Cam selection profile for propane use 1

[tbrookswillys]

How do you refigure from original cam profile,to regrind specs for propane use.I have a willys F head four cylinder runing on propane now but would like to have the cam reground to optimize the fuel charge.As well as busting the compression ratio.

 

[patprimmer]

More lift more duration, wider lobe centres to keep the overlap reasonable.

What is busting the compression and how does cam effect that?

Regards

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[tbrookswillys]

I'm sorry about my spelling I meant boosting the compression ratio.I'm sure the engine is suffering from a 6.9.From what I understand to make the best use of the fuel being propane I need around 8 to 9.Wish I knew how many thousands to take of the head to attain this.

 

[patprimmer]

Propane will benefit from compression ratios up to 11:1, however it will be very difficult to obtain this with a side valve engine.

You can only cut the head so much before it hits the valves at full lift.

Regards

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[tbrookswillys]

I understand,their were two versions of heads in production,a 6.9 and a 7.4 which was supposed to be a high altitude version.That may be the very reason they stopped at 7.4.I guess the exhaust side would stay the same.These little engines are a little tuffer to gain advances in and I understand that,but love mechanical challenges.Thank you

 

[patprimmer]

You can cut to much off the head, then cut valve reliefs.

Another hot rodding technique on side valves was to relieve the block in the transfer port area.

This streamlined flow from the side chamber to the piston top.

The trick is to maximise airflow through the valves and chamber, with the minimum volume in the chamber.

Regards

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[franzh]

When those Willys engines were made, gasoline had octane values more closely resembling buttermilk. Older Model T engines had compression ratios as low as 5:1 to cope with unknown qualities of gasoline, and to keep head gaskets from blowing out. (If you look at almost any old garage photo you will see valve-in-block head gaskets hanging from nails in the wall. Blown head gaskets were just that commonplace. In the 60's, we did a good business repairing head gaskets on Jeeps and other flathead engines even though we had the heads cut flat and the blocks were not warped. They just blew after a while.)

You probably wont help the head gasket problem any but modern fuel qualities can tolerate a CR increase up to the mid 8's or 9's, and like Pat stated, propane works well in the 11:1 range. The higher the compression ratio, the more critical your ignition timing and air-fuel ratio needs to be tuned. Lower compression ratio engines can tolerate a wider range of fuel mixture and timing anomolies.

Franz

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[tbrookswillys]

So I would be better of concentrating my energy on cam profiles and head and block flow,since I have not to date had head gasket issues.Anymore insight would be great and I thank you both.

 

[jbthiel]

My initial thought is that you would use the same cam for gas or propane, assuming the same CR. My reasoning is that with either fuel you are air limited, not fuel. I am also assuming that you would have roughly the same combustion efficiency and thus about the same volume of exhaust gases.

As for the CR, if you had an OHV engine you could take advantage of the higher octane (which would also benefit from a little wilder cam). But since you have an L head you will be limited to around 8:1 for both fuels.

ISZ

 

[patprimmer]

Gas displaces more air from the inlet tract as a similar mass has a much higher volume than liquid fuel.

Gas is already gas, and therefore has a density much closer to air than does liquid fuel, so air fuel separation and consequential poor mixture distribution and fuel puddling are not such a problem, so gas can tolerate lower air speed and more reversion in the inlet tract and still retain drive ability.

Regards

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[tbrookswillys]

The engine has overhead valves for the intake with the exhaust in the block.Their is a L head which has the intake and exhaust both in the block,I have one of those too.I understand now that improvments can be made with a good valve job and porting of the heads for flow.These two engines share identical parts,in alot of areas.One that is not is the cam shafts,the L head on the intake side is taller and the exhuast is identical,I could run one of these but fear of breaking springs,which could be addressed if beffier aftermaket support.The whole process is to maximize the fuel which is now propane,this little engine runs well as is but I feel their is alittle more that can be done in conjuction with this fuel.It's using a Impco 100 and a model E converter,I have also wondered if their is anything that can be done to the 100.Just alittle something is to think about

 

[IceStationZebra]

Pat, you were right once again but not by much. ;-) I had also overlooked the cooling effect.

"For propane, the gas displacement effect is 4%, it means that the displacement of air by propane causes reduction in power of 4 % (volumetric efficiency decrease) from an equilevent gasoline counterpart. Gasoline on the other hand, provides evaporotive cooling of the intake air which increases the intake air density and increases the power. Test results show 6 % less power with propane than with gasoline."

==J.E Sinor Consultants Inc, The Clean Fuels Report, November 1992, Volume 4, No. 5

ISZ