1.25" vs 1.5" exhaust manifold comparsion test
#31
Evolved Member
The ported OE manifold and the Toxicfab part represent two different designs. The external and material differences alone will result in differences in exhaust gas velocity, resonance, and heat. As such, we have no way of knowing how much of the perceived difference between them is strictly due to differences in internal runner dimensions. It is reasonable to assume that the OE part generates a higher pressure ratio at virtually all operating conditions, which affects VE globally.
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.
The following 2 users liked this post by mrfred:
EvocentriK (Dec 23, 2019),
kikiturbo (Dec 14, 2019)
#33
Evolved Member
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...
The following users liked this post:
alpinaturbo (Dec 16, 2019)
#34
Evolving Member
iTrader: (4)
#35
EvoM Guru
iTrader: (50)
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.
#36
Evolving Member
iTrader: (4)
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 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.
#37
Evolved Member
iTrader: (25)
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.
#38
Evolved Member
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...
The following 2 users liked this post by kikiturbo:
alpinaturbo (Dec 18, 2019),
mrfred (Dec 19, 2019)
#39
Evolving Member
iTrader: (4)
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.
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.
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