Are the pre-cats really needed if the main cat is a new quality unit.? I understand that the pre-cats were used because 30 years ago the main could not function properly until very hot, hence the pre-cats. I am asking because I am redoing the exhaust on my very clean 88 and am not sure if I should replace them or just use a front y pipe with a new quality main-cat. I also do not want any additional fumes when driving or in my garage when parking, do the pre-cats really matter.? Thanks.

(its a summer Sunday car with Classic plates and no state inspection any longer, so I am not really worried about getting a fine for taking the pre-cats off)

Thanks.!

 

I think with the new (main) cats, pre-cats are pretty much not needed. just replaced the exhaust on my 90 - no pre-cat front y-pipe (flowmaster), new main cat (flowmaster), and new cat-back (corsa).

 

Thanks Joe, I am definitely getting a good new main cat and will probably remove the pre-cats since they are probably benign at this point anyway. This is a great site, I have lurked in past but am a new member. I have another question which is somewhat related which I will start a new thread since it may be a more complex question.

 

If you would still have to have the car emissions tested, pre-cats would help to pass any sniffer test. But not having to go thru that, you should be fine without them. In fact you could also remove the main cat. But if you are going to have a shop do the work, most all shops will refuse to remove working cats from a car. There is a big (5-figure ) federal fine if they get caught.

With a front Y-pipe without the pre-cats, just make sure that you have an O2 sensor bung welded in at the same location that it was in on the old pipe.

 

Are those small cans in the front Y pipe precats or resonators? My '74 with original exhaust has them as well and no cats were used that year.

I changed the front Y pipe on my '90 to no cans and noticed an improved (louder) exhaust note and and burbling, popping sound when off the gas.

 

Hi Mickey, the two on the front y pipe are the original pre-cats and the main cat is original too. I am in the midst of having the exhaust redone and was not sure of the pre-cats. I think I may get a y pipe without them and a very good main cat cause while I do want it to perform better and sound good, I don't want any more flumes then necessary. I think a modern day EPA main cat should be enough, at least I hope. (I do not like smelling anything at red lights or when I pull it in the garage. Thanks.!

 

I've installed a walker, 86+ OE style system on my 85. the replacement design has no pre-cats, only the main cat, and with walker quietflow mufflers. don't let the quiet in quietflow fool you, it sounds great. not "in-your-face" loud, but a good healthy sound. on my 90, I installed a flowmaster catless front-y-pipe, with a flowmaster main cat, and a corsa catback system. good sound, again not in-your-face loud, but louder than the walker. actually, of the two, I prefer the OE walker for sound. only drawback, the pipes and mufflers are aluminized steel, not stainless, whereas the flowmaster and corsa combo is stainless.

so, unless you're some sort of a purest on originally, with the new, more efficient, main-cats, pre-cats are a thing of the past -

 

Decided to go with the main cat only. Bought the Flowmaster front Y pipe and main cat, Walker rear Y pipe and KBD Targa Mufflers. Thinking it will be a nice set up with good sound for my stock 88. Should be installed in next couple weeks.

Thanks all for input.!

 

Your profile doesn't list location so not easy to see. I assume you checked the local laws and you don't need emissions testing for that old a car?

So you decided to go with the main cat. I don't know about the cat you bought but I got one from Random Technologies that was an exact fit. So, it had 2 pipe holes for AIR. If you didn't want to, it allows you to put in 2 bungs to block it off. If you do that, you can also delete the AIR system and clean up the engine bay. Obviously you will have to get a couple pipe cats to plug up the AIR pipes to the manifolds.

Not sure what you are trying to do but IIRC, the choke point on the L98 is the exhaust manifold so I'd replace that first with some Long Tube headers that are coated.

 

Hi Aklim, I'm in NJ with classic car plates so no emissions or visual testing anymore. Actually it passed inspection for the last time a few years ago with a 25+ year exhaust system before it was registered as classic so I am thinking it would probably pass now easily with this new main cat, although it won't see an inspection station again.

Worst case, if something is not right I will go back to a stock front Y with mini cats, but I don't think I will need too. I am hoping it will run and sound nice.!

Headers would have been cool, but the car is basically stock/original and since the manifolds are still in good shape I decided to just leave them for now. I am also hoping this will solve a strange vapor smell in the cabin, which I mentioned on a different post. Thanks.!

 

I don't know but some places are limited miles on classic cars so not sure what you are facing for rules if they allow you to drive a limited number of miles a year. If you don't have to keep it stock, life is good.

I don't get into sound and even if I did, it's a personal thing so you have to decide if you like what you are getting.

IIRC, some people have removed the vapor canister and vent to atmosphere at the back of the car or the lines are cracked which released the fuel vapor.

 

Its basically a Sunday car at this point, goes to cruise nights, driving around town and stuff. My insurance has a 3,000 mile limit per year, I don't get even close to that, it has 78,000 original miles on it now and about 90% of those were put on before 1998 lol...So no worries about mileage.

Good thought about the vapor canister, etc. I am going to have that checked out too. I am only semi-techy so I want a skilled person to check it out properly and get it fixed. That cabin vapor issue I am having is strange and not fun.

I have no intentions of selling it so I am looking at all this as "overdue" maintenance to keep it in good shape. Happy to say it hasn't cost me much over all these years so I guess now is the time and I don't mind spending a little cash, but not to much ha.! Thanks again.!

 

I had a very strong odor in my '90 with the engine idling when stopped. It happened about the time the injectors started to fail. I read that raw fuel in the exhaust was detrimental to the cat so i replaced the system from the manifold to the main cat which eliminated most of the problem.

 

yea, I am going to try to check everything...it does not have a distinct odor as funny as that sounds, but something is coming into the car...if its the exhaust that would be great, but I will find out in a couple weeks. Since I needed a new exhaust that was the best place to start. Thanks.!

 

Odor of what?

 

Thats the thing, it does not really smell like anything, but when driving I am getting burning eyes and a sore throat so something must be vaporizing or coming into the cabin. I drove around with working smoke and CO alarms and did not even get a beep. I am still hoping it is the exhaust which will be replaced in a couple of weeks as mentioned.

Exhaust installer is going to check whatever he can as far as oil burning on old exhaust, leaks, etc. then after exhaust is installed, I am going to have a good mechanic check everything he can within reason; heater core, other oil leaks, gaskets, trans, etc..and fix whatever the problem is, the car seems to run great, quick, smooth, etc....so I am hoping it is just a quirky thing that can be resolved relatively cheap and easy.
There is a small leak with power steering that looks to be the power steering pump, but other then that I can not see any major things wrong with it.

Last year I had the intake manifold and valve cover gaskets replaced as well as a new clutch and rear seal. (had a couple leaks ha). I am assuming the job was done correctly.

Anyway, don't want to bore you guys until I have some concrete answers to report back, I had another thread about this too and am really hoping it will be resolved by the mechanics soon.!

Since joining this site I have gotten some great insight and now have good ammo to tell the mechanic if this problem is other then the exhaust...thanks.!!