Smart questions
Smart answers
Smart people
Join Eng-Tips Forums

Member Login

Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

vintageAP (Automotive) (OP)
14 Jul 06 16:47
Hi all, new here - great site!

 I'm investigating propane conversions for performance engines and understand that because of the higher octane with propane a higher mechanical compression ratio is desired for optimum performance.

  Does anybody have this information handy or experience with this?

  I'm sure that the same laws apply as with gasoline engines; too high and pre-ignition will come into play, but about where is that magic number? In gasoline engines there are factors that won't apply in a propane fuled engine such as quench area, puddling of liquid fuel, etc.. Am I still looking for the same aproimate A/F ratio - 14.7? Will cylinder temp affect flame travel and pre-ignition in the same way with propane? Any info and discussion is appreciated.
patprimmer (Publican)
15 Jul 06 8:23

Why won't quench apply?

Of course cylinder temperature will affect flame travel and pre ignition. Burning hydrocarbons is a chemical reaction. Heat will accelerate that action. To much heat will cause a spontaneous reaction.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

kenre (Mechanical)
15 Jul 06 9:29
Very hard to quote a compression ratio without knowing what duration the camshaft is.

My  LPG 350 chev i have recently built, havent fired it up yet, is right on 10:1, the max i can go according to the manufacturers of the particular camshaft i am using. They develop and test all there cams on there own dyno.

Helpful Member!  franzh (Automotive)
15 Jul 06 9:45
Both Pat and Kenre have a point, there is too much information needed to make a recommendation, but again, what is good for us may not be good for you, and frankly, thats not the purpose of this forum.
If we were to say that ONLY 11.3:1 will work, you will have to build the engine around that CR, not the other way around.
Quench works to induce turbulence in the combustion chamber and it works with all fuels.  The greater the quench action, the faster the turbulence and corresponding flame propogation action.  Large open chambers have relatively low quench and need more ignition timing to develop the same combustion pressure than a small chamber and tight quench.
The tradeoff is that tight quench areas can bring in pockets of unburned or not fully burned Hydrocarbons.  Vapor fuels have an inherent advantage in that they more easily mix with air and develop fewer pockets of unburned HC's.

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

vintageAP (Automotive) (OP)
15 Jul 06 15:44
"The tradeoff is that tight quench areas can bring in pockets of unburned or not fully burned Hydrocarbons.¬†¬†Vapor fuels have an inherent advantage in that they more easily mix with air and develop fewer pockets of unburned HC's."  

- This is what I'm referring to. A tight quench will mix still liquified fuel much better before combustion. An already gaseous fuel will not benefit from that.

I'm not looking for an exact compression number, that will be for me to determine with experimentation. Let's face it though, changing the compression in an engine is time consuming and can be costly. I'd much rather start in the correct range. For example; a street driven gasoline engine is tunable up to about 11:1, an alcohol race engine likes 13:1 much better, a top fuel nitro-methane goes beyond that etc..

Of course the camshaft makes a big difference, but I can swap a cam in an hour..... :)

My goal here is to take advantage of the octane and gaseous fuel in an engine. To build a purpose-built engine, if you will, rather than using parameters in an engine designed for gasoline, and having those parameters compromise the efficiency of the propane engine.
MikeHalloran (Mechanical)
15 Jul 06 22:33
So, mill the heads on a junkyard engine, and add gaskets until it stops knocking and pinging, then build a good engine to that ratio.  I could swear I've read that propane is good to 15:1 or more.

Mike Halloran
Pembroke Pines, FL, USA

patprimmer (Publican)
16 Jul 06 1:42
There is Propane and Propane.

If it is not pure and contains reasonable amounts of Butane the octane will suffer. Also I have been told there are different isomers with different octane ratings.

11:1 will be safe with any commercial Propane and any camshaft.

Quench does a lot more than evaporate fuel. It transports the flame front across the chamber, thereby increasing burn rate, and reducing required advance, while still allowing peak cylinder pressure to build at about TDC.

