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ed_ma61
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Registered:
May 2002

Re: 7MGE bore spacing and overbore limit

Thu, 14 August 2003 13:09

oldcorollas wrote on Thu, 14 August 2003 20:11

raw and grunty old tech, like a motor _should_ be...i like the backyard raw motor

stewart, you and i, bud, have some beers to be sunk between us Smile

anyway, steve, here's a *basic* list of what you can easily do to a 7m to shake it up a bit. keep in mind, there are many, many conversations to be had with regards to each of these points, and each of them can be taken to 'silly' extremes - but then youre running into serious motec only territory...

intake:
-cai
-intake pipe
-throttle body/ies
-single vs twin inlet plenum with ACIS
-custom chop manifold with ITB's
-manifold porting and plenum porting
-port matching

head:
-intake porting, from mild to wild
-bowl can have massive improvemnets
-valve seats and seat cutting
-OS valves
-chamber shaping
-decking for CR increase (plenty of meat)
-valve unshrouding
-polishing
-ex valve porting - big gains again
-ex seat cutting
-headers 6-2-1 or 6-3-1 (dunno there?)
-hi flow 2.5" zorst

CAMS
-up to 9mm lift before head recess machining and Shim under modification required
-duration up the ying yang
-valve springs (?)

PISTONS
-truly mssive piston valve clearance
-allows plenty of scope with cam choice, compression machining etc
-pistom crown shaping and polishing
-rings - your call Smile

RODS
-grind and beam polish and peen
-ARP bolts essential

BLOCK:
-GTE block w/ oil squirters (reduce temps a LOT)
-again, given piston tolerances, you can decrease the block deck height significantly (i chopped mine 40thou!!)
-oil return chamfering etc
-external oil cooler fitting stock on some 7mge's
-2 cranks available - single counterweight and double (later models) single is lighter, but less balanced
-i dunno if thyre all like this, but my crank is forged (out of a GTE)
-crank machining, lightening etc

OTHER:
-squish clearance is in your hands - can go to 35thou with stock 7m rods.
-piston squish surface area is ~30%
-head squish area is around ~20-25%

ive happliy squeezed 10.7:1 with basic non-dodgy machining (up from 9.2), and could easily get 11:1... and get this - such machining STILL maintains a non-interference piston/valve fit!!

if you wanted total interference fit, you could go easily to 11.5-12:1 AND run big lift big duration cams, and STILL not have clearance issues (this is with plain old cast ACL jobbies - so not sure how crazy you'd want to go on them anyway!) if you wanted to go custom pistons, the world is yours...

its all shades of grey really - how far down the scale youre prepared to go, what youre prepared to spend and risk, and what you reckon the ECU will run before a motec is required Very Happy

hope thats a start Rolling Eyes

as i said each point is a conversation piece!

cheers
ed

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