10 replies to this topic

[Alexalanmills]

Hi people I have standard (not cooper) 998 mini. I have fitted a mini sport CA3 road/rally camshaft and 1.5 cast rockers, I currently have a single HS4 carburettor and am looking to make an upgrade was hoping to gain some advice on which carb would be most beneficial for my car ?
All help is much appreciated :)

[adamg1380]

Have you still got the same needle? I'd have thought the right needle in a HS4 would work pretty well.

[Cooperman]

What do the regulations say about carb changes for whatever sort of motorsport you are doing?

You might be better off with twin HS2's if the regs allow it.

[rally1380]

I know it's not what the OP is aking....but a well modified cylinder head would also help make things a bit brisker.....aswell as a better carb setup.

 

Twin HS2's on a good manifold get my vote.....cheap too.

[Alexalanmills]

I was thinking twin HS2's but just wanted some more opinions I'm not experienced at all with tuning engines so thanks for your help people. Also the car is intended for road use with occasional track use I guess just want it to go faster !

[jaydee]

Forget the HS4, use twin HS2s or, an HIF44, i dont think you'll have problems with regs if only doing trackdays or autosolo

As said above, dont forget you need a good cylinder head, with chambers polished and opened, valve seats cut, bigger valves and minimal porting (none at all if its a 295) and skimmed to about 10.5:1 CR

[rally1380]

Forget the HS4, use twin HS2s or, an HIF44, i dont think you'll have problems with regs if only doing trackdays or autosolo

As said above, dont forget you need a good cylinder head, with chambers polished and opened, valve seats cut, bigger valves and minimal porting (none at all if its a 295) and skimmed to about 10.5:1 CR

 

HIF44 on a standard (ish) 998???

[rally1380]

Another thing that hasn't been mentioned but i'm sure is worth suggesting is a good inlet and exhaust manifold + exhaust system...should help release a few more horses!!!

[jaydee]

 

Forget the HS4, use twin HS2s or, an HIF44, i dont think you'll have problems with regs if only doing trackdays or autosolo

As said above, dont forget you need a good cylinder head, with chambers polished and opened, valve seats cut, bigger valves and minimal porting (none at all if its a 295) and skimmed to about 10.5:1 CR

 

HIF44 on a standard (ish) 998???

 

 

Believe it or not, its the easiest way to make a 731 cam work on a 998, together with a decent cylinder head.

[rally1380]

 

 

Forget the HS4, use twin HS2s or, an HIF44, i dont think you'll have problems with regs if only doing trackdays or autosolo

As said above, dont forget you need a good cylinder head, with chambers polished and opened, valve seats cut, bigger valves and minimal porting (none at all if its a 295) and skimmed to about 10.5:1 CR

 

HIF44 on a standard (ish) 998???

 

 

Believe it or not, its the easiest way to make a 731 cam work on a 998, together with a decent cylinder head.

 

 

And they say size isn't everything!  Big carb it is then.....every day's a school day!

[Cooperman]

The key to better power from a 998 rests a lot with the head. Whilst the standard 12G940 head of the 1275 is quite good, or at least not quite so bad, the standard 998 head is really poor in respect of its ability to flow mixture in. This is due to the bad shape of the combustion chambers where the valves are shrouded.

So any really meaningful improvements to a 998 must start with a better cylinder head.

Engine modifications require a coordinated solution, so if fitting better carburation it will be of little use unless the head can flow the available additional mixture in. Imagine trying to fill a bucket with water, having a larger diameter water pipe from a large tank, but still having a very small tap.

The compression ratio is also important and for a 998 a figure of around 10.2:1 to 10.5:1 is usually good. 

So, before going much further and being disappointed, get a really well gas-flowed head, do the compression ratio calculations, fit the cam, use a decent exhaust manifold (ideally a 3-into-1 tubular free-flow), a good exhaust system and a pair of HS2 carbs on an alloy polished manifold.