Analyze these flow numbers...
02-28-2003, 11:29 PM
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Analyze these flow numbers... First off the heads were flowed on a Superflow 1020 bench. They were set up on a 4.030 bore because they didn't have a 3.9. I am not trying to race flow benches here. I had these heads flowed so I can compare them to the heads that are on my car now, which I ported. I plan to flow those heads next week.
If I can find a stock head I'll flow it for comparison on this bench.
The guys at this shop say their bench reports about 3% low. Who knows how much the larger bore helped.
The heads were flowed with a clay radius intake and no pipe at 28in. H2O. The intake ports are 229cc, ex. 86 cc, with 2.02/1.57 valves.
Lift In. Ex.
0.1 66.2 66.6
0.2 144.4 118.0
0.3 212.8 155.5
0.4 249.3 189.5
0.5 264.2 213.0
0.55 265.0 219.5
0.6 271.5 223.7
They numbers looked ok until 0.5 inches of lift. Any idea what happened? I think the exhaust numbers look alright. I should have some pictures of the the ports in the next few days.
If I can find a stock head I'll flow it for comparison on this bench.
The guys at this shop say their bench reports about 3% low. Who knows how much the larger bore helped.
The heads were flowed with a clay radius intake and no pipe at 28in. H2O. The intake ports are 229cc, ex. 86 cc, with 2.02/1.57 valves.
Lift In. Ex.
0.1 66.2 66.6
0.2 144.4 118.0
0.3 212.8 155.5
0.4 249.3 189.5
0.5 264.2 213.0
0.55 265.0 219.5
0.6 271.5 223.7
They numbers looked ok until 0.5 inches of lift. Any idea what happened? I think the exhaust numbers look alright. I should have some pictures of the the ports in the next few days.
03-01-2003, 12:26 AM
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Re: Analyze these flow numbers... Hello,
I recently had a friends CNC head flowed on the same bench. You are right in "NOT" to race flow benches. The only reason that I'm commenting is because we used the same Bench and Bore plate. It was 1020 also. This is a very good bench. Our bench typically flows 15 cfm lower than 600's or more for others. Thats why when I see claims of 330 it is realy irrelevant, it might be so that bench! Same as Dyno figures. they are really only meant to be tuning or "sampling tools". Comparing the two flow # from different benches is rediculous and ignorant. Regardless, here is an example. I recently had my LS6 heads ported by Induction Specialties in Miami FL. They Flow 299-301(Port to Port) at .600 and level off to .750(My cam is a solid Roller .638 lift) What counted is that on that bench the flow number before was 245 @ .600, 241 @ .700. Max before was 251 @ .550. Stock the head was perfect for the stock Z06 cam. Now we decided to keep the air vane(Swirl Ramp). We know that we could have easily got 315 by continueing to raise the roof. However we retained and actually raised the numbers on the swirl meter since we increased the velocity. We did two things to see where we were for coparitive purposes. we flowed the head on a 600 accross the street and picked up 19 cfm at certain spots. Cetain spots is key here! why because the benches had NOT ONLY different numbers, but different curves. So it is not even possible to do a % ratio between the two. Then we put a LS1 head with larger intake valves(2.05 to our 2.02)on our 1020. These heads were done by CNC heads in Florida for United Racing engines. They claimed the heads flowed 310 CFM. Also, they completly removed the swirl ramp(Cheating in my book..thats easy air flow). They did ecactly what the heads you have mentioned did. from .550 to .650 they hit a flat spot. They did not drop like my stock LS6 but slowed in flow increase. The picked back up at .700. They flowed 265.3 @.600 and 271 @ .700. So much for 310. But hey that was on thier bench. So, maybe.
Two things are gospel to me
Before and after on the same machine
MPH MPH MPH MPH MPH.
case in point. Jason from thunder goes almost 130 MPH. Yet his car only dynos 463. Now how come all of Carteks car's that dyno 478 can't go faster than 127-128 when they weigh 400lbs less.
It is because dyno Number mean **** when comparing to OTHER dyno's.
