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Registered:
February 2004
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 2Ltr 2tg questions (NEW ONES!) I think..
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Sat, 21 February 2004 16:01
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In the quest for big revs and mitsubishi-crushing power I'm trying to put together a cheap 2L 2tg using 18r-g pistons on T series rods swinging from the 3t crank but I'm not 100% sure it's gonna work.
I'd be grateful if anyone could set me straight on a few things!!
-1. will they fit? - if I shorten the skirt? what comp piston would be easiest to get 12-12.5:1 I've heard 18rg pistons come in 8.something thru to 10.something. Suspect compression will be way too high or too low without further work.
-1b. will the stock pistons melt or disintegrate or anything?? they're not THAT bad are they?
-2. gudgeon pin right size, but wrong place? I might be able to work with this seeing how theres 2 crank and 2 conrod options but any suggestions would be much appreciated. Will go back to a 70mm stroke if I have to.
-3. I'm not sure that 320i / 304e @ roughly 12mm cams intended for a 1600cc will flow well engough for big revs in a 1800-194O. head is 44.5mm valve type with a little porting done etc. would I be better off keeping the short stroke so theres more flow to go around??
-4. thanks for reading this far!!
-5. The 3t-c and 2t-g cranks are both forged correct?? if not - is the 3t-gte crank forged?
-6. Whats to stop me machining a 4cyl crank- a 2t or 3t - in such a way that if you looked at it longways it would look rectangular in profile? like one of those anorexic billet atlantic cranks! assuming a forged crank is tougher than a billet one, it ( the forged one when lightened drastically by said maethod ) should still *theoretically* be quite strong right??
-7. if the pin location of the 18rg pistons is problematic I could theoretically reduce and offset the crank journals to shorten or lenghten the stroke - right? But then I'm looking for conrods again and it all gets too hard. or does it?
-8. can pressed gudgeon pins be upgraded to fully floating on on 18rg or T series piston?
Any advice at all from ppl with Big bore 2tg experience would be much appreciated!! thanks
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Location:
Rocklea qld
Registered:
February 2003
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Re: 2Ltr 2tg questions (NEW ONES!) I think..
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Sat, 21 February 2004 20:44
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Souns like a big waste of time and money. Im pretty sure its been covered before and was found that it wouldnt work. Just buy a 2ltr stroker kit for the 2t or just get a 18rgu and work that. Would save you lots of heartache and money in the long run.
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Location:
Tasmania
Registered:
May 2002
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Re: 2Ltr 2tg questions (NEW ONES!) I think..
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Sun, 22 February 2004 02:03
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To build a 2 liter 2T-G, it is a simple recipe with not many options. These are the things you MUST use:
3T block or 2T block modifyed.
3T or 3T-GTE crank (both the same).
2T or 3T conrods (all the same length).
After market 89mm or 88.5mm 3T pistons.
Must use 3T pistons of some sort, not 2T.
Pistons:
http://www.beckracing.com/page51.htm#SECT1
http://www.wiseco.com/PDFcatalogs/sc-toy.pdf
These wiseco pistons will give high compression and the valve clearance you need for the twincam.
The cheap option is to use standard 3T-c pistons (can get 1mm over at 86mm). This will only be a 1.8 liter motor, but still a good thing.
If you want to use 18R-G pistons, you can but you will need to keep the 2T crank I think. This is still a good thing and was common back in the day. They are 88mm giving 1703cc I think. Most people to go with the 3T crank.
Use any cams and valves you want. The 2TG head can easily flow as much as it needs to. Don't stop having idears about how to do stuff differently, but I think you will end up with the above formula for a practical engine.
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Location:
Melbourne
Registered:
August 2003
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Re: 2Ltr 2tg questions (NEW ONES!) I think..
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Sun, 22 February 2004 09:05
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If you want to use 18R-G pistons, you can but you will need to keep the 2T crank I think. This is still a good thing and was common back in the day. They are 88mm giving 1703cc I think. Most people to go with the 3T crank.
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Something to keep in mind here is that in standard form the 85mm/70mmcylinder dimensions of 2T lead to a very rev-happy motor which needs to be kept 'on the boil' to perform.
This is because for each revolution a 397CC volume is swept and ignited, driving the rotating assembly through only a 70mm stroke. Proportionally, the bore/stroke ratio in 2T is 1.21:1.
When lengthening the stroke to 78mm on the standard bore, the resultant 443CC volume drives the rotating assembly through a 78mm stroke. The bore/stroke ratio in this case is 1.08:1, so much closer to square. This motor would, all else equal, be more 'torquey' in its delivery than the over-square 85/70 motor given above.
With me so far?
If you now increase the bore of 2T to 88mm deliver 1703CC with 18R pistons and 70mm (2T) crank, your bore stroke ratio will be 1.25:1. (Can you hack camming up then revving out the motor to 8000+ RPM every day to make it perform? Can you live with a 4.3:1 (originally available in D or T axle I think?) or higher short final ratio to keep the motor on the boil through the gears? etc. etc.)
Alternatively, the 85/78 motor described above will not require reboring to suit your pistons, only the 3T crank is needed. Standard 3T-C pistons can be used (with machining for valve releifs). The resulting bore/stroke ratio will be 1.08:1 and the total capacity 1770CC. It's a larger displacement (and a much more usable one) with no overbore required. Think about it.
For interest's sake, the 1mm overbore to fit off-the-shelp cast 86mm 3T pistons (1mm oversize) will net an increase of 42cc to 1812cc. I'd not go to the expense of a rebore unless the block required it, as 1770CC vs 1812CC after the cost of the bore is not bang-for-buck, the difference will be three-fifths of stuff all.
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Registered:
February 2004
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Re: 2Ltr 2tg questions (NEW ONES!) I think..
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Thu, 26 February 2004 13:19
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Thanks for your advice ppl. The block has already been bored out to take 88.5mm pistons, so if one can use 18rg pistons with the 2t crank then I'll give that a go in 1.8L form
I agree it would be EASIER and SMARTER to use a 3t bottom end to displace 1800cc, but I want it to rev like a demon not tow caravans.
" Can you hack camming up then revving out the motor to 8000+ RPM every day to make it perform? "
You make it sound like a bad thing....
Supposing it turns out bad, has anyone got a spare set of (cheap!) 89mm 3t pistons? 
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Location:
Melbourne
Registered:
August 2003
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Re: 2Ltr 2tg questions (NEW ONES!) I think..
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Thu, 26 February 2004 13:44
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Supposing it turns out bad, has anyone got a spare set of (cheap!) 89mm 3t pistons?
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CelicaRA45 is selling some. Arias forged pistons, 88.5mm, ~10.5:1 on 3T bottom end. $700. Send him a PM.
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