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Non-Factory Spark Plug Gap Setting
Hi All,
Quick question: After modifying the ignition system, is there any logical method or rule of thumb for changing the factory-recommended spark plug gap? Engine in question is an '86 Corvette 350cid V8 engine with [305 heads] TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug wires. If anyone can shed more light on the effects of the 305 V8 on the 350 block, I'd appreciate that as well. I think the head casting number is 62426. Best Regards, Jim |
"Drink" > wrote in message ... > Hi All, > Quick question: After modifying the ignition system, is there any > logical method or rule of thumb for changing the factory-recommended spark > plug gap? > Engine in question is an '86 Corvette 350cid V8 engine with [305 heads] > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug > wires. > If anyone can shed more light on the effects of the 305 V8 on the 350 > block, I'd appreciate that as well. I think the head casting number is > 62426. > Best Regards, > Jim Any additional gap will depend on whether or not you can produce the voltage required to jump the gap and still maintain a strong spark. If you think you have that available open it up a bit and try it. Not as good as knowing what results you will get because of the work required to take them out and regap. Go to some of the after market ignition sites and see what they recommend and at what voltage level. -- Dad 05 C6 Silver/Red 6spd Z51 72 Shark Black/Black/4spd |
"Drink" > wrote in message ... > Hi All, > Quick question: After modifying the ignition system, is there any > logical method or rule of thumb for changing the factory-recommended spark > plug gap? > Engine in question is an '86 Corvette 350cid V8 engine with [305 heads] > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug > wires. > If anyone can shed more light on the effects of the 305 V8 on the 350 > block, I'd appreciate that as well. I think the head casting number is > 62426. > Best Regards, > Jim Any additional gap will depend on whether or not you can produce the voltage required to jump the gap and still maintain a strong spark. If you think you have that available open it up a bit and try it. Not as good as knowing what results you will get because of the work required to take them out and regap. Go to some of the after market ignition sites and see what they recommend and at what voltage level. -- Dad 05 C6 Silver/Red 6spd Z51 72 Shark Black/Black/4spd |
When standard points ignitions were the norm, voltage was about 15,000 to
30,000, depending on who you asked. Gap was .035". When HEI began, there was 60,000 volts and the gap was .060" HEI dropped to 45,000 for reliability and the gap went to .045". See a vague pattern? If you want to check, set up one plug wire and a plug outside the engine where you can see it. Start the engine and let it run at various RPMs and see what the spark looks like. A good solid spark that is blue in color should give you good ignition. Shut off the engine and open the gap some. (Or set up a video camera and don't shut off the engine.) Do this a few times and also try closing the gap. When you find the strongest spark for the widest gap, go for it. The idea is that a wider gap exposes more spark and thus more initial flame to the air/fuel mixture. However, you need a strong spark to break through the mix and to ignite it. So you have a compromise of wide gap and hottest spark. "Dad" > wrote in message ... > > "Drink" > wrote in message > ... > > Hi All, > > Quick question: After modifying the ignition system, is there any > > logical method or rule of thumb for changing the factory-recommended spark > > plug gap? > > Engine in question is an '86 Corvette 350cid V8 engine with [305 heads] > > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug > > wires. > > If anyone can shed more light on the effects of the 305 V8 on the 350 > > block, I'd appreciate that as well. I think the head casting number is > > 62426. > > Best Regards, > > Jim > Any additional gap will depend on whether or not you can produce the voltage > required to jump the gap and still maintain a strong spark. > > If you think you have that available open it up a bit and try it. Not as > good as knowing what results you will get because of the work required to > take them out and regap. Go to some of the after market ignition sites and > see what they recommend and at what voltage level. > -- > Dad > 05 C6 Silver/Red 6spd Z51 > 72 Shark Black/Black/4spd > > > |
When standard points ignitions were the norm, voltage was about 15,000 to
30,000, depending on who you asked. Gap was .035". When HEI began, there was 60,000 volts and the gap was .060" HEI dropped to 45,000 for reliability and the gap went to .045". See a vague pattern? If you want to check, set up one plug wire and a plug outside the engine where you can see it. Start the engine and let it run at various RPMs and see what the spark looks like. A good solid spark that is blue in color should give you good ignition. Shut off the engine and open the gap some. (Or set up a video camera and don't shut off the engine.) Do this a few times and also try closing the gap. When you find the strongest spark for the widest gap, go for it. The idea is that a wider gap exposes more spark and thus more initial flame to the air/fuel mixture. However, you need a strong spark to break through the mix and to ignite it. So you have a compromise of wide gap and hottest spark. "Dad" > wrote in message ... > > "Drink" > wrote in message > ... > > Hi All, > > Quick question: After modifying