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poeee
PostPosted: Mon Sep 05, 2005 3:09 pm 
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I was thinking (never a good thing!).

Because the 1098 uses the same block and con rods as the 998, I was wondering what the compression ratio would be if you used a 1098 crank and the shorter 998 pistons. Would the comp ratio be suitable for forced induction and to what extent could you boost it? Would be a hell of a lot cheaper than getting deep dish pistons, thats for sure!


Ignor ALL THAT! I got muddled up... new question is this...

Because the 998 uses the same block and con rods as the 1098, I was wondering what the compression ratio would be if you used a 998 crank and the shorter 1098 pistons. Would the comp ratio be suitable for forced induction and to what extent could you boost it?

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Last edited by poeee on Mon Sep 05, 2005 8:35 pm, edited 1 time in total.

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aaron
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PostPosted: Mon Sep 05, 2005 3:46 pm 
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You would have to deck the block quite alot to get it to run. Dropping 100ml in engine capacity that is 25ml per bore. :shock: yes it would drop your compression ratio, but i think way too much. Good idea but i think it would be easier to work the head and drop the compreesion ratio that way. maybe use thick pistons and dish them out more. Would interested to see if i am right on this, but i think i am close to the mark :wink:

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drmini in aust
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PostPosted: Mon Sep 05, 2005 3:50 pm 
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998 pistons are 0.148" longer than 1098 not shorter, they will hang out of block. :cry:
This is `coz the stroke of a 1098 is .296" longer....

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aaron
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PostPosted: Mon Sep 05, 2005 5:16 pm 
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as they say upside down miss jane?! Brain malfunction for me. i was thinking 1100 rods on a 998 crank :oops:

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Aaron

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fuzzy-hair-man
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PostPosted: Mon Sep 05, 2005 6:19 pm 
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aaron wrote:
as they say upside down miss jane?! Brain malfunction for me. i was thinking 1100 rods on a 998 crank :oops:


1098 rods are the same as 998 rods aren't they? I thought they reduced the piston height for the 1098, so the pistons didn't come out the top of the block and the compression ratio was reasonable.

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drmini in aust
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PostPosted: Mon Sep 05, 2005 7:23 pm 
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Yep, all A series rods (except 970S which are 1/8" longer) are the same length (5.750"). 998 & 1098 just have different pin to crown height in the pistons. :wink:

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poeee
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PostPosted: Mon Sep 05, 2005 8:33 pm 
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I told ya it wasn't a good thing when I start thinking!

Anywho... I'll ask the question again, around the other way!

Because the 998 uses the same block and con rods as the 1098, I was wondering what the compression ratio would be if you used a 998 crank and the shorter 1098 pistons. Would the comp ratio be suitable for forced induction and to what extent could you boost it?

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drmini in aust
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PostPosted: Mon Sep 05, 2005 9:08 pm 
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Depends what 1098 pistons.. I've seen some Oz ones that hardly had the crown attached to the skirts... :shock:
Assuming good ones, you would still want to deck the block, probably by .120" or so- but yes it would help lower C/R. You won't have any squish area though.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:
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Booglie
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PostPosted: Tue Sep 06, 2005 7:58 pm 
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A 998 engine will run with 1098 pistons although very crappy, i had a setup like this in a van and with a 60 thou bore it had less power that an 850
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poeee
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PostPosted: Tue Sep 06, 2005 8:27 pm 
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Booglie wrote:
A 998 engine will run with 1098 pistons although very crappy, i had a setup like this in a van and with a 60 thou bore it had less power that an 850


That is actually good news for the reason why I asked the question. The reason why it ran bad is because of the low compression, but... low compression is what you need for a turbo or supercharger... hmm...

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Spaceboy
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PostPosted: Sat Sep 10, 2005 4:38 pm 
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unfortunately, that makes it a pig off boost
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miniVan
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PostPosted: Mon Sep 12, 2005 1:23 pm 
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you could run some seriously high boost though..

i looked into that.. it is cheaper to deck the block than it is to CC the head too
machining the head flat (which you should do in a rbuild anyway is the same price as decking it to any height (within reason)

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poeee
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PostPosted: Mon Sep 12, 2005 3:22 pm 
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You'd deck the head with a rebuild, well I would, it saves any possible costly implications!

Whether you'd need to deck the block much at all, you'd have to do measurements.

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