Sorry for the book. Got on a ROLL
Randy
I recently had a friends CNC head flowed on the same bench. You are right in "NOT" to race flow benches. The only reason that I'm commenting is because we used the same Bench and Bore plate. It was 1020 also. This is a very good bench. Our bench typically flows 15 cfm lower than 600's or more for others. Thats why when I see claims of 330 it is realy irrelevant, it might be so that bench! Same as Dyno figures. they are really only meant to be tuning or "sampling tools". Comparing the two flow # from different benches is rediculous and ignorant. Regardless, here is an example. I recently had my LS6 heads ported by Induction Specialties in Miami FL. They Flow 299-301(Port to Port) at .600 and level off to .750(My cam is a solid Roller .638 lift) What counted is that on that bench the flow number before was 245 @ .600, 241 @ .700. Max before was 251 @ .550. Stock the head was perfect for the stock Z06 cam. Now we decided to keep the air vane(Swirl Ramp). We know that we could have easily got 315 by continueing to raise the roof. However we retained and actually raised the numbers on the swirl meter since we increased the velocity. We did two things to see where we were for coparitive purposes. we flowed the head on a 600 accross the street and picked up 19 cfm at certain spots. Cetain spots is key here! why because the benches had NOT ONLY different numbers, but different curves. So it is not even possible to do a % ratio between the two. Then we put a LS1 head with larger intake valves(2.05 to our 2.02)on our 1020. These heads were done by CNC heads in Florida for United Racing engines. They claimed the heads flowed 310 CFM. Also, they completly removed the swirl ramp(Cheating in my book..thats easy air flow). They did ecactly what the heads you have mentioned did. from .550 to .650 they hit a flat spot. They did not drop like my stock LS6 but slowed in flow increase. The picked back up at .700. They flowed 265.3 @.600 and 271 @ .700. So much for 310. But hey that was on thier bench. So, maybe.
Two things are gospel to me
Before and after on the same machine
MPH MPH MPH MPH MPH.
case in point. Jason from thunder goes almost 130 MPH. Yet his car only dynos 463. Now how come all of Carteks car's that dyno 478 can't go faster than 127-128 when they weigh 400lbs less.
It is because dyno Number mean **** when comparing to OTHER dyno's.
Sorry for the book. Got on a ROLL
Randy
03-01-2003, 12:27 AM
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Re: Analyze these flow numbers... Hello,
I recently had a friends CNC head flowed on the same bench. You are right in "NOT" to race flow benches. The only reason that I'm commenting is because we used the same Bench and Bore plate. It was 1020 also. This is a very good bench. Our bench typically flows 15 cfm lower than 600's or more for others. Thats why when I see claims of 330 it is realy irrelevant, it might be so that bench! Same as Dyno figures. they are really only meant to be tuning or "sampling tools". Comparing the two flow # from different benches is rediculous and ignorant. Regardless, here is an example. I recently had my LS6 heads ported by Induction Specialties in Miami FL. They Flow 299-301(Port to Port) at .600 and level off to .750(My cam is a solid Roller .638 lift) What counted is that on that bench the flow number before was 245 @ .600, 241 @ .700. Max before was 251 @ .550. Stock the head was perfect for the stock Z06 cam. Now we decided to keep the air vane(Swirl Ramp). We know that we could have easily got 315 by continueing to raise the roof. However we retained and actually raised the numbers on the swirl meter since we increased the velocity. We did two things to see where we were for coparitive purposes. we flowed the head on a 600 accross the street and picked up 19 cfm at certain spots. Cetain spots is key here! why because the benches had NOT ONLY different numbers, but different curves. So it is not even possible to do a % ratio between the two. Then we put a LS1 head with larger intake valves(2.05 to our 2.02)on our 1020. These heads were done by CNC heads in Florida for United Racing engines. They claimed the heads flowed 310 CFM. Also, they completly removed the swirl ramp(Cheating in my book..thats easy air flow). They did ecactly what the heads you have mentioned did. from .550 to .650 they hit a flat spot. They did not drop like my stock LS6 but slowed in flow increase. The picked back up at .700. They flowed 265.3 @.600 and 271 @ .700. So much for 310. But hey that was on thier bench. So, maybe.
