1275 tuning - Questions about Vizard and a few more

[GeorgeHurst]

Hello there,

I am now the proud owner of a 1275 Ital engine! Having spent the last 8 months saving up and acquiring parts to warm up my 1098, I managed to get a 1275 for £150 on eBay so am now going down my 'long term/dream' route

I would like to tune this engine somewhat, ideally to be a really nippy engine, and would like to push as much out of it within my technical and financial limit, I suppose 'fast road' would be what I am looking for, and have a couple of questions about how to get there - if anyone can offer advice from similar engine builds or general knowledge I'd be very grateful.

From research on here and in Vizard's bible I have come up with the following plan...

Carb: HIF44 with BDL needle, on Metro alloy inlet
I have read Vizard's advice about modifying SU's and see that there are lots of suggested modifications, i.e. thinning down the butterfly, getting the most out of the inlet etc - I wonder though, if I were to do some/all of these mods to the carb and inlet, would I risk making it too 'large' / 'high flowing' for the engine? Should I just stick to a standard HIF44? Or indeed go for a HIF38 with these mods? (I currently have an HIF38 which I am looking to sell to get a HIF44)

Head: Standard 12G940 (not big valve head)
I have a spare one of these and might have a go at porting it slightly - in line with Vizard's 'stage 1' suggestions of smoothing out the valve guide boss etc and then cutting 3 angle seats, but will stick with a standard one for the moment.

Exhaust: LCB from Marina, into Cherry bomb muffler and then 1.75" stainless pipe

Cam: ???!
This is where I get particularly confused... I am slowly getting to grips with the different factors in cam selection, but am finding durations and lift and how that links into everything else a bit confusing - does anyone have a suggestion of a suitable cam for my application?

Timing: ??
Should I be using a duplex setup or simplex with the Metro tensioner arrangement?

Handling and braking: advice on camber needed
Poly bushes throughout, SAE 30 in all 4 dampers to stiffen, lowered at front and rear by 1.5" (1 spline on the torsion bars, blocks on the rear), Midget disc brake setup with Metro 4 pot calipers, 5.5" x 14" wheels on 165/70 tyres

I understand when lowering the front that the camber needs to be adjusted by shimming the eyebolts, suggestions of by how much would be appreciated.
I also wonder if 'bumpsteer' is a problem when lowering the front, as someone pointed this out to me the other day.

Apologies that this is so long and characteristically waffly, but if you managed to read this far, your advise would be much appreciated!

Cheers for your ears,
George

[PSL184]

As far as head and cam is concerned I am running a big valve 940 with a 266 cam. This pulls very well throughout the rev range and will rev alot higher than I want it to... I have a theoretical top speed of 119mph which is more than I need

[GeorgeHurst]

Thanks PSL, 119 would definitely be more than enough for me too Acceleration is more my thing, rather than scary top speeds if you know what I mean...
Do you think a 266 cam would be equally successful with small valves, its only a difference of about 3mm on the inlet valve isn't it?

[PSL184]

I don't know how much difference the head makes - I would guess at "not that much" in reality. Mine also breathes through an LCB and single silencer 38mm system.

[GeorgeHurst]

Yeah I would think that too...
Sounds like I would have a similar setup to you, do you happen to know a ballpark hp figure for your engine? I need to know roughly to satisfy my ego and to tell the insurance company!

[PSL184]

Roughly around the 80bhp mark - It's not over stressed. Total work was a rebore, balanced bottom end (inc flywheel), big valve head, hif44, lcb etc - I wanted something that was going to be reliable rather than quick but it turned out to be both

[GeorgeHurst]

haha, Ideal That sounds like about the level I would like to get. One day I want to supercharge, I just love that sound, but that is a serious saving up job!
Any other suggestions for cam, carb mods etc gratefully received...

