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Dual HS2 vs dual HS4 for 1500

Posted by oldag98 
oldag98 Avatar
Jeff and Brittany Brackenridge
Choctaw, Choctaw, Oklahoma, USA   usa
1975 MG Midget Conversion
1976 MG Midget 1500 "Yellow One"
1977 MG Midget 1500 "Dunkirk"
1979 MG Midget 1500 "Parts Car"

Does the US 1500 really need dual HS4's, or will the dual HS2's from a 1300 be sufficient for a slightly hotter street car? I have both on my 1500 Midgets, but don't really see much difference in performance between the two. If you look at the stock ZS, I can't really see where it would flow more air or fuel than the dual HS2's. This makes me think that maybe the dual HS4's might be overkill on the 1500. Even with a hotter cam and headers, I can't see where a set of 1300 HS2's with non-poppet valved butterflies, K&N filters, and maybe richer needles and softer springs would not be able to keep up with the induction requirements of the 1500. What are your thoughts?
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Midhurst80 Avatar
Bob Killam
Midhurst, Ontario, Canada   can

I have the dual HS2 carbs on a 1500 and have found them give all the punch the little engine can deliver. Turning up the power and RPM on the 1500 is more than the design can handle. If you want to move way up go get a the older engine as a start.
spitfire50 Avatar
Paul Mugford
N.H., USA   usa

Jeff,
You are probably right, but you would more likely need stronger springs to keep the carb pistons from going wide open before the engine needs the full air flow the carbs can give. Classic Motorsports magazine ran a great article on the subject this year which can give you a feel for how little is lost using the smaller option. The big gain most people get when changing carbs comes from having new carbs not from having bigger carbs.
Good luck,
Paul
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90632D Avatar
Fox Trapper
Various, USA   usa

A whole lot of folk, myself included, have had quite good results running a pair of HS2's on a 1500 engine.

The HS4's only exceed the HS2's at high rpms. Something a 1500 is rarely going to see, especially one that does not live on a track.
wildwood Avatar
rick howe
wayne, n.j., USA   usa

So then wouldn't a single HS6 work just as well as a pair of HS2 if then the manifold is opened up to match the carb and get more air flow ?
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90632D Avatar
Fox Trapper
Various, USA   usa

I've never actually installed it, but my understanding from those who have is the HS6 single works quite well on the 1500, up to something around 4,000 - 5,000 rpm.
trzavie Avatar
Al S.
Vast, Midwest, USA   usa

I have had both the HS2 with K&N's and the HS4's on my car over the years. There is not
all that much difference between the the two in normal driving. Both are way ahead of
the Stromberg. My HS2's were the kind used on the MK 3 with the PVC valve. Many years ago I had to
sort out an issue with my HS4's so a good friend loaned me the HS2 set until I
figured out that it was my waxstat jets causing the trouble with my HS4's. I'm not sure
what needles were on the HS2's, most likely not the proper ones for the K&N's! I put
my HS4's back on and over 20 years later I'm still happy with them. Recently my friend
moved south to retire and I aquired the HS2 set (amoung other parts) from him. One day
I will see which needles were on those carbs. If I had my choice on the HS2's I would
pick the MK 4 HS2's with the crankcase venting right into the body of the carb like
the HS4's have. Best of luck which ever you choose.
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oldag98 Avatar
Jeff and Brittany Brackenridge
Choctaw, Choctaw, Oklahoma, USA   usa
1975 MG Midget Conversion
1976 MG Midget 1500 "Yellow One"
1977 MG Midget 1500 "Dunkirk"
1979 MG Midget 1500 "Parts Car"

So the concensus seems to be that the HS2's will work fine on a road going 1500. If anyone has a differing opinion, please post and let me know why. Also, why then did BL use the HS4's on the 1500, instead of sticking with the HS2's from the 1300?
Spitnut64 Avatar
John Mills
Milwaukee, WI, USA   usa
1970 Triumph Spitfire MkIII "Sarah Jane"

In reply to a post by oldag98 Also, why then did BL use the HS4's on the 1500, instead of sticking with the HS2's from the 1300?

