Flow bench numbers
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The most I've ever gotten out of a 1.9 head was 137 cfm @ 10" of water (intake port). But that did not produce good power (there's a lot more to an engine than airflow quantity). Most of my racing 1.9 heads produce 127-128 cfm with a good power curve. A stock 1.9 intake port should be around 88-89 cfm. A ported 'street' 1.9 head with a 1.72" intake valve will get around 108-115 typically, depending on who's doing the porting. With stock valves, you'd be very lucky to break 100 cfm.
1.9 with 2.0 Intake valves
Bob,
I vaguely remember you stating in a post on Classic Opels many months ago that the 42 mm 2.0 Intake valve bumped the flow up to 102 cfm @10". Foggy memory... If I remembered this correctly or didn't take it out of context, how much porting was required w/these valves to get this flow number? Meaning... was this an easy number to get, or did you have to work at it?
Thanks
Paul
Bob,
I vaguely remember you stating in a post on Classic Opels many months ago that the 42 mm 2.0 Intake valve bumped the flow up to 102 cfm @10". Foggy memory... If I remembered this correctly or didn't take it out of context, how much porting was required w/these valves to get this flow number? Meaning... was this an easy number to get, or did you have to work at it?
Thanks
Paul
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Re: 1.9 with 2.0 Intake valves
Your memory is not foggy. But as you said that's with the larger 2.0 inlet valve. I stated to willis it's hard to break 100 cfm with stock valves....stock 1.9 valves. With a 2.0 valve it's not too hard at all. If you port the heck out of a 1.9 head with a 1.9 valve, you can break 100 cfm, but the port will be larger than the valve, which is a no-no. Throttle response will suck, and you may gain a few hp on the top end and give up a lot everywhere else. With a larger valve more proportionate to the port size, the low-lift airflow will improve, and you make gains everywhere in the powerband.Paul said:
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OK this is way over my head ......but I just had a 1.9 head modified (1.72 intake/1.50 exhaust) in nearby Mexico at a respected porting shop and watched as he flow tested the finished head with 28" of water and 198CFM on the intake side...I do not recall the exahaust side. I am not certain this is good or not. He will test a stock head next time so I can see the percent of improvements....Any idea how this numbers would equate to one another???RallyBob said:
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Specify that the next head be flowed at 10" of water like Bob's to get a fair comparison.
Harold
Harold
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In the book 'Smokey Yunick's Power Secrets', he goes into great length about why they use 28" to flow rate heads.
I am not sure what my point is in bringing that up, but wanted to share it. I think we all recognize Bob as the master when it comes to porting and documenting the differences between Opel heads. It is also important to measure them all under the same conditions, which Bob has done.
That said, I have no understanding of why RallyBob does it one way or the other and it may be that 10" is a better test for an Opel head and 28" is best for a small block chevy.
I am throwing it out there for information, in the hopes that I learn more from the responses of those 'in the know'.
Thanks,
I am not sure what my point is in bringing that up, but wanted to share it. I think we all recognize Bob as the master when it comes to porting and documenting the differences between Opel heads. It is also important to measure them all under the same conditions, which Bob has done.
That said, I have no understanding of why RallyBob does it one way or the other and it may be that 10" is a better test for an Opel head and 28" is best for a small block chevy.
I am throwing it out there for information, in the hopes that I learn more from the responses of those 'in the know'.
Thanks,
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Because Rallybob has a limited budget! My flowbench will go up to 15" of water. Most heads are flowed at 10", or 25", or at 28". Generally the higher the number, the more accurate the flow can be measured, especially with minor changes such as valve seat angle, etc.asdasc said:
I really wanted a Superflow 1200 flowbench, but it cost about $12,000 back when I got my Superflow 110 flowbench ($2800), and required 230 volt wiring. I could not justify that! I believe the maximum amperage draw was something like 48 amps @ 230 volts. I would have had to rewire the building!
To convert from 10" of water to 25", multiply X 1.54.
To convert from 10" of water to 28", multiply X 1.67.
That said, 198 cfm @ 28" of water converts to 118.5 cfm @ 10" of water. Quite nice for a 1.9 head, and far more than stock (88 cfm @ 10"). In fact is is just a touch less than a stock 2.2 head (122 cfm @ 10").
Bob
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How do these things work?
