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stileguy 11-22-2005 09:31 PM

Displacement Increase Combinations
For those of you out there wondering how to make a larger displacement engine for cheap. here is some possibilities, first i'll show stroke and bore of the usual subaru engine sizes then ill explain the effects of mixing and matching.
engine size/bore/stroke
2000cc/92mm/75- best bore/stroke ratio for big revs
2200cc/97mm/75- better than 2l low down and with aftermarket rods and pistons can rev like 2l
2500cc/99.5mm/79- heaps more torque lowdown, less revs to play with.
2145cc/92mm/79-2l bore with 2.5crank with 2mm shorter conrod- greater conrod angularity produces more leverage on crankshaft and creates much more low down torque than 2l but less topend due to rev limit similar to 2.5 engine,(budget autox engine)
2435cc/97mm/79- the best power combo here, almost same bore/stroke ratio as 2l engine, does not rev as freely as 2l due to 2.5 crank but revs more than 2.5 due to great bore/stroke ratio.
my ideal budget stroker: legacy 2.2 block with 2.5 crank, forged rods 2mm shorter than stock with forged pistons identical to stock wrx but 97mm instead of 92mm with version 6 STI heads and cams with .6mm version 6 STI 3ply stainless head gaskets
however i like the 7800rpm shiftpoint and 25psi boost of my EJ207 STI motor with only a set of forged rods and ARP bolts for safety.
some of you may notice some displacements familiar, many tuning houses do exactly this and charge you the earth. most of these parts are off the shelf. (not always subaru parts)
have someone measure your conrods and find a set of off the shelf ones identical which are 2mm shorter from bigend/wristpin centre to centre. these will work fine.

04roadtuned 01-29-2006 10:23 PM

what if you wanted a budget motor for road racing with high revs?

knot04 01-30-2006 11:07 AM

usually "budget" and "up-graded internals" dont collide in the same sentence, however if you are simply looking for high revs, go with rods and the entire vlave train.

GetUpInDer 01-30-2006 12:49 PM

[QUOTE=knot04]usually "budget" and "up-graded internals" dont collide in the same sentence, however if you are simply looking for high revs, go with rods and the entire vlave train.[/QUOTE]

Good call!

04roadtuned 01-31-2006 10:15 PM

haha too true, i over looked that

Blu_MaTiC 02-05-2006 12:20 AM

would it be possible if you got money like that swap a Sti motor piece by piece

joker97 02-15-2006 12:06 AM

hey could you explain the physics behind more bore more torque; more stroke less revs; and the best bore/stroke ratio thingy? i'm real interested in these things!

stileguy 06-14-2006 07:51 AM

the physics is very complex and best understood by reading some books by corky bell a thousand times each....longer stroke gives more torque because it changes the conrod angularity- what this means is that the piston pushes the crank with more "leverage" due to the longer throw in the crank, larger bore gives more torque because you can fit more intake charge into the engine. however the larger components weigh more and with a longer stroke the bigend section must cover more distance for one revolution. the same way that when ice skaters spin on axis with their arms out then pull them in they increase in speed, centrifugal force etc etc etc, this is a very simple explanation and does not even begin to touch the surface of how bore-stroke ratios affect on road performance. educate yourself, and make decisions about what is right for you instead of taking the word of a guy who needs your cash to feed his family or finance his own toys, go in and tell them what you want and ask how much it will cost, if they dont co-operate with you shop elsewhere.

imbeterthanu 06-14-2006 10:32 PM

dude were did u come from. have u been hidding? nice write up btw!Thumbs Up

stileguy 06-15-2006 10:40 AM

i was on here about 6 months ago but got sick of reading about utecs and up-pipes and cat backs as this seems to be the extent of the modifying that goes on here, read some of my other posts such as the compressor surge problem and fix which i found and you will see why i got sick of exhaust questions etc, now however the forum has more in depth content and more experienced people to discuss the finer details. i have been modding subarus here in australia for the last 10 years, i originally started out playing with my own cars and then moved to working on the cars of people who i beat at the track, so now i have ppl send cars to my house from 500km away and leave me a bundle of cash and i work on it in my spare time and send them back complete packages for a fraction of the price which shops charge them.....word of mouth is the way i get project cars now and i only do complete jobs(mechanically speaking), it must be finished completely before i send it back to the owner for my own piece of mind, i never return a car to the owner that is still in need of a final tune, that would be asking for trouble. i love doing it so my labour charge is very low, i usually make $1000au for each project which takes about 6 weeks.

imbeterthanu 06-15-2006 11:02 PM

yeah man. i know who you are. i was around when u first came here. like i said u just went into hybernation. but i do know that u know your shit!

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