HIF4 vs HIF38

[alex_holden]

Is there any practical difference between a HIF4 and a HIF38? I believe they're both 1 1/2" HIF carbs...

[picky]

I think its only the part number, SU decided to have a range eg HIF4, HIF5, HIF6 etc and each number increase is an increase in bore of 1/8" I think. The 38 in "HIF38" stands for 38mm bore, which is 1 1/2" as you say. On ebay, try searching for HIF* and that will come up with all combinations

[bmcecosse]

HIF 44 is larger bore = 44 mm bore! They both will fit on the MG Metro inlet manifold - indeed they both have the same external dimensions. Ideal for a 1275 engine - slightly large for a 1098 - but it would work, and ideal if you are planning later to go up to 1275cc.

[JimK]

Errrm, he says HIF4 not HIF44...

[bmcecosse]

Ahhhh - missed that - well spotted - very old design - avoid!!

[alex_holden]

Are you sure you're not thinking of the HS4? The HIF4 looks very similar to the HIF38.

[JimK]

So HS4 != HIF4 != HIF44.

Well, I'm glad that's clear...

[Kevin]

Is there any practical difference between a HIF4 and a HIF38 ? I believe they're both 1 1/2" HIF carbs...

Apart from 2mm I wouldnt have thought there is really a difference and wonder if the HIF4 was for the overseas market for some reason.
Over here its normally only the HIF44 as mentioned by BMC that we see, and to quote that site
http://www.minimania.com/web/Item/MAX10 ... Detail.cfm

http://www.minimania.com/web/Item/MAX10 ... Detail.cfm

Or could it just be a different way of describing an HS4

[chrisd87]

So HS4 != HIF4 != HIF44.

I don't think that's correct. The HS4 and HIF4 are both 1 1/2 inch carbs, whereas the HIF44 is a 44mm one (approx 1 3/4"). The HIF38 is a 38mm carb, which is about 1 1/2".

I don't think the HS4 and HIF4 are the same though, because the HIF4 has the float chamber under the carb, whereas the HS4 has it beside.

[alex_holden]

Chris, != is a programmer's way of writing "doesn't equal" so you're agreeing with Jim that the three carbs are different from each other.

The reason I asked BMC if he was confusing the HIF4 with the HS4 is because he said the HIF4 is a very old design but it actually looks almost exactly the same as a HIF38.

I wish I hadn't started all this now especially since the carb I was looking at turned out not to be a HIF4 after all ;)

[JimK]

Chris, != is a programmer's way of writing "doesn't equal" so you're agreeing with Jim that the three carbs are different from each other.

I forgot that it's not a common expression. I'm getting code-blindess and keep ending normal sentences like this;

I wish I hadn't started all this now especially since the carb I was looking at turned out not to be a HIF4 after all ;)

How did you tell? Was it actually a HIF38?

[alex_holden]

The plastic bit at the top of the damper looks different on the HIF4. I think the one I'm looking at is either a HIF38 or a HIF44 (I suspect the former) and I've asked the seller to measure it to be sure.

[chrisd87]

Chris, != is a programmer's way of writing "doesn't equal"

Ah. Apologies about that then. I only ever used QBasic and BBC Basic, a very long time ago!

[bmcecosse]

Didn't actually know there was an HIF 4 - assumed meant HS 4 - which is hopeless. But what you really want is an HIF 44 anyway - so look out for one of them! I asked about an HIF 38 on minifinity - but got no sensible offers so far!! Last 2 HIF 44s I bought were £5 each - so that's your target price.

[Packedup]

I've never come across or heard of a HIF4 either...

But in terms of carb size, depends on the engine. A small bore A series really is going to be over-carbed with a 44, unless fitted with a silly cam and only driven above ludicrous rpm. So a road going 1098 in standard to moderate tune is best off with a 38. Or a 4, if such a thing exists, I suppose.

People far too often seem to think the answer to more power is to slap on a bigger carb - All that means is at best you're simply not using the full potential, and more often than not you're actually losing low and mid range power, and struggling to make any difference at crank snapping revs.

A 44 is better on a 1275 engine or larger, where it'll give better top end over a 38 without sacrificing a great deal of low end torque.

Given the 38 was standard on 998 Metros, there should be plenty around without starting to look into what must be rare or mythical HIF4 carbs!

[alex_holden]

That's what I thought. I'm not likely to be swapping to a 1275 any time soon so I'd rather have a HIF38 and not lose low-end power. One of the two carbs I've got my eye on is from a 998 Metro. Still waiting to hear back from the seller on the measurement, but I suspect it's a HIF38.

[chrisd87]

The HIF38 I have in my garage I got from a scrapped F-reg 998 metro, and it has an additional weakening device to improve part-throttle fuel economy (as described in the Vizard book) - does anyone know if that would be a problem fitting to a 1098? (for my distant tuned engine project!)

[bmcecosse]

That would be excellent on a 1098. Probably not the right needle - but you can work on that later. meantime - search for an MG Metro alloy inlet manifold to mount the carb on!
The beauty of an SU carb is that the venturi is self adjusting - and so even if a 44 carb is a bit large for a 1098 - the venturi will only open as much as is required - so the idea that power (or torque!) will be lost with a larger carb is not true. I have an HIF 38 on my 1098 and it's great - but I also now have another (£5) HIF 44 just needing 'Vizardised' - and then it will be taking over from the 38. Recent report in minifinity tells of considerable power increase (all measured on a RR) when a 38 is replaced with a 44 carb - certainly that was a standard 1275 engine - but the extra power was quite considerable. If I can get half that extra on my 1098 I will be delighted!

[Onne]

This may seem a weird question, but would one use the same needle in the HIF38 and 44 for a 1098?

[Packedup]

This may seem a weird question, but would one use the same needle in the HIF38 and 44 for a 1098?

Only with a fair amount of difficulty, and most likely utter over-fueling on the 44! The HS2, HS4 and I believe HIF38 all share the same jet inner diameter, but the HS6 and HIF44 are a size up (and I don't know if they share or not).

So you could use your existing 1098 Minor needle in the 38, but not the 44. Though it probably wouldn't be suitable given the different carb characteristics.

As for venturi size, all i can say is not only does Vizard state you shouldn't go too big (or at least he did in the edition of teh bible I had a fair few years ago), but my own real life experience is small gives better low end, larger gives better top end, and just right loses a little of both but pulls nicely through most of the range.

Too many people are hung up on max power figures, and too many reviews are centered around them. A 44 may indeed give the most power on any engine it's bolted to (provided everything is optimised), but that's not much use if it's all at the top end and there's nothing in the normal range you use on the road (I'd guess 1500 - 3000 for town driving). So I stand by preferring to stick with a 38 for a road going A series. Bear in mind you can still increase overall flow by modifying the carb, without then having the lower charge speed through using a larger bore.

If one size of SU could fit all, I very much doubt cost cutting BL would've used so many different sizes at the same time. Why bother making a HIF38 for the 998 Metro when they had an inlet and HIF44 on the 1275 model?