The Triumph Dolomite Club - Discussion Forum

Are HS8 carbs a straight swap for the HS6's in the Sprint?

No, you'll need larger diameter carb mounts with a 2" diameter hole (the club supply these) and you'll need to reamer the inlet manifold ports to 2" too, preferably matched to the carb mounts to avoid a step.

Also, to get their benefit you'll need an uprated camshaft which in turn will require valve clearance adjustments.

I have an unused set of the club 2" aluminium mounts, if anyone wants them send me a pm.

I went for a pair of 45DHLA instead.

There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Bumpa wrote: ↑Wed Mar 02, 2022 9:23 am There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Agreed, a hotter cam is in my wishlist though I cannot see how I can improve the exhaust breathing.

ham204 wrote: ↑Wed Mar 09, 2022 4:16 pm

Bumpa wrote: ↑Wed Mar 02, 2022 9:23 am There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Agreed, a hotter cam is in my wishlist though I cannot see how I can improve the exhaust breathing.

Assuming you have got rid of the standard exhaust, with its daft routing, you are probably correct. There isn't room for a better manifold.

Saying that, people can get more power out of a Sprint, so that implies that the manifold isn't that big a limitation.

cleverusername wrote: ↑Wed Mar 09, 2022 5:01 pm

ham204 wrote: ↑Wed Mar 09, 2022 4:16 pm

Bumpa wrote: ↑Wed Mar 02, 2022 9:23 am There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Agreed, a hotter cam is in my wishlist though I cannot see how I can improve the exhaust breathing.

Assuming you have got rid of the standard exhaust, with its daft routing, you are probably correct. There isn't room for a better manifold.

Saying that, people can get more power out of a Sprint, so that implies that the manifold isn't that big a limitation.

The log manifold, for all the scorn I heap on it, doesn't actually flow THAT badly. You can get a bigger bore downpipe and open up the exit holes in the manifold to match. Which'd probably be enough to cope with a pair of 2" SUs and a warmer cam.

Steve

cleverusername wrote: ↑Wed Mar 09, 2022 5:01 pm

ham204 wrote: ↑Wed Mar 09, 2022 4:16 pm

Bumpa wrote: ↑Wed Mar 02, 2022 9:23 am There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Agreed, a hotter cam is in my wishlist though I cannot see how I can improve the exhaust breathing.

Assuming you have got rid of the standard exhaust, with its daft routing, you are probably correct. There isn't room for a better manifold.

Saying that, people can get more power out of a Sprint, so that implies that the manifold isn't that big a limitation.

There is a better four branch works style manifold (Equal length pipes)
Mega expensive and hard to get hold off.
Hence why folk don’t change this.
Unless your going all out racing I’ll keep with the standard manifold

Minis the old proper ones use to benefit from bigger carb(s)
without any engine mods or tweaks.
So what you said is technically wrong.

Changing to a LCB (Long Centre Branch) manifold was also more beneficial.

SprintV8 wrote:
Minis the old proper ones use to benefit from bigger carb(s)
without any engine mods or tweaks.
So what you said is technically wrong.

Your local petrol station will benefit of the HS8's. Otherwise it's not much use on a std engine. The HS6 are not restrictive and oversized.

One of my sprints has 139 hp at the rear wheels with std cam and HS6 by optimizing the head and raising compression ratio. The sprint engine in std form is restrictive, not the carbs. Bigger carbs on a std engine will result in slower airspeed through the venturi so low rpm torque will even be less.

Jeroen

cleverusername wrote: ↑Wed Mar 09, 2022 5:01 pm

ham204 wrote: ↑Wed Mar 09, 2022 4:16 pm

Bumpa wrote: ↑Wed Mar 02, 2022 9:23 am There is generally no benefit to be gained from fitting larger carbs unless the engine is altered to let it breathe more easily, such as larger valves and performance camshaft. Putting bigger carbs on a standard engine can actually reduce performance as the velocity of air passing through the carb will be reduced.

Agreed, a hotter cam is in my wishlist though I cannot see how I can improve the exhaust breathing.

Assuming you have got rid of the standard exhaust, with its daft routing, you are probably correct. There isn't room for a better manifold.

Saying that, people can get more power out of a Sprint, so that implies that the manifold isn't that big a limitation.

I have a straight exhaust apart from the up and down to avoid the rear axle.