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pre detionation

C

cak1983

Well-known member
went out the other day and my new 383 i just built started acting up.I stopped and pulled the plugs out and 4 of them were melted together.I changed the plugs and backed the timing off and headed back to the hill.Come to find out my hei spring kit i just bought wore out the plastic bushings within 5 hours of run time.It was advancing my timing way to much. Just curios if anyone has a solution or ran into this.
 
Your mechanical advance can only travel so much I wouldn't blame the bushings just yet. The bushings that support the weights will not change your total timing if their wore out or broke.
 
34 is as far as I like to go with a 383 on a lighter boat with a 2.68 but if you have a 2to1 or a heavy boat 34 degrees is too much. Also did you verify your marks are correct. I have seen tab's, balancers off by 20 degrees let alone some old balancer otter rings slip. You should zero your tdc marks before running it again!
 
it is a 12' hull very heavy 2.37 rotator 78" 3 blade stump puller .torqe rolls like a bi***
out of the hole it is a snail but once it gets on plane it will pin you in your seat. it takes off faster on dry than it does in the water
 
Since you have that bad of a torque roll that tells me she is a very heavy boat or has a lot of weight for it's bottom. I use the 78'' prop to combat the torque roll everyone knows the 80 or 82'' prop will make more thrust but the 78 is best for you, the boat will run better in the water! With that heavy of a boat and that ratio any little thing can set it into detonation things like, too much head to piston, to much cylinder pressure, iron heads with compression over 9.5 to1. I would start with a tdc tool and double check your timing tab and marks!
 
Not much to add here, I think Dave has you more than covered. But one thing that I've experienced with the centrifugal weights is that they "can" over-advance when the bushings are worn out, because they go over center. This seems to be more of an issue with the HEIs BTW. But really not much. The biggest thing is if they're worn they don't repeat worth a damn (they stick), and you may see 34deg one minute and it may really be capable of 36 or 38 the next when it breaks free. Another thing I see done all the time that drives me nuts is the use of extended tip plugs. They expose the electrodes to way too much heat in a airboat application and not only can you melt em, but it's the cause of a lot of ignition breakdown and pre-ignition I see a lot of you guys have. JMO

Felber
 
I posted the pic of the none extended plugs I use the NGK's and I have a hundred on hand all the time! The Vortec's and LS motors use the extended tip plugs and boy do they like to detonate when you run the hill!
 
Thunder,will these plugs your talking about work in my buick? If so how much for a set
 
Olf Art":npx5n1zi said:
Mike, what plug do you like for a SBC in an airboat application ?

olf
Click to expand...

Ken,

It all depends on which head you use. SBCs come with the short washer face in the early years, then came the "peanut" taper seats that were short in the early '70s through the mid '90s. Then the Vortec used the same plug as the LS series engine. Pic below of Dave's

DSC_0311.JPG


Now all the heads that use washer seat 3/4" reach such as most aluminum heads and any of the engines I build, the NGK # is R5671A. Now the heat range is up tp you. I send my engines out with 7s and if they're extreme HP I use 9s after break-in and final tune (EX R5671A-7) Remember that NGK numbers run in reverse for heat range. The higher the #, the colder the plug. Also NEVER EVER, EVER, EVER run a platimum or any other super, duper trick of the week plug in high load/HP applications. The area of the positive electrode is so small it overheats very easily, so do yourself a favor and run old-school large electrode stuff.

BTW That number I posted also works perfect in all the LS heads I've used/seen. I prefer the washer seat personally because there are more plugs available and I also think they're a little less prone to loosening JMO.

Felber
 
WOW... I am running a AC M43lts.. If I am reading this right I am using the wrong plug.. My engine is a vortec 383 with the GM aluminum fast burn heads. That kinda erks me a little.. If I am reading this right the shop I got the engine from should have told me the right plugs to use.

Mike is the EX R5671A-7 plug the one I should be running? It is supposed to be 425 horse. Thanks in advance..
 
Yes you should run this NGK plug, most places don't realize how quick heat will build up in an airboat motors combustion chamber and in the tips of the spark plugs!
 
Thanks!! Do you have a number you would suggest? And while I am at it... What do you gap them at? Thanks!!
 
By you saying run the NGK 7s is this the number I ask for EX R5671A-7 or is it this R5671A? Sorry if that sounds dumb but I just want to make sure I got it right..

The ignition is HEI it looks like the stock one to me but it does have the Red cap. If stock or aftermarket HEI makes a difference and you can tell me how to tell the difference I will run out there and check.

Thanks for the help!!!
 
Smugglers Blues":1h8dx8dd said:
By you saying run the NGK 7s is this the number I ask for EX R5671A-7 or is it this R5671A? Sorry if that sounds dumb but I just want to make sure I got it right..

The ignition is HEI it looks like the stock one to me but it does have the Red cap. If stock or aftermarket HEI makes a difference and you can tell me how to tell the difference I will run out there and check.

Thanks for the help!!!
Click to expand...

The Fast Burn heads are just like the LS heads. They accept both the taper-seat and washer-face plugs. The R5671A-7 # I gave is spot on for you in a washer-face. And as long as you have a good coil, I gap em at .045". If the engine doesn't make a lotta steam, it will pick up some power and fuel economy by opening the gap, but on airboats I prefer the slightly tighter gap for reliability of the ignition under high loads.

Note to all...These are RACE plugs and the average counter guy at AutoZone is gonna look at you like you just flew in from Mars when you give him that PN, so I suggest mail ordering them or getting them from Dave or I, if you don't have a good parts store or speed shop local.

Felber
 
Felber,
I picked them up at Bennett Auto here in Ft. Laud. You have to give the the stock # on the box I think it was 4091. They had them there from the warehouse in a hour. You are right about the other part #.
 
Good tip. I have a habit of not using the stock number because I base all my custom plugs by the code which denotes all it's characteristics.. I.E. all I have to do is change 1 number to change from a washer face to a taper seat, or change from a 5/8" hex to a 13/16" etc. etc...

Felber
 
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