There is one theory (I am still to be convinced) that a faster burn rate suppresses detonation as it consumes the fuel and oxygen before the mixture has time to detonate. Also with the later optimum spark timing, the piston is moving up slower or building compression slower as the burning fuel is building it's pressure.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

franzh (Automotive)
16 Jul 06 9:29
Thre is also a factor called the critical compression ratio, where by compression, the air and fuel mixture can reach a combustion temperature as in a diesel engine.

US spec Propane (Commercial grade vs HD-5) has a CCR somewhere around 12.5:1, and again, this depends on the purity of the fuel, usually between 90 and 95% propane, the balance being propylene, ethane, butanes, and other minor fractions.  Of all these fuels, propane has the longest burn duration, and the highest octane, and the highest resistance to ignition.  The other fuels tend to diminish the combustion quality of propane.  If the combustion chamber is largely open, the CCR can go a bit lower, if it is smaller, it can go higher.  Small chambers will combust the fuel faster during the maximum crank-angle leverage point.

On a variable compression ratio lab engine, the chamber volume is altered during operation until the engine begins to knock, thusly determining the actual compression ratio.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

automotivebreath (Automotive)
16 Jul 06 21:49
The highest compression ratio that can be designed into a propane engine depends on many variables as mentioned before. It's important to understand why. As this chart displays, the ignition temperature of LPG is much higher.

Also remember the energy content of propane s lower than gasoline. Compared to gasoline the energy content of propane is 74%.


vintageAP (Automotive) (OP)
17 Jul 06 16:20
"automotivebreath" - If I'm interpreting your chart correctly then the higher ignition temp of LPG (because of the octane I'm assuming) is the reason that the pre-ignition point is higher and is functionally the reason a higher static compression ratio can be used to get the best efficiency from a LPG engine. Please advise if I am not interpreting this correctly?

"patprimmer" - By those numbers 12:1 seems to be a safe place to start to build a high-efficiency LPG engine. Given that a real-world use would take into account that the fuel would be bought from different sources and vary in quality in those fractions I'm thinking 12:1 would be a very good starting point. Feedback?
automotivebreath (Automotive)
17 Jul 06 20:31
Detonation is the spontaneous combustion of the remaining fuel/air mixture in the chamber during combustion. The initial combustion at the spark plug is followed by a normal combustion burn. Excessive heat from the flame, hot engine parts, inlet gas temperature and building pressure can cause the end gas in the chamber to explode. With the high ignition temperature of LPG; elevated combustion pressures are possible.
patprimmer (Publican)
17 Jul 06 23:23

It depends where in the world you are. You did not say, but reference to Propane rather than LPG suggests USA.

I believe that the Propane sold in the USA is fairly pure high octane stuff. The LPG sold in many other regions contains quite a lot of Butane and is substantially lower octane. I would expect that 12:1 might be OK in the USA. 11:1 is the max I would recommend as safe under all conditions in all engines in NON USA regions


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

rdd48856 (Chemical)
22 Jul 06 20:01
Propane doesn't have isomers....insaturates (propene and butene)as well as waxes are the ones you should be worried about, as they tend to decrease easily octane rating.
GunMuse (Industrial)
29 Jul 06 0:52
Ok let me see if my thinking is right here. While propane has a lower energy rate it is more stable than diesal according to the chart?

Since Compression makes the burn-rate(explosion) grow expotentially at what point of compression does LPG surpass the 87 octane with nice 9.5 to 1 ratio?

GunMuse (Industrial)
29 Jul 06 1:10
Ok One follow up on this before someone answers. I have a couple of propane powered trucks.

The delivery system seems very "crude" at best.  It would seem to me that a MFC valve would be better suited than a "power valve".  

There doesn't seem to be anyway to really achieve fuel mileage from LPG automatically allowing for elevation and driving conditions.

