the chip all figured out?
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Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
U want numbers? Ok try these.
Lets look at airflow per cylinder:
For a 383ci mtr @ 6500rpm thats only 48ci/cyl with only 3250 (6500rpm/2) intake strokes per min.
And with 1 ft3 = 1728ci we have (48ci/1728)x3250strokes/min = 90cfm each cyl (or 720cfm entire eng @6500rpm).
Well with a optomistic volumetric effecency of .9 produces a flow of only 81 cfm each cyl.
So this kinda throws out those 240ish cfm flow numbers as a realistic number (man sometime i out figure and surprise myself
).
I see u posted u understand thats not what really flowing through the head. But for comparision thats what the head can flow. Its just a guide line for comparision and can be helpful.
And really what we all want is low restriction with high flow numbers with maintaining good port velocity at low flows. What i'm saying is a head that flows 240cfm @ .5" lift with a small runner (180cc) would be my choise over a head that flows same but has a larger runner (195cc). No way it will ever get to see 240cfm without supercharging.
Choke point is the vlv from what i've read but everything between the vlv and atmosphere that adds restriction will reduces flow and power. That why sometimes even the air filter can be the power thief.
Look at each part to reduce restrictions and do the best u can with ur own buget.
Good luck. cardo0
For a 383ci mtr @ 6500rpm thats only 48ci/cyl with only 3250 (6500rpm/2) intake strokes per min.
And with 1 ft3 = 1728ci we have (48ci/1728)x3250strokes/min = 90cfm each cyl (or 720cfm entire eng @6500rpm).
Well with a optomistic volumetric effecency of .9 produces a flow of only 81 cfm each cyl.
So this kinda throws out those 240ish cfm flow numbers as a realistic number (man sometime i out figure and surprise myself
).I see u posted u understand thats not what really flowing through the head. But for comparision thats what the head can flow. Its just a guide line for comparision and can be helpful.
And really what we all want is low restriction with high flow numbers with maintaining good port velocity at low flows. What i'm saying is a head that flows 240cfm @ .5" lift with a small runner (180cc) would be my choise over a head that flows same but has a larger runner (195cc). No way it will ever get to see 240cfm without supercharging.
Choke point is the vlv from what i've read but everything between the vlv and atmosphere that adds restriction will reduces flow and power. That why sometimes even the air filter can be the power thief.
Look at each part to reduce restrictions and do the best u can with ur own buget.
Good luck. cardo0