12g202 is it worth doing up for N/A?
Turbo Mini Forums

i have a 1098 and im wanting to know if i should keep my 202 or go 295? the 202 is in good shape its stock as far as i know i will measure the valves and thickness of the head its self tomorrow as i still need to clean it and its dark out

so i know the 202 has more meat on it than the 295 but from what i have read the heads are on par once some one has worked them properly so what would i be looking at having done for a 1098 N/A bigger valves?

Number Inlet dia. Exhaust dia. Nominal cc Standard fitment
12G202 1.156"/29.36 1.00"/25.4 26.1 997 Cooper, Austin 1100 Mk



:) and the

Number Inlet dia. Exhaust dia. Nominal cc Standard fitment
12G295 1.218"/30.93 1.00"/25.4 28.3 998 Cooper, MG1100


Hope this helps at all

Edited by Chalkie on 3rd May, 2012.

The chamber shape needs altering, as the standard size valve is shrouded now, if you put a bigger valve in without altering the chamber you would end up with a worse head.

one day boost will be mine!

Wez is correct. The chamber needs to be 295spec. Bigger inlet and exhaust is necessary. Minispares sell these quite cheap.

The 202 can be made to work well, it just requires a bit more work than the 295, though they can be picked up for peanuts compared to the 295.

WWW.TURBO-MINI.COM

ok so what size valves should i be looking at installing given i or someone de shrouds the head?

i think the figures Riding Low provided are the limits on valve sizes? so im guessing bigger is better for mas flow but what about low ish end torque can 25.4/26.1 valves provide fast enough moving air to pull from say 2.5k? 3k?

if i do go 25.4/26.1 do i then have to make the chamber something like the 295 shape their for decreasing the CR to a still useable point for N/A

any way im off to clean the head and take some measurements and pics.. i found a cracked spring retainer to so maby ive been reving the 1098 to hard??

I started modding a 202 using the stencil from vizards other book, I've still got more to fetch out of the chamber and it's already 28cc, I'll guess it would be 30ish maybe more once opened out to the suggested shape so for n/a it will need a skim to bring it back to a useable cr.

one day boost will be mine!

ok the head is about 2.737" think factory heads should be about 2.75" and i should have at least 0.080" buffer after skimming the head witch is measured down the rocker oil feed hole after measuring my head 2.555" that leaves .182" to skim to get a CR of 12-12.5 as recommend for max power "if you cant get much in there then squeeze the heck out of what you can get in there" so that should be enough meat depending on how nuts i de shroud it right?

the valves i have now are 27 and 30.5 form what i can measure with a flat battery in the calipers
the seats look good on the intakes and the ex should lap up ok.. i think ill keep my valves for now as they are in good shape but ill have a go at the chambers i think..


the yellow book tuning the a series engine buy david vizard 3rd edtition shows and explains what to do and after reading it i feel comfortable to have a go and see what happens..

i think that hardest part will be consistency.. fig 9.11 shows the shrouded small bore head and results by how much is removed around the inlet
it shows that measured from the center of the valve out to the chamber wall
0.680" (57.5cfm @.345"lift) gain 0 cfm factory
0.800" (70cfm @.345"lift) gain 12.5 cfm
0.900" (71.5cfm @.345"lift) gain 14 cfm
1.000" (72.5cfm @.345"lift) gain 15 cfm

so i think going to a 1" rad vs a 0.800" rad a difference of 2.5cfm is beyond worth doing my self and what i need as id like to keep all the meat i can for CR so .8" will do me i think considering im keeping the valves as above 27mm and 30.5mm

EDIT: do you think i should do anything aroung the ex valve?
: the head mesures about 25.5cc now
: the piston + space to top of deck is 7cc
: what else do i need to figure out CR ?

the dyno run gave 48hp @ 6200 rpm and 51 ft 3700rpm
my cam sheet reads max valve lift of .3462" cam lift .2643" rockers 1.31 and a 270 duration
carb is a 32/36 DGV
123 ign stock internals

Edited by Turbo This.. on 4th May, 2012.

ok so i have ground chamber number 4..

it measures 27.5cc before i started it was 25cc

i have only "removed" material from the inlet valve reign the rest of the chamber has just had a super light pass to "flatten" the sand casting dimples

i made a scribe from an old buggered valve by welding a small 2mm rod to it on the flat face i then cut it to give a point to scribe a radius of 0.800" as Davids book suggests.. using this guide i ground it out and blended the sharp lines out i think i am doing good so far.. what do you guys think??



in this picture below i have marked out the intake valve with an 0.800" and 1" radius from the center line of the guide out and i also marked the exhaust at 0.800" how ever i did not grind it out to that line to try save on cc i ended up grinding the exhaust to 0.650" and the intake to 1"













also who knows how much volume the small bore AP250MT MonoTorque head gaskets hold when compressed ?

i measured the bore and stroke to the best of my ability and came up with
Bore 65.6mm (top of the piston says 40) im yet to look up what it should be for a 1098 +0.040"
Stroke 84mm im yet to look up the 1098cc stroke lengh ?

