So I am in the final stages of my build and I have had lots of time to think about extra mods. I have I medium sized street port on an s4 motor pinned with s6 rotors. I am running a bnr stage 2 managed by a microtec lt10. I am shooting for about 330whp. Is it going to benefit me to port the s4 manifolds? If so what will that do for me?

 

I dont know on a rotary but I know on regular piston engines there can be a lot of power to be made from ths. Its not so much the larger ports that gain anything but more of getting out casting flaws. I did it to my 4runner many moons ago and I dont feel I gained much actual power but it smoothed out the whole power band it felt like. Granted my 4Runner only made 150 horse so if I gained lets say 10 I dont feel it would be too noticable. I dont know much about turbo applications either, this may be a whole different story when theres pressure in there rather then vacuum.

Edit; My stock manifolds were terrible looking also, there were burrs all over the insides of the runners and it looked like a 2 piece construction because there was a line the whole lenght that appeared to be where they were put together. Hope this helps

 

I doubt you gained 10 hp on the 4runner. Not trying to be rude but your example isn't realistic.

For the thread starter, No it is not worth porting your stock manifolds, especially if your horsepower goals are 330hp.

 

There isn't enough wall thickness to do much with. The runner length is the problem for big top end numbers.

 

If you already have the manifold off the car, polish the inside of the runners with a 40 and then maybe an 80 grit sandpaper roll. All the areas after the fuel injectors shouldn't be too smooth because supposedly that hurts atomization of the fuel or something. I'm not sure why that is; it doesn't make sense to me, because one of the main points of fuel injection is to keep fuel droplets from sticking to the walls of the manifold.

As far as reshaping some of the ports, well I don't see much of a gain there because you are just going to introduce a step change, where the diameter gets bigger then smaller again. I wouldn't tear down the engine to the point of removing the manifold just to polish the inside of the runners. That's a lot of work for questionable gain.

how do you figure that?

 

A smooth surface will PROMOTE droplets forming in a moving air environment. small imperfections create a layer of turbulence (very small layer) that prevents fuel from forming droplets on the walls of the intake manifold.

 

Basics of tuned intake runner lenghts
The new R1, aprilia'setc have intake runners that get shorter as the rpms increase.

 

Mazda did that 20 years ago to win Le Mans.

 

Fair enough.

The s4 T2 intake manifold has the shortest runners of all the turbo 13B intake manifolds. So clearly there's more going on than just that--the port timing is different than the later engines, and it has the least "lift" in terms of the physical area of the intake port runners. Compare the 13BT to its opposite in terms of design and dimensions, the 13B-RE. The s4 also has a significantly different plenum design than the RE or REW which are better on top end power.

The tuned runner lengths are found on the s5 nonturbo and Rx-8 engines. The VDI system (S5, Rx-8) and variable fresh air duct (Rx-8) have longer and shorter passageways depending on rpm.

 

Well yes Arghx,
There are multiple contributing factors, not JUST runner length
I think the difference of the ports probably make a lot more difference than the intake manifold simply could, right?
I didn't know the RX-8 or S5 had variable tracts, that's interesting!

 

Thanks for the input guys i dont wanna waste time on anything that is not gonna be worth it.. Done that plenty in my career as a rotorhead already lol! So how bout switching to S5 mani's? I have heard of guys doing an FD manifold but heard it can be complicated. Would staying with the stock S4 manifold be best then?

 

People have made over 450whp on stock port motors. You have a street port already, and only are looking for 330whp. Leave your manifold alone. There are no worthwhile gains to be had here.

 

General rule for cutting restrictions: Find the narrowest part and widen that, or if you can't widen it only then do you bother smoothing out the path (make direction change more gradual). The restriction increases dramatically as area decreases. Everything wider will be insignificant by comparison. Like a bottle with a bottleneck.

So look at the ports, see what's as narrow as the ports or in the same ballpark, and worry only about that (if there even is anything that narrow). Even something twice as wide will only be 1/16th as important.

 

s5 lower s6 upper thats it

 

i though tthe main advantage was less air friction with the walls of the manifold. kind of why golf ***** have dimples. air-air friction is less than that of air-metal


i have ported manifolds, but i cant tell much difference. maybe 5%?

 

I highly, highly doubt I gained 10 horse as well. Was just saying the gains are minimal, if any. And to add to that, you never wants a gloss/mirror smooth surface on the intake, you want it semi-rough or the airflow will get 'lazy' and wont acheive very good mixture of the air/fuel. You want it to 'swirl' in the runner.

No, its not worth it, unless you have a crazy ammount of time on your hands. I just happened to have a extra set for my 4Runner, and was out of school working part time and had more time then I knew what to do with any decided to try it. If I could go back I wouldnt have done it and ordered a 5 minute abs workout routine lol.