Turbo swap questions and thoughts..
 

Ok- so my NA motor has a bad oil seal and its time to overhaul.. I've been planning to swap in the TII motor. I know its going to be more expensive than buying a TII and fixing it, but this is what I've chosen to do already. (and i've converted all the drivetrain + tranny to TII components already)

-I plan to rebuild the TII motor once it arrives w/ new seals and whatnot. I may smooth out the ports, but am not sure about a street port. Can someone explain to me the timing involved with enlarging specific sides of the intake port/exhaust port? I believe if the intake port closes later it removes some of the low end torque, and increases the upper rpm power? While making the port open earlier will increase overall rpm performance? I have no idea if this is accurate, but would like to know this before I start to tinker w/ any port designs.

-While rebuilding the motor I plan to install S4 NA rotors in to up the compression. (i'll also use the correct counter weights). I believe this should increase performance all-round, and especially the low rpm torque, where the turbo is not fully spooled. Should I bother upgrading to 3mm apex seals if i dont plan to up the pressure past say- 14psi. I dont need alot, i'd like to stay near stock levels. And would Atkin's rotary apex seals be good for this application?

-I am going to be experimenting with turbochargers and turbo lag. I will have a fmic. so the topmount's not going to be used.

-I plan to install a Haltec standalone and get it tuned by corksport. (just a healthy base tune to start with).

-I know the stock turbo needs the wastegate ported to allow for more boost. As far as the stock turbo~ at what RPM does it reach 1/2 of your max boost levels, and at what RPM does it reach Full boost? @what RPM range does full boost start to fall? and finally, at max rpm (7 or 8K rpm) what psi do you avg?

-What turbo (if not the stock turbo) be best suited to the motor? I'm NOT looking for max boost, but overall the least amount of turbo lag and more boost per more RPM range.


Thanks guys!

i dont recomend running 14 psi on the stock turbo, i would say no more than 12. Also im not sure about high compression rotors with a large amount of boost is to good of an idea.
How ever im not to sure on the dirfference in cmopression between turbo rotors and n/a but i do know the n/as are much higher. I dont think you would need to move to a larger turbo for your aplication seeing as i dont think youll be able to max out the stock turbo witht the high compression seals.

N/A rotors are about 0.6 of higher Compression. you are looking at a 9.1 to a 9.7.

This is a bad idea.

Especially at the levels of boost you are talking, you won't make it around the block. 6-8psi MAXXXXX! Or you will loose your seals.

I have a N/a-Turbo... Done tons of research.. You should do the same.

Why do i hear people running 20+ pounds of boost on 2mm apex seals (run of the mill seals).. So If i were to run the stock S4 NA rotors (i think the comp ratios were 9.4-1 or something). Also, i always hear people using high comp NA rotors in a TII motor.. Am i just reading things wrong or something?

And why would the turbo be out done if the compression ratios were higher- seems to me that the 2 have nothing to do with the other.. I believe that the higher comp rotors will increase power and effeciency of the motor with out maxing the turbo... while the increased boost levels will not max the turbo, but make it less effecient at the higher boost levels (less effecient means that more energy is turned into heat)...

Isnt 'maxing a turbo' actually maxing the effeciency of the turbo... so it'd be the max point where you cannot generate more boost due to more of the energy being converted into heat. (and i know the waste gate has its limits)

I would like more specific answers....


Oh ya- Would it be better to get an S5 TII motor , or a S4 TII??? I'm thinking S5 since its newer and more updated.. And since I'm gonna run a standalone ecu not really worried about making it work...

Honestly i never said anything about maxing out the turbo. There was a specific reason why MAZDA did not use the same rotors/housings/intake on the N/A block and call it a day. For ANY turbo specific car EVERY manufacturer uses lower compression pistons, or rotors in this case. A turbocharger FORCES air and fuel mixtures into the motor at an increased rate (pressure) and draws it back out. Thus excelerating the combustion process. By lowering the compression it allows for various "boost" levels without jeopardizing the seals. More pressure = less life/ relaibility. It has been done sure. I am doing it now.. Is it the best idea- NO. NO Intelegent builder would ever suggest doing this unless you don't mind rebuilding after every race. With a setup like this you also would be hard pressed to shift after 6k rpms... More compression is a bad thing when it comes to boosting.. There is such a thing as too much of a good thing..

Try it out if you like, it will be fine for a while (very little). Is it worth your time?

Good luck.

This is something that I also have been thinking of trying. I hope to see more pros and cons on this thread.

you can run as much boost as you want on any compression,

tuning just becomes far more critical!!!! timing will have to be less agressive, and more fuel will be needed, to avoid detonation!

