Low compression (ex-Gulf 3.5) running LPG

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Valhalla
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Low compression (ex-Gulf 3.5) running LPG

Post by Valhalla »

Hi there,
I'm a newbie to this forum, but I have had an ongoing issue for some time now. Years ago I made the mistake of taking a "short-cut" to a rebuild on the wife's RRC, and I sourced one of the NOS ex-Gulf low compression V8's that were on sale through various independents. To cut a long story short, the build was pretty bad, and I had to fix a number of issues before it would even run for the first time. I subsequently got a StarGas system fitted with mixers at the carb elbows (1.75" SU HIF44 retrofitted), and over the years managed to get a lot of LPG problems ironed-out (poor installation, etc.) to the point where the running was just about acceptable.
Since then, life changes, and I now run a diagnostics one-man-band business in the middle of nowhere. And then another of these wretched 3.5 ex-Gulf engines turns up in a RRC. And it runs like a sack of spuds, apparently "always has done, since the engine was changed"

Short question - has anyone successfully got an LC Stg.1 or early RRC with 8.13:1 CR running on LPG in any way or form, or is this just a losing battle? The theory says its a losing battle, but I know that with a decent ignition system and lots of time, you can get one of these to run, it just never gets any better than high-idle speed, then its all gutless. :roll:



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ChrisJC
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Post by ChrisJC »

I've never come across anybody trying LPG on an 8.13:1 engine. I've run 9.35:1 and 10.5:1 which is fine.

As a benchmark, my 10.5:1 engine developed 135BHP on petrol and 99BHP on LPG. An 8.13:1 will clearly produce less, hence your comment about it being gutless!

Chris.
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Quagmire
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Post by Quagmire »

My Dad's 110 is an 8.13:1 and that runs fine on gas, in fact I am currently driving around in it while I change the front axle on my 90.

His 101 also runs on gas, I think they have a weird (but again low) compression ratio compared to other engines - 8.25:1 I think?
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

Valhalla
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Post by Valhalla »

Quagmire wrote:My Dad's 110 is an 8.13:1 and that runs fine on gas, in fact I am currently driving around in it while I change the front axle on my 90.

His 101 also runs on gas, I think they have a weird (but again low) compression ratio compared to other engines - 8.25:1 I think?
Yes, in both cases the 101FC and the Stage1 V8 (and possibly the early 110's?) got the LC 8.13:1 engine. I think they both got the same "derate" camshaft at the same time, which was part and parcel of the power-limiting hardware for both. My theory is that the ex-Gulf engines are fitted with the "derate" camshaft, as the engines were destined for 101FC support. On the other hand, who knows what has been built into these engines???!!! In case anyone hasn't come across these engines, they are absolutely dreadful!! Because they were built as "special builds" by LR around the early 1990's, they had a "parts-bin" lottery by a few personnel that weren't all that familiar with the Rover V8. Example was a combination of long dipstick and short tube, meaning that they were "full" at around 2.5litres of oil, and the oil pickup strainer was barely covered.

What sort of LPG systems are you running on the vehicles that you have? I am encouraged at bit by response, so maybe with a bit of fettling I can get this latest RRC to run something like smoothly. My theory at the moment is that the engine is not breathing properly (back to the Gulf build?) as the manifold pressure falls away much too sharply on throttle opening. This means that the LPG vapouriser is more-or-less pushing the gas into the engine, rather than seeing a steady depression from the intake elbows.

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Post by Quagmire »

The gas systems are both single point with mixer rings on each carb.

These are fed from a bigas M84 vaporiser. The gas side goes from this to the mixer rings via a y-piece and each length of hose between the carb and the Y is the exact same length. Old pic of my 90 below, with mixers attached but no vap fitted:

Image

Gas is fed to the vaporiser via 8mm flexible pipe.

The 110 (and my 90, pictured above which is not low compression) both have simple closed loop systems fitted and these will keep the mixture around stoich when cruising. The closed loop simply controls a stepper valve on the gas feed to the carbs based on what the lambda sensor sees.

One thing I would say is that the 110 and 90 both run better than the 101, but they both have programmable ignition (Megajolt) and are using ford coilpacks, which gives a much bigger spark than the standard rover setup. The ignition table for LPG is quite different to the Petrol settings and has more advance.

The 101 is on the normal dizzy, and so cannot be advanced so much. All is fine until you sit in traffic on a hot day and then it seems to get a little unhappy with a little miss here and there- I think the lack of advance causes it to run warmer.

All the vehicles run normal NGK plugs, gapped to the upper end of the tolerances set out in the LR manuals. I have also used Champions and Denso plugs with no issues.

You dont need fancy plugs or leads to make LPG work well, no matter what people say. Just route the leads correctly and keep them separated properly.

All the LPG gear was purchased from Tinley Tech - have a google, they are v helpful.
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

Valhalla
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Post by Valhalla »

Thanks for the comprehensive description and pictures!

