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Author Topic:   Spark Plug Gap
C2W
Dirt Full Roller

Total posts: 70
posted April 25, 2005 08:20 PM  
I am upgrading to a high output coil and module in my distributor. What kind of gap can I set on the plugs now that I am getting more spark?? Thanks.

redneck racing
Dirt Forum Champ
Total posts: 860
posted April 26, 2005 02:33 AM  
Not for sure but im thinking you can run about .060. Eddie

49mtmod
Dirt Maniac

Total posts: 127
posted April 26, 2005 02:45 PM  
Do a search for Steve Hendrens post on this subject. I believe his comment was something to the effect that he saw small gains on the dyno with larger gaps but saw huge losses when the gap was too much.

Even with a good ignition system we only go .035.


outlawstock17
Dirt Forum Champ
Total posts: 1363
posted April 26, 2005 06:31 PM  
yep, .035" max even with a good ignition. race gas is harder to fire than street gas and can snuff out a weaker spark that has to make a huge leap, causing a miss when the engine is loaded.

powerglides
Dirt Freak

Total posts: 374
posted April 28, 2005 09:41 AM  
.035 for me also. Good hei dist.

C2W
Dirt Full Roller

Total posts: 70
posted April 28, 2005 02:49 PM  
Thanks for the help guys.

crc1124
Dirt Maniac

Total posts: 143
posted April 28, 2005 05:51 PM  
Why only .035? Bone stock hei chevy is gapped at .045. I had an oldsmobile with the junk 307 and the gap on it stock was .060. I've always gapped mine at .045 with no problems. .035 sounds more like a points set up.

racer19x
Dirt Full Roller

Total posts: 26
posted April 28, 2005 09:06 PM  
We go with a loose .040 Accel HEI and coil

mikekuhlman
Dirt Full Roller

Total posts: 34
posted April 29, 2005 07:20 PM  
I run .045 never had a problem. good luck racing!

beachracing
Dirt Forum Racer

Total posts: 94
posted April 29, 2005 08:10 PM  
All manufactures had gap set for best fuel mileage, as well as epa standards, etc. Of course in racing, nobody cares about gas mileage unless it's in Nascar,etc. Just about everybody I know will use .035 on their plugs. It's not uncommon to run a bigger gap with systems like msd boxes, but most units that only run an hei, and no ign. box work best at .035. If you are in a humid area, adding ignition timing will make a motor more lively as well.

rogracer2
Dirt Maniac

Total posts: 119
posted April 30, 2005 07:15 PM  
Your quote..."If you are in a humid area, adding ignition timing will make a motor more lively as well." I'm wondering what you're meaning...do you mean to advance the ignition timing? If so, how much? Also, what does pre-ignition mean? Do you have too large a gap in the plugs, or is the ignition timing too advanced?


eenfield
Dirt Maniac

Total posts: 116
posted May 01, 2005 06:31 PM  
Why did the OE's gap their plugs wider? Because of the above mentioned emissions constraints they were looking for every last gain they can get....They were allowed to run the wider gaps because of lower RPMs, lower octane fuel, and lower cylinder pressure.
Race cars dont operate the same as a stock type car, and place higher demands on the ignition system.
Closeing the gap helps ensure the incoming fuel/charge gets lit.

crc1124
Dirt Maniac

Total posts: 143
posted May 02, 2005 08:28 PM  
I stand corrected. I just checked Accel's web site because I run their U Groove header spark plugs. Right there in black and white ".035". Guess what I'll be doing tomorrow? I'm glad I found this sight! You never know what you might learn.

C2W
Dirt Full Roller

Total posts: 70
posted May 03, 2005 11:07 AM  
Thanks for the help guys. This has been very insightful.

beachracing
Dirt Forum Racer

Total posts: 94
posted May 03, 2005 06:39 PM  
upping your ignition timing(distributor) about 2-3 degrees will make a world of difference by creating more combustion heat(horsepower), and a slight increase in torque, and as long as your car has no cooling concerns, the temp will rise about 5 degrees, or so. I read on here constantly about too much timing will cause detonation, which makes no sense if it is a low ratio motor. I've heard of people running as much as 44 degrees, seeing increases, and their car never sees 200 degrees. as long as valve to piston clearance is not an issue, you can get away with alot of 9.1/9.5to1 motors. I don't run race fuel, which is a waste of money for a low ratio motor. The cheapest gas at the pump, and set the timing @ about 36-39 degrees. The other misconception is that head chambers are THE deciding factor in how much timing you should have, it is part of it, but you have to account for head gasket, spark plug type, fuel, and piston dish( dish configuration). This site is great, and will help you, but don't be afraid to experiment, ...it can make a difference at the flagstand.

outlawstock17
Dirt Forum Champ
Total posts: 1363
posted May 03, 2005 07:23 PM  
beach, what does electrical timing have to do with piston to valve clearance? that is a function of lift, duration and mechanical timing. you're using oranges in your recipe for applesauce...

beachracing
Dirt Forum Racer

Total posts: 94
posted May 04, 2005 06:44 AM  
I'm sorry, it was a brain fart!, I was thinking about cam timing. Too much working in the sun has fried my brain!!

beachracing
Dirt Forum Racer

Total posts: 94
posted May 04, 2005 06:45 AM  
I'm sorry, it was a brain fart!, I was thinking about cam timing. Too much working in the sun has fried my brain!!

97dirt
Dirt Forum Racer

Total posts: 94
posted May 04, 2005 03:08 PM  
I've always run my timing and plug gap the same,ie...36 deg. of timing,36 plug gap,more timing,more gap,or less timing less plug gap

A&M Motorsports
Dirt Maniac

Total posts: 117
posted May 05, 2005 09:37 AM  
quote:
Originally posted by eenfield:
Why did the OE's gap their plugs wider? Because of the above mentioned emissions constraints they were looking for every last gain they can get....They were allowed to run the wider gaps because of lower RPMs, lower octane fuel, and lower cylinder pressure.
Race cars dont operate the same as a stock type car, and place higher demands on the ignition system.
Closeing the gap helps ensure the incoming fuel/charge gets lit.

Pre ignition is caused by increased cylinder temperatures and not enough octane in the gasoline. What actually happens is the fuel ignites before the valves have closed on the compression stroke. Way too much ignition timing would do the same thing but it would have to be waaay to much. As long as you have a stock engine run the high octane pump gas and you'll be fine.
Octane is the chemical added to gasoline to prevent pre ignition in higher compression engines. It actually is in all gasolines and has to be there. I have actuall worked in plants that make the octane for gasoline.

------------------
Artie Perilloux
A & M Motorsports

[This message has been edited by A&M Motorsports (edited May 05, 2005).]

eenfield
Dirt Maniac

Total posts: 116
posted May 05, 2005 04:14 PM  
A&M, I was just curious, did I miss something, or were you just adding to my post?

rogracer2
Dirt Maniac

Total posts: 119
posted May 05, 2005 05:48 PM  
How much is too much for ignition timing? If its supposed to be 8 BTDC, is 12 BTDC too much?

BCracing
Dirt Full Roller

Total posts: 32
posted May 15, 2005 08:46 PM  
Rog--you are timing with the vac. adv. still hooked up--if your rules allow you to you should get rid of the vac. adv. if your not sure how to do that do a search on this website on how to do it, you want your total advance to be between 32-40 on a SBC

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