HS8 2" or Hitachi 1" 3/4SU,s
Discussion
Hi guys, I don't want to bore you any more on this one.
As in the title, what do you think? I've bought a pair of Hitachi SU,s off ebay thinking they we're better but others seam to think I went wrong. Someone from the Datsum forum has offered me a straight swap for some HS8's, should I consider this or not?
I need help!
Thanks again to those who read this, that can read, and....well I have just come back from the pub and think my spelling has not done too bad..
As in the title, what do you think? I've bought a pair of Hitachi SU,s off ebay thinking they we're better but others seam to think I went wrong. Someone from the Datsum forum has offered me a straight swap for some HS8's, should I consider this or not?
I need help!
Thanks again to those who read this, that can read, and....well I have just come back from the pub and think my spelling has not done too bad..
Adrian,
SUs or Hitachis?
If you mount them to the original manifold, there will be no point, as the runners are smaller, and there will be a step in the intake tract. The vacuum signal your 2.5 generates may not suffice either, and you could have trouble tuning them. Are you planning to build a high performance engine to require these? On the up-side, Jags came with 2" SUs, so there should be a good selection of needles available. None the less, They're probably more than you need.
Why were people criticising your initial choice? They're better than CD175IIs.
Richard Good makes a triple 1.75" intake that you could fit SUs, Hitachis, or even CD175s to.
Truth is, you could even have a decent lathe operator make you needles, if needed. These don't exactly involve the world's most difficult machining operations.
Best,
B.
SUs or Hitachis?
If you mount them to the original manifold, there will be no point, as the runners are smaller, and there will be a step in the intake tract. The vacuum signal your 2.5 generates may not suffice either, and you could have trouble tuning them. Are you planning to build a high performance engine to require these? On the up-side, Jags came with 2" SUs, so there should be a good selection of needles available. None the less, They're probably more than you need.
Why were people criticising your initial choice? They're better than CD175IIs.
Richard Good makes a triple 1.75" intake that you could fit SUs, Hitachis, or even CD175s to.
Truth is, you could even have a decent lathe operator make you needles, if needed. These don't exactly involve the world's most difficult machining operations.
Best,
B.
For background info - not sure which manifold you have, the original 2000/2500 saloon manifolds had 1 1/2" strombergs (SU later) but have a square cast mount, and can be opened out for 1 3/4 or larger carbs. Not sure what the Vix 2500 had originally, but I think it was the export manifold which was already 1 3/4" ?.
Anyway, I agree that without opening out the whole manifold 2" carbs are probably wasted. My 1 3/4 SU HIF6 worked really well on a tuned 2500 (heads and cam), using an opened out saloon manifold on a kit car. Took a bit of fiddling around with the needles though.
Anyway, I agree that without opening out the whole manifold 2" carbs are probably wasted. My 1 3/4 SU HIF6 worked really well on a tuned 2500 (heads and cam), using an opened out saloon manifold on a kit car. Took a bit of fiddling around with the needles though.
It's been a L-O-N-G time since I did that (20 years ?) - it was in a kit car (Marlin) and I used Triumphtune head, medium cam, and pair of HIF6 from scrappers, and opened out the saloon inlet manifold myself for a smooth flow. 'fast road' cam and stage 2 head. Needles were supplied by TT also - um.... something like AAD or ADD ??
I'm sure there will be groans from some readers, but I do remember a big debate about whether 3 x 1.5 SU (or Strombergs) were better for flow than 2 x 1.75. this debate was running even when I did my Marlin 20 odd years ago ... I didn't go with 3 simply because I couldn't find a manifold. I've been told 3 carbs are a nightmare to balance, but I don't see why...
Others have installed the Lucas PI system, which is good for power, but (grabbing armour here) unfortunately isn't very reliable and is prone to lots of mechanical issues, all of which seem to cause huge fuel consumption....I bought 3 PI saloons and ended up converting all of them to carbs. Power drops, but fuel consumption and reliability was VASTLY better...
Theoretically a 3 carb manifold could have almost 6 straight inlet tubes.....
Others have installed the Lucas PI system, which is good for power, but (grabbing armour here) unfortunately isn't very reliable and is prone to lots of mechanical issues, all of which seem to cause huge fuel consumption....I bought 3 PI saloons and ended up converting all of them to carbs. Power drops, but fuel consumption and reliability was VASTLY better...
Theoretically a 3 carb manifold could have almost 6 straight inlet tubes.....
Edited by RCK974X on Sunday 13th January 22:48
When I bought my 2500M it already had twin HS8's on it. I'm not sure about the build state of the rest of the engine but it certainly had a lightened flywheel and a Stage 2 head. It had been used for Hill Climbs, which is also what I bought it for. Unfortunately it needed big ends doing and as the Crank was already on limit and badly warn, the only budget effective option in the short term was to source a second-hand engine (ebay). So, now its running a standard 2500 Saloon engine with HS8's. The guys at Mass in Huntingdon did a great job of setting it up and it runs fine but is only delivering stock bhp - around 100... I'm plotting a fast road engine build at some point, I'll probably try it with the HS8's & if not happy then look to a tripple Weber conversion....
Do you know what inlet manifold you are using, is it std but bored out for the extra dia? Cheers.
Warwick67 said:
When I bought my 2500M it already had twin HS8's on it. I'm not sure about the build state of the rest of the engine but it certainly had a lightened flywheel and a Stage 2 head. It had been used for Hill Climbs, which is also what I bought it for. Unfortunately it needed big ends doing and as the Crank was already on limit and badly warn, the only budget effective option in the short term was to source a second-hand engine (ebay). So, now its running a standard 2500 Saloon engine with HS8's. The guys at Mass in Huntingdon did a great job of setting it up and it runs fine but is only delivering stock bhp - around 100... I'm plotting a fast road engine build at some point, I'll probably try it with the HS8's & if not happy then look to a tripple Weber conversion....
It's a long time since I fiddled with 2500 engines....but that manifold was what I would call the 'later' (post 74) or 'export' manifold, and as far as I can remember was originally made for 1 3/4" carbs....
So it's probably been opened out for the 2" carbs.
The earlier 2000 saloon manifold was what I used, it's shorter/squatter than that one, and was originally made for 1 1/2" two bolt Strombergs, but as I said, I wondered why it had square carb mountings, until I found a pic of a US spec TR6 with same manifold but 1 3/4" carbs on it...and my modification path was then clear...
That was when BL also swore black was white that the 2000 manifold would not fit on a 2500PI engine, and tried to sell me (and friends) a much more expensive one....but of course it DID fit. Perfectly. Just needed one locator pin removed from head !!
So it's probably been opened out for the 2" carbs.
The earlier 2000 saloon manifold was what I used, it's shorter/squatter than that one, and was originally made for 1 1/2" two bolt Strombergs, but as I said, I wondered why it had square carb mountings, until I found a pic of a US spec TR6 with same manifold but 1 3/4" carbs on it...and my modification path was then clear...
That was when BL also swore black was white that the 2000 manifold would not fit on a 2500PI engine, and tried to sell me (and friends) a much more expensive one....but of course it DID fit. Perfectly. Just needed one locator pin removed from head !!
Edited by RCK974X on Friday 18th January 03:23
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