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1098 head
https://www.ausmini.com/forums/viewtopic.php?f=2&t=36660		 Page 1 of 1
Author:  cookie720 [ Fri Oct 12, 2007 11:14 pm ]
Post subject:  1098 head
On a standard 1098 Leyland from 1974, what head do they have? Will a 12g295 do anything to the performance without doing any major modifications to it (just new valves etc , unleaded conversion and general cleanup)
The 1098 is standard, hopefully will soon have 1.5" carb and full exhaust.
Author:  Spaceboy [ Sat Oct 13, 2007 12:25 am ]
Post subject: 
yes

http://www.ausmini.com/forums/viewtopic ... light=1098
Author:  cookie720 [ Sat Oct 13, 2007 12:26 am ]
Post subject: 
:oops:
Author:  mini-dunger [ Sat Oct 13, 2007 12:36 am ]
Post subject: 
If you are going to the trouble of converting it and putting new valves in you may aswell give it a tickle with a grindstone.You will unlock a few HP and Nm without much extra cost.

I on the other hand have spent a fortune :roll:
Author:  drmini in aust [ Sat Oct 13, 2007 7:07 am ]
Post subject: 
Be careful when modifying a 295 head, the ports in these are bloody good to start with.
If you bung a stock 295 head onto a 1098 with the stocko dished pistons still, the C/R will be very low, below 8:1.
You can deck them by .060" or so, but don't take lots more or they are prone to blowing head gaskets.
If building a fresh motor, it's much better to use flat top pistons with a 295 head. :wink:
Author:  Anto [ Sat Oct 13, 2007 9:57 am ]
Post subject: 
+1 on what the Doc says, my mate fitted a 12G295 to his standard compression 1100 without decking it at all, it almost seemed slower than the 12G202 unless you were really revving it.

If you've got a 12G295 then use it, decking it .060" should be fine. If you don't have one, I'd go over your existing 12G202, you can get decent performance out of them with some porting and chamber work (and deck it whilst your at it, get the CR up a bit).
Author:  cookie720 [ Sat Oct 13, 2007 12:49 pm ]
Post subject: 
We have a 12g295 in an 850 motor right now which ran when it was all together, i was just thinking if its not too much work would i be able to put one in the 1100 without changing anything else, obviously not, what are you referring to when you say .060?
Author:  drmini in aust [ Sat Oct 13, 2007 1:12 pm ]
Post subject: 
The combustion chamber size in a 1098 head (12G202) is 26.1cc, that usually gives a C/R of 8.5:1.
Total volume including gasket and piston dish is about 36.6cc.

But the chamber volume of a stock 12G295 head is 28.3cc, ie 2.2cc greater. So total volume is now 38.8cc.
This extra volume will reduce your compression ratio to 8.07:1.
(I just worked it all out). :lol:

Shaving the head by .060" (1.6mm) will get the C/R back to about 8.5:1 or so.
Note this is really low by today's standards, if running a sporty cam (eg an RE13) you want it to be 9.5:1 or more for 98 octane fuel for best performance.
You will only get this in a 1098 by using flat top pistons to begin with.
Yes Vizard talks of shaving these heads by .100" or more, but you won't keep head gaskets in it.
Author:  d1ck0 [ Sat Oct 13, 2007 5:19 pm ]
Post subject: 
Seeing you're the great mathematician Doc, how does a 12G202 on a 998 go? Cause thats what ID10CY has got. Unless its got a 1098 crank of course.

Cheers

Dicko.
Author:  drmini in aust [ Sat Oct 13, 2007 5:29 pm ]
Post subject: 
d1ck0 wrote:
Seeing you're the great mathematician Doc, how does a 12G202 on a 998 go? Cause thats what ID10CY has got. Unless its got a 1098 crank of course.

Cheers

Dicko.

It's worth about 4HP with no other mods. I did it to my MiniMatic 998 when the old 998 head cracked. :wink:

I'll work out the C/R differences tonight, but right now I'd say just deck the head .040 or .050" whilst it's off. 8)

<edit>
OK a stocko 998 is 8.3:1 C/R with 24.5cc head chamber and total chamber volume of 34.2cc including piston dish and gasket.
If you fit a stock 202 head to it, the total chamber volume increases by 1.6cc to 35.8cc.
This will reduce the C/R to 7.97:1.
Like I said, deck the head before you fit it. :lol:
Author:  d1ck0 [ Sat Oct 13, 2007 5:39 pm ]
Post subject: 
Thanks Doc, It still on there at the moment. The motor was rebuilt about 3 years ago (for the previous owner), and when going through all his invoices its got the really good "rebulid engine as required" with a total $ amount.

No details of what went into it or anything. I'll pull the head off one day to investigate, but at the moment nothings broke (except the speedo cable that went today) so I'm not going to tempt fate by just doing it to look.

Cheers

Dicko.
Author:  gafmo [ Sat Oct 13, 2007 8:22 pm ]
Post subject: 
drmini in aust wrote:


Note this is really low by today's standards, if running a sporty cam (eg an RE13) you want it to be 9.5:1 or more for 98 octane fuel for best performance.
You will only get this in a 1098 by using flat top pistons to begin with.
Yes Vizard talks of shaving these heads by .100" or more, but you won't keep head gaskets in it.

you have shaved my head..and it has to be close to .100 and havent had problems with gaskets....luck i guess :lol:
Author:  drmini in aust [ Sat Oct 13, 2007 8:24 pm ]
Post subject: 
gafmo wrote:
drmini in aust wrote:


Note this is really low by today's standards, if running a sporty cam (eg an RE13) you want it to be 9.5:1 or more for 98 octane fuel for best performance.
You will only get this in a 1098 by using flat top pistons to begin with.
Yes Vizard talks of shaving these heads by .100" or more, but you won't keep head gaskets in it.

you have shaved my head..and it has to be close to .100 and havent had problems with gaskets....luck i guess :lol:

It's a 202 not a 295....maybe thicker, but I agree yours is on the thin side now... :wink:
Author:  gafmo [ Sat Oct 13, 2007 8:41 pm ]
Post subject: 
:lol: opps 295 heads...must admit i need a shave on my head...not sure if I'll let anyone touch that one :shock:
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