14 replies to this topic

[Sk3Tch]

Hi there everyone iv got a 998 mini and i want to build a really torquey low down grunt of an engine. I need to stay 998 for insurance reasons otherwise i would go 1380!! Some one has mentioned about using a 1275 crank but to be honest i havent got a clue. Can anyone out there help me??

[Pooky]

fyi a standard 1275 will probably have more torque than a mildly modified 998 and be cheaper on insurance...

[Sk3Tch]

My insurance is 2 and a half grand due to being a mechanic with 6points! so need to keep it 998!

[Cooperman]

You could bore it out by +0.080" which gives 1061 cc and fit Hastings flat-top pistons. Then fit a better cam such as a Kent 256 which will give excellent mid-range torque when combined with a better inlet and exhaust system. Fit a 12g295 head if you can find one, or modify the standard 998 head and set the compression ratio about 10.2:1.
Leave the flywheel at standard weight.
An alternative cam would be the 510 from the early Cooper 'S' which is also a nice mid-range cam when fitted to a 998.

[Sk3Tch]

Would a stage 3 head help torque in any way. I no it would help in bhp but its a lil run around and i want to concentrate on the torqs!!

[bmcecosse]

The AEG 510 cam is the LATER model S cam - early cars had a lesser cam ( AEG 148) which was same timing as the AEA 630, but with 1/2" lobes. Better cam will be the MG Metro. Up to you about head - I wouldn't hesitate to fit the 940 head - but there will be a bunch of folks along in a minute to say this will only work at high revs etc!! It's not true of course - but as you are a mechanic - i'll leave you to be the judge. Worth doing - the head may only cost you £10 or so if you look in the right places!! If you don't like it - the head will sell-on without any problems!

Edited by bmcecosse, 30 September 2009 - 10:01 PM.

[Cooperman]

The expression 'Stage 3, etc' really means very little.
The head you want on a 998 is the Cooper 998 head which is part number 12G295. You could mildly gas-flow it, but it's such an improvement over the standard 998 head that it's worth trying to find one on ebay or in the Mini Mag/World ads.
The 998 really is a nice engine and so much smoother than a 1275. We have a 998 here bored to 1061 with the 295 head and some other nice bits and it gives 68 bhp at 6000. it is smooth all the way up from about 2500 rpm, although, of course, it doesn't have the torque of a 1275.
There is never much point in going to 1380 as it's expensive to bore properly and the block is then, effectively, at max safe bore and any further bore to 74 mm can go through the bore walls. A good size for a 1275 is to 1330 cc, i.e. +0.060".
You can't fit a 1275 crank into a 998 as the crank is a different size in respect of main and big-end bearings.

[Sk3Tch]

Im goin to have my original conrods stress relieved and have the crank wedged and a new set of flattop pistons, cam and such like. Plus i was thinking along the lines of 1 and 3/4 su carb jetted acordingly- is this a good thing to do??

[bmcecosse]

That work on the engine - would only be sensible if you plan to rev the nuts off it! Yet you say you want 'torq' - which implies not revving it hard! You need to make up your mind!

[Cooperman]

If you are going for mid-range torque rather than a 'screamer' which will really rev, then you don't actually need a wedged crank or stress-relieved rods, the standard ones are fine up to 6500 rpm. It doesn't hurt to do it, but you won't notice any gain in torque,. With a 'hot' cam and a balanced crank ass'y then wedging and stress relieving will permit very high revs wit peak power at well over 6000 rpm.
As 'bmcecosse' says, you could fit a 12G940 head from a 1275 if you either pocket the block deck or set the valve faces deeper into the combustion chambers by about 0.040" I think - he knows the exact figure. It's your choice after all.
When I said the 510 cam from the early cooper 'S' I did mean from the 1275 Mk 1 & Mk 2. The very early cam was phased out after the 1071. I just didn't want any confusion with the John Cooper 'S-Works' cars. I had a 510 in my 1964 Cooper 998 rally car back in 1965, if I remember correctly, which at my age I might not be doing, but it was a great cam. My grandson has a 510 in his 1061 cc former 998 engine. The MG Metro cam is very similar to the Kent 266 which is another great mid-range cam, although with the power and torque slightly higher up the rev range than the 256.

[bmcecosse]

The AEG 148 cam was used in the first of the 1275 S engines too - replaced by the slightly better AEG 510 during 1966.

[Cooperman]

You beat me to it, I just looked it up. I guess my '64 Cooper must have had the 148 as it came out of a '65 Cooper 'S'.
Ah well, another senior moment - do I come here often?

[Sk3Tch]

Thanks every 1. Looks like a have a lilbit more research to do and a rethink of my shopping list.
Many thaks

[huw_jenks]

An absolutely mahoosive ram pipe? I saw a 17" one on Ebay a few weeks ago. In David Vizards book he says for torque, a long rampipe will be really helpful.. K&N used to make one called the 'Torque Ram' or something, anyone know about it?

[mini7boy]

Rather than trying to choose between competing non-expert opinions on this forum, why not read the words of an expert?

These articles cover the 1098, but as the author of them says, the 998 and 1098 are similar enough that many of
the comments apply equally well to the 998. Pay particular attention to the section in the second article that specifically
addresses the cylinder head issue.

Here are a three excerpts to give you a flavor of Russell's approach to things:

"When I build race engines I still chase torque as the most important factor. Getting out of corners quickly and accelerating away is more important in most racing than outright top speed. When it comes to top speed in a Mini, I've done a lot of testing with a GPS (no chance for tacho, tyres or other variables to throw out the results) and, without a doubt, a Mini on narrow tyres and no flares, with 145-150hp, will not go over about 123mph on a flat road. But, a similar Mini with 115- 120hp will still do 118-120mph."

"I do not like the use of the 1275-type heads (12G940, etc) as these are too big for the small-bore motors. Yes, they will make the horsepower if you rev them hard enough, but I can still make more horsepower, with a better spread of torque, using the smaller heads.

"The smaller heads have much better airspeed and better filling, which in turn produces a better spread of torque throughout the rev range - and it is torque that accelerates the car. When using 1.218" valves the 295 head flows the same as the 940 head with 1.3", but the 295 head is doing it with smaller volume right through."

These articles were written by Graham Russell of Russell Engineering in Australia. He is one of the leading A-series experts in Australia
and his shop has: an engine dyno, chassis dyno, flowbench, cam grinder, balancer. He tends to build engines using cams of his own
design and manufacture and also does a brisk business selling his cams separately to both road and race customers.
He builds both road and race engines.

He grinds his own cams, ports cylinder heads and builds complete engines for road use as well as for front running Mini racecars.

http://www.minimania...?DisplayID=1881

http://www.minimania...?DisplayID=1882

http://www.minimania...on/ArticleV.cfm

take note of his clever valve adjusting method covered starting near the end of the second article.

Here's a good article by Keith Calver on the 1098.

http://www.minispare...x?ty=ad&aid=174

Edited by mini7boy, 02 October 2009 - 08:05 AM.