tunning a 1256

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tunning a 1256

Postby ross.cheeks » 30 Jan 2007, 23:08

hi recently bought a chevette and am looking for some ideas on ways of getting some extra power out of it. not looking at throwing loads of money at it or for silly power gains just enough to give it a bit more poke.
a few people have said just change it for a bigger engine but thats not an option at the mo as mr insurence man would want to much money.

my thoughts were exhaust,carb, cam and prehaps some head work.

cheers ross
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Postby Shellysowner » 31 Jan 2007, 02:20

The first thing to do is change the carb and the air filter. To be honest there's little point in doing anything else to it unless you do a fair bit of head work as the head is the most restrictive element of the 1256. If you're doing head work then you'll want to do the cam and exhaust although good luck with getting an exhaust manifold, unless you are willing to spend £175. Having said that I am reliably informed that you can get up to around 75-80bhp and a significant increase in torque without changing the exhaust manifold.

Basically the long and short of it is that anything other mild tuning of the 1256 is not the most financially sound thing to do - unless you're an idiot like me or are very lucky with getting tuning bits for cheap.
Doive wrote:I remember last summer being in another Chevette with a quite mad driver, and we were drifting round A class roads at 65mph with the tail sliding progressively on the corners. It was fantastic.

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Postby Shoveitpusher » 31 Jan 2007, 10:14

a lighter flywheel and lower final drive, 185/60x13 used to be the normal method, will directly increase performance, sticky tyres, suspension and brakes will indirectly increase performance and will certainly increase your driving experience.

stage 1 would be filter and carb (webbers are always nice) and a manifold (you could have a go at making your own). electronic ignition is always useful.

then bigger valves and the head work mentioned below. if you can change a cam without taking the engine out you can do that at this point otherwise wait until the engine needs rebuilding.

the flywheel may or may not come off with the engine in, but obviously there is more work involved to get the desired effect.
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Postby ross.cheeks » 31 Jan 2007, 10:42

ive been offered an exhaust system inc manifold, so thats kinda sorted.

as for carb upgrade what would you recommend.
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Postby Shellysowner » 31 Jan 2007, 12:17

ross.cheeks wrote:ive been offered an exhaust system inc manifold, so thats kinda sorted.


Well if only we were all as lucky as you!

The carb kinda depends on the rest of the set-up. If you're going for mildly tuned then something like a Weber 28/36 whereas if you're going to do the headwork and the cam etc. you'll want something a bit beefier, perhaps a sidedraught 40 DCOE. Piper cams will re-grind your standard cam for about £100 if that helps.
Doive wrote:I remember last summer being in another Chevette with a quite mad driver, and we were drifting round A class roads at 65mph with the tail sliding progressively on the corners. It was fantastic.

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Postby ross.cheeks » 31 Jan 2007, 22:30

ross.cheeks wrote:ive been offered an exhaust system inc manifold, so thats kinda sorted.


soz got a bit ahead of myself its a standard manifold :cry:
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Postby Gordo » 01 Feb 2007, 10:46

What sort of budget and skills do you have?

Way back as a poor student/unemployed person I did some rather successful tweaking on a tight budget. I did , however, have access to some machining equipment and I was a former "A" (advanced) Grade Automotive Engineer, with some experience of modifying cars, which helped.
I'd estimate AT LEAST 30% more torque, which was my main aim for a good drivable club car.

In no particular order.

Cold air induction from the opening to the right of the radiator into the stock filter housing, having removed the extension with the temp' control valve etc.
Turned up a radiused inlet for the carbie - I believe it would be easier to modify a 1 1/2" SU one, though.
Smoothed out the carbie bore and radiused the piston - make sure you don't compromise the 'seal' between them and thinned out the butterfly shaft to minimize restriction.
Radiused the sharp internal edge at the inlet manifold where the carbie mounts - careful you don't go too far.
Had inlet manifold built (welded) up at the head face and opened out to suit the head - more later.

