AirGap intake mods for Propane fuel?

[Leftcoaster]

I read that they started putting propylene in it among other things. Floor sweepings that would previously have been flared off at the refinery. Nowadays I think of LPG as the meat pie of fuels; you never know what’s in it from one day to the next.

"The meat pie of fuels - - "

Great expression! but the meaning may elude those who haven't sampled Australasian meat pies, or better yet, quality versions with mashed potato topping. Yum

[cjperformance]

Oh yeah a good potato topped meat pie with sauce is great tucker !

[BigBlockMopar]

...
Steel/iron heads and block, get it as hot as you can then check clearances. With iron heads and block it is quite possible to have the valve length grow more than the block/heads will !!

What's worrying me is that the nervous vacuum gauge (19-21" swing) starts right at start up, even with a cold engine.
That would mean a valve would already be partly open, but that doesn't make sense when they all have lash.

[cjperformance]

...
Steel/iron heads and block, get it as hot as you can then check clearances. With iron heads and block it is quite possible to have the valve length grow more than the block/heads will !!

What's worrying me is that the nervous vacuum gauge (19-21" swing) starts right at start up, even with a cold engine.
That would mean a valve would already be partly open, but that doesn't make sense when they all have lash.

Did you check valve seat concentricity?

[BigBlockMopar]

When I lapped the valves and seats I did look for contact and thin/thicker lines on the seats and valves.
Nothing appeared wrong at the time.
A simple leak test later with valves mounted and brakecleaner shot into the ports showed no immediate leakage.
The (new) exhaust valves have rotators on them.

Any serious valve leakage should come up during a cranking compression test I would think.

[cjperformance]

When I lapped the valves and seats I did look for contact and thin/thicker lines on the seats and valves.
Nothing appeared wrong at the time.
A simple leak test later with valves mounted and brakecleaner shot into the ports showed no immediate leakage.
The (new) exhaust valves have rotators on them.

Any serious valve leakage should come up during a cranking compression test I would think.

Maybe you should look at putting regular hydro lifters back in it and reasses.

[tinnitus]

Back in my college days we converted a GMC 1500 with a TBI set up to run on Natural Gas as part of a SAE sponsored competition. We actually used a TPI intake with some modified gasoline injectors. We didn't know that wasn't supposed to work but it actually worked very well. We were fortunate to have a Siemens injector manufacturing facility local to us and they supplied what eventually became the "blue top" injector which was used on the OE CNG vehicles for a short while. I think the injectors eventually were marketed as a 160lb/hr gas injector. Not even close to as simple as a mixer but it had fantastic manners and driveability.

[cjperformance]

Back in my college days we converted a GMC 1500 with a TBI set up to run on Natural Gas as part of a SAE sponsored competition. We actually used a TPI intake with some modified gasoline injectors. We didn't know that wasn't supposed to work but it actually worked very well. We were fortunate to have a Siemens injector manufacturing facility local to us and they supplied what eventually became the "blue top" injector which was used on the OE CNG vehicles for a short while. I think the injectors eventually were marketed as a 160lb/hr gas injector. Not even close to as simple as a mixer but it had fantastic manners and driveability.

Excellent, yes the high storage pressure of CNG would allow for adequate flow thru a basic regular type injector. Great project.

[user-23911]

Back in my college days we converted a GMC 1500 with a TBI set up to run on Natural Gas as part of a SAE sponsored competition. We actually used a TPI intake with some modified gasoline injectors. We didn't know that wasn't supposed to work but it actually worked very well. We were fortunate to have a Siemens injector manufacturing facility local to us and they supplied what eventually became the "blue top" injector which was used on the OE CNG vehicles for a short while. I think the injectors eventually were marketed as a 160lb/hr gas injector. Not even close to as simple as a mixer but it had fantastic manners and driveability.

Excellent, yes the high storage pressure of CNG would allow for adequate flow thru a basic regular type injector. Great project.

No, it needs the pressure dropping first (single stage regulator), injectors won't even open against high pressure and a varying storage pressure gives a varying flow.
Storage pressure for CNG is anything from 2MPa to 4MPa depending on cylinder type and the country you're in.

