18 replies to this topic

[leigh]

ive seen on here that it is not a good idea to put a hif44 onto a 998 engine...which is fine due to the 998 not being able to take all the air coming out of the carb...

BUT, what if you were to change the cylinder head to a 12g940?? Bigger valves,

im saying this due to me building up a fast spec 1275 atm over the next year (im poor so can't do it all at once, haha, plus its gona be 1 hell of a bigbore) but i have a 998 in my mini atm and im planning on putting the 12g940 head onto this to give it a bit more power and a hif44 (as i have both lying around doing nothing.)

just wondering if i will have problems or shall i just stick with the basic 998 carb?

all i want is a little bit more poke out of my daily drive!


thanks alot

Edited by leigh, 19 January 2009 - 09:32 AM.

[leigh]

Bump - does anyone know if this will be ok?

Thankyou,

[Big_Adam]

No, it won't work. Just use a 38 or Hs4.

[lrostoke]

I'd stick with the standard 998 1.5" carb, probably with an AAM needle.

You are probably aware the 998 block needs pocketing to fit a 12g940 head, you may be capable of doing this yourself, but if your not thats money that could be spent on your 1275 (being poor)

[Pauly]

Im running a HS4 with an AAM needle on a k&n cone, and it flies, really responsive and pulls throughout the rev range.

Paul.

[Dan]

which is fine due to the 998 not being able to take all the air coming out of the carb

Err, that's not how carbs work. Or engines in fact, not unless they're running forced induction. It's the movement of the engine that causes air to flow through the carb under atmospheric pressure, the engine will only take in almost as much air as it displaces nomatter what carb is fitted and the carb won't be trying to supply any more. The problem is that the 998 doesn't move enough air to setup a venturi in a 1.75" carb until it's doing around 4000rpm or so. It doesn't matter what head is fitted, what size valves you have or anything else. There just isn't enough air moving.

[G_A_C89]

I have a HIF44 on my 998 city E with a stage 3 head and a LCB manifold and it runs very well : ) however they un-adjust there self's very quickly then they don't run well at all.
hope that helps leigh.

does anyone know how to adjust an HIF44 without using the colour tune tool?

[Dan]

however they un-adjust there self's very quickly then they don't run well at all.

No they don't, this is the sign that you have the wrong carb on your car. It should stay in tune with minor fluctuations in climate, fuel quality etc. but yours doesn't because it has no latitude or tollerance with your engine because the engine doesn't draw enough air to make the carb work properly. Your engine will work better and produce more power with a different manifold and a smaller carb.

To tune without a Color Tune you have to have a very good, accurate tacho and a good ear for what the car is doing. How to do it is described in the carb manuals and many Haynes manuals. You should find a plateau in the speed developed while turning the mixture screw that lasts for one full turn, the ideal idle tune is one third of the way along the plateau. You can then assess the tail pipe, you are looking for specific rhythms in the engine. In your case however you can't properly tune your car without a rolling road session. When using just a Color Tune or tuning by ear you rely on someone else already developing the right needle for your carb, in other words home tuning kits are designed for keeping standard cars or well prepared cars in tune, not tuning from scratch.

[rozzer1275]

The only thing I know off that a home mechanic can measure emissions at load and revs, is a wide band lambda,

[Pooky]

I've just bought a 1062cc (998 bored out 80 thou) small bore short engine which I will be using with a standard 12G940 head, The choice of carbs I've got are twin 1 1/4" SU's, HS4 or HIF44.

What should I go for?

[Dan]

The only thing I know off that a home mechanic can measure emissions at load and revs, is a wide band lambda,

You could probably carry one of those Gunsons Gastesters with you if you ran it off an inverter. Or are they 12V? I've never dealt with one. Or leave a couple of Color Tune's in and get a lipstick camera and DV deck to film what the flame looks like as you drive. Bit of messing around though and an RR is going to be better.

Pooky, I'd go for the twin HS2s but then I like twins. It's that or the HS4, the overbore isn't going to make that much of a difference to the volume of gas moving, or more importantly to the gas speed. Not enough to get the best out of an HIF44 anyway. Min's +60 and runs twin HS2s very, very well.

Edited by Dan, 22 January 2009 - 12:58 PM.

[Pooky]

Ta! I like the twins too

[WiredbyWilson]

Ta! I like the twins too

Twins are best

But a weber FTW - the noise is soooooooooooooo

[Dan]

Noise is wasted power. With a Weber it's the sound of petrol being hosed into the engine!

[Pooky]

Ta! I like the twins too

Twins are best

But a weber FTW - the noise is soooooooooooooo

I was talking about Melanie and Martina from Fun House