View Full Version : changing to the 1.2 head
I have read on here about people changing the head on a 1.4NV to the early 1.2 carb head.
Does this make a huge difference in performance? I have a 1.2 head but obviously it would mean getting the manifolds changed to match the ports on the head. Are ythe valves in the 1.2 head not smaller than in the 1.4?
Is it a big enough difference to justify the expense of getting the manifold ports machined? Also can I put my kent .51 cam in this head?
Would be graet to hear from folk who have actually done it,
Thanks
phunkynova
31-05-12, 07:00 PM
You would be better off putting a C14SE head on but then you need a inlet manifold with round ports to match the SE head which has bigger valves as standard.
the valves are the same size, but the compression ratio will be higher.
Jon_nova1
31-05-12, 09:01 PM
1.4 head is square, 1.2 is cathedral. you need to run the 1.3 inlet with the 1.2 head, I did this many years ago and plonked a 1.6 astra carb on it, to be fair it went well for a 1.4, it was quicker off the line than a GTE, but lost out when aerodynamics took thier toll
the valves are the same size, but the compression ratio will be higher.
Would the compression ratio make a noticeable difference? i.e. would changing the head on a car with kent cam and 4 branch manifold etc make that much difference?
The longest straight on knockhill is probably about 1/4 mile uphill, is the car likely to go much faster with the change of head or will it be negligable on such a short run? this is the main place for advantage with lack of speed at the moment.
1.4 head is square, 1.2 is cathedral. you need to run the 1.3 inlet with the 1.2 head, I did this many years ago and plonked a 1.6 astra carb on it, to be fair it went well for a 1.4, it was quicker off the line than a GTE, but lost out when aerodynamics took thier toll
The car is pretty quick off the mark as it is, it is 40 mph onwards that the other more powerful cars pull away, in all honesty due to the lightness of the car and the carb, pulling away immediately my nova does well but fades....awww
If I do change the head from the 1.4 to the 1.2, are there any modifications required or do I just follow haynes and put in a new gasket and borrow (reluctantly) the inlet from my SR?
The Kent cam in my 1.4 is a 051 and is designed for 1.4 injection. I am using an electric fuel pump so will this cam still work effectively in the 1.2 head if I blank the fuel pump bit?
it should work ok. you really would benefit from getting the head ported & bigger valves fitted,
you could just get the 1.4 head skimmed down a lot & then fit a vernier puller to get the timing right.
Thanks for that, so fitting the 1.2 head wouldn't make a massive difference without further work carried out to it?
Getting the 1.4 head skimmed sounds like an easier and cheaper option.
The cam comes with a vernier pulley but I have had to set the valve timing by trial and error, even for the ignition timing the markings are on the inside cover which isn't on this car. For some reason vauxhall didn't put the marker that's the 1.2 and 1.3 block, they put it on the 1.4 cover.
A bit of an inconvenience but, I have selected the wrong gear a few times at first when getting used to the box selector etc, and have way more than redlined it so i assume that if the valve setting was miles out I would have found out then.
i was thinking more on the lines that you need to take a stack of bits off another car to make the 1.4 work with the 1.2 head, so, why not raise the compression the old fashioned way...
obviously you need to do the old compression calcs with perspex & a small syringe with oil to get the cc's right for the various bits, so you can work out how much you want skimming off. its not too hard to do.
I see what you mean. I have seen a thread in the guides section that explains working out how much to be skimmed.
As the head has to come off anyway, would I still have to measure this before putting the 1.2 head on or will it just work when fitted?
Wieghing up the easiest and cheapest options for a bit more speed...................
the 1.2 would work straight away, but with higher compression, you'd need to use super unleaded petrol, if you aren't already
never used super unleaded, does it make a good difference then?
well, stick a high compression head on your engine & watch the detonation on normal crappy unleaded.....
super u/l is a must if you are running 11:1cr
Thanks for that, I'll try it with the car the next time I fill it up even as it is.
This week I have to buy a torque wrench and gasket set.
The next week is to take the inlet etc of the SR,
The following week....work up the courage to take the head off, change cams etc and hopefully not bend any valves/burst pistons when I start the car!
the main trick is to strip & clean the hydraulic tappets...
you get them out & keep them in number order. then you compress each one in a vice or g clamp, & pop the clip off with a small screwdriver. then undo the vice/clamp. you then pull them apart & clean up the inner, outer & spring, and do not use anything abrasive. use petrol on a rag, or a non scouring cleaning chemical, and once clean & dry, put them back together, wipe some oil round them & fit them into the cleaned head. when you time the engine up, they will compress ok, and when you are ready to turn it over, make sure the spark plugs are out & wind it over on the key. they will pump up when the oil pressure builds. once you have seen the light go out on the dash, its time to put the plugs in & fire her up.
Thanks for that, I'll save this thread in my favourites so i can find it easily when I reach that part. I could do the tappets now as I have the 1.2 head sitting in the garage, or would sitting for a few weeks after cleaning dry them out again?
Looking at the super unleaded...this may be a stupid question...is it a different type of petrol all together or is it stuff with additives, e.g. in my 1960 mini I add a valve additive to protect the car, also you get ron increasing additives?
1. the tappets will be fine dry. the problems only arise if they are still full of oil when you assemble the head... people have snapped followers..
2. super unleaded is a higher ron fuel, and is better suited for higher comp engines. it will have some extra additives to get more power output.
Thanks, more advice please........
1. What cylinder head gasket should I use, 1.2 or 1.4? I wenyt today to buy one, they both look exactly the same except a small indentation on the out side of a corner, the shop suggested the 1.2 as it was a known make gasket.
2. Head bolts, the bolts in the car were put on by the previous owner less than a year ago and he never got the car going. I have done under 1000 miles. The guy in the shop said these would probably be fine so long as I haven't overheated the engine or had a cracked gasket etc causing them to stretch.
3. looking through the stuf for the car from the previous seller, he said it is a 1.6 vauxhall head he put on it for bigger valves and ports. It still has the oblong inlet ports. This head works apart from a poor idle but that may also be the kent cam and doesn't bother me anyway. Will I lose any power by putting on the standard 1.2 carb head, or is this 1.6 head no better than the 1.4 anyway?
Thanks again for the advice.
1. 1.4... its the bore thats important
2. new bolts every time, do not skimp on it.
3. i'll check
Jon_nova1
21-06-12, 08:59 AM
the 1.2 would work straight away, but with higher compression, you'd need to use super unleaded petrol, if you aren't already
The 1.2 head with 1.4 block? i never once used super unleaded in the year i was driving it around iirc i only got a slight knock when i accidently put a fivers worth of diesel in with £15 worth of petrol and that went as the diesel got diluted
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