Cylinder head port sizes.
03-11-2014, 11:24 AM
#1
Cylinder head port sizes.
I've had a couple things on my mind lately, in regards to cylinder heads. We all know the importance of airspeed/velocity, and the benefits of a smaller properly shaped port, on a N/A engine. The intake manifold design, port runner design, all come into play, to help pack the cylinder with air, when you are relying on 14.7PSI of atmospheric pressure, to fill the cylinders.
BUT, my question involves superchargers. Lets say a whipple, or roots blower in a marine application. I'll share my theories, or thoughts, and I'd love to hear whether I am right or wrong.
On a street driven vehicle, that often cruises down the road, under 2000RPM, in vacuum, might benefit from the smaller port size. To keep throttle response and efficiency up. Now, lets say a marine engine. That rarely operates in the 1200-2800RPM range. At 3000, 3500 Rpm, with roots or a whipple, how detrimental is port size? How about at 6000RPM?
I guess what I am getting at, is at what point, will you see a LOSS of power, by having too large of an intake runner on a blown application? Lets say one was building a basic 540CI blown marine deal. And he had two choices. Lets say a 355CNC Dart, or a 335CNC dart. Would the 355cc setup give up anything to the 335CC, or vice versa, if all other things were equal. Or, say a 320CC Dart, vs a 360CC dart. I'd love to hear/see some dyno observations on this topic.
I have an old B&M book here from 20 years ago. They talk about this, and one of the statements was, "in all of our testing, we have yet to see a drop in power, from using too large of an intake port" on their blown setups. I also remember an engine builder on here a few years ago, stating the intake port size, can in a way act as a restrictor plate, on a forced induction setup.
I understand the importance of head flow, exhaust flow, cam design, etc, I'm just trying to wrap my head around port size. I have heard many say "that head is way too large for a xxx engine", or ''That head is way to small for a xxx engine". Granted I dont believe slapping some 410cc BMF's on a 454 are the way to go. But I am curious if a 310cc will outperform a 345cc on a blown 540 or something like that. The idea that the larger head might be unresponsive and lazy down low, goes with theory. However, i've seen some marine blower engines with some large 360cc ports, that were far from being lazy in any way shape or form, when boost is added into the mix.
Maybe Haxby, or Eddie Young have some input on this?
BUT, my question involves superchargers. Lets say a whipple, or roots blower in a marine application. I'll share my theories, or thoughts, and I'd love to hear whether I am right or wrong.
On a street driven vehicle, that often cruises down the road, under 2000RPM, in vacuum, might benefit from the smaller port size. To keep throttle response and efficiency up. Now, lets say a marine engine. That rarely operates in the 1200-2800RPM range. At 3000, 3500 Rpm, with roots or a whipple, how detrimental is port size? How about at 6000RPM?
I guess what I am getting at, is at what point, will you see a LOSS of power, by having too large of an intake runner on a blown application? Lets say one was building a basic 540CI blown marine deal. And he had two choices. Lets say a 355CNC Dart, or a 335CNC dart. Would the 355cc setup give up anything to the 335CC, or vice versa, if all other things were equal. Or, say a 320CC Dart, vs a 360CC dart. I'd love to hear/see some dyno observations on this topic.
I have an old B&M book here from 20 years ago. They talk about this, and one of the statements was, "in all of our testing, we have yet to see a drop in power, from using too large of an intake port" on their blown setups. I also remember an engine builder on here a few years ago, stating the intake port size, can in a way act as a restrictor plate, on a forced induction setup.
I understand the importance of head flow, exhaust flow, cam design, etc, I'm just trying to wrap my head around port size. I have heard many say "that head is way too large for a xxx engine", or ''That head is way to small for a xxx engine". Granted I dont believe slapping some 410cc BMF's on a 454 are the way to go. But I am curious if a 310cc will outperform a 345cc on a blown 540 or something like that. The idea that the larger head might be unresponsive and lazy down low, goes with theory. However, i've seen some marine blower engines with some large 360cc ports, that were far from being lazy in any way shape or form, when boost is added into the mix.
Maybe Haxby, or Eddie Young have some input on this?
03-11-2014, 11:56 AM
#2
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The more power it makes na the more power it will make blown its that simple if your trying to get everything out of the motor. But if your not trying to get every last bit of power out of it and it is forced induction there is no sense in spending all the money to get the best heads money can buy.
