GTR Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
4,586 Posts
Discussion Starter · #1 ·
Nobody has been able to answer this about the RB26 Cast Manifolds...Is it because;

1, Nissan were trying to restrict the power to 280hp for the "Japanesse Agreement"?

2, Nissan did it to help spool up on Std turbos?

3, Nissan stuffed up? (much like the early oil pump crank drive)

4, ?????

:popcorn:
 

·
Registered
Joined
·
2,359 Posts
If you Google gas flow through convergent and divergent ducts it will explain why they make the manifolds convergent a bit boring but good for keeping gas speed up and temps down.
 

·
Registered
Joined
·
4,586 Posts
Discussion Starter · #3 ·
If you Google gas flow through convergent and divergent ducts it will explain why they make the manifolds convergent a bit boring but good for keeping gas speed up and temps down.
:runaway:Crikey!

I will read into it....But this would mean that porting them would be a bad Idea? What about if you are running larger turbos? (i.e 2530's)
 

·
Registered
Joined
·
265 Posts
this post is purely speculation.... ....



i got a good one for you guys if per say the speed of the gas comming in to the intake is at 500kmh the goes threw the intake valve to produce power then the exhaust valve is open but at that same time the intake valve is closed.. wont the gas be at around the same speed or some other speed because compression stroke gave it speed due to some physics law because the way i see it the gas will have the same speed in & out unless some restriction or modification into the combustion chamber could help scavenge those gas faster
 

·
Registered
Joined
·
3,481 Posts
:runaway:Crikey!

I will read into it....But this would mean that porting them would be a bad Idea? What about if you are running larger turbos? (i.e 2530's)
I've run 137 mph in the quarter on standard ported manifolds. 2530 turbos.

The factory gives you the standard gasket as a template .

Way back when, Mr. T old us to even use the N1 stainless manifolds, add material to the manifold,and port them more.
 

·
Registered
Joined
·
2,359 Posts
The convergent/divergent thing might be a good theory, but I think its more like them limiting power a bit.

I think you gain response and power matching it.
When I ran my 2540s I opened mine to match the gasket but on the smaller standard turbos I think it is best left
 

·
Registered
Joined
·
2,359 Posts
Its because the 2540's are crappy turbos. Mismatch of compressor wheel to exhaust wheel. Thats what causes the issue.

If you had a good turbo on it, life would have been different.
I was happy with mine no shuffle and good power, they came in a little late but they were the old plain bearing type
 

·
Registered
Joined
·
1,992 Posts
I'm amazed at how poorly the exhaust manifold ports match up to the head ports on that side. On mine the exhaust manifold overlaps the head ports by 5 to 7mm in a few places so theres a fair amount of porting needed on that face too.

I'll be fitting a set of standard but rebuilt ceramics back on mine in the next couple of weeks so I can use the car for a while on a few trackdays before hopefully having the funds to fit a RB30 with -10's on it maybe next year.
I have already ported the maifold to head face and also removed the sharp edges and casting marks inside the 'collector' part of the manifolds but left the manifold/turbo port the standard size as it matches pretty much spot on with the turbine housing entry.
I would have thought that opening this face up along with the turbine housing entry to the standard gasket size would raise the boost threshold and increase lag with the standard turbos.

I could open up the manifold/turbo port and also turbine housing entry to the the gasket face just to see what its like if anyones interested ? I won't be able to give a before and after dyno result unfortunately as the car hasn't been dynoed before and is currently pretty standard but when its back together it will basically have on it: modified twin turbo pipe, 2.5" id downpipes, 3" decat pipe, 3.5"exhaust system, M's filters, E-manage and 1 bar boost. Basically the maximum spec that people might run on standard turbos. I could give an idea of at what RPM I start to see positive boost appear and at what RPM I get 1 bar on the gauge, that sort of thing. Maybe get it dynoed at some stage in the future. Yay or nay ? :)
 
1 - 12 of 12 Posts
Top