Unless you're out of power a lot, I'd not sweat the cost differential. EIther NG or gasoline is going to be way more expensive than operating off the mains when they work.

The practical advance of NG if you're on the city system or propane if you use it for other things and have a decent size tank, is you don't have to worry about refueling. This can be a nuisance if you're out for a day or more.

Propane/NG coversions should work as good as the kits are (I know nothing of this company however). There's not any need to derate. Most portable generators croak early because of lack of maintenance more than anything else.

motorsnorkel.com used to be uscarb.com

I bought a tri-fuel kit from them two years ago. I do not have NG nor a large propane tank. (I'm in the MD suburbs of DC.)

I have six 20# propane bottles that I use for my BBQ Grill and the 7500 Watt portable generator. Fuel cost is just abut a wash between gasoline and propane.

What is important IMHO is the availability of propane when there is an area wide power outage and the gas station have no power to run their pumps. I have two rental centers with their own generators that will sell me propane.

The carbs on the generators are whistle clean... I do run them periodically to keep the windings and brushes dry and in good shape.

I see no downside. (I do wish I had NG.)

US Carb is a good outfit to deal with in my experience.

Join their forum and read what they have to say... also, the company will answer any questions that you may have.

"he stated that there is no de-rating using ng rather than gasoline because of the ability to fine tune and get the gen to run at the designed 3600 rpm on ng."

Not true.

Ionized, can you please elaborate? If not true, how much is the defeating? Thanks.

Damn autocorrect! How much is the de rating?

Lots of confusing info out there re de-rating. Much of it doesn't understand that the propane or NG does not need to be atomized...

My 7500 Watt Generator carries a full 7500 watts on either gasoline or on propane.

GOTO the forum I suggested and you'll see numerous threads on the subject... and it is difficult to sort out the what from the chaff.

I answered without enough consideration. The prime mover will, without a doubt, produce less power with nat gas than with gasoline. If the prime mover produces more power than the alternator can accept, there will be no decrease in electrical output,. If the prime mover is under-rated with respect to the alternator, eletrical output will decrease.

IC engines can be modified to increase thermodynamic efficiency with nat gas by increasing the compression ratio a lot because the knock resistance of the fuel is much higher. How easily that might be done depends on the engine in question.

I noticed something interesting about Generac's small to mid-sized stand-by generators a few weeks ago while perusing the specs. As the capacity increases in a certain range, the prime mover displacement stays the same. The alternator capacity must be what is changing alone. In the same range, the electrical output does not change between propane and nat gas. As the total electrical output increases with the same prime mover above that range, there is a penalty with nat gas.

The energy available in the same volume of these fuels: diesel > gasoline > propane > nat gas

This post was edited by ionized on Fri, Sep 19, 14 at 17:45

I too did a conversion last year using US Carb's kit. Loved it. Piece of cake to install and I can now run using any 3 of my fuel choices. I had a NG line run to the back right next to my plug for the transfer switch, but this baby can run a good amount off a typical 20lb BBQ tank. Too cool.

A 20# propane bottle will allow running at a given load for about the same duration as 5 gallons of gasoline... about!

I feel more comfortable storing a 20# bottle than five gallons of gasoline. Also, the propane will not go stale.

Again, wish I had NG.

I helped someone increase the compression years ago on a older 10hp briggs that was on natural gas by heating the head and using welding rods specifically for cast iron and reducing the dome in the head and retesting. I know other people have had good luck on some briggs engines by just removing the gasket and using a thin copper gasket or high temp silicone. I would check valve clearance with no gasket and then have a shop cut that much off the head so you could still run a off the shelf gasket.

The go cart and garden tractor pulling/ racing forums might be helpful as they know what heads swap around from what engines like putting a 10hp head on a 12hp block for example and boost compression.

Before the internet it was just redneck trial and error engineering.

I have seen not one post on the US Carb Forums where an owner did any mod such as this on a portable generator.

Not one.

Since there is less energy in any given volume of fuel, cylinder pressure will drop with ng. By increasing the compression ratio you can get the cylinder pressures back up to what they were with gasoline. That way you can recover some, maybe all, of the losses associated with the change in fuel.

Taking advantage fo the greater inherent knock resistance of the ng compard to gasoline would require increasing the compression ratio and pressure even higher. The engine may not tolerate it at a number of levels. Gains in electrial power output will only be realized if the generator is oversized with respect to the prime mover.

This kind of activity would definately be characterized as a hobby rather than a practical activity. Most people will just buy a larger genset.

I agree Ionized it ran fine but had a little rpm lag causing more voltage drop and sag than he wanted even though it would recover once the load stabilized. He had a bigger engine/replacement solution but really didn't want to use it so we modified that one.

I probably discounted too much the advantages of taking up the compression ratio a notch. The increased thermodynamic efficiency will, of course, increase fuel efficiency. The backyard engineering might be worth it if you are running propane or running the genset a lot. I doubt that your max cylinder pressure increases much or at all if you just match the gasoline engine power output.

So I've read all of the comments and still do not know the short answer. Do you lose electrical power output capacity on a gasoline generator when running on propane or nat gas?

Yes or no please and approx what % loss if any.

Thanks.

You would lose around 10% with Propane and up to 20% with NAT. NAT can vary in gas composition. However this is not an exact science like and what type of generator eg. inverter generator vs a standard generator. Inverters work different on how they produce electricity however they still lose power but the difference is generally a little less. Your cheapest option in the city is NAT but you need to factor how much wattage you can lose. I have a inverter generator I run on Propane and I generally lose about 8% compared to when I run with gasoline.