What exhaust for Marina 1275?

[philthehill]

Declan
Many thanks for the info.
That is the manifold I would be using with your modifications listed and of course you now have the option of fitting it to your 1275cc engine without incurring any restrictions in the gas flow.
Regarding the camshaft - except for the MG Metro the 'A' Series standard production camshafts (non Cooper) are all much of a muchness with very little variance in the cam timing. Even the 1275cc Marina camshaft timing is the same as the 1275cc Midget/Sprite camshaft.

For general consumption:-
Full details of standard/production camshaft lobe timing is given in the Vizard 'A' Series tuning book.

Just been reading the Vizard book, Tuning the 'A' Series - Section Exhaust Systems, Part 1. In the section Exhaust Manifold Power gains Vizard states after extensive testing that "The standard (manifold) (i.e. Pt No's: 12G787/12G3538) produces the best results per pound spent"...........I rest my case.

Later in the chapter he goes into detail regarding the 1275cc Metro cast iron LCB exhaust manifold.

He also states when comparing the standard Cooper 'S' manifold (similar to the one in this link https://www.ebay.co.uk/itm/CLASSIC-MINI ... SwridaAMMA) with a LCB that "the LCB has an advantage but it is not that much until we consider engines over 80hp"
Phil

[Mark Wilson]

I've a 1275 Midget engine, which I'll be marrying up with an HS4 (which I acquired from Roy!). I have a Metro alloy manifold like this https://www.ebay.co.uk/itm/Classic-Metr ... Swax5Y28If ( mine was a lot cheaper, and has the water connections missing).

I was intending to use a cut down 1098 exhaust manifold with this, connected to a standard exhaust. Having followed this thread I'm now thinking I should acquire a Marina 12G787. The question is, do I use this with its attached inlet manifold, or should I grind it off and use my Metro manifold? And will the standard Minor exhaust clamp directly on to the 12G787 manifold?

Mark

[philthehill]

My advice is to use the Marina manifold complete with throttle bracket and insulating blocks. See my post in parts for sale.
The HS4 will bolt straight on as original.
Use the adapter exhaust pipe listed in my post above.
At the end of the day there is very little difference between the 1275cc Midget engine and the 1275cc Marina engine. The twin 1 1/4" HS2 carbs fitted to the Midget gave a very small increase in power but not that much. Their fitment was mainly to meet expectations as MGs and SU carbs went together like strawberries and cream and had done so for many years previous. American market 1275cc MG Midgets ended up just using the single SU carb with a host of add ons to combat pollution.
Using Marina parts including the air cleaner will ensure that it will all bolt together and can be tuned with factory spec settings without any encountering any problems.
I would suggest upgrading the exhaust pipe to the same size as the adapter pipe/Marina exhaust to give good flow characteristics.

[irmscher]

And don't forget to upgrade the brakes while you are at it as it will take some stopping

[Mark Wilson]

Many thanks Phil. There would definitely have been a fight over the Ebay HS4 & manifold if it wasn't so far away! The HS4 I got from Roy is a right hander, so although I've got a connector plate I'm going to have to adapt it. I am intending to use an MGB air filter as it looks more Minorish, but can change to a Marina filter if this doesn't work out.

I've fitted Wolsey 1500 brakes and a servo, so should stop OK!

Mark

[philthehill]

Mark
Manifold BL Pt No: 12G3538 was also fitted to 1275cc engines.
The top stud is off set to the left of vertical so your carb may fit.
Note: The BL parts list illustration is wrong. See also post below.
A good move on the brakes.
Phil

[Mark Wilson]

Just remembered that I'm in the deepest south-east next week. The Ramsgate package is now spoken for! Thanks for the alert and advice Phil.

[philthehill]

Mark
Well done.
Happy to be of help.
Please let us know how you get on.

Phil
...................................................................................................................................
As an aside - I have just physically examined a 12G3538 manifold (number cast on to it) and the illustration in the BL Marina parts list is wrong!

