M20B27 on LPG - Developments

[StuBeeDoo]

I thought I'd post this here as I'm now going to start playing with the engine management.

As most of you probably know, I built my latest engine looking for a nice flat torque curve rather than the bragging rights that big BHP brings.

So, the engine spec is;-
eta bottom-end fully rebuilt.
731 'head fully rebuilt to standard spec, but it's been skimmed twice and only has 2 "references" left. I've no idea what the c/r is now, but I'd guess it's nearer 10.5 than the standard 10.2.
325i cam, TB, injectors and AFM.
320i inlet manifold with the throat relieved as much as I dared to make the most of the bigger TB.
Standard "log" manifold - no intention to replace this as I'm running an E36 'rack and don't want to throw mega-money at a BTB3.
I haven't a clue what spec. the chip is, although it's marked "Alpina 2.7".

The LPG set-up is;-
OMVL R90E vap.
Millennium/Leonardo closed loop control with the O2 sensor in the front down-pipe
Mixer downstream of the AFM with 39mm venturi
Iwema vacuum-operated AFM flap opener.

I've been wanting ever since I started running LPG to get an ignition map suited the LPG. For 3 years I've been running into dead-ends - until today. After talking to Richard at Motoscope this morning, we've decided that a Miller W.A.R chip is the way to go from here. He told me he's never been particularly impressed with MegaSquirt and for what I'm likely to gain the likes of Emerald wouldn't be cost-effective.


At the moment, the engine runs far better on LPG than it does on petrol. TBH, I was surprised how much better because up 'til today it's never run on petrol for more than a quarter of a mile since it was built. I've put this particular issue down to 2 things;-
The "AFM delete" that the engine runs with on LPG
and
the dubious generic chip in the ECU.

I rarely run on petrol, other than for very cold starts, these days. This morning I decided to drive to Motoscope (50-odd miles from home) on petrol to see what it's like. It feels like the mixture is weak at low revs, the car has a bad jerk which isn't there on LPG. Also, I'd never realised just how much difference AFM-delete makes. The throttle response on LPG is far better than on petrol, but part of this is undoubtably down to the petrol fuelling being "off". It's fine cruising at a constant(ish) speed. On a flat bit of road, with no wind, holding 3k rpm, the swing-o-meter was showing 30+mpg.

So this morning, Richard has done a power run, on LPG, so that I have a base-line for the mods and as a comparison against a standard 325i (on petrol) purely for my own geeky interest. When I go back to have the W.A.R chip set-up, I'll have petrol figures as well for an "ultimate petrol/LPG comparison".

The current figures are 161bhp and 179lbft. The 325i on the same rollers made 176/165.
Comparing the figures at 500rpm intervals, my engine is at least 10bhp up on the 325i (8bhp up at 2k rpm) all the way from 2.5k to 4.5k, after which the gap narrows and my engine stops making power at 5.4k at which point the 2.5 is making 5bhp more and in another 600rpm it finds 11bhp on top. The torque graphs are pretty similar-shaped, but at 2k the 2.7 is 22lbft up and at 4.5k it's still 10lbft up.


I'm not planning any internal changes to the engine. The furthest I may possibly go is getting a cut-and-shut mod done on some spare inlet manifolds to get the 325i TB to fit properly on the 320i runners.
I had thought about getting a Miller MAF to go with the W.A.R chip, but I can't see the point at this stage. IF I ever get 'round to upgrading the LPG front-end to sequential, then I will fit a MAF. But as long as I stick with the single-point LPG, it's not necessary.
I also want to have a go at mounting the LPG mixer directly to the TB at some point, which will mean ditching the standard inlet boot and fitting a silicon elbow, and I'll have to figure-out a way of getting mixture through the ICV.

The aims of fitting the W.A.R chip are;
Hopefully find a few more LPG mpg by getting the ignition timing right for the higher RON of LPG.
Getting both the fuelling and ignition right for running on regular unleaded. Currently I'm having to use Super, because it pinks badly on regular. I'm not bothered if doing this sacrifices a bit of power due to the very limited time the engine ever runs on petrol. I just want it right in case of unavailability of LPG - such as when we're touring 'round the far north of Scotland.

I think I'm about 15-20bhp and roughly 10lbft down on what the engine ought to be capable of. But at the end of the day, if all I achieve is to improve the mpg by 10%, I'll be happy. Any power and torque increases will be a bonus.

The W.A.R chip will be ordered this week. Watch this space..........

[daimlerman]

Subscribed...

My 2.7,with a very similar spec,but including a Miller MAF,showed 178.3bhp with a flat torque 'curve' at 190ft/lb.This was running on standard unleaded,of course.

