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| 1098 pistons/998 crank = good forced induction comp ratio? https://www.ausmini.com/forums/viewtopic.php?f=5&t=10811 |
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| Author: | poeee [ Mon Sep 05, 2005 3:09 pm ] |
| Post subject: | 1098 pistons/998 crank = good forced induction comp ratio? |
Quote: 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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| Author: | aaron [ Mon Sep 05, 2005 3:46 pm ] |
| Post subject: | |
You would have to deck the block quite alot to get it to run. Dropping 100ml in engine capacity that is 25ml per bore.  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 
Cheers aaron |
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| Author: | drmini in aust [ Mon Sep 05, 2005 3:50 pm ] |
| Post subject: | |
998 pistons are 0.148" longer than 1098 not shorter, they will hang out of block. 
This is `coz the stroke of a 1098 is .296" longer.... |
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| Author: | aaron [ Mon Sep 05, 2005 5:16 pm ] |
| Post subject: | |
as they say upside down miss jane?! Brain malfunction for me. i was thinking 1100 rods on a 998 crank 
Cheers Aaron |
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| Author: | fuzzy-hair-man [ Mon Sep 05, 2005 6:19 pm ] |
| Post subject: | |
aaron wrote: as they say upside down miss jane?! Brain malfunction for me. i was thinking 1100 rods on a 998 crank
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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| Author: | drmini in aust [ Mon Sep 05, 2005 7:23 pm ] |
| Post subject: | |
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.
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| Author: | poeee [ Mon Sep 05, 2005 8:33 pm ] |
| Post subject: | |
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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| Author: | drmini in aust [ Mon Sep 05, 2005 9:08 pm ] |
| Post subject: | |
Depends what 1098 pistons.. I've seen some Oz ones that hardly had the crown attached to the skirts...
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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| Author: | Booglie [ Tue Sep 06, 2005 7:58 pm ] |
| Post subject: | |
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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| Author: | poeee [ Tue Sep 06, 2005 8:27 pm ] |
| Post subject: | |
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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| Author: | Spaceboy [ Sat Sep 10, 2005 4:38 pm ] |
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unfortunately, that makes it a pig off boost |
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| Author: | miniVan [ Mon Sep 12, 2005 1:23 pm ] |
| Post subject: | |
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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| Author: | poeee [ Mon Sep 12, 2005 3:22 pm ] |
| Post subject: | |
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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