HIF44 vs HIF38

[sowden]

Hi all,

just harvesting some opinion here about the whys and wherefores of the above.

I have had a look at past threads, and it seems that although the HIF44 may be a bit big for my application (warmed up 1098), I could probably get a good one cheap and so if it will work, I'll have it! I have an alloy inlet, an oselli torquemaster, which I think is the right size.

Thoughts and opinions anyone? Upsides / downsides? I presume it will actually work and so my basis for use is sound if nothing else!

Cheers,

Russ

[PSL184]

Yes it will work fine but you will have to trial different needles to get the right balance between sufficient fuel delivery and throwing fuel into the engine (which will just be wasted). In standard for the HIF44 may deliver too much fuel.

[Peetee]

It would work but wouldn't be ideal.you are likely to loose torque and have higher fuel consumption relative to a HIF38.

[PSL184]

I don't agree with Peetee on this occasion. I can see how you would get higher fuel consumption (if incorrect needle was fitted) but how would torque be effected?

[Longdog]

Hi Sowden and all.For what it's worth I think the fact that the 44 was typically fitted to the 1275 is the key.The barrel of the 38 is probably more suited to the smaller engines in relation to the amount of lift on the piston at part and full throttle openings.The 44 will do the job if jetted corectly but the correct section of the needle won't be exposed for a given RPM.I had a "breathed on" 1098 with a12G295 head and standard cam which I chose to run on a 38 so I don't know from experience how a 44 would perform,it's just a theory.

[PSL184]

Certainly I agree that the 38 is a better choice for a 1098... I was just confused as to why the torque of the engine would be effected?

[chrisd87]

Presumably due to the larger bore of the carb the velocity of the air will be lower = less torque. I think...

I have an HIF38 on my 1098 and it's great, but I suppose it depends on what you want out of the engine. If you're looking for all-out power at high revs then the HIF44 might be a good choice, however I suspect you're not in which case you should stick to the 38.

[PSL184]

Presumably due to the larger bore of the carb the velocity of the air will be lower = less torque. I think...

....but the inlets are the same for a 38 or a 44 aren't they?

[bigginger]

I thought that 38 and 44 were the inlet size in mm - is that wrong, then?

[Matt]

a 38 is 38mm and a 44 44mm ;)

[PSL184]

Choke size is 38 and 44... The inlet manifolds are the same for both.....?

[IslipMinor]

The larger the choke size the less low and mid-range torque the engine will produce, but the higher the maximum power could be, BUT, the terms 'large' and 'small' are relative to the engine size and state of tune. For a 948 or 1098 a 1.5" or 38mm HIF carb is quite 'large', but for a 1275, it is barely large enough.

Bear in mind that the HIF range flows considerably more volume than the same size in the H, HS or HD series, so just fitting the same size HIF is quite an 'upgrade' in itself.

For normal/high road states of tune a 1.5" or 38mm is plenty big enough for either a 948 or 1098. If you fit a 1.75" or 44mm you will have consideraly less torque at low and mid-range engine speeds, which is exactly where you need it for everyday use.

For all-out power, with the right cam etc., an HIF44 could be fitted, but the combination of cam and choke size will mean that it will not be very driveable on the road.

What carburettor(s) do you have fitted at the moment?

I would not suggest fitting either an HIF6 or HIF44 to a road 948 or 1098, but if you have everything else and it's cheap, then give it a go and let us know the results please!!

[Peetee]

I have seen different alloy inlets for both 38mm and 44mm carbs. The standard 1098 engine is long stroke and not a good revver. everything about the standard set up is ideal for good torque. there are not many 1100cc engines that will pull cleanly from tickover in top gear so clearly the cam profile is an excellent design. If you stick a oversized inlet and non matching carb you will affect the torque because, as mentioned earlier, the gas speed is reduced. Moreover the non matching componants create eddys as the gasses roll over or bump into the steps.
This is very much a generalisation as there are so many other factors in optimising engine output. Achieving ideal 'before and after results' can prove to be very hit and miss.

[PSL184]

Ahhhh, I see... Thanks chaps

[Matt]

the choke sizes are different.

For the old motor club mini we bought a brand new minispares alloy inlet, the inlet bore was the right size for a '38 but we had to grind it out slightly for the '44

[picky]

I've driven a tuned 1098 with a hif38 and then i "upgraded" to a 44. Big dissapointment. Lots more changing down a gear when you wanted to accelerate, you needed lots more revs with the 44 fitted. Possibly more powerful at higher revs in theory with a 44, but it was not noticeable to me.

hope that helps,

Picky

[PSL184]

the choke sizes are different.

For the old motor club mini we bought a brand new minispares alloy inlet, the inlet bore was the right size for a '38 but we had to grind it out slightly for the '44

Cheers for that Matt - I must check mine as I had assumed they were all the same and I've no idea which inlet I've got

[bmcecosse]

The only problem will be if you suddenly 'floor' the throttle - and the bigger carb will tend to gasp horribly, unless you hold the piston down with heavy spring and/or thick oil in the damper - which kind of defeats the purpose. There is also unlikely to be enough flow from a 1098 even at full chat to lift the piston right up - especially if a heavy spring has been fitted. The HIF 38 works well on a 1098 - on a 44 bore manifold. No harm in having a step-up in the air flow. HIF44 definitely works very well on 1275 (and slightly larger) engines - especially if Vizardised. The 38 benefits from Vizardisation too!

[Kevin]

Yes you should ideally have the correct inlet manifold to suit the carb size just measure the opening and you will know what size you have, also as Roy has said there is not a problem with using the smaller carb with the larger manifold bur the other way round will affect the flow as you are trying to get 1 3/4" 44mm into a 1 1/2" 38mm hole.
Also remember that the Marina engine ran on an 1 1/2" as standard it only changed with the A+ Ital engine. And as also mentioned (if you read Vizzard) the HIF44 is only of real benifit at higher revs.

[bmcecosse]

And only then if there is sufficient airflow demand from the engine to lift the piston right up.