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Auto Engine - compression ratio vs. octane

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bk_maynard(at)yahoo.com
Guest

Posted: Wed May 13, 2009 7:24 am Post subject: Auto Engine - compression ratio vs. octane

  Would someone have a rough idea of what compression ratio I could run on my chevy auto<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

Conversion if I run 100LL  instead of regular unleaded?

 

Specs for my 3.4 V6 are 9.0:1 for regular.

 

 

 

Thanks,   Brad



          [quote][b]

s_korney(at)hotmail.com
Guest

Posted: Wed May 13, 2009 8:18 am Post subject: Auto Engine - compression ratio vs. octane

At least 10:1 with 100LL



Best... Steve



Date: Wed C 13 May 2009 08:17:42 -0700

From: bk_maynard(at)yahoo.com

Subject: Auto Engine - compression ratio vs. octane

To: engines-list(at)matronics.com

            Would someone have a rough idea of what compression ratio I could run on my chevy auto 

Conversion if I run 100LL  instead of regular unleaded? 

Specs for my 3.4 V6 are 9.0:1 for regular. 

  

Thanks C   Brad

           	  Quote: 	
		  http://www.matronics.com/N========================http://www.matronics.com/contrib=============== 	
Hotmail® has a new way to see what's up with your friends. Check it out.  [quote][b]

jrccea(at)bellsouth.net
Guest

Posted: Wed May 13, 2009 8:34 am Post subject: Auto Engine - compression ratio vs. octane

Theoretical limit is 11.2:1 with premium autofuel.  I  don't think I'd go that high.  I do know from experience that 9.5:1 is  OK on premium with 28 degrees advance on an O-200, but I have trouble on  shutdown with regular.

 JimC

 [quote]   ---

MONTY(at)bpaengines.com
Guest

Posted: Wed May 13, 2009 8:53 am Post subject: Auto Engine - compression ratio vs. octane

I  don't think I would use 100 LL in an auto engine for a couple of  reasons.

 1.  Avgas burns at a slower rate

 2.  One of the products of combustion with leaded fuel is lead  bromide, which is somewhat corrosive and abrasive.

     Aircraft lubricating oil has an additive package to deal  with lead bromide whereas motor oil does not.

  

 an  interesting side note.  I rebult a Ford Flathead for a 46 Coupe I have and  the engine is considerably pumped up.  I ran it on the dyno here in the BPE  shop and ran it on 100 LL.  mixture was not quite right and during the  process of straightening out power valves, jetting, etc. I also tested with 91  Oct mogas.  The CR on this engine is 9.25:1 which is quite a bit for a  flathead.  The engine made slightly more power on mogas with the timing not  changed.  FYI

  

 Monty  Barrett

 Barrett Precision Engines

 [quote]   

   --

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Wed May 13, 2009 8:59 am Post subject: Auto Engine - compression ratio vs. octane

If compression were the only consideration, it would be so simple.  It 

isn't that simple.



Cam design plays more of a roll in detonation limits than compression 

alone.  You can easily make 8.5:1 compression produce 145 pounds 

cranking pressure if you know what you're doing.  Likewise, 11:1 can 

produce less than 140 pounds with the right lobe separation angle.



I recommend measuring the cranking pressure.  145 pounds cranking 

pressure is easy with 100LL.  155 would be a little on the edge.   

Anything in the 130 range (125 to 135) is a piece of cake.

--

_________________
Gary
AuCountry Aviation
Home of Team Grumman

frank.hinde(at)hp.com
Guest

Posted: Wed May 13, 2009 9:13 am Post subject: Auto Engine - compression ratio vs. octane

Interesting..And seems to be evidence that mogas is better  for an aircraft engine too, assuming its not a turbo'ed 540.

  

 I know my IO 360 loves mogas and runs well even with 10%  Ethanol blends...Although I have not flown it above 15000ft so cannot attest to  vphase seperation, water fallout predictions.

  

 Frank



   From: owner-engines-list-server(at)matronics.com  [mailto:owner-engines-list-server(at)matronics.com] On Behalf Of Monty  Barrett Sr

Sent: Wednesday, May 13, 2009 8:41 AM

To:  engines-list(at)matronics.com

Subject: RE: Auto Engine -  compression ratio vs. octane

 

 I  don't think I would use 100 LL in an auto engine for a couple of  reasons.