The graph is posted in the wiki,for those interested.

Be very interested to see how you get along with the Miller WAR device.

[TouringTash]

Hopefully the crank has survived in my eta 2.7 so once the engine is out I can then confirm its rebuild time and then i'll add some more dyno data to the pot.
Just will have to try and not listen to a certain local engine fettler whispering naughty suggestions about snails and chargers.
Well not till the rest of the car is how I want it.

[petrol_1]

Hi

I m also running a similar spec also on lpg
my spec s are

STD eta bottom
731 'head mild porting
325i cam, inlet manifold TB, injectors (AFM now replaced with Ants MAF conversion +++)
hotung manifold
currently running Ant + 4 degree chip for lpg

The LPG set-up is;-
OMVL twin vap.
Stag 6 sequenical injection (closed loop control with the O2 sensor off std motronic )

Mine would also pink (up hill )on regular petrol , but never pinks on lpg


My best mods so far
lpg ( so i can afford to run it !)
Ants Maf drives so much better its like having 500 cc more ! pick up is really crisp, better mpg too

hotung m fold pulls well and sound great
not been on rollers , but it pulls v well gussing poss 170 ish , but its the torque thats this cars all about

my next build is a v hi comp 2.8 NA with a v mild cam (still want torque over power ),
after thats it s saving for a rotrex on lpg for me .

[StuBeeDoo]

The current figures are 161bhp and 179lbft.

At 5.4k and 4k respectively.

[e301988325i]

subscribed

[StuBeeDoo]

Malcolm, Alex..... What's all this "subscribed" nonsense? I frequently see it on threads (usually single-word posts, as here).
I don't understand.

[StuBeeDoo]

BTW, for anyone who hasn't noticed the change in my sig. - the W.A.R chip is now on order. The invoice from Miller says "10-12 days delivery", so I assume that means it will be here the second week in January.

[e301988325i]

When you have nothing constructive to add, but are interested in the thread and wish to follow it via 'view your posts', when a new post is added the thread in question is highlighted and jumps to the top of that list.

[daimlerman]

Malcolm, Alex..... What's all this "subscribed" nonsense? I frequently see it on threads (usually single-word posts, as here).
I don't understand.

Means that I get an automated email response to each new post!

My max torque of 190ft/lb comes in at 4k,peak power,178bhp,at 5250rpm,
So my power band is a little wider than yours,only difference in spec is LPG and inlet manifold,I'm using a 325 item!

[StuBeeDoo]

Thanks for filling me in. I just click "View your posts" every time I log-on.

[StuBeeDoo]

If anyone's remotely interested, I've over-laid my graph onto the 325i one. OK, so it's a bit gash, and probably not 100% accurate, if you want to be pedantic.
I could scan it.

[petrol_1]

Yep scan it lets see

Whats made you go for Miller ?

Has any one run a ported out ETA manifold compared to std 325 one
ie i know the ETA ports are really small and restrictive but the runners are longer for max torque over 325 i one so a opened out one may work

[eta]

You will never port an eta manifold ou over the length of the runners so there is little point in doing this.

Stubeedoo your figgures for your set up sound similar to mine. I have a simailar setup. Log manifold, eta bottom end but mine has an 885 head and 325i inlet manifold. Maybe its the log manifold that is restircting our engines?

I will be seeing in January how a new exhaust system will change power output. What kind of fuel economy do you get from LPG?

[StuBeeDoo]

OK, so here's the scanned comparison. Yes, I know it looks gash - and maybe even BS - but it's as close a comparison as I can do at the moment.

The black plot is the 325i and the red one is my 2.7.

Whats made you go for Miller ?

The middle and both ends of it is that all I really want is to get the thing mapped correctly for the LPG. I've had several generic chips with my 2.7s and none of them have been spot-on, even on petrol.
With the Miller, I can book some dyno time and play with it at will and the dyno is less than an hour away. Getting the Motronic remapped has turned into a logistical nightmare as there is nowhere that can do it within 300 miles of me. A bonus with the Miller is that I can have up to 4 switchable maps.

Maybe its the log manifold that is restircting our engines?

If that does turn-out to be an issue, I'll live with it. I'm not going back to an E30 steering rack, and I refuse to throw mega-money at a BTB3.

What kind of fuel economy do you get from LPG?

Currently I'm getting 17-18mpg commuting and 22.5-23.5 on a decent run. As above, it's improving the economy (by optimising the ignition map) that I'm most concerned with.

