zxrazorxz

so i got most of the work done porting my exhaust housing and i put them next to each other and it seems that its not much different.. anyway.. i wanted the clubs opinion on the port and advice on what i should do to make it better

thanks

PercentSevenC

If it were me I'd square off the closing.

zxrazorxz

oh?. how come you say that .. i just used my pineapple racing ep3a template is there benefits to squaring it off?

PercentSevenC

More port area without changing the timing. I've also heard claims that square ports spool turbos better than rounded ones. Though if you have any reading material that contradicts me I'd love to see it. There doesn't seem to be a whole lot of information on exhaust port shape out there.

zxrazorxz

yea i noticed there wasnt alot of info on what the best shape was. but thanks for the input.. what about the chamfer do i need more?..

PercentSevenC

Hard to tell from the pics. The factory bevel is ~2mm, which is what I'd try to match.

RotaryEvolution

iTrader: (30)

most people who have attempted squaring off the trailing edge reported no real gains in response or top end power, it just affected idle quality and made it more lumpy.

you're not talking about much more port area by squaring them off, but it does have adverse affects on airflow. if square trailing ports were superior i would really have to ask why no one uses it.

2a+RoN

Adverse affects on airflow? Could you explain or post some evidence of this? As far as I was taught by someone who spent way too much time on a flowbench, there were some good flow benefits of having a square trailing edge.

PercentSevenC

Karack, I think you may be misunderstanding what I mean. I have a very hard time believing that you would honestly say "no one uses" that type of port, because the majority of exhaust ports I've seen are like that, including the factory ports and ones done by some very big-name engine builders. Perhaps you thought I meant making the corners of the ports sharp 90 degree angles? What I meant was simply to have a straight closing edge rather than the long arc seen in zxrazorxz's ports.

RotaryEvolution

iTrader: (30)

i'm not going to go get a airflow bench to prove a point. besides, there is boosted engines, non turbo engine and actual combustion to take into affect, most of which put bench flow diagrams in the "does not apply" area. you aren't dealing with air directed at a port, you are dealing with a volatile combustion process with air moving all directions.

sure airflow bench test result give a general idea as to the maximum airflow capability of an airflow path but there are far too many other variables to take into account for.

this is like arguing as to which is superior: smooth intake runners or rough ones. who has the time to run a rounded port on the dyno then recut the port squared off then retune the engine to provide results? which also will vary depending on the retune which renders results inconclusive.

hopefully you can see that the only way to tell the answer to your question is a very vague answer to which a few horsepower may apply at the cost of idle quality(this is known to be true). so it depends if the OP wants to attempt to see if it helps at the cost of idle quality or not, to which he may never truly know if it did help power levels or not.

what i thought we were referring to was a box edge for the top of the port. i realize the stock ports are rather flat but they do have rounded edges.

PercentSevenC

My large streetport engine's exhaust ports have a straight closing edge and it idles smoothly at 800 RPM (and could possibly go lower if I didn't have such a crappy carb setup). So I wouldn't say that they are "known" to cost idle quality.

RotaryEvolution

iTrader: (30)

no need to beat the horse again, there's plenty of threads about porting on the site already. you can also see examples of some of the "box" ports.

https://www.rx7club.com/showthread.p...pstart+porting

Jeff20B

iTrader: (13)

Percent's on left and stock (R5) on right. Squaredish closing edge.

2a+RoN

You stated it caused adverse flow affects, so I was just curious as to where this came from. It sounded like you had first-hand experience or facts stating such. No need to buy a flowbench, although I think a lot can be learned from them..

The one that taught me a little about porting did have the time to test on the dyno, and said he found most of his power in exhaust ports.

PercentSevenC

Thanks Jeff. I knew that pic was around somewhere, but I couldn't be bothered to find it.

RotaryEvolution

iTrader: (30)

i don't doubt it, my comment was aimed at more squaring of the port over even the stock squared off port closing. i generally use the stock port closing edge as my starting point and simple expand it from there. the opening edge is where alot of the controversy comes from, does a more rounded edge produce better results or a squared leading edge? no one really seems to know.

biggest problem is there isn't much room to play with without modifying the port sleeve, omitting it gives alot more room to play with but most manifolds are made to use the sleeve otherwise you have the exhaust gases trying to taper down to exit the manifold, this also causes flange warping and gasket blowout issues.

2a+RoN

I made my own sleeve to account for exactly that. The stock sleeves flow like ****, and as you said, omitting them comes with its own sets of problems.

Percent, that port looks pretty good, reminds me of the port my boss did for a customer's EP road race car.

zxrazorxz

whoa LOL looks like a heated debate, I appreciate the info about the straight closing edge, but these templates came from rob at pineapple racing, an also well know builder/shop maybe I'll give him a dingle