Well that kind of explains alot. My low end feels the same as before, maybe a little better, due to the other mods I did, that got negated by the porting. Also the lumpy idle now, and the backfiring, which I kind of like. Oh well, live and learn.

 

You really didn't mean to say overlap did you?

 

ahh you guys are making no sence

 

Yes and no. From a technical aspect, only porting will change overlap. However, many confuse reversion and overlap so I covered the misnomer too.

 

So yeah weve had alot of answers and no explanations, and no proof that cutting it out will effect the performance at all.

 

http://www.yawpower.com/Flow%20Testing.html

see #1 little more than 1/2 way down

 

whoa ok that makes sence, obviously i would need a flow tester to actually perform any porting, although i dont think il need one to cut the slits.

 

Got the intake manifold off and now ive begun the "process" What a pain to get that gasket off, not too bad tho. Im going to make the grooves tomorrow and paint the intake itself, aswell as make stainless blocking plates for the emmissions.

 

Started the procedure today, making the grooves with a 1" cutting disc from demel, as it got smaller i used it for the smaller ports. I sanded the coolant passages to make them smoother, they were as dirty as the f word.

Im going to be blocking off all the excess passages now with jb weld and making my blocking plates. Sadly i dont have any acess to stainless so alum will just have to do. Although it wont matter because impainting the intake red.

Is that plate between the intake and engine nessasary. Does it really stop any heat, it is only plastic....

 

Well thanks for the answers on the last post hahah, dont worry. I got it all back together with the new blocking plates and blocking plugs. I did all the porting myself with a dremel and painted the intake with engine block paint. (409 ford) red. Worked great. After sealing everything up i noticed a definate increase of power in the highend and better idle for low end power. Yet all this could have been due to the fact that i might have had leaky o rings before the gasket was replaced, but the car has never ran as fast or as good. I had to actually idle down my car 400 rpms after changing the gasket because it seemed like the engine was getting more air. The port was a good thing in my mind.

 

Did you take any pictures of the work that you did?

I am debating on what I want to do to the intake manifold on mine. I am going to rebuild the carb soon and I plan on doing a small bit to increase airflow (removal of tabs and such) but I am not sure how much I want to play around with the intake manifold. Should I go all out and make a large plenum under the carb, or just do those groves?

 

I've port matched my intake at the same time as doing the rats nest and headers... it seems to me that it spins faster, ie tach raises more quickly, but I think that the lowend torque may have suffered a bit. If I had my druthers, I'd by a stock intake and switch them out to really see the difference the porting made.

 

Yeah i got pictures, il upload them in a few days.

My only recomondations are that to not port match the primarys like its been covered many times on this thread, yet just make the grooves and rid the intake of the shutter valve and any unnecessary ports from the emmissions. I also knife edged the runners where they meat the engine, yet all of this isnt forsurely going to work or have any benefits unless you have a flowtester. I didnt have one myself but the work i did definately helped with gas milage and some flow.

 

Ok reversion is not a bad thing nor can you prevent it ever! Smoothing the transition between the forward pulse and the reversion pulse greatly helps in reduction of turbulence into the manifold and the aftermath of forward movement into the turbulent air.

Overlap is simply the two ports being open at the same time were the leading intake pressure zone can be caught into the trailing low pressure zone of the exhaust and aid in pre charging of the intake and drawing out that of dirty left over gases to increase power.

The harnessing of reversion timing is why the renesis makes so much more power. This is also the concept of DEI tuning seen in the later 13b motors.

This being said port matching the intake manifold is always a good thing however yes you do not want to kill the velocity if it is prevented. Your power band is going to based upon your port timing and length of the intake runners to determine the amount of time the pulse will travel between its lead and reversion.

Cutting the channels in the manifold has not been solved to my knowledge however I was in a discussion not to long ago about it. The best conclusion we could agree on why Mazda cut channels in latter models was to air in low RPM vacuum and worked bettor then swapping spacers.

Here are some pics of an intake manifold I did.

 

I am posting again because I wanted to make sure no one go the wrong impression on my ^ post. The biggest key to intake design is velocity you do not want to make drastic changes that will kill the velocity. The above example of intake porting is not claiming any improvements, the entire runner system is ported to keep flow higher then just porting them down however the large bowels at the end may cause large drop in velocity hurting power. The above photos were shown and the manifold was ported to be used as a documented piece and test results. Be aware how DEI and reversion work and keep in mind intake velocity, do your best to find a good medium between all of these and not work to just one. There is a reason the S ports are nearly matched and the P are not from factory! The results of this excrement were that the stock nikki carb can in no way flow enough volume to utilize the port size of the ^ manifold. It would take boost to even come close to utilizing runners of the shown size. I like the bowl size of the 12A motor more but the timing is to short as well to utilize such a large P running setup.

And have fun on your next porting experiment!

 

Port matching the intake to the irons reduces the velocity though the entire intake runner, not good The step transition between the intake and irons maintains the highest velocity possible. There really isn't any reason to port match unless running high boost. If anything, I would round off/ease the square edge on the intake, but not much at all. Only enough to reduce the turbulence eddys at the squared off step.

More benefit would be gained by working the runners in the irons themselves.