5 replies to this topic

[benjwildeboer]

Ok, some of you may have seen my turbo thread that I posted yesterday asking how to do it, well after doing quite a bit of reading on turbo minis etc. I've decided against it.

I am therefore wondering what to do with my mini power wise. I'm probably going to tune up the 998 (nothing crazy) but I am wanting at somepoint to swap the 998 with a 1275 (or maybe even a 1380 - although I'm not sure if I'll bother, it's going to be K'd one day).

So therefore (after doing quite a bit of reading on here and other websites - and usign the search button lol) I've come up with a short list of parts that I'm looking to buy at some stage to put on the 998, and then later transfer over to the new 1275.

• full exhaust system (single box)
• LCB manifold
• Twin 1.25" SU's (do I need to change the jetting for the 998/1275?)
• Kent 266 cam

Does this make sense? The only thing I'm not too sure about is the cam. I've been reading up and it seems like the one to go for, although I'm tempted by a lairier one. This mini will not be my daily driver but more of a toy, and I love the kick a good cam gives when its in the power band.

Also, is a stage 3 head interchangeable between the 998 and 1275? This looks to be a bit pricey at the moment though...

I am already on and will be on a very tight budget so all of the above (and eventually the 1275 itself) will be ebay specials which I'll hopefully pick up for not much. Would there be any other parts that I should add to the list (and maybe ones I should take off?).

And I don't suppose any body has a rough idea of what sort of power I should be expecting with this little lot, with both the 998 and the 1275?

Thanks very much
Ben

[998dave]

MG Metro inlet manifold, K&N air filter.

Cam may not be suitable for both - I'm not an expert.

Carbs should be about right,

2 x 1.25"
1.25" = 31.75mm,
(31.75/2)*(31.75/2)*Pi*2 = 1583 mm2

1 x 1.75"
1.74 = 44mm
(44/2)*(44/2)*Pi = 1520 mm2

So choke size at least it should work.

Heads aren't straightforward interchangeable,

[benjwildeboer]

MG Metro inlet manifold, K&N air filter.

Cam may not be suitable for both - I'm not an expert.

Carbs should be about right,

2 x 1.25"
1.25" = 31.75mm,
(31.75/2)*(31.75/2)*Pi*2 = 1583 mm2

1 x 1.75"
1.74 = 44mm
(44/2)*(44/2)*Pi = 1520 mm2

So choke size at least it should work.

Heads aren't straightforward interchangeable,

thanks for the info. So it doesn't look as though the twin carbs actually pose much of an advantage over say a HIF44, or am I missing something?

Only my dad's always told me to steer clear of twin carbs if possible as they are quite hard to set up and keep running right apparently?

I missed the K&N off my first list aswell, I'll get one of those. What advantages does the MG inlet manifold provide?

thanks again
Ben

[Cooperman]

For a 998 the best head is the 12G295 which is the original 998 Cooper head from 1964 onwards. It is an 'open-chamber' head and flows so much better than a modified later basic 998 head.
You can't use this head on a 1275 lump.
A single carb is fine so long as it's at least 1.5".
We have a 998 modified which I built as a development engine. Spec is as follows:

Bored to 1061 cc, that's +0.080"
Flat-top Hastings pistons
an original 510 Cooper 'S' cam
Original Cooper 3-into-one tubular exhaust manifold
HS4 1.5" SU on a Howley alloy inlet manifold, polished and matched to the head
A 12G295 Cooper 998 head with slightly larger inlet valves, 33.5 mm, and gas-flowed with a comp. ratio of 10.3:1
1.625" diameter exhaust pipe with centre-exit RC40 exhaust box

This gives 68 bhp at 6000 rpm without the air filter and 66 bhp with the filter.

That's not bad when you consider that the standard 998 Cooper gave 55 bhp.
It waqs also a fairly low-cost build which is smooth at low revs and in traffic, whilst giving excellent performane when revved to 6000 or just over. with a 3.2 finaql drive it will cruise all day at 80 mph and is so much smoother and nicer to drive than a 1275, but lacks the low-end torque of the bigger engine, as you may imagine.

[benjwildeboer]

thanks for that cooperman, sounds like a good set up.

I was reading a thread earlier that mentioned putting a 12g940 head straight onto a 998 without modifying the block at all.

It says that this is possible if you don't have high a high lift cam (I'm assuming a standard one will be fine?).

Would this be a worth while mod? Or is it easier to just modify the 998 head (or buy a 12g295)?

cheers
Ben

[benjwildeboer]

So, after doing a bit more research (and searching of ebay) the plans changed slightly.

I think I'm gonna try and go for a single Hif44 now isntead of a twin set up. I'm assuming this would perform best on an MG Metro inlet manifold?

The real area I'm having a bit of trouble with is the head side of things...

I'm now thinking of trying to get hold of a 12g295. Then the cams is where I'm getting confused. Theres a dirt cheap bp300 on ebay at the mo but I've read in a few places that it'll just be too instense? How lairy are MG Metro cams?

Is it worth getting 1.5:1 or 1.3:1 rockers? Or double valve springs?

I want this engine to have real kick. I don't mind particularly if it's a bit of a *woman of ill repute* to drive, the only prerequisits are that it's as powerful as possible and as cheap as possible!

Thats why I'm steering in the direction of the MG cam, but I'm worried it won't give enough kick? But then again, beggars can't be choosers I guess.

any input?

cheers
Ben

EDIT: forgot to mention, are cams from the 1275/998 etc. interchangeable? Ie if I buy a cam that was out of a 1275 will it fit my 998?

Edited by benjwildeboer, 06 June 2009 - 08:52 AM.