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Mark

2500S Inlet Manifold Modifications

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Hi all

I am going to fit a 2500s inlet manifold to my Vitesse along with a pair of HS6 carbs. My intention is to fuel inject in the not to distant future but for now want to get the car up and running.

 

I have read or heard somewhere that the ports on the manifold can be made to flow better. Has anybody done this mod and if so are there any pics of where the material should be removed from. 

Thanks

Mark

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MrS may like to comment on his experience, but mine was with the same - well, a 2.5 engine from a saloon, so same difference -  bonnet fouling.

Two reasons:

1/ the Vitesse was designed for Strombergs.  Much lower profile to the dashpots.

2/ the saloon engine was canted, tilted to the right, so the manifold was designed to lift the carbs up and run them level.    When the engine is fitted upright in a Vitesse, the carbs poke upwards and foul the bonnet, esp. the front one.

 

The angle is about 7 degrees, I think.    One solution would be to have the manifold-to-head face ground at that angle to bring the carbs down.

OR, put bulges in the bonnet and to use the slight adjustment possible in the angle of the float chambers, as they are bolted to the body of the carb (maybe not all HS6s!)

 

John

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Hi,

 

I built up a 2 ltr ME series engine for my Vitesse, and when I did so I did the work you mention to unshroud ports 2 & 5

 

Have a look here; http://retrorides.proboards.com/thread/62127/1969-triumph-vitesse-megasquirt-motorbike?page=3

Thanks for the info and link, I'll have a look.

 

MrS may like to comment on his experience, but mine was with the same - well, a 2.5 engine from a saloon, so same difference -  bonnet fouling.

Two reasons:

1/ the Vitesse was designed for Strombergs.  Much lower profile to the dashpots.

2/ the saloon engine was canted, tilted to the right, so the manifold was designed to lift the carbs up and run them level.    When the engine is fitted upright in a Vitesse, the carbs poke upwards and foul the bonnet, esp. the front one.

 

The angle is about 7 degrees, I think.    One solution would be to have the manifold-to-head face ground at that angle to bring the carbs down.

OR, put bulges in the bonnet and to use the slight adjustment possible in the angle of the float chambers, as they are bolted to the body of the carb (maybe not all HS6s!)

 

John

 

 

The front carb actually cleared the bonnet by about a quarter of an inch, but to play it safe I bought some sprint carbs so there is now plenty of room.

 

thanks all

 

Mark

Edited by Mark

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I actually fitted mine with CD175s (Rover V8), so bonnet fouling wasn't an issue anyway. However, that just brought another world of pain when it came to fuel needles!

 

Had I not ended up going EFI, then Sprint carbs would've been next on the list

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Checked the air flow through the manifold tonight and I was surprised at the differences. 1 & 6 flowed more than double 3 & 4 and almost double of that through 2 & 5. Results were consistent. So I think lots of gains to be made. 

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Fuel distribution is a factor also and impossible to measure without a running engine.  The CW mk 1 manifold mod involves adding material IIRC.

 

Nick

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Fuel distribution is a factor also and impossible to measure without a running engine.  The CW mk 1 manifold mod involves adding material IIRC.

 

Nick

 

 

Hi Nick

 

Yes I understand that.  I think getting the inlet ports to flow as equal as possible to start with will aid with the equal distribution of fuel.

 

I will go carefuly and measure flow as I go. I had a set of SAH webber manifolds about 30 years ago that were ruined by a so called specialist who just bored them out and said it would allow more air to flow.

 

Mark

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Fuel distribution is a factor also and impossible to measure without a running engine.  The CW mk 1 manifold mod involves adding material IIRC.

 

 

Yes I had to add quite a lot of metal to the MK1 manifold to get everything right. 

 

Alan

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Checked the air flow through the manifold tonight and I was surprised at the differences. 1 & 6 flowed more than double 3 & 4 and almost double of that through 2 & 5. Results were consistent. So I think lots of gains to be made. 

 

Meant to ask before how did you measure the airflow? 

 

Alan

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Been unable to post as I spilt tea on my apple keyboard and killed it, bought a cheapo PC one all the keys are in the wrong place but it works.

 

 

Meant to ask before how did you measure the airflow? 

