OD's engine build
 

Ok. Lets get this started.
Because of a recent unexpected happening, I have done a 180 degree turn from selling out to keeping the car and building an FI RX8 engine.
The reason for this thread is because I will be going down the road less travelled and some folks may be interested in what all was done and the results.

Yall know I love the road circuit, and I use my car for frequent DD. Not all the time, but multiple times a week. This car is built to be enjoyed--right? So my demands on the car is a frequent street driving with 3-4 track events a year.

A little history. I have blown a few engines, some as a result of my own learning curve ( yep I was stupid) and some from just plain bad luck. My engine's have been pretty fragile it seems. Least little thing and BLAM!
I have a street tune per Cam at Pettit racing and when comparing it to the ones I can see --it is right where it should be?
My cooling system is great, my fuel supply is the 09 fuel pump assembly and I have never had a problem with pressure or a/f's.
All but one engine have blown on the Road Track, all on the back straight at Road Atlanta--its the highest consistant load area the car experiences with accelleration from 55 to 140 in 3-4-5-6 gears ( you would think fuel pump--right? Buts its not). That has been looked at and fuel delivery is OK.
My self imposed redline has been 7.5-8K
I do run a snow water meth set up.
Sparkplugs always look great.
We cant figue out what is happening. Its not rotor specific It could be front, it could be the rear.
Doesnt seem to be the amount of boost related--blown with 7psi and blown with 10.
No misfires seen.
Running high test pump gas with approx 4% ethanol content per test at gas pump.

l No warning of problems--just a little stumble and then the skip of death--takes 1-2 secs.
Last engine I popped a vacuum line and that caused a stumble, studder and then it blew.


Ok-- with all this in mind It seems my engines could use a little cushion?.

So I have decided to follow the footsteps of Rote 8 and have Pettit (Cam) fit the rx7 turbo low compression rotors into my engine. That will lower the compression ratio to 9:1 versus our 10:1.
My Pettit blower has enough Oompphh to it to flow the amout of air I need to continue approx 300rwhp even with the lower compression rotors.
By using these rotors I see these benefits:?
1- decreased charge temps ( verified by Rote) without w/m useage
2- less static compression at TDC
3- have the taller RX7 apex seals
4- heavier rotor and lower rpm ( but still the same as my self imposed one 7.5K-8K)
5- wider tolerance for pump gas
6- no noticeable difference in off boost driving.

I also hope just for more insurance to get my dwell adjusted so I can use a better ignition coil---I just dont trust the oems even though I have never had a known problem with them--- i change them about once a year.
Off course other things will be done to the engine in addition-- like balancing, cleaning up the ports, and Cams little secrets:)

All comments and ideas are welcome on this thread.
Other than Rote8--i dont know of anyone else running the lower compression rotors?
I hope to send the engine to Cam by next month.
I have a feeling that this is going in the right direction for the type of driving I do?

I'M BACKKK!

OD

Welcome back. ! Glad you changed your mind. GOOD LUCK with the build. Keep us posted

Good on ya. Best of luck with this build.


PICTURES! : D

Kool Beans

Well, I am glad to see you making progress to get back on the road. While this is my first rotary I am familiar with lowering compression in forced induction applications so this seems like a no brainer to me.

Good luck OD

Have you ever tried the BHR coils? Seems like a no brainer to me, especially in an FI application. I know you said it doesn't register any misfires, but it's something to think about....


If you do end up getting the RX7 rotors, definitely keep the revs down below 8k. I don't know specifically how much heavier they are, but all that added weight sloshing around would probably cause havoc on your bearings....


Take all that with a grain of salt though, since I'm just a newb. Glad you are back OD! I always enjoy your random threads of intense contemplation.

intense contemplations----I like that!
Thanks guys--appreciate the well wish's.

Has anyone ever installed a knock counter on the rx8?

I do have a set of ls2 coils waiting to be installed---just have to get my dwell adjusted--which will happen.

Are the 7 turbo rotors that much heavier?

go here

https://www.rx8club.com/attachment.p...1&d=1300985016

talk to the thin man seen here in this pic hiding his face with his right hand

http://mysite.verizon.net/res6kmrq/PA085079.JPG

buy him lunch

(when i think of the place Ill add a pic here later)

profit


ignore the one from Trinidad. he's kinda sketchy.

Good Luck with the build OD!

Excellent
All is right in the world again
Welcome back OD

:lol:

I don't have a specific weight, but Mazda said that is the main reason they were able to raise the redline on the Renesis to 9,000. I think it is a coulpe pounds. Let me do some looking and I'll see.

Apparantly it's only about .2 pounds. Here is a linky... http://www.mazdatrix.com/faq/rotorwgt.htm

1989-95 13B-Turbo Rotor Weight: 4328g Static Compression: 9.0:1
2004+ RENESIS 4218g : 10:1


So basically the only difference is .2lbs The Twin-Turbo's Rotors weights 9.5lbs... Renesis rotors weigh 9.3.... For those of yall who cant do math ;)

Knock counter?

Hmm well static weight is not a good comparison. If all the weight is near the outside of the rotor rather then near the center it can make a big difference.

Right... But it would be pretty hard to find that info. At least I would think so. Considering that the most area is on the outside (you know, cuz of science and stuff), that a lot of the weight would be gone on the outer surface.

Good to have you back Denny
now what are you going to do with the R3?

Right, also the psi of centrifugal forces would also take some importance when dealing with proper mounts and seal height i would think.

Rick!
I have talked to Rick a bunch of times---we are both old farts:)
Rick and Cam have also been talking. Paul and Rick are exploring how to strengten the renesis engine for FI.

The rx7 rotor face is thicker. Thats the extra weight. They also have the taller apex seals.
Think about it. There is a reason Mazda went with a lower compression rotor with their turbo models.
9K redline on this renesis engine was a Mazda mistake anyway!

The off boost power available between a 9-1 versus a 10-1 compression ratio is very little in this engine design. Not really noticeable.

Remember also, I am not shooting for max power/performance. I am OK with approx 300rwhp. I am shooting for best FI realibility.

Hey Slver----car sure is looking good dude!
R3 will be sold. Inspected next week and the rebuilt title will then be on the way. As soon as I get it, I will put it on autotrader etc. It will be one hell of a buy for someone.
OD

Rote8 has never really said much about his low compression rotors - wonder why ?

I have been swapping PM's with him for some time. he is just not a "Hey look at me" kind of guy.
His car is doing well.
He confirmed what Mazda said some time ago about the lower compression not affecting off boost driveability, lower charge temps, and our compressor is capable of providing enough air for the rwhp number I want. He did have to change pulley size and his tune is difference due to the maf limitations.
I forget how many miles he has on his engine? Maybe he will come in at some point.

less spicey doritos!

Look forward to new vids of you tearing up Road Atlanta OD :)

OD, is there enough room in the side housings to extend the intake ports enough to create a Miller-cycle effect where the intake ports are still open into the compression "stroke"? I genuinely don't know if the coolant jackets would be in the way or not; but if it it is, then it seems like you would get a variable compression effect (10 at idle and then dropping lower as the extended ports opened).