Two things are gospel to me
Before and after on the same machine
MPH MPH MPH MPH MPH.
case in point. Jason from thunder goes almost 130 MPH. Yet his car only dynos 463. Now how come all of Carteks car's that dyno 478 can't go faster than 127-128 when they weigh 400lbs less.
It is because dyno Number mean **** when comparing to OTHER dyno's.
Sorry for the book. Got on a ROLL
Randy
I recently had a friends CNC head flowed on the same bench. You are right in "NOT" to race flow benches. The only reason that I'm commenting is because we used the same Bench and Bore plate. It was 1020 also. This is a very good bench. Our bench typically flows 15 cfm lower than 600's or more for others. Thats why when I see claims of 330 it is realy irrelevant, it might be so that bench! Same as Dyno figures. they are really only meant to be tuning or "sampling tools". Comparing the two flow # from different benches is rediculous and ignorant. Regardless, here is an example. I recently had my LS6 heads ported by Induction Specialties in Miami FL. They Flow 299-301(Port to Port) at .600 and level off to .750(My cam is a solid Roller .638 lift) What counted is that on that bench the flow number before was 245 @ .600, 241 @ .700. Max before was 251 @ .550. Stock the head was perfect for the stock Z06 cam. Now we decided to keep the air vane(Swirl Ramp). We know that we could have easily got 315 by continueing to raise the roof. However we retained and actually raised the numbers on the swirl meter since we increased the velocity. We did two things to see where we were for coparitive purposes. we flowed the head on a 600 accross the street and picked up 19 cfm at certain spots. Cetain spots is key here! why because the benches had NOT ONLY different numbers, but different curves. So it is not even possible to do a % ratio between the two. Then we put a LS1 head with larger intake valves(2.05 to our 2.02)on our 1020. These heads were done by CNC heads in Florida for United Racing engines. They claimed the heads flowed 310 CFM. Also, they completly removed the swirl ramp(Cheating in my book..thats easy air flow). They did ecactly what the heads you have mentioned did. from .550 to .650 they hit a flat spot. They did not drop like my stock LS6 but slowed in flow increase. The picked back up at .700. They flowed 265.3 @.600 and 271 @ .700. So much for 310. But hey that was on thier bench. So, maybe.
Two things are gospel to me
Before and after on the same machine
MPH MPH MPH MPH MPH.
case in point. Jason from thunder goes almost 130 MPH. Yet his car only dynos 463. Now how come all of Carteks car's that dyno 478 can't go faster than 127-128 when they weigh 400lbs less.
It is because dyno Number mean **** when comparing to OTHER dyno's.
Sorry for the book. Got on a ROLL
Randy
03-01-2003, 04:54 AM
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Re: Analyze these flow numbers... Im sorry but flow benches are calibrated to flow a very specific amount of air at a very specific pressure drop. If bench is leak checked and recalibrated, and operator checks for valve leakage and has head clamped down, i see no reason for big differences in flow testing. Im not stirring up things i just disagree that people can and should use"different bench" as a excuse or a crutch for lousy or inaccurate flow results.
03-01-2003, 06:38 AM
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Re: Analyze these flow numbers... Every bench is different. Believe me. The 600 uses one air pump that tends to pull air more to the side of the cyl. The 1020 bench uses two pumps to try to pull air directly from the FULL area of the bore. These do give different results. If you ask ant professional head porter, they will tell you that the advertised flow number means dick. It is the before and after that counts. Also, you correct in saying that leakage should be checked. That is standard procedure to ensure repeatability(accuracy) from test-to-test regardless of what bench. Also, all of these dry flow benches still are not as accurate as a wet flow bench. That is what a motor really sees. Pro stock people use wet benches(People like GM). So yes, our final numbers may vary, but, regardless whether a 600, 1020, or a wet bench we can still use before and after test with in a same bench to establish gains or losses.
Not trying to be MR know it all, just sharing what I know.
Randy
Not trying to be MR know it all, just sharing what I know.
Randy
03-01-2003, 07:18 AM
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Re: Analyze these flow numbers... I agree with comparing before porting/valvework flow numbers with after porting/valvework numbers on the same bench.
That is interesting how the airpump(s) work between the different model benches.
Chris
That is interesting how the airpump(s) work between the different model benches.