[daimlerman]

Stu,did you have a look at this in the wiki?

http://www.e30zone.net/e30zonewiki/inde ... an%27s_2.7

My torque 'curve' is very much flatter than yours....

[StuBeeDoo]

My torque 'curve' is very much flatter than yours....

I thought that Malcolm.
But this evening I had a flash of inspitation. I downloaded your graph (hope you don't mind), plotted my figures onto it as accurately as I could, freehand, and..... Hey presto.........




Yours are the black traces, mine are the red. Not so much difference now. Looks like the difference before was simply down to the different graph/software set-ups - for instance, my graph has the torque line-spacing at 5lbft intervals and yours are at 10lbft.

With the exception of peak power, I think I should be able to closely match yours when I get the pukka ignition map up-and-running.

Edit:- I've just had a thought - shall I put the 325i plots against ours?

[daimlerman]

Interesting!

I guess the differing outputs are down to the cheap gas stuff that you are running!

Hope you are able to optimise your ign to get a better result....

Yes,plot the 325i,then we can see just what the capacity increase is really worth.

[e301988325i]

With the exception of peak power, I think I should be able to closely match yours when I get the pukka ignition map up-and-running.

Edit:- I've just had a thought - shall I put the 325i plots against ours?[/b]

I'll dig out my LPG dyno chart and PM you the points to plot on?

Don't forget that we'll never match petrol because 5% or so of the inducted air is LPG, so 95% air : 5% lpg whereas when running on petrol, the fuel takes up a much smaller percentage of the intake volume and the petrol spray cools the air which makes it denser getting more air into the cylinder.

[daimlerman]

We really need to find out what you gas guzzlers need to do to match or better the equivilent petrol power.

Stu is owning up to about 23mpg on LPG,on a similar decent run I get about 32mpg on unleaded,so overall,Stu's running costs for fuel will be what,30% less than mine?

Probably better to use Gareth's cost per mile as a better indicator!

[e301988325i]

We really need to find out what you gas guzzlers need to do to match or better the equivilent petrol power.

Stu is owning up to about 23mpg on LPG,on a similar decent run I get about 32mpg on unleaded,so overall,Stu's running costs for fuel will be what,30% less than mine?

Probably better to use Gareth's cost per mile as a better indicator!

We could match petrol power but it costs and that defeats the object, we'd have to run sequential injection, LPG at a fuelling level for maximum power and adjust the ignition timing to suit. I am led to believe it is possible to outstrip sub 100octane petrol with LPG in this way.

My lpg average is 22.4mpg over 9,000 miles, an average of 11.5pence per mile, I reckon with the loss of economy and the lower cost of LPG I'm saving 40% or running for 60% of the cost of petrol.

My best and worst mpg on lpg over a tankfull was 28mpg and 18.5mpg respectively.

Malc you will get 32mpg, putting it nicely, conserving momentum well, and it's not really comparable to the normal 25mpg for a 325i. What do you reckon your pence per mile is even at 32mpg?

[daimlerman]

I can get 32mpg by using the extra torque of the bigger engine to my advantage,at today's cost locally(119.8p),I reckon about 17p per mile...

Bloody hell!....that means it costs me almost £7 for the trip to and from work!

Now when I were a lad,petrol used to cost 4/10 a gallon,and spark plugs cost five bob....

[Brianmoooore]

An engine optimised to run on LPG should produce more power than a petrol one, as demonstrated by the obvious power advantage of the two LPG powered Focus's (Foci?) in this years BTCC championship, and most LPG powered cars get a better mileage than a similar petrol one, as long as you measure miles per unit weight, rather than per unit volume.

[StuBeeDoo]

Thanks for the input/comments, lads.

Alex, I got your PM. I'm working on the graphs, but I'm running out of different coloured pens.

[StuBeeDoo]

OK, I've plotted Alex's figures onto the "communal graph". I'll not have time to scan it and get it hosted this evening, though - sorry.

It's interesting (well, to me at least) that all 4 engines produce very similar-shaped plots. Alex's is the only one with any real modifications. When I get the graph posted, I'll include in the text the spec. of each engine.

[StuBeeDoo]

OK, so I've done the graph with 4 different plots on. It should be borne in mind that only 2 of the plots (mine and the standard 325i) were done on the same dyno, the other 2 were both done at different locations.

Plot 1 (black) is Daimlerman's 2.7. It runs on petrol and is an eta/731 engine with 325i inlet manifold, TB, injectors and one of Ant's chips. IIRC at the time it was on a cast iron exhaust manifold. The only deviation from "standard" is a Miller MAF conversion.