I have been buying up the propane powered trucks because, frankly they are super cheap.  I bought a 94 3/4 ton chevy with a 5 speed for $400 nobody at these farm auctions wants to go near propane because of its low power.  I think that LPG could achieve 30 MPG

turbocohen (Automotive)
29 Jul 06 18:43
11:1 is safe.  LP in the USA is not consistently free of heavy's which is a metering accuracy issue so you need some margin for cylinder to cylinder distribution errors.

The bigger issue is ignition system capability.  11:1 takes its toll on gasoline ignition coils, wires, plugs and other goodies.  

I run a stock 6 liter LS-2 Chevy at 10.9:1 that runs ok on 87 octane gasoline but at reduced output.  It scoots on bp Ultimate and is slightly improved with liquid phase injected lp..  about .2 sec faster 0-60.  (comparison measured with 40lb more vehicle weight after changeover to LP system)
JBlack (Mechanical)
29 Jul 06 22:30
"Am I still looking for the same aproimate A/F ratio - 14.7?"

I believe that the stoichometric A/F ratio for propane is ~15.3
GunMuse (Industrial)
30 Jul 06 15:24
Liquid phase injected.  Wouldn't that defeat one of the benefits of LP by injecting it in liquid form.

I would suggest a custom computer to play with the timing on the fly if your going to be switching between Gas and LP on compression over 10.5:1.

As I was saying it looks to me that the efforts to use LP have been crude at best.  From its fuel delivery to any sort of addon's to increase power for LP.

I would like to try LP in a 2 stroke setup with an injecter setup (Like Diesal)and a lubrication system like convention 4-strokes.  4 valve heads with and evactuaded exhaust system.

Unfortunately only college kids seem to be able to get grants to use their "experience" to help us all.

turbocohen (Automotive)
30 Jul 06 22:36
Atchooly one of the advantages of metering lp as a liquid with the metering tip located in the stock fuel injector port is the latent heat of vaporization.  The recalibrated oem ECU with tweaks for LPG was a gift from a friendly Canadian GM guy whom I made a duplicate LS-2 lpi injection system for.

The mass air flow meter aint a liar..  Higher charge density + higher octane equivalence = (fill in the blank).

Truth is the retrofit was damn easy.  The LPI injectors have 10% less static flow than the stock gasoline ones did but they can open up to 600psi.  And the fuel pump delivers 4bar boost pressure above static tank pressure while the engine cranks over to facilitate .5 second hot restart.  The calibration mods were not complex..  primarily modified the authority limit to allow closed loop all the way to wot, eliminated cold start enrichment, reduced accel enrichment just a tad and reassigned an open channel for fuel rail pressure and temp compensation.

Runs the same as with the stock gasoline system but goes like a scalded hog.

As for college kids..  I sponsored many of them.  About 60 teams so far.   A lot of these kids become engineers and some are a real asset to alternative fuels hobbyists.
franzh (Automotive)
31 Jul 06 7:21

Those college engineering competitions were fun, werent they?  Many of the students we mentored have moved on to good positions at OEM's, research labs, and to teaching.  I get mail from them all the time thanking me for the direction we provided.

Natural Gas Vehicle Challenge's
Propane Vehicle Challenge's
Ethanol Vehicle Challenge
Formulae SAE


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

GunMuse (Industrial)
1 Aug 06 3:00
I have a 54 Mack Truck that came from the factory with LP on it(We contacted the Mack Museum to verify).  I would like to bring that beast back to life.  Most of the Mack enthusiasts that interested in the truck stop being so as soon as they find out its not diesal and run scared when they find out someone ordered a propane engine 62 years ago.  I think a modern day upgrade of a classic that did propane would really be a valuable marketing asset to the right corp.