Tapped the heat risers in the head and plugged with slotted cut down bolts - measure carefully and you should be able to get a level finish at the port.
Drilled out inlet at face to, I think, 1 3/16" diameter and 1/4" deep, centred on old port and matched manifold.
Opened up port by, I think, at least 2mm all round and removed that awful step at the guide. Leave the guide intact as far as the valve support goes.
The exhaust was opened up 2mm-ish at the sides and top. NOT at the area nearest the head as the casting is very thin near the manifold face! this was also opened out, paying special attention to the radius at the inside of the curve as it leaves the valve.
Standard valves were used - with new thinwall guide inserts - the valves were machined for a narrower seat - about 40 thou (1mm) for the inlets and 60 thou (1.5mm) for the exhausts with a back cut of unknown angle. Polished with fine emery and a lathe (a drill would do).
Seats in head were opened up to suit the valves with a very light top cut of 30 degrees and bottom cut of 60 degrees which was blended into the opened up throat areas.
the combustion chambers were opened up to the gasket/bore to ensure the valves were unshrouded and generally smoothed over - particular attention was paid to the area around the plug. Don't know what the CC was but as near as I could to get them even.
Head then skimmed 80 thou (2 mm - may have been a bit too much as would pink badly under 3k rpm until it carbonized up a bit - even with a whole bottle of octane booster!
Valve springs were single coil, heavy duty Ford Kent ones with 1mm spacers.
Standard exhaust manifold was used - inlet was matched to the ports and the outlets were opened out to match up with front pipes a size larger than stock (1 5/8"?) - remember you match to the INSIDE of the pipe. The internals were then opened out to suit.
The exhaust was basically a larger version of the stock one - down pipes made a size larger than stock feeding into a 2" system using a single triple pass (least I thought it was until I realised I could see right through it) muffler mounted in the stock location with heavy wire backup to the mountings - I cut off the stock ones and adapted them to the muffler - getting the "U" bend over the diff' was a cow but worth it - however now I'd use a doughnut sectioned to suit.
Bottom end basically stock with rebore, full crack test, new oil pump and timing chain.
Distributor was rebushed and set to 4-6 BTDC
Needle was modified by trial and error
Clutch was a standard aftermarket replacement - stronger than the OEM.
Spark plugs were Champion RN7YC @40 thou - sports coil!
Almost forgot, larger fuel line was fabricated, using the stock fuel pump.

This lot brought 1/4 mile down to 18.2S - a 5 sec' improvement, IIRC!
Up to around 90mph, it would embarrass a lot of 2 litre cars and was a great club car as it was SOOO easy to drive.
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Postby Shellysowner » 01 Feb 2007, 11:18

Crikey Gordo, that was one whole load of effort you put into that 1256 (you never told us more about the inlet manifold btw).

I had my suspicions that those valve springs would fit - the part number is VS5.
Doive wrote:I remember last summer being in another Chevette with a quite mad driver, and we were drifting round A class roads at 65mph with the tail sliding progressively on the corners. It was fantastic.

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Postby Gordo » 02 Feb 2007, 05:59

Shellysowner wrote:Crikey Gordo, that was one whole load of effort you put into that 1256 (you never told us more about the inlet manifold btw).

I had my suspicions that those valve springs would fit - the part number is VS5.


Had the time but not the money so ...

Which bit about the inlet manifold? Forgot to mention that where it's built up around the outlet - you can see how it narrows down, it'll need to be faced off and carefully relieved to clear the rocker cover - or you may prefer to do some relieving on it instead.
I faced off the rocker adjusting nuts to ensure they actually 'locked' as they were too high on the stud, I also had to "relieve' the breather 'tube' as the rockers were tapping on it - mind you, as I said, I had taken rather a lot off the head.
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Postby ross.cheeks » 16 Sep 2007, 15:02

how much power would be a realistic target for a tuned 1256, im planning on building up a decent engine.

im looking at getting the bottom end all lightened etc, head work ( are bigger valves a possiblity?),reground cam (what spec do they do?) single 45 and ones of these much talked about exhaust manifolds :P

im gonna do this bit by bit i think and get the brakes and suspension sorted out first but i like to have a plan of what im doing.
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Postby Gordo » 17 Sep 2007, 10:28

What's your budget? :wink:

As I said, I was lacking money but I understand you should be good for over 80hp at the wheels but it's liable to be rather "peaky".
Can't remember if I mentioned some other things.
With very high spring rates, there is a possability that the rocker studs will pull out of the head - I didn't push that far - options, if it is a problem are pinning the studs, this is where you carefully drill into the head and stud base and insert a pin that locks the stud in place - not for the faint hearted. Alternatively, you can have some screw in studs made up and, after carefully tapping the head, screw them in with locktite or similar to prevent them loosening.
There were some detail differences in the early and later heads, the early heads had a smaller diameter rocker nut, solid rather than hollow pushrods and narrower guide slots. I used an early head with hollow pushrods - I used this combo so I could file the guides for the pushrod clearance while lining the rockers directly over the valves for better geometry.
Kent and Piper used to do reground cam's - personally I prefer new ones, or at least ground on a new casting but hard to get hold off.