OK I'm speculating here but given what has been said - that HS4's only shine at the higher RPM's where most Spitfires don't live - could Triumph have had in mind better highway performance for non-overdrive Spitfires?
90632D Avatar
Fox Trapper
Various, USA   usa

The HS2 work quite well on a track going 1500 as well. Just the HS4's will work better at the top end.

The 1500 is not incapable of spinning up. It does. It solidly can go into the RPM range where the HS4's give better performance than the HS2's. I would speculate that BL chose to let the engine have the breathing capacity to make the better power.

Just as a V8 can run fine on a 500 cfm 2-barrel carburetor, but can make a bit more power with a 750 cfm 4-barrel carburetor.
wildwood Avatar
rick howe
wayne, n.j., USA   usa

A+ Foxthumbs up smiley
spitlist Avatar
Joe Curry
Sahuarita, AZ, USA   usa

Having previously run HS2's on a 1500 engine that was modified to increase the compression ratio, I can safely say that unless you radically modify the engine, to include radical cam, and much better breathing, the HS2's are sufficient. It is when you really start putting a real demand for increased fuel that they start to be deficient.

Joe



Edited 1 time(s). Last edit at 12/14/2011 10:46AM by spitlist.
ras111 Avatar
Richard Singerman
Dollard des Ormeaux, Quebec, Canada   can

Adding my 2 cents: My 1976 Spitfire actually originally had a HIF6 which I changed out for a Weber DGV. The Weber was far better at the low end but really lacked at the high end. I moved to dual HS4s this year and will never look back! Can't really comment on the difference between HS2 and HS4.....but do suggest you try different needles - really made HUGE difference for me on the HS4s. Looking back, the HIF6 actually worked very well too! Good luck.
oldag98 Avatar
Jeff and Brittany Brackenridge
Choctaw, Choctaw, Oklahoma, USA   usa
1975 MG Midget Conversion
1976 MG Midget 1500 "Yellow One"
1977 MG Midget 1500 "Dunkirk"
1979 MG Midget 1500 "Parts Car"

OK, those running the dual HS2's and HS4's, what needles and springs do you have in them?
chappy444 Avatar
Bill Chapman
Bel Air, MD, USA   usa
1975 Triumph 1500 "The Little Red Car"

I switched from the Weber DGV to the HS4's very happy i did it.
i am running ABT needles now...
~B
90632D Avatar
Fox Trapper
Various, USA   usa

In reply to # 717055 by oldag98 OK, those running the dual HS2's and HS4's, what needles and springs do you have in them?

7's.

Let me know if you ever find those.

In all sincerity, there's a whole lot of needles that will work. Some simply work a bit better than others. It's a bell curve thing.

As well altitude and engine setup. From simply changing the timing to changes in camshaft profiles. These all affect the fuel mixture flow and the particular needle diamter needed for that particular condition.

1/2 science, 1/2 black magic or art.
spitfire50 Avatar
Paul Mugford
N.H., USA   usa

Hi,
+1 to Fox Trapper's comments. Even changing from a paper air filter to a K&N can change the ideal needle, but you will probably still be OK with the same ones.
Paul
trzavie Avatar
Al S.
Vast, Midwest, USA   usa

Joe Curto should be able to get you close if not the exact needle selection for any
SU and K&N or stock airbox combo.
spitlist Avatar
Joe Curry
Sahuarita, AZ, USA   usa

In reply to # 717114 by trzavie Joe Curto should be able to get you close if not the exact needle selection for any
SU and K&N or stock airbox combo.

Don't be so sure, I talked to Joe Curto about my own HS2's on a Spit 1500 and he send me a pair of needles for an MGA 1500. They did not work at all.

Joe
trzavie Avatar
Al S.
Vast, Midwest, USA   usa

In reply to # 717128 by spitlist
In reply to # 717114 by trzavie Joe Curto should be able to get you close if not the exact needle selection for any
SU and K&N or stock airbox combo.

Don't be so sure, I talked to Joe Curto about my own HS2's on a Spit 1500 and he send me a pair of needles for an MGA 1500. They did not work at all.

Joe

That's pretty close Joe, they were for a British car anyway!
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