Corey,
I thought the spark plug adapter you referenced was for doing compression testing on the older T heads.
Cool topic.

 

Yes it is, as well it is used to allow for a smaller modern plug to be used, I guess one would install it and never take it out.

 

i was curious about the thread adapter too, i would imagine the hard part would be finding a plug that is long enough to make up for the added material since you'd want the spark in the chamber.

 

http://gtgravelyparts.com/6_6HP_engineparts.html

Scroll down and you'll see the adapter with the correct reach spark plug, now will the new plug hit the older slant hoods?

 

Hands down the best plugs for the T head are the Champion W89D and W95D.
Here is a list of plugs I have tried, best to worst:
Champion W89D
Champion W95D
Motor Master "1" (old)
Champion 3X
Champion W18
AC 73 (old)
Champion W80N (has multiple electrodes- if anyone is thinking of supercharging an L with a smog pump, this is the plug to use)
Champion W20
Autolite 3076/Champion W14
Champion W10
Champion W8J

The spark plug adapters are great. If you have a hard starting L, you can put an Iridium plug in it and reduce your starting problem. Any plug for a Chevy Vortec V8 will fit. The new plugs do not hit the hood.

 

And if I may ask how did you come to this?

Longevity? Resistance to fouling? Heat range?

 

For the 7.6 Convertibles, the absolute best plug you can get is the Denso IWF16. This plug also works in the newer Kohler and Onan powered machines, and in the Jenkins head. It is an Iridium plug, so it lasts an extremely long time.

 

Theo655 said"Champion W80N (has multiple electrodes- if anyone is thinking of supercharging an L with a smog pump, this is the plug to use)"
I hadn't thought about it before but I certainly am now. :thThumbsU
Has this been done? It really isn't fair to just put things like that out there without a proper explanation. If it wasn't a holiday in Canada today I would be heading out to the local Pick-N-Pull to find an air injection pump.


Matt

 

A GM smog pump can be used as a centrifugal supercharger (similar to a vortech or procharger on big engines) for a small engine. It creates around 3-5 pounds of boost with the stock pulley. My neighbor used a Volkswagen smog pump as a supercharger for a 6.6 L. The Volkswagen ones are even better than the GM ones, as they are actually a small Roots blower, similar to the GM 71 series superchargers, but in miniature. With the GM pump, it must be set up to blow through the carburetor. With the VW pump, the carburetor goes on one side of the pump, and the other side goes to the intake. The Champion W80N is a retracted tip multiple electrode plug with a cold heat range. This type of plug is ideal for use with a supercharger to avoid detonation. Timing must also be retarded slightly.

 

And how does the ancient T-head respond to being "blown"... ?

 

Very well, actually. It almost doubled the power on my neighbor's machine.

 

I would think that a small amount of boost would do wonders for a T head engine. 4 lbs of boost and it might equal the power of an overhead valve conversion. The best part is that supercharging doesn't require an increase in RPM to make more power thereby making it an ideal solution for our little T heads. So now I am officially on the hunt for a Volkswagen air pump but I will be using an NGK plug as I have found them the best in every vehicle I have used them in. My C8 has one in it now. Champion are at the bottom of the list for me. I have had them fail too often for my liking.

Matt

 

That plug is only for the ones with the large slanted plug. Champion makes the best large industrial plugs and just about the worst small plugs. I would recommend a Denso IWF20 for a C8. I'm not sure what the NGK equivalent is. Also, the VW smog pumps of the type you need came on 60s-70s gas powered cars. Later ones are electric centrifugal pumps and would not work in this application. Most belt driven centrifugal pumps (GM, Ford, Toyota) will work if you don't find a VW one.

 

Just looked it up, the NGK equivalent to the IWF20 is the BR6HIX.

 

I have never tried the large Champion plugs but I will when we finish rebuilding my sons 51 L. My bad opinion of the Champions started because once on a tour with my motorcycle when I was younger they left me stranded way out in the boonies at the side of the road. I was trying to figure out why the plugs would spark when I checked them outside the engine but not when they were installed when I heard a loud roar coming up the road and about 30 or 40 very mean looking motorcycle club members pulled up beside one totally terrified 17 year old (ME) 360 Honda rider. Those motorcycle "Gang" members after teasing me about my "Rice Grinder" showed me what was wrong with my plugs and the leader took me to the closest town to pick up a set of NGK's for my bike. He told me to always use NGK plugs as they were the only good thing made in Japan. I have always used them since.

Matt

 

The large Champion plugs, from 18mm to 1 1/4 inch diameter, are all industrial and agricultural plugs, much heavier duty than standard automotive plugs.

 

Galen Suiter makes an adapter that allows use of standard plugs in the L model Gravelys.

Contact info
Galen Suiter
Coosada, AL
334-285-310 nine

Email: gravely at elmore.rr.com

 

He sells them through GT Gravely enterprises too

 

I have nothing to add. Just poking in to say this is an awesome thread!

 

Thanks for all the input, seems as though the Champion plug may be the best for the 5-6.6 HP T- Head engines. Like I've mentioned I've had good luck using Autolite brand plugs in all variants of the T-Head engine, that doesn't mean I'm unwilling to try something new.

 

I was looking through a NAPA catalog I have, and it appears that NGK surprisingly makes the large Gravely plug as well, part number G2Z.