Thoughts on an LPG-only track car

[handpaper]

As title, here's what I'm planning :

Total removal of the original fuel system - pump, tank, filler, fuel lines, fpr, injector rail and injectors.

Fitting of either one 100 litre LPG tank on the rear seat pan or several smaller tanks in place of the petrol tank. I've seen 10" given as a minimum ground clearance for an underslung tank, so I may have to put up with 60-odd kilos fairly high up in the car.

Swirl pot, almost certainly in the engine bay as it's the only legal place for it. Calculations based on fuel consumption at the 'Ring give a figure of 15 ml/second at full chat, so it would have to be at least 300 ml to provide a decent safety margin.
I'm not sure how an LPG swirl pot would work - since there's no fuel pump or return line in the system how would it get rid of gas fed in when the liquid was away from the dip tube?
Would it just recondense under pressure?

Replace the AFM with a bit of pipe. I'm hoping the Motronic ECU doesn't vary ignition timing (much) with load, otherwise something must be devised to fool it. I already have a throttle body-mounted mixer venturi fitted.

Advance the ignition timing, either by moving the crank position sensor or re-keying the bottom pulley wheel. It may be necessary to slot the bolt holes in the distributor cap and turn it slightly, or re-key the rotor arm for this to work.

Increase compression by whatever means is least complicated. Machining the block is simplest on the face of it, but may cause valve-to-piston contact.
By my calculations, to achieve a CR of 12:1 I must reduce the combustion chamber volume from 53.3 cm^3 to 37.8 cm^3.
This equates to skimming 2.8mm from the block. How feasible this is I don't know.

The only thing listed here that I can't do myself is the compression increase, annoying since it's the one most likely to give a decent power gain (10% according to theory).
More may come from fitting a six-branch exhaust manifold and, if possible, a hotter cam.

Hopefully I'll have something worth playing with in a month or so

Comments and suggestions welcome

[Jon_Bmw]

Sounds like fun. I am just getting seriously interested in LPG. Been doing some searches on this and the lpg forum to try and minimise the stupid questions I will undoubtably ask.

This would be similar to your current setup, venturi type with closed loop control via a Leonardo ECU or the like. I am not sure whether I will need an emulator to trick the ECU on an m42. I know its a pretty thick system, so at the moment I am presuming you don't.

This looks to be a good fun project, your compression ratio target is very high Will the increase levels of octane really get rid of Det that is likely to occur? Do you think you'll have to alter the timing to match?

[march109]

Jon he already stated that he was altering the timing!

You haven't said what engine your talking about but as you said the CR chamber is 53.3cm^3 I'll assume its a late M20B25.

I would have assumed you'd not need a swirl pot with LPG, but since you asked I am not too sure.

Incresing the compression sounds fun, I personally would not want to be making the compression chamber volume that small, I would assume you will get piston to valve contact with 2.8mm off the block so some non interference pistons (deep pockets for the valves!) might need to be ordered if you are serious. Probably worth noting I am not 100% sure if you will get piston to valve contact, so get some play doh and test it.

Though if your skimming the block carefull adjustments of the timing will need to be made anyway and the mods you've mentioned to do it may help but a vernier pulley may just have the range needed to sorts it, if not slipping one tooth and a vernier pulley may sort it, probably not 100% the best way to do it but a simple uncomplicated solution none the less, just then make sure you make your own timing marks for the new timing configuration.

Why are you increasing the CR anyway? AFAIK E30s are pretty happy on LPG stock, if its just the 10% energy penalty your trying to offset surely safer and easier would be a mild mods to the engine. Like you said 6branch ect ect, this is the route I would go personally. 10% equates to 17bhp on these old anchors, you could just about get that with bolt on mods IMO, or I would be looking at a 24V 2.5 with LPG and induction/exhaust mods.

[Jon_Bmw]

Oh yes, so he did. I missed that paragraph. In my defence it was 2 in the morning and I was tired.

[JazzMan]

Only issue I can think of is cold starting on LPG. My M54 engine needs to run on petrol until it's warmed up a bit then switches over to LPG.

Also on the M50/2/4 type manifold it needs to run on petrol when idling, not sure if this is an issue with the M20 as its a completely different manifold design.

[handpaper]

Swirl pot is definitely needed as LPG tanks aren't available baffled or foam-filled.
According to this useful resource my prospective CR is actually quite conservative, especially as it's static - dynamic CR is likely to be quite a bit lower.
The idea is to optimise the engine for LPG; 'classic' performance mods can wait or be used to increase power further.
Turbocharging would be fun; potentially silly power without having to drop the CR, but I'm not sure how much I trust a gas venturi and stepper motor-controlled valve to keep the mixture right......

If anyone does know how far I can skim a late 325i block without interference, I'd be delighted to know.

