Non-Factory Spark Plug Gap Setting
 

Hi All,
Well, I'm almost done with the engine swap and got my built-up V8 in the
Jeep. I got to thinking and have a quick question. After modifying the
ignition system, is there any logical method or rule of thumb for changing
the factory-recommended spark plug gap? I did a lot of hot rodding and a
few drag races when I was a kid but there's gotta be a better approach than,
"Let's open the gap a little more and see how it does."
Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other than
they were from an '86 Vette and I couldn't have 'em:), I'd appreciate that
as well. I think the head casting number is 462624 and the flow could be
better.
Best Regards,
Jim
P.S. I know the Jeep's not a hot rod and don't intend to ever drive it like
that. But, when the guy I asked the TPI about said, "There's no way in hell
you can do what you're talkin' about; TPI, computer, to That transmission in
a thirty year old Jeep? You don't know what you're doin'. No way." I had
no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Hi Drink,
Your head casting number: 462624, is for and '75 to '86, 350"/400"
76 cc chamber 1.72", and 1.94" or 2.02" valves:
http://www.mortec.com/castnum.htm That's pretty low compression, so I
would use the stock gap of .o45" unless you bought a cam and a way for
it to breath, (bigger than Throttle Port Injection) and can turn it
tighter than stock.
If you take .060" off the head and .080" of it's intake ports, you
may get another compression, maybe up to nine to one:
http://www.----------.com/shaveHead.jpg
God Bless America, ßill O|||||||O
mailto:--------------------

Drink wrote:
>
> Hi All,
> Well, I'm almost done with the engine swap and got my built-up V8 in the
> Jeep. I got to thinking and have a quick question. After modifying the
> ignition system, is there any logical method or rule of thumb for changing
> the factory-recommended spark plug gap? I did a lot of hot rodding and a
> few drag races when I was a kid but there's gotta be a better approach than,
> "Let's open the gap a little more and see how it does."
> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other than
> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate that
> as well. I think the head casting number is 462624 and the flow could be
> better.
> Best Regards,
> Jim
> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it like
> that. But, when the guy I asked the TPI about said, "There's no way in hell
> you can do what you're talkin' about; TPI, computer, to That transmission in
> a thirty year old Jeep? You don't know what you're doin'. No way." I had
> no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Hi Drink,
Your head casting number: 462624, is for and '75 to '86, 350"/400"
76 cc chamber 1.72", and 1.94" or 2.02" valves:
http://www.mortec.com/castnum.htm That's pretty low compression, so I
would use the stock gap of .o45" unless you bought a cam and a way for
it to breath, (bigger than Throttle Port Injection) and can turn it
tighter than stock.
If you take .060" off the head and .080" of it's intake ports, you
may get another compression, maybe up to nine to one:
http://www.----------.com/shaveHead.jpg
God Bless America, ßill O|||||||O
mailto:--------------------

Drink wrote:
>
> Hi All,
> Well, I'm almost done with the engine swap and got my built-up V8 in the
> Jeep. I got to thinking and have a quick question. After modifying the
> ignition system, is there any logical method or rule of thumb for changing
> the factory-recommended spark plug gap? I did a lot of hot rodding and a
> few drag races when I was a kid but there's gotta be a better approach than,
> "Let's open the gap a little more and see how it does."
> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other than
> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate that
> as well. I think the head casting number is 462624 and the flow could be
> better.
> Best Regards,
> Jim
> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it like
> that. But, when the guy I asked the TPI about said, "There's no way in hell
> you can do what you're talkin' about; TPI, computer, to That transmission in
> a thirty year old Jeep? You don't know what you're doin'. No way." I had
> no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Hi Drink,
Your head casting number: 462624, is for and '75 to '86, 350"/400"
76 cc chamber 1.72", and 1.94" or 2.02" valves:
http://www.mortec.com/castnum.htm That's pretty low compression, so I
would use the stock gap of .o45" unless you bought a cam and a way for
it to breath, (bigger than Throttle Port Injection) and can turn it
tighter than stock.
If you take .060" off the head and .080" of it's intake ports, you
may get another compression, maybe up to nine to one:
http://www.----------.com/shaveHead.jpg
God Bless America, ßill O|||||||O
mailto:--------------------

