Best spark plugs for the 575SCi?
 

I am looking for opinions on spark plug manufacturers for the Mercury Racing 575 SCi. I am currently using an NGK R5673-8, but just had 2 of them fail at about 40 hours of use. I was expecting to get a little more time out of them. What are you all running in your 575's? Thank you for the feedback.

The plugs you are running are too cold. With NGK plugs, the higher the number, the colder it is. You should be running a 7 series plug. In you case, NGK R5673-7.
Eddie

Eddie Merc is still recommending R5673-8 thru out all 575 sci engine serial runs. Just wondering is plug fouling the issue as to why you are saying -7 instead of 8. Thank you for your time

Will post this as well we have seen a few bad plugs coming from NGK as of this year that have never been experiencing before. Not large amounts but one here and there.

Factory plug is the NGK R5673-8. Merc# is 33 - 8134214

That's all I have for info. Have done nothing with these motors other than some ported throttle bodies.

Edit in: BUP sent his post faster than me. LOL. Time for more coffee.

40 hrs.....that's great :D I have run both the NGK and MR41T plugs (same same) Recently I started using the AC R42TS plugs (1 range higher AC, 2 higher NGK) and it seems to be a lot better. However, I chickened out before a recent poker run and put some NGK-8s back in cause I knew I would be WOT all day :D

It may not be just the plugs, the stock tune startup enrichment is retarded, AFR from 8-9 until fully warm. The stock tune is rich all around. Also scan for intermittent engine coolant temp and MAP sensors issues. I have had one of each over the years, not enough for the code, just readings that didn't make sense. Both issues caused fouled plugs.

I hear you I don't feel like working on boats today but will have to and I don't drink coffee.

Great plug cross chart here http://www.dragstuff.com/techarticle...reference.html

I dont have 575s but im running NGK 8s in my blower motors with just shy of a hundred hours so far

The last set of 575 SCI we did I used the R5674-8, it's a colder plug; but the center electrode is extended, instead of shrouded. Being the piston is inverted (dished) you can expose the spark into the chamber. I would worry more about the head gaskets burning out from heat, than running a colder colder plug. If you are fowling plugs at 40 hours, you need to start looking elsewhere. If being 2 plugs, better check ignition wires, sounds like a lead issue, unless you are seeing oil on spark plugs.

I've had much better luck with the 7's since those engines are so rich. As long as you are running the recommended 91 octane or better, you will have no issue at all with the 7's. It will run cleaner and is less likely to foul plugs at idle with the colder plugs. Now this only holds true for stock engines. In 4Bus's instance, he's changed pulleys (I believe), so it all depends on the boost he is running as to which plugs I would run.

As Mark (MER) mentioned, you may be in need of an ignition system tune up. If the plug wires are more than 3-4 yrs old, change them out. Same for the cap and rotor.
Eddie

And if you are running overly rich - fuel - fuel fouling on the spark plugs like Ron said - MAP, coolant temp, TPS sensor(s), weak ignition components, ,fuel pressure regulator, and finally the injectors. Stuck open and or pulse width too wide could be any of these areas where the problem lies.. Totally agree with the cap and rotor and now a days the coil as well. Coils do not last like they use to, even when properly mounted.

You have to remember that Mercury has to make that engine completely idiot proof. When that engine leaves Merc, they have no idea what half wit, dumb ass is going to get it and put 87 octane in it and run it on the wood. They would rather see you foul a plug than melt it down and them have to pay for it. Now, if you follow their directions and use 91 octane or higher, you can easily run the 7's with much better results (in a stock engine, which the OP has). The same reason applies to why it runs so rich. They have to set it up to where it is pretty much as bullet proof as it can be. Unfortunately, that doesn't always yield the best results. In this case, the 7 is a better choice.
Eddie

Yes you are correct about the octane requirement but we know how people also look at saving costs at the pumps as well. OMC & Volvo marine engines use to recommend 89 octane and most did not followed that either, then you would get the guy in wondering why his motor is having issues with cylinder / piston problems, especially with the crappy gas today. Even E-0 is crappy at the pumps.

You got that right

One other thing to consider. A 500 efi runs 6's. It makes 470 hp at the prop. A 575 makes 525 at the prop. Does going up 50 hp, on basically the same long block, warrant using 2 heat ranges colder? I realize that they have different cams, but the 575 also have 1.25:1 less compression than the 500.
Eddie

All this talk makes me think I should change my wires. They're stock from 2002 with over 400 hours on them. Stock coils and program too. I've changed the cap/rotor/plugs 3 times and just use the stock stuff/gap. Boat still runs the same MPH as when the engines were redone 200 hours ago. It does feel crisper when I put new plugs in. I've had 2 injectors go wide open above idle but only noticed that because of the difference in fuel consumption from L to R engine, er, I mean S to P.
Sounds like a winter project. Woohoo, 110 here I come.

Most already know this, supercharge engine = lower compression ratio and you are comparing Throttle body injection to multi port injection. TBI in a 2000's engine. A little behind in the tech area on that one.

Also forgot the 575 SCi has IAT (intake air temp) sensor that also can cause rich running conditions / spark plug fouling related problems.

Whoa....tell me more about the injector dumping off idle, I am having a similar problem (I think) on starboard right now

Maybe, but the bpw vs IAT enrichment table is so tiny on the ecu mapping I doubt anyone would notice

3.25 8lbs pulleys, full roller conversion, mls gaskets, arp studs, 120 stats, adjustable fuel regulators, and I tuned it using afr and mefi burn.

