HIF6 vs HS6

[spock345]

I am trying to decide on which carburetors to put on my 122s in place of the weber DGEV that is currently on it.

I have a set of HS6 carburetors from an early 60s 122 or 544. They should have the correct needles for the car. The caveat here is that the throttle shafts have a good amount of play.

I also just acquired a set of HIF6 carburetors with the linkage and airbox that are from a 70s 140 (I think). There is virtually no play in the throttle shafts on this pair. From a cursory inspection these seem to be in much better shape, even if they are completely filthy.

Is there any reason not to go with the HIF6 given that the throttle shafts aren't bouncing around. They seem like a better design.

The motor in question is a B18D that I will be bumping up to B18B compression and a D cam.

[vwbusman66]

IMO, I'd run HS6's. Simpler, easier to get parts for, IIRC they actually flow marginally more air than HIF6's.

Then again, they're SU's so take the "better" one with a grain of salt.

[spock345]

Originally Posted by vwbusman66

IMO, I'd run HS6's. Simpler, easier to get parts for, IIRC they actually flow marginally more air than HIF6's.

Then again, they're SU's so take the "better" one with a grain of salt.

From everything I have found online the HIF6s flow a bit better than the HS6s (240cfm vs 210cfm). Although I am worried

The simplicity is a big part of why I am considering the HS carbs even though they will need machining. Although supposedly the choke is better on the HIFs.

[vwbusman66]

Originally Posted by spock345

From everything I have found online the HIF6s flow a bit better than the HS6s (240cfm vs 210cfm). Although I am worried

The simplicity is a big part of why I am considering the HS carbs even though they will need machining. Although supposedly the choke is better on the HIFs.

Maybe I have them switched RE the flow advantage. IMO I'd go with the HS's, especially since you're sticking with the B18.

The chokes (if you're referring to a mechanical/manual enrichment device) on both sets of HIF's I've had sucked. Either barely worked at all or seemed to never come off entirely. Depending on the year of Volvo HIF's, you may only have a front choke like my '71 142S.

[spock345]

Originally Posted by vwbusman66

Maybe I have them switched RE the flow advantage. IMO I'd go with the HS's, especially since you're sticking with the B18.

The chokes (if you're referring to a mechanical/manual enrichment device) on both sets of HIF's I've had sucked. Either barely worked at all or seemed to never come off entirely. Depending on the year of Volvo HIF's, you may only have a front choke like my '71 142S.

I think mine are from a '72 or later car as they have enrichment devices on both carbs.

[59volvo]

Originally Posted by spock345

I think mine are from a '72 or later car as they have enrichment devices on both carbs.

fyi

[283SD]

In my 45+ years working on cars with Skinners Union Carbs, in your case I would use the HS6 carbs, never liked the HIF carbs.

[spock345]

Interesting, while digging around I found some threads on British car forums that seem to lean towards the HIF carbs while harping on their float adjustments. I would think that setting the float height is pretty easy.

Originally Posted by 283SD

In my 45+ years working on cars with Skinners Union Carbs, in your case I would use the HS6 carbs, never liked the HIF carbs.

Any particular reason why?

I would just send the carburetors out to be refurbished but I rather like working on carbs and there is a plague on. The HS6s would have to go out to get machined, the HIFs throttles aren't really worn at all so I could do the overhaul without machining. I've priced out what needs to be done and the HIFs come out quite a bit cheaper.

My one big worry is the needles. The needles in the HIF carbs are BBB and the HS carbs are ZH. The ZH seems a bit lean for what I am going for (B18B compression with a D cam) and I am worried that since the BBBs were fitted to a B20B that it would be too rich.

[alschnertz]

I drove a '72 B20B (+0.030") from 1993 to 2006 year round in temps. of -10F to 100F.
Tried HS6 and HIF6 carbs.

Maybe I was lucky, but I much preferred the HIFs after they were sorted out.
They were very reliable and rarely needed any attention.

[spock345]

So the HIF6 has a sprung needle, would it be possible to swap the an HS unsprung needle into a HIF?

Edit: The piston from one of the HS6 carbs fits in the HIF. So I think I could theoretically run a HS6 needle in a HIF6 carb. Giving me access to the B18 specified needles.

[alschnertz]

Posted something and then realized it didn't really answer your question.
Whoops.

[spock345]

Well I have been looking at the specs. A 100HP B18D, which is what I've got should have either SM or KG needles.