65.6mm squared * 0.785*84 / 1000 = v 283.76cc sweped volume per cylender *4=1135cc

c= block + head gasket + chamber C= 8.75+ head gasket + 27.5 c= 36.25cc

v+c/c=CR

283.76+36.25/36.25= 8.83:1 CR WITH OUT HEAD GASKET 8:1 with a gasket volume of 4.1cc

so if my maths is right i dont need to skim it? i will be skimming it tho as id like to run a CR of something like 12.5-13

Edited by Turbo This.. on 6th May, 2012.

if your using it for n/a then 8:1 will be to low especially if your using an uprated cam, thats what i meant when i said it will need a skim. but 8:1 cr would be a shame to waste it....... get a turbo on it. lol
i think the head work looks good, but im sure one of the TM head guru's will let you know for sure.

one day boost will be mine!

thanks man well i have had thoughts to ad a turbo lol but i really don't know what is involved and what gains there are at what stages like from a basic blow throw carb and dissy to fuel injection and a computer running the show

tomorrow i will proceed to clone another chamber or two..

Good effort so far, looks like you're on the right track. A small bore head gasket will probably be around 2.8 - 3cc volume I would think.

WWW.TURBO-MINI.COM

ok thanks phil

so useing a gasket volume of 3cc i get a CR of 7.3: and 2.8cc gasket gives 8.26:

the CR is kinder proving to be difficult to maintain accuracy

EDIT: well i got distracted cleaning the yard.. so no work was done today on the mini.

Edited by Turbo This.. on 6th May, 2012.

well i have been busy with work (installing solar electric systems) so the mini has gone no where how ever i have the day off tomoz so i plan is to get my electrical license sorted as im fresh out of tafe and just need to do paper work after that i need to ring around for new suspension bushes for the work ute as they are almost non extant ! its a 87 model Toyota hilux then if i have time i shall do my dammed to finish the head get it the the shop for a shave and all that fun stuff im having withdrawals from not driving the mini !

well i got my sparky license sorted =D YAY!

I also got the mini head sorted YAY!







Quite chuffed to be honest im happy with my effort for a first timer.. the chambers all measure about 28.5cc it will be interesting to see how equal they are after the head has been skimmed hopefully not to bad i think ill need about 12.5cc chamber volume to get my 13:1CR but that might be hard so may well just pull the lump and fit some flat tops and a zero deck that should give me 20cc in the head to get 13:1CR dono im much undecided..

I had in mind the beak radius needed to be bigger than the way you did it.

Maybe I am wrong.

Rusty by nature

advantage: yess i think your right now that you point it out i had another read in the book and it recommends a 0.18" radius so ill have a measure and see what i have and fix it if need be = D thanks for the heeds up i would have missed that if you did not point it out..

I agree, a slightly larger radius is needed. Other than that it looks a good effort.

WWW.TURBO-MINI.COM

Thats lookin fantastic! i love how much an individual stance can be made with these heads in regards to chamber shape/size...


I love modded 202 heads, much easier and cheaper to come about than those 295's/206's... Much nicer to play with as there is more meat to take off, that and they can be ported and flowed to out perform a modded 295 due to the "more meat" in the casting

here's mine, valves are turned down cooper s valves, most of the magic happens in the ports with this one rather than the chambers, has been shaved 65thou (limit of a 202)



flows better than a stock 295, and just looks nice i reckon... helped my 1100 get to 54hp on the rollers...

Keep up the good work mate!

“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson

On 15th Jun, 2012 mattsmadmini said:

most of the magic happens in the ports with this one rather than the chambers

Rusty by nature

Trying to find some port pics... and RE13

“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson

well its been a while the other day i took my head to a local shop and they said id be up for all most 400 ausie bucks for a shave to get a comp somewhere in the 12.5-13:1 my instant thought where ok thanks bye of cause i looked around and found that meany other shops had no interest in a cast iron head ether much to my appointment's so im gona slap a turbo on it and be done with it! well more or less.. ill have some magnesium guides, re faced valves, 3 angle seats and a surface cut should do me fine i thing please let me know if im wrong!

i will lookk into the head and block a bit more tomoz

magnesuim guides.. that should be very interesting

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

a kim is normally about 80$ to 100$ i got a hold head rebuilt in oz for about 600$ lol..

i think that shop is ridding you mate.

Hi,

found a dyno plot of a 202 headed NA with (I did a head for a long time ago. just bigger intakes std ex and limited porting sw5cam on a stf 998 bottom end) did another with a lot better porting on a 80+ block that made quite a bit more power (68 bhp with a +80, 998 sw 5-07 same dyno.. more than most ''tuned'' 1275's make on the same dyno)



:)

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Edited by Sir Yun on 24th Jul, 2012.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/