For street use, the valves are already a reasonable size - if you madify them correctly - but you used to be able to get bigger ones. I never got round to it but you may be able to get unfinished Mini ones (also 7mm stem) you can finish to length - this would also have a couple of other advantages - optimum valve installed height (they are a bit thin under the seat), range of valve springs, lightweight spring retainers and machined collets - I lost two engines due to valves pulling through the stock ones.

Stock sump design is terrible for harder driving - I used to overfill by a litre and would still have the oil light come on under hard braking. Bolt an old sump to a scrap block and add wings - make sure you allow clearance for when it's installed - or get an accusump.

They used to run 45 Webers or Dellortos - usually sidedraft but the real deal was a downdraft with a big hole in the bonnet. I'd love to see what could be done with a throttle body and full engine management.

Jack Knight used to do a SCCR conversion for the gearbox but down here there've been a few conversions using the old RWD Toyota Starlet gearbox but I never tried it, myself.

If that LSD diff is still for sale, though, I'd make that a priority, you don't need anything too strong and heavy but an LSD would certainly be a benefit.

Starting with the suspension is a good idea, high cornering speeds will be a huge benefit for keeping your average up and it'll give you mre control later.

Don't forget the advantages of lightening - plastic windows and a gutted interior can make a fair difference.
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Postby Shoveitpusher » 17 Sep 2007, 11:53

just remind us what the car is for - reason i ask is certain forms of motorsport limit what you can do.
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Postby ross.cheeks » 20 Sep 2007, 10:21

im looking at eventually going down the road rally route so the carb is gonna be limited as you can only use 2 chokes.

as for budget its not going to be huge but enough. not thought of a figure yet.
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Postby shoveitnz » 09 Dec 2007, 20:10

oooh - interesting as I am now thinking of putting my 25,000 chevette engine into my HB viva as the ford one I was gonna fit wont go in easily...

how about getting a cheap supercharger from a mini and bolting it to the otherside - lots of room- sod the comp ratio...just not too much boost.
I reckon it would blow through the carb ok at low boost. Maybe a lighter spring in the stromberg to help it richen- or different needle...or carefully turn needle down

no worries about space! :D
NZ desperately needs more immigration and fresh blood. Our eyes are getting far too close together!

http://retrorides.proboards86.com/index ... 155&page=1

http://www.vauxhallviva.com/vivaforum/v ... hp?t=10258
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Postby Gordo » 10 Dec 2007, 08:24

shoveitnz wrote:oooh - interesting as I am now thinking of putting my 25,000 chevette engine into my HB viva as the ford one I was gonna fit wont go in easily...

how about getting a cheap supercharger from a mini and bolting it to the otherside - lots of room- sod the comp ratio...just not too much boost.
I reckon it would blow through the carb ok at low boost. Maybe a lighter spring in the stromberg to help it richen- or different needle...or carefully turn needle down

no worries about space! :D


You nutter! 8)
have a look around for a low compression head - may find one in an old Bedford van - clean it up and put in some old Chevette valves ...
As for the exhaust, I'd personally I'd just open up the stock manifold and run a slightly larger front pipe into a 2" system.
If you do a blow-through setup, don't forget you'll need to have the float bowl operating at the same pressure and you'll need to do something about the fuel pump - perhaps an electric one with a regulator referenced to the boost.
Have you considered a turbo' instead - may be easier to set up a draw through setup that shouldn't need an intercooler with moderate boost.
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Postby ross.cheeks » 10 Dec 2007, 12:06

would a carbd turbo set up of something like a renault 5 or montego/maestro be a better option for turbo'ing. not gonna do it myself was just wondering.
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Postby pbottomley » 10 Dec 2007, 20:02

They didnt make a low compression head fro the Viva range (not sure about chevannes?), lowering the compression was done via special low compression pistons in the 1256 HA Van...

The much ealier Vans had 1054cc and 1159cc engines and these vans used special thick gaskets. the 1057cc had a copper spacer gasket and the 1159cc engines used an ever so non safe Asbestos spacer gasket.