[cjperformance]

Back in my college days we converted a GMC 1500 with a TBI set up to run on Natural Gas as part of a SAE sponsored competition. We actually used a TPI intake with some modified gasoline injectors. We didn't know that wasn't supposed to work but it actually worked very well. We were fortunate to have a Siemens injector manufacturing facility local to us and they supplied what eventually became the "blue top" injector which was used on the OE CNG vehicles for a short while. I think the injectors eventually were marketed as a 160lb/hr gas injector. Not even close to as simple as a mixer but it had fantastic manners and driveability.

Excellent, yes the high storage pressure of CNG would allow for adequate flow thru a basic regular type injector. Great project.

No, it needs the pressure dropping first (single stage regulator), injectors won't even open against high pressure and a varying storage pressure gives a varying flow.
Storage pressure for CNG is anything from 2MPa to 4MPa depending on cylinder type and the country you're in.

What are they dropping working pressure to with these injectors?

[BigBlockMopar]

Maybe you should look at putting regular hydro lifters back in it and reasses.

Been thinking about that. Dropping in another set of hydr. lifters would be 'easiest', but leakdown issues with the previous new set was what made me convert them to solids.
Will do a compression test today with a screw-in tester the locate the misbehaving cylinder (The push-on tester and some 12bar of cranking pressure makes it not a one-man job).

[cjperformance]

Maybe you should look at putting regular hydro lifters back in it and reasses.

Been thinking about that. Dropping in another set of hydr. lifters would be 'easiest', but leakdown issues with the previous new set was what made me convert them to solids.
Will do a compression test today with a screw-in tester the locate the misbehaving cylinder (The push-on tester and some 12bar of cranking pressure makes it not a one-man job).

Was leakdown the lifters or oil feed related? Maybe use a different brand if lifters were at fault.
Comp test sounds like a good plan.

[user-23911]

so I suspected a too tight lash eventhough I reset the lash twice on the engine stand at .003". Rechecked the valves today while it's quite a bit warmer. Found some a tiny bit too tight but even after relashing them to .004-5" the issue still remained. Maybe I should up the lash to .006"?

Everything I've played with that's got factory solid adjustment and pushrods, it's always about 0.012 inch or a bit more.......it's too tight.

If it's 0.003 inch then it's OHC and no pushrods.


The storage pressure for CNG I mentioned is actually 10 times that.well over 1500PSI.
Reducing the pressure, you'd expect 100 PSI or less to inject it using an EFI type injector.


There's something called a Wobbe index, it's for different mixes of CNG or LPG.
https://en.wikipedia.org/wiki/Wobbe_index

[cjperformance]

Storage pressure of CNG for vehicle use is around 3200 psi iirc?, i have done LPG licencing and at the time (1992) we got a look at a couple of CNG systems, one on a passenger car type setup, 253ci V8 using a cng vapour carb/mixer and also the setup they were working on for our passenger busses using converted diesel engines , vapour carb and a bank of cng containers on the roof under a fiberglass cover. It was a long while ago niw and i can not remember what they stepped pressure down to for the vapour carb but 45psi seems to ring a bell, i could be way wrong as thats my only CNG encounter!

[BigBlockMopar]

Joe, the lifters are converted to solids on a hydraulic cam. Hence the very tight lash.
Having done the compression test (with help of a friend and my push-on tester, the readings webt off the scale, over 12 bar on the 4th revolution of the engine while cranking.

My conclusion is that some or at least one lifter manages to still fill itself with enough oil and pump up and hold the valve off the seat during idling.
Most likely because the spacers I made allowed for the plunger to rise a bit.
At around 1000rpm the vacuum gauge appears smooth again.

I could either keep ‘screwing around’ with the converted lifters, get a new set of hydraulic lifters, or step ip to a roller cam I’ve been eyeballing for awhile.

The latter has my preference I think, but that will take a week or 2 to finalize before all the parts shipped are overhere.
I don’t think the valve(s) will like being lifted off the seats that long.