17 replies to this topic

[tim]

I'm on with restoring my 1275gt into bit of a retro rally car spec.

I have a choice of a few bit I have in my garage to make a good engine for it.

My plan is to have a fun car just for going for a blast every now and then down country roads general hobby car.

It wont be used for commuting or long distance driving!

I have a few choice of parts and would like to know whats best to put together a fun engine for this car.

I have a 1293 A series that need a rebore with 731 cam and 12g1805 head,lightened flywheel,back plate with orange clutch (pre-verto) and 1.5 high roller rockers.

Also got an A+ engine that's standard 1275 with 12g1817 crank and 530 kent cam with mg metro head.

What I want to know is whats best way to go with my choices?

I have got a set of +40 thou flat top pistons to go in either block or put 1293 (dished +20thou) into A+ block and go from there???

Dont mind getting either block or both rebored and happy to buy new bearings and re-balanced crank.

Should I get centre main strap also fitted to which ever I build?

Other add ons I have are set of twin 1 1/2 Su's and LCB,Servo brakes with mg 4 pot calliper, vented disc's fitted and rear mini fins.

I would like to stick with the A series engine as its more in keeping with the car,but is there any pro's or con's for having A+ with verto clutch?

Lastly was thinking of buying Aldon electronic ignition for engine and adjustable timing gear for cam drive.

Any opinions on buying either?

Cheers tim

[nicklouse]

you can use any flywheel with any block.

 

you can use any head with any block.

 

pistons depend on the cam and the head.

 

putting the "best" bits together does not always make the best engine.

 

I would not bother with the high lift rockers

 

I would start by finding a machine shop that knows A series engines and then get the parts checked and tested.

 

then you know what is actually worth considering.

[carbon]

Flat top pistons in a 1293 will result in a very high compression ratio, over 12:1 using a standard head.

[nicklouse]

Both cams seem to be rather hot. I would say that they are too much for the S head unless that had been well worked on.

And here is the problem.

Both cams are going to want quite a bit of compression and a good head.

Or change the cam and keep the head. Or....

Time to do some measurements and some calculations and then see what works best.

[Cooperman]

The 731 is not a very good cam and was not highly rated even when first introduced.

Don't use flat top pistons in a 1275, use 21253 pistons and set the CR to around 10:1.

If this is not a true rally car, then a 266 or MG Metro cam would be better. If you are intending to do historic rallies, then it is a different matter.

[Spider]

I'd suggest starting off with how you want / expect the engine to perform and plan from there, ie, a easy to drive, but not so spirited engine or a high reving screamer, or something in between.

 

As Cooperman has said, the 731 while a good cam profile, is not at all ideal in a 1275. It's also ancient in terms of profile. Also, from your post, I'm guess you haven't had a lot of experience with hotted up Minis. See if you can find a few owners with varying states of engine tune, so you can try a few different engine combinations to see what you may really like. It's one thing to express it in words, but another to drive it for yourself.

 

Just my own suggestion as well, given your experience, I wouldn't suggest trying to building up some fire breathing dragon first up. Also, sell the twin 1-1/2's and fit something easier to live with like a HIF44.

Edited by Moke Spider, 29 September 2016 - 08:36 PM.

[tim]

Thanks for responses so far,lots to think about.

Still could do with an idea on which block to use? 

A+ or A series ? is there much difference?

Cam wise I have had a mini that had a 286 with high lift rockers and cooper s head and was good fun.

So looking for similar if not more fun 

Whats pro's and con's with the +40 flat top pistons?

is high compression a big problem?

[Spider]

For what you are contemplating building, either A or A+ will be fine.

 

Just my opinion on how I like these cars to behave on the road, but IMO, about a 286 Cam is as far as I'd recommend going that dept, If the head on your last was just a stock Cooper S head, then look to that area for better gains. All the power that these engines are capable of making is locked up in the asthmatic cylinder heads that these cars have.

 

In regards to flat top pistons, there's no easy or straight forward answer to that. Ultimately, it will come down to compression ratio, if you can fit flat tops and still end up with the piston close to or at the deck of the block, with the CR that you are seeking, then the engine will make slightly better power than fitting dished pistons for the same CR. Flat Tops give a smaller squish area than dished pistons will and that's where those small (almost academic) gains will come from, but I would necessarily set out to build the engine with flat tops for this reason in isolation.

 

'High Compression' a problem? There's also no straight forward answer to that either! I choose the fuels that I want to run with and work it out from there using a Dynamic method. Perhaps an answer is that too much compression is a problem.  eg, some engines I've built, are 'on the limit' for compression with only 9.5:1 Static CR and others, at 12.5:1 Static CR I'm still looking for ways to raise it further.

