22 replies to this topic

[chairchild]

Just pondering this one - as I'm still slowly collecting the parts to make my high mpg 1098, which will run at around 13:1 CR (yes, I know, it's stupidly high, but thats the point)

But....


After I've been running it for about a year, and it's been nicely run-in, I'm tempted to go turbo, using the mirage manifolds and a T2 turbo :wink: I'd be tempted to keep the CR reasonable, and just use the MG Turbo CR of 9.4:1-ish, with max boost of 7psi


Now then - what are the downsides of using a head spacer to lower the CR? As the head I'll be using will be HIGHLY modified, and I dont really fancy forking out for one of the same spec, but with a lower CR






Not really after silly Bhp, just a reasonable power hike

[Dog]

Lookin in a Minispares cataloge I got from Bingley... yu can get a multi-layered steel head gasket...
Says its ideal for NA, and force engines...

[MAGA7INE]

It will detonate like a pinless hand grenade in Basra with a plate! I would use a 12G295 (cooper 998/MG1098), head with 28cc chambers (nominal) as standard and keep your other head. This should give you a good CR for a turbo, if you give me your bore and piston dish, I can work this out for you exactly.

A stock 12G295 head will out flow ANY modded small bore head, so you can keep your modded (12G202?) high comp head for another high comp engine and use the 12G for your turbo.

Decompression plated destroy your squish band and promote hot spots at the edges of the combustion chamber. To get down from 13 to 9 you will be looking at several mm I would think!!!! They promote detonation.

At a push you could use a morris minor etc 12G202 head as they have enough chamber volume to get you where you want to go, but cooper 998 heads are hardly rare and would provide a performance boost as well

[Sprocket]

MiniSpeed do a steel gasket twice as thick as standard and also a standard thickness one too. Maybe not enough cc for what you want bet at least its a little more. As for a spacer, something in my mind says stay away from that idea but cant explain it other than it just doesn't feel right.

[chairchild]

hehe, I knew that they were bad for one reason or another, but I wasn't entirely sure of the exact reasons!

The head will have this spec (well, if I can find somewhere to do the ceramic stuff anyway!)

Mg 12G940 head - converted to unleaded
exhaust valve guide boss reduced
wedged head (3 degrees)
inclined valves (3 degrees)
ported exhaust throats
ceramic coated combustion chamber+throats (thermal barrier type)
3-cut valve seats




By themselves, they dont really do much - but add them all together, and I should get a nice bump in burn efficiency! (there are SEVERAL other little "exotic" bits for the rest of the engine as well, which are on the same principle)

So I was just gonna turbo it, on the same spec head, to see if that meant it could make more power as well - purely out of curiosity!

[AlexF2003]

mod the head....

then run 10psi

Alex

[chairchild]

hehe - I doubt my pocket will allow for that just yet, since this will be my daily-driver to get me to work. And I dont think my pocket will allow for the cash needed to convrt to turbo :-s

[AlexF2003]

£60 to make the chambers bigger.....

if you cant afford that you cant afford to run a turbo!

Alex

[Sam]

£60 to make the chambers bigger.....

if you cant afford that you cant afford to run a turbo!

Alex

Wheres that from Alex?

[DaveCoxon]

Wheres that from Alex?

Two posts above?

[AlexF2003]

http://www.morspeed....g_mini_page.htm

[The Matt]

How far can you take the chambers out to on a 12G940? I need 28cc to get the correct CR for mine (non-turob, but odd piston/bore combination).

EDIT: sorry. I'll start a new thread!

Edited by mini mad me, 04 February 2006 - 06:21 PM.

[chairchild]

Alex, the head will be machined to get me down to around 13:1 CR, so I dont think I'll be able to take out enough to do it that way


But either way, it's looking like I'll have to modify another head, instead of using this one

[AlexF2003]

a std 12g940 will do 28cc easy... 30 odd is possible but with more riskj of wrecking the head.

Charchild... run a different head!

Alex

[Dog]

Morspeed do a really sexy head.

Says they can get he CR down to 7.0:1 imagine the boost on that!!