Chris
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03-01-2003, 09:00 AM
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Re: Analyze these flow numbers... I am not an expert, and I may have this wrong but the bench operator tried to explain to me how their bench is calibrated at 25in H2O but is set up to flow at 28 in. Other benches are calibrated at 28 in. and are flowed at 28 in.
I could have that backwards. The guy was talking a mile a minute.
That makes a difference in flow reporting, so I was told.
Anyway the heads that are on the car now made 386 rwhp on the Dynojet. We'll see how much the new heads make on the dyno once I install them. I think it will be interesting to compare head flow numbers and dyno numbers, just as a benchmark. I don't drag race, only some open track (road course) stuff. Mostly my car is for daily use. I just enjoy making it faster.
I could have that backwards. The guy was talking a mile a minute.
That makes a difference in flow reporting, so I was told.
Anyway the heads that are on the car now made 386 rwhp on the Dynojet. We'll see how much the new heads make on the dyno once I install them. I think it will be interesting to compare head flow numbers and dyno numbers, just as a benchmark. I don't drag race, only some open track (road course) stuff. Mostly my car is for daily use. I just enjoy making it faster.
03-01-2003, 05:51 PM
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Re: Analyze these flow numbers... Yes my SF600 bench is calibrated at 25" also, but you have the ability to flow at different pressure drops by using a correction factor. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
03-02-2003, 12:16 AM
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Re: Analyze these flow numbers... You can't compare numbers universally. The bottom line is every bench is different whether it be a couple cfm or 20cfm. Testing procedures, type of bench, fixtures, test conditions....it all matters. Just because a set of heads flows great according to ls1tech LS1/6 port standards, doesn't mean squat.
I think it should be ls1tech rules to post before numbers along with the final flow numbers. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> I've seen some ridiculous flow numbers lately and I've ruined many a ports trying to see what can be pulled out of these heads.
I think it should be ls1tech rules to post before numbers along with the final flow numbers. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> I've seen some ridiculous flow numbers lately and I've ruined many a ports trying to see what can be pulled out of these heads.
03-02-2003, 10:04 PM
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Re: Analyze these flow numbers... 229 cfm is fairly normal for Stage II heads. And yes those heads are turbulent after .400 lift. You can change the shape of a couple areas in the port and it will make them very turbulent and high lift numbers will suffer.
What I can't believe is LS1 heads with less than 210cc ports that flow 270+ at .400, often times 30+ cfm higher in the mid lifts and yet they don't make WAY more power or run any better. 300cfm at .600 is doable.
Stock LS1 heads flow 238@.600 on my bench, I've seen 250+ at that lift on other benches....don't know what to say but look at the before/after. I'm hung up around 295@.600 on my bench and 265@.450 with the stock valve and valvejjob, but peak flow seems to be coming out right around there with differences in porting each time. But 57cfm increase isn't too shabby. Opening the ports up doesn't seem to making much of a difference for me. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
What I can't believe is LS1 heads with less than 210cc ports that flow 270+ at .400, often times 30+ cfm higher in the mid lifts and yet they don't make WAY more power or run any better. 300cfm at .600 is doable.
Stock LS1 heads flow 238@.600 on my bench, I've seen 250+ at that lift on other benches....don't know what to say but look at the before/after. I'm hung up around 295@.600 on my bench and 265@.450 with the stock valve and valvejjob, but peak flow seems to be coming out right around there with differences in porting each time. But 57cfm increase isn't too shabby. Opening the ports up doesn't seem to making much of a difference for me. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
03-02-2003, 10:39 PM
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Re: Analyze these flow numbers... Stupid qustions . How does a wet bench work. Were carbs originally flowed at 25" water and heads at 28" H2O? Why the difference in pressures? Thanks to all in advance! <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
03-02-2003, 11:53 PM
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Re: Analyze these flow numbers... What type of cams would work well with those flow numbers? Even if the numbers vary from bench-to-bench, does the general shape of the graph stay the same? Meaning, it would still hit flatspots between .500 & .600 regardless of the bench?
And, these were setup on a 4.03 bore...isn't common consensus that the larger bore will inflate numbers? Damn, wish there were other heads to be flowed on the same bench.
