Will a roots blower benefit from cylinder heads?
07-04-2004, 10:34 PM
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Will a roots blower benefit from cylinder heads? I get an inconsistant answers on this question.
Has anyone swaped Heads only and found improvement?
A Roots blower is a positive displacement device that increases the Mas Air charge into an engine. Each revolution provides a fixed amount of Mass Air Flow (MAF), so the blowers exhaust port Mass flow is independent of pressure. This takes a little getting use too as it is contrary to what happens in a turbo or centrifugal blower or natural aspiration. The roots blower only cares about what RPM it is turning and as long as there is enough power to turn it pressure will build until it is released or something breaks (in general).
Improving Cylinder Head flow only relieves the manifold pressure and can’t create additional Mass for combustion. This seams pretty fundamental and no one has talked me out of this yet.
So will an improved flowing head from AFR or TEA increase power on a roots blower car?
Has anyone swaped Heads only and found improvement?
A Roots blower is a positive displacement device that increases the Mas Air charge into an engine. Each revolution provides a fixed amount of Mass Air Flow (MAF), so the blowers exhaust port Mass flow is independent of pressure. This takes a little getting use too as it is contrary to what happens in a turbo or centrifugal blower or natural aspiration. The roots blower only cares about what RPM it is turning and as long as there is enough power to turn it pressure will build until it is released or something breaks (in general).
Improving Cylinder Head flow only relieves the manifold pressure and can’t create additional Mass for combustion. This seams pretty fundamental and no one has talked me out of this yet.
So will an improved flowing head from AFR or TEA increase power on a roots blower car?
07-04-2004, 10:56 PM
#2
Originally Posted by billc5
So will an improved flowing head from AFR or TEA increase power on a roots blower car?
With a capitol "Y".
Better heads will show even larger improvements on a car with a "pressurized" intake tract. The better flowing intake and more importantly exhaust ports are worked that much harder with positive manifold pressures. A weak flowing head just creates higher "boost"...AKA backpressure and the additional heat that goes along with that (obviously not desirable).
Typical AFR head swaps (or any high flowing efficient piece) on blown applications typically show boost values dropping and HP figures climbing with the same pulleys used in the baseline tests. Swap some pulleys and get the boost figures back to where they were previously and even more horsepower and torque will be made.
It's a winner all around....You will be glad you took the plunge.
Regards,
Tony
PS Rick Sperling, one of the owners of AFR, currently has a Magnason Intercooled supercharger on his stock LS1 2001' C5 (auto trans)....he is currently making around 440 RWHP....I expect that figure to approach or exceed 550 RWHP with a small cam and the 225 heads....He is ALSO waiting patiently for their release
07-05-2004, 03:19 AM
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It depends on the amount of air the S/C can push. It has a limit. I read an article where they used multiple heads with the same S/C. The psi dropped with the better flowing heads. In the end they made similar power because the smaller head flowed the same amount of air at a faster rate because the psi was up. The ported heads allowed on 6psi while the stock heads allowed 9psi with the same pulley. There isn't an infinate amount of air a cylinder can take with denotation so you need to figure out what point you are at. Also, remember that forced induction inproves the cfm of your heads. A head that flow 240 may flow 300 w/ forced induction because of the increase in velocity. If you change the pulley or you go with a larger s/c you can compinsate for the loss in pressure and still maintain the same amount of psi with the larger heads. This will in thoery give you more power. Also, think about denotation. Too much air and fuel can cause too much load on the piston similar to running really high compression which can lead to engine failure. Another and cheaper way to get more air into the cylinder is to run a bigger cam. (remeber to run a wide lsa and 8 degrees more duration on the exhaust side) This way you maintain the psi and still increase the amount of fuel and air inputted into the chamber. Finally, remember that we run 10.25 to 1 in our motors which is not ideal for high boost. If you want to go extreme, forge the bottom end and run 8.5 to 1 compression. You can also lower your compression by running a larger chamber. 6.0 may be the trick. Sorry I bounced around but its late and I have to boogey. Good luck 
Last edited by Bowtieman4life; 07-05-2004 at 03:25 AM.
07-05-2004, 08:25 AM
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Thanks for the incite
The blower can’t just be turned faster to increase flow without losing efficiency. A Roots blower generates more heat per CFM as the RPM increases and this effect is exaggerated past 12000RPM, My 3.3 inch pulley is turning at 12750 now. There is a point when the reduced Manifold pressure and the increased CFM provides no temperature advantage.
