Hello,

Would this car suffer any damage from running with no cat? I am looking at purchasing one for a good deal, but the car has just a straight pipe.

From what I remember, even a catback exhaust can damage these sensitive engines. Is this true running with no cat? Don't know how long it has been this way but the car drives just fine.

Thanks!

 

Yes, you can blow your motor by running no cats, unless you have enough back pressure. Unless you have a ported waste gate (which I don't recommend doing), and a perfect tune with a Power FC, you are running the risk of running lean and causing detonation in the engine, especially at low temperatures. To avoid this problem, you should either have the stock down pipe, a stock or high flow cat, or a cat back, which will create enough back pressure to prevent running lean. Plus, CA has brutal smog laws, and you can get screwed up the *** by cops, especially in the bay area where I live.

This has been discussed many times on this forum. Do a search about running a straight pipe, I am sure something will come up.

-Daniel

 

If the car was tuned and setup to run without a cat, there are zero issues and its actually better for the motor as there is no back pressure and thus less heat. However if your running a stock computer with no cat, that is a no no.

The engine isn't that sensitive, its the owners that don't do any research before modding their cars. FYI, adding a catback by itself, regardless of the size, does nothing harmful to a completely stock car.

thewird

 

I'm running a straight through exhaust with a proper restrictor plate on the stock ecu with no bad effects. If you do plan on using that exhaust id highly recomend a boost controller to help out with creep on those cold days.

 

The owner has had the car for a few years but has only put a few thousand miles. It is unknown how long it has been running this way since he bought it that way, but I am 99% sure that the car is completely stock otherwise. The clutch doesn't seem so great either.

Hooray for clueless owners. Needless to say, this car needs to be rescued by someone that actually cares for these cars.

 

You can easily check if the computer is stock by pulling the kickpanel on the passenger side and having a look. Stock is on the left, PowerFC (a popular aftermarket standalone as its plug and play) is on the right. Also if it says something like Pettit computer or so then that is safe as well as that is a reflashed stock computer to support a variety of mods including open exhausts.



thewird

 

stock car + no cat = boom

Five years ago i was an idiot owner, and guess how i blew my first motor?

 

get a pfc (or equiv) and youll be great. i made 340rwhp on stock IC and just pfc, full exhaust, 1600cc secondaries ,intake and non-seq

 

Sorry, but this is wrong. A boost controller will not protect the OP from boost CREEP. It's only good for controlling SPIKE.
If the owner isn't familiar with the car and prepared for things, I recommend he remove the pre-cat (if it's still there), replace the mid-pipe with a quality high-flow cat and call it a day. There might be some performance sacrifice but less risk. I don't live in CA. but understand he would never pass emissions without a cat anyway. There's also the added benifit of less smell and noise.

 

I will probably be purchasing the car. I'm hoping too much damage hasnt been done. Will eventually move onto a PFC.

But I'll still need it to pass emissions properly. Does anyone have any recommendation on where to get a cat?

 

omitting the restrictor pill from the wastegate line should bring it back down to reasonable boost level until an engine management system is installed.

most people think that the boost controller can lower boost levels because they are removing that line which meters the wastegate pressure levels higher in the stock system.

 

Boost controller is still good to have on any modded RX-7 as it gives you adjustability and you can set it up to have its own boost cuts or warnings. I don't tune anyone's car unless it has a boost controller in it. You'd be surprised how many people don't even have a boost gauge in there car and want it tuned. A boost controller doubles as a boost gauge as well.

thewird

 

http://www.rx7store.net/product_p/highflowfd3s.htm

 

I prefer this one:
http://rx7.com/store/rx7/fdexhaust.html

 

mkiv98,

The midpipe itself doesn't blow the motor per say, a midpipe greatly reduces back pressure which is a good thing. But it can also be bad because by freeing up the exhaust the car has secondary effects on boost levels which is bad, very bad. It's those higher boost levels that WILL blow the motor unless you control back down the boost or are actually tuned.

Runing a midpipe can cause either one or all of these three things:

1) Elevated boost due to a free flowing exhaust. Easily fixed with a boost controller
2) Boost spike. Easily Fixed with a boost controller
3) Boost creep (elevated boost due to inedequate size of the wastegate). Easily fixed by porting the wastegate.

On a stock ECU just make sure that you are able to maintain the boost to 10 psi max, rock solid boost pattern (i.e. no spikes nor creep!) and you will have nothing to worry about. If you have an aftermarket ECU just make sure that the car is tuned to run safely at whatever boost level you are running.


Edit-
Do you mean damage from the midpipe? It's either an off/on kinda thing. Either the motor is blown or it isn't. There are magnitudes of severity of a blown motor but the fix is essentially the same. Take engine out and rebuild.

FYI you will have issues in passing smog with the PFC particulary as the check engine light doesn't come on when you turn on the key, which as you know it's an automatic fail. Not a deal breaker and can be rigged but I just thought you should know before you go out and purchase one.


IMO and if I could do it all over again this is what I would do:

MED SMIC, M2 closed box intake, DP, resonated midpipe, racing beat CB, ported wategate, boost controller, water injection, 10 psi max boost, AST deletion, radiator replaced with a fluidyne. All on a stock ECU.

 

thank you montego. that post has all the information I need.

last time I drove this car (months ago), it seemed like it might have wanted to grind if shifting into second quickly (will have to try this again to see if I am remembering correctly). is this also a common issue?

 

2nd gear grinding is not really a common problem but it can happen. Grinding 5th gear is a very common problem though. As the 5th gear syncro goes out due to due to mishifting from second to third.