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Old 03-14-2004, 06:34 AM   #1
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exhaust manifolds

looking for a fix to repeated spark plug wire burn up on right side booot and wire fry about every 2500 miles . spark plugs have sparks half mteal shield on bottomside also instaled insulating sock help some but not a fix.also have torn down @ presenttime and manifold crack. plan on usemanifold replacement ? until wire burn up is cured. have long rarge plans to removed 454 replaced with 502 grate engine from pace & than banks exhaust.? is this a sane plan
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Old 03-14-2004, 07:05 AM   #2
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Burned plug wire:

David

The destruction of the curbside rear plug wire is indeed common. If you suspect your manifold leak is in the area of the plug that continues to self-destruct, there well may be nothing at that would protect the wire until the manifold leak is fixed.

After containing the exhaust gases (manifold fix), a premium plug wire with a protective sock or ceramic insert and proper support to prevent contact with any part of the manifold should fix your wire burn problem.

As far as the 502, I think it's a great idea, and well may be there in the near future myself. There should be no height differences (the 502 is a bored 454), just be aware of height restrictions if the heads are raised to lower the compression ratio to compensate for the larger displacement, as there is not much room for vertical growth in the dog house cover without modification.

To install anything larger than the 502, most of the engine builders go to a stroker kit, and the height issue becomes even more critical.

Please keep the Forum posted on your progress, as this is an issue close to all MoHo ownerís heart (and pocketbook!).
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Old 03-14-2004, 07:59 AM   #3
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as i recently posted, my two front plug wires were burnt at the caps after maybe 4000 miles and a year+ of travel.
I replaced the whole set with Accel High Heat wires (ebay $35 or Jegs $79) expecting better performance, they are rated at 1100 degrees, and the caps have a special coating. Accel also tells you not to use an additonal heat shield, I removed the tubes fomo those fron two plugs, that seemed to do little to help my old wires anyway.
The other choice is Jacobs Ceramics. More expensive but even more serious heat resistance.
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Old 03-14-2004, 08:34 AM   #4
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Quote:
Originally posted by ALANSD
........The other choice is Jacobs Ceramics. More expensive but even more serious heat resistance.
I had a notorious boot meltdown problem and can report that after 2 years and 10K miles, the ceramic Jacobs look and perform like new.
Underestimating the extreme danger of an 'open' spark in your engine compartment could lead to a very regrettable situation.
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Old 03-14-2004, 08:48 AM   #5
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Thumbs down exhaust or header leaks

In my case I replaced with ceramic wires and still burned one up...then got new headers and took routing looms to secure wires away from hot spots and have had no more problems...jem
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Old 03-16-2004, 09:01 AM   #6
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Headers would help with that problem and a bunch more

Don
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Old 03-17-2004, 08:44 AM   #7
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exhaustmanifoldreply

thank you dennis peterh alands & all members for your input . your thoughts made me take a real close look @ header flanges and seen under cuts in same, refinished flange. brought new proform gasket with metal inserts around exit ports. will revela outcome when I know if this fix was succesful.
Thanks again for your help. If it was easy everyone would be doing it.
p.s, pace raised the price of the 502 to $5,250.00

www.paceperformance.com
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Old 03-27-2004, 08:01 PM   #8
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for 87 mh

Am I not understanding you?? How can a stroker motor need more room than a stock baby. Unless there is some new technology I am not familar with ,the stroker is a crank. It fits in the block. Does not change the height.
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Old 03-29-2004, 07:54 AM   #9
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Theory on high profile heads.

Quote:
Originally Posted by moisheh
Am I not understanding you?? How can a stroker motor need more room than a stock baby. Unless there is some new technology I am not familar with ,the stroker is a crank. It fits in the block. Does not change the height.
One of the ways to maintain a low compression ratio after installing a stroker crank (and/or boring) is to install high domed heads. This could necessitate heads with a higher profile than "stock".

By maintaining the same (or close to to same) compression ratio while increasing the size of the displacement of an engine (either by boring or stroking) you are able to utilize the same grade (Octane Rating) of gasoline that the "original" engine was rated for.

It is my fundamental belief that the economic benefits gained by purchasing 87 octane gasoline far outweigh the marginally better mpg afforded by a high compression engine requiring 92 (or higher) octane rated gasoline.

Simply stated, the price premium for a gallon of 92 Octane is usually at least 10% higher than the price of 87 Octane fuel. I have been unable to find documentation that would confirm that an engine with the compression ratio raised to the point that it would require the 92 Octane fuel would repay (in mileage performance) a 10% fuel savings as compared to an engine running on "regular" fuel.

Granted, there are other ways to lower compression ratio (piston rod length, or the height of the piston itself), my point in the original post was to caution the installer that the room under the doghouse is extremely minimal, and any change in the engine profile (whether it be heads, air filter, carb, high rise valve covers, or any other modification to "original") could well require a change in the dog house cover.
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Old 03-29-2004, 09:45 AM   #10
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moisheh

Your assumption is correct, increased displacement by stroking is a simple crankshaft replacement. I've never heard of 'high dome' heads, however there are tall rocker covers to enclose non-stock valve train components. Those covers usually interfere with a/c compressors, alternators, etc., not overall engine height.

The way to manage compression is by purchasing the proper pistons for your stroke, rod length, and combustion chamber design. Nearly any compression ratio can be obtained, high or low, simply by asking and paying!!! I have built several 502s that run quite happily on regular fuel with C/R around 8.3:1 w/iron 119cc heads; or c/r around 9:1 w/aluminum heads and 119cc chambers. Aluminum cools better and can tolerate higher c/r without detonation. However aluminum is more expensive.

The Chevy BB (big block) IS one of the few engines with two different height blocks. So long as you are not working with a heavy duty(4500 series and up) truck donor engine you will have nothing to worry about. The 'tall deck' blocks are used to build VERY big motors. Up to 700 cu.in.!

Hope this helps.

Take care
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