 1.  Avgas burns at a slower rate

 2.  One of the products of combustion with leaded fuel is lead  bromide, which is somewhat corrosive and abrasive.

     Aircraft lubricating oil has an additive package to deal  with lead bromide whereas motor oil does not.

  

 an  interesting side note.  I rebult a Ford Flathead for a 46 Coupe I have and  the engine is considerably pumped up.  I ran it on the dyno here in the BPE  shop and ran it on 100 LL.  mixture was not quite right and during the  process of straightening out power valves, jetting, etc. I also tested with 91  Oct mogas.  The CR on this engine is 9.25:1 which is quite a bit for a  flathead.  The engine made slightly more power on mogas with the timing not  changed.  FYI

  

 Monty  Barrett

 Barrett Precision Engines

 [quote]   

    

[b]

larry(at)macsmachine.com
Guest

Posted: Wed May 13, 2009 9:35 am Post subject: Auto Engine - compression ratio vs. octane

Hi Frank,

I've used 87-octane with 10% ethanol for the last two years and only on 

one occasion did "phase separation" occur. The aircraft had set for 4 months

with less than a gallon in the tank after the pre winter annual 

inspection. The small amount of fuel did look nearly opaque and gray. I 

drained the remaining

and added new fuel when flying weather returned. No telling how long the 

gas had set in the retailers tank before I got it.



Larry McFarland 601HDS at www.macsmachine.com



Hinde, Frank George (Corvallis) wrote:

 	  Quote: 	
		   Interesting..And seems to be evidence that mogas is better for an 

 aircraft engine too, assuming its not a turbo'ed 540.

  

 I know my IO 360 loves mogas and runs well even with 10% Ethanol 

 blends...Although I have not flown it above 15000ft so cannot attest 

 to vphase seperation, water fallout predictions.

  

 Frank



 ------------------------------------------------------------------------

 *From:* owner-engines-list-server(at)matronics.com 

 [mailto:owner-engines-list-server(at)matronics.com] *On Behalf Of *Monty 

 Barrett Sr

 *Sent:* Wednesday, May 13, 2009 8:41 AM

 *To:* engines-list(at)matronics.com

 *Subject:* RE: Auto Engine - compression ratio vs. octane



 I don't think I would use 100 LL in an auto engine for a couple of 

 reasons.

 1.  Avgas burns at a slower rate

 2.  One of the products of combustion with leaded fuel is lead 

 bromide, which is somewhat corrosive and abrasive.

     Aircraft lubricating oil has an additive package to deal with lead 

 bromide whereas motor oil does not.

  

 an interesting side note.  I rebult a Ford Flathead for a 46 Coupe I 

 have and the engine is considerably pumped up.  I ran it on the dyno 

 here in the BPE shop and ran it on 100 LL.  mixture was not quite 

 right and during the process of straightening out power valves, 

 jetting, etc. I also tested with 91 Oct mogas.  The CR on this engine 

 is 9.25:1 which is quite a bit for a flathead.  The engine made 

 slightly more power on mogas with the timing not changed.  FYI

  

 Monty Barrett

 Barrett Precision Engines



      



 *

 *

frank.hinde(at)hp.com
Guest

Posted: Wed May 13, 2009 11:14 am Post subject: Auto Engine - compression ratio vs. octane

Good input Larry..Sounds like the remaining fuel absorbed the water from condensation.



Fit for the lawnmower only after 4 months is a certainty now..



Thanks



Frank



 



--

Ed Anderson

Joined: 10 Jan 2006
Posts: 475

Posted: Wed May 13, 2009 1:53 pm Post subject: Auto Engine - compression ratio vs. octane

Given that the lower the octane rating, the more energy a specific volume of gasoline has, I am not surprised that with auto fuel you got more power than with 100LL.  The higher octane fuel has less energy content and only real purpose is prevent detonation with high compression engines.  Many believe that higher octane means more power than lower octane fuels, but only if you are able to run higher compression or   forced induction systems (which in effect increase compression ratio).  

   

100LL contains approx 120,000 BTU/Gallon whereas 87 Octane contains approx 125,000 BTU/Gallon or about 4% more energy.  

