20 replies to this topic

[Brams96]

Here's a bit of info regarding the power delivered by twin carbs compared to singles. As you can see a single 1.75" carb will give the same power as twin 1.25" carbs at 50-100bhp so comes down to throttle response I guess. Also there was a discussion about Carbs http://www.theminifo...hp/t113083.html

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[Cooperman]

Here's a bit of info regarding the power delivered by twin carbs compared to singles. As you can see a single 1.75" carb will give the same power as twin 1.25" carbs at 50-100bhp so comes down to throttle response I guess. Also there was a discussion about Carbs http://www.theminifo...hp/t113083.html

Surely a lot of it is down to the suitability of the inlet manifold. If a 1.75" carb was mounted on a standard 998 cast iron manifold and that was compared to a polished and modified alloy twin manifold with 2 x HS2's, then the HS2's would flow better due to the straight-in nature of the inlet tracts. Maybe the issue with a Mini is the inability to get a really straight-ish run into the head from a single because of the proximity of the bulkhead.
Take the 1275 GT with its single carb and 55 bhp, then consider the Innocenti 1300 of the same era with, technically, the same block. The Inno with twin 1.25" SU's gives 75 bhp compared to the GT which struggles to achieve 55 bhp. The Inno has the same head with the same size valves and the standard 510 cam (different part number, but the same profile). The 1275 GT inlet manifold really was junk.

[Zac]

I went to list them on the auction site and just couldn't do it.... I spent so much time carefully making sure everything was right with them... I'll keep my single HS4 for the moment, just incase i have any problems. I just have to give these things a go though. Now, I'll have to go make a manometer for setting them up.

Cheers for the good discussion, this forum really is brilliant

[Dusky]

 

Here's a bit of info regarding the power delivered by twin carbs compared to singles. As you can see a single 1.75" carb will give the same power as twin 1.25" carbs at 50-100bhp so comes down to throttle response I guess. Also there was a discussion about Carbs http://www.theminifo...hp/t113083.html

Surely a lot of it is down to the suitability of the inlet manifold. If a 1.75" carb was mounted on a standard 998 cast iron manifold and that was compared to a polished and modified alloy twin manifold with 2 x HS2's, then the HS2's would flow better due to the straight-in nature of the inlet tracts. Maybe the issue with a Mini is the inability to get a really straight-ish run into the head from a single because of the proximity of the bulkhead.
Take the 1275 GT with its single carb and 55 bhp, then consider the Innocenti 1300 of the same era with, technically, the same block. The Inno with twin 1.25" SU's gives 75 bhp compared to the GT which struggles to achieve 55 bhp. The Inno has the same head with the same size valves and the standard 510 cam (different part number, but the same profile). The 1275 GT inlet manifold really was junk.

 

What was the difference with the inno inlet? As I think the 1275GT did have twins too?

[nicklouse]

Here's a bit of info regarding the power delivered by twin carbs compared to singles. As you can see a single 1.75" carb will give the same power as twin 1.25" carbs at 50-100bhp so comes down to throttle response I guess. Also there was a discussion about Carbs http://www.theminifo...hp/t113083.html

Surely a lot of it is down to the suitability of the inlet manifold. If a 1.75" carb was mounted on a standard 998 cast iron manifold and that was compared to a polished and modified alloy twin manifold with 2 x HS2's, then the HS2's would flow better due to the straight-in nature of the inlet tracts. Maybe the issue with a Mini is the inability to get a really straight-ish run into the head from a single because of the proximity of the bulkhead.
Take the 1275 GT with its single carb and 55 bhp, then consider the Innocenti 1300 of the same era with, technically, the same block. The Inno with twin 1.25" SU's gives 75 bhp compared to the GT which struggles to achieve 55 bhp. The Inno has the same head with the same size valves and the standard 510 cam (different part number, but the same profile). The 1275 GT inlet manifold really was junk.

What was the difference with the inno inlet? As I think the 1275GT did have twins too?

No the GT did not.

[ucchockey]

I have twin 1.5" su carbs on a 1293. The throttle response is indeed better than when I was using a single 1.75" carb. They sound better and look better too. Higher speeds you don't really notice a difference.