[UweM3]

one thing for sure, I would not go on the Ring with a LPG tank on the rear seat pan.....
It really begs the question, is it worth the hassle??? For a road car, fair enough. How many Ring miles (or total miles) will you need to run to break even??
Is the a LPG station near the ring? I don't know how many laps you are planning to do per weekend, but I am at the petrol station at least 3 times a day! I wouldn't fancy to loose even more time by driving further to get LPG.
I want to get back on the track ASAP!

edit
how's about any weight penalties??

[march109]

Good point, strictly speaking are you allowed through tunnels oron euro star and alike with lpg? I remember Brian saying once that strictly speaking it wasn't legal to drive some places with LPG. IIRC Dartford tunnel is one such place.

[handpaper]

LPG tanks are strong, Uwe, much stronger than petrol tanks, safety isn't an issue here. The car will be caged, too.
Over 200 laps (my typical annual total), running on LPG should save about 600 euros in fuel costs, but that's not really the point. I'm more interested in exploring the potential of a cheap and readily available 110-octane fuel
LPG is available from the Texaco in Kelberg (just down the road from TTE) and a couple of places in Mayen. 80 litres should be good for at least 15 laps, so for a full day I'd be filling up twice. Not too bad.

[UweM3]

I am not worried about the tank, I would worry about ME when that thing rips out of the floor on impact!!
Kelberg and back approx 10miles. I can see the 110 octane fuel benefit, but let's be honest as long you don't seriously upgrade your engine hardware there's no BIG gain with a 325 engine.
You need to make a very very tidy job of this if you keep running it on track. Does anybody know if there is a restriction for LPG powered cars on trackdays?? Can't imagine, but for sure you will not see the Eurotunnel from the inside (...which would't bother me TBH for the savings you make on the journey)

[JazzMan]

Eurotunnel is the only thing you can't go through with LPG these days.

[Brianmoooore]

Does anybody know if there is a restriction for LPG powered cars on trackdays??

None that I've ever heard of.
It would make no sense at all to ban LPG but allow petrol, but the other way around would make sense!
You prevent the LPG tank from ripping free by mounting it properly. Load spreader plates that you would be happy with for seat belts are adequate for the job.
Requirement for road going cars is 30g.

[Brianmoooore]

Only issue I can think of is cold starting on LPG. My M54 engine needs to run on petrol until it's warmed up a bit then switches over to LPG.

Also on the M50/2/4 type manifold it needs to run on petrol when idling, not sure if this is an issue with the M20 as its a completely different manifold design.

I've never seen or heard of an LPG set up that needs to idle on petrol! Sounds like your injectors are wrongly sighted.
The only reason your M54 needs to start on petrol when cold is because there is a temperature sensor that stops it switching to LPG until the coolant is warm, and there is no possibility of the vapouriser freezing, however much you load up a half cold engine. As long as the engine isn't ragged until warmed up, it's safe to start on LPG.

[Brianmoooore]

Advance the ignition timing, either by moving the crank position sensor or re-keying the bottom pulley wheel. It may be necessary to slot the bolt holes in the distributor cap and turn it slightly, or re-key the rotor arm for this to work.

Not quite that simple for optimum timing. LPG needs more initial advance than petrol, but less total advance.

[handpaper]

I've never used Eurotunnel, the prices are daft compared to Norfolkline, especially at the times I travel
A full 100 litre tank will weigh about 60Kg (20Kg tank + 40Kg for 80 litres of fuel).
Let's assume a really horrible impact, say 100Km/h straight into the wall at Breidscheid. The car will crumple by at least one metre, the deceleration will be up to 45G. The straps securing the tank will experience a maximum stress of 2.7 tonnes, which is well within their capabilities. The seat pan isn't weak either; it's made to have seatbelts attached to it.
What the driver would look like after a 45G impact would worry me more

To start with, I'll track prep the car (strip, cage etc.) and remove all the petrol stuff.
Later on I can start playing with the ignition timing, when time and funds allow I can look at increased compression or turbocharging. I'd like to experiment with getting the best from LPG with a N/A engine, but FI has the potential for more power at reasonable cost...

[Brianmoooore]

Any problems with a properly fitted LPG tank in a crash, won't be of any concern to anyone in the car!

[handpaper]

Advance the ignition timing, either by moving the crank position sensor or re-keying the bottom pulley wheel. It may be necessary to slot the bolt holes in the distributor cap and turn it slightly, or re-key the rotor arm for this to work.

Not quite that simple for optimum timing. LPG needs more initial advance than petrol, but less total advance.

So more advance at idle and low revs/load, less at high revs?
Since the engine will spend most of it's time at high revs, would it be worth retarding the ignition to suit?

[northloop]

Nice idea James.

In comparison how much would a chipped diesel cost to run I wonder?

[JazzMan]

Only issue I can think of is cold starting on LPG. My M54 engine needs to run on petrol until it's warmed up a bit then switches over to LPG.

