16 replies to this topic

[Shawbags]

Here again , i'm picking up a 12g202 tomorrow as you I have learnt its a better head to start with , should I leave the block standard apart from a gentle skim or will it make a lot of difference if I go for porting and can I have it machined to take bigger valves , obviously I have to weigh up the cost involved ,  shawbags (Chris ) .

[Anthony30]

Just a couple of things for you to think about.

 

 

Mg Metro/Kent 500 camshaft

Mappable ignition

Maniflow cooper freeflow manifold, and exhaust. (1.625 is said to be optimum for a 998)

Maniflow inlet manifold.

Fuel filter

bigger battery

Uprated alternator.

 

You really need to find out what C/R you want to have with the 12g202 head, so it can be skimmed to get the chamber size correct, if needed. Has the head been converted for unleaded use? 'Cooperman' has wrote quite a bit on calculating C/R. It might be worth rebuilding the engine.

[timmy850]

A 202 head has larger chambers then a 998 head, so you'll need to get the head skimmed a bit to bring up the C/R to at least as high as you have now.

Have a read of these too. This 202 head on a built 1100 engine has 1.260″ inlet and 1.070″ exhaust valves and gets over 100hp on the engine dyno with standard sized ports
http://russellengine...ct-68mm-part-1/
Opening up the ports a bit gave an extra couple of hp
http://russellengine...ct-68mm-part-2/

I've got about 6 of the 202 heads now, I seem to keep getting them from everywhere!

[Anthony30]

Have you got the yellow bible? Very useful book.

[Shawbags]

Just a couple of things for you to think about.

 

 

Mg Metro/Kent 500 camshaft

Mappable ignition

Maniflow cooper freeflow manifold, and exhaust. (1.625 is said to be optimum for a 998)

Maniflow inlet manifold.

Fuel filter

bigger battery

Uprated alternator.

 

You really need to find out what C/R you want to have with the 12g202 head, so it can be skimmed to get the chamber size correct, if needed. Has the head been converted for unleaded use? 'Cooperman' has wrote quite a bit on calculating C/R. It might be worth rebuilding the engine.

Apparently when the engine number was checked one of the lads on here said it was already a high compression engine , I do get your drift and will use any advise I get off here i'm not going to mess about I will do it properly , cheers.

[Shawbags]

Have you got the yellow bible? Very useful book.

no not yet I will be buying it .

[Shawbags]

A 202 head has larger chambers then a 998 head, so you'll need to get the head skimmed a bit to bring up the C/R to at least as high as you have now.

Have a read of these too. This 202 head on a built 1100 engine has 1.260″ inlet and 1.070″ exhaust valves and gets over 100hp on the engine dyno with standard sized ports
http://russellengine...ct-68mm-part-1/
Opening up the ports a bit gave an extra couple of hp
http://russellengine...ct-68mm-part-2/

I've got about 6 of the 202 heads now, I seem to keep getting them from everywhere!

I'm paying £50 doesn't seen too bad.

[Shawbags]

the more info I get the I think i'm making a rod for my own back lol .

[Steve-O 2014]

So is the 12g202 a good option for 998 owners over the pricey 12g295 head? 

[petey81]

Yep

[Shawbags]

^{Ive picked it up and it all looks ok obviously I will have to check it over properly but it looks in good nick and the chap I had it off was very informative £50 .}

[Shawbags]

Ok so I have to find out the compression ratio I have never done this before so I need help I,ve been looking for a post by Cooperman that explains it and cannot find it , to save Cooperman writing it out again can anyone tell me how its done or tell me where I can find his post , cheers Shawbags.

[Anthony30]

So is the 12g202 a good option for 998 owners over the pricey 12g295 head? 

I think AC Dodd wrote an article somewhere about 998 cylinder heads, mentioning the 12g295 inlet ports are slightly too big, in his opinion. I'm sure a heavily modified 12g202 could match a 12g295, just needs more work.