Here's a side note question. "Why is propane cost increasing its not tied to the cost of a barrel of oil but seems to flucate with it?"

turbocohen (Automotive)
1 Aug 06 17:41
Propane is the bastard child of oil refining.  So are the companies that market it.  The big oil companies are busy marketing other fuels and lp is a nuisance for them.  In the past much of it was flared off because it was safer than allowing it to pool on the ground.
franzh (Automotive)
2 Aug 06 11:28
Propane is indeed tied into the price of oil production.  In Texas, about 75% of propane comes from Natural Gas, the rest from raw crude.  Propane is a residual from the refining, distillation, and condensation process of "making" other hydrocarbon products.
As Turbo stated, for many years, propane and butane was flared off, the cost to transport was more than the product sold for.  That is no longer the case.
LPG is a cost break-even for refineries now, as the product usage is growing.  It is the worlds third most widely used motorfuel and one of the most versatile fuels (home and business heating, cooking, industrial and recreation uses, motorfuel).
Gee, sounds like a marketing spiel, doesnt it?


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

patprimmer (Publican)
2 Aug 06 19:33
It's pretty handy for making plastics like Polypropylene and Polyethylene, brake fluid, coolant, detergents to list just a few.

It can also be used to make various intermediate products that are then used to make a very wide range of plastics and chemicals.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

vintageAP (Automotive) (OP)
4 Aug 06 15:13
Thanks all for the continuing great info! To run this thread just a little bit farther and elaborate on some info provided:

My original thought was to use propane in the gaseous state using a standard-type mixer replacing a carburetor. I'm intrigued though with the thought of LPG injection. This may present some disadvantages, but I'm also seeing some distinct advantages that are desirable.

Modern FI gasoline engines run a fuel pump pressure of about 35lbs (varies for make and system but let's use that as a number) and regulate the fuel rail pressure with a regulator. Am I oversimplifying here or could I just feed LPG to the regulator and regulate the pressure to the correct PSI (whatever that is determined to be) using all of the OEM system intact? Would a gasoline fuel injector not handle LPG in the same manner if the supplied fuel pressure was where the compensation was made?

This would certainly make things easier on a late model and using the feedback functions would be sweet.
vintageAP (Automotive) (OP)
4 Aug 06 15:20
Also to add; if the A/F ratio needs to be 15.3 (thanks JBlack) then that compensation could be done electronically at the O2 sensor. The computer would never even know........... :)
franzh (Automotive)
4 Aug 06 17:26
Do NOT even attempt to run liquid LPG through a gasoline system, it wont come close to handling the pressures.  This topic has been discussed many times on this forum.  To keep LPG liquid at 100 degrees F, you would need around 190 psig.  Underhood temps can exceed 200 degrees, and over 350 psig would be needed.
I've seen gasoline injectors blow themselves apart at 125 psig.
The gasoline injectors do not flow enough volume for liquid LPG use, hence the necessity for specialized injectors (re Turbocohens previous life).


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

vintageAP (Automotive) (OP)
4 Aug 06 17:58
Hmmmm..... I overlooked that. I knew it too........... :)

OK, Turbocohens injectors. These replace the gasoline injectors in a FI LPG conversion? Are these readily available? Will they run with the signal supplied by a typical modern FI control circuit?
vintageAP (Automotive) (OP)
4 Aug 06 20:17
So slap me. Turbocohen is a user name not a brand name.  :(
turbocohen (Automotive)
5 Aug 06 12:34
Geez Franz.. never considered branding thyself.  lol

It takes a bit more moxie to open the LP version of Deka II when the fuel tank temps are elevated during a hot start after a 20 minute hot soak.  These are modified gasoline injectors with higher operating pressure capability and additional attention to low leak rate due to the smaller molecule of lp.

