View Full Version : Best Carbs with 87mm liner kit

12-23-2002, 02:52 AM
I just finished upgraditing the cylinder head of my TR4A, installing oversized valves and porting it. i also have a mild street camshaft and 87mm linner kit. i still dont have a complete set of carburators, so i was wondering what the experts think i should install in my triumph. the 175 stromberg, 1.5 SU or a set of DCOH (40mm) webber carbs.

not many people know about british cars here in Guatemala, so the advice of experts will be very much appreciated.

Jack Edwards
12-23-2002, 03:04 AM
i just did similar work on my 4A, ran out of money before I got a cam, it's on my Xmas list. The mechanix I go to occasionally says that the SU's will give me the best performance, I haven't tried them yet, I have a set off a parts car to rebuild. Will let you know when I get them done. I'm also working on a 59 3A should send the frame out for sand blasting & powder coating after the 1st.

Gary Pope
12-23-2002, 10:35 AM

I think the original carbs on the TR4a are SU HS6 1.75" diameter. I would recommend going with these carbs. They are very simple, reliable and have great performance. mossmotors.com can supply you with every part for the SU's.
Don't put Strombergs on, they will be a poor choice. The Webers would work, but you will need a manifold which will get expensive and maybe more tricky to set up and maintain.

12-25-2002, 04:34 AM
With all that extra breathing room in the head you are going to need the extra carburation. The SU 1.75's are a good choice but might end up being a little weak if you go any further with the engine. Weber's are very expensive. I would look on Ebay for Dellorto (sp) Dhla 40's or 45's. They are an improved Weber and they stay in tune much better. I have had one on my 68 spitfire since I got it and it has never given me a lick of trouble. Also consider adding a 4-2-1 header and sport exhaust. You won't see much improvement unless you get the gasses out of the cylnders. Stay away from the 4-1 header as it is made for racing applications and will actually cost you power in the normal street range.

01-05-2003, 01:27 PM
Glad to hear you're making progress!!! My 2 cents on this long and contetious debate is go with 175 SU's The next even better thing is 200 SU's off the jag (or others) these can be fitted and offer all the air /fuel mix the old 2.2L can stand.HS8 is good HD8 will work as well. The down side is $$ most likely the HS6's can be found for less money than any other option(though some people will pay you to TAKE strombergs!!)
MD (mad dog)

01-31-2003, 02:46 AM
thank you for the advice ... i think i also should mention that altitudes in guatemala are very variable. you can be in on hour on a sea level and the city is normally 3000 mts above sea level, and i have heard that this really affects the engine performance, which of these three options do you think are going to work better considering the engines specs and the the altitudes. again, help will be very much appreciated.

02-01-2003, 01:31 PM
Mr P, you should have seen all the guys re-setting their carbs at the VTR in Breckenridge,Co two years ago(11200 ft!!)The answer is that NO carburetor can compensate for great changes in altitude. You just lose some pep when your higher than usual, worst case is some minor plug fouling.
Modern cars have fuelinjection, the computer compensates for air desity changes, but you cant burn what aint there (and thats air).Even modern cars lose some HP as the air gets thin ,they still run smoothly. but less peppy.
I still say HS6's for the best go for the $$
MD(mad dog)

02-03-2003, 03:07 PM
The adjustment of carbs for altitude is a tricky thing for most "conventional" carbs, with their settings based on a best conditions compromise. The SU (and Z-S CD) carbs are different since the operate on the "constant vacuum/velocity/depression" principle. Auto Restorer Magazine did an excellent article on SU Carbs in their Jan 2003 issue. In the article the author states that SU carbs compare the Manifold Absolute Pressure against ambient pressure to determine mass airflow. This means the mixture is controlled by the airflow and the carbs are not affected by altitude or ambient air pressure differences. The same would apply to the Zenith-Stromberg CD carbs, since they are a cheap-cousin knockoff of the SU design. Britsh ingenuity at its best graemlins/england.gif

02-04-2003, 04:01 AM
thank you soo much for your help gentlemen ... it is people like you who encourage me to continue on this 4 yr journey ... thank you!!!!