I just wanted to share a rebuild I did recently w/ the rest of you guys. If you have any questions I'll be more than happy to answer. Sorry photos are off my cell phone as my wife doesn't like the SLR camera in the garage. I can't blame her there.

 

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Did you use a template to do the porting? I'm going to use the racing beat template to do mine. I also ordered NRS ceramic apex seals.

 

No template. I have built quite a few of these guys and know how far I can go. Be careful if you are doing this for the first time as there is not as much room for error on these plates as there is in the rx7 plates.

However there are some areas to clean up and help flow. Mazda did as good as you can do with casting these ports.

 

good job...!!!

 

Thanks

 

So how do the Renesis motors idle after a port job?

 

Very nice. You have to go very radical to change the idle. That or go super rich at idle. Both will cause it to lope. Of course the crazier you go on the port work the more fuel it needs at idle. This one runs like butter.

 

So far, we have not been able to port in enough overlap to effect the nature of the idle and who would want to anyway (unless one is incorrectly concerned with matters of vanity)?

The cool thing about the Renesis is that we have three intake "stages" and they allow us to get a little bit closer to a very flexible engine, in terms of idle quality, torque across the RPM band, and total airflow potential. At this point, the porting that is most effective will show improvements where it counts the most in the Renesis; from 3K-7K rpms (+/- a few rpms here or there).

People have a very strange way of viewing the RX-8, overall, anyway (just my opinion).

 

is it just me or do these seem very easy to rebuild?

 

My apologies to Rotary Inspired if I am barging in here;

The Renesis is a somewhat easy engine to build, generally speaking, but to build it in a way that will last much longer than they do from the factory or for more power-making capacity takes some knowledge, skill, and attention to detail. Like most other things, what our customers pay for are the areas where we builders have direct knowledge and personal experience. Each builder has their own versions/opinions of these and that is what differentiates one builder from another.

In my own case, all my rebuilds have come to me after being boosted and ruined. I built them for boosting purposes and have never lost an engine since.

The potential is available and there are a lot of good rotary builders out here.

 

This is correctly spoken. Some people for some reason want a lopey idle. Why, IDK.

[/QUOTE]The cool thing about the Renesis is that we have three intake "stages" and they allow us to get a little bit closer to a very flexible engine, in terms of idle quality, torque across the RPM band, and total airflow potential. At this point, the porting that is most effective will show improvements where it counts the most in the Renesis; from 3K-7K rpms (+/- a few rpms here or there).

People have a very strange way of viewing the RX-8, overall, anyway (just my opinion).[/QUOTE]

Correct no porting of the side ports is going to yield any increases under 3K rpms. You will have to go to a PP to see more power and torque in those areas.

No issues w/ you chiming in. I am one who feels that the more openly we speak about these engines the the more we all learn. A persons work speaks for itself and if it makes good power and runs a long time everyone wins.

The key to these things are the clearances. For example the side seals. On turbo motors I cut these to .02 mm and N/A I cut to .01. The renesis has a little more clearancing from the factory and at the same time the side seals shrink due to the heat trapped by the exhaust ports. This is one reason we see lower compression earlier in the life of the engine, besides the premature apex seal wear in comparison to older 13B's.

Just some random thoughts.

 

You said that you did not use a template to do the porting. So did you just port going by the shadow of were the seal rides on?

 

Yes you can get an idea of how much room you have from the wear mark on the side seals. You can also set up the front plate on the engine stand take a rotor place it on the front iron and then insert the eshaft into the front plate and rotor (make sure you have the stat gear in place or you will have major issues). From there you can rotate the shaft which will rotate the rotor. When doing this you can then put your fingers in the port and feel for the corner seals and side seals. From here you can get a good idea and then lay a piece of plexiglass over the port and draw your layout. You can now cut it out and set it over the iron and use the same test to make sure you have not gone to big before cutting on the iron itself.

Understand as you port towards the water jacket you are opening the port earlier, which is good and creates more midrange power and torque. Be careful here as you need to support at least 1/2 of the corner seal. I would suggest more support for your first time and go from there.

As you port up on the top of the port face you will shift the power band up in the RPM range. The key here is how you close the port. The closing edge must be radiused in large ports as the side seal will dip into a large port and the leading edge will collide into the closing edge of the port if it is not radiused. This will cause loss of compression and lead to another rebuild.

Also don't get over focused on the port face as the bowl inside the runner produces the biggest gains besides opening the port earlier.

You are more than welcome to contact me via PM and I can discuss it in more depth w/ you. If you have a set of plates I can even port them for you as well.

 

On side seal clearance to the corner seals what is the Minimum clearance? I have seen .016" is the maximum but no mention of min. I have built a few older engines (FB,FC,and FD) and have always kept my clearances at .002-.003"

 

Those clearances you talk about are in inches and the measurements I was stating are in MM. I cut mine a little tighter than factory as it aids in cold starts and building compression. On a N/A motor you can get away w/ zero clearance as long as the side seal does not bind up on the corner seal (great cold starts). The only time I increase to .05mm (.002inch) is when the motor is built for high boost as it gives a little more room for the seal to grow from heat. Hope that helps.

Everything you stated will work just nicely.

 

OK thank you very much. The reason I was asking about Minimum clearances was in my engine the side seal to corner seal clearance is currently about .015" and I want to get as much out of it as I can while still N/A.

 

The bowl is where the gains are in the renesis, you're right
A good port work should also not be considered as a mad grinding process only, there are times (and rpms ranges) where adding some material in said bowl may help flow.
Even if we disagreed in other circumstances i tend to like your approach. Have you got the lower intake manifold for that engine? Some work should be done to it as well. Removing the castings is no big deal, working the APVs for what is possible is "productive" (as much as porting a renesis is) though.

I don't like porting an engine without templates for a reason: accuracy.
Small differences in port dimension and shape can be counter-productive if you don't have an engine management with independent rotor tuning capabilities. The templates are not 100% accurate either, i know (what imprecise machines we are!) but using a cnc mill to port an engine is science fiction for a poor enthusiast like me

 

you will still only gain about 10 bhp max peak NA with porting over a fully optimized non-ported Renesis regardless, that's all there is .....

 

Agreed, that's around 16-20bhp over a non optimized built renesis though! I'd say it is well worth the hassle once you have your engine torn apart.
a 10hp difference is no joke around a race track and the overall beefier powerband is a good thing too.

If i didn't track my 8 i wouldn't consider any engine modifications during a rebuild except the usual longevity mods. I guess it all comes to the use one have to do of his car.

 

That motor is already up and going and running around. I did not port the runner of the LIM. The funny thing was that another buddy of mine had an 8 and drove this one and asked me why it was smoother revving than his. I had a chuckle over that.

I guess I should state that once I have one port finished how l want it I make a paper template off it and transfer to the other iron. I save all my templates I make this way for a later use.

Nothing is ever perfect when you let a human touch it, but we can get close enough many times.

 

The lim can benefit from some small amount of work. I never have liked the VDI and I did away with it, sealed it up and smoothed that entire entry barrel .
I have never believe this engine was really supposed to go to 9K anyway. To each his own i guess.
I do pull good g/sec of flow before 8K.
OD

 

Seems fairly happy at 9krpm to me...

 

trouble is--youre engine is not built for repetitive 9K running!
od

 

It hasn't exploded due to revs yet, 's fine by me :D