We finally got my turbo installed yesterday. It was very difficult getting the car started. We finally got it to start and it was idling like crap. We checked and found no vacumn leaks. We finally decided to check the spark plugs. They were in pretty bad shape. The were NGK 10.5's with about 4000 miles on them (100+ passes at the drag strip). I have decided to go with NGK 9's all around. The question is how much power loss could be attributed to bad plugs? I have heard 10 to 15% at the wheels.

Thanks in advance for your imput

 

Yes, from my butt dyno, I would say also around 10%. My new plugs made the same difference in power as my DP when I installed it.

And no more backfiring at high RPMs

 

I said god damn!

 

I have seen as much as a 30 RWHP loss on the dyno from bad spark plugs

Jason

 

Yep, we really felt my fouled plugs on the top end during tuning. After swapping out some fresh ones it was a night and day difference.

change those plugs often

 

Simple answer.

If your spark plugs are in question, replace them.

 

Kind of an open ended question. I've seen cars not start with bad plugs. I guess they lost ALL of their power.

 

I clean my plugs every time the car starts to run weird and then its fine for about 2k miles. I did this 3 times on a set of 9s before I just decided to change them but they were still going strong. My method is to clean off the end with 2000 grit and then let them soak in carb cleaner overnight. Its totally works its not in my head because my car would hardly run before I cleaned them and it would be perfect after. pettit ecu every 2k miles on pfc have had the same plugs for 5k miles running great. Depends on the tune.

 

this is stupid, fouled plugs can cause a COMPLETE power loss

so there is no threshold where they cause "maximum" loss

edit: damn, just saw what turbojeff posted

 

Anyone care to comment on the platinum 9's as far as how easy it fouls compared to the regular plugs

thanks

 

Would it be possible the car would produce normal peak TQ numbers but then because of breakup at top you'd loose some peak HP ?

That may be the case with my dyno measurement (250rwhp at 260tq)

 

Remove your plugs and you will loose 100% power.

 

I have had plugs fouled so bad the car would not start. As soon as I put new ones in it started up.

 

I just change my plugs like everytime i change my oil. Every time i change the plugs i can see that they are in pretty ruff shape. I always feel a difference after i change the plugs.

 

Man...that must be pretty expensive to change them everytime you change the oil.

 

That seems a bit excessive.

 

Frequent plug changes on a turbocharged rotary is a good thing however you should not be going through plugs with each oil change. Even one set every other oil change is pretty frequent...I change mine once a year (about 8K per year in my FC). There are lots of things to take into account for plugs wearing out prematurely...first is detonation and we all know how easily an FD or FC can ping. This will wear the electrodes very quickly so make sure the car is running correctly (dyno + wideband). Another thing to take into account is what you are feeding your car in terms of fuel and oil...additives to either generally cause a bit of buildup on spark plugs and many many gas stations put additives in your fuel at the station. Then there is the ignition system...a simple amplifier like an MSD 6A actually goes a long way in terms of plug life and IMHO is a better choice than the WAY expensive HKS twinfire or even the jacobs rotary pack.

 

I used to change my plugs every other oil chang ebut that was in a piston car and the plugs were a little over a buck a piece. I'm looking forward to using dino juice in my FD rather than Mobil 1 as in my other cars.

Also what plugs are suggested for use in street driving with the stock twins, full 3" exhaust with highflow cat, PFS purple ECU, large street port...

 

i've lost 4-5 mph in the 1/8th mile because of bad plugs before. same as jason, i've had the car not even want to start before because of the them. i usually have to change my plugs every 5k miles, but i use the copper ones instead of platinum

 

i change my oil about every 2k miles. Im running a T78 and im tuned for 19 psi (although i rarely go above 13 psi). I do a lot of hard driving and i only put about 4k miles a year on the 7. I dont see how 2 sets of spark plugs a year is really gonna break me, considering all the money i have invested in the car already . Plus i change them myself, they are really easy. Trust me when i say changing your spark plugs often keeps your performance numbers up to par.

Adam

 

 

4CN Air: NGK 5255 BUR9EQP

 

i kinda agree above with the guy that said he changes his plugs each oil change.. lets say you change your oil every 2000 miles..a ngk plug goes for what now? 10 bucks (well where i get mine) so thats 4 all together ( F U to you 20b guys ) but anyway, thats 40 bucks added to your oil change which is like another 20 call it.. thats 60 bucks every 2000 miles.. why not? sure its not really necessary but is it worth it? YEAH

will it cause harm? no

so whats the big deal, its actually helping the car cause its fresh..

 

Or you could save some money and clean them good with this

Cleans the most fouled plugs in about 30 seconds. Then just wash them off and dry them. They look brand new.

 

I gave up on stock plugs along time ago. I use NGK b10egi's they are so much better.

Chris