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Old April 10th, 2006, 09:56 AM   #1
SanDDrag'N
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Default detnation

Im having a problem with detnation in my 400. i will give u a run down of the motor. i picked it up for $1600 the bill owed at the the shop. the motor has between parts and shop work $6000 into it.

10.5 to 1 comp, complete head work ported polished valve job milled,
large cam ( dont have the specs off hand), oil restickters, harland sharp roller rockers,

electrical: msd 6al, msd coil, accel dist, 8.8 plug wires, new 145 amp alt, elec water pump

timing 12 init and 36 full adv.

detnation dont start till it gets to about 150, runs at about 170. and mostly it only happens at holding speeds. this is also running 94 octane

iv tried hotter pugs and gapped them to .55 still the same

Any ideas would be very helpfull

thanks: Steve
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Old April 10th, 2006, 02:15 PM   #2
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Hotter plugs? You're going to want to run cooler. Back off the advance on the ignition a little bit and see what you get.
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Old April 10th, 2006, 06:41 PM   #3
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Quote:
Originally Posted by GreaseMonkey
Hotter plugs? You're going to want to run cooler. Back off the advance on the ignition a little bit and see what you get.
Bingo - you can also try richening the fuel mixture, but I'd start with a colder plug and retarded ignition first
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Old April 10th, 2006, 09:41 PM   #4
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Quote:
Originally Posted by chris1044
Bingo - you can also try richening the fuel mixture, but I'd start with a colder plug and retarded ignition first
now are you gettin this
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Old April 11th, 2006, 11:42 AM   #5
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now are you gettin this

????
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Old April 11th, 2006, 12:08 PM   #6
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Slap a half tank of turbo blue in it and a set of NGK's.

My buddy has a 383 (10.5 to 1) in his nova that likes around 99 octane. During the cruise we couldnt find and race fuel so we settled for premium and some octane boost.

350 splaied main caps, stroked to 383, AFR 195's, comp rollers, 525 lift cam

Temps were alot warmer (205 instead of 185) in traffic.

Some timing and tuning will clear it up...
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Old April 11th, 2006, 03:03 PM   #7
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Are these Alum. or cast heads???

If alum, ignore the rest

If they are cast and you have a true 10.5:1, you will have to pull some timing.

That is too much compression for pump gas and cast heads, especialy if those are reworked stock heads, they have a poor combustion chamber design are prone to detionation.


You can try some colder plugs, set timing too about 30-32 total and add a little fuel.

Good luck,

Adam
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Old April 11th, 2006, 08:26 PM   #8
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????
i know this guy
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Old April 11th, 2006, 08:32 PM   #9
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WTF are you talking about - am I a moron or were you asking the guy who started this thread if he's getting the info?
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Old April 11th, 2006, 08:43 PM   #10
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WTF are you talking about - am I a moron or were you asking the guy who started this thread if he's getting the info?
no just an inside joke between the two of us thats all
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Old April 11th, 2006, 08:49 PM   #11
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one of a couple problems could be wrong with the engine that no one has mensioned. if its built with the correct heads. if its a true 400 then the heads needed to be moded to fit. the stock 400 head have steam holes between the chambers and help keep the cylinders cool since their cast so close together. if some used stock chevy head from any other motor they will cause detenation you cannot stop no matter what. i would suggest pulling the heads if the easy stuff doesn't work. most likely you find the wrong heads for your block
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Old April 11th, 2006, 08:53 PM   #12
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Why would a Chevy head be on a Ford 400M?

I know the heads are interchangeable from other engine (add Cleveland series) but I didn't know they had to be modded for the 400.

*EDIT: WHOOPS!

Last edited by Captain Ledd; April 11th, 2006 at 09:16 PM.
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Old April 11th, 2006, 09:00 PM   #13
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they cant be! but they are the heads the 400m came with!

i have a set of clevland heads but they need to be re worked and ported yet and after my latest expense its going to be a bit for that!

will try the cooler plugs here in a few days!

thanks for the tips folks
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Old April 12th, 2006, 10:27 PM   #14
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what everyone else said...
timing is too high for the compression ratio you are running. Im at 9.?:1 small cam and flattops in my 400. 10 degree's initial and the motor will ping without 93 octane.
You can bush cleveland pistons to get different comp ratio's since there werent many made for modifieds.
projectbronco.com has alot of 400 info.
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