15 replies to this topic

[JonnyAlpha]

Hi;

 

Contemplating a head change.

 

I may be able to get my hands on a 12G295 head and a 12G940 head. From reading the 12G295 (as long as its standard) will need skimming to bring back the compression ratios on my A+ 998 block and if fitting the 12G940 i'll need to pocket my block and poss plug re-drill some of the water holes?

 

Which would be the better of the two options.

 

Also considering an EVOLUTION001 cam from Mini Spares?

 

What other modification would I need to do to the heads (Valves, Springs etc).

 

Tks

Edited by JonnyAlpha, 04 August 2018 - 01:07 PM.

[Retroman]

Either 12G295 or 12G940 might need skimming it depends on how your engine measures up....

 

Are the pistons dished ? how big is the dish ? how far down the bore? how big is the bore ? and then CC's in the head

 

The 295 head may need harder lead free exhaust valve seats too.

 

A 940 head can sometimes go straight on, again needs measuring carefully, you need a minimum of 0.020" between the block and

 

exhaust valve at full lift, the higher lift the cam the more likely it can't be done without pocketing the block [engine strip job]

 

With an MS evolution001 cam is highly likely that the exhaust valve will hit the block.

 

The water holes block to head are not an issue, the water pump pulley can be...needs to be small

[Mrpeanut]

Either 12G295 or 12G940 might need skimming it depends on how your engine measures up....

Are the pistons dished ? how big is the dish ? how far down the bore? how big is the bore ? and then CC's in the head

The 295 head may need harder lead free exhaust valve seats too.

A 940 head can sometimes go straight on, again needs measuring carefully, you need a minimum of 0.020" between the block and

exhaust valve at full lift, the higher lift the cam the more likely it can't be done without pocketing the block [engine strip job]

With an MS evolution001 cam is highly likely that the exhaust valve will hit the block.

The water holes block to head are not an issue, the water pump pulley can be...needs to be small

Decent lifts on the evo1 so I don't think it'll work. I had same dilemma as the op but as I have an sw5 I didn't risk a 940 and will stick my 295 on.

[JonnyAlpha]

Wont know about the pistons until I get the head off but they should be standard flat?
So if fitting the 12G940 I would not be able to use th Evolution001 Cam. What about the Evolution
001 in the 12G295 or is the standard cam ok?

What would be better or least work v performance 12G295 or 12G940?

[Dusky]

295 is the easiest hands down.

[Retroman]

A 295 head in good nick is the best option, just needs to be the correct CC's for your motor

 

Any cam in the 264/266 area is a good improvement...Mg Metro, MD 266, SW5, Kent 500, MS001 all cheap power.

 

A 940 head does loose out slightly on a 998 below 1500 revs as its pulling 20% less air than a 1275 and the gas speed is low

[absx2]

The single biggest improvement to the performance of your 1000 HLE is to change the diff ratio from 2.95:1  to 3.44:1. The gear ratio is far too high for a 998 and even 1300 Metros struggled with it. 

Then go for a free flowing exhaust system like an RC40 although I prefer Maniflow as they last for years. 

This usually means a change of manifold as per stage 1 kits so that would be your best bet. 

Camshafts have a sweet spot and the 2.95 diff is not  going to give it to you as the final drive is too high making the gears too far apart to keep the low powered 998 on cam.

There are big improvements to be had by cleaning up the valve areas and a little de-shrouding as per Vizard on the standard head if you are on a budget.

 

A while ago I changed a gearbox for a friend with a city E with one of the many I had kicking around as his was crunching in 2nd gear

It had a 3.44 diff and he could not be convinced that i hadn`t swapped the whole engine as it had so much more go .

[Retroman]

We were talking heads

 

Absx2 is very right  2.95 diffs are a bad idea even in a 1300cc motor they reduce acceleration and top speed

 

They were fitted for economy reasons and mean you can't pull the skin off a rice pudding

 

http://www.retromini...d=19&chapter=20

[JonnyAlpha]

So,

Couple more questions:

 

1. If it turns out that the 295 head is Ok and I get it can I use the Evolution001 Cam Shaft with it?

2. If the head is OK but the valves and springs need changing, what should I buy as a replacement? 

3. To get the best performance from fitting the head / cam / stage one kit I should consider changing the FD ratio to 3.444 by switching out the pinion and crown wheel. Anything else required if changing the FD (Special Tools / Gasket / Seals etc). 