[bmcecosse]

George - you MUST get a big valve head - don't waste any time modifying the standard valve head. You can of course bore out the throats - and fit the larger valves if you can't find a big valve head! There is useful work to be done on the big valve head though - especially on the exhaust ports, but also some gains on the inlets. Let the Wizard be your guide. The MG Metro cam is the one to go for - it was designed by Rover the way it is ( 252 inlet and 268 exhaust) for good reason, and it WORKS! The tensioner/single chain will be fine - just don't fit stupidly strong valve springs - or daft high lift rockers! And yes - an HIF 44 will be ideal - Vizardise it if you like. But the most important thing will be to get that 1275 base unit into top condition - no point trying to modify a knackered engine! It will only end in tears. Strip down, inspect and rebuild. We are always here to advise -just post up the pictures.

[GeorgeHurst]

Thanks Roy, salient as ever Is the big valve head really that different to the standard? I thought the only difference was slightly bigger inlets. They always seem to go for alot on eBay - but maybe the sale of two standard 12G940 heads would cover it, or indeed Beaulieu autojumble this weekend might throw something up.
I spoke to the guy I bought it off and he rebuilt it 5000 miles before removing it from the car, that was admittedly 10 years ago, so a strip down and thorough inspection is definitely coming up. Am going to start a thread in 'Resto Projects' to update on the progress...
Do you have any advice on shimming the eyebolt - from previous threads on here I seem to remember that you had done so on your car?

[bmcecosse]

You really DO want the bigger valves to get any decent power - so either bore and fit - or get a big valve head ! I'll try to check tomorrow if I have a spare set of big inlet valves.........
The camber angle needs to be set for YOUR car - but I used 3/8" thick steel plates against the chassis legs - and i think one washer at one side to make them ~ equal. Measure by standing the car on a flat surface - and put a spirit level on the front tyres - upright on the centre line. Ok there will be a slight bulge in the lower sidewall - but as long as both sides 'bulge' the same it doesn't matter too much. You only want a very slight inward lean at the top of the tyre. Measure how much space you get from the tyre wall when you hold the spirit level vertically against the lower sidewall. It's v important to make sure the nut securing the eyebolt in the chassis retains full thread grip of the eyebolt - and it should be a self-locking Nyloc.

[GeorgeHurst]

Ok, great thanks, my studio/workshop is next to an MG specialist who sometimes has Moggies in, so might set the camber and then double check with him to be sure...
If I wanted to bore out the inlet and fit a bigger valve, would it be possible to do it on a milling machine and then use a 45deg countersink to recut the seats, and then simply buy 4 bigger valves (35.6mm?) from Minispares and slot them in? I'm friendly with the guy who works next to me and he has a milling machine and can skim heads. What 'bit' would he use to bore out the port? I'm thinking that actually might be a better route to go down as the big valvers seem to go for ~£100!

[GeorgeHurst]

Sorry Roy, I didn't see that you said you would have a look for some valves... that would be really good of you, thanks, please do let me know if you find any

Does anyone else have a 'tuned' 1275 fitted? Cam suggestions so far are 266 or Metro, and would be interested to hear if anyone else uses these or indeed something different...

[charlie_morris_minor]

if you are going to all the problem / fun of rebuilding the engine, I would put it on a rolling road as the final step and they will be able to get the correct needle for your engine. Having the rolling road print out is also a nice thing to have as well as it shows you all the hard work was worth while

[Alec]

Hello George,

Yes a milling machine would bore out the inlet tracts but you cannot just countersink them. You need (after fitting new guides if you intend to) use the guides to machine the seats to ensure they are concentric. What I do is use a small grind stone in a mandrel driven by a die grinder to cut three angle seats. Quite easy to do if you have machine shop facilities.
Modifying the internals of the carburettor is purely for racing in my view, not applicable to a road car.

Alec

[IslipMinor]

The first iteration of our 1380 had a big valve 12G940 head (1 5/32", 1.4" valves), HIF6 on Titan inlet manifold, cleaned-up (no internal gubbins) MG Metro airbox with K&N filter, LCB into 2" o/d exhaust, 3 x 2" bore Jetex silencers to keep the noise sensible (92 db), Kent 266 cam, 1.5 rockers, 8.7 CR (a mistake by a very well known A-Series engine tuner in southern England at the time - not anyone on this board!! Should have been ~9.5 CR), Aldon Ignitor ingition, double (stronger) valve springs, centre main bearing strap, balanced etc. On Aldon's rolling road it produced 100 bhp and >=100 lbf. ft. torque from 2,500 - 5,000 rpm. Went very well and pulled like a train. Happy poddling around town or revving up to 7,000 rpm on track days.