The 12G3538 manifold has the ability to mount a 4 stud carb, or a 2 stud carb - top stud orientated to the left, or a 2 stud carb - top stud orientated to the right.

[Chipper]

That's interesting; I take it the ESM large bore exhaust matches the Maniflow 1 5/8" LCB? I notice it's a fair bit cheaper than the Maniflow exhaust system that matches their manifold, currently selling at £140 + postage on a popular auction website...

My Traveller has a 1275cc MG Midget engine, currently fitted with the exhaust manifold from a 948cc Minor, hooked up to a standard size, albeit stainless steel Minor exhaust system, and a HIF44 on a 'Flowtech' alloy inlet manifold. It goes pretty well (e.g., will go to 'off the clock' speeds flat out on a private runway!), but I suspect it would go even better with the 1 5/8" large bore & LCB set up...

[philthehill]

Chipper
If you improve the amount of fuel/air accessing the cylinder you need to improve the ability of the exhaust gas to leave the cylinder.

As regards the Maniflow exhaust system - You will not find better.

The Marina 12G3538 manifold with the ESM adapter pipe and the ESM large bore exhaust will not see you go wrong pound for pound.

With the larger exhaust flow capacity there is a better chance that the speedo needle will go round the clock past the fuel gauge and even much further

As I have said on several occasions tuning and modifying the 'A' Series has to be done as a package to get the best out of it.

Phil

[liammonty]

For what it's worth, I've seen quite significant benefits going from a Marina 1275 exhaust manifold on a Birmingham Morris Minor Centre (now DMG) free-flowing exhaust to a Maniflow small bore system including their LCB manifold.

Engine spec is:
948 block overbored to 1030
Flat top pistons (static CR in the order of 9:1)
998 Cooper con rods
Block 'align-bored' to accept 'real' camshaft bearings
Minispares inlet manifold
12G295 head
HIF 38 carb with Mini airbox and K&N filter
A succession of cams - Swiftune SW5-07, MG Metro, and latterly, AC Dodd RT

Currently using 'Road Torque' cam from AC Dodd - don't recall the exact spec of it, but I believe that duration is in the order of 250 degrees on both inlet and exhaust, but with relatively high lift. So hardly wild. The car was set up on a rolling road before fitting the LCB, and after fitting it. With the Marina manifold, it was tough to get the fueling right through the rev range, but with the LCB fitted, it was far easier to get set up, and the performance increase was very noticeable, equating to about 5 bhp on the dyno IIRC, but that doesn't tell the whole story as it is very much more driveable throughout the rev range and not just at peak power. I know this goes against the theory that's been explained, but I suspect that the level of cam overlap at which the LCB begins to be beneficial is less than what is generally thought.

[philthehill]

The requirement for a LCB manifold and its pipe size and the length of the individual pipes is dependent upon many things but the overlap (when both valves are open) in degrees of the inlet and exhaust is used as one of the main deciders.
Interesting spec for your 950cc engine. I built a 950 to a similar spec except that it ended up as a 998cc, it had a Cooper 2A948 camshaft, lightened flywheel and ran a pair of SU HD4 1.5" carbs. It ran very well.


Here is the spec for AC Dodd cams which includes the RT cam.

[Monty-4]

Just thought I'd add a couple of pence. I have the same rear axle and fuel tank clearance issues with the Maniflow exhaust (1.5") as described earlier in the thread regarding the ESM one. If building mine again I'd likely go for the cheaper pipes rear of the manifold! Getting a flexi-join to mate the manifold and pipes up also makes things a lot easier when asembling it all.

Another vote for the ACD-RT cam from me, I'm now running it in my 1098 (+0.060") with just little twin HS2s. Very nice torque and yet to be put on a rolling road.