Drink wrote:
>
> Hi All,
> Well, I'm almost done with the engine swap and got my built-up V8 in the
> Jeep. I got to thinking and have a quick question. After modifying the
> ignition system, is there any logical method or rule of thumb for changing
> the factory-recommended spark plug gap? I did a lot of hot rodding and a
> few drag races when I was a kid but there's gotta be a better approach than,
> "Let's open the gap a little more and see how it does."
> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other than
> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate that
> as well. I think the head casting number is 462624 and the flow could be
> better.
> Best Regards,
> Jim
> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it like
> that. But, when the guy I asked the TPI about said, "There's no way in hell
> you can do what you're talkin' about; TPI, computer, to That transmission in
> a thirty year old Jeep? You don't know what you're doin'. No way." I had
> no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Thanks Bill. I've looked through several cast number charts and have
found about three different stories. One site said "58cc chamber/305
head/'76-'78/not enough flow for larger cid engines" and another echoed your
info. Even still, that site said "1.94 in/ 1.50 exh" valves. Having a real
time trying to get multiple sources to agree but have slowly figured out
some of the errors.
I've a 273/282 cam in it and was gonna go with .035-.040 gap on the spark
plugs but got to wondering if I can present a better spark by opening it up.
..045 sounds better if you think it's not too much.
Thanks again for the tip.
Jim

"L.W. ("ßill") ------ III" <----------@cox.net> wrote in message
news:4169F17D.507E8CCA@cox.net...
> Hi Drink,
> Your head casting number: 462624, is for and '75 to '86, 350"/400"
> 76 cc chamber 1.72", and 1.94" or 2.02" valves:
> http://www.mortec.com/castnum.htm That's pretty low compression, so I
> would use the stock gap of .o45" unless you bought a cam and a way for
> it to breath, (bigger than Throttle Port Injection) and can turn it
> tighter than stock.
> If you take .060" off the head and .080" of it's intake ports, you
> may get another compression, maybe up to nine to one:
> http://www.----------.com/shaveHead.jpg
> God Bless America, ßill O|||||||O
> mailto:--------------------
>
> Drink wrote:
>>
>> Hi All,
>> Well, I'm almost done with the engine swap and got my built-up V8 in
>> the
>> Jeep. I got to thinking and have a quick question. After modifying the
>> ignition system, is there any logical method or rule of thumb for
>> changing
>> the factory-recommended spark plug gap? I did a lot of hot rodding and a
>> few drag races when I was a kid but there's gotta be a better approach
>> than,
>> "Let's open the gap a little more and see how it does."
>> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other
>> than
>> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate
>> that
>> as well. I think the head casting number is 462624 and the flow could be
>> better.
>> Best Regards,
>> Jim
>> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it
>> like
>> that. But, when the guy I asked the TPI about said, "There's no way in
>> hell
>> you can do what you're talkin' about; TPI, computer, to That transmission
>> in
>> a thirty year old Jeep? You don't know what you're doin'. No way." I
>> had
>> no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Thanks Bill. I've looked through several cast number charts and have
found about three different stories. One site said "58cc chamber/305
head/'76-'78/not enough flow for larger cid engines" and another echoed your
info. Even still, that site said "1.94 in/ 1.50 exh" valves. Having a real
time trying to get multiple sources to agree but have slowly figured out
some of the errors.
I've a 273/282 cam in it and was gonna go with .035-.040 gap on the spark
plugs but got to wondering if I can present a better spark by opening it up.
..045 sounds better if you think it's not too much.
Thanks again for the tip.
Jim

