best spec 1.2 ???

[5_door owner]

alrite then. i've got a mint condition 1.2 engine all on a stand an eveythin in my shed (not jus garden shed quite spacious)

so i want to build it up slowly then either use it for track or on road. i'm thinkin of a re-bore to around 1250-1300cc complete with pistons ect..

now over the course of rebuilding it im looking at spending about a grand on it probably more as it will be over the course of a few months(?year?)

so im just wondering what spec i'd be able to get for the money and what power figures.

please can you list all that can be done to the 1.2 and what parts ill be needing,

cheers fella's

(oh and btw i know i could just get another bigger engine and do it to that, but that'd be no fun :twisted: )

[Geth]

Im doing pretty much the same thing with mine. Don't let anybody tell you the 1.2 will be a waste of time. The fun is in trying to get 1.2 to go as fast as it possibly can.

This is what I'm doing at the moment.

Carb
Webber 32/34 twin choke carb. Very easy to come by. I think you need a 1.3 inlet manifold and an adapter to put them together. I got the whole setup all put together from ebay with a K&N air filter (Don't forget the K&N) for less than ?100. You could go for the DCOE twin 40 setup but that will cost around ?700.

Cam
Get a Kent or piper cam kit. A fast road cam will create higher lift and more power between 2000-6000 revs. A complete kit with springs and followers etc. will cost around ?250. Kent cams say you can get around 8-10 Bhp from an AST1 cam.

Outlet
Anything should be an improvment on the 1.2 exhaust system. You can either get a second hand 4-2-1 system of a 1.3 for around ?30 or a new 4-1 performance exhaust for around ?140. Although the 4-1 will require the rest of a 1.3 system anyway as the 1.2 exhaust won't match up.

As for the rebore, I don' know how much you can over bore a 1.2 by (I will find out in a few weeks when I get mine done). If you can take it up to 1.25 you should see a decent increase in power and your compression ratio will inrease aswell. With tthe combustion chamber in a 1.2 being 130cc you will get ratio of 9.6:1 (1250/130 9.61). You can then skim the head to get it up to around 10:1. These figures can be re-jigged depending on how much the engine is overbored but you should get the idea.

I don't yet know how much power you will get out of this as from reading other peoples's experiences, adding up the numbers never seems to be what you get. Give me a month or so and I'll get it on a rolling road to see what it's pulling and set up the carb.

Oh yeah. I'm not toosure how long a 1.2 will last on a track. You might blow it up in half the time it took to build it.

Sorry for the long winded reply but I'm pretty bored/stoned.

[Aragorn]

the 1.2 bottom end is just as strong as the 1.6 etc, its bearings rods caps bolts etc are all capable of the same power levels as a 1600 block and will me more rev happy since the stoke is shorter

for big power u'd need a set of 40's, 1.4SRi head (b+ mods preferably and compressoin ratio calculated and head skimmed to 10:1), 290-300degree cam, decent zorst system, high rev limit (7500-8000?) with arp rodbolts

you should be able to see the friendly side of 105bhp if not a tad more with higher rev limit

[burgo]

to make a 1.2 a 1.3 you use 1.4 crank and rods

[Aragorn]

why bother doing that when u could just buy a 1400 block for pennies

and its 1300 rods and crank and 1200 pistons makes 1403cc engine

[burgo]

why bother doing that when u could just buy a 1400 block for pennies

and its 1300 rods and crank and 1200 pistons makes 1403cc engine

DOH :oops: i knew it was a combination of some of them to get something else

[Stuart]

so far "we" have a 1.2 head (no stupid EGR crap to fill in) with 1.6 diameter (but 1.2 length) valves cut in with 3 angle seats. (?300 ish) Head porting to suit the new cuts and some ramp porting to try and squeeze a few more CFM of air in due to gas speeds. Heavy skim. nearly 2mm off it lmao, some combustion chanber work but not much as it will upset things like the burn and compression ratio.

Cam we have a 285 piper but im binning it in favour of a 300+ cam BUT with the idea of revving to 8K and seeing as benji munched a set of lifters in not long, id look to fit solid lifters (?250 a set). I shall be looking into making my own. An AST1 is a bit of a waste of time if your gunning for "max power", but it might be a bit more driveable low down .

the bottom end had a 1mm overbore and some pocketing of the pistons to accept silly lift/duration cam. Also the pistons slightly intrude into the head. the gasket takes up this gap.

bottom end, rods were de seamed and shot peened oh and arp bolts, crank polish new bearings etc.

i belive the bottom end build wasnt far off ?900ish maybe more with full VAT etc.

it will be getting Twin 40's and a modified 4 branch exhaust


couple this to a CR gear box with a >4 final drive and you should see a rather nippy 1.2

i did some rough simulations with GT Power at work and it claims about 130Bhp @ 8K but thats not including proper losses etc so id say more like 120 MAX on a good day with perfect conditions .

TBH if i get over 100 ill be happy.

with a webber 32/34 you WONT see more than about 80 unless your on an iffy RR

[w_wall_2001]

i know someone who has a 1.2 block overbored to fir 1.67 pistons and rings, diffrent crank etc, a 1.2 head with i think 1.4 valves, cam etc with twin 40's with a corsa spi rocker cover

[DrivingSpanner]

reving to 8k stu.... I wonder where you got that idea from!!!

[burgo]

so far "we" have a 1.2 head (no stupid EGR crap to fill in)

which isn't to hard if you good witha dremel

stu i ended up doing the bolt method