Turbo help!
Re: Turbo help! maybe you misunderstood my point
you can make up for high compression with octane, once you cant go any higher in octane THEN the compression has to come down to make MORE power then that. so im assuming you do this as people on here most certainly do.
of course l/c engines are safer, safer because they can operate at higher output with lower octane demand.
see the vette up there? 700rwhp, and high compression, just like harlan/rob raymers 700hp.. 700=700= about the current borderline for head sealing, reguardless of boost level with comparable intake temperatures.
the only reason the car's you've seen arent making same hp high compression vs low compression is b/c high comp. cars have to limit their timing to stay away from detonation.. if they would fix it with octane then all is the same.(see vette above)
effective compression page
http://www-unix.oit.umass.edu/~tcroy/effectivecr.htm
that being said effective compression really is not comparable like said above the detonation limit is not in the same position for each.
i maintain that hp level @ set intake temperature is what pushes the heads, not 'boost level'
its a good discussion for sure, i'd like to see some data like dyno graphs for some identical cars that have gone the separate ways.
you can make up for high compression with octane, once you cant go any higher in octane THEN the compression has to come down to make MORE power then that. so im assuming you do this as people on here most certainly do.
of course l/c engines are safer, safer because they can operate at higher output with lower octane demand.
see the vette up there? 700rwhp, and high compression, just like harlan/rob raymers 700hp.. 700=700= about the current borderline for head sealing, reguardless of boost level with comparable intake temperatures.
the only reason the car's you've seen arent making same hp high compression vs low compression is b/c high comp. cars have to limit their timing to stay away from detonation.. if they would fix it with octane then all is the same.(see vette above)
effective compression page
http://www-unix.oit.umass.edu/~tcroy/effectivecr.htm
that being said effective compression really is not comparable like said above the detonation limit is not in the same position for each.
i maintain that hp level @ set intake temperature is what pushes the heads, not 'boost level'
its a good discussion for sure, i'd like to see some data like dyno graphs for some identical cars that have gone the separate ways.
TECH Regular
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Re: Turbo help! </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MIGHTYMOUSE:
<strong>
15psi boost making 600rwhp has the same cyl pressure 5psi 600rwhp
<img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wouldn't cylnder pressure have more to do with TQ?
While breathing ability, Rpm, and TQ at a given Rpm determine hp.
Basically , woulnd't, or couldn't cylinder pressure be different on on 2 600 hp blown motors if the tourque is different between the 2.
No?
Couldn't or woulnd't the one with higher TQ (if that was the case) have more cylinder pressure and the other just have better breathing characterstics at maybe a higher Rpm ?
<small>[ January 29, 2003, 07:20 PM: Message edited by: Rpm2800 ]</small>
<strong>
15psi boost making 600rwhp has the same cyl pressure 5psi 600rwhp
<img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wouldn't cylnder pressure have more to do with TQ?
While breathing ability, Rpm, and TQ at a given Rpm determine hp.
Basically , woulnd't, or couldn't cylinder pressure be different on on 2 600 hp blown motors if the tourque is different between the 2.
No?
Couldn't or woulnd't the one with higher TQ (if that was the case) have more cylinder pressure and the other just have better breathing characterstics at maybe a higher Rpm ?
<small>[ January 29, 2003, 07:20 PM: Message edited by: Rpm2800 ]</small>
On The Tree
Joined: Feb 2002
Posts: 188
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From: Chicagoland
Re: Turbo help! I understand your point perfectly. Assuming all else equal, in the same exact configuration, with the same effective compression.. the turbo engine with lower compression & high boost will make more power than the one with high compression & low boost.
I'm not bringing detonation/octane into this.
I couldn't find any good links to show you, other than this one:
http://www.datsuns.com/Tech/Tech_blowerintro.htm
(at the bottom)
It's a pretty well known fact, but like I said, there is give and take. Making a 6:1 engine for 50psi isn't really a good idea <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> Most people like 8.5:1, but some have gone to 9 or 9.5:1.
I'm not bringing detonation/octane into this.
I couldn't find any good links to show you, other than this one:
http://www.datsuns.com/Tech/Tech_blowerintro.htm
(at the bottom)
It's a pretty well known fact, but like I said, there is give and take. Making a 6:1 engine for 50psi isn't really a good idea <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> Most people like 8.5:1, but some have gone to 9 or 9.5:1.
On The Tree
Joined: Feb 2002
Posts: 188
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From: Chicagoland
Re: Turbo help! It's not a matter of agreeing, it's a matter of test results as it has been tried in the past. You can talk in theory, bench racing, based on cylinder pressures all you want, but experiments that have tested this (that I have been told about) showed the lower cr/high boost gave more power. I believe Bruce Crower did a test a long time ago, varying the CR & boost levels a bunch, and had lots more power at low CR and very high boost. I'll see what I can dig up around here (lots of engineering data & SAE stuff), who knows, maybe I'll prove my point wrong <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
There are lots of variables that come into play, so it is very difficult to really say the CR is all that changed - dropping the CR incorrectly can mess your quench, efficiency of different compressors/exhaust side at different boost levels (if you are using a turbo), cam specs etc.
There are lots of variables that come into play, so it is very difficult to really say the CR is all that changed - dropping the CR incorrectly can mess your quench, efficiency of different compressors/exhaust side at different boost levels (if you are using a turbo), cam specs etc.
Re: Turbo help! </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">I understand your point perfectly. Assuming all else equal, in the same exact configuration, with the same effective compression.. the turbo engine with lower compression & high boost will make more power than the one with high compression & low boost.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I have to agree with MIGHTYMOUSE... the only thing lower compression and more boost do is make for a safer combo on the given octane of fuel used.
A high compression, low boost engine will have to run higher octane fuel to obtain the same power numbers as the low comp/high boost engine... and they will make comparable power until enough octane becomes a problem for the high comp engine.
A high comp/low boost engine at 600rwhp, and a low comp/high boost engine at 600rwhp both have the same amount of cylinder pressure after ignition... thus the same amount of power output.... the difference is before ignition where the high comp engine has more pressure near TDC with the same amount of air/fuel mixture.. thus a higher chance of detonation with this set-up.
A high compression, low boost engine will have to run higher octane fuel to obtain the same power numbers as the low comp/high boost engine... and they will make comparable power until enough octane becomes a problem for the high comp engine.
A high comp/low boost engine at 600rwhp, and a low comp/high boost engine at 600rwhp both have the same amount of cylinder pressure after ignition... thus the same amount of power output.... the difference is before ignition where the high comp engine has more pressure near TDC with the same amount of air/fuel mixture.. thus a higher chance of detonation with this set-up.
Re: Turbo help! you're right, me and the mad scientist are talking from a thermodynamics standpoint, so this could understandably be a case where 'ideal' isn't 'real'
but i still want to see it
but i still want to see it
On The Tree
Joined: Feb 2002
Posts: 188
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From: Chicagoland
Re: Turbo help! Yup I hear ya. I'd definitely like to bring some data into this discussion.
I did talk to an engineer yesterday, he confirmed what I was saying (even though he used bigger words and more acronyms than I did <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> ) and is going to find me some info.
I may do some searching through some more books, or SAE papers. It's nice having those resources around <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
I did talk to an engineer yesterday, he confirmed what I was saying (even though he used bigger words and more acronyms than I did <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> ) and is going to find me some info.
I may do some searching through some more books, or SAE papers. It's nice having those resources around <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
