SU carbs on Stromberg manifold?

[fandeland]

Hello,

I intend to upgrade my USA spec 4.2L engine with 2" HS8 SU to replace the original CD175 Stromberg. I'd like to get rid off the secondary throttle housing meant for emission control. Will i be able to reuse my current primary inlet manifold and fit the HS8 to it?
Thanks

[PeterCrespin]

Not without work. You would need to fill in the lower stud holes where the secondary bts on and the re-drill for two new studs slightly higher up in the 'square' SU/Strangleberg stud pattern. You would then be left with carbs closer to the engine, even with a fibre heat insulating spacer, so your air filter setup would no longer line up as original, although with the later XJ6 style it wouldn't affect much. Might be easier just to remove the secondaries and spindle and plug the holes, leaving all the mountings as standard.

Hopefully you would notice a difference but maybe only at wide open throttle and high revs which is the only time a 1/4" increase in choke diameter would be relevant to any significant degree. It would be interesting to get before and after data - if not from a dyno then a smartphone app or timed rolling acceleration over a known distance etc.

Pete

[Woolfi]

"Hopefully you would notice a difference but maybe only at wide open throttle and high revs which is the only time a 1/4" increase in choke diameter would be relevant to any significant degree."
I think the difference in power would be like Pete said mostly at wide open throttle. But the difference in choke sqare is bigger than you "think" , if you measur (!!!) and calculate.
The HD8 has 2,00", which are 50,8 mm.
The Stromberg has 1,75" , which "are" 44,45 mm. But this is NOT correct. I have measured the carb mouth of my Strombergs and wondered a lot, that they have only 41,5 mm. The HD8 has full 50,8 mm.
Measure your carb mouth's, that you can see, that I am correct.
If you calculate the difference in carb mouth area, the difference is 1,498 wich is + 50%.
If my information is correct, the Stromberg has 210 cfm, the HD8 has 300 cfm.
It is an interessting question, how much difference in real power this difference of + 50% in carb mouth square would generate. Like Pete said, if you do this conversion, try to measure the difference in power. Neasuring is much better than believing. "Spent" work mostly generates felt difference in power. But the gain often is only existing in the brain of the "spender".
Also you have to check, that the square of the original "inlet-pipes mouth" is not smaller than the HD8. A chain is only strong as the weakest part of it. Maybe it is possible, to make this mouth a little bit bigger.
Maybe the conversion will generate 20 "ponies" ? ? ? The difference in power will be "upstairs" in the rev range.
Maybe the result will be lower you have hoped or lower, than the amount of work ou have spent. For you this would be worthless, but for ALL other 4,2 owners, which have the same idea, your results would be worthfull. You would be the "scientist", which had proven the hypothesis: 2 HD8 generate (much) more power, than two Strombergs on a 4,2.
You would get the "Nobel-price" from the E-type community, for doing this excelent "scientific" work. The price in 2012 was given to David (Heuer) for his excelent work about air-filter and primary-pipe conversion.
Excuse my simple english.
Wolfgang Gatza

[fandeland]

Sounds like I have been assigned a challenge here! :D
I was humbly asking whether the SU would physically fit the inlet manifold (bare the secondary) fitted on US engines. Sounds like there is there a possibility with some rework on the manifold that I'm prepared to do.
I'm keen on trying to measure the power difference, if any, with a smartphone BUT I'm asking everyone patience... The engine is still in bits and pieces in the barn, the body is being repainted and I'm only able to work on the car 3 weeks per year (due to distance between me and the car). So it might take a couple of years before I can give a feedback... In the world of home restoration, I suppose this is expected..
Thanks