14 replies to this topic

[axnutty]

So im building a new engine for my car. Ive decided on the following spec and would like to know if anyone has anything similar or could advise i do something different.  At the moment the block is with the engine builders and I intend to ask them to do the following:

 

Use the linered 1275 block. Rebore the existing liners +020 to take to 1293.

Use 21253 pistons

Deck the block so its square to the bores but also so the pistons are level with the top. Desired CR is 10.5:1

Line bore and fit new cam bearings

Line bore the crank tunnel to ensure striaght.

Regrind the crank and journals +020 (it needs it) re tuffride and balance.

Machine the centre cap to take a strap ( do I want to use the 4bolt type (PeterMayEngineering or am I okay to use the 2 bolt steel strap type - cars intended rev limit will be 7k)

Drill block to take extra studs (future proof it if you like whilst builders have it)

New core plugs.

 

Rebuild using the metro turbo oil pump

New dizzy drive

544 (style) camshaft (tempted to go 649 but that maybe too much?)

New standard followers

New duplex gears and chain

Timing given by offset key rather than vernier

ARP conrod bolts.

 

Top end, for the moment at least, a 12G940 MG metro head with standard 29.4 exhaust and 35.6 inlet valves, standard rockers, twin HS2 11/4 SU's

 

 

 

Is this engine sound like a good useable build? Would you do anything different?  Is there anything I have missed or anything thats not needed? I appriciate the head is nothing special and I could replace in the future with something a bit more special.  Are there any tolerances I should ask the engine builders to build too? For instance I am best building it to slack tolerances or tight ones? (As I need to ring them early next week thats perhaps the most important question!)

 

I hate to ask this last question, because I dont really care about figures, but the inevitable, how much power do you think I would be looking at with this build?

 

 

[mk1leg]

why not just get a MED motor cheaper in the long run.......

[nicklouse]

A few comments. Why have the crank tunnel line bored if you are thinking about but not fitting a 4 bolt centre strap. You talk about having the block drilled for it to future proof. Hardly as you will need the engine out an line bore it for the 4 bolt cap. Do it once and do it right.

Get the head done so that you can get it all matched with the block and piston heights.

Sorry twin carbs I would not bother and 1 1/4s defiantly not.

Remember the head is the main thing that controls how the engine is. Putting a hot cam in with a standard head is a bit pointless.

7k on a standard head......

Are you a commeriner? Do it once and do it right. Might take a little bit longer but once it is done it is done.

I had a hot head so had a short motor made to suit as my then current one was not suitable.

And think on about flywheel and clutch plate and spring.

[Stiggytoo]

Don't bother with drilling for 11 stud head. Pointless.

[Cooperman]

First of all what is the car to be used for. A 544 or similar is for a competition engine rather than a road car. In fact the specification does say 'competition' really.

The first and most important thing in getting more power & torque is a fully gas-flowed cylinder head. The better head is the key to releasing performance from the A-series engine.

A centre main cap with just the 2-bolt strap and high-tensile bolts is OK for 7000 rpm, especially if the engine is balanced. However, if you use the 544 cam the engine revs will be high to get the power, like around 6400 rpm for peak, and I wouldn't use 21253 pistons for those sustained revs. In fact with my 'S' engine, which has the 286 cam (not too dissimilar from the 544) I use Karl Schmidt piston (c.£450 per set if you can find them) to ensure sustained high revs are OK.

If you do choose the 544 cam, you will need a close ratio straight cut competition gear set and a low final drive ratio, say 3.76:1 or 3.9:1.

For carburation a single HIF44 or twin HS4 carbs will be needed together with suitable induction & exhaust systems.

Again, this is not a very ideal spec for a road-going Mini as it would be very 'cammy'. I have used the 544, 286 and 649 cams in rally cars, but would never consider one for the road as at normal road revs there will be less power/torque than with a 'softer cam'.