My stock afr numbers used to get in the low 9s under boost if I left it there. When my engine guy tore them down he suggested that I clean them up because he was seeing dangerous fuel wash. My oil was always black at 20hr oil change intervals stock, now it looks so clean at 20 hrs I want to out it in something else :D

I agree merc was trying to be super safe with this engine, and maybe even for the xr drive. The flat tappet cam was a joke in a gen 6 engine, very restrictive. Stock I would hold it wot for 30 miles and wouldn't even get a rise in oil or water temp. So much life to be found in these engines, and merc really missed with ecu tune IMO. So safe it was nearly unsafe :/

Mine has Ngk Y R5's with s pretty big gap. I am running msd's and chillers. I would hate to see the heat in 4bus motor w o the chillers. But mine never fouled a plug. My buddy said they are too much though. I am just worried about un burnt fuel. Arizona Speed set mine up.

Port and Star engines were getting to 5-7 gallons off on fill ups so I sent the injectors in. One would go max flow as soon as he started raising the pulse width. Another one dribbled a bit at idle, dirty, the rest were a little low on flow, dirty. Four years later, same thing. He said the Merc/Chev injectors are crazy expensive so he got some from a Volvo? Something like that. There's a slightly different ohm/impedance?, can't remember, but when run side by side with the other injectors they flow the same.

Other than the consumption discrepancy I didn't notice anything running.

The engines are slightly fat at idle but no soot build up, just a stumble off idle, be it 5 minute idle or an hour, trying to get on plane that clears up before I'm on plane. Then, to clean the plugs, I hammer the limiters. Mercs system kills fuel so it works great!
Haha kidding, stupid limiter design.

You're running a hot plug in a blower motor and you are worried about the heat in my engines?

The cool northeast air, col lake waters, and my 120 degree stats are my chillers :) I have recorded movies using tuner pro on very hot summer days on long sustained runs, no knock or timing retard, I'm ok with my set up :D

Split fire

Volvo on their TB injectors only were used in their highest offering 315 hp 5.7 350 GXI models back in 2001 thru 2003 or 04. They ran fuel pressure at 29 to 31 psi for that app. just some info.

Yea. Im running a hot plug in blower motor and i am worried about your set up. I know tha 250 blowers make lots of heat over 6 psi. Thats why i have chillers to keep the heat down. 250s make lots of iheat

IR temp gun, and knock sensor monitoring show no difference in the 3.5 in pulley to the 3.25 (6-8lbs). I am approaching 100 hrs with this set up, based off data I collected, not what I "heard".

When they Blow up like mine did you can REALLY wake them up- Alum heads- 509- full roller- smaller pulley- SMITH POWER and then Young Tune -- Yea Baby!

Great discussion. Thanks for all the feedback. I replaced the two bad plugs and it runs great. My engines are stock and I am running 93 non-ethanol gas, so I will probably change to the -7s in the future.

When I was tuning drag cars I always used ngk plugs to "find" the tune as they would show the heat mark earlier than any other plug. BUT they wouldn't last 20 passes in a 13:1 motor with a .038 jet in a pro fogger, so once I got it where I wanted I switched to the cross ref auto lite racing plug

Now I read this....after getting 16 new R5673-8 plugs delivered yesterday.....LOL. All joking aside I have run these plugs with the 256 blowers and now with 8-71's
I have not had any bad ones but there is always a chance of getting one. I replace the cap and rotor every year and wires every 3 years.

that explanes why your blowers sound a little dufferent as far as the rpm sound. Sounds like your motors are turning tons of rpms. But uts just your blowers spinning faster.

It is safe to say a hotter plug is better. Un burned fuel will cuase fouling and inburnt fuel at higher rpms. But that is just what I have heard

Engines spin at 5800+, so it's not just the blowers. Are you just trying to get under my skin?

It's safe to say that? Says who? A hot plug is also a great way to burn a hole in the top of a piston of a supercharged engine that already makes higher egts than n/a. Maybe you should stick to sanding bottoms, rather than telling people that a plug 4 heat ranges hotter is safer. Unburied fuel should be handled with proper fuel air management, not with a plug hotter than then surface of the sun.

No i am not trying to get under your skn. My boat spins 5800 too but the rpm of the blower is different cause i have 3.5s. Just sounds different. My pistons look like brand new after 142 hours w yr5s. Stock 575 engines w intercoolers and msds

You can take any motor from any car and go 1 heat range higher and it wont hurt it. In the old days we did it to help the engine use less oil. Yea thats right . One heat range hotter actually cuts down on burning oil in some cases. I tried a set R5673 8s in one hour of use it fouled plugs. I guess my electronics and stuff are flowed for lots of fuel . My motors are stock though

thanks Rob for all the things you have posted over the years. You have helped a lot of us. And made a lot of us laugh :)

The guy who set my deal up told me the only thing he was worried about was fuel. No marina fuel at our lake was one of the things he stressed because of water could be in the fuel or something cause there tanks were old. Then im pretty sure he was atomit about burning all the fuel in the engine and it has yR5s in it since about 2008 and it has had no problem. He told me to just leave it like it is.And its fast. Kinda cool cause he did not reinvent the wheel. He just put chillers msds and did some dyno work to stock motors to gain about least 125 hp without even cracking an intake bolt! Pretty smart guy.

MCPRODESIGN - I disagree. The motor will tell you what heat range it wants. Not a catalog nor just sayying 1 hot range hotter than stock no matter what.

There's more to it than that.

ok i agree. Not all applications are the same. But we tried it in a few cars that burned oil and it helped.

But back to this discusion. Merc 575s sci's will live for years with Hotter plugs. Is a 250 blower really that much more than a na motor. Only the heat when you crank them up. A 250 is a supercharger but a pretty weak one. Now if i put a 671 on it. That would be serious blower. But i heard they dont make as much heat.