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View Full Version : Head swap on a 998cc?



Creatrixx
05-17-2007, 09:44 AM
I haven't even gotten my car yet and I'm already so full of questions. Thanks to everybody for giving me so much help already!

Just found out my 1980 Mini takes leaded gas and I'll need to include an additive. I'd really rather not. However, instead of just changing the valve seats, I'd prefer to do a head swap with something that will improve the overall efficiency (and/or power) of the engine. If I had to choose between power and efficiency, I'd go with efficient. I've got a 998cc. Any suggestions?

Thanks!
~Melissa

Bugeye58
05-17-2007, 08:02 PM
Melissa, I think all of the heads after about 1974 were fitted with hardened seats, so no lead shouldn't be a problem. The stock 998 head ain't bad to start with!
Jeff

Creatrixx
05-18-2007, 10:52 AM
I read that it was much later than that, actually. My boyfriend wants to port a head and do all sorts of things to it, so I'm not going to complain about that. I think he's just excited that I'm getting something small and classic. Heck, so am I.

The article I read on leaded fuel and minis is here. (https://www.minimania.com/web/SCatagory/CYLINDER%20HEAD/DisplayType/Calver%27s%20Corner/DisplayID/1166/ArticleV.cfm)

My engine number isn't listed in his "safe" list.

Bugeye58
05-18-2007, 08:35 PM
Melissa, the article also states that unless you're contemplating intergalactic mileage, don't worry about it.
I thought the unleaded heads went back further than that, though.
I ran unleaded gas in a '63 Sprite for many, many miles, and noted no problems with the valves when I pulled the head to change a gasket.
Jeff

dklawson
05-18-2007, 09:48 PM
I'm not sure what year the hardened inserts showed up. I assume it's later than we think because it's a topic that comes up on one of the U.K. based Mini sites I frequent. I'm sorry I can't advise you on a suitable swap. I'm only familiar with the heads for 1275s.

Creatrixx
05-22-2007, 12:47 PM
We used a chart with the casting numbers to find something that will work while we were at Imports at Carlisle. We're going to do more than put in hardened seats, such as porting it.

Thanks!

ThomP
05-26-2007, 04:43 PM
The best head for the small A series is the 12G295. Then comes the 12G206. If you get one of these heads, make sure you have the combustion chamber sized for your 998 as most were originally for an 1100 cc engine. If you don't re-size the combustion chamber the compression ratio will be too low and you will NOT see an increase in HP. Somewhere around 24.5cc should give a compression ration around 9.5:1, depending upon head gasket, whether the engine has been bored and piston to deck clearance. The 12G295 is already ported better than a standard head and will only provide 1-3 more HP by porting it further; very little gain for bunches of work.

Creatrixx
05-29-2007, 11:07 AM
Wow, that was a lot of information. Thank you so much!