Boosting high comp FG LPG engine

[Molch]

The back story is I blew my FG engine doing some stupid shit. I've rebuilt the head and now discovered some bottom end issues to. So I'm pulling it next weekend to further inspect.

Now I'm tired of having no car and considering buying a $600 09 FG LPG engine and bolting my turbo and intake manifold on it. Was considering bolting my head on also but don't want to do that just yet. Will keep building my engine as tile and money permits

So have been investigating comp ratio and I'll be jumping from 8.8:1 to 10.7:1 so going to run e85 only.

Chose the lpg engine to have a go at high comp for lower down torque and also because they have stronger rods then a full NA.

My calculations say 10psi boost on high comp is about the same as 22psi boost on low comp so this is my target max boost (not sure if valve springs will be ok, so may install my Turbo valve springs.)

If I go down this path I was going to grab a petrol or lpg stock tune and review the timing tables etc then tune my original maps to lower boost and get timing right.

I'll upload for tunes to here for people to poke at and use if they go a similar path!

Am I nuts?

[JVK]

No you are not nuts, others have done before. In fact i bought a bf wreck for the same reason. They have the bigger rods and hi-comp(thought they were 11.0:1) though.
The question is Molch since you were using the Mamba like i was will you be able to go as low as 10lb and maintain that throughout the full rpm range ?
It will be interesting thats for sure. If you need a gas tune to compare im sure i have a 2008 fg dedicated gas tune i could send or upload in the tune repository for you if i still remember how.

[Molch]

Re the comp ratio My understanding is the newer ecolpi are 12.0:1 and the older egas are somewhere between 10.3;1 and 10.7:1 depending on what source I read.

Yeah not sure if I can keep the boost that low. I have since gone an external 50mm progate welding to the turbine rear housing so will be a test that's for sure!!! Will have to also play around with springs etc to see if i can find the right sweet spot.

[JVK]

I think since you have gone external gate there should be no reason why you cant keep it at that boost. Was thinking you still had internal and thought that low was going to be hard to maintain. I uploaded the tune in the repository for lpg, should be able to veiw it soon after HP clear it.

[Molch]

Cheers JVK,

Been calling wreckers and getting prices so think im going to go ahead this weekend and use it as a learning excersize for how the lpg engines go.

Ive started to look at the standard timing and trying to extrapolate the data out to higher load has been interesting. I couldn't figure out why it was higher timing down low and lower timing up high until i found this about lpg

"When an engine is converted to run on LPG as a single fuel engine the ignition timing should be revised to give more ignition advance than the petrol engine at low speeds, and less than the petrol engine at higher speeds."

I'll keep massaging the timing , Im now torn between using the xr6NA timing as a baseline and adjusting due to higher comp and boost or using the timing table from say a xr6t as the baseline and pulling timing out for the increase in static compression.

[will15]

I run 11:1, 12psi on pump fuel and e85 with a ls1 comes down to the tune and how low in the rpm the boost comes on to stave of knock.

[45T-XR]

Cylinder head design/efficiency plays a large role also!

[dynotunz]

Im running fg na engine with 20psi on e85 and it has done about 10k since it was put in just keep the fuel up to it and the timing under control and it will be ok

[Yortt]

Im running fg na engine with 20psi on e85 and it has done about 10k since it was put in just keep the fuel up to it and the timing under control and it will be ok

Out of interest what was your applied ignition timing at maximum torque.

[dynotunz]

hey mate I would have to check my log but it only wanted 12 or13 deg I ran it up with more in it but it didn't make any more it was also starting to run out of injector at the same time so just left it there now have bigger injectors and pumps but have not run it again

[Yortt]

Interesting! thanks for the reply

[45T-XR]

hey mate I would have to check my log but it only wanted 12 or13 deg I ran it up with more in it but it didn't make any more it was also starting to run out of injector at the same time so just left it there now have bigger injectors and pumps but have not run it again

That's not far off what my engine took around peak VE also. I built it 4-5 years so the only real thing available then was the Atomic cosworth pistons. I think the comp was around 8.5:1. Stock cams/cylinder head/manifolds etc.