Ok guys. I'm in the process of freshning my motor and I'm going to replace the rotor housings. I need really good exhaust ports to help with spool. I'm hearing that I need to keep the opening close to stock. What about the width? How wide can I go? ...and th closing: how high can I go before it hurts me? My old ports were flat at the bottom and slightly rounded at the top. My ports were probably opening a little early. I'll get pics up later. I'm considering a square port this time for the extra area. What do you guys think? This is a half-bridge with a 67mm(72mm with 1.22ar back side).

 

Porting is like politics. Despite the unarguable port timing methods you're going to have to pick a style and stick with it. For now (coming from a street engine perspective) I'm quite content with a flat opening at the bottom and an oval closing at the top with a 2mm radius.

Match your ports to your needs but I suggest that you impact the exhaust ports as little as possible. I personally prefer to "adjust" the closing port time more than the opening to preserve the combustion process.

The hardest part to internal combustion is getting the air into the engine... If you didn't know that or know what it means I suggest you consult a professional to pick your combo.

I suggest you look at some of BDC's posts as he has very good insight to the process. There's some other very nifty guys out there but their porting techniques I consider to be once again "politics."

 

my "race" exhaust ports used to keep the oringinal shape so as to maximise port area V the timing
[ these where turbo mild ported 6p engines , or very large extend ports ]
and would go out to 10- 11 mm from the edges, and take the roof up about 3mm,, no insert

this brings boons ( over the stock port and insert ) in the mid range TQ, but does make for a louder and more loping idle

IMO if its not going for 300 + ATW HP,, then its not all that necessary , and the stock port is AOK

 

....

 

....

 

....

 

No pissing on peoples threads.

~S~

 

Sorry. But that guy should be banned of all forums.

I agree with bumpstart with exhaust ports. Retaining original shape. Width is about right and lifting the port is also about right.


Everyone has a different style and will yield slightly different results.

 

3:stock-PineApple medium-Japanes race.

 

Okay...are the insert and sleeve the same thing?

 

yes,, note that when you remove the insert you may need to port match the exhaust manifold runners to suit


many US builders will retain the sleeve , for velocity and for shielding the engine cooling system from some of the heat
but i think there becomes a point where its a restriction and it must go
and there isnt massive ill effects or reliability issues
i have done 100 000 km on one set of housings done thus



porting in progress-



finished-




my most extreme port ( a little squarer than above ) alongside a stock one



sequence showing a port taken to specs in my top post,, compared to a stock one




stock port,, with the insert removed closeup




a profile showing trialled port progressions-






and to show i even tried the alternatives--

oval closed ports,,interestingly a smoother idle and most definitely quieter than the abrupt shut ports shown above
- but not quite the same response out of the same turbo, and down a little on top end power over the abrupt shut shaped ports above

 

Here are some of the ports I have tried and had good results w/ turbo cars. I am sure some would disagree, but like I said it has worked great for me.

I have a photo a FD exhaust port by Rick Engman. He might know a thing or 2 about these motors. It is in a bitmap format which has to be small to be attached to a post. I can email it to someone if they can post it larger.

Next few are a couple I have done. I try to port down as little as possible to prevent loss of the power stroke. Again some people port down more than I do. I will port down a little on a turbo motor, but I do not port past the bottom of the bevel on a N/A motor.

Anyways onto the pics

 

bumpstart,

This is a big help. Thanks.

How high are the square ports?

What are the pros and cons of your "most extreme port " compared to the ports in the second pic? Loudness is not a concern. lol

 

IIRC they went up 5mm , the angle of the pic is a little deceptive

pro- makes the most of port area V timing change
con- took WAY too much time to do for relatively small returns beyond the time invested already in the other port

pro- very abrupt close has some benefits in spool
con -same shut brings a loud bark while the OEM taper close and further rounded port tops bring more of a drone
( on the same exhaust system )

rounded tops and the tapered edges may well reduce shock on the apex seal
though generally the results there are inconclusive,,, as other reasons have made for any fails


i think for almost double the man hours in the fine finishing ,, the extreme example should be reserved for those wanting the last poofteenth
but i dont think that the recommended port has yet reached any limit to make the extreme port style necessary

rounded top ports IMO only serve ( in turbo engines ) to temper the noise and reduce shock on the apex seal

however,, in NA application,,a different kettle,, and the rate of close and degree of overlap may well be critical to make inlet port interactions at certain RPMS

it is in NA application that you will see the rounded ports being more common as they tailor that interaction by their shape

 

Interesting!!

 

Graciously provided by RotaryInspired and simply converted to a jpg.

Interesting how it seems to run contrary the "maintain the port-opens timing and increasing the port-closed timing" perspectives. It almost to the point of being a foil to the Japanesse Mild Race porting earlier in CEWRX7R1's post.

 

Agreed.


~S~

 

Paul Yaw taught me similar concepts as Engman's ports also...

 

Whats the diffrences?

 

i would expect more exhaust energy at most rpms with some trade in TQ before that turbo spools
i also wonder if yaw also uses a little less timing down low off boost to get the turbo on earlier

and thus i would surmise that the foil to the point

is that one camp tries to make best of the exhaust flow in terms of area
whilst not compromising the engine power stroke especially at slow burn speeds
and so strive to keep off turbo TQ down low as a primary design feature and conceding only EC timing and hence also some volumetric efficiency at some rpms due to EC timing overlap with inlet open timing

and the other concedes that the engine power stroke win is irrelevant
in the context to getting TQ from the turbo working sooner
and so changes EO timing while minimising losses of inlet to exhaust with EC timing


the difference i suspect is in the driving sensation
one with more off throttle TQ
the other with an earlier and more savage kick from the turbo

my main concern,, what is the difference at WOT in the exhaust temps?
and wonder are yaws exhaust housings larger than the norm?

PS
might well trial that one soon to see how it compares to the other two styles,, looks much like the RB 13b template upside down

 

This thread is fascinating.
I just cut a pair of housings for a build using the Pineapple medium street port templates.
Deeper on the leading edge and about 1mm more (rounded) at the trailing edge which is a bit hard to see in the pic.



FWIW,
Crispy

 

Things I have noticed from a rounded top versus a squarer top are in the mid range and top end.

The rounded top exhaust ports seem to produce more of an effect in the midrange power 4-6K, while the the squared top has more effect on the upper rpm 6K+ all else being equal.

On idle I haven't noticed any real difference between the 2.

I am not the best at using words discriptively as I am a very visual person. Anyone else car to express the differences they have seen.

 

Can you clarify what kind of effect? Drop in torque? Drop in HP?. A shift in the power curve?

I'm exploring options and willing to try something new.
TIA,
Crispy

 

When I was experimenting on the ports it was on my own car. The car was street tuned and never saw the dyno, unfortunately. I wish I had taken it, but I never did.

The best way I could describe is like the effect when you port the intake ports w/ a later closing, and how it shifts the powerband up. The flatter top exhaust port has more of this effect. It wasn't huge but it was "part of the package" so to speak.

The rounded port closing was more rounded than what I can see in your ports Crispy.

Again, I screwed up by not getting any hard data and I wish I had now. I just don't like the number games on dyno's as sometimes I feel it is easy to get carried away by a number and not focus on the reliability side and how the car is running is all aspects. Again, this is my experience and why I stayed away on that build, but its kicking me in the rear now.

Hopefully before December I'll get some dyno testing in and see if I can show it on the dyno. I have it planned in my schedule anyway.

 

These ports should do good for you if I'm seeing the pic correctly.

~S~