[tim]

Tempted to go for flat top +40 pistons and A series block it is 11 stud and matches head.

The head has had some work with ports opened up and smooth chambers.

Been reading about KC 530 cam and sounds like it go well with high lift rockers,it's classed as mild race.

Anyone think this would be good combination?

[carbon]

Not for road. Might be OK for track toy.

 

You'll also need a close ratio box and low final drive to get it singing.

Edited by carbon, 30 September 2016 - 05:00 PM.

[Cooperman]

Don't 'over cam' the car. Before you decide on the final spec you need to decide where you want the power and torque band, then select a cam from the cam graphs which are all available. For example, if ylou want to be using between 6000 & 6800 rpm when wanting maximum power then a 286 would be ideal. But with that you will need a SCCR gearbox and a low ratio final drive. It will need to be really revved, so expect more frequent re-building.

For road use the 26/MG Metro/SW5 would be good cams as they give maximum power at below 6000 rpm. It is so easy to listen to so-called 'experts' who have never tried to live with such 'over-cammed' engines in real life.

I have a 286 in my Cooper 'S', but it is horrible on the road and is really only at home on a rally when pulling high revs. 

A 530 is truly a 'track only' cam and even a 286 requires specific gearing and a low ratio final drive.

The 266 or equivalent is a superb cam for road and track day use.

[AlexMozza]

My specs are 1330, with a Stage 4 head. Swiftune sw5 cam, standard rockers and twin hs4's.

This has made it fast enough on the road, but with good torque, and mainly drivability. 

It will sit in traffic fine, with a really nice idle, yet when needed will put one hell of a smile on your face.

 

You can match a good engine, to a well set up car, whats the point in having loads of power, if it drives like a sack of potatoes! 

[Cooperman]

My specs are 1330, with a Stage 4 head. Swiftune sw5 cam, standard rockers and twin hs4's.

This has made it fast enough on the road, but with good torque, and mainly drivability. 

It will sit in traffic fine, with a really nice idle, yet when needed will put one hell of a smile on your face.

 

You can match a good engine, to a well set up car, whats the point in having loads of power, if it drives like a sack of potatoes! 

That sounds like a really nice specification.

I bet it drives very well on twisty roads with all that mid-range torque.

You know, so many people over-cam their cars then don't like to admit they got it wrong and put up with the sometimes unpleasant driving they end up with.

One of the nicest Minis I ever owned was a 1330 cc Innocenti 1300 Export. It had a standard engine with a 510 cam, 10.2:1 CR, a 3.44:1 FDR and standard Cooper gear ratios. It just went beautifully in all conditions and on normal roads it was a real pleasure to drive briskly. The engine would pull from 2500 to 6500 with really excellent torque at 3000 to 4700 rpm. That is exactly what is needed.

Edited by Cooperman, 30 September 2016 - 06:30 PM.

[AlexMozza]

 

My specs are 1330, with a Stage 4 head. Swiftune sw5 cam, standard rockers and twin hs4's.

This has made it fast enough on the road, but with good torque, and mainly drivability. 

It will sit in traffic fine, with a really nice idle, yet when needed will put one hell of a smile on your face.

 

You can match a good engine, to a well set up car, whats the point in having loads of power, if it drives like a sack of potatoes! 

That sounds like a really nice specification.

I bet it drives very well on twisty roads with all that mid-range torque.

You know, so many people over-cam their cars then don't like to admit they got it wrong and put up with the sometimes unpleasant driving they end up with.

One of the nicest Minis I ever owned was a 1330 cc Innocenti 1300 Export. It had a standard engine with a 510 cam, 10.2:1 CR, a 3.44:1 FDR and standard Cooper gear ratios. It just went beautifully in all conditions and on normal roads it was a real pleasure to drive briskly. The engine would pull from 2500 to 6500 with really excellent torque at 3000 to 4700 rpm. That is exactly what is needed.

 

 

 

it does drive very well, the CR is 10.35:1, wanted it closer to 10.1 but ill live with it! 

With a standard box, but X Pin diff and a 3.1:1 ratio, and most importantly 10 inch wheels! Coupled to a set of Protech shocks its the bees knees, having set up classic race cars for a living does come in handy!

I'll stop thread jacking now!

[tim]

Be nice to hear such thoughts on 12g1817 crank,is it the one to use if in good condition???

also flywheel set up verto or lightened pre-verto with lightened back plate,it has orange diaphragm fitted.

Last bit is it worth investing in the adjustable timing chain and aldon dizzy??

Plan is to stick with 731 cam and high lift rockers,not bother with KC530!