From the sound of it, the closed-loop system that you have employed could be a bit further than the chap who owns this particular RRC wants to go. It is, I have to say, the most logical way around the whole issue. One thing that strikes me is that a stepper-motor & valve controlled gas flow to the engine could lend itself pretty well to direct manifold entry at the penthouse, which would overcome the issues of poor airflow before the carbs on near-closed throttles.

I had a bit of an improvement today from this RRC, using a bit more static advance than has previously been possible (now successfully "hiding" all manifold vacuum from the vacuum advance on the distributor at idle) and this has help alongside a tweak or three to the vaporisor. I still think that the vaporisor needs a good service, but the vehicle has become driveable agian today.

I was convinced that I saw the root cause of the poor inlet manifold depression this evening, but my pressure transducer turned-out to have gone flat-battery, so I'm not so sure now. This accompanied a "no hot-start" after a short run, so there might be something there even now.....

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Post by softdash3.9 »

My Range Rover Classic was an export car with a 8.13:1 CR 3.9 which ran on LPG (Bigas sequential injection) fine, however since the rebuild I have changed the pistons to 9.35:1 CR items now :wink:
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Post by Valhalla »

An uprate to 9.35:1 pistons and a pukka "standard" camshaft was the option that I gave the chap, when all else fails.

As it happens, I have been able to tweak a bit more out of the current system, to the point that the vehicle will just about pull at WOT mid-engine-speed (as long as the skin on the rice pudding isn't too thick :wink: )

The vapouriser needs a service, other than that, all the easy bits are covered.

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Post by Valhalla »

The plot thickened a bit more last week, when this RRC turned back up on my doorstep again. This time it was really running badly, so I took the liberty to replace all the pukka NGK BPR5EIX plugs with the conventional NGK BPR5HS units - and the quick minded will spot the glaring error that this poor engine has suffered in the past. An NGK plug uses the "E" to denote 19mm length thread, the "H" is for the shorter 12.7mm thread. What had happened was that someone had replaced the original plugs for LPG specials from NGK (after I had fixed this car last year), but failed to notice that they were much longer (and the military V8 heads are machined deeper for the 24V plugs). Fortunately the pistons are well dished......5 out of 8 of the plugs are now fit for the bin, they don't fire at the electrode.

Anyway, the engine ran much better, but it was clear that it was just as unhappy on petrol as it was on LPG, so until the root cause of that is sorted-out, then making the LPG system perfect is not going to be possible.

Thoughts at the moment from me are that the oil is thinning too much when the unit is really hot (or the oil pressure is not good under these conditions) and this is leading to tappet partial collapse. I have got to find a way of measuring this properly (and cleanly :roll: ) before going any further. As the engine oil (changed by myself last year) had been completely trashed with petrol dilution, then there may be a fair chance that the tappets are not in the best of health!

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ChrisJC
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Post by ChrisJC »

I doubt if the tappets would leak down, nomatter how thin the oil. I've always had to dismantle them in the past to empty them.

Unless they're knackered of course.

Chris.
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R/R P38 4.6 V8
R/R L405 4.4 SDV8

Valhalla
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Post by Valhalla »

When I say the oil was thin, I may have understated the dilution!! What came out of the sump was 6.5 litres of fluid with the consistency of water when it was cold. Having mentioned that, it's true that the tappets did not appear too knackered when I looked at them with the inlet manifold gasket out of the way, with plenty of valve lift on show for the cylinders that were inducting/exhausting. I think that proper DTI measurement is called for.

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Post by bodger »

Quagmire wrote:The gas systems are both single point with mixer rings on each carb.

These are fed from a bigas M84 vaporiser. The gas side goes from this to the mixer rings via a y-piece and each length of hose between the carb and the Y is the exact same length. Old pic of my 90 below, with mixers attached but no vap fitted:

Image

Gas is fed to the vaporiser via 8mm flexible pipe.

The 110 (and my 90, pictured above which is not low compression) both have simple closed loop systems fitted and these will keep the mixture around stoich when cruising. The closed loop simply controls a stepper valve on the gas feed to the carbs based on what the lambda sensor sees.

One thing I would say is that the 110 and 90 both run better than the 101, but they both have programmable ignition (Megajolt) and are using ford coilpacks, which gives a much bigger spark than the standard rover setup. The ignition table for LPG is quite different to the Petrol settings and has more advance.

The 101 is on the normal dizzy, and so cannot be advanced so much. All is fine until you sit in traffic on a hot day and then it seems to get a little unhappy with a little miss here and there- I think the lack of advance causes it to run warmer.

All the vehicles run normal NGK plugs, gapped to the upper end of the tolerances set out in the LR manuals. I have also used Champions and Denso plugs with no issues.

You dont need fancy plugs or leads to make LPG work well, no matter what people say. Just route the leads correctly and keep them separated properly.

All the LPG gear was purchased from Tinley Tech - have a google, they are v helpful.
8MM pipe ..isnt that a bit small the pipe on mine is 16mm that runs from the vap to mixer ??????

ps: the only way on LPG is copper core HT leads :)
remember it's only a bodge if it DOSN'T worK

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Post by Quagmire »

8mm from tank to vap :)

Vap to mixer rings... no idea what size, much bigger than 8mm though!
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

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