Tim

I just got my heads back from being machined for twin plugs, Im wondering if I should just get 6 more of the plugs I already use? or do I need to go to another heat range?

I know I have to use less ignition advance with the twin plug set up.

Also im thinking of having the a thermal barrier applied to the combustion chambers and piston domes, would this affect the heat range of the plugs I need and willl it affect the ignition advance that I have to use.

thanks fo any help.

BTW the engine is a 2.2 with all the racy mods you would expect 10.5:1 cr rad cams, etc

Steve Weiner-Rennsport Systems

Hi Tim:

First, heads can be machined for the street 14mm plugs or the RSR 12mm plugs. You'll need to get the plugs that fit,...

Heat range is determined by compression ratio, cam profile and operating RPM range. Sometimes fuel is a factor, too.

I would suggest the same heat range on the bottoms as the upper ones. You should use no more than 26-28 deg total advance with any twin-plug setup.

A thermal barrier will affect heat range and I'd suggest doing a series of plug cuts to check your mixture too, if you decide to do that.

Tim

Thanks Steve,

I opted to go for the 14mm plugs rather than the 12mm, it seemed like I had more options regarding heat ranges etc with the 14, Ive found with the narrow spacing of the head studs on the 2.2, I need to get some arp nuts to give clearance for the plug socket

Ive dry fit the plugs I use already (WR4DPO) and they are just flush with the surface of the combustion chamber, so no clearance issues either!!

I have decided to go with the thermal barrier on the heads, valve faces, and exhaust ports, I am planning on sending them to Swain Tech for coating, any comments? I had my headers done with jet-hot already, Ive only just discovered the other coatings people, one is in your neck of the woods if im correct

Tim

Juan Lopez

Tim,

How important/beneficial is the thermal coating?

As to the plugs, I have always used same plugs on either side (and 14MM) since my mechanic we had a lot more options.

We did install an electromitive after trying out several options (factory twin plug and 2-msd). Electromotive proved much more reliable once we worked out a problem with the pickup (it burned twice due to a clearance issue).

Let me know how it goes. Also, any ideas on the ultimate 2 liter engine. I have to rebuild my motor and I'm looking for the ultimate formula.

I am using the 906 you recommended!

Thanks/regards, Juan

Tim

Juan, Im still trying to get a read on the benefits of the thermal coatings, lots of people use them (porsche,F1, nascar) but not to many people talk about them.

Total cost to do my heads and valves is $300, Im hoping that there are some benefits, and NO detriments to having this done

Steve Weiner-Rennsport Systems

Hi Tim:

For street cars, the 12mm plugs are a limitation, but for race engines, its no issue,..

IMHO, your "4" heat range plugs are a little warm for a race plug. I'd use a 3 as long as you can open the gaps up to .040 (min), and back that up with a real good ignition like MSD, so you can use that gap without misfire.

Coatings do work,.......... Some parts get thermal barriers and some parts would get a thermal dispersant. Other items get anti-friction coatings. A lot of race engine builders do not tell the whole story to protect some of the work done for their clientel.

In most cases, many many hours were spent on an engine dyno with lots of expensive instrumentation to find out what works and what doesn't.