I have an '86 non-turbo RX-7 and have an '87 turbo motor in the garage that I want to put in the car. What will I have to modify to make this work? I've gotten two different sets of advice from local shops. One said the computer should handle 6-8 psi of boost, and the other said I would have to change out the computer or add boost controls. What do you think?

i think you need to do a lot of searching in this forum...there's so much crap in here that you don't even need to post until you're actually doing the swap.

OK- please note that I WILL be using a turbo II motor! But am asking about slightly higher comp rotors. This has been covered before and I have yet to read about people having troubles with this... I also asked about 3mm apex seals... I'm not shooting for shitloads of power, but rather an extremly drivable car with a wide smooth powerband. i dont need lots of power, but would like to ditch the lag and have a more broad and flat hp /tq curve.

Or basically a turboII motor that has a bit more grunt w/o the turbo aiding, and have the turbo not peter out only a few thousand rpms after it starts...

Oh- Please read my first post.. I would like some info about where the stock turbo picks up at and when it starts to drop a bit.. :)

isnt running plumbing for the turbo on an NA car rather expensive?? when i owned my firebird i was told itde be better off with a super mailny becuase the plumbing is expensive

SuperRotorMan, maybe you haven't noticed, but Rotary's don't take well to superchargers..

I've never seen one make more then 230rwhp..

And uh, plumbing? Are you saying some custom fabricated pipes jusify's buying a twice as expensive superchargers, over a turbo? Note, the supercharger needs custom fabricated pipes too..

Maybe because the firebird has a lot of KITS premade..notice, the RX-7 does NOT.

Get a porting template from Mazdatrix, Racing Beat, etc. Much easier for the beginner then having to learn (through failure :) ) how to port.

3MM apex seals are really no better then 2MM. Many have had good experience with Atkins seals, many have not. In general it's hard to go wrong with Mazda factory seals.

Of course, with higher compression tuning becomes more important.

You'll have no lag with a ported high compression engine and the stock turbo.

OK.

Whoa! The wastegate needs to be ported so that you can better CONTROL your boost, not increase it. Boost levels on the stock turbo completely depend on mods.

Hybrid stock turbo.

"-I know the stock turbo needs the wastegate ported to allow for more boost. As far as the stock turbo~ at what RPM does it reach 1/2 of your max boost levels, and at what RPM does it reach Full boost? @what RPM range does full boost start to fall? and finally, at max rpm (7 or 8K rpm) what psi do you avg?"

yeah just like aron said the wastegate is there to controll boost not increase. keep in mind its a valve which opens and DIVERTS exaust flow meaning that you will have less boost the more it opens hense the term waste gate.
Also and i say this by experience, i would not use the stock turbo for anything other than stock boost levels and stock engine. I blew my stock s4 turbo and then a s5 turbo running only 8psi of boost with a extremly high flowing engine (ie; no emissions and completly open exaust) so unless you want to be replacing turbos every year like me get something upgraded like a hybrib or such that can handle it.
Im looking into the stage 2 or 3 bnr upgrade with the TO4b.

Aaron Cake, thank you for answering! and for correcting me on the wastegate stuff. (i know what they do, but didnt word it right). and RylAssassin, what I was looking for with that comment of mine was simply when the stock turbo reaches its prime, or sweet spot if you will. Its quite tipical of most turbo's to reach full boost and then fall off (level off) since it's effeciency goes down as you reach higher rpm's. I was simply looking for a reference as how the stock turbo behaves.

So~ with that said, The overall responce of the motor would be optimal with a mild port job, high comp rotors (clost to stock boost levels), and lots of careful tuning. Oh ya- The car has a borla exhaust... (want to keep it quite and driveable :))

-So- about a hybrid stock turbo~ what would be hybrid about it? larger intake turbine?

Looks like kompressorlogic and Aaron Cake covered most everything. :)

The counter weights on all models in series are identical. No need to change them. The OEM setup rear counter is built into the flywheel. You use counters according to series of rotors you use. Do not use rotors that are more then one letter apart from each other. Since you converted the drive train you will need to use the TII S4 flywheel or a aftermarket S4 turbo flywheel. The front CW needs to be any S4 counter.

The comp ratios are S4 TII 8.7.1 and S4 NA 9.4.1 and that is quite a jump. As stated there is absolutely no reason he can't run whatever boost he wants with a proper tune.

I believe they pretty much gut it out like take all the internals and replace them. Like new compressor wheel seals etc. I called rx7store.net and this is what the guy said although he dident seem to know much. Also the front housing is replaced i believe to accomidate the new compressow wheel. Im going to try to call BNR tomorrow once again (there the hardest ppl to reach it seems) and get the straight answers. Rx7store.net has there hybrids done by them.
And to answer your question on where its peak power is these hybrids peak at around 3800-4000rpms with a max boost of 15psi acording to the websight.