At that point I would be just as well off with a smaller 3.2in pulley for $100 and get no benefit from the $2500 head job. I am already making around 440RWHP or +428gm/sec @ 6000rpm without the cylinder Heads.
Tony if you can garranty a modest 10% gain in HP on either the 225 or 205 heads alone even after tuning for the improved conditions, you have an order.
The blower can’t just be turned faster to increase flow without losing efficiency. A Roots blower generates more heat per CFM as the RPM increases and this effect is exaggerated past 12000RPM, My 3.3 inch pulley is turning at 12750 now. There is a point when the reduced Manifold pressure and the increased CFM provides no temperature advantage.
At that point I would be just as well off with a smaller 3.2in pulley for $100 and get no benefit from the $2500 head job. I am already making around 440RWHP or +428gm/sec @ 6000rpm without the cylinder Heads.
Tony if you can garranty a modest 10% gain in HP on either the 225 or 205 heads alone even after tuning for the improved conditions, you have an order.
07-05-2004, 08:31 AM
#5
i know in the cobra and Lightning world, guys are barely gaining from LT headers and opening up the exhaust. sometimes they are loosing power! this has been the results for years and takes tons of tuning to get the power back. again they run roots blowers and actually their heads (the dohc) flow GREAT stock. what is the deal?
07-05-2004, 09:21 AM
#6
I once had a customer with a 306 Ford, roots blower, ported heads and was running 11.0's @ 123, he could only generate 4 psi of boost and was convinced the heads were bad, he wanted more boost. I removed the killer aftermarket heads, installed a set of ported stock heads, with stock diameter valves, his boost increased to 14 psi, and the car went 11.6's @ 117.
Boost is a measurement of restriction.
Don't cam a blower car like a nitrous car, it is a fine line between underscavaging and overscavaging a blower car. This little fact is how we put these 306 Fords with .550" hyd roller cams in the 8's. Everyone is putting big exhaust ports and big headers on these things, and making less power, they are overscavaging the engine. This is why a blown engine cares less about headers and exhaust then a N/A or Nitrous combo. A 115 LSA cam is a must. I can guarantee 10%, with the right cam.
BTW, we do the heads on the fastest Lightning trucks, such as Johnny Lightning, Dantes and others, as well as many, many other fast blown combos.
Boost is a measurement of restriction.
Don't cam a blower car like a nitrous car, it is a fine line between underscavaging and overscavaging a blower car. This little fact is how we put these 306 Fords with .550" hyd roller cams in the 8's. Everyone is putting big exhaust ports and big headers on these things, and making less power, they are overscavaging the engine. This is why a blown engine cares less about headers and exhaust then a N/A or Nitrous combo. A 115 LSA cam is a must. I can guarantee 10%, with the right cam.
BTW, we do the heads on the fastest Lightning trucks, such as Johnny Lightning, Dantes and others, as well as many, many other fast blown combos.
07-05-2004, 09:33 PM
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Thank's Brian,
Yes I agree with your observation and plan to install your heads soon. The key will be to utilize the available Mass of Air and not waste it out the overlap. The experience with a roots blowers suggest that high flowing exhaust ports arn't the way to go.
I guess you here the contrary all day long as I do.
Bowtieman4life suggests that 10.25CR is not optimum, but I think if you can hold off the detonation then 10.25CR is ok. The MP112 roots blower is undersized as it is for a 5.7L motor so I would hesitate to lower Compression and lose bottom end torque. I am looking for fun on the street, not low ET's.
My statement.........Improving Cylinder Head flow only relieves the manifold pressure and can’t create additional Mass for combustion..........is were I am coming from. Brian is the first guy that understood immediately. A positive displacement Blower builds mass from RPM and is independant of the pressure at the blower exhaust port.
For example when we exchange the heads, I expect the Mass Air Flow to be the same (same pulley and RPM). I will only gain power if the utilization of Air is greater than before. If the utilization improves and the pressure drops power is created from combustion and reduced blower power. I suspect that the manifold pressure should remain the same, by increasing the exhaust port pressure, and reducing the intake pressure, this should leave more in the chamber for combustion.
Anyway that is the plan. I now think that a 10% improvement is optimistic, if we are only utilizing the air through the over lap, a gain of 25HP is more relatistic.
But then agian I could be wrong.
Yes I agree with your observation and plan to install your heads soon. The key will be to utilize the available Mass of Air and not waste it out the overlap. The experience with a roots blowers suggest that high flowing exhaust ports arn't the way to go.
