re-gapping plugs gives more boost??

Hi,

After having my cats out and a restrictor ring fitted to my car I was only getting 1bar. I got fed up with this today and whipped the plugs out and re-gapped them from 0.8mm to 0.9mm, I'm now getting 1.1 bar! Is this normal? Would I get further gains if I got some iridium/platinum plugs and put them in?

Cheers,

Paul.

DO NOT use platinum plugs:eek:

Care to elaborate on why I cant use platinum plugs?

I've just got cheap NGK's in there at the moment.

Paul.

I'd like to know too! I used to use platinum ones on my MkIII, I don't recall hearing a problem with them on the MkIV and I can't think why it would be but I'm always up for ejerkayshun

BTW you can't get more boost from changing the spark plug gap, you can from cooler damper air though.

-Ian

Originally posted by Ian C

I'd like to know too! I used to use platinum ones on my MkIII, I don't recall hearing a problem with them on the MkIV and I can't think why it would be but I'm always up for ejerkayshun

 

BTW you can't get more boost from changing the spark plug gap, you can from cooler damper air though.

 

-Ian

Umm...read the original post mate !!

I DID get more boost from changing the gap on the plugs!!

Paul.

You changed the gaps and you got more boost the next time you drove it but I would mark that up as a coincidence. Boost is a factor of wastegate setting and exhaust flow. Neither are affected by the spark plug gap. A larger gap is asking for misfires at high boost and that's about it.

I got 1.3bar of boost yesterday instead of 1.2 the day before. It was cool and damp air instead of warm and sunny. I also had a passenger and a bag in the car but I'm not attributing the change in boost to that

-Ian

There is an issue with Platinum plugs which escapes me now...a search may reveal all.

The only reason I can think of (and it's tenuous at best) for the gap affecting the boost is if the car was under gapped before and not able to make a spark big/powerful/clean enough to ignite the mixture fully and therefore the exhaust going to the turbine wheel was not hot/fast enough before. Now you have improved the burn the turbine has sped up and hey presto, more boost.

However I too can't see this really happening - can you run the car for a week and tell us how it goes? Recording the boost on the same stretch of road (same direction) every day also noting the weather?

Originally posted by Ian C

You changed the gaps and you got more boost the next time you drove it but I would mark that up as a coincidence. Boost is a factor of wastegate setting and exhaust flow. Neither are affected by the spark plug gap. A larger gap is asking for misfires at high boost and that's about it.

 

I got 1.3bar of boost yesterday instead of 1.2 the day before. It was cool and damp air instead of warm and sunny. I also had a passenger and a bag in the car but I'm not attributing the change in boost to that

 

-Ian

The car has been hitting 1bar boost since the cats were taken out immediately until I re-gapped the plugs. I then drove the car straight away after and I was getting 1.1 bar boost. Unless the air temp changed by a couple of degrees in 25 minutes then I doubt it was that!

There must be some connection between the extra boost and the plugs, any more ideas??

Paul.

Originally posted by Alex Holdroyd

There is an issue with Platinum plugs which escapes me now...a search may reveal all.

 

The only reason I can think of (and it's tenuous at best) for the gap affecting the boost is if the car was under gapped before and not able to make a spark big/powerful/clean enough to ignite the mixture fully and therefore the exhaust going to the turbine wheel was not hot/fast enough before. Now you have improved the burn the turbine has sped up and hey presto, more boost.

 

However I too can't see this really happening - can you run the car for a week and tell us how it goes? Recording the boost on the same stretch of road (same direction) every day also noting the weather?

I like that explenation...it sounds like what is happening. There was a tiny bit of missfiring before I changed the gap when the car was cold.

I can check the boost every day, yes. Theres no guarantee that the air temp is going to be the same everytime though - I havent got anything to measure it.

I've checked today already and the cars hitting 1.1 bar today too.

Paul.

slight hijack, but is it normal to get the same boost, i tend to get different level of boost everytime i drive the car ?

The miss whilst cold is common in cars with too small a gap - that's the trade off for security from a more costly misfire higher up the rev range.

FYI - I perplexed at this and I do not recommend anyone else widening the gap on their plugs because of this one car's reaction to it. And those of you with Iridium's - you cannot re-gap as it would fook the electrode.

Paul, what condition were the plugs in when they came out, did you clean them, or just re-gap them?

I would recommend that we get input from CW or a.n.other engine expert.