[timmy850]

Ok so I have to find out the compression ratio I have never done this before so I need help I,ve been looking for a post by Cooperman that explains it and cannot find it , to save Cooperman writing it out again can anyone tell me how its done or tell me where I can find his post , cheers Shawbags.

You'll need to know:

Volume of the head chambers

Volume of the dish in the pistons

Stroke

Bore

Gasket volume (about 1.4cc for 998)

Ring land volume (about 0.6cc)

 

If you have a standard 998 the volume of the individual cylinder is 998cc/4 = ~249.66cc

The volume of the standard 998 head is 24.1cc

The dish volume of a piston is around 8cc for a low compression engine? I can't find the official figure..

 

Total uncompressed volume = 249.66 + 24.1 + 8 + 1.4 + 0.6 = ~283.8cc

Total compressed volume = 24.1 + 8 + 1.4 + 0.6 = 34.1

 

Compression ratio = uncompressed volume / compressed volume 

C/R = 283.8 / 34.1 = 8.3:1

 

If you had a head with an extra 1.6cc, (like a standard 202 head) your C/R would be 7.9:1 . To bring this up you'd need to either: skim the head or have less dish in your pistons or bore out the engine with larger pistons or fit a longer 1098 crank and pistons or a combination of these...

 

The head volume list is here:

http://www.minimania..._casting_number

 

I use the C/R calculator in this post, you just need to know the stroke of a 998 (76.2mm) and the bore sizes are the same as a 1098.

http://mk1-forum.net...&p=64979#p65018

 

 

 

So is the 12g202 a good option for 998 owners over the pricey 12g295 head? 

I think AC Dodd wrote an article somewhere about 998 cylinder heads, mentioning the 12g295 inlet ports are slightly too big, in his opinion. I'm sure a heavily modified 12g202 could match a 12g295, just needs more work.

 

Have a read of this one too:

http://russellengine...cylinder-heads/

Edited by timmy850, 03 February 2015 - 02:07 AM.

[Anthony30]

 

Ok so I have to find out the compression ratio I have never done this before so I need help I,ve been looking for a post by Cooperman that explains it and cannot find it , to save Cooperman writing it out again can anyone tell me how its done or tell me where I can find his post , cheers Shawbags.

You'll need to know:

Volume of the head chambers

Volume of the dish in the pistons

Stroke

Bore

Gasket volume (about 1.4cc for 998)

Ring land volume (about 0.6cc)

 

If you have a standard 998 the volume of the individual cylinder is 998cc/4 = ~249.66cc

The volume of the standard 998 head is 24.1cc

The dish volume of a piston is around 8cc for a low compression engine? I can't find the official figure..

 

Total uncompressed volume = 249.66 + 24.1 + 8 + 1.4 + 0.6 = ~283.8cc

Total compressed volume = 24.1 + 8 + 1.4 + 0.6 = 34.1

 

Compression ratio = uncompressed volume / compressed volume 

C/R = 283.8 / 34.1 = 8.3:1

 

If you had a head with an extra 1.6cc, (like a standard 202 head) your C/R would be 7.9:1 . To bring this up you'd need to either: skim the head or have less dish in your pistons or bore out the engine with larger pistons or fit a longer 1098 crank and pistons or a combination of these...

 

The head volume list is here:

http://www.minimania..._casting_number

 

I use the C/R calculator in this post, you just need to know the stroke of a 998 (76.2mm) and the bore sizes are the same as a 1098.

http://mk1-forum.net...&p=64979#p65018

 

 

 

So is the 12g202 a good option for 998 owners over the pricey 12g295 head? 

I think AC Dodd wrote an article somewhere about 998 cylinder heads, mentioning the 12g295 inlet ports are slightly too big, in his opinion. I'm sure a heavily modified 12g202 could match a 12g295, just needs more work.

 

Have a read of this one too:

http://russellengine...cylinder-heads/

 

He mentions having a high comp engine, which is 10.3:1 ish C/R as standard I believe with flat top pistons?