Inspector71

I'm still new here so I apologize in advance if this has been done to death. Way back in 1982 or 83, I was still living in California. I took my 79 GSL to a shop that raced Mazdas and Hondas on Winchester Road in San Jose. They replaced my bad clutch with an Rx2 clutch, the owner saying it was stronger (and stiffer). I got to talking to him and asked him about turbo-charging the 12A. He said it would reduce engine life to about 40K miles. Say a 12A or 13B is turbo charged, driven on the street, not raced just accelerated for fun, is that still true today? Thanks for any insights you all can provide.

DocHoliday89

iTrader: (10)

Turbocharging technology and knowledge have come a loooong way since the early 80's. An engine is an ecosystem. A turbo motor will last just fine as long as it has sufficient cooling, lubrication, fuel pressure, and a good tune. If all of those systems are healthy and sufficient, why would engine life be shortened?

Inspector71

You just made my day. I have an 84 SE and am looking at either another gen 1, or maybe a gen II like the 86 I had and should have kept. I want to keep one fairly stock and the other to be turbo-charged. I toyed with the idea of a gen III until I saw the prices. Wow. Seems to me the gen II would be a great choice and give me the extra umph. I want. Anyway, your answer is greatly appreciated.

eliminster

Why not get a 87-92 turbo 2 that way you can still keep it mostly stock minus a few reliability mods.

lOOkatme

iTrader: (19)

good question.

I think turbocharging an engine does shorten the lifespan of an engine. sometimes drastically.

Turbocharging an engine carries a lot more risk, which means maintenance is a lot more important. It also dumps more heat into the engine. We have found that the root cause of engine failures has mainly been the apex seal rocking over the bump in the housing right by the spark plug hole, in this particular spot there is reduced cooling in the housing due to the design of the housing. This reduced cooling area grows in size due to heat and the seal rocks over the "hump". This eventually leads to a high cycle fatigue failure of the apex seal. Turbocharged engines just have so many more catastrophic failure modes (wastegate, fuel, ignition, tune, etc).

We combat this root cause with colder spark plugs.

The risk with turbocharged engines is greater if mechanical failures occur, especially with all aftermarket equipment is installed and might not work well together. just look at the build threads on this forum. lots of blown engines. Rebuilt engines are also not always put together right and toleranced correctly leading to even more blown engines.

Another leading cause of failure is carbon build up of the seals. We combat detonation and heat with more fuel and use the fuel as an aid to cool combustion temps. This low AFR results with a lot of carbon build up in the motor which leads to stuck seals.

What does seem to work is running OEM seals, OEM internals, with viton water seals. run water injection to control detonation and clean the engine from carbon build up. It also cools combustion chamber pressure/heat. Run a little 2 cycle oil to reduce carbon build up and lubricate the housing which helps with the above. Do maintenance regularly, fresh oil, fresh radiator fluid yearly, spark plugs, fuel filter, etc. Getting a good tune works well, but its tough to know who tunes well.

Overall, it depends on the person who is modifying the car and how in tune they are with the car. It seems to be more successful if the person can build and tune the car themselves (with help of experienced individuals) because they care about the engine and car and will take extra care and time to get everything right.

BLUE TII

iTrader: (9)

The most reliable way to turbo charge a non turbo rotary is to completely install the factory turbo engine and peripherals into the non turbo chassis.

If you search you can find complete engine/trans/harness/ecu set-ups for sale on ebay for TII or 3rd gen.

Stock 2nd gen TII usually go 150-200,000miles if not modified by the owner.

Stock 3rd gen usually go 100-150,000 miles if not modified by the owner.

It is really us tinkering with them that makes turbo rotaries so unreliable.

scathcart

Increased combustion chamber pressures and temperatures due to turbocharging will absolutely accelerate engine wear.
To the point of 40,000kms/ engine, no, but housing and seal longevity is certainly reduced compared to its naturally aspirated counterpart.

DocHoliday89

iTrader: (10)

I gave the guy an answer he could use as a starting point for research. High compression motors run higher combustion chamber pressures and last just fine so long as everything is built to handle it. Engineering deficiencies aside, what ever wear would be associated with adding a turbo is negligible unless you don't maintain it properly. I still feel my answer was sufficient for his question.

DocHoliday89

iTrader: (10)

Also, if you want info on adding a turbo to a NA 13b, do a search for Rx7_Nut13b. He's done it. It is considered to be very challenging to safely turbo a NA motor because it uses higher compression rotors and detonation (bye bye apex seals) is much more likely. Searching for a cheap turbo motor to rebuild (as said by one of the guys above) would be a good idea. Plus you would be able to drive your car while rebuilding the motor.

eliminster

Another user on here who has turboed na rotaries before is aaroncake he even has a YouTube series he is doing on his restomod 76 Cosmo with a na turbo motor in it. My recomendation instead of sourcing the parts for a turbo swap or conversion why not go ahead and see what kind of deals you can get on stock or near stock turbo II I've seen multiple for sale on Craigslist and other sources where worst case you would need a rebuild which would be better overall in my opinion than turboing a na car. Also remember that if you are turboing a na car the transmission and diff are not designed to handle that load and could fail prematurely.