Originally posted by Alex Holdroyd

The miss whilst cold is common in cars with too small a gap - that's the trade off for security from a more costly misfire higher up the rev range.

 

FYI - I perplexed at this and I do not recommend anyone else widening the gap on their plugs because of this one car's reaction to it. And those of you with Iridium's - you cannot re-gap as it would fook the electrode.

 

Paul, what condition were the plugs in when they came out, did you clean them, or just re-gap them?

 

I would recommend that we get input from CW or a.n.other engine expert.

The plugs are in good condition. They have been in the car for around 3k miles. I didnt clean them, just re-gapped.

Iridium plugs are next on my list, I just havent got around to buying them yet!

Paul.

Clearing up a misfire may well cause higher boost as the engine is running sweeter and generates more exhaust, I agree with that. Keep an eye on it and see what happens.

Still interested in the platinum issue though.

Chris - I get different boost every time I drive mine but that's because the wastegate can't cope with the state of tune, so it varies depending on external air temperature and if a butterfly flaps it's wings in africa it seems. A stock car should have very consistent boost, anything decatted may well start to vary.

-Ian

The standard Toyota plugs are platinum I believe anyway aren't they?

Originally posted by SimonB

The standard Toyota plugs are platinum I believe anyway aren't they?

And they run stock boost fine. You might as well throw the book out of the window once you start modding.

On the platinum plugs, I think there was an article on http://www.mkiv.co.nz about them.

Originally posted by Alex Holdroyd

The only reason I can think of (and it's tenuous at best) for the gap affecting the boost is if the car was under gapped before and not able to make a spark big/powerful/clean enough to ignite the mixture fully and therefore the exhaust going to the turbine wheel was not hot/fast enough before. Now you have improved the burn the turbine has sped up and hey presto, more boost.

I'm not a engine expert but it is possible that this could of happened, although I agree its unlikely.

The more powerful spark (set at right gap) could increase exhaust gas velocity as it burns hotter and and would expand due to the extra thermal input. The would drives the turbines faster and cerat higher boost.

If you knew the area of the turbo you could calculate the velocity increase and the rise in temperature required to generate that extra .1Bar.

Originally posted by Paul R

Care to elaborate on why I cant use platinum plugs?

 

I've just got cheap NGK's in there at the moment.

 

Paul.

Take from MKIV.co.nz

"Platinum tipped plugs are a no-no, as they retain too much heat which in turn can cause detonation."

Originally posted by Terminator

Take from MKIV.co.nz

 

"Platinum tipped plugs are a no-no, as they retain too much heat which in turn can cause detonation."

I assume this only applies to TTs? I think a lot of NAs have platinum plugs (mine certainly does).

I would assume so, but I assumed with a restrictor ring Paul was referring to plugs in a TT.

I use platinum plugs in all my NA engines and they are fine.

Originally posted by Steve W2

I'm not a engine expert but it is possible that this could of happened, although I agree its unlikely.

 

The more powerful spark (set at right gap) could increase exhaust gas velocity as it burns hotter and and would expand due to the extra thermal input. The would drives the turbines faster and cerat higher boost.

 

If you knew the area of the turbo you could calculate the velocity increase and the rise in temperature required to generate that extra .1Bar.

It wouldn't be a 'more powerful' spark, it would either spark or it wouldn't. No matter what voltage the spark has when it went off it would ignite the fuel mix the same way so it's not going to change the burn characteristics of the fuel either

If it's misfiring you won't get as much exhaust and therefore the turbo won't get as much shove, fix the misfire and the turbo boosts correctly again.

-Ian

Originally posted by Ian C

It wouldn't be a 'more powerful' spark, it would either spark or it wouldn't. No matter what voltage the spark has when it went off it would ignite the fuel mix the same way so it's not going to change the burn characteristics of the fuel either

 

If it's misfiring you won't get as much exhaust and therefore the turbo won't get as much shove, fix the misfire and the turbo boosts correctly again.

 

-Ian

Your right, but a longer spark gives a bigger ignition path and which can effect the specific heat release of a combustible mixture. If the heat relaease occurs across a larger area the flame can burn hotter as the mixture of fuel is burning more evenly through the cylinder. If it burnes in a very local point you may not burn all of the fuel as they can be encapsulated in pockets.

This applies to combustion engines on sucha small scale its not worth talking about so I will shut up:)

Although I have noticed you are following me round again:D