"L.W. ("ßill") ------ III" <----------@cox.net> wrote in message
news:4169F17D.507E8CCA@cox.net...
> Hi Drink,
> Your head casting number: 462624, is for and '75 to '86, 350"/400"
> 76 cc chamber 1.72", and 1.94" or 2.02" valves:
> http://www.mortec.com/castnum.htm That's pretty low compression, so I
> would use the stock gap of .o45" unless you bought a cam and a way for
> it to breath, (bigger than Throttle Port Injection) and can turn it
> tighter than stock.
> If you take .060" off the head and .080" of it's intake ports, you
> may get another compression, maybe up to nine to one:
> http://www.----------.com/shaveHead.jpg
> God Bless America, ßill O|||||||O
> mailto:--------------------
>
> Drink wrote:
>>
>> Hi All,
>> Well, I'm almost done with the engine swap and got my built-up V8 in
>> the
>> Jeep. I got to thinking and have a quick question. After modifying the
>> ignition system, is there any logical method or rule of thumb for
>> changing
>> the factory-recommended spark plug gap? I did a lot of hot rodding and a
>> few drag races when I was a kid but there's gotta be a better approach
>> than,
>> "Let's open the gap a little more and see how it does."
>> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other
>> than
>> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate
>> that
>> as well. I think the head casting number is 462624 and the flow could be
>> better.
>> Best Regards,
>> Jim
>> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it
>> like
>> that. But, when the guy I asked the TPI about said, "There's no way in
>> hell
>> you can do what you're talkin' about; TPI, computer, to That transmission
>> in
>> a thirty year old Jeep? You don't know what you're doin'. No way." I
>> had
>> no choice:) I'm sure it'll manage the trails just fine.

Re: Non-Factory Spark Plug Gap Setting
 

Thanks Bill. I've looked through several cast number charts and have
found about three different stories. One site said "58cc chamber/305
head/'76-'78/not enough flow for larger cid engines" and another echoed your
info. Even still, that site said "1.94 in/ 1.50 exh" valves. Having a real
time trying to get multiple sources to agree but have slowly figured out
some of the errors.
I've a 273/282 cam in it and was gonna go with .035-.040 gap on the spark
plugs but got to wondering if I can present a better spark by opening it up.
..045 sounds better if you think it's not too much.
Thanks again for the tip.
Jim

"L.W. ("ßill") ------ III" <----------@cox.net> wrote in message
news:4169F17D.507E8CCA@cox.net...
> Hi Drink,
> Your head casting number: 462624, is for and '75 to '86, 350"/400"
> 76 cc chamber 1.72", and 1.94" or 2.02" valves:
> http://www.mortec.com/castnum.htm That's pretty low compression, so I
> would use the stock gap of .o45" unless you bought a cam and a way for
> it to breath, (bigger than Throttle Port Injection) and can turn it
> tighter than stock.
> If you take .060" off the head and .080" of it's intake ports, you
> may get another compression, maybe up to nine to one:
> http://www.----------.com/shaveHead.jpg
> God Bless America, ßill O|||||||O
> mailto:--------------------
>
> Drink wrote:
>>
>> Hi All,
>> Well, I'm almost done with the engine swap and got my built-up V8 in
>> the
>> Jeep. I got to thinking and have a quick question. After modifying the
>> ignition system, is there any logical method or rule of thumb for
>> changing
>> the factory-recommended spark plug gap? I did a lot of hot rodding and a
>> few drag races when I was a kid but there's gotta be a better approach
>> than,
>> "Let's open the gap a little more and see how it does."
>> Engine in question is an '86 Chevy 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 as compared to Vette heads (Sorry, no further info on those other
>> than
>> they were from an '86 Vette and I couldn't have 'em:), I'd appreciate
>> that
>> as well. I think the head casting number is 462624 and the flow could be
>> better.
>> Best Regards,
>> Jim
>> P.S. I know the Jeep's not a hot rod and don't intend to ever drive it
>> like
>> that. But, when the guy I asked the TPI about said, "There's no way in
>> hell
>> you can do what you're talkin' about; TPI, computer, to That transmission
>> in
>> a thirty year old Jeep? You don't know what you're doin'. No way." I
>> had
>> no choice:) I'm sure it'll manage the trails just fine.