Plot 2 (green) is Alex's modified 325i on LPG. The spec. is 9.4 compression, 64mm TB, M30 AFM, E30Zone wild chip, BTB3 manifold and 36mm LPG mixer venturi and Leonardo mixture control.

Plot 3 (red) is my 2.7 on LPG. eta/731, 325i TB on modified 320i inlet manifold, cast iron exhaust manifold, Viezu "Alpina 2.7" chip, AFM-delete, 39mm venturi and Leonardo mixture control. At the time of the run, the engine had only 9k miles on since a full rebuild.

Plot 4 (blue) is Mick's absolutely bog-standard face-lift 325i running on petrol. IIRC, the car (and I assume the engine) had something like 105k miles on it.




Whilst I understand what Brian is saying above about the science of calculating cost/mpg comparisons, it's always bugged me from day one that my LPG consumption is higher than just about everyone else who are running M20s quote - even when I had the 2.0. I've got a pretty good idea what mine does on petrol now (roughly 29-31mpg over 200 miles cruising at 65-75mph), so if I can't get within 10% of that (it's currently at least 25% worse, possibly nearer 30%) by fine-tuning the ignition with the Miller chip I'll have to go over the LPG hardware with a fine-tooth comb to see if I can find anything amiss.

[e301988325i]

That's great Stu, I think we can comfortably say my plot should be lower than both the 2.7's, showing dyno discrepancies, but that's not the point, the shape of the curves is so similar for all the engines. With mine and the 2.7's dropping off more at higher revs, mine strangled by the LPG mixer, yours and Malcs by the 731 head. The stock 2.5 shows much less of a drop of torque at higher revs.

[StuBeeDoo]

Stu is owning up to about 23mpg on LPG,on a similar decent run I get about 32mpg on unleaded

I ran mine on petrol for 200+ miles on Christmas Eve. OK, so it's not accurate because I didn't do a brim-to-brim, but it was whisker over 30mpg, cruising at 65-75. I don't think that's too far off, actually. I never realistically expected anything over 31mpg on a similar run before I had the LPG on the 2.0 (and the LPG consumption has been virtually identical with both the 2.0 and the 2.7s).

[e301988325i]

How is your lambda wired in Stu? 23mpg doesn't seem too bad, I reckon my 325 on petrol was doing high twenties on a long run. Have you checked your lpg system for leaks, I keep thinking I should check all the joints again, I know it's not leaking when parked because my garage never smells of gas.

[StuBeeDoo]

How do you mean "wired-in" Alex? I didn't run it through the DME, if that's what you're asking. I just ran ignition live to one of the white cables, the other white to earth, and the black and the grey to the Leo as per the instructions.

Have you checked your lpg system for leaks, I keep thinking I should check all the joints again, I know it's not leaking when parked because my garage never smells of gas.

I don't think it's leaking when parked for the same reason as you, but acutally I haven't checked for leaks - it's something I never seem to get 'round to. I need to get one of the aerosol leak detectors off Tinley's. I do occasionally get a brief whiff of gas when driving, but I've always put it down to exhaust fumes because unless it's raining hard I always have the sunroof tilted.

[daimlerman]

So really,Stu,it's fuel consumption when on LPG that is your main issue.Your petrol consumption is close enough to mine for 'driving style' to make the difference.

Would a multi-point system be more efficent?

[StuBeeDoo]

Would a multi-point system be more efficent?

Marginally. The ignition being "off" is hopefully more of an issue. The very fact the timing could be anything up to 6deg retarded has got to be the starting point in finding more power and economy.

The W.A.R chip is only about a third of the price of a decent sequential front-end kit. Ergo the front-end kit will be the last upgrade - if it's necessary.

[Gunni]

Since it´s gas, it´s not the same as liquid injection systems(petrol) and thus distribution of the energy is more even.

[eta]

I had an LPG car before. It was a PT crusier 2.0l petrol. I had it converted at great expense using a Nicols Mclaren sequential injection system. The car ran aproximately 35 mpg on petrol but only managed 24-28 mpg on LPG. This means I got ~74% of the fuel economy I got on petrol on LPG.

StuBeeDoo you are getting 75% of your petrol economy on LPG. I don't think you are going to get much better. The "problem" with LPG is the energy per unit volume of the fuel it a lot less.

The energy per unit volume for LPG is 25.3 MJ/Litre and for petrol the value is 34.2MJ/litre.

Therefore LPG Energy density/petrol energy density = 25.3/34.2 = 0.74%

You are not going to get the LPG fuel economy to with in 10% of the petrol economy. I don't think its possible.

[Gunni]

The real concern is not unit volume but unit cost.

i.e cost per mile.