I guess you here the contrary all day long as I do.
Bowtieman4life suggests that 10.25CR is not optimum, but I think if you can hold off the detonation then 10.25CR is ok. The MP112 roots blower is undersized as it is for a 5.7L motor so I would hesitate to lower Compression and lose bottom end torque. I am looking for fun on the street, not low ET's.
My statement.........Improving Cylinder Head flow only relieves the manifold pressure and can’t create additional Mass for combustion..........is were I am coming from. Brian is the first guy that understood immediately. A positive displacement Blower builds mass from RPM and is independant of the pressure at the blower exhaust port.
For example when we exchange the heads, I expect the Mass Air Flow to be the same (same pulley and RPM). I will only gain power if the utilization of Air is greater than before. If the utilization improves and the pressure drops power is created from combustion and reduced blower power. I suspect that the manifold pressure should remain the same, by increasing the exhaust port pressure, and reducing the intake pressure, this should leave more in the chamber for combustion.
Anyway that is the plan. I now think that a 10% improvement is optimistic, if we are only utilizing the air through the over lap, a gain of 25HP is more relatistic.
But then agian I could be wrong.
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07-05-2004, 11:18 PM
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Boost is merely the difference between the air that the blower forces into the intake, and what can travel through the heads/valves and into the cylinders on an intake stroke. IF the heads are a bottleneck, then opening them up will increase the volume of air going into the cylinders, but at a lower pressure (the mass of mix entering the cylinder wont actually change). This will relieve pressure in the intake, dropping apparent "boost".
AIR heats up when compressed regardless of whether it is done by a centrifugal or roots type compressor. This is the Ideal Gas Law, and is not disputable... By increasing head flow and thus dropping restriction/boost, the air in the intake will be cooler allowing more timing and maybe even a leaner mixture without detonating - this is where the extra power will come from in my opinion. I agree that roots blowers cannot actually flow any more or less CFM into the intake regardless of the mods AFTER the blower compressor (mods/IAT before the blower can still have an affect. A blower trying to pull air from a vacuum, or extremely light, hot air, will make very little output). Now if we are not actually moving more mass of mix into the cylinders by increasing head flow, then we should take advantage of the lower boost and cooler mixture temps by increasing timing and/or leaning out the mix while avoiding detonation to make more power.
In conclusion, I would predict that bolting on the heads without tuning will not increase power if the engine sees EXACTLY the same timing and AFR as before. If you tune it (or the PCM adjusts its own LTrims/etc. or gets rid of any KR that may exist from the hotter/higher boost from before), this is where you would see a power increase.
EDIT: Or do what Tony says and pulley up to get back to the original boost level (and thus manifold air temperature) and keep the tuning the same or perhaps more conservative to account for the higher Volumetric Efficiency that will result.
Now this is all theory so take it with a grain of salt - I'd love to hear about empirical results, especially those that may disagree with this theory
.
AIR heats up when compressed regardless of whether it is done by a centrifugal or roots type compressor. This is the Ideal Gas Law, and is not disputable... By increasing head flow and thus dropping restriction/boost, the air in the intake will be cooler allowing more timing and maybe even a leaner mixture without detonating - this is where the extra power will come from in my opinion. I agree that roots blowers cannot actually flow any more or less CFM into the intake regardless of the mods AFTER the blower compressor (mods/IAT before the blower can still have an affect. A blower trying to pull air from a vacuum, or extremely light, hot air, will make very little output). Now if we are not actually moving more mass of mix into the cylinders by increasing head flow, then we should take advantage of the lower boost and cooler mixture temps by increasing timing and/or leaning out the mix while avoiding detonation to make more power.
In conclusion, I would predict that bolting on the heads without tuning will not increase power if the engine sees EXACTLY the same timing and AFR as before. If you tune it (or the PCM adjusts its own LTrims/etc. or gets rid of any KR that may exist from the hotter/higher boost from before), this is where you would see a power increase.
EDIT: Or do what Tony says and pulley up to get back to the original boost level (and thus manifold air temperature) and keep the tuning the same or perhaps more conservative to account for the higher Volumetric Efficiency that will result.
Now this is all theory so take it with a grain of salt - I'd love to hear about empirical results, especially those that may disagree with this theory
. Last edited by Draco; 07-05-2004 at 11:25 PM.
07-05-2004, 11:35 PM
#9
More Flow is GOOD!!
