Projected nose plugs in the RENIX

Looking for some input from knowledgeable spark pluggers -

A regular plug for a 90 RENIX is a NGK FR5 (7373.) Hohum, runs ok does the job. For the 92 its a projected nose design FR5-1 (7252) which is also what the 2.5 uses. The projected nose is .200" longer after surveying Autolite and Champions, too.

My question - why not use them in the 90? The heads on 90, 92HO, 96, etc are using the same reach and thread. Are the chamber differences that much? The pistons are all flat tops, right? And the plugs go in relatively sideways.

Projected nose plugs are one of the old school power improvements to get wider heat range capability in the engine for better running. Since the factory spec'd them for the 92 up and 4 cylinder, I speculate there's a benefit for us, too.

Observations?

I'm surprised 5-90 hasn't been in on this.

Spark plug tip placement has everything to do with how the valves are arranged in the head. The manufacturer places the spark plugs in a place where it can most efficiently ignite the air fuel mixture. My feeling is you can't likely gain anything from relocating them. The one thing you can do though is to index them to put the ground electrode in the same position in each cylinder making for consistant combustion between cylinders. There probably isn't anything to gain from that in a stock engine though.

I believe I used Renix (7373) plugs when I first got the '93 motor, and it ran. Though I bought the 7252's soon after, and once since then. I don't remember differences, and it's really not worth a set of plugs to me to try it again.

The projected nose design just moves the actual spark gap .200" further into the chamber. There may not be any potential - they existed for the 2.5, and the factory may have moved on past them due to some Renix quirk. They did go to them later.

Reading Gordon Jennings article on plugs, heat ranges, etc. brings up the issue that no one maker has a lock on the perfect heat range for an engine. Swapping around at plug change times may get you a better application, or not be anything special.

I've got a set coming in, it's been three years on the last set. I imagine I may need new ones and saw an opportunity.

Update FYI - installed the plugs, runs like it has new plugs. Adjusting the TPS and getting a tank of gas seemed to do more, so I can't say they would be worth the effort at startup. Long term may or may not be worth it, like slipkid says.

They do fit without interference, and the aux gap in the plug hasn't been a issue. For the same price, there's nothing lost in trying. I used the later model ones for a '04 GC, ZFR5N.

With the TPS adjust (before the plugs,) it has run a lot better that even before I replaced it. The idle rpm's are a little lower, as others have noted, and the slight hesitation (bogging, power loss, off the cam feeling?) has been markedly reduced under 2800 rpm. There's a smoother transition to high power over 3000 - but still a step, like another two barrels slowly tipping in. It gives the feeling of much better acceleration.

I might go up against the new 300 hp V6 Camaro at work, before he breaks it in and the new wears off. It's my only chance . . .

TiRod said:

I might go up against the new 300 hp V6 Camaro .

Click to expand...

Really 300hp? makes my LS1 seem like a real piece o crap!:scared: