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Discussion Starter · #1 · (Edited)
I have shamelessly stolen most of this from www.pngclub.com, and will link the threads, as it is their work and they deserve the credit.

http://www.pngclub.com/forum/showthread.php?93474-*INFO*-Tuning-your-SPI-8v-Engine

"I have to say, i had these mods on my old 1.2i, and they are well worth doing

Thanks to Aragorn for the guide

This guide is aimed at tuning the 1.2i engine as opposed to the 1.2 tuning guide posted by MC, although a lot of his stuff will apply he simply suggests changing to carbs for the 1.2i which isn't really and option for some people (k plate cars) and others may simply not want the hassle of carbs and prefer the reliability side of injected engines. I have performed all the mods in the first section myself and have had good gains from it (I'm awaiting RR readouts but have had an 18.8 sec 1/4 mile in my bros car with quite a high 60ft (2.9secs) his car has no rear seats and cobra Monaco's tho so some weight saving going on)

The 1.2i (C12NZ) makes 10HP less than a 1.2 carb as standard, however it
makes identical torque due to the different design of cylinder head.
The engine also has a number of factors which restrict it compared to the
carbed engine. The Cylinder head is very restrictive compared to the
1.2carb version. It has very small square ports with bad flow characteristics
whereas the 1.2 carb head has much larger cathedral ports and bigger valves
which flows much better, its these restrictive ports which help the 1.2i
make the same torque as the carbed engine even tho it makes much less
power, however that torque is available over a shorter band which is why
the 1.2is are slower. Unfortunately the carb head will not fit streight
onto the 1.2i becuase the inlet manifold wont line up, i give some
instructions later in the guide about swapping heads but as i mention
there this only works if your fitting the SRi injection system or twin
40's and is not what i'd designate a cheap mod. I am going to look into
mounting the SPi throttle body on a 1.2carb inlet manifold which will
enable you to fit the carb head but i havent got round to this yet. The
other restrictions are the cam which has lower valve lift and the engine
has a restrictive cat fitted, thats what were going to work on here mainly.

Exhaust:
The first mod i would suggest is to fit a better exhaust system right from the manifold back, there are two approaches here depending on the age of your car and how much hassle you want come MOT time, if your car is a H or J plate then you don't need a cat at all, if its a K plate you will need a CAT for the MOT unless YOU can prove to the tester that the engine was built before august 92 (depends on the tester, only real date stamp on the engine is the cam).

If you don't need a cat (or don't mind refitting the complete original system come MOT time) then the first step is to find an SRi (or late 1993 GSi) exhaust manifold with lambda probe port - the engine needs this sensor to run properly so you need a hole on the manifold for it. Then you want either an SRi or GTE/GSi downpipe and a full system for a GTE (Ashley do a nice 2" system for ?130, or you can use a std system from scrappy)

If you do require a cat for mot then you can do it a different way, if you find a SRi in the scrappy and get entire exhaust from it, then get a decat pipe for the sri system and that way you can refit your cat for mot and put the decat on at other times. I personally would take the first approach and if your car needs a cat then modify the cat of the original 1.2i exhaust to fit the GTE system, that way you can fit the middle section of the 1.2i system for mot and return to the GTE/Aftermarket system afterwards. Or you can find a friendly MOT tester

Cam:
The standard cam on this engine is very restrictive, fitting a cam from a higher spec model will give great gains (I'd recommend getting one from an injection model(SRi, GTE, GSI) although an SR one would work too. If you want to fit it yourself the head needs to come off and the gasket and headbolts will need changed while your there

Air Filter:
The standard airbox looks ****e but does the job fine to a point, just remove the handle section off the front of it and throw it in the bin for extra noise - if you want an upgrade there are a few cheap ways of doing it...
You can use my guide to making a cheap induction kit here: http://www.novaload.net/forums/viewtopic.php?t=90933
Or you can get a 1.2i Corsa airbox and fit then then either shove a cone on the end or use an SRi airbox with performance element
don't bother wasting money on a green induction kit as its ?70 you can spend elsewhere - the Corsa top box shouldn't cost more than a 5er and neither should the sri airbox

These are the main cheap mods for this engine before you start hitting big money, and the majority of it is cheap stuff (air filter shouldn't cost more than ?30 if you follow my guide, cam is probably about ?30 then another ?30 for the bits to fit it (unless you pay a garage), exhaust is a bit more but the advantage is that its usable on a larger engine you may fit in the future

Weight:
If you want to go fast your main enemy in a small engined car is weight, lots you can do in a nova to lose it but it reduces flexibility, removing the rear seats and rear belts will save you about 20-30kgs and the car can still look cool, if you want **** then you can remove all the door panels, fit Plexiglas windows and ditch the dash board, you could probably shave off 70kgs in total if you did all that and thats gonna be similar to the difference of driving alone and driving with a passenger which will be very noticeable in a 1.2i nova

Suspension and Brakes:
Acceleration is one thing but if you car handles better and stops faster you can drive faster as you wont lose as much speed through corners and can leave braking later, a good quality matched spring and shock kit is what you need - springs alone wont help handling much (they will help but just not very much) and some Astra GTE16v (or Cav 2.0) 256x24mm disks and callipers will help stopping power greatly Do not underestimate tyres either, ****e tires will make a huge difference to the cars performace and handling and stopping characteristics, best for the nova would be some 6x15" wheels with ET49 offset and 195/45R15 tires, Uniroyal Rainsports and Goodyear EagleF1's are good grippy tires and are decent in the wet too. Don't go sticking ET38 or 7" wide alloys on and expect the car to handle well, it wont.

Service:
I'd recommend giving the engine a good service while your here, new rotor arm and dizzy cap, new plugs and leads (don't buy performance crap, just standard NGK plugs and normal Bosch or whatever leads, also do an oilchange with a new filter and replace the thermostat if your taking the head off to fit the cam

Gearbox:
A point often overlooked in tuning smaller engines - the standard 5 speed 1.2 boxes are very wide ratio, you ain't got a lot of power so theres no point having gearing that can manage 150mph when the car will only do 105 an F10CR box from an SR or F13CR box from a GTE would be a good choice and fitting a 418final drive to either of those boxes would give an excellent gearing for acceleration

Taking it further:
At this point your not gonna get any major power hikes without spending lots of money - its arguable wether its worth it at this point but as long as you only buy stuff thats transplantable onto a new engine you should be alright in terms of wasted investments.
The head is very restrictive so fitting either a 1.2 carb head or a 1.4SRi head(skimmed to sort compression) would be the next step
You could then either fit the complete 1.4SRi injection system (arguably a waste of money) or fit some twin 40's (these can be fitted to a larger engine in the future if required)
if you used the 1.4sri system you might need a remap but it does have a lambda so it might work out whats happening by itself
fast road and rally cams are available with varying attributes - a 285 cam should be alright in the std engine and you should be able to push to a 295 if you fit the SRi stuff or twin40's

fully modified with worked sri head, 40's 295 cam full exhaust etc you could see the friendly side of 100HP

So there we are - hopefully that will answer most of your questions and provide a solid base to work on

Aragorn"
 

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Discussion Starter · #2 · (Edited)
Less specific to the c12nz and written for the NOVA:

http://www.pngclub.com/forum/showthread.php?93429-*INFO*-1.2-8v-Tuning-Guide

"Before commencing any engine modifications, it is advisable to ensure that all of the basic components are working well. This will save time and money. The engine itself should be in sound condition with no unusual knocking noises and no smoke. Theres no point spending money on an engine that is going to fail. Also check that the ignition system is in good working order. If in doubt use new plugs, leads and distributor cap, nothing fancy, as long as they work, there fine.

This guide is based at getting power on a strict budget. Even this will cost money, so if your only driving this particular car for a short while until you can afford something faster, dont bother, save your money. If however you see it as a project to get a quick little engine car and have fun, then these tips should be helpful. The only way you can really save money on any modification, is to do it yourself. If you are paying someone else, then change your pay details so that the money goes direct to the garage!

One last thing, if you have limited power, dont fit big body kits and wheels, I guarantee they will slow you down. I lied, another note, lose weight, drop the huge stereo system, and if you can bear it, strip some interior, it will make more difference than spending ?500!

Ok, on to tuning the 1.2:

You need to start hunting around the scrap yards.

Exhaust
You need to get a system from a GTE/GSI ideally. The SR models will still be an improvement, although I believe diameter will be bigger on the 1.6`s. Get the manifold, down pipes, and full system. The design is better with the twin down pipes, and this will flow the gasses out quicker. You will probably have to shell out around ?50 for the lot, but it will be far better than buying a performance back box.

Head
Stick with the one you have. It flows well, and will start costing to much money to play around with. If you really want to help, match the manifolds to the head by cutting the gaskets to the size of the manifolds and then taking metal out of the head to match the gasket. Personally for a beginner Id say not to bother. Its quite involved and you could do more damage than good. Cost ?0

Camshaft
Once gain the GTE/GSI is the best source. The camshafts are interchangeable, so the SR one will fit too. This will give increased duration and lift, but beware, try to use the followers that are with the new cam, and in the correct place. Also look at the amount of wear. There is no point picking a cam coz it is suppose to have 2mm higher lift over a longer duration if there is 4mm of wear on the followers. Try buying new ones if you can stretch to it, and come to mention it, buying new ones for the standard cam will probably bring back a few missing ponies. Costs: Cam: ?25

Inlet
The simplest and cheapest way forward is to find yourself a 1.3sr. It must be a 1.3 and not the 1.4 as they are very different. Youll need to take the carb and its manifold. The manifold will fit on the 1.2 head, and hey presto, you have a twin choke. This isnt the ultimate solution, but it is a vast improvement. Cost is gonna be ?50 plus from a scrappy.

Now this should get you SR (ish) performance. Not a rocket ship, but it will be more fun to drive. There is a lot more to do, but realisticly, its not worth the extra expense. Dont overlook the brakes and suspension!

Insurance is a consideration. Youll need to declare the carb and exhaust, both of which will have minimal effect on your premiums, if any at all. The camshaft however will never be noticed. Id bet money on that.

This all adds up to around ?125 (not bad for a 15+ bhp increase), you might be able to get bits cheaper or even for free, some scrappies might charge more, so expect to shell out between ?50 and ?150. Dont forget about consumables such as head bolts and gaskets, coolant and most importantly youll need a haynes manual!

Ste L"

SUMMARY:
INLET: C16NZ inlet, with a C18NZ throttle body and C14NZ injector.
CAM: Replace cam with one from a C16SE/E16SE or 1.3sr Nova
EXHAUST: 4-1 manifold, decat, straight through, nice backbox.

WITH TOO MUCH MONEY: Fit a different head or machine the one you have
Fit the crank and rods from a 1.3sr, which makes a 1400 really tourquey engine and apparently goes like stink, as I've heard from a few different sources.

These will also work on the C14NZ, apart from the 1.3 crank & rods, as the only real difference between it and the C12NZ is the bore size. This also means, you can buy a C14NZ, do all these mods, then fit it to your car using the standard loom, and plug in a different ecu.

Hope this helps, if I have got anything wrong in my summary, tell me and I'll edit.

ADDITION: Doing masses of work isn't worth it, look at fitting something like a C16SE or the standard 2.0 16v C20XE, as they have more power, and then mod that. Not much extra work, not much extra on the insurance. If you're like me and don't fancy attempting an engine swap though, most of the parts to mod the 8v are cheap, but not too easily found.

2nd Addition:
I have put a cam in from an e16se (Nova GSI) along with a panel filter, drilled and derestricted airbox, decat, straight through and sportex back box, and the car is a lot faster and nicer to drive. The cam is well worth it, I got mine for £20, cost about £30 after getting the bits to fit it (new head bolts ect). It runs great, has slight overfuel (which makes exciting noises in the exhaust) and now has a lovely cammed idle. I've knocked a whole second off 0-60 and several seconds 85-95 and a shocking 10mph added on the top speed (on the same bit of track of course), due to the power band relocation. I'd definitely do it again and highly recommend it.

- Alex
 

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"and more in-depth is fitting the crank and rods from a 1.3sr, which makes a 1400 and apparently goes like stink" hmmmmmmmm tempting lol,
also question for rob, is the 1.4 8v and 1.6 8v the same cam or is one better
1.4 sr uses a 6.13 lift cam, the highest stock lift. the 1.4 spi uses a soft cam. the c16se cam is pretty good.

as for the rods and crank, it does work but it makes a torquey engine. good for grunt but not massively revvable.
that should fit fine.
 

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Discussion Starter · #6 ·
1.4 sr uses a 6.13 lift cam, the highest stock lift. the 1.4 spi uses a soft cam. the c16se cam is pretty good.

as for the rods and crank, it does work but it makes a torquey engine. good for grunt but not massively revvable.

that should fit fine.
What's bad about it being torquey? what kind of power could you expect with just a bottom end change? I know everyone hates what power questions, but what can be expect? a nice 60-70bhp, or suddenly a 100bhp beast?
 

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what bottom end?

in all seriousness, spending weeks doing cams etc and pissing around, you may aswell buy a c16se, f13cr, 4into1 mani and fit that.
 

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possibly. do you do the speed limit or not?
 

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Krazee, ho are you planning on doing all this work to your engine, bearing in mind resources n this are fairly scarce and you have very limited mechanical knowledge?
 

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Is this a tutorial thread, or a help thread?
 

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A bit of both I'd say! Just thought I'd add, ive decided against doing any serious tuning on my engine now, after serious talks with Courtenay, Redline, Kent Cams and Autosprint.

None of them reckon I'd see past 80 bhp even after spending a substantial amount of money. In light of that I just don't think it's worth it, so going to put the money I've saved towards a new car.
 

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1 down, 1 to go.

Really isn't worth it
 
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But when you can afford to run two cars you can afford to not piss about with a stupid engine and buy something that actually has some power to begin with and is ridiculously easy to tune further. Rather than literally throwing cash at a brick wall.
That would imply someone is actually going up to a brick wall and throwing coins and notes at it. :shocked:
 

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But when you can afford to run two cars you can afford to not piss about with a stupid engine and buy something that actually has some power to begin with and is ridiculously easy to tune further. Rather than literally throwing cash at a brick wall.
The only thing stopping me running two cars is insurance at the moment. I'll have a serious car and this would be my bit of fun on the side. People don't seem to see the point, if I wanted outright power then you're right I wouldn't bother, however that's not what I wanted, I just wanted a bit of fun.
 

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That would imply someone is actually going up to a brick wall and throwing coins and notes at it. :shocked:
Shhush you, lol

The only thing stopping me running two cars is insurance at the moment. I'll have a serious car and this would be my bit of fun on the side. People don't seem to see the point, if I wanted outright power then you're right I wouldn't bother, however that's not what I wanted, I just wanted a bit of fun.
But you'd get more fun from more power for less money... Lol. Or still shite power for more money.
 

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Or I'd have the satisfaction of more than doubling the original power :)

As I said, I'll have a serious car with plenty of power and this will be a project on the side. However come the end of the show season, I'll be changing to something with substantially more power, so this project will have to wait a couple of years.
 
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