4. Can the FD parts be picked up SH?

5. There is a lot of talk about changing to unleaded by fitting valve seats - should I do this?

 

Thanks 

[Retroman]

1 Yes

 

2 Let me know I can get them all new at good prices

 

3 I would go 3.76 [standard small bore fitment before the economy obsessed fun police got involved]

You would probably be as well doing the whole diff, cross-pin, bushes the lot, it's false economy not too.

You will need gaskets and seals.

No special tools, other than either a 1 1/2 inch ball joint spanner or socket for the diff pinion nut.

 

4 Yes crown wheel / pinion. Wearable parts buy new, make sure you use the RHP bearings [unless using existing]

 

5 Having the exhaust seats machined for unleaded is worthwhile, and not expensive either.

[JonnyAlpha]

Just been reading up about compression ratios. Some very important maths to do to.
What compression ratio should I be aiming for and how / does the CAM and indeed valves, to be fitted need to be factored into the coalition.
I.e. different CAMs needs different compression ratios.

[Retroman]

Depends a lot on what cam you choose, also depends on the quality of the fuel and temperature, Vizards yelow book covers it well.

 

There are 2 compressions static and dynamic

 

Static is the one normally talked about and calculated from the various measurements; bore / piston dish / volume above piston at TDC and volume of combustion chamber, most Minis fall in 8.7 to 10:1, for a relatively standard road motor that's what's needed. But a highly tuned Mini might go 11 to over 13.5:1

  The link below is a good help crunching the numbers.

 

https://jscalc.io/ca...RNEglVkKLQir11T

 

 The dynamic compression is a lot more involved and tends to be used when optimizing things for a high output motor. The link is to the calculation for Petrol Pete's 998 screamer with a VP3SP cam.

 

http://www.theminifo...age-101?hl= dcr

 

I will be doing some calculations for a build using an evolution001 cam in a 998 +060" soon. I will be aiming for 9.7:1 static or thereabouts, we will see how it checks out on a dynamic calc, need to do a dry build first.

[JonnyAlpha]

Sorry combining two threads, I need some advice on a head that I may be buying, two of the valves are stuck?

Thread is here.

[JonnyAlpha]

1 Yes

 

2 Let me know I can get them all new at good prices

 

3 I would go 3.76 [standard small bore fitment before the economy obsessed fun police got involved]

You would probably be as well doing the whole diff, cross-pin, bushes the lot, it's false economy not too.

You will need gaskets and seals.

No special tools, other than either a 1 1/2 inch ball joint spanner or socket for the diff pinion nut.

 

4 Yes crown wheel / pinion. Wearable parts buy new, make sure you use the RHP bearings [unless using existing]

 

5 Having the exhaust seats machined for unleaded is worthwhile, and not expensive either.

 

So looking at the pics in my other thread it may need new valves etc, what type and how much? Valves, Valve Guides Springs etc?

[JonnyAlpha]

OK so I have closed the valuation thread as I picked up the head today.

 

I also checked a couple of local engineering factors for quotes on refurbishing the head (Barum Engines LTD and KAR Engine Services) Barum Engines quoted £185 to strip, clean and skim the head. They also mention hardened unleaded valve seats and said that they could supply but I could get them myself and they would fit them. So total around £200, but this does not include renewing springs and any valves just cleaning up the existing ones. They did not mention painting?

 

KAR quoted £395 to fully recondition a 12G295 head, fitting unleaded valve seats, new valves, guides, springs, skimming to suit your engine and painting in colour of your choice ready to fit.

 

Any thoughts on these prices?

 

What other machine shop services out there does anyone recommend.

I have looked at a couple:

 

JonSpeed - £575 for a complete recondition but no mention of skimming? It does mention that the price includes a £200 surcharge which will be refunded when you send in your old head - so total cost = £375 but again not sure if this includes skimming (probably not)

http://www.jonspeedr...=14471&cID=2089

 

Calver ST - £496 complete recondition + big valves (not sure I need them , also mentions a surcharge but this says £95 is added if a head is not returned? So cost is £496 - again no skimming.

 

All in all a lot of moola - I was only looking at about £200 to recon this head?