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MG MGF Technical - Sparkling question

Hi all,

A question for all people that have a more or less tweeked VVC-engine(headwork done).

What type of spark plugs do you use since your engine isn't standard anymore? Is there a need for "colder" plugs when the engine produces more power? (hence generating more combustion heat?!)

I'm asking because I've done some headwork to my VVC and since then I've noticed that the standard plugs have deteriorated strongly.

I've already mailed DVA with the same question but I think he's on holiday or to busy to answer, so folks, please your opinion and/or experience.

Regards, Arend
Arend Groen

Try some new ones as I have found more duff new plugs in the last 24 months than the previous 10 plus years. Generally I only run to just over 100bhp per litre but the standard heat range plugs are perfectly adequate for the road use they get. Rapid failure of known good plugs may indicate a significant change in combustion chamber characteristics, for example has the head been skimmed by more than 10 to 15 thou. With a quoted standard compression of 10.5 to one, plus or minus 0.5 of a ratio, if your at the upper end of that variation and then increase compression further this may well have abearing.

Rog
Roger Parker

The observation that there have been so many defective spark plugs recently is a little worrying Rog! :o(

Arend - not heard DVA recommend specific spark plugs following head work.

HOWEVER

Is your car a VVC with a full port, and still running with the standard MEMS? I know that Dave Livingstone ran a similar set up, and found, at our last RR session at G-Force that his engine was running notably lean. Fortunately, he already had an FSE adjustable fuel pressure regulator, so the fuel pressure in the fuel rail could be increased, and increase fuel delivery. He consequently got an additional 10bhp! (Now a 183bhp engine!!!)

If your car is running lean, the combustion camber can run far hotter - and this may result in the spark plug deterioration that you've seen.

I'd suggest that you find a rolling road local to you that has a broad-band Lambda sensor and either fit an adjustable fuel pressure regulator, or remove the standard FPR and gently squeeze it in a vice to increase the regulated pressure...

A bit more on this can be found here: http://www.mgf.ultimatemg.com/group2/fuel_rail/index.htm
Rob Bell

Thanks Rog,

I'll try to sort out what C/R it has.

Rob,

I wouldn't describe it as a full port, because I've done it myself, with the help of Dave Andrews website, and I was a bit afraid to go to far. I am running with the standard MEMS. I do already have a adjustable FPR but, as you mentioned, adjusting without a rolling road etc. isn't easy to do right.
I do know that a lean running engine runs hotter and I agree with you that this could be the cause for the worn plugs.
There are company's here that have a good rolling road etc. but they aren't cheap and they have a waiting list of, at least, two months.

Arend
Arend Groen

Nice work Arend! :o) I intend to port my own head too - but I'm lucky in being a fair bit closer geographically to DVA's pad in Milton Keynes - so will probably pop up to DVA towers to do the work :o)

Regarding the fueling. I presume that you are using the 'factory MGF' set up on the FSE? In these circumstances, it is 'better' to run slightly rich rather than slightly lean. Overfuelling has its own problems, not least, bore wash - but it is the lesser of the two evils.

What I'd do is book the car into a RR (money well spent - or do as we do in the UK, book the RR for a day, and arrange with friends to perform a 'rolling road day shoot out' so to spread the costs). In the mean time, enrich the FSE by turning the regulator 1/4 of a turn - and until you've had the fuelling checked, don't use full power.

In the mean time, keep an eye of the colour of the deposits on the exhausts (although I suspect that burning unleaded will always result in black tail pipes), and monitor the state and colour of the spark plugs.

Keep us posted on how you get on Arend.
Rob Bell

Arend, check the fuel pump is giving the correct pressure, use a gauge to do this otherwise it is guess work. After testing the standard pump I found the pressure dropping off at higher demand and replaced it with a higher rated pump.(It now copes with 8500rpm and 220BHP;-)) This could be the source off a weak mixture and the plug problem.
mike

Rob, Mike,

I don't have a FSE, I've found a FPR from an unknown make (Italian?) at a scrapyard (1 euro), about a year ago, which had a little cap on top of it. I've removed the cap and underneath there was a little screw, which was factury adjusted at 3 bar. I've made myself a little manifold to connect this FPR to my fuelsystem with an extra connection for a gauge. Before the headwork was done I've run this at about 3,4 bar which went pretty well, in my opinion. I haven't touched it since then. Maybe I should turn it up a bit now, but as Mike says, I don't know if the fuel pump can cope.

I'll try to keep you posted although I haven't much time at the moment.

Regards, Arend
Arend Groen

This thread was discussed between 10/11/2004 and 13/11/2004

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.