 

Alan

 

Hi Alan

 

I used a carburettor balancer and a vacuum. Basic but gives pretty consistent readings.

 

 

post-741-0-23757100-1466335763_thumb.jpg

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I used a carburettor balancer and a vacuum. Basic but gives pretty consistent readings.

 

Ah carbalancer! hadn't thought of that.  Been using the dyson playing with piston lift and found it would lift a 1.75 carb about 50%.

 

NB. When you were measuring flow and applying vacuum to one port did you have the other 5 ports taped off?   Just interested as I'm a bit puzzled why 3&4 were the worst not 2&5.

 

Alan

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Ah carbalancer! hadn't thought of that.  Been using the dyson playing with piston lift and found it would lift a 1.75 carb about 50%.

 

NB. When you were measuring flow and applying vacuum to one port did you have the other 5 ports taped off?   Just interested as I'm a bit puzzled why 3&4 were the worst not 2&5.

 

Alan

 

Hi Alan

 

No all the ports  were left open. I may be wrong but my thinking was to get an idea of how the air would naturally be drawn in through the ports and how the air preferred to flow as the ports were shaped, then try and get each to flow an equal amount of air by re-shaping.  I think this way I may get them close to flowing the same amount, but struggling a bit at the moment. This may not be the best way.

 

Mark

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Hi Alan

 

No all the ports  were left open. I may be wrong but my thinking was to get an idea of how the air would naturally be drawn in through the ports and how the air preferred to flow as the ports were shaped, then try and get each to flow an equal amount of air by re-shaping.  I think this way I may get them close to flowing the same amount, but struggling a bit at the moment. This may not be the best way.

 

Mark

 

Hi Mark

 

I asked as when hooked up to the head and inlet valves closed/closing/opening most but not all air flow when a port is sucking has to come either through the carb inlet or via the balance tube. I was just wondering if the other ports were fully open when you were measuring the draw on a single port via measuring at the carb port that there could well be a tendency for another port to be supplying feed so that the measurement at the carb port would misread.

 

Just a thought?

 

Alan 

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That's interesting Mr Speedy. Wasn't the later manifold supposed to be the all singing, all dancing one to have? 

Sounds like the original Mk1 is better  :unsure:

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That's interesting Mr Speedy. Wasn't the later manifold supposed to be the all singing, all dancing one to have? 

Sounds like the original Mk1 is better  :unsure:

 

 

 

I don't know about the manifold, but the later heads certainly flow better. From what I could see the runners were still masked, although I didn't do any actual flow testing on it, I just worked on a 'line of sight' principle

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Mr Speedy,

 

The cylinder head on my .69 PI is a realy good casting compared to a "spare" 2500 head that I have - terrible coreshift, I asume it will flow less than the 69 PI head. Relaying on eyesight to judge the flow is often totaly unrealiable. Exhaust ports are very unintuetive. Even a flow bench is not always dead on correct. there is nothing like a steady flow in a running engine. 

 

Gunnar

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Hi all

 

Managed to get the 2.5s inlet manifold to flow pretty equally across all of the ports with my amittedly basic/crude method. 2.5 across all ports using the calibration on my Gunson gauge. Flow through 1 & 6 fell as soon as I started to knife edge the casting in the other ports. Wether this is going to be an improvement I don't know. I will put the car on a rolling road as soon as it is up and running with the only mods to a standard 60,000 mile engine being an unleaded head, my own manifold and exhaust system and sprint carbs. This will be the starting point and from then on I will be able to see what mods make a real difference, megajolt/squirt different cam, fuel injection.

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post-741-0-49094700-1468085952_thumb.jpg

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I would imagine the 'after' is how the designers originally envisioned it.

 

It's well recorded that hand built engines on test rigs at the Triumph factory often put out significantly more power than the production line engines with their horrible core shifts and non fettled flash. IIRC, the Dolomite Sprint engine prototypes routinely recorded 150BHP.

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Hello, Very interesting,I am in the process of fitting a pair of 2" SU's on a 2500 sedan manifold to a US market TR6 that I am rebuilding/upgrading/was upgraded in US as well.(I have to upgrade the needle setup +, ??) Regards,Michael.

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