Originally Posted by billc5
My statement.........Improving Cylinder Head flow only relieves the manifold pressure and can’t create additional Mass for combustion..........is were I am coming from. Brian is the first guy that understood immediately. A positive displacement Blower builds mass from RPM and is independant of the pressure at the blower exhaust port.
I have to disagree....In fact, if a 10% increase (were talking 44 HP based on your combo) wasn't found bolting on a set of our upcoming 225 heads, I would be VERY surprised and extremely disappointed. My hunch is the 205's would show you that kind of gain.
Simple physics....Better flowing (efficient) head always equals more power.
Same better flowing head with BOOST equals even MORE power.....
I also disagree with your theory on exhaust port flow with a roots style blower. The intake side of your cylinder head equation just went up some given significant percentage....It only makes sense that it needs a much better exhaust port to get rid of it all, or else you won't completely evacuate the cylinder and will dilute the next intake charge ultimately to the point the engine is internally "choking" on its own burnt gases and will stop generating power.
Jerry, the owner of Magnasun Superchargers, practically begged me to try and design a cylinder head that has a 100% intake exhaust ratio. That is of course impossible (unless you have a weak suck intake port!), but I think you see where I'm going here.
Bottom line, nothing is etched in stone and this is certainly my opinion I am expressing, but I have witnessed many a dyno test to back it up.
Lets see what Rick's Vette (the car I referred to earlier) making EXACTLY the same power you are currently, puts down to the rollers after a SMALL cam and a set of AFR 225's.
I'm betting 530-550 RWHP....Should be very interesting.
Regards,
Tony Mamo
PS I also wanted to mention that my "theory" excludes detonation and low octane fuel issues. Take stock headed "boosted" engine combo....tune for max performance, swap heads for more efficient higher flowing heads of your choice, also tune for max performance (including changing pulley for same as baseline boost levels), and witness a bunch more HP and TQ produced.
Last edited by Tony Mamo @ AFR; 07-06-2004 at 01:41 AM.
07-06-2004, 08:01 AM
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The problem I see with turning the blower fast to recover the lost boost or Air Mass is that the thermal efficiency goes to Hell at speeds over 13000 RPM. Thermal expansion of the rotors may begin to effect performance and we are operating outside of the safe conditions. Delta temperature doubles between 6000 and 13000rpm and HP required goes up times 4.
The empirical evidence is demonstrated with the addition of Exhaust Headers, which drops the Intake Manifold pressure and hence reduces Mass in the Chamber. Tuning could not bring back more power than before. This is a very predictable result.
With exhaust headers I lost about 4% power which includes the power requirement for the blower. So this is why I suggest that we should be able to recover about 5% with a head designed to recover the lost mass air.
But we wont know until we do it will we?.
The empirical evidence is demonstrated with the addition of Exhaust Headers, which drops the Intake Manifold pressure and hence reduces Mass in the Chamber. Tuning could not bring back more power than before. This is a very predictable result.
With exhaust headers I lost about 4% power which includes the power requirement for the blower. So this is why I suggest that we should be able to recover about 5% with a head designed to recover the lost mass air.
But we wont know until we do it will we?.
07-06-2004, 08:42 AM
#11
Originally Posted by billc5
The problem I see with turning the blower fast to recover the lost boost or Air Mass is that the thermal efficiency goes to Hell at speeds over 13000 RPM. Thermal expansion of the rotors may begin to effect performance and we are operating outside of the safe conditions. Delta temperature doubles between 6000 and 13000rpm and HP required goes up times 4.
The empirical evidence is demonstrated with the addition of Exhaust Headers, which drops the Intake Manifold pressure and hence reduces Mass in the Chamber. Tuning could not bring back more power than before. This is a very predictable result.
With exhaust headers I lost about 4% power which includes the power requirement for the blower. So this is why I suggest that we should be able to recover about 5% with a head designed to recover the lost mass air.
But we wont know until we do it will we?.
The empirical evidence is demonstrated with the addition of Exhaust Headers, which drops the Intake Manifold pressure and hence reduces Mass in the Chamber. Tuning could not bring back more power than before. This is a very predictable result.
With exhaust headers I lost about 4% power which includes the power requirement for the blower. So this is why I suggest that we should be able to recover about 5% with a head designed to recover the lost mass air.
But we wont know until we do it will we?.
Bill,
Even with LESS boost and the same pulleys, I believe significantly more power will be available.
