This spark plug heat too cold?
Thread Starter
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
This spark plug heat too cold?
I have been using Autolite Racing AR3934 plugs gapped at .045" per recommendation from part guy (circle track racer). I cannot hear any signs of detonation or preigntion, but I think it is running too rich.
The plugs are blackish, its kind of "baked-on" and doesn't wipe off easily. The insulator has some white on it, but is still black-ish.
Could this plug be too cold?
I am at ~3500ft elevation, running a Mighty Demon 750 with 74/83 jets.
Compression ratio is 10.4:1 with .049" quench.
Thanks!
:cheers:
The plugs are blackish, its kind of "baked-on" and doesn't wipe off easily. The insulator has some white on it, but is still black-ish.
Could this plug be too cold?
I am at ~3500ft elevation, running a Mighty Demon 750 with 74/83 jets.
Compression ratio is 10.4:1 with .049" quench.
Thanks!
:cheers:
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Re: This spark plug heat too cold? (VETDRMS)
Spark plugs are the last item to tune. A plug too cold for the street may be just fine for racing at WOT. Or maybe I should have said a plug that works well racing at WOT can be too cold for the street. I’ll admit I’ve never dialed my plugs in but have tried a little. Once ignition and carb is tuned then start using colder plugs just one step/number at a time. Keep testing until you still have a dry plug with the color you want. Lots of plug changes and not much fun. :banghead:
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Re: This spark plug heat too cold? (VETDRMS)
The 3934 is a non-extended tip/non-resistor plug and it is very cold for a low compression engine. While that is good for a race car it is not good on a street driven car.
If you what to stay with a non-extended tip/ non-resistor plug I would recomend the Autolight 393 but it has a 3/4 hex rather than a 5/8 so you will have to make sure you have clearance.
Personally on a street driven motor I would recomend an extended tip resistor plug. It will be a much cleaner burning plug. I would recomend an Autolite 3923 or 3924 for your compression. You did not say how you got to 10.4 compression but if you used a dome piston you will have to check for clearence with the extended tip. With a small dome you should be fine but should always check.
If you what to stay with a non-extended tip/ non-resistor plug I would recomend the Autolight 393 but it has a 3/4 hex rather than a 5/8 so you will have to make sure you have clearance.
Personally on a street driven motor I would recomend an extended tip resistor plug. It will be a much cleaner burning plug. I would recomend an Autolite 3923 or 3924 for your compression. You did not say how you got to 10.4 compression but if you used a dome piston you will have to check for clearence with the extended tip. With a small dome you should be fine but should always check.
Thread Starter
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Re: This spark plug heat too cold? (Pete79L82)
Pete79L82 Thanks for the good information. :yesnod: I thought this was probably a little too cool for my application, however the car has been running very good.
The compression is actually 10.25:1. (my bad)
I forgot that we went with a .010 deck height instead of a .005" deck height
(10.25 vs 10.37)
74cc Chamber
Bore: 4.155
Stroke: 3.75
Gasket thickness: .039
Deck Height: .010
2V Relief Flat Tops: 5cc
Gasket Bore: 4.200
CR: 10.25:1
Makes me wish I would have gone with the .005 deck height. :smash:
The motor will be street driven, but will see a lot of track time this spring. Would a swap be worth it?...as easy as it is. I also plan on installing a 100-150 shot of N20...
You've always had great advice in a lot of threads i've read, thanks for sharing the knowledge. :yesnod: :cheers:
[Modified by VETDRMS, 6:47 PM 10/26/2003]
[Modified by VETDRMS, 6:48 PM 10/26/2003]
The compression is actually 10.25:1. (my bad)
I forgot that we went with a .010 deck height instead of a .005" deck height
(10.25 vs 10.37)
74cc Chamber
Bore: 4.155
Stroke: 3.75
Gasket thickness: .039
Deck Height: .010
2V Relief Flat Tops: 5cc
Gasket Bore: 4.200
CR: 10.25:1
Makes me wish I would have gone with the .005 deck height. :smash:
The motor will be street driven, but will see a lot of track time this spring. Would a swap be worth it?...as easy as it is. I also plan on installing a 100-150 shot of N20...
You've always had great advice in a lot of threads i've read, thanks for sharing the knowledge. :yesnod: :cheers:
[Modified by VETDRMS, 6:47 PM 10/26/2003]
[Modified by VETDRMS, 6:48 PM 10/26/2003]
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Re: This spark plug heat too cold? (VETDRMS)
I thought this was probably a little too cool for my application, however the car has been running very good.
The heat range of a plug will not change the performance of a motor. If the plug is to cold the electrode will not stay hot enough to burn off any contaminates which will cause it to foul easily. It the plug is to hot the electrode will overheat and start to deteriate rapidly. The heat range you are running now is the range I use in 14.0-1 compression motors. It is to cold for your compression even when you run at the track. But I would recomend using it when you use the N2O.
Pete
Thread Starter
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Re: This spark plug heat too cold? (Pete79L82)
I thought this was probably a little too cool for my application, however the car has been running very good.
The heat range of a plug will not change the performance of a motor.
The heat range of a plug will not change the performance of a motor.
I will try the 3923 plug, and see how they look after a few 100 miles.
Thanks!