Since then has had a Kent 276, the CR put up to 10.4 and and a K&N circular filter with stub stack fitted. At the last MGOC rolling road session it produced 112 bhp, and still can poddle and rev, whichever is required! The Metro airbox was costing ~6 bhp, even with the K&N filter element, but makes the intake veeeeeery quiet - the circular K&N is very raspy around 3,000 rpm.

I have a complete Metro Turbo set up, all beautifully flowed etc. by Peter Burgess, just waiting to be put on when I get a bit of time! Will be looking for the magic 138 bhp (100 bhp/litre!!!!).

[bmcecosse]

The old BMC 544 (~ 286) is great for power - but does drop a bit lower down. The MG cam was designed to give decent power but still retain reasonable economy. It all depends what you want from the engine - and how hard you are willing to rev it! Without expensive balancing/lightening/main strap etc - best not to run much past 6000 rpm - if you want the engine to last!!
Any machine shop will know how to open up the valve throats - not the ports!! It's a mistake to make them TOO big. The seats need to be correctly centred on the guides as mentioned above - but only a very thin 'pencil' seat is needed for inlet valves - the 3 angle thing is old hat !

[Alec]

Hello BMCE,

"but only a very thin 'pencil' seat is needed for inlet valves - the 3 angle thing is old hat !"

I agree with the first part, but not the second. Not new I agree but non the less it still works.

Alec

[hotrodder13]

Hello there,



Exhaust: LCB from Marina, into Cherry bomb muffler and then 1.75" stainless pipe


Cheers for your ears,
George

i have a custom made manifold with a stright through cherry bomb all 1.75" and its is to loud but it does get everyones attention

[linearaudio]

Any experiences with the Swiftune SW5 cam, anyone? That seems to be another favourite with the Mini boys now MG Metro cams are getting thin on the ground!

With IslipMinor's 6BHP loss through the MG Metro airbox, remember that is on 100+ BHP, losses at 80 BHP would be much less, and it is beutifully quiet if you are considering long distance cruising!
The mods to the carb would theoretically get it to flow like the next size up. For around 80BHP you may not quite be needing that, and remember it will then need a "b*stard" (sorry-it wouldn't allow me to use the correct word- only seen as a swearword nowadays ) needle profile rather than one of the standard recommendations. Not a problem if you are going to get it set up on an SU friendly rolling road though!
Des Hammil has written an entire book about "power tuning" the SU carb, and shows how to check and modify your needle at any rev point, even quantifying how many seconds of pressure with emery paper it takes to remove .001" in diameter. An interesting read if nothing else.
Many people seem to reckon on advancing the cam around 4 degrees, this worked noticeably on my slightly warmed 1098 Metro some years back (yes, 1098 ) The standard Ital exhaust manifold isn't that bad flowing, being of the LCB type in cast iron, and quieter/more robust than a tubular one, just another thought if you are on a budget! Also, the good old RC40 exhaust is still stupidly cheap in its basic form for the Mini- a bit of pipework extension etc and a very sporty note, even in the twin box version!

[bmcecosse]

The SW5 is a very soft cam (only 244/244) - and has high lift (extra 38 thou) , which in itself is more damaging to the valve train - and makes it difficult to use with a 940 head on a small bore engine. Many of the Mini lads are now realising it's not that great and are moving on. Good torque very low down - but soon flattens out! Advancing by 4 degrees just takes up the inevitable slack in the chain - yes it is a good idea. Some of the Vizard carb mods are extreme - but the basic ones are well worth doing, and don't make the car in any way undriveable.
With the 'pencil' seat Alec - there is no room for 3 angles - it's just a v thin line. Possibly worth working on the valve head seat area - but not something I have worried about in the past.
And sorry George - I can only find 3 large valves, and one of them is obviously past it's best. Best just get some new ones I think - i'll hang on to these as spares for my own BV heads.