There certainly are limits to the various blowers based on their displacement and ability to move a fixed amount of air, and how fast you can effectively spin them. Assuming you had a large enough roots style blower to bring the boost back to its former levels with the stock unported heads, then as Ive said before, even more power could be produced.
I think you might be able to spin the blower a little faster and get the boost values closer and have very satisfactory results....
I will be looking forward to the results from Rick's car...
Tony
07-06-2004, 10:21 AM
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Tony,
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
07-06-2004, 10:40 AM
#13
225's...
Originally Posted by VortechC5
Tony,
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
While the 205's would still provide you with significant gains, I am confident the 225's would provide you with more. In a boosted application, a little more runner volume in a street application is not a big deal (because of the pressurized intake tract), and the 225's will offer more flow on the exhaust side as well.
Call me at AFR whenever you get a chance and I can get into more detail with you, but if it were me, I would wait for the 225's.
Thanks,
Tony
07-06-2004, 01:09 PM
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Originally Posted by Tony Mamo @ AFR
Bill,
Simple physics....Better flowing (efficient) head always equals more power.
Simple physics....Better flowing (efficient) head always equals more power.
PS I also wanted to mention that my "theory" excludes detonation and low octane fuel issues. Take stock headed "boosted" engine combo....tune for max performance, swap heads for more efficient higher flowing heads of your choice, also tune for max performance (including changing pulley for same as baseline boost levels), and witness a bunch more HP and TQ produced.
I would just hate to see someone be disappointed slapping on some 205s/225s without retuning for max performance on a Roots blower setup. On a centrifugal blower, I do believe the compressor will flow more air with better heads in ADDITION to seeing gaines from tuning.
This is a great topic - some interesting points being made, and no one is getting upset!
07-06-2004, 02:06 PM
#15
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Originally Posted by VortechC5
Tony,
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
I am planning on ordering a set of the 76cc 205s this week. I am running a Vortech supercharger and live at high (7000 feet) altitude. Based on what you said earlier in this thread would I be better off to wait for the 225s? I am planning on running a small 218/218 .558/.558 114 cam.
Please explain if this is true or only for certain type of superchargers (ie: Turbo).
Last edited by PREDATOR-Z; 07-06-2004 at 02:26 PM.
07-07-2004, 10:58 AM
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If someone is still under the impression that cylinder heads have no or little benefit for performance on a roots blown motor than I have one thing to say, "Don't turn on the TV" you might just see something called "Top Fuel" or "Pro Mod", these programs have full time cylinder head porters trying to get the most flow for maximum power......even the exhaust side.
The blower on there cars flow well over 1000cfm, and there heads don't. Yet a head that flows 500cfm will make more power than a head that flows 450cfm.
Let me put this in different terms, boost is pressure, pressure is caused by restriction. A cylinder head is going to restrict flow, NO MATTER WHAT, but to what degree.
OK, I will follow somebody else's train of thought, let's say flow stays the exact same, and with the given fact boost creates heat, and the boost drops with the new heads. You would still gain power for the simple thought that the temperature would drop with less pressure.
The blower on there cars flow well over 1000cfm, and there heads don't. Yet a head that flows 500cfm will make more power than a head that flows 450cfm.
Let me put this in different terms, boost is pressure, pressure is caused by restriction. A cylinder head is going to restrict flow, NO MATTER WHAT, but to what degree.
OK, I will follow somebody else's train of thought, let's say flow stays the exact same, and with the given fact boost creates heat, and the boost drops with the new heads. You would still gain power for the simple thought that the temperature would drop with less pressure.
07-08-2004, 09:26 AM
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Originally Posted by Sidewayz 4.6l
If someone is still under the impression that cylinder heads have no or little benefit for performance on a roots blown motor than I have one thing to say, "Don't turn on the TV" you might just see something called "Top Fuel" or "Pro Mod", these programs have full time cylinder head porters trying to get the most flow for maximum power......even the exhaust side.
http://www.automotive.eaton.com/imag...s/M112flow.gif
It demonstrates the difference in flow between 5psi and 10psi as a function of rpm. For example at 12000rpm the there is only a 15 CFM difference which would not even support the 20 HP required to achieve this increase.
http://www.automotive.eaton.com/imag.../M112power.gif
This is suggests that the Mass Air for combustions is a function of RPM and not pressure dependant. This also gives a good indication that the blower wont provide ever increasing power with RPM.
but then again I could be wrong.