[liammonty]

The requirement for a LCB manifold and its pipe size and the length of the individual pipes is dependent upon many things but the overlap (when both valves are open) in degrees of the inlet and exhaust is used as one of the main deciders.
Interesting spec for your 950cc engine. I built a 950 to a similar spec except that it ended up as a 998cc, it had a Cooper 2A948 camshaft, lightened flywheel and ran a pair of SU HD4 1.5" carbs. It ran very well.


Here is the spec for AC Dodd cams which includes the RT cam.

Thanks Phil - even shorter duration than I remembered then! Interesting that you built a similar spec 950. I wanted to keep the original block, but the engine was past its best so I rebuilt it while I ran a cheap £100 replacement engine in the car for a bit. The rebuilt engine is lovely - still really smooth as the standard 948s are compared to a 1098, but far livelier. It pulls a 4.22:1 diff nicely and the rolling road reckoned it’s making around 55 bhp - a big improvement over its original 37! It uses no more fuel unless driven really hard, either. That cam suits it beautifully. I had terrible trouble with 3 SW5-07s that chewed up the distributor drive gears repeatedly, so then switched to an MG Metro one. That resolved the dizzy drive gear issue (I think there was a problem with Swiftune’s billets used for their cams) but the MG cam was too much for the engine and it had little low end torque. Very happy with Adrian Dodd’s now.

[philthehill]

Here is a picture of the 948cc engine bored to 998cc I built in the 1970s. It had the three white metal camshaft bearings fitted, cooper S oil pump fitted, new 2A948 camshaft and lightened cam followers fitted, duplex fitted, cleaned up 12G295 head with stronger valve springs and better valve guides fitted, Cooper S water pump fitted with larger drive pulley, lightened flywheel fitted, stronger clutch fitted, Cooper S distributer fitted, sports coil fitted, 998cc Cooper fully floating rods and 998cc powermax pistons fitted, Janspeed LCB fitted and a Midget performance exhaust system.
I am surprised to hear about your distributer to camshaft drive problems. I always purchase Kent billet cams.
I am in slow time building a similar spec 998cc engine based on a 948cc Sprite engine but with either a 12G 940 or Cooper S 12A 185 head.

[nkm198]

Finally got around to fitting Marina combined manifold, HS4 carb, aftermarket air filter and big bore exhaust. Power increase is noticeable, fuel consumption seems about the same as when running with Minor ancillaries. I was worried it was set too lean – rad cap was hot for the first time ever, and heater actually noticeable, not the usual 'mouse breathing on my foot'. But rad was cool at the bottom, and plug check (twice on different plugs, after different journeys) shows them digestive biscuit--coloured. Thanks to all on here who offered help and advice. I'm very happy with the outcome.

[paul 300358]

The marina 1275 air filter will not fit a 1098 with a mini alloy inlet and HIF38 carb, it hits the bonnet!! You have to fit the alloy elephants trunk to mate it to the carb Ah well, back to the sports filter.

[MorrisJohn]

If you keep everything Marina you will have less trouble setting everything up which can be a problem especially if you have a mix and match engine assy.

Resurrecting an old post here. I’ve been reading this thread and, taking Phil’s advice, using the information within it for planned upgrades (from 1275cc Marina engine with HS2, 1098 manifold, standard exhaust and air filter to Marina HS4, Marina 12G3538 manifold, K&N cone filter and with larger bore exhaust to fit manifold).

My question is, nowhere have I seen any reference to the distributor. Is there be any requirement to replace or modify it as part of this planned package of upgrades? I have been told the HS2 and HS4 advance differently and so swapping the carburettors can lead to incorrect vacuum advance?

[panky]

Once you finalise the spec of your engine maybe you could sent the dizzy to be re-curved by the likes of AC Dodd or the Distributer Doctor.

[philthehill]

Vacuum advance differences between a HS2 and a HS4!!!
That is a new one on me - I have never come across any difference in vacuum pull between a HS2 and a HS4.