Yes definitely hugely different designs. It would make sense also if the general efficiency of the design (merge angle/scavenging etc) influenced the low flow range of behaviour more than peak flow, especially given the turbine isn’t really spinning up the compressor much at that point and it’s closer to NA than turbocharged in terms of engine dynamics. On the other hand It’s a little odd to me that this could be the case, though, as despite the manifold design differences they all converge on the turbine and hotside which will present the same restriction regardless of the manifold used between the cylinder head and the turbo.

It just seems like when you feel the car with larger runner manifold, the handover point from NA to Turbo ‘modes’, if you will, is higher up and the transision feels smoother.

When on Boost / at peak load the exhaust gas velocity being higher in smaller runner designs would transmit more exhaust energy to the turbine, up to a point where the gas flow is impeded (folks have thrown out some numbers like 650-700hp). So perhaps for me at my far lower than that power level I should use a 1.25” runner manifold that’s still more efficient in design than the oem log but not a big flow design. Probably splitting hairs though, as @mrfreds testing showed.

 

For 1.25" tubular manifolds, I think that the sharp transition from the large exhaust port to the much smaller 1.25" tubing for the manifold that I tried is a significant contributor to the difference in feel.

 

Most of the aftermarket manifolds I have seen use short transition in the cnc machined flange that not only makes a transition to a smaller cross section round tube, but also transitions from oval to round. I think this is the the worst design possible and could throw in some unwanted pusle reflections in the mix. Also, in the case of full frame systems, I think it is a bad idea to go from a large exhaust port down to small dia tube and then open up to the T4 (for example) port area. just keep the port area constant and make the transitions as smooth as possible..

As for the subject of feel... We all run somewhat long lift and long duration cams and by having such a restrictive manifold we maybe get into a situation where the manifold "negates" that overlap and shifts that tq peak back down...

 

240Z Twin Turbo I believe the following information would be beneficial to our other members http://morrisonfabrications.com/tech...sition-flange/. These guys have a lot of respect for Ron Shearer's design fundamentals, I found their cut away photos very insightful.

 

Wow, that is a nice looking manifold. Totally addresses the port-to-runner transition. I think that will be my next manifold after my crappy GTSpec manifold cracks a few more times.

 

Mr Fred,

I agree it's a stunning looking piece of hardware. The oval entry is so well executed, especially when you see the cut aways for both the 1.25" & the 1.5" primaries vs the ported transition manifold flange that other top level shops utilize.

I'm hoping Father Xmas will leave one under my tree, however; I just bought some cams & springs, I'm pushing my luck.

Thank you for all the work you share with us, I truly appreciate it as other members do too.

All the best for Xmas mate.

 

I had not previously seen that so thank you for sharing. It would be interesting to see the difference between having the transition and not having the transition in terms of response and power. My manifold is a small runner and it has the transition done in the flange, which is of course very abrupt. If I do another manifold I will have a buddy of mine CNC a flange with a proper transition similar in design to what is offered by AMS for the GTR shown below.

 

On the T4 manifold I build I ovalize every tube and have a special tool that forms the oval end of the tube (even though only cyl nr 1 starts with the straight tube, the others start directly with a bend) so that it is a natural transition from oval to round... It is a pain in the a$$ to do due to thick wall...

 

Happy New Year 240Z TT,

You're very welcome, sorry for the slow reply. That's looks as good as it gets, great looking design. If you had your mate do something similar, that would be amazing with the flange having an extension where the oval to round transition is smooth over the longer distance. You're a lucky man, good on you & I hope it works out well. Post up pics when you can.

 

kikiturbo Happy New Year,

You're manifolds sound very well designed, the process would take extra time doing the ovalization, but; the end result would no doubt pay dividends. Do you have any photos of your work you'd like to share.

Thanks mate.