david.clement@verizon.net wrote:
> I have read a couple of tech articles on the design philosphy behind project
> nose plugs. The idea for using the projected nose is it's further into the
> chamber so the incoming charge will cool the tip allowing a higher heat range
> to burn off deposits.
>
> Now the 5224 and 3924 are both projected nose plugs (the 5225 is just porjected
> more) and why DC chose to change the recomend plug from 3924 to 5224 in 97 is
> anyone's guess. Could have been for emissions or economy or they may have found
> the engines run better.
>
> If you have a detonation problem going to the cooler 3923 plug may help (there
> is no 5223).
>
> The magnum head design is a closed chamber quench design. This design is
> supposed to create a lot of turbulance in the chamber that makes the engine
> less suceptable to detonation. However the piston and the head have to come
> very close to each other (0.040" is considered about perfect) for this to work,
> the magnum engines as delivered from the factory have the piston about 0.050"
> down in the cylinder so the gap is on the order of 0.090" which negates most of
> the advantage of the quench design.
>
> FWIW, the 360 with magnum heads I built for my 68 Barracuda has the block
> machined for zero deck, that is the top of the piston is even with the top of
> the block. The head gasket I am using has an 0.039" compressed thickeness
> making the qunch distance 0.039". Even with 10.6:1 compression in this engine I
> have no detonation problems and the engine runs fine on 89 octane middle grade
> fuel. Once I get a few more miles on the engine I will be experimenting with 87
> octane to see if I can save a buck or two on a fill up. The open chamber heads
> that came on the 360 would have detonation problems with 93 octane at 10:1
> compression so the quench design really seems to work. BTW, I do not have a big
> cam in the engine, it's a 268/280 duration with a little over .5" lift with the
> 1.6 ratio magnum rockers. Estimated power is 375HP.
>
> Dave Clement
> 99 SLT+ CC 4X4
Thanks Dave! Thats the kinda info I was looking for. I couldn't quite
figure out why they did a plug change for engines that were virtually
unchanged.
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