Some different 998 CR questions etc
Turbo Mini Forums

Right, Shauna wants a bit more go from her 998, and turbocharging it is the route we're going down.

Now, it will be a 998 A+ block (think these have 6cc dished pistons?) Mg metro cam, megajolt, R5 T2, NO intercooler, and only want a sensible 80ish bhp from it and to retain or improve the mpg.

She is currently bidding on a head on ebay that I first thought was unskimmed but reading it again myself He says the height of the head is 2.66 inch, so that makes me believe its had a 2.5mm skim and around 21.6cc chamber size if that's correct? And I've worked out the CR to be 9.1 using a calculator.

What sort of boost level, if any can we use on this engine? And will it be near 80odd hp mark? This is a daily driven car so if this is not viable then please let me know.

Thanks.

Do you have the 998? Some were dished, the later ones were flat top.

Spoiler.

They don't die, they just get faster!

Yeah I already am in possession of the block, it's definitely an a+ and I'm pretty sure they're dished but I'm 120 miles away from it atm. It came out of an 88 jet black.

No you're not having a spoiler

Good luck! mine was an 88 with flat tops.

Or bang a 12g295 on there if all else fails.

My stepsisters one is flat top 2. Its a 84 metro engine. Am amazed of the abuse it can take day in day out...

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

It is a 12g295 head.

They don't die, they just get faster!

The metro turbo ran 4-7 psi on 9.4CR with no intercooler (if my memory is correct), so I'd say that is a reasonable figure for an 80bhp 998.

Also, I thought A+ 998s were all flat tops? even so, could always give Mr. Benross a call, did a fantastic job on my 998 head. once you know what pistons you have you'll know what cc you need in the head.

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

Not all 998 A+ engines were flat top, there were high and low CR versions.

However, most are the high compression type.

You basically need 28cc plus the had gasket to get to around 9:1. I would say a head with 2.5mm skim is a non-starter.

I would aim a little below 9:1 anyway.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Would that be with the dished pistons Wil?
This is the calc i used, by what you have said saying it needs 28cc for 9:1 I'm not sure if it's accurate or not.

The calculator I knocked up in excel says you will need 30cc in the head, pistons and deck height in order to get 9:1

Edit: + gasket too

Edited by jakejakejake1 on 8th Jan, 2014.

See if this one works:

https://docs.google.com/spreadsheet/ccc?key...aUE&hl=en#gid=0

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

Standard cam you should be able to just stick a 12g940 on without pocketing? Or even a slight pocket of the block. Surely this will give you a larger chamber size. And a hell of a lot more free performance?

12g940's have a small chamber size Dev, you wouldn't think that logically, but because of the extra cc of a large bore if the head chambers were large the CR would be low.

12G295 - 28cc
12G940 - 21.4cc
998 head - 24cc

the 28cc quoted is the compressed volume you need plus the head gasket (around 2.8cc). You can make this in the head if you have a standard 295, or a highly modified 940.

I've done various combinations in the past. but I run close to 8:1 on my race engines, so have 6cc pistons and large head chambers.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Ah course because of the deep chamber in the head..too late last night lol id still go 940 may be cheaper have a head worked then buy an already done 295?

Nothing is definite yet, just thinking about different ways to doing things, because getting an unskimmed 295 for not an extortionate amount of money isn't easy!

Whilst that may be true Carl it will most likely be the best way to do it.

If something is worth doing, it's worth doing half of.

if you want fuel efficiency id be looking at going for a high expansion ratio but the problem with that is having no IC the charge once compressed (due to dynamic CR) will be HOT! so dose not favor a non IC ed setup

high expansion ratio uses more of the energy from the air and fuel being burnt rather than dumping it down the exhaust

any reason for no IC or just to make it simple and cheep?

imo what id look at is peek cylinder pressure and the temperature rise gained by the compression

imo static Compression means nothing Dynamic compression is where its at

The reason for no intercooler is to make everything look as stock as is possible

If the head is useless I wont be using it, there's no point spending money on something I don't want. I only bid on it because I was told it was unskimmed. I'm in no rush so hopefully I loose this one and a unskinmed one comes along.

They don't die, they just get faster!

My 91 neon 998 had dished pistons, used a hif38 on that and it went alot better then standard

I also have a 91 neon, might has flat tops

It's cool, got outbid, wooooooo!

They don't die, they just get faster!