chopping a std hs2 manifold

[turbochargedstu]

im currently waiting for the modified head to come back for my '64 elf. it was a bit gutless so i have added a simonbbc electronic dizzy kit, RC40 centre and backbox with a rc40 to standard manifold link pipe. i dont want it to look overly modified so want to keep the hs2 carb and airbox.
im just wondering if its worth sticking with the set up i have (link pipe and std manifold0 or if i would get much gain by carefully chopping the inlet manifold part from the standard manifold and adding a freeflow type exhaust manifold. any opinions are grateful.

[ivor badger]

If you are leaving the HS2 on the std manifold, you might as well not bother with all the other bits.

[mk1]

If you are leaving the HS2 on the std manifold, you might as well not bother with all the other bits.

Couldn't agree more.

If you are wanting a little more grunt, go for a modified head (or ofset rockers) first, then an H or HS4 (1 1/2" carb), then the extractor exhaust, then the dizzy mods to make it all run sweet.

[turbochargedstu]

im getting my newly modified 12g295 back next week. the further freeflow is just an idea.
surely the hs2 with the correct needle and jet would be good. its only a 998 std elf. im not after a fast road speeder.

[mk1]

The HS2 is more or less on its limit in a standard 998. You can do all the fannying about with it that vizard suggests in his book or just fit a bigger one. You will never turn it into a road rocket, but to get the benefit of the modded head you really do need a bigger carb or maybe carbs.

M

[turbochargedstu]

hmmmmmmm. twins..............!

[mk1]

Twin 1 1/8" work very well on mildly tuned 850's & 998's. Although with a decent 295 twin HS2's would probably be a better bet.

M.

[Lord Croker]

An HS4 on an MG Metro water heated inlet manifold, with LCB exhaust manifold & 1.75" system works very well with a 12G295 head on my 998 engine & doesn't make it look too highly modified.

[turbochargedstu]

the thing is under the bonnet all looks standard. even the brass radiator. if i start altering things too much then i may as well just turbo it.

[madaboutcherry]

these would look nice,
http://www.ebay.co.uk/itm/221132432756? ... 1423.l2649

[Chalkie]

The hs2 carb is restrictive rubbish carb at the end of the day mine looks nice as a Orniment on my shelf

standard 850 with a hs4 on give a good power boost over hs2

twin hs2's would give you 2 1/2" ( 1 1/4" + 1 1/4" = 2 1/2") alot more air and fuel mix also air box can restrict alot unless modded well

Vizard wll cover it

[mk1]

Not true that 2 x 1 1/4" carbs gives you an effective 2 1/2" throat, as only on cylinder is ever sucking through 1 carb at any given time. The advantages achieved are mainly through better distribution

[guru_1071]

twin hs2's would give you 2 1/2" ( 1 1/4" + 1 1/4" = 2 1/2") alot more air and fuel mix also air box can restrict alot unless modded well

this is a bit of a 'tfm' thinking though....


in reality

its not the overall size of the carb that makes the difference, you also have to consider the relation ship between the airspeed over the bridge and the resultant height of the damper and the position of the needle, on an 850 its perfectley suited to the 1 1/4 due to the size of the engine etc, this is why a car running a set of twin 1 1/4's is more punchy than if it has 1 1/2s as the engine has to be working harder to get the same affect through the carb, its only when the engine reaches a certain amount of load that the 1 1/2's will start to out perform the smaller carbs.


someone i know who is a bigger fan of su's than me saw a pair of twins that had been 'modded' by an expert, the buyer couldnt understand why they wouldnt work.

the 'expert' had bored the bodies out and removed the bridge (thinking that a huge round hole would allow for the maximum amount of air to pass through) all that happened was that the venturi affect was lost and the petrol couldnt be sucked up out the jet tube.

an expensive mistake!!!

[Chalkie]

I always thought as its over 4 cylinders it gave much better flow though it is on a 5 port hmm okay well I guess you learn something new everyday I take this on board as a learning experience

Dose this count with 7/8 ports where they have carb per cylinder?

and did you mean TMF thinking?

Thanks
Stephen

[ivor badger]

The hs2 carb is restrictive rubbish carb at the end of the day mine looks nice as a Orniment on my shelf

standard 850 with a hs4 on give a good power boost over hs2

twin hs2's would give you 2 1/2" ( 1 1/4" + 1 1/4" = 2 1/2") alot more air and fuel mix also air box can restrict alot unless modded well

Vizard wll cover it

You weren't paying attention in the maths class were you.

Area of circle = R squared x pii

HS2 = 0.625 x 0.625 =0.390 x 3.142 = 1.227 sq in x 2 = 2.45 sq in

HS4 = 0.75 x 0.75 = 0.5625 x 3.142 = 1.767 sq in

[mk1]

Good point well made

[Chalkie]

The hs2 carb is restrictive rubbish carb at the end of the day mine looks nice as a Orniment on my shelf

standard 850 with a hs4 on give a good power boost over hs2

twin hs2's would give you 2 1/2" ( 1 1/4" + 1 1/4" = 2 1/2") alot more air and fuel mix also air box can restrict alot unless modded well

Vizard wll cover it

You weren't paying attention in the maths class were you.

Area of circle = R squared x pii

HS2 = 0.625 x 0.625 =0.390 x 3.142 = 1.227 sq in x 2 = 2.45 sq in

HS4 = 0.75 x 0.75 = 0.5625 x 3.142 = 1.767 sq in

Ah no Unfortally I never had a maths teacher from year 10 onwards just surplys or free periods! need to work on my maths better to be honest. Thanks though, Ill save the calulations and work alot more on my maths

Thanks guys!

[Frogeye61]

OK, now the discussion about the twin carbs, though with a larger total area, can only use one carb at a time due to the firing order and placement.
For maximum flow a single 1.75 HS6 from for example Volvo or Jag, but that won't work on the small engine.
I would simply use the single HS4 and leave it at that. In fact if nobody convinces me otherwise, that's my plan for a 1098 with 12G295.

[guru_1071]

Ah no Unfortally I never had a maths teacher

think of all those free holidays to france you missed out on!

[ivor badger]

Ah no Unfortally I never had a maths teacher from year 10 onwards just surplys or free periods! need to work on my maths better to be honest. Thanks though, Ill save the calulations and work alot more on my maths

Thanks guys!

You also seemed to have missed out on the English spelling and grammer. This is not a reflection on yourself , but the current educational system.