SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: NORDIC454 on June 26, 2011, 11:10:03 AM
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Found out yesterday morning that I have been running the wrongs plugs in my BBC. They are about 3/8" shorter than the nw ones I put in. I easily saw a 30% increase in power after the swap. Had no idea!
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Give us some more information.
What heads do you have?
What plugs were you running?
What plugs do you have now?
Your information might keep someone else from doing the same thing. :thumbup:
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I have some old closed chamber heads that run the longer plugs, but I believe the open chambered heads all ran the short ones. If you have aluminum heads they usually used the long ones also.
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you should have the shorter reach plugs in brandon...990's are open chamber
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990 square port heads. the number I was running was AC Delco R44T. bthe new one's which I got from Brad are Autolite racing AR3933.
it runs alot cleaner, with way quicker response.
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you should have the shorter reach plugs in brandon...990's are open chamber
he was running very short plugs. i bet they werent even sticking out of the hole at all......the AR3933's are the plugs that all the racers use with the 990 heads, what i use on the southwind (990s) and in the race boat (TFS heads). He had a plug that cracked on the porcelain and i had another set of plugs for him to use. the difference in length of plugs made him nervous....but obviously the smile on his face when he got on it was proof they worked better. I think he said he picked up 3k in rpms too. amazing what the difference in a bad plug can make.
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heres the difference....
from this...
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fstatic.summitracing.com%2Fglobal%2Fimages%2Fprod%2Flarge%2Facf-r44t_w.jpg&hash=ce31de4d8b7140ef82dbcea1a1e3c755ba9e9860)
to this...
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fstatic.summitracing.com%2Fglobal%2Fimages%2Fprod%2Flarge%2Ffrm-ar3933_w.jpg&hash=749647e12b5c31961400ca63b4c7a3ecd0a54289)
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he was running very short plugs. i bet they werent even sticking out of the hole at all......the AR3933's are the plugs that all the racers use with the 990 heads, what i use on the southwind (990s) and in the race boat (TFS heads). He had a plug that cracked on the porcelain and i had another set of plugs for him to use. the difference in length of plugs made him nervous....but obviously the smile on his face when he got on it was proof they worked better. I think he said he picked up 3k in rpms too. amazing what the difference in a bad plug can make.
300 RPM's ;)
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Hmmm....I'm running ac delco R43T in my 049 oval port heads. I was told to run the short plugs in them. Now i am a little confused. Wonder if I could see some power and response gains like brandon experienced when changing plugs. Very interesting.
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he was running very short plugs. i bet they werent even sticking out of the hole at all......the AR3933's are the plugs that all the racers use with the 990 heads, what i use on the southwind (990s)
Brad, didn't Terry and Kyle work on your boat last year when it was running like crap at Parker?
When they pulled the plugs, they found the long ones and some of the ground straps were closed (no gap).
You put in a set of short ones and it ran fine after that.
I just ran a long and a short plug into a 990 head we have in the garage. The short one ends right at the end of the casting and the long one threads into the head at least a 1/4".
AR3933's are what I run with the aluminum heads and the closed chambered heads.
Good luck trying to get those out after the threads get burned and carboned up.
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yes ron....an equivalent to the 3933s are what we put in there....I was running an even longer plug before the 3933s
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The R43 is the plug I just ran into the head that lined up with the inside.
Didn't know they made an extra long.
AR3339's are the ones that stuck into the 990 head too far by at least a 1/4"
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Short plugs in the 990's here
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i'll just stick with the short reach...i stuck one of the old plugs out of the old motor back into the cyl. head and i like what i saw...i guess if your reaching for a little more and you want to worry about your pistons hitting you can always index your plugs right
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heres the difference....
from this...
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fstatic.summitracing.com%2Fglobal%2Fimages%2Fprod%2Flarge%2Facf-r44t_w.jpg&hash=ce31de4d8b7140ef82dbcea1a1e3c755ba9e9860)
to this...
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fstatic.summitracing.com%2Fglobal%2Fimages%2Fprod%2Flarge%2Ffrm-ar3933_w.jpg&hash=749647e12b5c31961400ca63b4c7a3ecd0a54289)
I wouldn't run the bottom one with 990s unless I was using flat tops at 8:1. Something else was wrong. How old/worn out/beat were the original plugs?
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How do I find out what kind of heads are on my BBC. There is a casting # on them. Does that have any meaning? I'm currently running the Delco R44T spark plugs and the motor seems to run fine. Of course, if I can get it to run better with longer plugs then I'd be game for swapping them out ;)
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So i ended up diggin around in my tool box and found one of the old plugs i pulled out that were too long. its the same length as the AR3933's.
It never hit the piston or anything, but it burnt the electrode up real good. i assume by it sticking out too far, its in a hotter area of the combustion chamber ?? or just a crappy plug ?? or sign it was running too lean ?? i dont know.
ill take a picture of it and post it up.
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[attachimg=1]
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ar 3933 and 35 are for most aluminum heads. most cast iron heads would use ar 12 or ar22. you will run into some early cast iron heads that will require the long reach .
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ar 3933 and 35 are for most aluminum heads. most cast iron heads would use ar 12 or ar22. you will run into some early cast iron heads that will require the long reach .
thanks terry, I was about to call you for clarification.
so brandon. change your plugs ;) dont throw those 3933's away either.
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Brad, that's preignition. Wrong heat range, lean, too much timing, etc.
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A spark plugs heat range is the rate at which it transfers heat from the plug to the head. There are even little water jackets around the plugs. If you've got that much hanging out of the head it cant tranfer heat as well. PLUS all the shrp edges to heat up and turn into a glow plug basicly.
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Open chamber = short reach plugs
Closed chamber = long reach
Brandon if the plugs made a world of difference then you should be able to tune it with the short reach plugs...might need a hotter spark...you can do that with plugs as well...i got a brand new set of accels your welcome to have or try
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Nordie
Open chamber = short reach plugs
Closed chamber = long reach
Exactly :banghead: and
Open chamber alum = long reach
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Nordie
Open chamber = short reach plugs
Closed chamber = long reach
Exactly :banghead: and
Open chamber alum = long reach
Most of us are broke ass jet boaters aluminum heads are something we jack off to while reading a jegs magazine while on the shitter
Why do aluluminums require long reach? Raised exhaust ports or just more meat there due to the softer metal
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Because the have more threads in 'em generally.
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Most of us are broke ass jet boaters aluminum heads are something we jack off to while reading a jegs magazine while on the shitter
Why do aluminums require long reach? Raised exhaust ports or just more meat there due to the softer metal
I was totally agreeing with you, just added the aluminums in there.
Banging my head because this is what I posted in the second reply. It's gone full circle now.
I agree most of us are broke ass jet boaters. Have only worked 2 monthes this year and things don't look good. I'm more of a Summit guy than a Jegs guy that catalog gets me off.
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I'm not exactly an idiot, but these are the stupid little things that will get me in trouble. These plugs did make a world of difference. I am going to guess because the plugs I took out were the same plugs that I installed when I rebuild the motor last season. I have done a LOT of tuning since then, including a complete carb rebuild. So they were probably pretty bad, I just didnt realize it. I will switch back to The correct size and hopefully it will have the same effect.