[axnutty]

So line boring the crank tunnel, 4 bolt centre strap, 11 stud block are not necessary for this level of build, fair enough.

 

Carb choice is simply because the car is a midget and thats what I have at the moment, and like the top end, is easily changed at a later point. (I am guilty of concentraing on the bottom end with my research I admit) But surely I could build up a bottom end first and then build a head to suit that? Does it have to be the other way round?

[axnutty]

The car will be used for autotests, hillclimbs and fast road. So I will take your advice and say a ~285 duration cam as a maximum. Its not like it high sustained revs in those disciplines for very long periods of time like circuit work... would you still recommend against the 21253's?

[Cooperman]

Is the car for racing, sprints or hill-climbs? If so then to be competitive you need to do everything before using it.

If it is a road car, then aim for a lower specification to avoid disappointment.

If you do part of the work you will gain little, so it's better to do a complete build at one time, then get the engine set-up accurately.

Be very aware of how cam graphs and gearing work together to ensure that the cam chosen has characteristics which suit the gearing and vice-versa.

[Cooperman]

The car will be used for autotests, hillclimbs and fast road. So I will take your advice and say a ~285 duration cam as a maximum. Its not like it high sustained revs in those disciplines for very long periods of time like circuit work... would you still recommend against the 21253's?

For autotests you need high low & mid-range torque with low-ish gearing. For hill-climbs you need good power, usually at high revs and close ratio gearing to keep it on the cam. A good hill-climber will not be ideal for autotests. I have a full-on 'S' engine with a 286 cam, 11:1 CR, etc and as a rally car on tarmac it is superb. On some events there are autotests and it is poor at them. In fact a Mini with a standard 'S' engine will beat me every time if well driven.

All this will not give a 'fast road' car. In fact on the road at cruising revs it will be slower.

As for pistons the choice is yours. A 285 cam or similar will need high revs and you need to be aware that the 21253 is not intended for those sort of revs. They may prove OK, but they will be at the top of their design revs/compression.

[Turbo Phil]

Coopermans advise is sound as usual. For the cost and work involved I would definately go with 11 studs, though.

Phil.

[gazza82]

Didn't someone have problems with a turbo oil pump in a 'standard' engine recently? Standard pump may be the better option.

Edited by gazza82, 25 June 2015 - 10:59 PM.

[axnutty]

Cooperman, im interested, can you divulge your exact engine build spec? Id be interested to see what you yourself run. Id disagree slightly though, hillclimb car need power from low down and plenty of torque.Well thats what I have in my 205 anyway and that seems to be doing okay at least. Although I do understand that a "jack of all trades" means your specialised at nothing, and that an autotest car is not a hillclimb car. Perhaps a better anology of what I will use that car for is "fun and clubman motorsport." 

[axnutty]

So as an update; ive obviously got carried away bottom end and not carried away top end. Given the car is a toy and not a serious weapon, I cant substantiate the need for expensive pistons etc. So if I ask the machine shop to simply:

Regrind crank and balance.
Line bore and fit cam bearings
Rebore 020 and fit 21253 pistons and accept a 6500rpm limit
Fit a 544 cam at most
Centre main strap and 11 stud drillings as theyre in there, but really its not all that necessary.
Deck block height so its square mostly but also so pistons are level. (or am I way off the mark here)

Do some more research top end this weekend!

[ACDodd]

Hill climb is low gearing and high rpm work. Read full race cam etc. Auto test mild cam ie SW5-07 with stock rockers ie grunt from idle.
Save the money and don't do the line bore if its not needed and invest in a cylinder head.

Your budget needs to be set by inspection. After this you will know what money is required for parts and machining. Then what's left can be used for completing the spec.

AC

[The Principal]

Last time I fitted a 4 bolt centre main bearing cap line bored and 11 stud drill plus the cost of refacing the thrust washer faces cost me £600 in labour plus the steel bearing cap that also excluded cleaning the swarf from the block.