19 replies to this topic

[bigrob]

Hi guys.

Just having a thought as soon im going to have a spare 998 which im thinking about rebuilding and sorting.
Now ive read the optimum reliable bore size when re-boring a 1275 is to take it upto a 1293?

Is there a recommended bore size to take the 998 up to?
Obviously i want as much power to reliability as possible, an im not one for 1275's. i like to be able to say its still a 1l haha

Cheers
Rob

[Gr4h4m]

It's all about the size of pistons that you can get and it any extra machining is required for things like offset boring.

I think, graham Russell sells pistons upto 120?

IMO I wouldn't bother worrying about it and go for what you want a spare 998 is cheap to find at the mo, so get one and stick it somewhere safe :)

I did start researching about making a square l bore using a 998 and an 850 crank but the specailist stuff was adding up like the special bearings that you would have to had make... And I had started on my build or I might have been tempted to try it...

[bigrob]

Yeah ive already got the spare one. I wasnt sure as to what to do with it haha. Would it not be worth doing then? Its done a fair miles, smokes etc and needs a rebuild. I just thought as its going to be conpletely stripped i might aswell rebore

[Cooperman]

It's a personal choice.

You can go up to +0.080" with no problems and that will give a few more bhp and a slight improvement in torque, but on the road you'll probably not really notice it.

Most people just go to the next size up, like +0.020".

In reality, the build quality and component selection is more important than just going to a big oversize, unless the engine is for competition and the regulations allow it.

[bigrob]

Oh fair enough. So just using quality parts really is the main aim then?

[Cooperman]

Use the best quality parts, have it accurately machined and then assemble it with great care to ensure that everything is properly matched, the cam timing is spot-on, the valves are all well-seated and lapped-in, the compression ratio is as required, the manifolds are matched to the head and everything else is set properly like ignition timing, valve clearances, ignition system, etc.

[bigrob]

Im going to be building over the next few months so i've plenty of time to take care with it. Its been suggested to me that if im going to be doing it properly then to get every part of it blue printed?

[HarrysMini]

It's not so much of a problem with the 998 but I'm not a fan of boring to the max as the A series is getting rarer and no more will ever be made. Yes, it's true the 998 is much more plentiful than the 1275 but they will still run out, and then they will be damned expensive as well!

The more blocks that are bored to their absolute maximum (i.e 1380), the more that will end up in scrap yards, completely ruined.

If you are reboring due to wear then the next size up will suffice, if you are boring for power then, as Cooperman says, you can go bigger. But going to the biggest size rather than, say, the next size down, won't really get you much, if any, more power. 

 

You have to remember that over boring in itself won't increase power, but I presume you are planning on having other work done rather than just the rebore if it is power you're after. 

 

As has been said though, the quality of parts is more important than over bore size as you could build an engine with the biggest bore size with poor quality components that creates less power than a standard bore with good quality work and components.

[Cooperman]

I knew a guy who built a 1380. However, he had a 296 cam, twin HS4's, but he couldn't afford a decent head or a close ratio gearbox with low final drive ratio. He then wondered why it was virtually un-driveable!

A little knowledge is a dangerous thing. He would have been better going to 1293 (+0.020"), fitting best quality pistons, a 266 or 276 cam, a really well gas-flowed head at around 10;1 C.R., duplex timing chain and then assembling it very carefully and accurately. Then he would have had a really nice driving car with good road manners and reliability.

[bigrob]

So research into my desired set up is probably my best tool in that case then? And a deep wallet! Haha

[HarrysMini]

Definitely. Research and knowledge is key when building any engine. A good book to read would be Tuning BL's A series by David Vizard. Although read it one chapter at a time, when I first got it at 13, I was a bit overwhelmed at all the information when I read too much of it in one go. It's a great book though.

You could get a Haynes manual but I have found them to be pretty useless to be honest, you may get on with them though. I think the yellow and the light blue ones are the best. Also, a Haynes manual doesn't really go into detail about the engine.

 

Another resource to look into is the Ultimate Mini Builder 1380 engine building DVD. That's great if you want a step by step tutorial to stripping down and building an A series. Also you get 10% off of that with your TMF+ discount.

 

Your best bet is to talk to an engine specialist. Tell them exactly what you want to get out of the engine, what it's use is going to be etc. 

[Cooperman]

I often think that some folks go about engine re-building from the wrong direction.

Before considering to what specification to build to it is necessary to decide for what the car is to be used.

If it is just on the road, then it should be remembered that the Mini is a true classic car. It will never be a quick car in the way modern cars are quick.

The best to aim for is a reasonable 'classic car' performance with good reliability and smooth power delivery, especially in traffic.

Re-boring the next size up, gas-flowing the head, increasing the C.R. to around 10:1 and improving induction & exhaust will make a 998 drive very nicely and will not cost mega-bucks.

I see you are from St. Albans. I was born in St. Albans and have very fond memories of driving home there in my first Mini 850 and my first Mini-Cooper 998.

[Gr4h4m]

After reading the above and watching the DVD I also found This very useful...

http://www.amazon.co...=dp_ob_title_bk

[bigrob]

Yeah ive been reading through vizards a series tuning guide since i was about 12, and its only recently started to make sense ha.


Yeah im in wheathampstead and there's definitely some brilliant roads around here

[Cooperman]

Wheathampstead to Codicote flat out late at night is fun!