   

Ed  

     

Ed Anderson  

Rv-6A N494BW Rotary Powered  

Matthews, NC  

eanderson(at)carolina.rr.com  

http://www.andersonee.com  

http://www.dmack.net/mazda/index.html  

http://www.flyrotary.com/  

http://members.cox.net/rogersda/rotary/configs.htm#N494BW  

http://www.rotaryaviation.com/Rotorhead%20Truth.htm[url=http://www.dmack.net/mazda/index.html][/url]  

        

  

From: owner-engines-list-server(at)matronics.com [mailto:owner-engines-list-server(at)matronics.com] On Behalf Of Monty Barrett Sr

 Sent: Wednesday, May 13, 2009 11:41 AM

 To: engines-list(at)matronics.com

 Subject: RE: Auto Engine - compression ratio vs. octane  

  

     

I don't think I would use 100 LL in an auto engine for a couple of reasons.  

    

1.  Avgas burns at a slower rate  

    

2.  One of the products of combustion with leaded fuel is lead bromide, which is somewhat corrosive and abrasive.  

    

    Aircraft lubricating oil has an additive package to deal with lead bromide whereas motor oil does not.  

    

   

    

an interesting side note.  I rebult a Ford Flathead for a 46 Coupe I have and the engine is considerably pumped up.  I ran it on the dyno here in the BPE shop and ran it on 100 LL.  mixture was not quite right and during the process of straightening out power valves, jetting, etc. I also tested with 91 Oct mogas.  The CR on this engine is 9.25:1 which is quite a bit for a flathead.  The engine made slightly more power on mogas with the timing not changed.  FYI  

    

   

    

Monty Barrett  

    

Barrett Precision Engines  

  [quote]  

--

_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

andrew(at)oc384.net
Guest

Posted: Wed May 13, 2009 3:12 pm Post subject: Auto Engine - compression ratio vs. octane

In that case is there an aviation oil including the additive that can  be run in auto conversion engines?  Or can the additive be bought and added when filling up with 100LL?  If you’re flying into places w/out mogas it sounds like you need it.  

   

-Andrew  

   

       

From: owner-engines-list-server(at)matronics.com [mailto:owner-engines-list-server(at)matronics.com] On Behalf Of Monty Barrett Sr

 Sent: Wednesday, May 13, 2009 10:41 AM

 To: engines-list(at)matronics.com

 Subject: RE: Auto Engine - compression ratio vs. octane  

  

  

     

I don't think I would use 100 LL in an auto engine for a couple of reasons.  

    

1.  Avgas burns at a slower rate  

    

2.  One of the products of combustion with leaded fuel is lead bromide, which is somewhat corrosive and abrasive.  

    

    Aircraft lubricating oil has an additive package to deal with lead bromide whereas motor oil does not.  

    

   

    

an interesting side note.  I rebult a Ford Flathead for a 46 Coupe I have and the engine is considerably pumped up.  I ran it on the dyno here in the BPE shop and ran it on 100 LL.  mixture was not quite right and during the process of straightening out power valves, jetting, etc. I also tested with 91 Oct mogas.  The CR on this engine is 9.25:1 which is quite a bit for a flathead.  The engine made slightly more power on mogas with the timing not changed.  FYI  

    

   

    

Monty Barrett  

    

Barrett Precision Engines  

  [quote]  

--

dean.psiropoulos(at)veriz
Guest

Posted: Thu May 14, 2009 7:49 pm Post subject: Auto Engine - compression ratio vs. octane

The big automotive engines of the 1960s took compression ratios to their

ultimate state of the art with premium leaded auto gas.  Ratios from 10.5 to

11.5 to 1 were common place with 100 octane auto fuel.  Since the unleaded

mandate, computer analysis has advanced the state of the art in combustion

chamber technology so that 9.5 to 1 ratios are possible on regular unleaded

fuel (87 octane) without detonation.  If you use computerized engine control

with knock sensing you could probably go even higher.  And with avgas being

the equivalent of somewhere around 110 octane autofuel, the sky should be

the limit (not quite but it would be an interesting exercise to see how high

one could go using a modern auto engine with avgas).



Dean Psiropoulos

RV-6A N197DM

Struggling with erratic idle on 0-360

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri May 15, 2009 5:58 am Post subject: Auto Engine - compression ratio vs. octane

I had a friend who regularly ran his 426 Hemi Charger on high octane Avgas

before the advent of 100 LL.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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