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Really boring questions
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Author:  adamstuart [ Sat May 08, 2010 8:19 pm ]
Post subject:  Really boring questions
A few questions on bores, their output and stability.

998:
How big a bore can you go?
How stable is this bore?
What is needed to go to this bore?

1275:
How long is 1380 likely to last, under what conditions?
Author:  drmini in aust [ Sat May 08, 2010 8:30 pm ]
Post subject:  Re: Really boring questions
adamstuart wrote:
A few questions on bores, their output and stability.

998:
How big a bore can you go? +.120" is easiest max, but you can get to 68.0mm.
How stable is this bore? No problem, these blocks are pretty thick.
What is needed to go to this bore? For +.100" or +.120", a set of pistons and a bore+hone job. For 68mm you need Imp pistons + 1100 crank, or bike pistons (more $$$)

1275:
How long is 1380 likely to last, under what conditions?
As long as a 1275 rebore would. ie same as original. But I like to go with 1360, it leaves another bore job for later. No power difference.
Author:  adamstuart [ Sat May 08, 2010 8:45 pm ]
Post subject: 
Thanks dr mini, if something was to go wrong with a 1380 bore could it be sleeved and the engine still be good? Or if a 1380 dies then it's dead.

Also, what kind of output would the 990 +.120 give?
998+120=1118?
Author:  drmini in aust [ Sat May 08, 2010 9:30 pm ]
Post subject: 
You can bore a 1380 to 1400 (if it was offset bored to 1380 or sooner).
Graham Russell can sleeve either a 1380 or a 1400 back to whatever size you need, from 1275-1380.
Author:  Kennomini [ Sun May 09, 2010 10:22 am ]
Post subject: 
So their is no hp or torque difference between the 1360 and 80? or just not enough to notice in a fast daily driver?
Author:  drmini in aust [ Sun May 09, 2010 10:40 am ]
Post subject: 
True.
And once you bore further to 1400 or more, the cylinder walls get thinner and ring sealing gets worse.
This is why turbo 1275 motors are usually kept to +.060" or less.
Want more cubes, stroke it. :wink:
Author:  micowen [ Sun May 09, 2010 11:26 am ]
Post subject: 
Sorry to jump in with a question, but do you guys reckon that it would be a bit stupid to take a mild stroker 998 and bore it to 100 thou? This is for a daily driver mind you, not for the track.
Would you if you could or is this in the overkill basket?
Author:  poeee [ Sun May 09, 2010 11:37 am ]
Post subject: 
If you want more CC's out of your 998, just simply go to the next usable bore size and put a 1098 crank in it.
Author:  drmini in aust [ Sun May 09, 2010 1:19 pm ]
Post subject: 
poeee wrote:
If you want more CC's out of your 998, just simply go to the next usable bore size and put a 1098 crank in it.

No problem boring a 998 or 1098 block to +.100", block is thick & pistons are cheap.
A 1098 crank and +.100" pistons will give you 1188cc.
No substitute for cubes, if you want good torque for a roady. :P
Author:  adamstuart [ Sun May 09, 2010 2:30 pm ]
Post subject: 
drmini in aust wrote:
Want more cubes, stroke it. :wink:


What is involved in "stroking it"

inbeforelamejokes.
Author:  drmini in aust [ Sun May 09, 2010 2:37 pm ]
Post subject: 
adamstuart wrote:
drmini in aust wrote:
Want more cubes, stroke it. :wink:


What is involved in "stroking it"

inbeforelamejokes.

Stroking an engine means increasing the stroke of the crank.
A few ways-
998 motor- fit a 1098 crank & pistons, stroke is 7.5mm longer, it adds 100cc.
1275 motor-
1. get a big journal (1.750") 1275 crank, have the big ends offset ground down to 1.625", use Cooper S rods, deck the pistons 1.5mm. This gives about a 3mm stroke increase (more possible if you go undersize on the big ends).
Cost: around $240 for crank grinding.
OR
2. Get a longer stroke crank made, say 86mm stroke. Cost $,$$$.
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