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V8i Optimising


mr.t
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I have an LPG powered V8i, that has a sweet running well serviced engine..... BUT is somewhat.......well slow!

My last 4x4 was a V6 Shogun with (standard) 170ish HP and would blow this into the weeds.. sadly..

It does have a blowback arrestor in induction pipe that reduces CSA of inlet massively, so that is heading towards the bin/Ebay!

...the purpose of the thread...

I am not after blinding performance, but want the thing to run as it should...

Is there anything that would massively effect its power that I should be focusing on.. ie Advance, Timing, Tuning etc ...

...I know it sounds a bit stoopid. ie All the above should be checked... What I really need to know is there any common issue on these V8's that effects performance when everything runs ok..

...It runs the same on LPG and Petrol by the way...

Cheers

M

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sounds like the timing may need sorting out. change all the ignition components for good genuine ones as a start. run NGK plugs with them for a good quality spark.

the other thing that will affect the power output is the weather. when it's cold the LPG system will develop less power than when it's milder, i noticed this with mine when the last cold snap finished and we got "normal" temps, the old girl would absolutely fly along, but now it's gone cooler again, the power is slightly down.

so it may be worth having the LPG mixture checked out, and adjusted - it's wuite common on the older single point systems to have to adjust them for summer and winter settings to compensate for the change in the weather.

you say it runs the same on LPG and petrol? when i change back to petrol on mine, there is a quite considerable change in the way it performs, as it will power along much better, with quicker acceleration, and more power.

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Definitely very similar on both LPG and Petrol...

... It has Magnecor Leads but may need Spark Plug change...

The system is an old Single Point Stargas install (circa. 2000), not sure how tuneable...

BUT, it is a common lack of power, so will look at the common items..

...Question.... Should sucking on the vacuum unit pipe on the distributor do something.... should I stop being able to draw breath??

M

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Sucking on the vac advance should make the baseplate rotate in the dizzy- you'll be able to see it move quite clearly.

Whats the timing set at? On my 3.5 i set the timing by ear, taking it out for a few test runs between tweaks. Its set so that i *just* get pinking under heavy load when on Unleaded. Its definitely more advanced than 6 BTDC, but not by much.

You should get noticeable difference between petrol and LPG. I switch the 90 back to petrol when i need to overtake, or if i really feel like treating myself.

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I have an LPG powered V8i, that has a sweet running well serviced engine..... BUT is somewhat.......well slow!

My last 4x4 was a V6 Shogun with (standard) 170ish HP and would blow this into the weeds.. sadly..

It does have a blowback arrestor in induction pipe that reduces CSA of inlet massively, so that is heading towards the bin/Ebay!

...the purpose of the thread...

I am not after blinding performance, but want the thing to run as it should...

Is there anything that would massively effect its power that I should be focusing on.. ie Advance, Timing, Tuning etc ...

...I know it sounds a bit stoopid. ie All the above should be checked... What I really need to know is there any common issue on these V8's that effects performance when everything runs ok..

...It runs the same on LPG and Petrol by the way...

Cheers

M

You need to establish if its running right or not first. If it is then you want performance mods, if its not then you need to find the issue.

Cams and/or lifters wear on these motors, so if everything else checks out ok, this might be worth looking at.

The stock motor is all low end revs and grunt, and literally strangles itself at higher rpms. Combine this with fairly tall diff gearing, tall transfer high ratio gearing and only a 4 speed gearbox (if auto) then yes it can blunt performance.

If you want more umph the basic tuning rules apply, get as much air in as pos, as big a bang without breaking anything and get the hot gases out as quick as pos.

A decent free flow induction setup will help. As will a nice free flow exhaust, but these won't produce huge gains.

For more power you really need long tube exhaust manifolds, the longer the primaries the better - sadly these are almost impossible to get in the UK and usually expensive.

I don't know how tunable the stock ECU is, if its limited then switching to Megasquirt or even a 4 barrel carb setup is worthwhile.

Swap in a sensible cam and maybe some decent heads and bing - it'll feel like you gained a 100hp (although probably not quite that amount).

But there's no reason you couldn't see 200bhp+ out of it and still remain very nice on the road (on or off). Either that or try and pick up a 4.6 and swap it in, easy way to gain 40+ bhp.

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I am not after blinding performance, but want the thing to run as it should...

Nope I won't be spending any money on performance mods! It is a a toy that I use to get to work and play with at the weekends..

...I will go through it with general tests and tweaks... centre box removal, blow back trap removal... timing.. plugs and leads and that it I think...

I will keep you posted...

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How many miles has it got on the clock?

Units that are around the 100,000 mile region will be wearing their camshaft lobes. There are exceptions to this, as so much depends on how it has been maintained and whether or not it spent more time up to temperature than warming up. (i.e. one used as a company car going up and down the motorway will have less wear for the same mileage as one going to and from the shops).

See RPi's page for more.

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Cheers for that...

I know the last owner of 4 years as he is a colleague... He warmed it up so he could switch straight onto LPG... Stood having a fag while it did it!

He was a plodder, which sometimes doesn't help... He had a short commute which won't have helped..

We'll See.. the price I paid for it I could afford to put NOS on it .... haha

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I have been running lpg for a looong time in many v8 powered landdies, on all the single point systems there is a power lose, on the multi point system i use on my 3.9 very little or none depending on how i set it. You must get it to run right on petrol first and leave the air filter alone changing this will not help at all and even make things worse. The sparking system needs to be in very good condition because the higher resistance at the plugs will find any problems you didn’t know you had. A spark increasing device of some kind is a good idea, non resister plugs help but most important the timing for lpg is much more advanced than petrol, as it is much slowing burning i run mine at 15d of extra advance so about 20 in total. So unless you have something to retard the timing back to normal when on petrol it might well pink. I use a device that switches this automatically. Oh yes and make sure your vac on the distributer is working 9 times out of 10 they don’t

Steve

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I am always interested in these posts. I have a 3.9 V8 Auto and feel much the same about the power.

