Building a CNG engine.

[BugginTT]

Im in the process of building an aircooled VW, and I am wondering as to the possibliity of building it to run on CNG. The engine design is cabable of copression ratios in the 13:1 range. I am planning on using a forced induction intake system, and would like to know if CNG shares any similar properties with petrol as far as being assisted by turbos. I would also like to know about the fuel delivery needs.

I would really like to have a nice classic car, with a good amount of performance, and a clean footprint.

I thank you on advance for any knowlage that could be provided.

[CraziFuzzy]

Re: Building a CNG engine.

My suggestion would be to look at some custom heads with hardened valve seats. VW valves are notoriously fragile anyways, and the lack of lubricating film from the gasoline might do them in faster. Other than that, it sounds like you're going the right direction.

[afvman]

Re: Building a CNG engine.

You're already in the 'sweet spot' for natural gas with a CR of 13:1. If you add turbo boost, it might be going too far. I think you'll be pleasantly surprised at the output w/o the turbo.

I still remember asking Joe Mesquita, who held the regional drag race title for his class running on natrual gas, what he did differently to build the engine. He looked at me and said, "I just drive it." So, I talked to the shop forman and Jeg's who built the engine what he did differently to run on natural gas and he looked at me and said, "I just built a strong big block chevy. I didn't know he what fuel he was gonna' use." CR was 12:1, but that's what he'd have built for any drag race engine.

I do agree about the valve/valve seat issues, especially on a VW, but wish you luck!

afvman

[BugginTT]

Re: Building a CNG engine.

I was planning on using Chevy valve train, as far as valves, seats, and rockers, so I don't think finding strong parts will be an issue. Since I want forced induction, I was planning on a comp ratio of 8:1 with petrol. What is a good low range compression ratio for CNG? Would around 10:1 be good for around 5Lbs of boost? How about fuel delivery? Would braided stainless be good for lines, or would I need hardline?

If any of y'all deisel conversion guys have tips on running with boost, let me know.

On another note, what kind of power differences are there?

[younkin]

Re: Building a CNG engine.

One problem will be heating the regulator since it is air cooled, I have thought of running oil through the regulator instead of coolant? You will need to install external oil lines, let me know if you have questions, Jim

[BugginTT]

Re: Building a CNG engine.

I have already planned on running a dry sump systtem, and a good selection of coolers, so I shouldn't have an issue running another few lines. Would I need special injectors? I am planning on running a stand alone EFI, and good injectors. Would I need different injectors, or just different seals?

Thanks to everyone who has posted.

[younkin]

Re: Building a CNG engine.

If the CNG system you are putting on is a Fogger or aspirated type you just put a mixer in the intake hose hose. If it is Injected type then you will have to drill the manifold and put in the nozzles. Are you going with an aftermarket injection system or stock? I started working on VW's in the 70's and know more about them than I want to remember..... I am overhauling a 64 dualport this weekend. If you have any more questions let me know, Jim
[email protected]
801 427 2284

[neongreen]

Re: Building a CNG engine.

Dont worry about getting your CR too high. I don't think it's possible with a VW motor. The heads for those motors make it almost impossible to get one to 11:1.
If you can get it to 10:1 be happy and run all the boost you want. CNG is 130 octane.
My ranger is turboed, has 8.5:1 compression and can run 27psi with no detonation. Granted, it's running on (gasp!) E85 and E85 removes heat (as does any liquid fuel) through fuel vaporization. You won't get that advantage with CNG but the octane rating is 15-25 points higher than with E85. 15-25 octane points is a BIG difference.
Just keep an eye on cylinder head temp as well as oil temp.
And make sure you have dang good exhaust valves and seats.

[wrenchmonkey]

Re: Building a CNG engine.

DON'T USE A TURBO WITH AN ASPIRATED SYSTEM! You wanna use a sequential system if you're planning on forced induction.