Compression Ratio vs Blower Boost
08-11-2008, 09:01 PM
#11
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With a lower static cr, you are able to pack more air/fuel in to get to your desired cr vs having a smaller chamber so when it lites you have more energy vs a lesser amount of air/fuel?
08-12-2008, 06:28 PM
#12
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I have been running 4.7lbs on 9.5:1 static engines. I like the combo because I run the small 177 blowers on 470cid engines and I don't have to spin them too fast to get the desired effective compression. I run no intercoolers. Picked up about 8mph from no blowers.
Bt
Bt
08-13-2008, 06:06 PM
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Blue Thunder, I looked at your profile,now cut that out.
However,to answer your jab....For example,we know the new generation of EPA regs has impacted diesel engines.Presently there seems to be definite challenges at the OEM's,who are trying to satisfy several masters. The Duromax seems most successful. Mercedes filed a patent pertinent to the upper end only,which includes aneroid control/boost but excludes the bottom end.
I'm suspicious,a dry sump and or vacuum system could offer some small part in solving issues with the diesels,subject to total design. I'm also suspicious there may be opportunity to apply similar theory to the forced induction marine engine.
Specifically,as crankcase vacuum draws piston blow by the vacuum must absorb some part of the cylinder chamber pressure which in turn may be construed to lower the chamber CR.
Further,I have puzzled over how a few inches of vacuum can increase horsepower as it does...Granted,the short answer is, vacuum scavenges parasitic oil thereby creating less resistance and more horsepower/torque.
However,to answer your jab....For example,we know the new generation of EPA regs has impacted diesel engines.Presently there seems to be definite challenges at the OEM's,who are trying to satisfy several masters. The Duromax seems most successful. Mercedes filed a patent pertinent to the upper end only,which includes aneroid control/boost but excludes the bottom end.
I'm suspicious,a dry sump and or vacuum system could offer some small part in solving issues with the diesels,subject to total design. I'm also suspicious there may be opportunity to apply similar theory to the forced induction marine engine.
Specifically,as crankcase vacuum draws piston blow by the vacuum must absorb some part of the cylinder chamber pressure which in turn may be construed to lower the chamber CR.
Further,I have puzzled over how a few inches of vacuum can increase horsepower as it does...Granted,the short answer is, vacuum scavenges parasitic oil thereby creating less resistance and more horsepower/torque.
08-13-2008, 06:21 PM
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My uneducated opinion would be with a vacuum under the piston, less pressure (resistance) on the underside of the piston during the power stroke would result in more power.
08-13-2008, 06:22 PM
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One could ask,what is the ideal compression ratio vs blower boost. However,there are several variables that cause that question to be more or less abstract.
Therefore,the question asks for opinion on a window range including invited variables.
For a base line we are wondering if the compression ratio should be as high as possible to safely accept 87 octane. The cam,heads,displacement and etc. will be included in the decision. (92 octane min. may be more logical)
The blower would then be responsible for sufficient boost to create below Sea Level density altitude. The boost number should be low enough to allow significant blower underdrive,subject to blower size.
The slow turning blower would require less horsepower,produce less heat and allow simpler density altitude management.
We realize the general thought is 8.5 compression and higher boost. However,for marine application,perhaps the compression could be 9 + and boost somewhere under 5 lbs.
Is it possible an improved net result would be more safely achieved ?
Therefore,the question asks for opinion on a window range including invited variables.
For a base line we are wondering if the compression ratio should be as high as possible to safely accept 87 octane. The cam,heads,displacement and etc. will be included in the decision. (92 octane min. may be more logical)
The blower would then be responsible for sufficient boost to create below Sea Level density altitude. The boost number should be low enough to allow significant blower underdrive,subject to blower size.
The slow turning blower would require less horsepower,produce less heat and allow simpler density altitude management.
We realize the general thought is 8.5 compression and higher boost. However,for marine application,perhaps the compression could be 9 + and boost somewhere under 5 lbs.
Is it possible an improved net result would be more safely achieved ?
This really depends on the blower and intercooler (if available) design. If, power vs. detonation is the ideal goal then you have to maximize compression to the superchargers most efficient pressure/rpm and then add in the intercooler. Roots style superchargers on motors work best between 4-7psi, therefore, depending on the engines flow and supercharger size, this is where you want the boost to be. Some go higher, some go lower, but you certainly get to a point of no benefit with traditional roots superchargers. Therefore, 9:1 compression works pretty good with the roots. Centrifugals work well, so it would be ideal to run 10-20psi, but, you can't typcically run low enough compression to run these high boost levels (can get away with 15 and below on some applications) because there is a major issue with low speed torque. Therefore, 8-8.5:1 compression works pretty well, and then 8-12psi. With a screw, it's similar to the centrifugal, but you can get away with the lower compression. So you can run 10-15psi and setup with 7.5:1 compression.
Of course, there is far more involved in this. If the blower is too small, you may need compression to help bring up power. But the main key is the same thing, you want your motor to be able to flow as much air as possible then maximize the engine with the supercharger.
Thanks
08-14-2008, 01:23 AM
#18
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My understanding is the power increase comes from the addtn'l ring seal from the aid of the vaccuum,I think I have heard of running low tension oil rings w/ vacuum pump to aid in sealing also,Smitty
08-17-2008, 10:34 AM
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A note of trivia...Auto Verdi is a brand of dry sump oil pumps that several NASAR teams are using.The pump is said to be long lived,produce adequate vacuum and oil pressure and require minimum operating horsepower. The lobes resemble a roots blower vane. The lobe design is thought to produce less pulsation than the gear type pumps. Therefore, the impact on vacuum,oiling and harmonics may be improved.
The question has been asked if a screw type vane would be a further improvement.
The question has been asked if a screw type vane would be a further improvement.
