43 replies to this topic

[MiniMadMan1996]

Hi there

I'm looking at building a fairly decent 998 engine that will give some poke, The current spec i'm looking at doing is as follows

Block
- Bored to +0.40

 

Bottom end
- lightened and balanced crank
- worked rods

 

Pistons

- Minispares +0.40 flat top

Cylinder head
- 12g295 stage 3 (heavily ported, double valve springs, running standard valves still though) Guess that would still be a stage 3?

- cooper s forged 1.3 rockers

Carburation
- Twin HS2 (modified butterflies and spindles)

Cam - I'm struggling to decide with either a sw05 or possibly a kent 276

 

Exhaust

- maniflow freeflow manifold
- maniflow road RCM system

Gearbox
- Looking at either going for a full sccr or a close ratio helical box?
- 3.4 diff with x pin
- sc drop gears (Just for that orgasmic whine!)

Can't think of anything else at the moment

[Cooperman]

As the 998 doesn't have much torque you could consider going to +0.080" with flat-top pistons. That gives 1060 cc.

You won't make a 998 'quick', just not quite so slow  .

A 12G295 can take slightly larger inlet valves which help a bit.

Don't 'over-cam' it. The SW 5 would be good, but a 276 will mean a very narrow power band, no real torque lower down and it would not be nice to drive on the road. I built a 998 at 1060 with a standard Cooper 'S' 510 cam (because I happened to have one lying about) and it was very nice.

Best gear set is the original 998 Cooper ratios which are still much wider than the SC CR competition gear set.

My advice is most definitely not to fit SC drop gears. They are totally unnecessary in a 998 and are, quite simply, horrible to drive any distance with In my 'S' which has them I have to wear ear plugs on any journey over about 10 miles.

3.44:1 FDR will be ideal with an sw5 or a Kent 266 cam, but if you go to a 276 with a SC CR gear set you will need a 3.9:1 or 4.1:1 in a 998 as first gear is very high and a 276 in a 998 will need a lot of revs to pull away from rest due to a lack of low-end torque.

If it's a road car, then build it for good torque rather than absolute maximum bhp.

[MiniMadMan1996]

Yeah I've been told that in a 998 torque is better than power, As far as bottom end modifications go, could I almost leave it standard apart from a balance? 

The 295 I've got has still got the standard valves in it, and hasn't had the unleaded seats put in either.

Also, I didn't list, what type of clutch and flywheel would be good? Originally I was looking at an ultralight weight one, but I've tried to steer away from that idea now

Cheers

[carbon]

I think you will be very lucky if you can get Cooper S forged rockers with 1:1.3 ratio. Even using offset bushes I am only getting 1:1.25 measured as valve lift.

 

+1 for Cooperman's comments about cam selection. The SW5 profile is essentially the 510 with about 20% extra valve lift, so the SW5 cam with your forged rockers should work well in a fast road 998.

Edited by carbon, 12 November 2015 - 05:55 PM.

[MiniMadMan1996]

You can get the forged cooper s rockers on minispares, 12G1221

And yeah i'm looking more to the sw5 now, will also help in mot as emissions are meant to be better, not that my mot tester works at swiftune as well  

[coopdog]

yeah looks like you'll get about 60ishbhp with that spec :)

[PhilipGCaldwell]

Sir,

Please please take my advice, do not put a 276 in, I put one in my fast road 998 and regret it enormously, just dead below 2500 rpm, get something that provides a much more sensible power band, SW5 is much better.

 

Also, don't put a big bore exhaust on, stick to the 1.75 inch system, larger than this saps power out a small bore

 

see my build thread, and trust me from the cam, I have the real life experience on it

 

Phil

Edited by PhilipGCaldwell, 13 November 2015 - 09:47 PM.

[MiniMadMan1996]

Yes I am defo thinking of going sw5 now, and the rcm exhaust is 1.75"  

[PhilipGCaldwell]

Definatelty, the trick with life in general is learning from other peoples mistakes, my cam choice of 276 was a mistake and I regret it massively, if my engine is ever out again it is without doubt getting an sw5 put in it.

 

Its all preferance but I wouldnt discount the hif44 carb on a 998, I have one with an ITG ram air kit and am very pleased with it,piece of cake to tune it too

[MiniMadMan1996]

Yeah, I should have gone with the sw5 to start off with, I know they guys as swiftune so I could probably get a bit of a discount as well, And I just like the look of twins, along with the ram pipes they'll look awesome  

[PhilipGCaldwell]

Aye, twins do look purdy. If you put a 276 in, I will hunt you down and slap you :)

[MiniMadMan1996]

Hahaha, nah think i'm set on the sw5 now  

[Cooperman]

You really do not need to fully balance a 998 with an SW5, 266 or 510 cam. With any of those cams you won't need to use more than around 6200 rpm and a 998 is a very smooth engine, when compared to a 1275, up to 6500 rpm or even higher.

By all means lighten the flywheel a bit, but not too much.

 

I built a 998 with a 295 gas-flowed head, 10.2:1 C.R., +0.080" bore, flat-top Hastings pistons, an HS4 on a Howley alloy manifold, 510 cam, Aldon 'Yellow dizzy, 3-into-1 tubular ex. manifold, RC40 single-box exhaust system, 850-type pressed steel rockers (welded across the tops), slightly lightened flywheel. It had 65 bhp at 5800 rpm at the flywheel. The torque was excellent (for a 1060 engine). FDR was 3.44:1 and gear ratios were standard. It was very nice to drive and quick for a 998-based classic Mini. My Grandson & I built it using mainly stuff I had in my stock of old Mini bits.

 

As above, keep well away from the 276  in a road-going 998. I once put a 286 in a rally 998 and it had virtually nothing below 4000 rpm. It had 73 bhp at 6700 rpm, but was horrible on the road sections of rallies, despite a 4.1:1 FDR and only 13 mph/1000 rpm in top. It had to have a SC CR gear set to keep it on the cam.

[MiniMadMan1996]

Ah right, I'll have to note all of this down, as far as clutches concern, will a standard 998 clutch be ok? Or would an ap racing clutch be better?

[PhilipGCaldwell]

Also listen to Cooperman with any advice, he knows his beans. 12g240 is a good head but would need relief pockets cutting out if you went down that route.