The Triumph 2000 / 2500 / 2·5 Register Forum

Hi

This question may have been discussed many times, but I still would like to know if someone has knowledge of fitting PXTH604 manifold into Triumph 2000/2.5pi saloon. Let's decide that we talk of mk2 cars in this case, and let's forget the details of connection to exhaust pipe. We can also forget RHD related problems, because my car is LHD. It has original 2M100 starter motor. (I guess Lucas M418G would be a bit bigger.)

I have no commercial connection to following
http://www.rimmerbros.co.uk/Item--i-RR1400A
http://www.moss-europe.co.uk/Shop/ViewP ... dexID=6056

To summarise, is the PXTH604 a straight bolt on?

No, it won't fit. The primary pipes come down right where the main front suspension cross member is.
Talk to Chris Witor, he does proper 6 branch manifold for our cars.

Thanks!

I had to ask first here, because suppliers seem to be focused on other (sexy) Triumph models Answer is what I was already fearing of. It just happens that I might I have a used TR6 item available in my country where it can be checked before buying. (It might still be possible to modify the most front secondary branch (6/1) to give room for cross member.)

I've just posted something similar, here:

viewtopic.php?f=8&t=5087

The manifold I've got isn't like the Phoenix one in the pictures, it's a 6 to 1, not a 6 to 3 to 1. I can't find a pic of it anywhere.

We are going to attempt to fit it this week. Fingers crossed that it fits!

Hello Christopher,

you might like to have a look at this and possibly do more research.

Extract from Tuning Manual,

6- 1, these are for highly tuned engines, because resonance only gives engine assistance at high RPM. Back pressure disappears, when compared with the standard system. these two factors give a loss of high speed torque, but a lot of power concentrated in a narrow band at the top. It is more critical than ever that primary lengths are identical, otherwise there will be a series of flat spots and misfires up the range.

This immediately rules out 6 cylinder Triumphs, especially because of the impossibility of getting equal length primaries.

Also, later in the manual,

.... must use an exhaust design 6-3-1,. (NOT 6-2-1, NOT 6-1, they DON'T work)

The author is a respected if rather controversial figure but has decades of Triumph high performance engine experience.

Alec

I have a 6-2-1 TR6 manifold fitted to my MK1 PI.........

Yes had fabricate a bit and esp because car is auto

Oh, well those aren't very encouraging words for a 6-1!

I'm going to try it anyway, can always go back.

It's not a race car, so perhaps it's not as critical. I just want a bit more power (wherever the power is isn't such a big deal) and I no longer want it to sound like a Trabant.

I'll report back here on whether it fit and if so, how it sounds and drives.

And what exactly are 'primary lengths'?

Hello Christopher,

you haven't anything to lose unless you need to do a lot of modifying of the rest of the exhaust system?

Primary lengths are the lengths of the first section of a manifold before they merge. It can be very difficult for manufacturers to get this right and sell a product at a reasonable cost. I have seen some dreadful manifolds around. It is a very complicated subject and the principles are based on acoustics in pipes.

Good luck.

Alec

I see. That's very scientific isn't it. Very interesting. So I suppose cars with transverse engines are much easier to get the primary lengths right for, as all cylinders are the same distance from the rear of the car.

We're going to see if the manifold fits and then construct the rest of the exhaust system. If it doesn't fit then we'll put the old one back on. If it does fit and runs like &^*$ then perhaps I'll look into carb balancing/new needles and if that doesn't work then we'll put it back how it was!

The rest of the exhaust will be made up of things laying around, so apart from the time attaching it and welding it together, it's not a big deal as long as we keep the existing mountings too. Maybe we'll try initially with just a middle silencer and if that's too extreme then we can always cut the back pipe and add another under the boot.

My mechanic here in Germany often lets me help him and/or stand around trying to look useful. He's well qualified and I have a feeling that he likes undertaking unusual tasks on my old and unique (for here) Triumph. It makes a change from changing brake pads and fixing punctures on Fiestas. Together we were able to get my overdrive working a few months ago.

Everyone was right. It doesn't fit! Crossmember. To make it fit would require some extreme bodging and bashing to move the edge of the pipes away, so I'll leave it and sell the manifold to someone with a TR6!

How did you get on with yours TRPi?

Looks like Witor is the only option, which is fine but with VAT and postage to Germany it's going to cost a small fortune.