The parts needed to make a lpfi system are on the road in asia and the EU but on the shelf in the US.  Problem is the LP industry here is not in step with the EPA and CARB.  If they adopt the relavent fuel quality standards THAT ARE ALREADY REQUIRED for gasoline retailers then the maybe the US market will get so called taxi tested OEM lpfi injectors and pumps..  The future availability of proven LPG liquid phase port injection hardware depends on the LP marketers taking the responsibility for deploying fuel detergents.  Since auto use is relatively minimal except for forklifts, there is no united front to establish requirements for using LPG motorfuel additives.
Here is a link to a page with the lp injectors I put on the GTO LS2 :

and a pic of the pump is here
franzh (Automotive)
5 Aug 06 12:41
There is currently a working group looking at establishing a motorfuel grade propane in excess of HD-5, especially to work with LPPFI to enable them to comply with the EPA and ARB.  I am a technical member of that working group (at this point, it is is initial phases, similar to what HD-5 started out as in the late 60's).

We sure are off topic by this point, arent we?


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

turbocohen (Automotive)
5 Aug 06 17:46
Vintage AP, the injector driver requirements are dependent on the injector coil impedance and performance expectations.  The good news is that a stock gasoline engine O2 sensor will shift close enough to LP stoichiometry to work ok with a little biasing.  Forget the worring with the numerical a/f ratio, just shoot the o2 sensor output from a reliable location that measures a good average of all the cylinders.

My ecu switchpoint voltage is initially .380mv after 7 sec and .460mv hot.
GunMuse (Industrial)
11 Aug 06 23:54
"comply with the EPA and ARB"  This is the problem I have with most research.  More concerned with the EPA than the advancement itself.

Isn't the sheer fact that propane is a huge improvement over gasoline enough some paper pushing weasal has to create a new standard on how to restrict engine performance before the technology is released.

GregLocock (Automotive)
11 Aug 06 23:58
Why shouldn't a new fuel have to meet the same external standards as the old one?

After all, I could take a current gasoline engine and get a measurable improvement in efficiency if I didn't have to meet EPA. Presumably there is some social mechanism that ensures that the EPA target is meaningful.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

GunMuse (Industrial)
12 Aug 06 12:26
You just proved my point.  You could increase effiency as we all have done if you didn't have to meet epa requirements.

In fact by doing so you will have decreased the amount of toxins produced per gallon of fuel consumed.  Truly greener thinking anyway.

You will consume less fuel overall. Truly conservative thinking and better for national defense.

You will have engineered an advancement that can be improved upon by someone else who may gain experience in the field of engineering by seeing your idea's in action and actually improve upon them.

Most engineers are more tinkerers than inventors and as such need to see odd ball idea's actually work to think up improvements.

Lawyers in congress and especially those "who seek to save the enviroment" want to "engineer" a result instead of seeking a standard.

I have a 350 chevy with no smog equipment, no cat convertor, straight up a 1960's style engine build but with all the modern equipment and thinking and it Passes epa.  But then again its technically illegal because I didn't drain the power by adding all that garbage required by law back onto the engine.

I am not saying that propane shouldn't meet a standard.  But that is not what this guys role will be. He will be setting up regulations on how to licence the guy who does the install(creates schools to get the licencing from). Getting a list of "mandatory equipment" written into law.

Anything beyond setting a standard for air quality, any attempt to "require a device" is just an attempt to kill the use or graft money into the grant system.  In a free society we don't tell others how to achieve greatness we just set the bar and see who gets over.

GregLocock (Automotive)
12 Aug 06 20:18

Take a million of your smog producing devices down to LA, and see what LA's inhabitants think of the soup of HC, CO and NO2 they produce.

Tailpipe emissions /are/ a real world concern.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

franzh (Automotive)
12 Aug 06 23:17
The reason for ARB and the EPA is concerned about establishing a fuel standard is consistency, the same reason gasoline (oops, petrol) is regulated.  At this time, there is no legal standard for LPG, and as stated earlier, HD-5 is a touchy-feeling non-regulated, non mandated fuel.  All manufacturers require it but there is no way to verify usage in the field.  There are no field test kits, and even when taken to a lab, it takes an GC-FIC at minimum.