Inspector71

This is really important information to help someone like me who has a strong grasp of ignorance make up his mind. I was thinking I would go with a gen II Turbo II model after all. Makes more sense. And I like the idea of putting in a turbo motor, one built that way as a package or unit, rather than adding stuff on to an existing motor. makes a whole lot more sense now that I've read these posts. I should have kept my 86 Sport model. I have one more probably incredibly stupid question. Why not super charging?

j9fd3s

iTrader: (3)

there isn't particularly anything wrong with a supercharger, although there are a few reasons it is pretty rare.

first and fundamentally the rotary emits a lot more exhaust energy than a piston engine of the same size, so simplistically, it is good at driving a turbo.

secondly the factory went turbo, so most of our setups start with the factory turbo to start.

thirdly, the roots style kits offer low end, but don't breathe up top, so hp isn't increased much*. centrifugal superchargers only offer a linear boost curve, so you get 1-2psi at the bottom end, and max boost up top, so they don't spool up like a turbo.

*there was a 164rwhp roots supercharged FC at sevenstock one year, and an uncorked S4 NA will typically 150-155rwhp.

BLUE TII

iTrader: (9)

There used to be a couple Super Charger kits for the NA rotaries before FCs were so old and no one wanted to spend money on them.

One is a roots blower with intake manifold and I think Atkins might still sell this.

The other was a Paxton centrifugal SC kit from Nelson.

The problems with Super Charger on rotaries-

1) Our 1967-2002 rotaries have a bunch of overlap so the boost goes right out the exhaust.

This is why we make less power on a given turbo versus a piston engine. On a turbo the air/fuel in the exhaust spools the turbo so it makes up for the larger turbo required (except the initial cost outlay).

On a SC you have the problem of fitting a large enough SC under the hood to make any power. This is why SC rotaries are limited to ~200rwhp. On the other hand a bone stock 87-88 TII dynos 150-175rwhp and putting an turbo back exhaust on pushes it over 200rwhp. This is the least powerful stock turbo RX-7 available to us.

2) The drivetrain on NA RX-7s is marginal at stock power levels. Drive an NA RX-7 hard and you go through transmissions and rear ends. Put a SC on it and you have to upgrade clutch, trans (and driveshaft), rear end and axles with TII driveline parts. Not to mention you need some ECU to run the extra fuel for the boost.

I don't have to point out that all these things are already on a stock TII that you can pick up for $1,000-5,000 and can handle 400+ RWTQ with no problems.

3) The rotary has a 2 bearing eccentric shaft. Putting a SC on the front bearing puts tremendous stress on the bearing and causes E-shaft whip. You must run a (loose) Gilmer drive set-up for reliability. You can wipe out a rotaries front bearing by over tightening the stock accessory belts- I have seen this 1st hand. You will wear out belts quickly at high rpm if you use another belt style loose enough to protect the front bearing and it slips.

4) Rotaries love to rev, Super Chargers not so much. If you want to rev out a SC you have to gear it so it isn't doing much at low rpm and low rpm torque suffers. You can't get away from the parasitic drag of trying to rev out a SC or the E-shaft whip.

5) Cost. A Super Charger kit costs more than a whole running RX-7 TII.
Even if you want to fabricate- a SC alone big enough to make decent power on the rotary costs more than a RX-7 TII.

Inspector71

Than all the years I owned Rx7s (from 1979 to 2009) from you all and I appreciate it. Some of this is technically over my head at this point, by I get the part about exhaust and boost and so forth. I can see why super charging would be a waste.
Not to step on toes, when I lived in California, I was acquainted with more than a few Porsche 944 owners who denigrated first my gen 1 cars then my 86 gen II because they were Japanese. I always wanted to build a set up to show them what these cars can do for a lot less money. Ah, the good ole days. Anyway thanks for this education today. I am going to have to print this. Very good.

eliminster

The fen 2 turbo II was actually a very good competitor for the 944, and once fully modified between the two I believe the rx7 puts the power to the ground a little more effectively with the more linear power band but doesn't quite have the cornering potential as the 944, but that is my opinion based on driving my t2 vs some of the local 944's I've driven with .

j9fd3s

iTrader: (3)

its funny how 25 years ago, the 944 was the better of the two, but now the 944 looks tacky and dated, and isn't invited to the Porsche meets, while the FC just looks great.

Inspector71

When I get the gen 1 done and paid for, and find a gen II turbo, I'll start working on my Porsche buster