spark plug Q
 

I'm running a 509 with 10:1 compression, and Merlin aluminum heads.

I have trouble finding anything better then 91 octane, so I retard the timing a bit, and keep an eye on the plugs. So far everything seems good.

My Q is,
I am about to replace the bosch platinum plugs, and having a hard time finding them locally. So I started reading, and it seems the bosch platinum plugs, and not real well liked, even though I have had good luck with them so far in this motor, and my Mustang seems to really like them as well.

my plug has the # FR8DPX stamped on it. From what I read these don't do well with detonation. Should I use something else?

thnx
-Shane

I would a plug in the same heat range as an AC R42T. That is one step cooler than stock R43T's and not quite as cool as the R41T's that went in the Merc blower engines.

I'm running an NGK Iridium UR6IX and I'm planning on going to their racing plug with the cut back electrode to reduce the risk of detonation. I would recommend a -6 heat range in NGK. I have an MSD 6M ignition with the MSD Blaster HVC-2 coil, so no worries about fouling.

I used to run the Bosch plugs, most of the guys on the forums do not like them. I have been using the AC Rapid Fire #1's and had good luck with them.

I have had great success with accel u-groove plugs..can find them in varous heat ranges...ac's work well but can only find std heat ranges around here..

An NGK 6 heat rating is the same as an AC 43. He would be better off going to a 7 which is a little cooler.

Stock Plugs on Merc NA engines are AC MR43T or NGK BR6FS.
The M on the AC is for marine and is really not needed.

You're absolutely correct, I meant to type a -8 which is what I'll be running. That's what I get trying to eat lunch and read forums at the same time.

I've always ran r43t in everything else, and since I'm a "if its not broke, don't fix it" kinda person, I think I'll just go back to the AC delco's but run a 42.

I tried Bosch platinums in my 03 Cobra. Ended up detonating and blowing the plug out of the number 1 cylinder. Had it timeserted and ran cooler NGK plugs after that.. Liked NGK a lot better and worked a lot better. I know this was on a car, but still not a fan of Bosch platinum..

Well I should have done some checking before I bought the r42t's. they are different then the bosch platinum plugs that are in it now. I was worried about hurting something, so I didn't install them. The bosch plugs seemed like they were longer?

Head work was done by Jim V, and I have the paperwork at home.

Can anyone tell me what plugs i should use?
Heads are Aluminum Merlin. # WOR 014C

I have had great results with NGK BCPR6ES...Whats the timing @ ?
Info...8.0:1 CR with 6 PSI @ 32* timing. Also aluminum heads, no stat.

I've been running about 32-33 degrees of timing. Dist is locked.

10:1 compression 91 octane fuel, seems to be about the best I can get.

Perfect...try those,$2.99 each.

thanks.
would those be the equivelant to the Bosch Platinums I am running now. the motor runs really good, and I don't wanna mess anything up.

Its just a standard plug. Or if it runs good as is leave it.

I'm curious if the the plugs I'm running are too hot. My engine is 10:1 CR with AFR heads, Crane Hi-6 box and PS-92 coil. AFR's website suggested to start with Autolight AR3935, which is what I've been running. This is their racing plug and the hottest plug in this series. Should I cool it down with a cooler plug?

This is probably a dumb Q,
but will I notice a loss in power with a cooler plug?

No loss of power with a cooler plug.

Is it the threaded section that is shorter on the R42TS's??? That is most likely because of the Merlin heads. You don't need that exact plug. Just something in the same heat range.

Griff,
I had R42t's not the R42ts's, maybe that was the difference.

The R42T was noticably shorter threaded area then the Bosch's.

The threaded area is the same length. Only the tip sticks out a little more.

If I were you I would go to a water/alcohol injection to gaurd against det....