HD-5 does not guarantee the elimination of heavy ends in fuel, just a vapor-pressure, propylene, and corrosion standard.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

turbocohen (Automotive)
12 Aug 06 23:51
Heu Gunmuse , got data to back up your thinking that your 60's 350 chev passes todays?
Put your car on a set of rolls and at least run an ole 3 bag ftp cycle.  Just tryin to keep this thread honest.

Respectfully, Tubinator
franzh (Automotive)
13 Aug 06 14:45
I also want to know how that EPA test was run.  If you mean a tailpipe sniff test for a '60's era vehicle, thats a piece of cake, but a full blown EPA FTP-75 or US-06?  No way.

By the way, thanks to organizations like the EPA to force the automakers to develop the high efficiency engines we have today, like the ones that get mid 20's mpg in a 4000 lb car, engines that last 200,000 miles instead of the 60's and 70's junk that was worn out at 75,000 miles.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

turbocohen (Automotive)
13 Aug 06 22:04
Ditto Franz!  It had to be said right here and you the man!
Every 60's car ever built would fail an 06 even without starting it lol.  
GunMuse (Industrial)
13 Aug 06 22:57
Sniff test yes.

By 60's style- Meaning - No smog pumps, no cat convertor.  Stateing this didn't mean running a 40 year carb and low tolerance engine.

And you guys totally missed the point.  

If you make a LAW that requires a cat convertor you are saying that there is ONLY one way to accomplish something.  

The EPA in the USA has become an industry that gets a specific tweak into law to force the use of a specific patented item for mega bucks.

The point I was trying to make is that Goverment should set standards to achieve not laws on how to achieve them.

turbocohen (Automotive)
13 Aug 06 23:03
Standards are required to allow commonality of fuel requirements.  Cats are required, oxy sensors are a must for feedback, its good science bud.
GunMuse (Industrial)
13 Aug 06 23:17
Its good science TODAY.  Its also restrictive thinking. And your argueing with me about standards when i agree they should be there.

If I invented an engine tomorrow that met or exceeded all requirements it would still be Illegal to sell it because it didn't have a cat or oxy sensors.  See the problem?  Society sets a goal and yet when you achieve that goal

Millions of dollars worth of state and federal testing are required to profit from doing so.  Laws have to be rewritten, that means a couple of years go by while it goes into a research committee of lawyers who will pander for money to allow my idea to be an exception or part of new law.

My end all point that your not getting is by just meeting or exceeding the standard is not enough and it should be.

Anyone want to guess how many millions in legal fees chrysler just went through to put a 4 cylinder diesal in their new Jeeps.  Not because meeting the standard was hard but because the law didn't have exceptions for 4 cylinder diesals, EPA laws that were written to PREVENT the sale of 4 cylinder diesals in the 80's(Remember the BMW imports that threatened jobs recovery in the US.)

EPA standards on propane will most like just increase the cost to the consumer to a point that its not profitable to research propane engines.  Without profit there is no progress.  Enviromentalists will sacrifice all profit without regard to "Good science"

franzh (Automotive)
14 Aug 06 7:25

Nope, wrong again.  If you developed an engine tomorrow that would meet upcoming emissions standards and continue to meet them without degradation, you would NOT need an O2 sensor or catalyst.  The catalyst is needed to convert the residuals after combustion that came from a fuel that is varying in quality across the country but still within standards, plus an engine that is constantly changing its performance profile, the O2 sensor is there to keep the catalyst happy.

There are NO laws preventing a 4 cylinder diesel, just to ensure that the resulting tailpipe standards are where they need to be.  The EPA does NOT get a kickback from any company for doing so, just aint happening.

Legal fees?  Hmm, anytime anything is developed and introduced, the legal eagles get involved.  Thats just part of the progress.  I agree that a diesel engine is needed and sorely missing from the US shores, but blame the public for their perceptions rather than the lack of good products worldwide.  The reason more diesels are not for sale is not the manufacturers, its the lack of sales.

