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Head work.
https://ausmini.com/forums/viewtopic.php?f=5&t=8978		 Page 1 of 2
Author:  scotty [ Mon Jul 11, 2005 2:15 pm ]
Post subject:  Head work.
Now that I have the 295 head off and ready to be worked on, I would like to know how much I should shave and port the head? As I would like to give it some stick every now and again. I don't plan on super/turbo charging this motor, so I don't believe compression will be much of an issue. Although I may upgrade to a small weber in the near future.
998 Currently running - 1100 crank, twin 1&1/4 SUs, mild street cam, extractors/zaust.
Cheers.
Author:  FatMaserati [ Mon Jul 11, 2005 2:29 pm ]
Post subject: 
Just remember, you want to increase the size of the ports at the top, not the bottom. I'm sure this is a well known fact, but on my engine that fell to bits - built by a moron - the head was ported, but the guy who worked on it increasesd the port size towards the bottom of the port, which effectively does nothing.

As for shaving, you probably don't need much, but I'll wait until someone gives you a proper measurement.
Author:  drmini in aust [ Mon Jul 11, 2005 3:08 pm ]
Post subject: 
If you have normal dished 1098 pistons (which were 8.5:1 with a 202 head) I would shave the 295 by .075" or so.
Reason- the 295 head has BIG chambers at 28.3cc, way bigger than the 202's 26.1cc.....
998 Coopers had D-top pistons to get the C/R up to 9.0:1 with this head. 1098 Sprites had flat tops for the same reason.

Original head thickness was ~2.750" so measure it and see where it's at. :wink:

These heads don't need a lot of porting work, compared to lesser heads.

<edit> if you want to port it yourself, I'd get a copy of Vizard's big yellow book.. less chance of f***ing it up. 8)
Author:  minimechanic [ Mon Jul 11, 2005 10:04 pm ]
Post subject: 
My engine is presently being rebuilt, i think i will have to make a couple of mods while im in there so I rekon i wouldnt mind a bit of head ( on my mini engine ).
Author:  scotty [ Mon Jul 11, 2005 10:47 pm ]
Post subject: 
I have already noticed a huge difference in bolting a 202 head back on. Goes like a hered of turtles stampeding thru penutt butter (very slow!). So I kind-of have an idea as what to expect from some headwork now. But will have take some measurements and make some calculations...
Author:  drmini in aust [ Mon Jul 11, 2005 10:58 pm ]
Post subject: 
If it is a stock 295 you have, you will be lucky if it had 8.0:1 C/R before.

To get the best from a 295 head and a sporty cam, you want it to be 9.0:1 C/R at the very least. 9.5 is probably the most you can get with dished pistons even after you shave it .075".
10:1 or so would be better, but you would need flat top pistons then. :wink:
Author:  scotty [ Mon Jul 11, 2005 11:06 pm ]
Post subject: 
Thanks Kev, running these dished pistons at the moment. They'll do for now, I guess.
Image

The 295 head is bog stock at the moment.
Author:  Coop [ Thu Jul 21, 2005 1:17 pm ]
Post subject: 
is that suppost to look like that, theres all crap ontop of the pistons ?
Author:  awdmoke [ Thu Jul 21, 2005 2:07 pm ]
Post subject: 
Normal carbon buildup. Same thing happens inside the heads.
Author:  Spaceboy [ Thu Jul 21, 2005 3:02 pm ]
Post subject: 
that looks good.. you'll have to clean all that crap off the block so your gasket seals properly.
Author:  scotty [ Thu Jul 21, 2005 3:30 pm ]
Post subject: 
Did that with a razorblade. Now running a standard 202 head while the 295 goes to the shop for shave, valves, and a port job 8) .
Author:  Spaceboy [ Thu Jul 21, 2005 4:13 pm ]
Post subject: 
theres nothing like a good headjob
so much more powa
Author:  Coop [ Thu Jul 21, 2005 7:18 pm ]
Post subject: 
i agree :)

Quote:
theres nothing like a good headjob
Author:  supercharged 850 [ Fri Jul 22, 2005 3:34 am ]
Post subject: 
Coop wrote:
is that suppost to look like that, theres all crap ontop of the pistons ?


Compared to many i've seen, those look pretty clean :shock:
Author:  drmini in aust [ Fri Jul 22, 2005 7:50 am ]
Post subject: 
And folklore sez it's a good idea NOT to scrape all the carbon off the edges of the piston, as it helps the rings seal....
I dunno if true, but I've seen a few cleaned ones smoke for a while afterwards. :lol:
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