Gold Member
03-11-2014, 12:08 PM
#4
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I am no expert by a long shot but I would say If I understand your thoughts correctly, that as long as you keep the intake plenum and runners under the boost level you want the size of the runner should not hurt the performance throughout the rpm band, and the intake signals wont effect the air volume as much in the plenum. it most likely will effect low RPM, low boost power/torque. I would like to see some test resuts if anyone has the time and means to do so!
03-11-2014, 12:50 PM
#5
I guess maybe it boils down to, at what point, does the intake port size become a restriction, causing a power loss. I mean, if lets say a 325cc port is not restricting the airflow, than going to a 345, should theoretically, not gain any power, and possibly cause a loss of low end/out of boost, flow and efficiency.
Lets say you have a N/A 540. And were to use a 305cc AFR cylinder head. That head, might work really awesome, and hands down be the head to use, from idle to 6000RPM on that build. But, you throw a blower into the build combo. Would that 305 still be the head to choose, or would the 325 version, or 345/357 be the head to choose.
Apparently what I am getting at, is, does the boosted engine, allow for a larger runner size, over a N/A, without negative results.?
Lets say you have a N/A 540. And were to use a 305cc AFR cylinder head. That head, might work really awesome, and hands down be the head to use, from idle to 6000RPM on that build. But, you throw a blower into the build combo. Would that 305 still be the head to choose, or would the 325 version, or 345/357 be the head to choose.
Apparently what I am getting at, is, does the boosted engine, allow for a larger runner size, over a N/A, without negative results.?
03-11-2014, 01:09 PM
#6
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iTrader: (2)
I guess maybe it boils down to, at what point, does the intake port size become a restriction, causing a power loss. I mean, if lets say a 325cc port is not restricting the airflow, than going to a 345, should theoretically, not gain any power, and possibly cause a loss of low end/out of boost, flow and efficiency.
Lets say you have a N/A 540. And were to use a 305cc AFR cylinder head. That head, might work really awesome, and hands down be the head to use, from idle to 6000RPM on that build. But, you throw a blower into the build combo. Would that 305 still be the head to choose, or would the 325 version, or 345/357 be the head to choose.
Apparently what I am getting at, is, does the boosted engine, allow for a larger runner size, over a N/A, without negative results.?
Lets say you have a N/A 540. And were to use a 305cc AFR cylinder head. That head, might work really awesome, and hands down be the head to use, from idle to 6000RPM on that build. But, you throw a blower into the build combo. Would that 305 still be the head to choose, or would the 325 version, or 345/357 be the head to choose.
Apparently what I am getting at, is, does the boosted engine, allow for a larger runner size, over a N/A, without negative results.?
My buddy built a 450" Chrysler twin turbo 60 pounds boost 350cc intake runner 3500 horsepower.
03-11-2014, 01:42 PM
#7
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This is basics, so if someone wants more technical at this point don't get all rowdy.LOL.
SC/TC don't add velocity, even though you would think cause' more air in the same space should move faster right ?
Not really. Here's why.
They are compressors.
They take more air volume and compress it down to a smaller space then if it wasn't compressed.
SC/TC don't add velocity, even though you would think cause' more air in the same space should move faster right ?
Not really. Here's why.
They are compressors.
They take more air volume and compress it down to a smaller space then if it wasn't compressed.
03-11-2014, 01:57 PM
#9
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iTrader: (1)
Roots / Screw are positive displacement.
Screw compresses air in it's 'screws'
Roots compresses air in the intake manifold
===================================
Extreme example:
A 7.5:1 big headed 8-71 bown BBC can work pretty good.
How about a 7.5:1 big headed BBC with turbocharger or ATI/Vortec ? Dog for a while until the mojo starts to flow. Not so much fun.
ATI/Vortec/etc are centrifugal with gear ratios. IE: step up gears.
Turbochargers are exhaust (rpm/load/etc) driven.
Thus Roots/Screw are very popular in the I/O world because from idle to where ever, they respond 'right now.' Always full boost when the throttles are wide open now matter what rpm.
Centrifugals increase with rpm, again they have gearboxes.
TC needs rpm and load to make them to do more.
Last edited by SB; 03-11-2014 at 02:01 PM.
03-11-2014, 02:12 PM
#10
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A compressor adds more air, but packs this larger amt smaller than if not compressed (ie: N/A). So......a blown engine may not require a larger sized cylinder head than it's N?A twin.
PS: Some Roots/etc add a lot of heat which will expand the air. So........bigger runner may be needed.
Remember, thus why intercoolers needed, cooler air is good for obvious reasons but one not so obvious is for the air/oxygen to stay 'smaller' and less likely to be restricted.
Again, don't think we should get too technical on this unless people want...but that may become never ending.
