Porting AJP exhaust manifolds

[itiejim]

I'm gradually getting to the stage of putting my AJP back together and have been looking at the exhaust manifolds. I'm amazed at how poor the match is between exhaust port and the manifold - they're totally different shapes

The heads are already ported and gas flowed and I wondered whether any clear benefits had been identified in carrying out a little fettling to the manifolds - though I think it will be impossible to make them match perfectly...

Anyone done anything with them that they'd like to share?

[Steve_T]

The mismatch may well be intentional to reduce reversion, a perfect port match may not improve things.

[itiejim]

Steve, I wondered about that, however, the restriction appears to be in the manifold rather than the head - ie the manifold overlaps the exhaust port rather than vice versa.

[Steve_T]

Tbh what we need to understand the heads is a flow bench. I would expect that most of the restriction is at the valve seats, considered work in other areas will have a positive effect but not as much as getting this area right.

[Jackal83]

Anyone got a picture of this mismatch????

[Nickccc]

The manifold is circular, the exhaust port is a d shape.
I'm with Steve the valve is the bigest restrictor in the system. I doubt
there's anything to be had, also you would have to considerably open the
port up, who knows what's behind there. I don't think myself or Harry touched
this area, so probably not worth it. Feel free to have a go, just don't junk
your heads in the process.
You'd probably be better off matching the manifold to the d port on the head.

Edited by Nickccc on Wednesday 30th December 17:11

[itiejim]

I'm away in Rome atm but can take some pics when I'm back in the new year.

Effectively, the exhaust port is not round, whereas the exhaust pipe and manifold flange both are. This means that a part of the exhaust port is shielded completely. In addition to this, although the manifold curves down immediately from the flange, the thickness of the flange itself causes a significant obstruction where the internal edge of the flange sticks out into the flow.

Also, the standard of the welding where the pipes meet the flange is very poor - they're welded on the outside but on the inside you can see the pipes sticking through the flange and a gap between the two (this is obviously filled with weld on the outside).

Basically, there would appear to be lots of areas where improvements can be made but I didn't know if anyone had gone to the effort of trying to see if there are any tangible benefits!

[itiejim]

Nickccc said:

You'd probably be better off matching the manifold to the d port on the head.

Edited by Nickccc on Wednesday 30th December 17:11

Yep, that's what I want to do, the heads have already had sufficient work and I can't risk wrecking them!

[ridds]

I did mine when I welded up the cracks and had them coated. TBH it won't hurt opening them up just be careful you don't go through.

[clive f]

these are the flanges I had laser cut when I made the manifolds for my car, the shape is exactly the same as that in the heads, the restriction comes when you get to the manifold pipe itself, you can see from the pic below how the tvr manifold pipe is much smaller than the surface area of the flange.



It takes a 2" diameter pipe to cover the d shape in the flange, but 2 " is difficult to accomodate between the heads and the chassis, I used a 2" to 1 3/4" conical reducer which helps the gas flow.
personally I think Al Melling designed the engine with 2" headers in mind, the calcs show a 2" diameter pipe being best for outright horsepower, obviously pipe lenghts ect then having an impact on where you want your torque, but I don`t think mr melling banked on tvr putting his engine into such a restrictive engine bay.

definately make your flanges a good as match as possible to the heads, without damaging the pipe wall thickness, it will only be better than what it is already

[longbow]

The ACT manifolds are also port matched.

[Nickccc]

I've got the ACT manifolds so maybe that explains the hp gains on my car,
Harry's got them aswell so it must work. I saw the old manifolds from the Boss Cerb
they are matched aswell.

[itiejim]

Thanks folks, I'm not ready for another £1k of investment in the ACT pipes atm but I'll definitely have a go at matching them as well as possible. I'm also going to get them coated - outside only I think unless anyone recommends otherwise?

[itsallyellow]

The manifolds on the race car are matched, with equal length primarys etc. They are 2.25" aswell. Certainly seemed to work well. No back to back tests though

[itiejim]

Are they bespoke or off the shelf?

itsallyellow said:

The manifolds on the race car are matched, with equal length primarys etc. They are 2.25" aswell. Certainly seemed to work well. No back to back tests though

[itsallyellow]

One offs made by oz engineering. However when i had them made he said he kept the patterns etc to do other replacment sets.

Mike

[itiejim]

Thanks Mike, was it these folk?

OZ ENGINEERING LIMITED
29 MANCHESTER STREET, BARROW IN FURNESS, LA14 1QR

[longbow]

I don't think the race manifolds will fit a road car due to the fact that they route forward.

[itiejim]

Ahh, thanks. Back to the old packaging v performance compromise!

[high52kojak]

I have just had my manifolds off also and was shocked at the size of the step between exhaust and head. I had mine ground out to a similar shape to the port on the head. I also had them welded up and ceramic coated, thought it would be rude not to.
See my pic below of the standard port before Raceproved tweeked them. The photo is on its side but you can still see thge line where it matched up to the head. Thats quite a step in my view!