Also on the M50/2/4 type manifold it needs to run on petrol when idling, not sure if this is an issue with the M20 as its a completely different manifold design.

I've never seen or heard of an LPG set up that needs to idle on petrol! Sounds like your injectors are wrongly sighted.
The only reason your M54 needs to start on petrol when cold is because there is a temperature sensor that stops it switching to LPG until the coolant is warm, and there is no possibility of the vapouriser freezing, however much you load up a half cold engine. As long as the engine isn't ragged until warmed up, it's safe to start on LPG.

Thanks for clearing that up (I'm going from what the garage has told me) they have set it to switch to petrol while idling as well. I assume this is down to their not put the injectors in an ideal location rather than this being a general issue?

[ShakeyC]

Not a BMW but know a few guys who run lpg in thier j-wrc and track cars there is a specific safety requirement associated with the class/event which is set by the MSA and FIA which i thinks been covered already concerns safety requirements, external shut-off valve and they have to carry symbol on thier bumpers incase of fire for the track officals but does differ from series to series.

Couple of guys heavily skim thier heads cheapest solution or weld inside the head's dome around squish area to make use of that lovely high octane too without getting into trouble in scrutineering.

[carbonheadfred]

..........

[handpaper]

How far I can go with a simple head/block skim is something I'm still waiting for an answer on.
Looking at catcams catalogue, there is a 1mm difference in lift @ TDC between their 283 and 262 cams. Since both are claimed not to need any other modifications, I'd say at least 1mm can be safely removed from a head/block, bringing compression up to 9.7:1 and giving about 3% more power.
With regard to safety for a track/race car, a standard LPG install has solenoid valves at the tank, filter and vaporiser, so a battery shut-off would also cut the fuel supply at all three of these points. Bumper sticker is probably a good idea, though.

[ShakeyC]

Im pretty sure you need an external cut-off switch which is easily accessible by you/marshells as set by the MSA / FIA in an unfortunate event; i can't remember if lpg needs a specific sticker like those who carry nitrous tanks empty or not still have to wear one. What are you planning to race in, i can find out and give you a definate answer if you like.

Don't know what engine you have to say skim xxx amount off the head or xxx enlarged valve relief cut from pistons, best email Ant see what he can do for you regarding the head for cam and compression.

[UweM3]

How far I can go with a simple head/block skim is something I'm still waiting for an answer on.
Looking at catcams catalogue, there is a 1mm difference in lift @ TDC between their 283 and 262 cams. Since both are claimed not to need any other modifications, I'd say at least 1mm can be safely removed from a head/block, bringing compression up to 9.7:1 and giving about 3% more power.
With regard to safety for a track/race car, a standard LPG install has solenoid valves at the tank, filter and vaporiser, so a battery shut-off would also cut the fuel supply at all three of these points. Bumper sticker is probably a good idea, though.

when skimming loads of head or block make sure your cam timing hardware can take it. But I am sure you have already thought about that.

[handpaper]

Shakey - engine is a late M20B25, current CR 8.8:1, ideal CR for LPG is 12-14:1
What would a petrol cut-off do, other than kill the fuel pump? The solenoid valves in an LPG install cut the fuel off in three places immediately power is cut to them.
I'm not planning to race (though Toyo Tyres racing saloons looks fun); the car is a 'Ring/trackday tool at the moment, but I may give Keith Hancock a call tomorrow and find out about LPG elegibility

Uwe - yes, a vernier cam pulley would definitely be on the shopping list. 2.8 mm off the head or block would need 2.6° of retard on the cam; catcams can supply one with +/- 10° of adjustment.

[ShakeyC]

Its just an external manual engine kill switch so you or a marshall can physically turn the car off just incase for all petrol, lpg and electrical systems (kits are quite cheap) other than that generally an lpg certificate will suffice aparently.Everyone i spoke too said they used PRINS lpg system and to avoid older single point ones as higher risk of back fires and other problems.

Regarding your engine didnt realise it was that low c/r (you could well turbo it on lpg) doubt you can safely skim enough off without running into valvetrain issues the increased compression gains is lost by having to retard cam timing and less valve lift. You will better off asking Ant directly about increasing your compression what options are possible.

[handpaper]

A battery cut-off sounds about right then. I refuse to have my LPG conversions certified as a matter of principle - there are far more dangerous modifications I can perform which don't require a bit of paper saying that some muppet who has paid an annual fee considers them safe
Single-point mixers aren't too bad on e30s - the inlet manifold is cast alloy and won't be damaged by a backfire. Also, my mixer is a venturi type just upstream of the throttle body, so even if I did have an AFM/airbox they wouldn't be at much risk

The CR is standard for a post-87 M20B25 and yes, they do turbo quite well. Those who know have said that 11psi is safe on an otherwise stock engine on petrol; on LPG, who knows? 1 bar certainly looks feasible, and will more than make up for the power drop from running a venturi