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QuantumMotorsports · 01-16-2001, 08:06 PM

Okay, so I've had a Non HO 5.0 in my cougar since it came from the factory. I recently put on HO heads (as well as other HO parts) and used the same spark plugs. I didn't even think that they might be different. Recently I went to get new plugs and got a set for a 91 Mustang since that is the year of car the heads came off of (I realize that they are an 87 casting and are the same, but anyway) the plugs for the mustang had about a half inch less threads. So basically the plugs I've been using stick a half inch farther into the cylinder. I was worried about clearance probs with the pistons or valves, but since I've been running them for a while, and the plugs look fine, I don't think there are any probs. Anyway, I went ahead and bought the Mustang plugs, put them in, ran the car (without changing anything else) and if felt like it had lost a step, throttle response wasn't as fast and it felt like especially on the low end it was not as strong. I went and bought a set of cougar plugs (longer) of the same brand, same temperature rating and all and put them in, it runs like it did before, much better than the stang plugs. I'm curious as to whether anyone else has done this. My theory is that when the spark is farther out in the chamber it spreads easier when the fuel ignites. If someone wants to experiment on a dyno. You might try running the cougar plugs. If you want I'll get a part # for you.

------------------
Michael Black
Quantum Motorsports
Norman, Oklahoma

1988 Merc Cougar 5.0 HO, P&Ped heads, 2.25" custom mandrel bent dual pipes, T5 five speed tranny
15.43 @ 91.08mph (not shabby for a 3600 pound car)
60' 2.453 Street tires suck!!!

01-16-2001, 08:06 PM	#1
QuantumMotorsports Registered Member Join Date: Jul 2000 Location: Norman, Oklahoma, USA Posts: 597	Wrong spark plugs helping performance? Okay, so I've had a Non HO 5.0 in my cougar since it came from the factory. I recently put on HO heads (as well as other HO parts) and used the same spark plugs. I didn't even think that they might be different. Recently I went to get new plugs and got a set for a 91 Mustang since that is the year of car the heads came off of (I realize that they are an 87 casting and are the same, but anyway) the plugs for the mustang had about a half inch less threads. So basically the plugs I've been using stick a half inch farther into the cylinder. I was worried about clearance probs with the pistons or valves, but since I've been running them for a while, and the plugs look fine, I don't think there are any probs. Anyway, I went ahead and bought the Mustang plugs, put them in, ran the car (without changing anything else) and if felt like it had lost a step, throttle response wasn't as fast and it felt like especially on the low end it was not as strong. I went and bought a set of cougar plugs (longer) of the same brand, same temperature rating and all and put them in, it runs like it did before, much better than the stang plugs. I'm curious as to whether anyone else has done this. My theory is that when the spark is farther out in the chamber it spreads easier when the fuel ignites. If someone wants to experiment on a dyno. You might try running the cougar plugs. If you want I'll get a part # for you. ------------------ Michael Black Quantum Motorsports Norman, Oklahoma 1988 Merc Cougar 5.0 HO, P&Ped heads, 2.25" custom mandrel bent dual pipes, T5 five speed tranny 15.43 @ 91.08mph (not shabby for a 3600 pound car) 60' 2.453 Street tires suck!!!