SU HS8 Carbs and 4.6V8 - where to start with needles?

RoverAlex

RoverAlex

Active Member
Hello,

I have HS8 carbs on my 4.6V8. I had a search but could not find anything conclusive. There is probably someone that has been there and done it....so what needles should I go with to get something to work on? Engine has a fairly aggressive cam, trumpets rather than air box. Quite a few people simply say to forget the idea of the HS8....but that is what I have and what I am going to try to stick with.

Thanks in advance

Alex
 
Normally the rv8 manifold has hs6 or hif 44. Ron (sydneyroverp6b) has a 4.6 running the hifs. Ron, what needles are you running?

Rich
 
Hi Rich,

I am running BBW needles, but they have been polished to suit the engine spec as they were too lean.

Alex, are you running fixed or swinging needles? Given your engine spec, you'll need a much richer needle than what I am using. Really the only reliable way is to have them custom polished to suit your engine.

Ron.
 
Thanks Ron,

I'm thinking I could run the flowrates for bbw through my carb program then and compare the flow rates to hd8 to get an equivalent as a starting point at least?
 
Hello,

I'm not sure what needles I have. Fixed or swinging? Crikey I have a lot to learn!

Know anyone who will profile needles to suit my car?

I'm hoping that the HS8 is suitable....there is conflicting views out there!
 
These carbs seem right to my mind. The 1.75" carbs are on the limit on the 4.6 and with your sporty tune you're going for I think a slightly rougher idle won't hurt. That's the compromise... At low idle speeds the piston will be slightly uneven in how it behaves from my understanding.
 
Hello,

It actually idles beautifully once it has warmed up a bit (I don't have a choke). I have come to the conclusion that 1) I know very little about carbs and 2) I should take it to an old school rolling road who has a selection of needles, is experienced with profiling and so on rather than me stabbing in the dark at it and doing road tests, which may damage the engine.
 
Happened to come across this thread as I was Google searching for needle sizes on these carbs funny hey. Almost a year later and I am finally starting to get these set up. Seems to me that it gets lean after 2500RPM and feels pretty low on power (perhaps 110BHP).
 
I remember Des Hammill's book saying that the standard inlet manifold is quite restrictive - by cutting off the carb tower and fitting it along with the 1¾" carbs to an Edelbrock or Huffaker manifold (sorry but can't remember which one) you can get an extra 40hp. Might be worth looking into, specially if you're using bigger carbs too?
 
What I would suggest is get a wideband lambda kit, this will give a visual indication in real time of what's going on with the fueling, not cheap but will save you in the long term buy pinpointing the issue. You also need to find out exactly what the carbs are off, there should be a tag on one of the dashpot screws with a part number, if that's gone then it's a case of stripping the carb down to remove the needle and reading the letters off the shank. Once you've done these two things you'll be in a position to guesstimate whether chancing a replacement pair of alternative needles could work or leave it to a pro to tune.

Doing a little bit of reading in a period SU tuning book I've got the most common sources for HS8 carbs are Jaguar/Daimler 2.8 and 4.2 straight sixes and the P6 2000TC. Unfortunately the Jaguar/Daimler SU's have a different size jet to the Rover so it's hard to make a direct comparison to which needles would be richer or weaker. The VandenPlas 4 litre also comes out with HS8's being fitted, presumably a lot harder to come by?

Opening up the searching to HD8 SU's my book lists the Daimler 4 1/2 Majestic as being fitted with them, closest match on paper in terms of capacity to the Rover 4.6.

I had a pair of 2000TC HS8 SU's on my old 3.5 and that was fine, plenty of power available, but a slight midrange flatspot that eventually was found to be the distributer! The manifold was also opened out in the tower to make up for the larger diameter carbs, wish I still had it as it was brilliant!
 
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