I found a site that rather nicely plots the taper of each needle. https://classicminidiy.com/technical/needles

Comparing the BBB, KG, and SM needles shows the SM and BBB to be pretty close with the BBB slightly richer. The KG is quite a bit leaner than either the BBB or SM. I bet I could get away with it given I am running a better exhaust. Maybe.

At this point I would like to run the HS6 carbs but I am trying to figure out if it is feasible to run the HIF6s until I can sort out the throttle shafts.

[planetman]

You probably can.

But besides having to dial in the HIF6s, you will have to sort out the linkage.

We usually install KD needles in HS6 carbs for a B18 with a D cam.

We prefer to rebuild our own SU carbs and we try to keep all the parts needed for rebuilding in stock, but the 1 step we outsource is throttle shaft and bushing replacement.

And to reduce wait times for our customers, we usually have all 4 variations of rebuilt HS6 SU throttle bodies with new throttle shafts in stock.

[spock345]

Originally Posted by planetman

You probably can.

But besides having to dial in the HIF6s, you will have to sort out the linkage.

We usually install KD needles in HS6 carbs for a B18 with a D cam.

We prefer to rebuild our own SU carbs and we try to keep all the parts needed for rebuilding in stock, but the 1 step we outsource is throttle shaft and bushing replacement.

And to reduce wait times for our customers, we usually have all 4 variations of rebuilt HS6 SU throttle bodies with new throttle shafts in stock.

B18B or D? Does compression have a significant impact on needle choice?

I have all the parts for the HIF6 linkage. I actually have to find a linkage and springs to make the HS6 carbs work.

[klr142]

I had the HIF6s on my B20B/B20F back in the day and enjoyed them. People think they're more troublesome to set than the HS6s supposedly, but I was fine with them. I had them gone through before installing to replace my DGV, though. The HIF6s are not going to be "too large" for your B18B/D cam setup.

[spock345]

Originally Posted by klr142

I had the HIF6s on my B20B/B20F back in the day and enjoyed them. People think they're more troublesome to set than the HS6s supposedly, but I was fine with them. I had them gone through before installing to replace my DGV, though. The HIF6s are not going to be "too large" for your B18B/D cam setup.

Ok, that is good. I will probably be rebuilding both sets of carburetors (although the HIFs don't need much). Then I can experiment and see which ones I like more. I'll record how the BBB needles do on a B18.

[OttoB]

David Vidards book How to tune BL-A engines has good portion of good SU modification tips, hints and flow results.

[59volvo]

fyi
https://www.sucarburetors.com/products

[spock345]

Originally Posted by 59volvo

fyi
https://www.sucarburetors.com/products

I am doing most of the work myself. Except for the throttle shaft bushings. I am though contacting them about the concentric throttle spring parts they offer for HS6 carbs.

[Harry Tuttle]

Originally Posted by spock345

I am though contacting them about the concentric throttle spring parts they offer for HS6 carbs.

Good idea. Those straight-pull extension springs are what wears out the bushings, in my opinion.

[spock345]

Originally Posted by Harry Tuttle

Good idea. Those straight-pull extension springs are what wears out the bushings, in my opinion.

That is my theory as well. When I took mine apart the side with the spring was more worn than the other side. It is probably one of the reasons why HIF shafts last longer. Along with not having brass on brass moving parts (relatively high friction coefficient).

[JohnMc]

Worse than brass on brass, it's brass on cast alu on the HS carbs. This may have worked better with leaded gas (purely a guess? But maybe some evaporated fuel ended up in that area and helped?). Or they just never expected the Brit cars they were normally bolted to to last long enough for it to be an issue.

[spock345]

Originally Posted by JohnMc

Worse than brass on brass, it's brass on cast alu on the HS carbs. This may have worked better with leaded gas (purely a guess? But maybe some evaporated fuel ended up in that area and helped?). Or they just never expected the Brit cars they were normally bolted to to last long enough for it to be an issue.

I ended up sending the carb bodies out to Tom Bryant in Maine who replaces the brass with delrin for a decent price. I heard good things about his work. I think any modern option whether it be PTFE, oilite bronze, or delrin would be an improvement over the stock setup.

I'll post some pictures when I get them back.

I wish I had a drill press and reamers or I could be doing this work at home.

[klr142]

Originally Posted by 59volvo

fyi
https://www.sucarburetors.com/products

That's who(Rhys) I had do my HIF6s! He was very helpful and happy to help with setup tips as well.

[cwdodson88]

Rhys is the only person I will send stuff to anymore. Had 3 different people "rebuild" sets of carbs for me for different cars, Austins, MG's, Triumphs... Rhys was the only one that I did not have problems with, either right at install, or later down the road.