exhaust systems

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Re: exhaust systems

Postby Hurtzberg » Tue Feb 13, 2018 8:58 pm

Thanks Chris, that's an interesting option.
Andrew

1957 A35
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Re: exhaust systems

Postby Edosan » Thu Feb 15, 2018 10:25 am

Hi Chris,
Intererested in that exhaust, what does the manifold look like and is it similar to the Mini 1275 one in the picture below?

Thanks Ed
Attachments
1275 Inlet and exhaust.JPG
1275 Inlet and exhaust.JPG (176.84 KiB) Viewed 79 times
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Re: exhaust systems

Postby Chris T » Thu Feb 15, 2018 11:48 am

Not far off, though mine had an inlet manifold allowing more options. I have a separate water-heated inlet so I cut the Marina's(?) inlet off to eradicate the hot-spot (as recommended by Vizard). I'm possibly regretting that move as I now need choke for much longer, and even after short stops like trips to the supermarket.
Chris T.
Attachments
Little n Large.jpg
Little n Large.jpg (190.28 KiB) Viewed 78 times
Manifold.jpg
Manifold.jpg (132.88 KiB) Viewed 78 times
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Re: exhaust systems

Postby Edosan » Fri Feb 16, 2018 12:36 am

Thanks Chris, the bottom one in your first picture is the same casting number ie 12G 787. What is the exhaust diameter and assume it is bigger than standard A35. Is it the same as the other casting? I'm running a 12G295 head on a 1098 but with completely standard 11/4 SU set up. I do get more performance but think I would benefit from a 11/2 in SU and slightly larger diameter exhaust. I've already sourced the carb which was from a 1.3 marina so float chamber is on the correct side. Many thanks Ed
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Re: exhaust systems

Postby Chris T » Fri Feb 16, 2018 9:10 am

Hi Ed, the bigger 12G 3538 manifold has an internal diameter of about 36mm at the exhaust flange. My new 1.5" exhaust pipe provides about 35mm internal. The 12G 787 manifold & earlier exhaust I'd been using were standard A35 width.
12G 3538 vs 12G 787.jpg
12G 3538 vs 12G 787.jpg (121.3 KiB) Viewed 61 times

I'd been running a 1.25" SU on the 1275cc motor since about 2003. I wasn't interested in performance; avoiding downtime & promoting economy & reliability were key, so I retained the previous 948cc motor's ancillaries (with a few richer needle swaps in the early days).
I only changed to a 1.5" SU (with DZ needle) last autumn and was surprised by the astonishing performance improvement and even more surprised by an unexpected MPG improvement. I do a few motorway journeys and soon felt that the standard exhaust was probably too restrictive, hence the experimentation with a wider bore.
My current problem is that my 1.5" SU does not have a vac advance facility (it's the front carb off a twin set-up). I naively believed some advice on another forum that the vac pipe on the inlet manifold can be used. Don't try this! Ha-ha! The dizzy just runs permanently at max advance. I'm going to have to somehow drill the SU and insert a vac pipe.
BTW the 1.5 SU was a complete pig to drive initially and impossible to drive smoothly, either stalling on take-off or leaving melted rubber on the tarmac. Horrid and dangerous. I've improved this significantly by ensuring that all the accelerator rod joints are completely free to twist & turn however they like. I understand that cable operation is the answer, but I'm not interested in that route yet.

Chris T (With apologies to Alan for hijacking his Maniflow thread)
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Re: exhaust systems

Postby Paulc » Fri Feb 16, 2018 4:08 pm

Chris, I might have an 1 1/2, need to check the stores.
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Re: exhaust systems

Postby Edosan » Sat Feb 17, 2018 12:01 am

Thanks Chris, that's really helpful, think I may try the HS4 on the smaller bore manifold and my current exhaust first. Carb needs a rebuild first so its a bit down the line but good to know the options. do you happen to know if the HS4 fits the HIF38 flange just in case I do want to go down the bigger bore route? Are the two diagonal holes correct? All Best Ed
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Re: exhaust systems

Postby exminiman » Sat Feb 17, 2018 6:28 am

My current problem is that my 1.5" SU does not have a vac advance facility (it's the front carb off a twin set-up). I naively believed some advice on another forum that the vac pipe on the inlet manifold can be used. Don't try this! Ha-ha! The dizzy just runs permanently at max advance. I'm going to have to somehow drill the SU and insert a vac


Not sure this is right. Assuming you mean the thin (apx 3mm) pipe that runs from top of dizzy to inlet manifold, then it should not be a big issue. This device adjusts advance curve (timing) slightly at part throttle, for fuel economy and smoothness. Not having it wont make your dizzy run at max advance, it is not that significant.

All it does is uses the vacuum from in let manifold to expand a diaphram in dizzy to increase or retard timing very slightley at part throttle opening

In fact Cooper S and some MG midgets were fitted with 23D dizzys that dont have a vacuum adv/ret at all - assume they saw it as pointless ( excuse the pun)

:cheers:
Attachments
A2592700-9593-4028-9909-D9EAF14B5072.jpeg
Cooper S and Midget Dizzy - without vac advance retard
A2592700-9593-4028-9909-D9EAF14B5072.jpeg (15.22 KiB) Viewed 36 times
Last edited by exminiman on Sun Feb 18, 2018 9:10 pm, edited 1 time in total.
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Re: exhaust systems

Postby gazza82 » Sat Feb 17, 2018 1:44 pm

I'd be more inclined to look at the springs in the weights that handle the mechanical advance.
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Re: exhaust systems

Postby exminiman » Sat Feb 17, 2018 2:57 pm

:iagree:
gazza82 wrote:I'd be more inclined to look at the springs in the weights that handle the mechanical advance.
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Re: exhaust systems

Postby Edosan » Sun Feb 18, 2018 9:19 pm

Think you've got Chris wrong here, my take on his post was that he had tried linking the advance pipe to dizzy to another vacuum offtake on the inlet manifold and it was giving him too much vacuum. Maybe issue with springs as well of course! Anyone have an answer to the SU carb flange and whether HS4 fits diagonally on the HIF 38 flange holes? ie can square flange be used for both types? Thanks Ed
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