19 replies to this topic

[Pooky]

Been wanting to change from my twin 1 1/4's on my engine as I think I've got an air leak and also they're drinking fuel.

I've got the original HS4 with modified AAU needle on a Maniflow system that I used when it was just at Stage 1 but Win SU has just told me I should be using HIF44 with yellow spring on my new engine. I was just wondering what you guys thought...below is the full spec.

998+080 (1061cc), standard 12G940 head, standard rockers, Morspeed PH3 cam (270 duration), lightened + balanced crank, standard verto flywheel, straight cut drops, standard gearbox, 3.44 FD

I also don't know what needle to use in either my old HS4 or HIF44

I want to avoid a RR tune atm as I'm hoping to get up to ML Motorsport soon and have my Megajolt setup at the same time, so just need a carb and needle as a base

Sorry to be a pain!

[Kerrin]

Pretty sure winsu reccomends a 2" su off a jag or something for my 1380, I have a HIF44 fitted and it goes quick enough.

If you go on the forum at ML motorsports web site, or ring ML, AC is proably a good source of advice especially if you will be going there eventually.

I am surprised your twin 1 1/4" are that bad, do they need a rebuild?

[Pooky]

Pretty sure winsu reccomends a 2" su off a jag or something for my 1380, I have a HIF44 fitted and it goes quick enough.

If you go on the forum at ML motorsports web site, or ring ML, AC is proably a good source of advice especially if you will be going there eventually.

I am surprised your twin 1 1/4" are that bad, do they need a rebuild?

I was told they'd been rebuilt by the previous owner and I've stripped them down and can't find anything wrong with them (although I'm no expert). Had the carbs fitted and rolling roaded at Gerald Dale's Motorsport and he told me they had an air leak. I've also got a vacuum gauge that is reading low indicating an air leak...

[lrostoke]

This page shows what other people are using on different setups.

http://www.niksula.h...une/needle.html

Seems the HS4 would be fine, AAA or AAU seem popular choices

[Pooky]

This page shows what other people are using on different setups.

http://www.niksula.h...une/needle.html

Seems the HS4 would be fine, AAA or AAU seem popular choices

Thanks for that mate! None of those spec's are using a 1275 head though? Will this make a great deal of difference?

I know there's a few people on here with similar spec's to mine, it'd be interesting to see what they're using...

Vizard seemed to recommend a No.7 needle but I can't find this as a swinging needle, only fixed.



ABY looks a pretty close match to AAU (stage 1) and No.7, just a little richer but I guess I'll need that with the extra power...

[Grayedout]

An HIF44 would be far too much for any 998 running a standard head so stick with the HS4.

As for WinSU it is very good BUT it's only based on other peoples recommendations and can not replace a full rolling road session. Scott, who wrote, WinSU started it all off by asking people on the Mini-list what the spec of their car was and what needle they were running. The list of cars and needles linked above is that original list (my car at the time is on there: Graham Marshall) that WinSU started with.

Looking at my spec I was running an ADX needle which is slightly richer than an AAU and might be a good choice for you Pooky.

[Pooky]

An HIF44 would be far too much for any 998 running a standard head so stick with the HS4.

As for WinSU it is very good BUT it's only based on other peoples recommendations and can not replace a full rolling road session. Scott, who wrote, WinSU started it all off by asking people on the Mini-list what the spec of their car was and what needle they were running. The list of cars and needles linked above is that original list (my car at the time is on there: Graham Marshall) that WinSU started with.

Looking at my spec I was running an ADX needle which is slightly richer than an AAU and might be a good choice for you Pooky.

Thanks for that mate, might buy a few and play about.

by the way it's a standard head from a 1275 if that makes having an HIF44 more viable. What determines what size carb is required anyway? Head or block?

[MarkGTT]

the best way to do this if not on the rollers is with a wideband lambda sensor.. otherwise your 'best guessing'.

[Nightrain]

What determines what size carb is required anyway? Head or block?

The air consumption of the engine and it's still only a 1061cc, a HS4 will be fine and the twins would be better.

[jaydee]

ABY looks a pretty close match to AAU (stage 1) and No.7, just a little richer but I guess I'll need that with the extra power...

imho win su isnt very precise.
Dont use win su comparing tool, this one is loads better:
http://www.mintylamb.co.uk/suneedle/

[Ethel]

Use them all & any other info you can get. WinSU is only a rather fancy spread sheet, it will give different mods a numeric value (possibly a few for different rpm) and multiply them all together to get the results. It will give you a starting point and the performance figures will be based on proper formulas so it will show comparable trends - like how much your acceleration will improve for proportional weight savings or different gear ratios.

Mintylamb is useful for finding an alternative needle if you know where your current one is out.

[bmcecosse]

Go with the single HS4 carb - an HIF 38 would be better, and an HIF 44 can be used - but make sure on a decent alloy inlet manifold and NOT the standard inlet! Twin 1 1/4" SUs are fairly hopeless - sell them! AAA works well with my engine - roughly same spec as yours.

[Grayedout]

Twin 1 1/4" SUs are fairly hopeless

That's a very broad and 'hopelessly' in-accurate statement !

A properly set up pair of SU's work just as well as a single one and will actually give more torque on an equivalent engine.

[Pooky]

the best way to do this if not on the rollers is with a wideband lambda sensor.. otherwise your 'best guessing'.

Unfortunately I don't have a wideband lambda sensor (or even know what one is) and I'm well aware that this is all just guesswork. I am planning a RR tune in the near future, just have to save up the £300 odd quid it's gonna cost at ML with a Megajolt mapping too...


I really wish I could stick with my twins but I do think there's something wrong with them. I lost 5 bhp when I put them on and that was with them being professionally installed and tuned.

If going back to the HS4 doesn't get me anywhere then I'll probably keep the twins. Although the £100 or so quid would go nicely toward the RR

Thanks for all your help fellas

[jaydee]

With some work a single hs4 will give a good power and torque with a better fuel economy than twin hs2s.
Twins provide a better acceleration and throttle response, but doing some tuning to the single hs4 it can achieve the same result.

About having a first setup before going to ML, have you got a vacuum gauge? Theres some guides on the net about using it for engine tuning, with very good results.