2000mk2 with cd175

[jacobtns]

Hi, I'm planning to upgrade my 1970 2000mk2 with a gt6/vitesse cam, SU intake manifold, tr6 cast exhaust manifold, and a set of cd175 carbs.

Has anyone run these carbs on a 2000/gt6/vitesse? I'm thinking I'll start with a set of the later tr6 needles or maybe tr7 needles as that engine was the same capacity. I don't expect any to be perfect but wondered if someone might point me towards a good starting point.

 

 

 

[thescrapman]

Darren who rallies a Mk1 2000 used to run his car on twin 175 from a TR4. He has a 2.5 now.

there was a long thread on the subject at the time, but probably not accessible anymore.

Getting the TR6 front pipe sorted is something I need to do for my car, The main rail gets in the way. You have to rotate the alignment of the twin pipes 90 degrees as is drops and turns backwards, keeping the lengths the same.

it may be over-carbed with the 175s.

[James]

You're better off sticking with the same carbs and setup as those from a Mk2 GT6. That way you can use the same needles etc

175s are likely to be too big, will be harder to tune and give you no extra power at all... just doesn't make any sense.

 

[jacobtns]

Thanks, yeah google shows lots of good old threads bit they seem to be innaccesable now.

My existing cd150 would be the same as the gt6, just with different needles so it would be easy to just get the gt6 needles...but then because I will use the better later intake manifold I'll still end up having to make up adapter plates etc. And yeah I have heard that it may be too much carb, but I've also heard that the HS6 from later cars is an upgrade and given they are 1.75 inch I figured the stromberg's would be the same. 

I know there are old threads from people with gt6 who have used HS6 and cd175 so I would be very interested to hear from them.

Thanks for the tip on the TR6 exhaust, I have an existing stainless exhaust from the front pipe back so may end up just getting a 2 to 1 piece made up for that.

[RobPearce]

7 hours ago, jacobtns said:

but I've also heard that the HS6 from later cars is an upgrade

Unfortunately, no. The later cars used HS6 purely to share more parts with the 2500TC & S. It's not well balanced on the 2L engine.

I have read of people using the 175s (or HS6s) on GT6s but usually when they've done significant engine work to make it breathe more. The results, in most cases, were thirsty and loud, often hopelessly unreliable, occasionally a bit of an improvement in raw power.

[jacobtns]

1 hour ago, RobPearce said:

Unfortunately, no. The later cars used HS6 purely to share more parts with the 2500TC & S. It's not well balanced on the 2L engine.

I have read of people using the 175s (or HS6s) on GT6s but usually when they've done significant engine work to make it breathe more. The results, in most cases, were thirsty and loud, often hopelessly unreliable, occasionally a bit of an improvement in raw power.

Thanks for clarifying that, I'll stick with the cd150, which has the added advantage of keeping my life easy as well.

I'll spend the extra time/money having the standard manifold cleaned up to get better flow to cylinders 2 and 5.

[glang]

I think I read somewhere a carb somewhere between 150 and 175 would have been good for the 2L. Not surprising when you think twin 150 were used on the 1500 four cylinder engine....

[RobPearce]

Perhaps, but bear in mind that the 1500TC used HS2s. It's marginal whether the 1500 really needs twin 1.5" carbs.

[James]

My highly tuned 2 litre has approximately a 2" butterfly — when you work out the area it's about the same as twin HS4s

An SU has a relationship between inlet size and vacuum — fundamentally doesn't work properly if too big.

 

[TimW]

I'd also recommend keeping the cd150's or even swapping to HS4's (I prefer su's) but in regards to the cam if you don't have the cam yet and need to purchase one then I'd consider using the Newman PH2 cam instead. It's a little more frisky than the mk2 gt6 cam but still offers a stable idle and is a very  nice fast road cam. 

[jacobtns]

Glang I think it says that on Chris Witors summary of the different carbs used by the big triumphs.

I've found calculators that people use to determine the size carb they need, it uses the displacement of the engine etc to give max cfm and that suggests that even at 100% efficiency (for the engine-which it will never achieve) the cd150 should be sufficient.

Tim W, you've recommended the PH2 to me before on facebook, I'm definitely considering it, though I spoke to newman cams and they recommended the ph1. I've also talked to CW and he thought the standard gt6 cam would be better than his modified gt6 cam, which in turn is less cam than the 150bhp cam or PH2. So it's safe to say I'm confused and have no idea what to go with! 

(Un) fortunately a change in circumstances means I don't have a garage big enough to pull the engine at the moment so I have plenty of time to decide!

[jacobtns]

On 28/04/2021 at 04:32, James said:

My highly tuned 2 litre has approximately a 2" butterfly — when you work out the area it's about the same as twin HS4s

An SU has a relationship between inlet size and vacuum — fundamentally doesn't work properly if too big.

 

Cheers, that would seem to confirm cd150 are sufficient. Are you running an efi set up?

[James]

6 hours ago, jacobtns said:

Cheers, that would seem to confirm cd150 are sufficient. Are you running an efi set up?

Yep — https://sites.google.com/a/mintylamb.co.uk/triumph2000efi/