If I stomp the loud pedal into the carpet it goes ok, but I'll be lucky to get 150 mles out of my tank that way.

I've looked throught the Haynes manual about the timing but it mention's nothing.

This is the first I have heard about the Vacuum on the Distributor, What does it do? How do I test its working?

I have new spark plugs which helped a little.

I have a small leak in my exhaust (Manifold to downpipe) which makes a ticking noise, it is similar to pinking and it worries me it is hiding other noises like pinking or tappets.

I have had several attempts to cure the leak without sucess.

Is the a link to how to set up the timing on this engine?

Cheers

Brian

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This is the first I have heard about the Vacuum on the Distributor, What does it do? How do I test its working?

It advances and retards the timing depending on the engine speed. The vacuum is taken from the inlet on the plenum chamber. There will be a small pipe that goes from the distributor to the top on the right hand side of the plenum chamber, you want to remove this. With the distributor cap off, you want to suck on the end of the pipe. The distributor should then rotate its internal base plate.

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It advances and retards the timing depending on the engine speed. The vacuum is taken from the inlet on the plenum chamber. There will be a small pipe that goes from the distributor to the top on the right hand side of the plenum chamber, you want to remove this. With the distributor cap off, you want to suck on the end of the pipe. The distributor should then rotate its internal base plate.

Cheers, I'll give that a go in a bit and let you know how I got on.

If I want to check the timing is it a matter of twisting the dizzy a bit going for a drive, stopping moving it some more and contnueing until I am happy or is there a better way?

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It advances and retards the timing depending on the engine speed. The vacuum is taken from the inlet on the plenum chamber. There will be a small pipe that goes from the distributor to the top on the right hand side of the plenum chamber, you want to remove this. With the distributor cap off, you want to suck on the end of the pipe. The distributor should then rotate its internal base plate.

There is a black plate that says do not remove and within that the part the Rotor arm sits on.

I've sucked as hard as I can and nothing moves. I moved the centre part with a screwdriver so I can see where the movement should be I think.

Would this explain the real sluggishnes when cold, it will barely move in reverse without wanting to stall?

The pipe goes to an attachment on the side of the dizzy and there is another tube coming from that part that is blanked off.

Cheers for any help you can give.

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Haha.. I have the exact same manifold to downpipe issue...

Replacement Manifold (other cracked), new bolts and gasket hasn't cured it.. but I put that down to the 'Sheffield Land Rover Specialist' mechanic...

That is my next item to sort, theses annoying little leaks...

Power wise...Ordered service kit, plugs and leads and will go from there...

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Haha.. I have the exact same manifold to downpipe issue...

Replacement Manifold (other cracked), new bolts and gasket hasn't cured it.. but I put that down to the 'Sheffield Land Rover Specialist' mechanic...

That is my next item to sort, theses annoying little leaks...

Power wise...Ordered service kit, plugs and leads and will go from there...

Have you tried the Vacuum test as above? Would be great to hear if yours is ok?

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Try advancing the timing a little, they respond well. RPI do a power amp for lpg/petrol switching. A free flowing exhaust will help, don't change the manifolds, the OEMs are quite good and you'll loose low down torque. Free flow mufflers and 2.25 (auto) or 2.5 (manual) pipe from the V back is whats needed.

To get more torque: Viper Cyclone cam from RS or Crower 50229 from V8 Tuner will add an extra 27 ftlb at low rpm. 4.6 can result in 340 ftlb if done right which will blow a Shogun into the weeds.

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The diaphragms of the Vacuum Advance Modules are notorious for leaking due to the material used & the temperatures encountered right in front of the fan. When sucked, the internal baseplate should move. If it doesn't, replace it.

Here, you can get reworked modules which use a better material than the OEM stuff. Probably can there as well.

I replaced the OEM tube with EFi fuel hose with clamps because the end boots split. If you do this, you will need to cable tie it out of the way of the fan belt.

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Try advancing the timing a little, they respond well. RPI do a power amp for lpg/petrol switching.

They do, but they seem to go wrong with alarming regularity and for very similar money you could fit MegaJolt which is a far nicer solution.

I'd sort the vacuum advance first as that really won't be helping things.

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The diaphragms of the Vacuum Advance Modules are notorious for leaking due to the material used & the temperatures encountered right in front of the fan. When sucked, the internal baseplate should move. If it doesn't, replace it.

Here, you can get reworked modules which use a better material than the OEM stuff. Probably can there as well.

I replaced the OEM tube with EFi fuel hose with clamps because the end boots split. If you do this, you will need to cable tie it out of the way of the fan belt.

So the bit on the side of the Dizzy is replaceable, Great, thats all I needed to know.. Cheers :)

I'll see if that makes a diference.

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Brian, you may need to rotate the dizzy to get at one screw, so mark it's position well before loosening it off. You will also need access from above with the cap off, to ensure the arm hooks in to the plate. Otherwise it's a simple enough job.

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Well quick update.. Have plugs and leads sat on my desk... BUT.

Removed 'Flashback' valve and replaced intake hose, replaced air filter.

Step change difference in performance already, I think the restriction caused by the valve strangles the engine... obviously I shall not be running the LPG too low!

...next we'll see what plugs and leads do.

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