Ive almost finished my exhaust manifold for my red top. Its a HKS knock off. How much average hp and torque gains should I expect? Also what other benifits can I expect? will boost come on sooner? and harder? etc.
Ben
i was reading a writeup on SAUabout this very subject
If you believe that all Jap made bling items are best DON’T READ BELOW.
Flow Bench Test Results RB26 Exhaust manifolds. Test were done on a proper flow bench test at 25 inches of water. All figures are CFM.
UAS Extrusion Honed Factory Manifolds…182.7…167.4… …179.3…
Factory Manifolds…155.7…138.2…150.1. …
Stainles Manifolds…160.4…138.8…170.0
To further put in perspective the extrude honed ones are also match ported and different amounts of extrude honing is done in each runner to bring up the most restrictive ones and less on the better flowing ones. Flow bench tests are done to test before and after. This helps even up and balance the motor when in real time, whilst increasing overall flow. Less restriction means less heat and more free power and less stress on the motor.
… Max Variation…Average.
UAS Extrude Honed…15.3…176.46
Stock…17.5 …148.0
Stainless…31.2 …156.4
Plus stainless manifolds are more likely to crack, they do radiate much more heat and can’t be HPC coated to well if at all. Can’t improve on stainless unless roughly made and have jagged edges which these did not, and can’t extrude hone. More prone to cracking.
Factory ones unlikely to crack and don’t radiate as much heat and can be high temp black coated so will flow a fraction better in reality and perform better as they won’t cook the comp cover as much as stainless. As a general rule of thumb every 7c increase in temp you lose 1% of power and require larger intercooler to cope with increase in air temp coming out of compressor. Best part is much cheaper than expensive Jap Bling ones. It is possible that other stainless manfifolds perform better although I don’t think they would.We have simlar results which we will release soon for RB25 manifolds, waiting for the extrude honing to be done on a set to get exact figures. We have figures for stock and two stainless types tested.
now i know this is on a gtr but the idea is still the same.
Hi John, this might sound like a strange question, but which way did they test the flow? In the direction of the normal exhaust flow? If so, how did they block off the 2 cylinders they weren’t testing? If they blocked off the 2 non testing cylinders at the cylinder head flange, then I am not surprised that the centre cylinder flow less. The aerodynamics of the manifold would cause that.
The only real way to test flow equality it is with all three cylinders being used in the same time frame as the cylinder firing. But that would be difficult as the primary runners are not the same length, hence the pulses would reach the secondary pipe at different intervals, ie; create interference.
Perhaps a better porting result would be achieved if the primaries were of equal volume, as this would give the same result as equal length. That is where flow testing of equal length primary pipes, as you would find in any decent stainless steel pipe manifold, won’t show up their true advantage. Flow rate is not the only gain to be had from equal length primary pipes.
An example, the GTSR Group A exhaust manifold barely flows any more than the standard RB20DET exhaust manifold, but they make 25 rwkw extra. Why? Because of the extractor effect of the equal length primary pipes
you can read the whole thing at
http://www.skylinesaustralia.com/forums/showthread.php?t=77082