lizard head

C

cannon

Member
bought a pile of suff this weekend, when i got home found a lizard head still in a box. anyone ever run one? ideas? comments, good-bad
thanks
 
i lost one of those.....i was trying to sell it on ebay. auction ended.got the money and sent it out.3 weeks later i get a message "where is the head".ups lost it.it ended up on someones front door and wasnt returned. good thing i put ins on it.tk
 
The one on the right is a Lizard Head -

From some reports it is not really a great addition to your T. The compression is too high for normal bearings & it needs to run with a distributor to prevent knocking since the stock ignition system does not have enough range of adjustment. There are some reports of leaks as well. It appears that the "ScaldedDog Co." is not currently making them nor offering them for sale.

I think if I owned it I would definitely put it on something -- eBay comes to mind!!




PARTSGRP.GIF
 
Lizard heads are a very poor design. The plugs are moved over the pistons instead of over the valves where they should be. The detonation problems with these heads will wreck a lower end in no time. They also tend to leak everywhere. Just a really bad idea that thankfully had limited production. I agree; eBay is the proper resting place for this anomaly, unless there is a museum of really bad ideas somewhere.
 
Doug Money said:
Why is the spark plug over the valves a better idea?
Click to expand...
In that position you are igniting the fuel with the flow of mixture entering the combustion chamber -- with the plugs at the far side of the piston you are asking the fuel to burn against the natural flow of gasses - not overly efficient. I learned very early that relieving onself into the wind just did not give good results!
 
I am curious Jack, I have heard for decades that Hemi engines were more efficient than plug over the valves. I still am not understanding how having the plug over the piston is against the natural flow of gasses. Also, on a four cycle engine there is a full compression stroke after the intake stroke prior to ignition. Please continue.
 
Doug,

The hemi engine has the plug close to the center of the head which puts it between the valves thus decreasing the turbulence in the flow of the mixture. The shape of the head also adds to the smooth flow of the gasses.

T head engines used in fire trucks & early large cars usually had the plugs over the intake valves so the ignited fuel could burn toward the piston & exit on the opposite side on the exhaust stroke.

There is indeed a compression stroke but the mixture does not stop moving in the cylinder. The plug at the opposite side starts the burn in a position to cause great turbulence in the natural pattern followed by the burning mixture which has to be overcome to force the burned mixture out the exhaust valve.
A flat head engine asks the mixture to make a 90 degree turn on its way in and again out of the combustion chamber, disturbing its flow pattern really reduces the efficiency of this already compromised situation.

The Waukesha-Ricardo head is known to be very efficient & does give improved performance due to its combustion chamber design & correct plug placement. It is particularly good in that it does NOT increase the compression ratio.
 
Thanks for the info. I am trying to visualize what you said. So the problem is due to the position of the plug in the head on a Model T?
 
[. So the problem is due to the position of the plug in the head on a Model T?[/QUOTE]

Doug,

The plugs in a stock T are in a position to work well. The Lizard head has the plugs at the farthest point away from the valves - see the picture I posted earlier. The ignition of the mixture in this location is a major cause of the turbulence that is not wanted. This combined with the high compression & the combustion chamber design all contribute to reported poor results.

It appears that Mr. Yapp had the decency to stop making these & no longer offers them in his catalog.

The one good thing is that these heads look great painted green with the cast lizard painted red. I am sure there are several hanging on walls here & there.
 
I see what you are describing now. I didn't notice it at first. Thanks for the description and helping me understand this.
 
The turbulence that Jack speaks of results in uneven combustion which equals spark knock, and when you raise the compression appreciably the problem gets much worse. An automobile engine needs to have an RPM range which is very flexible. By design it must be able to run well at all speeds and under different loads. Having the plugs over the valves is the best place for them on a T based on its general layout and compression. You often see flathead engines on lawn mowers and pumps that have the spark plug in a location other than over the valves but these are fairly low compression engines designed to run at a governed constant speed, usually wide open.
 
Actually, turbulence is a good thing. It speeds up the burn rate which means less spark advance is needed. With a faster burn there is less time for the heat and pressure to ignite a second flame front in the far end of the chamber opposite the spark plug, which would cause detonation. More turbulence allows higher compression, as seen in modern engines running up to about 10 to 1 compression on regular gas (electronic controls enter in here, but also high swirl, high turbulence combustion chanmber designs. Do an online search for "combustion chamber turbulence" to learn a lot more. Also, there is a contradiction in terms in the last sentence: "a governed constant speed, usually wide open". 'Governed' means regulated, limited, usually by partially closing the throttle plate. 'Wide open' is unregulated; throttle plate open as far as possible. Can't have both at the same time.
 
Well I stand corected if you want to split hairs but the fact is that a utility engine running at a constant speed is usually running nearly wide open. Turbulence is not always a good thing. The main thing automotive engineers in the old days were looking for was lighting off the mixture where it had the most "squish", ie the most concentrated point in the combustion chamber, which is over the valves in an early flathead design; and letting the burn progress outward from there, away from the incoming mixture. Firing the mixture over the pistion contradicts this and this sort of turbulence results in knock. Turbulence is great in a hemi-head engine which was designed to achieve a more complete burn for maximum power. The swirl effect of this design and lack of predetonation and the resulting horsepower is what made them so popular. If having the plugs over the pistons in a T was such a great thing we would all be running lizard heads.
 
I ran across one a few years ago, had no idea what it was, and turned it over on the evil ebay for a tidy sum. $350 I think. That will buy a lot of other parts you may need.
 
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