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General Category >> Rubber Side Down! >> Head twiddling 101
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Message started by Armen on 06/10/16 at 19:02:27

Title: Head twiddling 101
Post by Armen on 06/10/16 at 19:02:27

So, I bought a junk head to dismember and see if there was some performance to gain.
HOLY CRAP! Who put a shelf in the exhaust port? Yes, a shelf. Never saw a port on an OHC engine so horrible.
Seems the first step is to find some smaller diameter valve springs (and light retainers)and seats. Then weld up the corner ahead of the exhaust spring seats. Then try to make the ex port look a little less horrible.
Anyone go down this path before?
Oh boy....
-Armen

Title: Re: Head twiddling 101
Post by justin_o_guy2 on 06/10/16 at 20:51:24

That exhaust port has been the topic of a few threads. Nobody has suggested such radical measures. I don't have any way to look at one, but I have read your posts. Based on what I have seen, I just gotta say
Give it your best shot... I wouldn't dream of trying it, but you just might win..

BUT, wait on a few guys who have been in there further than I..

Title: Re: Head twiddling 101
Post by Dave on 06/11/16 at 03:34:41

The exhaust port is really bad....it has shelf and a donut.

I trimmed most of the donut away, and just lightly radiused the sharp corner on the shelf.

It works a whole lot better - but as you noted.....it is not a stellar design on the exhaust port. The whole thing is anything but smooth.....it has lots of voids,curves, bumps and obstructions.

Title: Re: Head twiddling 101
Post by Armen on 06/11/16 at 16:22:52

Dave,
Got the 'shelf' thing, but not sure what you mean by the 'donut'. Got a pic of what you mean? Maybe a before and after pic when you de-donuted the port?
thanks
-Armen

Title: Re: Head twiddling 101
Post by Boofer on 06/11/16 at 18:49:38

How do you think they got the TSCC? All those shelfs and donuts are by design. ;D Okay newbs, what does TSCC stand for? Boofer :-?

Title: Re: Head twiddling 101
Post by Armen on 06/11/16 at 18:54:29

Twin Swirl Combustion Chamber (was head wrench at a Suzi-Q dealer when those models came out)
Stolen from Keith Duckworth of Cosworth Engineering.

Title: Re: Head twiddling 101
Post by Dave on 06/11/16 at 19:24:08

The donut is the restrictive/constrictive ring at the exit to the header. The hole can be made larger and smoother.

Title: Re: Head twiddling 101
Post by Armen on 06/12/16 at 07:38:17

Boofer,
The TSCC idea was to have the intake charge tumble forward while entering the combustion chamber. Earlier 2 valve heads did the swirl thing by offsetting the carb and causing the intake charge to circulate the combustion chamber in a horizontal plane.
With a 4 valve head, offsetting the carb doesn't work.
Making a steeper intake tract causes the intake charge to circulate on a vertical plane. Two intake valves gives the 'Twin' part of TSCC.
I can't see any way that a craptastic exhaust port could help or in any way cause swirl of the intake charge.
More likely explanation is that the stylists wanted to keep the engine height as low as possible, so they buried the valve spring pockets into the exhaust port.
Honda singles have short engines because they are dry sump. With the wet sump Savage motor, the shortness had to come from somewhere.
-Armen

Title: Re: Head twiddling 101
Post by justin_o_guy2 on 06/12/16 at 10:27:11

I enjoy posts by people who are knowledgeable.