For information the 1256cc low compression engine used by the post office was a massive 27.5 BHP, ideal for long moterway hills in a HB :shock: :wink: :D
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Postby Gordo » 11 Dec 2007, 08:04

Hence "may' find one - I know they were made and assumed a van would have one.
They were an option on the Chevette, as well, according to my manual -
Standard compression 9.2:1, min' head thickness 80.90mm (3.185")
Low compression 7.2:1, min' head thickness 82.17mm (3.235")

Bloody heck, I had a head with lightly opened up/deshrouded chambers with 2mm - 80 thou off it, as well as a clean up skim of the block - hate to think what the compression ratio was on it - went bloody well but pinked a lot under 3k until it carboned up a bit.
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Postby ross.cheeks » 28 Aug 2009, 14:14

rite, just had another read through of this as the time is finally here to start 'attacking' the engine, just a few questions:

the valve springs, kent vs5's, what do i need to do/modify to fit them?

you say about the early and lates heads and push rods, basically ive got a set of both, which am i best off using and if im going to mix and match is it the early head with the hollow push rods that im best off using?

what did you do to the valves and seats? would cleaning them up and just relapping them be ok?

lightening the flywheel, how much would need to be taken off etc? where is it taken from on the 1256 one? (dont worry wont be diy'ing that!)

any tips for 'diy' porting and polishing? :D



as for what ill be running itll be on:
single 40 dcoe
piper 285 cam (new followers)
gordo's 'favourite' exhaust manifold :lol:
new oil pump, timing chain, waterpump etc
electronic dizzy
redtop fuel pump and filter king
electronic fan
baffled sump
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Postby Gordo » 28 Aug 2009, 15:28

Not sure about the kent part numbers, I used HD ford 1600 springs with a 1mm spacer - however you MUST make sure you use new collets or at least inspect them regularly as I had a couple of valves pull through them - NOT GOOD!

I used an early head which uses solid pushrods as a basis, by using the wider, hollow pushrods I was able to file the narrower guides to align the rockers directly over the valve stems and not have them too sloppy.

Valves and seats really should have a 3 angle seat cut on each - after doing the valve guides - I found the thin wall type inserts worked very well. You want them with as little play as possible to preserve the seat and get a good seal.

IIRC, crital parts in the ports were the area by the inlet guide, that can be opened up a great deal (DO NOT remove the guide, leave three mmm or so around the end) and the short side radius of the exhaust, just behind the valve - take your time and don't just hog it out. Try and be smooth and try and think about what the incoming air/outgoing exhaust gases would like to do for easiest flow - it may take a bit of thinking as it isn't always obvious. Very hard to explain as well, if in doubt, leave it in place.

You should be able to take quite a lot off the back of the flywheel towards the outside, be generous witht he material you leave behind as strength is more critical than lightness. I'd suggest using a DTI on the friction surface and outer edge to ensure the disc is going to have material removed evenly - more in some parts than others will result in an imbalance.

Did you find my earliest postings, as they should help answer some of your questions?
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Postby ross.cheeks » 28 Aug 2009, 15:53

yeah i did, jsut wanted to clear up the few thing, got the general jist just wanted to make sure id understood them right, cheers for that.

as for the porting im gonna practice on the spare kadett c head ive got lying around
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Postby ross.cheeks » 28 Aug 2009, 16:04

the spacer for the spring, is that a proper part or just a washer?
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Postby Gordo » 31 Aug 2009, 11:58

ross.cheeks wrote:the spacer for the spring, is that a proper part or just a washer?

It was a proper valve shim - sits on the head under the spring - usually used for correctly setting valve seat heights for the right seat pressure - but I wasn't bothered with that, TBH.
You should be able to pick them up quite easily from an engine reconditioner but I doubt you'd need them unless using crazy rev's and with a high lift cam' you'll need to check the coil clearances anyway.
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Postby Gordo » 05 Sep 2009, 07:04

Should have mentioned it earlier, pick up a copy or two of the Mini engine tuning books (the late David Vizard was an excellent builder who explained thing beautifully) - they're similar in design and many modifications/tweaks can be adapted successfully.

just noticed the fuel pump - if it's a Vx 16V fuel pu,mp, it will NOT! work as it's for FI and potentially well over 50PSI whereas you need around 1.5-2PSI (some applications a bit higher) for a carb engine.
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Postby ross.cheeks » 05 Sep 2009, 09:12

the fuel pump is a facet red top cylinder type
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