prime_suspect

I've been talking with a guy through e-mail about purchasing his 93' RX7. I was asking if he had replaced the pre-cat with a downpipe, and he says that he simply bored the pre-cat out and it's just as good as using the downpipe. What do you guys say about this?

r0t0r-rooter

Here's a thread about gutted cats in general.
It's a very cheap alternative, but it won't reap quite the same benefits due to turbulence & piping size

https://www.rx7club.com/forum/showth...utted+downpipe

alberto_mg

it accomplishes similar goals of opening up the exhaust and getting some heat away from the motor, but its not the same.

I don't know if you have ever gutted a cat, but its usually done by getting a big screwdriver and stabbing in/out of the exhaust openings till you get most of the catalyst material out. Given that, there is bound to be a bunch of catalyst material still stuck in place and it is not a nice straight pipe like a downpipe is. It will be all jagged in there.

A downpipe is the same diameter throughout and the bends are mandrel bent so the flow of the exhaust is nice and smooth and more effective overall.

prime_suspect

Ok thanks.

Also though, he says it has 119k miles on the dash, but the engine has perfect compression, so he's pretty sure that it has been replaced at some point. Just not sure when. I has though, had the 3 original recalls done. I have several website saved, that serve as buyer's guides for the 3rd gens, but I just want a general opinion on how this is sounding.



Oh, and about that bored out pre-cat. Will the engine go out with that done? Or is as simple as having the downpipe installed?

rynberg

Personally, I would be leary of buying a car from someone who is too cheap to buy a $300 downpipe. I have trouble believing the car has been well maintained with such an owner.....

prime_suspect

Yeah, I'm somewhat iffy about the guy myself. He says that the odometer stopped at 119k miles, but the engine has perfect compression, so he knows that a new engine was put in, he just doesn't know when. I mean, he knew what I was talking about when I asked about the recalls and everything. He said that all the recalls had been done, and he has proof. But he still doesn't seem to know too much. However I found one being sold by an individual in Texas, about 300 miles from where I live. If I do decide to go through with getting an RX7, then I'm gonna call him and make sure it's worth going out there. It's a black 94' with 24k miles on it for $10k.

rynberg

If that's not a typo, then the car has a salvage title or a blown motor or something else (like flood damage).

jxc-rex

Suspect, I know the car you are talking about it's in Meridian. He's a neighbor of mine that knows quite a bit about rotary's he just isn't in to spending money on aftermarket mods (So yes he is cheap when it comes to stuff like that). He bought a '91 of mine a couple of years ago that had a blown seal and completely rebuilt the motor with new seals, housings, and gaskets. Since I've know him he has bought, sold, and resurrected many RX-7's.

I'm not trying to do a hard sell. Actually I'd recommend you take a look at a few before you buy. However, it wouldn't hurt to come on over and take a look, Madison is maybe 1.5 hrs from Meridian. You can take a look at mine too if you wish. She's a work in progress, but has a few of the mods you may be interested in. Good Luck!

DrunkenBowler

I say buy a downpipe. It's a simple solution. Drilling is to much work, ya know.

lilroach

I just recently bought a hks downpipe any complaints? Also anything i should look out for during install. I plain to reuse the old gaskets.

ludeowner

From what I hear the HKS DP is the easiest to install since it has a flatter upper pipe. You *should* be able to install it with all 4 factory studs, but you should get some stainless steel bolts to take the place of the studs in case the studs back come out when you are taking off the stud bolts.

Read my write up that I posted a while back. I tried to be as thorough as possible and include all the small details. Your HKS install should go pretty much the same...the only thing that may vary is your stud removal. It could do 1 of 3 things: #1 the stud could break (worst) #2 stud could stay in place #3 stud could come off. #1 is the worst thing that could happen, cause if enough of the stud breaks off, you may have to take off the entire turbo assembly to take out the broken stud, and that process is more time consuming.

My downpipe install thread:
https://www.rx7club.com/forum/showth...hreadid=211831

lilroach

thanks for the info. so you think i should invest in some studs and nuts? factory or do you know of any aftermarket. downpipe should be coming this week so i'm just trying to get prepared.

again thanks for the quick reply. you help out alot

ludeowner

Yah, I would go ahead and pick up some spare nuts and bolts to replace the studs incase they come out, or if you want to take them out. To replace the stock studs you can chose between hex bolts which may come close to the downpipe's pipe or some allen blots which will be easier to tighten but more likely to get stripped. You will have to get them from an auto store like NAPA. You can also get some PB blaster (penetrating oil) at NAPA. You will need that to help take the stud nuts off. I would also invest in small mechanix or leather gloves to protect your hands. When you are putting all that force on the studs trying to get them off and they break loose, you will be glad you have the gloves on to protect your hands.

You should also get a spare DP gasket for between the precat and main cat. You should not need the gasket for between the DP and turbo flange since that one is metal, so you can just reuse the old one. While you are at it get some crazy/super glue. If you need to, you can use to glue to stick the metal gasket to the DP or turbo flange so that you dont have to hold in place with your fingers.

EDIT: also check out this site in case my write up was a little confusing.

http://www.scuderiaciriani.com/rx7/d...e_install.html