I'm curious because I use similar equipment at work. Is it essentially just a matter of delivering a calibrated input and measuring flow out? I'm going to try a google search to see if I can find an explanation page. Again I'm clueless on how they work...is it a static measurement?
Believe it or not, some sleep apnea patients need up to 30cm (11.81") H2O pressure to splint their airway in order to keep breathing while asleep!
Todd
I'm curious because I use similar equipment at work. Is it essentially just a matter of delivering a calibrated input and measuring flow out? I'm going to try a google search to see if I can find an explanation page. Again I'm clueless on how they work...is it a static measurement?
Believe it or not, some sleep apnea patients need up to 30cm (11.81") H2O pressure to splint their airway in order to keep breathing while asleep!
Todd
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Todd, a flowbench is basically a calibrated shop-vac. For a given line voltage, barometric pressure, humidity, altitude, and temperature, the electric motor will be able to pass a certain amount of air through an orifice (these factor into the calibration of the flowbench when it's set up). The flowbench simply lets you know what percentage of this amount of air the cylinder head ports are allowing to pass through.neuropel said:How do these things work?
I'm curious because I use similar equipment at work. Is it essentially just a matter of delivering a calibrated input and measuring flow out? I'm going to try a google search to see if I can find an explanation page. Again I'm clueless on how they work...is it a static measurement?
Believe it or not, some sleep apnea patients need up to 30cm (11.81") H2O pressure to splint their airway in order to keep breathing while asleep!
Todd
Bob
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Jorge(George) did six steps .0100, .0200, .0300, .0400, .0500, and .0600.
I told him in "spanglish" that above .0450 lift is meaningless because of the rocker geometry.
I will get a copy of the spec sheet and flow a stock head next week for comparison.
His unit is a SuperFlo 600.
BTW
He thinks he can find a roller rocker that would work on an Opel. He mentioned maybe a VW or some other make. I told him yeah ....right! Go for it!
GOOD LUCK JORGE!
I told him in "spanglish" that above .0450 lift is meaningless because of the rocker geometry.
I will get a copy of the spec sheet and flow a stock head next week for comparison.
His unit is a SuperFlo 600.
BTW
He thinks he can find a roller rocker that would work on an Opel. He mentioned maybe a VW or some other make. I told him yeah ....right! Go for it!
GOOD LUCK JORGE!
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Hi Bob,
I fully understand that explanation! In reading back over the book info, he also said his flow bench was worth about $80,000!
The whole concept intrigues me so. It would be very interesting to be able to do the things you have done to a head and then compare them on a flow bench. But, like you have said in the past, doing it to an Opel head will never pay the bills. It is interesting none the less.
One comment you made earlier in this thread is that the better flowing head didn't always perform better. I figured it automatically would. Can you elaborate a little?
Thanks again for all your help,
I fully understand that explanation! In reading back over the book info, he also said his flow bench was worth about $80,000!
The whole concept intrigues me so. It would be very interesting to be able to do the things you have done to a head and then compare them on a flow bench. But, like you have said in the past, doing it to an Opel head will never pay the bills. It is interesting none the less.
One comment you made earlier in this thread is that the better flowing head didn't always perform better. I figured it automatically would. Can you elaborate a little?
Thanks again for all your help,
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It's only part of the recipe. If the airflow is great at .500" lift, but is crappy at .250" lift, and you have a .400" lift cam...you're in trouble! You will never reach that airflow numbers because of the lift of your cam, yet your valves are open at .250" at least twice for each cylinder's firing (as the valves open and as they close).asdasc said:
Port velocities cannot be forgotten either. A large port with no velocity on a low compression engine will be a dog....regardless of the airflow. And a short-stroke engine like a 1.9/2.0 Opel needs all the help it can get to increase port velocities or torque will absolutely disappear!
Bogb
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No Fuel!
Another consideration is that on the Flow bench there is not fuel in the mix - you are measuring 'dry' airflow.
The 'wet' flow when the head is on the motor and operating can be an entirely different animal!
Direction of flow, 'swirl' and fuel seperation are all "extras" that the 'dry' flow numbers on a flow bench show very little about.
Another consideration is that on the Flow bench there is not fuel in the mix - you are measuring 'dry' airflow.
The 'wet' flow when the head is on the motor and operating can be an entirely different animal!
Direction of flow, 'swirl' and fuel seperation are all "extras" that the 'dry' flow numbers on a flow bench show very little about.
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