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piston choice
https://www.ausmini.com/forums/viewtopic.php?f=2&t=91280		 Page 1 of 2
Author:  mooman10_0 [ Mon Dec 14, 2015 6:05 pm ]
Post subject:  piston choice
Hi everyone,
I have just torn down the 998 I will be rebuilding for my next project. It hasa 12g202 head and the fuel inlets seem to be nicely polished. Looks to have slightly bigger valves aswell. To my surprise it already had duplex timing chain. I will be fitting double springs and having head gone through maybe a little chamber work aswell if not much else needs doing. I am going to fit flat top pistons, question is should I just go 20 thou over or jump up to say 80 thou? (is currently standard), would 80 thou see much power increase (what I am after). I see you can go up to 120 thou, so at 80 thou I still have a few more bores left in it, and 998's arent overly hard to come by!!
It is also getting a GR 266ss cam.
Opinions/ thoughts?
Cheers,
Steve
Author:  gtogreen1969 [ Mon Dec 14, 2015 6:12 pm ]
Post subject:  Re: piston choice
Have you thought about dropping an 1100 crank in it?
Author:  mooman10_0 [ Mon Dec 14, 2015 6:18 pm ]
Post subject:  Re: piston choice
trying to make do with what I have crank wise (keep spend to a minimum :-)!
Author:  bluewhitecoopers1968 [ Mon Dec 14, 2015 6:30 pm ]
Post subject:  Re: piston choice
I wouldn't just throw in flat top pistons unless you have worked out the compression ration first. the cost of an 1100 crank will be minimal.. in fact probably cheaper than dual valve springs ( which wont make any extra horsepower anyway)
Author:  mooman10_0 [ Mon Dec 14, 2015 6:47 pm ]
Post subject:  Re: piston choice
my engine builder will be working out all compression ratio stuff, what should I be aiming for in terms of compression ratio?
Author:  gtogreen1969 [ Mon Dec 14, 2015 6:50 pm ]
Post subject:  Re: piston choice
bluewhitecoopers1968 wrote:
I wouldn't just throw in flat top pistons unless you have worked out the compression ration first. the cost of an 1100 crank will be minimal.. in fact probably cheaper than dual valve springs ( which wont make any extra horsepower anyway)

My thoughts exactly. Whilst everything is pulled apart the most bang for your buck would be an 1100 crank and camshaft.
Author:  mooman10_0 [ Mon Dec 14, 2015 7:01 pm ]
Post subject:  Re: piston choice
anyone have one lying around in good nic? Im guessing I would need 1100 pistons to go with it? I will be in Adelaide from Wed to Sunday will post in the wanted section :-) If I went with flat tops/ 1100 cc crank/ cam 266 ss, what chamber size should I be aiming to achieve? Im guessing that is all I will be needing to mention to the engine builder.
Cheers,
Steve
Author:  mooman10_0 [ Mon Dec 14, 2015 7:02 pm ]
Post subject:  Re: piston choice
Oh and how much should I expect to pay for a crank?
Cheers,
Steve
Author:  bluewhitecoopers1968 [ Mon Dec 14, 2015 7:17 pm ]
Post subject:  Re: piston choice
mooman10_0 wrote:
Oh and how much should I expect to pay for a crank?
Cheers,
Steve

You should get an 1100 crank for 80-100 bucks but journal condition is what you need to look at.... A regrind if needed would cost 300 or so. Pistons are the same for 998 and 1098, as are rods. Don't think flat top pistons are what you need to make hp. I'd go for around 10:1 compression and run on 98 octane. If you have no idea what I'm on about then talk to your engine builder. :)
Author:  mooman10_0 [ Mon Dec 14, 2015 7:23 pm ]
Post subject:  Re: piston choice
Seeing the motor seems to have had work done to it in the past I better check to see what crank is in it when I split the motor tomorrow. What numbers should I be looking for on the crank (998 or 1100)?
Cheers,
Steve
Author:  Karcraft [ Mon Dec 14, 2015 7:42 pm ]
Post subject:  Re: piston choice
Pistons are not the same for a 998 and 1100.

Same bore size but different compression heights due to the stroke.

Hope this helps.
Author:  gtogreen1969 [ Mon Dec 14, 2015 7:51 pm ]
Post subject:  Re: piston choice
As to the original question - I would go 80thou over. Like you said these blocks are easy to come by.
Author:  mooman10_0 [ Mon Dec 14, 2015 7:53 pm ]
Post subject:  Re: piston choice
cool, now to find a crank, first check to see what crank is in it tomorrow :-)
Author:  TheMiniMan [ Mon Dec 14, 2015 7:56 pm ]
Post subject:  Re: piston choice
he probly meant the same cost?

1100 cranks are a bit harder to find cheap "ready to fit"
but definitely instant more torque & capacity, "fairly cheaply"
small bores we "usually" set-up at 9.5-ish:1 CR depending (mainly on cam choice of course)
please don`t run "polished" inlet ports, , , polish the cmbstn chamber if you want to polish something
or even the exhaust ports if you must, but leave the inlets in a coarse emery finish.
Author:  mooman10_0 [ Mon Dec 14, 2015 8:00 pm ]
Post subject:  Re: piston choice
will take that on board :-)
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