Twin 1.5 carbs vs later single 1.75

[Scarlet]

What was the reason Hillman/Chrysler did away with the twin carbs and used the larger single one on the later cars?
What are the technical reasons they did this?
If I can understand the reasons maybe I can Google a solution using the twin carburettors.

[blekkja]

Simplicity maybe? I do really miss having the big single on my car. Felt it gave it more low down guts which in turn would be better for round town driving. Vs more of a top end on the twins. So guess it was what you were looking for. In the Avengers case especially midway through the run I suspect Chrysler was aiming for the family car type market and consequently set it up for better city driving.


And I think it was only the series 6 alpines that got it anyway, so when the facelift came out they all dropped back to 1.5

[Scarlet]

Thanks for the reply. Yes I heard the single was better for low down grunt.
I have an idea that (with everything else being identical apart from the carburettor set up)at lower rpm the smaller single gives a higher velocity allowing more mixture into the combustion chambers but at higher RPM it cannot give the same amount of volume as the twins
The twins on the other hand , at the same lower rpm the velocity of mixture is not as great because of sucking through a larger hole, thus less mixture enters the combustion chamber, but at higher rpm it allows greater volume of mixture to enter into the combustion chambers.
(volume at higher rpm-velocity at lower rpm
Just wondering if I am on the right track and to see what other people do to improve on things

[oldschool]

Yes I think you're on the right track Steve, as the single carb Hillman Avenger 1600 has slightly higher torque at lower RPM than the twin carb model and less HP at the top end. The cam makes a difference too of course. Those ones are a similar warm cam, while the SC Hillman 1500 and Chrysler 1600 have the pussy cam...putting twin carbs on them won't really help torque and HP.
I heard Chrysler ditched the twin carbs because of tuning problems and cost...more likely cost knowing Chrysler...lol
Higher velocity at a lower rpm requires less throttle...helping economy, while more volume at higher rpm helps power.
That fact is used in twin throat fixed jet carbies too. Many years ago when the first Honda Civics appeared I wondered why they went so well at speed, but were also very economical when driven normally.
I looked in the carbie and found the primary throat was only 20mm diameter, while the vacuum operated secondary was 30mm. My old Fiat X1/9 was similar...went well and also very economical.