And, these were setup on a 4.03 bore...isn't common consensus that the larger bore will inflate numbers? Damn, wish there were other heads to be flowed on the same bench.
03-03-2003, 12:40 AM
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Re: Analyze these flow numbers... Jantzer,
Hopefully I can get my hands on stock head and flow it on the same bench.
Don't you agree though, that the numbers seem to stall at .50 inches lift?
Supposedly these heads made 411 rwhp on a C5 with a hotcam and bolts ons. The owner also claimed the car had some KR during that run.
Is 229cc port volume on stock displacement LS1 kind of large?
I do find it amazing that some vendors are getting @300 cfm (at .600) on ports less than 210 cc volume.
The chambers on these heads are 63cc. Should I mill them for more compression?
Hopefully I can get my hands on stock head and flow it on the same bench.
Don't you agree though, that the numbers seem to stall at .50 inches lift?
Supposedly these heads made 411 rwhp on a C5 with a hotcam and bolts ons. The owner also claimed the car had some KR during that run.
Is 229cc port volume on stock displacement LS1 kind of large?
I do find it amazing that some vendors are getting @300 cfm (at .600) on ports less than 210 cc volume.
The chambers on these heads are 63cc. Should I mill them for more compression?
03-03-2003, 01:09 AM
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Re: Analyze these flow numbers... Jim,
All good questions. Maybe some of the experts here will post some answers.
Also, read the first post again. The 4.030 bore will probably inflate the numbers, but they didn't have a 3.9. I plan to flow my ported 6.0 heads and I am going to try locate some stock unported 5.7 heads to flow on the same bench. That should give some numbers for comparison.
I would think the shape of the graph would be the same on any bench, but I'm not sure.
<small>[ March 03, 2003, 10:54 AM: Message edited by: Speed Demon ]</small>
All good questions. Maybe some of the experts here will post some answers.
Also, read the first post again. The 4.030 bore will probably inflate the numbers, but they didn't have a 3.9. I plan to flow my ported 6.0 heads and I am going to try locate some stock unported 5.7 heads to flow on the same bench. That should give some numbers for comparison.
I would think the shape of the graph would be the same on any bench, but I'm not sure.
<small>[ March 03, 2003, 10:54 AM: Message edited by: Speed Demon ]</small>
03-03-2003, 05:48 AM
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Re: Analyze these flow numbers... </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Jantzer98SS:
<strong> 229 cfm is fairly normal for Stage II heads. And yes those heads are turbulent after .400 lift. You can change the shape of a couple areas in the port and it will make them very turbulent and high lift numbers will suffer.
What I can't believe is LS1 heads with less than 210cc ports that flow 270+ at .400, often times 30+ cfm higher in the mid lifts and yet they don't make WAY more power or run any better. 300cfm at .600 is doable.
Stock LS1 heads flow 238@.600 on my bench, I've seen 250+ at that lift on other benches....don't know what to say but look at the before/after. I'm hung up around 295@.600 on my bench and 265@.450 with the stock valve and valvejjob, but peak flow seems to be coming out right around there with differences in porting each time. But 57cfm increase isn't too shabby. Opening the ports up doesn't seem to making much of a difference for me. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Scott, pre 2000 5.7's flow 239 cfm at .600" on my bench and post 99"s flow about 245 on mine. Flow on my latest design is 270 at .450" and 305 at .575" both with stock valves and valvejob. My port volumes are around 215cc and my exhausts flow 200cfm at .575" with a 80cc port. I think our benches are real close, and i have compared same heads on my bench and my friend Joe Shermans in California and they were within 5 cfm also. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
<strong> 229 cfm is fairly normal for Stage II heads. And yes those heads are turbulent after .400 lift. You can change the shape of a couple areas in the port and it will make them very turbulent and high lift numbers will suffer.
What I can't believe is LS1 heads with less than 210cc ports that flow 270+ at .400, often times 30+ cfm higher in the mid lifts and yet they don't make WAY more power or run any better. 300cfm at .600 is doable.