As for increasing the cost of fuel due to the EPA?  If a finite fuel standard were to be introduced that everyone would use, I only see fuel sales increasing because the engines that use that fuel need a good reliable consistent fuel, more engines, more fuel, happier customers.

The price of fuel today is more governed by OPP (Other Peoples Problems) than the US regulations.

Lastly, we are WAY off topic for this thread, and no real place for a political discussion, I get enough of that at work!  Care to redirect this thread back to an engineering discussion?


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

turbocohen (Automotive)
14 Aug 06 23:40
skyooz me for hijacking Franz..  I am a supporter of advanced diesels however the EU typically has higher cetane levels on the order of 47-52 making it easier to meet lower smog numbers.  The diesel here in the US is barely 40 cetane and seldom higher than 47.  07 fuel will change drastically to accomodate new diesels with lower sulphur and hopefully higher cetane..  in the lab new clean diesels can beat dang near all CNG and Propane emissions except CO2/hp/hr.
High compression DI LPG numbers aint better than 07 diesel.  It is looking so good that I will bet diesel may make it into the indoor forklift market.
vintageAP (Automotive) (OP)
15 Aug 06 2:42
Hmmmm, about 12:1 then?............ :)
turbocohen (Automotive)
15 Aug 06 12:41
For a reliable hot rod, 11.  For a diesel conversion, 11 with supercharging up to 25psi.

Use an long life platinum plugs one or two heat ranges colder than suggested for gasoline and reduce plug gap .05-.08" otherwise coils and other lectronics let smoke out.  By using Denso iridium plugs the ignition coils and high tension wire will last a long time because they require less voltage under load than old fuddy duddy plugs.
marcdeluca (Electrical)
24 Aug 06 18:42
I have built a few lp engines, and my experience has been that you shouldn't go above 10.5:1 on older iron head engines.  I have a 454 in my old truck that has a vapor lp system, and when towing in the heat it will ping a little, and it is 10:1.  With aluminum heads, you could go 11:1, and perhaps that high with vortec heads if it is a Chevy.  Even though they claim it is 110 octane, it tests much lower than that.
vintageAP (Automotive) (OP)
24 Aug 06 20:57
Thanks Marc. Hmmm, now we're back down to what I can make a gasoline engine run at on the street, at 10.5:1. I know a lot depends on vehicle weight and load, and tuning. Full size pickup doing tow duty might be a little heavy for what I'm doing, but the info gives me a real-world paremeter.
patprimmer (Publican)
25 Aug 06 0:09
A lot depends on quench, head temperature, spark timing, plug heat range, cylinder head material, cylinder head preparation, A/F ratio, quality of A/F mix, bore size, cam timing, rod to stroke ratio.

It will go a full ratio higher than any petrol you can afford to buy and is widely available.

If it pings at 10:1, something else is not optimised.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

marcdeluca (Electrical)
25 Aug 06 10:50
My 454 has a roller cam and rockers, so it breathes pretty good.  It has the tamest cam I could get, because I wanted good torque.  This engine will also ping a little with 93 octane gasoline.  When it pings on either fuel, it is while towing in hills with fairly high ambient temps.  Just driving by itself doesn't get the engine hot enough to ping.  I'm sure you could get by with more compression in a lightly loaded car engine.  Try natural gas, it likes 13:1.  I have a Duramax with supplemental propane and natural gas, the cng is much more ping resistant than the lp.
patprimmer (Publican)
25 Aug 06 23:58
I would suspect that your coolant temperature is higher with the LPG than petrol.

I would suspect your spark timing and plug heat range might be optimised for petrol rather than LPG.

To get the most from any fuel, an engine should be built with that one fuel only in mind.

A smaller bore alloy head engine will tolerate more compression than an iron head 454.


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Back To Forum

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close