hey all, just trying to decide what carby would best suit a 1098 that has LCB's a hot little cam and a 1.75" exhaust?

cheers,
Matt

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Here am I sitting in my tin can far above the Moon
Planet Earth is blue and there's nothing I can do...



“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson

it all depends on how hot the cam is, how extensivly the head has been "tickled", how far the bores have been opened up?

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http://www.youtube.com/watch?v=nDMkVq1jRGU

well the cam is a GR RE13 number, havent touched the head or the bores yet, just going for something that i could get used to driving in for the time being...

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Here am I sitting in my tin can far above the Moon
Planet Earth is blue and there's nothing I can do...



“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson

A single 1-3/4 gets my vote- either an HS6 or the later HIF44.
It will outperform twin 1-1/4s if on a decent manifold (eg Russell Engineering 7", or a Minispares one).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

if you are going to eventually build it into something a bit wilder in the future or even go for a 1275 with some mods id go the 1"3/4 (hif44) with either minispares water heated manifold or the G.R. manifold (as mentioned by drmini aust). But as it stands now.....with only the cam and std other bits a freshend up 1"1/2 on a water heated manifold would do just fine.

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http://www.youtube.com/watch?v=nDMkVq1jRGU

HIF 44 Great carb

Go the twins, but remember the stock BMC / BL inlet manifold for twins was really really crap. If you binned it and went for a maniflow inlet, you would have a set up suitable for 998s to 1275s.



I love my twins!


That being said, a single 1 1/2" or 1 3/4" on a good (GR) manifold would do a pretty good job and be a lot cheaper!


Matt

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68 Deluxe.... it's shiny..... I like shiny!!

On an 1100 I would vote for single 1-3/4. Set it and forget it.

Single 1-3/4 flow rate is almost identical to 2 x 1-1/4's.

Pete

I'm with Matt , I love twins though they have to be in good condition , but for an every day car a single will be easier especially if you don't know how to tune twins .

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I like the look of twins, which is why I went for them. PITA when my accel cable broke the other day and I only had makeshift tools

But I still love them!

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina

This is a common fallacy, you can't just add the area of the twins and compare tha total to a single, because the twins' flow is intermittent- one sucks for 2 cylinders in succession, then it rests while the other sucks.
ie. firing order is 1-3-4-2 repeat, transpose 1 place to the right and it's 3-4-2-1 repeat.
so 3 and 3 suck, then 2 and 1 on the other carb.

Vizard covered this in his book but I don't remember chapter and verse.

A single 1-3/4 on a good manifold will way outperform twin 1-1/4s.
Each cylinder sees the area of a 1-3/4 carb, not a 1-1/4 one.

The balance pipe on a twin SU manifold doesn't contribute much flow at all, it's just there to stop the SU piston fluttering (dropping) in between cylinder intake strokes.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

twin hs2's or hs4's.

no lean 1st and 4th cylinder like with single carbs and probably better fuel economy and response with hs2's.

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I've just picked up a nice reconditioned HIF44 which I'm going to try setup on my 1100.Just got to try to source some needles in Adelaide to try out.The one in it (BBC) is going to be too rich I'd image. 1100 bored out 20 thou,295 head with oversize valves, 3 in 1 extractors , metro inlet , pulsar dizzy, pity its still only a standard cam at the moment.

i can recomend a HIF 44 good carby bowl is under the carby so during hard cornering it is less likely to starve for fuel also it was on a 1380 and it was good for cruiseing and putting the boot in
makka

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