486 replies to this topic

[1984mini25]

hi there, are you using an a series block? anyone used an A+ block with flat top pistons? surely the higher compression engine is better. just wondering.

love this thread by the way, im doing the same thing with an a+ engine soon

cheers Jaffer.

The one above and mine are both a+ 998s, in theory the higher the compression the better the performance. BUT ideally you don’t want to exceed anymore than about 10.5 ish. Another thing you have to consider is the chambers of the 12g940 head, despite the larger valves are in fact small than the standard 998 head. Which has the effect of razing the compression ration to begin with.

[In-a-mini]

I built my 998cc engine (well +40) from an A+ block with flat top pistons i zero'd the block but i didn't use a 12g940 head i had a few 202 heads kicking around. But remember the 1275 gasket has more cc in it than the 998. i had to have my head skimmed 40 thou to gain a compression of 10.5-1 (the head starts life out with 26cc) if i remember i needed 24.5 ish cc at the end but cant give a definate. So if you dont zero the deck you will probably be close with a standard 21cc un skimmed 12g940. I worked the head alot and cant remember what the cc went to. my next 998 engine i will use a 12g940 and longer cam.
The cost of my 998 engine was about £550 with new pistons mains bigends and thrusts, new exhaust valves followers diffpin seals gaskets etc. machining work was bore +40 skim block 20 thou skim head 40 thou fit pistons. the rest were bits i had around and the original engine

[PhilipGCaldwell]

All pistons back in with new rings, there was some confusion with the orientation of the pistons but I have cleared this up now hopefully

Endfloat is 5 thou (bought a dial gauge
main bearing caps torqued down, BE bearings torqued down

[LuckyThe1275]

Any progress?

[PhilipGCaldwell]

yeah, sorry, i decided to take out the crank again and have it all balanced, its all back in now, waiting on my new cam bearings to arrive (and i have the tool to insert them off my mate), once they are in iI can finish the rebuild and put it in the mini and see how goes

should have some pics next week

[twrminisport]

looking good man
How much longer do you reckon youve got to go?

Edited by twrminisport, 26 February 2011 - 11:37 PM.

[pickupmad87]

you should be looking at a quite beffy bhp out of that build ive done a simalar sort of build with my 998 and have managed o squeeze 76bhp at the wheels!

Engine spec:

998 bored + 60 thou
lightend balance and heat treated crank
lightend flywheel
kent 286 camshaft
stage three 12g940 head
HIFF44 carb

one thing i will say the 286 camshaft is very very lumpy at low revs. but once you give it sum revs it flys like **** off of a shovel!!!

[twrminisport]

286?!?! Christ what was that like?
Vizard, Calver etc reckon on a cam with overlap of any more than 270 to be way over in a 998 and a 276 is 270 on inlet and 280 exhaust.
The 286 is 280inlet and 290exhaust??

[pickupmad87]

286?!?! Christ what was that like?
Vizard, Calver etc reckon on a cam with overlap of any more than 270 to be way over in a 998 and a 276 is 270 on inlet and 280 exhaust.
The 286 is 280inlet and 290exhaust??

im not sure on what that means. the cam is a 286 that came from a trashed 1380 that i broke for its head and cam. the place i got my engernering done seemed to think it would be fine to put that higher cam in. before the negine was installed i took it to them to dial the cam in. alls been fine ever since apart from the lumpyness at low revs but thats to be expected with that sort of cam i suppose.

[twrminisport]

ahh fair enough
Interesting to know its possible and runnable in a 998.
Im thinking of a kent 276 or a Morspeed MSPD trackday cam for mine

[l_jonez]

Thought morspeed had stopped trading ?

[twrminisport]

i have a friend with one sitting in his garage

[twrminisport]

How we getting on then

[PhilipGCaldwell]

How we getting on then

Still no more progress im afraid, still waiting for the cam tool off my mate
Gonna make a start taking the engine out this weekend as Im going to use the gearbox off it as I know its 100% working order

Edited by PhilipGCaldwell, 16 March 2011 - 08:08 AM.

[Saxo-Fiesta-Mini]

nice work