Best Bet on my 90 SC... change stock headers to 95 versions?

arizona90

Registered User
As I now have a rather quiet stock exhaust, and to save my motor (headgaskets) because of the poorly designed ( I've read) stock headers, I believe the first thing I should do is to change my stock headers to 95 stock versions. My question is - should the 95 versions be modded out or left alone? I will eventually change out the whole system to get it to flow better but for now, is that one change alone going to give me some sort of safety regarding my headgaskets? Secondly, is there anyone recently modifying these headers that I can send them out to? I have a California SC that had a 1994 recall where they changed out the EEC and the cats. As I now live in a part of Arizona where cats are not mandatory, should I consider replacing them with downtubes? From what I've read here, it seems that maybe I need to replace the cats with highflow cats to avoid the potential dredded drone. Advice is greatly accepted. Marty
 
XR7Dave posted a great thread where he compared a bunch of exhaust options. The late manifolds do flow a little better than the earlies. I believe it was more about equalizing the flow in the primary tubes. One side does have a different angle at the collector, so you will have to modify the down tubes, may be a great excuse to go catless flow pipes, but be aware that that will cause significant change in exhaust sound (volume and drone). Check out some of the threads discussing that. If I was going to make those changes, I would port the manifolds. It isn't that hard if you have the tools/area to do a messy job like that, and will make a difference. If you don't have the stuff to port yourself, keep an eye on the classifides, they come up for sale pretty often.

Adam
 
As I now have a rather quiet stock exhaust, and to save my motor (headgaskets) because of the poorly designed ( I've read) stock headers, I believe the first thing I should do is to change my stock headers to 95 stock versions. My question is - should the 95 versions be modded out or left alone? I will eventually change out the whole system to get it to flow better but for now, is that one change alone going to give me some sort of safety regarding my headgaskets? Secondly, is there anyone recently modifying these headers that I can send them out to? I have a California SC that had a 1994 recall where they changed out the EEC and the cats. As I now live in a part of Arizona where cats are not mandatory, should I consider replacing them with downtubes? From what I've read here, it seems that maybe I need to replace the cats with highflow cats to avoid the potential dredded drone. Advice is greatly accepted. Marty


Are calling the stock manifolds headers? If so the only thing you need to do is port the outlet of the 90 maniflold and be done with it. Swapping to a late model manifold wont gain much. The stock cats are very restrictive so new down tubes are a good option and be better resonator. Detonation is more a cause of blown headgaskets. Running more boost and increasesing ACT temps would be what I would worry more about. Freeing up the exhaust will lower the boost a little as you remove restrictions caused by the stock exhaust. A 5% SC pulley than would be a nice mod for a little more power

Ken
 
I thought XR7Dave's study showed that the 95 manifolds were a better flowing design .

Are calling the stock manifolds headers? If so the only thing you need to do is port the outlet of the 90 maniflold and be done with it. Swapping to a late model manifold wont gain much. The stock cats are very restrictive so new down tubes are a good option and be better resonator. Detonation is more a cause of blown headgaskets. Running more boost and increasesing ACT temps would be what I would worry more about. Freeing up the exhaust will lower the boost a little as you remove restrictions caused by the stock exhaust. A 5% SC pulley than would be a nice mod for a little more power

Ken

When I read XR7Dave's study, it seemed to show that the 89/90 manifolds were a poor design as far as balance per runner compared to the 94/95's. My object is to let the car breathe better and have a good starting point when I start changing the exhaust system. From what I have read here, it seems that a decent system would be comprised of 94/95 worked manifolds, high flow cats leading into 2.5" tubes into the main resonator/muffler (that should be larger/longer than stock) then out to a 3" tube which would split to two final mufflers whose outlets would be downturned to the street and not straight out. I need to find out which muffler/resonator combination sounds the best (healthy but not droning) on my stock motor for the time being. I enjoy the power in the car but feels it needs to be uncorked a bit more for my liking. I appreciate your responses in helping me make my decisions. Marty
 