the ignition system, is there any > > logical method or rule of thumb for changing the factory-recommended spark > > plug gap? > > Engine in question is an '86 Corvette 350cid V8 engine with [305 heads] > > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug > > wires. > > If anyone can shed more light on the effects of the 305 V8 on the 350 > > block, I'd appreciate that as well. I think the head casting number is > > 62426. > > Best Regards, > > Jim > Any additional gap will depend on whether or not you can produce the voltage > required to jump the gap and still maintain a strong spark. > > If you think you have that available open it up a bit and try it. Not as > good as knowing what results you will get because of the work required to > take them out and regap. Go to some of the after market ignition sites and > see what they recommend and at what voltage level. > -- > Dad > 05 C6 Silver/Red 6spd Z51 > 72 Shark Black/Black/4spd > > > |
Gents,
Just wanted to thank the both of you for your advice. Very good stuff and much appreciated. Best Regards, Jim "Tom in Missouri" > wrote in message ink.net... > When standard points ignitions were the norm, voltage was about 15,000 to > 30,000, depending on who you asked. Gap was .035". > > When HEI began, there was 60,000 volts and the gap was .060" > > HEI dropped to 45,000 for reliability and the gap went to .045". > > See a vague pattern? > > If you want to check, set up one plug wire and a plug outside the engine > where you can see it. Start the engine and let it run at various RPMs and > see what the spark looks like. A good solid spark that is blue in color > should give you good ignition. > > Shut off the engine and open the gap some. (Or set up a video camera and > don't shut off the engine.) > > Do this a few times and also try closing the gap. When you find the > strongest spark for the widest gap, go for it. The idea is that a wider > gap > exposes more spark and thus more initial flame to the air/fuel mixture. > However, you need a strong spark to break through the mix and to ignite > it. > So you have a compromise of wide gap and hottest spark. > > > "Dad" > wrote in message > ... >> >> "Drink" > wrote in message >> ... >> > Hi All, >> > Quick question: After modifying the ignition system, is there any >> > logical method or rule of thumb for changing the factory-recommended > spark >> > plug gap? >> > Engine in question is an '86 Corvette 350cid V8 engine with [305 >> > heads] >> > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug >> > wires. >> > If anyone can shed more light on the effects of the 305 V8 on the 350 >> > block, I'd appreciate that as well. I think the head casting number is >> > 62426. >> > Best Regards, >> > Jim >> Any additional gap will depend on whether or not you can produce the > voltage >> required to jump the gap and still maintain a strong spark. >> >> If you think you have that available open it up a bit and try it. Not as >> good as knowing what results you will get because of the work required >> to >> take them out and regap. Go to some of the after market ignition sites >> and >> see what they recommend and at what voltage level. >> -- >> Dad >> 05 C6 Silver/Red 6spd Z51 >> 72 Shark Black/Black/4spd >> >> >> > |
Gents,
Just wanted to thank the both of you for your advice. Very good stuff and much appreciated. Best Regards, Jim "Tom in Missouri" > wrote in message ink.net... > When standard points ignitions were the norm, voltage was about 15,000 to > 30,000, depending on who you asked. Gap was .035". > > When HEI began, there was 60,000 volts and the gap was .060" > > HEI dropped to 45,000 for reliability and the gap went to .045". > > See a vague pattern? > > If you want to check, set up one plug wire and a plug outside the engine > where you can see it. Start the engine and let it run at various RPMs and > see what the spark looks like. A good solid spark that is blue in color > should give you good ignition. > > Shut off the engine and open the gap some. (Or set up a video camera and > don't shut off the engine.) > > Do this a few times and also try closing the gap. When you find the > strongest spark for the widest gap, go for it. The idea is that a wider > gap > exposes more spark and thus more initial flame to the air/fuel mixture. > However, you need a strong spark to break through the mix and to ignite > it. > So you have a compromise of wide gap and hottest spark. > > > "Dad" > wrote in message > ... >> >> "Drink" > wrote in message >> ... >> > Hi All, >> > Quick question: After modifying the ignition system, is there any >> > logical method or rule of thumb for changing the factory-recommended > spark >> > plug gap? >> > Engine in question is an '86 Corvette 350cid V8 engine with [305 >> > heads] >> > TPI, HEI ignition, headers, high voltage coil, "performance" 8mm plug >> > wires. >> > If anyone can shed more light on the effects of the 305 V8 on the 350 >> > block, I'd appreciate that as well. I think the head casting number is >> > 62426. >> > Best Regards, >> > Jim >> Any additional gap will depend on whether or not you can produce the > voltage >> required to jump the gap and still maintain a strong spark. >> >> If you think you have that available open it up a bit and try it. Not as >> good as knowing what results you will get because of the work required >> to >> take them out and regap. Go to some of the after market ignition sites >> and >> see what they recommend and at what voltage level. >> -- >> Dad >> 05 C6 Silver/Red 6spd Z51 >> 72 Shark Black/Black/4spd >> >> >> > |
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