Stock LS1 heads flow 238@.600 on my bench, I've seen 250+ at that lift on other benches....don't know what to say but look at the before/after. I'm hung up around 295@.600 on my bench and 265@.450 with the stock valve and valvejjob, but peak flow seems to be coming out right around there with differences in porting each time. But 57cfm increase isn't too shabby. Opening the ports up doesn't seem to making much of a difference for me. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Scott, pre 2000 5.7's flow 239 cfm at .600" on my bench and post 99"s flow about 245 on mine. Flow on my latest design is 270 at .450" and 305 at .575" both with stock valves and valvejob. My port volumes are around 215cc and my exhausts flow 200cfm at .575" with a 80cc port. I think our benches are real close, and i have compared same heads on my bench and my friend Joe Shermans in California and they were within 5 cfm also. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
03-03-2003, 06:42 AM
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Re: Analyze these flow numbers... A set of stock 99 heads flowed 225 CFM on my Superflow SF400 bench with the port stalling at about .400-.450" lift. My guess is that your heads were opened up quite a bit in the port area but not enough attention was paid in the bowl and short turn radius. Looks like the flow is seperating in the short turn area and windowing across the valve, stalling the flow at .500" and higher. Some additional work may need to be done in this area, including widening the floor and reshaping the radius.
Bottom line, air does not like to change direction, it wants to continue moving in a straight line, so a larger, smoother radius is most desirable. Hope this helps,
Paul J.
Bottom line, air does not like to change direction, it wants to continue moving in a straight line, so a larger, smoother radius is most desirable. Hope this helps,
Paul J.
03-03-2003, 11:14 AM
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Re: Analyze these flow numbers... </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LS1derfull:
<strong>Scott, pre 2000 5.7's flow 239 cfm at .600" on my bench and post 99"s flow about 245 on mine. Flow on my latest design is 270 at .450" and 305 at .575" both with stock valves and valvejob. My port volumes are around 215cc and my exhausts flow 200cfm at .575" with a 80cc port. I think our benches are real close, and i have compared same heads on my bench and my friend Joe Shermans in California and they were within 5 cfm also. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Those were my flow numbers on 98 LS1 heads with stock valves and valvejob. I'll test some 00+ heads and 6.0L heads and see what they do stock in comparison. Is there a difference in the valve job between the newer/older or is it just the valves? I'm using the backcut valves in the older head and 238@.600 is what I get. I might do 4.8's 5.3's 6.0's and both 5.7's just to see how they compare stock. I've never tested a stock 5.3 head.
I'm with you though, the stock backcut valves are tough to beat. I think with the right valvejob and backcut on an aftermarket valve, you can gain flow though. What's amazing to me is how throwing in a quality 2.02 Ferrea or Rev without being modified results in flow losses everywhere between .150 - .600 on my bench and REALLY bad in the mid lifts.
Paul is right, you can get excellent numbers without even touching the ports. The air is seperating from the shorts side. Well ported LS1 heads won't stall at .500, they should peak closer to .600 and hold or gain slightly above that.
<strong>Scott, pre 2000 5.7's flow 239 cfm at .600" on my bench and post 99"s flow about 245 on mine. Flow on my latest design is 270 at .450" and 305 at .575" both with stock valves and valvejob. My port volumes are around 215cc and my exhausts flow 200cfm at .575" with a 80cc port. I think our benches are real close, and i have compared same heads on my bench and my friend Joe Shermans in California and they were within 5 cfm also. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Those were my flow numbers on 98 LS1 heads with stock valves and valvejob. I'll test some 00+ heads and 6.0L heads and see what they do stock in comparison. Is there a difference in the valve job between the newer/older or is it just the valves? I'm using the backcut valves in the older head and 238@.600 is what I get. I might do 4.8's 5.3's 6.0's and both 5.7's just to see how they compare stock. I've never tested a stock 5.3 head.
I'm with you though, the stock backcut valves are tough to beat. I think with the right valvejob and backcut on an aftermarket valve, you can gain flow though. What's amazing to me is how throwing in a quality 2.02 Ferrea or Rev without being modified results in flow losses everywhere between .150 - .600 on my bench and REALLY bad in the mid lifts.
Paul is right, you can get excellent numbers without even touching the ports. The air is seperating from the shorts side. Well ported LS1 heads won't stall at .500, they should peak closer to .600 and hold or gain slightly above that.