V8 engine modifications for LPG

**100I** · 30th July 2007, 10:40 PM

I don't know exactly how it works in detail, it's part of their secret I guess. 12mths ago I could not find anyone in Brissy with a good enough working knowledge of anything at all to do with SVI, so I gave up looking & waiting in the end & chose a regular system.
Basically you can't fit SVI to any car you please just yet, only select vehicles so far but the list is growing.

Not sure if it was piggybacking or not.
What I managed to glean & the way it was explained to me at the time was the vapour injectors mimiced the original EFI (I gather using appropriate resistance values to make sure the ECU still 'thought' it was operating the petrol injectors) and it's this 'interface' that has to be specced for each vehicle's/manufacturer's ECU. What other differences between ECUs someone with EFI background might know. Whether directly operated by ECU or detoured via a piggybacked chip I don't know.
There was no mention of remapping ignition and such though so presumeably it just used the factory mapping, ignition curve and knock sensors in the usual way (and of course mine has none).

There were/are several SVI systems available or being developed in Europe tho so I'm sure some are more complex & adaptive - perhaps along the lines of a unichip style piggyback & injector 'mimic' all in one, which would be logical.

If I did understand it more I bet I'd be making a few dollars right about now

**Tank** · 31st July 2007, 12:10 AM

Originally Posted by PLR

Thanks Frank ,

As said i didn`t know also was typing when you posted your first explaination , don`t doubt what you say just didn`t see it .

" Not wise to shave heads as described " which description and why ?

I`m always happy to learn the reasons for doing or not doing something .

I`m interested in learning anyone ideas as to why and for no other reason than to understand .

Do you have an idea what a Unichip costs ?

Cheers

Because of the V8 configuration with an inlet manifold seated between the heads the height of the heads i s crucial because the inlet manifold has 3 surfaces, if you shave a large amount off the head surfaces, that brings the heads lower on the block and the 3 surfaces of the manifold have to be machined to match the surfaces they seat on. It also creates the problem of your rocker arms being closer (by the amount shaved off the heads) to the pushrods, which is akin to having longer pushrods so adjustments need to be made to accomodate.
Coopers in Sydney supplied and fitted a UNICHIP and Dyno-Tuned my previous Disco, which was not fitted with LPG, for $1500, it would something to think about if you dont want to rebuild your engine, Regards Frank.

**PLR** · 31st July 2007, 09:19 PM

G`day Dan

Yes , it`s hard to unfurl this is some of what i`ve found and part what i think but haven`t looked at ignition .

There are things called Emulators , what the do is tell the ECU the injectors are still working as normal .

They wire into the injector circuit .

On D2 and P38a they are required because the warning bells and whistles will show .

On a D1 they can be used but are not really needed ( though it may be a requirement for the ECU signal ) as in the way yours works now .

The LPG ECU piggybacks the EFI ECU , takes the signal from the EFI ECU and uses this to tell the LPG ECU when to open and close ( time ) the lpg injection .

The LPG ECU then uses the signal to alter the time of opening for LPG injection which is different to EFI injection .

Basically the Emulator fools the EFI ECU into thinking things are as normal .

The LPG ECU parasites the EFI ECU to use its signal and alters it for LPG .

On a D1 same applies but less work for the LPG ECU because of the simpler system .

The ignition , i`m not sure , don`t know if the GEMS or BOSCH have the range but in theory the knock sensors are supposed to alter timing for max before pings happen and are supposed to be able to run different grades of petrol .

The D1 because of the Dissy woulds still need more work though it may be that the LPG ECU can and does have the capacity for both ignitions

Cheers

**PLR** · 31st July 2007, 09:59 PM

Thanks Frank

I misunderstood your meaning of not wise , i thought you may have meant detrimental to the engine .

I have learnt something from the discussion though .

The 4.0 had an oil leak at the front of the engine which was a split end seal for the inlet gasket .

I torqued to spec and because of the head mods and after reading your post it dawn that clearence was possibly the reason .

On refitting i used less tension and it hasn`t leaked since but your post help to finalise the leak cause .

The Rover inlet manifolds are different to most V8s like Ford GM etc .

They only have 2 surfaces and the gasket seals the valley not the actual manifold .

To make the inlet manifold fit the heads are machined on the port surfaces and the inlet manifold is left untouched .

To raise the compression this way the scenario would be a dual fuel Disco taht has sticky valves ( common because they run rich ) .

Having a preference for LPG , while the heads are off the decision is made to raise the comp ratio .

Most of the cost will be as usual , the extra will be some more machining on the heads ,the cost of shims and alot more time to do it properly .

This will workout much more cost effective than fitting new pistons etc and will acheive a similar outcome .

I wouldn`t recommend anyone does it this way , there is alot of measuring not only dial and mic etc but ccing piston tops and chambers and as you say the rockers not only need lifting they have to run in the right place on the valve stem end for extended life and it`s time consuming .

It`s for sure a do it your self job it would be very expencive to pay to have the work done other than the machining of the heads which needs an engineer of coarse .

In my case i can do it pay for machining and it does work but i also understand what your saying .

Cheers

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