When I read XR7Dave's study, it seemed to show that the 89/90 manifolds were a poor design as far as balance per runner compared to the 94/95's. My object is to let the car breathe better and have a good starting point when I start changing the exhaust system. From what I have read here, it seems that a decent system would be comprised of 94/95 worked manifolds, high flow cats leading into 2.5" tubes into the main resonator/muffler (that should be larger/longer than stock) then out to a 3" tube which would split to two final mufflers whose outlets would be downturned to the street and not straight out. I need to find out which muffler/resonator combination sounds the best (healthy but not droning) on my stock motor for the time being. I enjoy the power in the car but feels it needs to be uncorked a bit more for my liking. I appreciate your responses in helping me make my decisions. Marty

The early manifold will support any HP you make up to 400. Is the later manifold better, maybe a tad but nothing your going to notice on a realatively stock motor. The important thing is to port the outlet on any manifold you use. best mufflers I could recommend are Bora mufflers. They are expensive but sound good


Ken
 
Also, if you are going to elimiate the cats altogether, you'd be better off pointing the tailpaipes not directly at the ground if they terminate just under the rear bumper (instead of just past it). This may enhance the drone effect, because the louder exhaust will bounce off the pavement and back under the car, making it sound louder inside. You can point them straight back like many do, or at least more at an angle if leaving the stock tailpipe look, or just extend them past the bumper and leave them pointing straight down.

You could also just leave the stock manifolds completely alone for now and repalce the stock resonator instead. It and the stock downtubes are very restricive, more so than the manifolds.
 
My question is - should the 95 versions be modded out or left alone? I will eventually change out the whole system to get it to flow better but for now, is that one change alone going to give me some sort of safety regarding my head gaskets?



I think you'll find it's the driving style that dictates head gaskets.

If the previous owner or yourself decides to work it, you will be into the gaskets regardless.

The exhaust is just venting for your foots attitude.:D

Paul
 
The 95 manifolds are better. If you are changing everything then why not get the better passenger side manifold? Driver side is still the same. Porting the outlet is not a big deal, but again, why not when you have it apart? If you want a pair of ported 95 manifolds with new studs installed, I can probably work that out, I think I have some spares laying around.

The rest of the exhaust is not that critical believe it or not. The stock cats are not that bad (we have made over 300rwhp many times with stock cats). If you replace them, I recommend a highflow version, but not a spun metallic core if you have any interest in them actually working as a catalyst and/or sound deadener. I've posted the part #'s for reasonably priced cats many times on here, search is your friend.

If you run cats, then the rest of the system is not so critical, sound wise, but if you eliminate cats then sound will be a major concern. For 300rwhp or less, pipes need not be bigger than 2.25". In fact 2.0" will work fine too as long as they are mandrel bent, and personally I would never use a crush bent piping system. www.mandrelexhaustsystems.com is hands down the best place to buy exhaust piping. I use their stuff all the time and highly recommend the stainless dual system with resonator. You will have to supply the down tubes though and I highly recommend the late model version as it fits much better than the early model one. You'll need a late model gas tank.

Keep in mind that the bigger the pipes, the louder the sound, and the lower the internal gas velocity. Velocity is your friend at lower rpms and lighter engine loads. If you spend most of your time driving normally, then a smaller exhaust system is superior to a an overly large one and it will be quieter to boot. I can't count how many SC's have been literally ruined with oversize, obnoxious exhaust systems.

I have had GREAT success using the Magnaflow cat/downtubes from Summit or wherever, and then connecting that to the mandrelexhaust system 2.25" rear section. Out back I angle the muffers at 45 deg rather than going straight back so that I can fit 18" mufflers instead of 15's. The extra makes a difference. Or you can go cheap and install a chambered muffer with packing instead of straight through. At the 300rwhp level it won't make a difference either way. I've actually made 350rwhp with this exact exhaust system, but boost was climbing pretty badly so it's not recommended at that level (21psi boost).
 
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