What's your ultimate vision for your ZR-1?

It really shouldn't the large secondary blades that are hanging. It usually turns out to the be the primary blade as it doesn't have much tension on it and jams with crud easier.

Take your finger and open the primary blade and slowly let it close.

[Aurora40]

Well, then pushing on the throttle assembly wouldn't drop the idle, would it? Because the primary doesn't get pulled back by it. Pressing on the little primary tang didn't do anything when it's in high-idle mode. Also, easing the secondaries closed would also ease the primary closed.

The primary is spotless, no crud. I cleaned it up well. It definitely has gaps around it, but these are mechanical in nature from the idle-stop screw. It doesn't make contact with the bore anywhere, so I wouldn't think it could hang up from interference. I didn't want to mess with the idle-stop, though, as the car didn't used to idle high until I did the plenum pull and cleaned the TB.

It only happens after heavy throttle, though this doesn't automatically rule out the primary since it too is open during heavy throttle. But light blips of the gas don't fix it, I suspect because the secondaries aren't being blipped. In gear hard blips will sometimes bring it down, I assume because then it's possible to blip the secondaries. Blipping it out of gear, the engine revs too fast to get the secondaries in. I wouldn't want to blip the motor up and back to 4-7k or anything, I don't believe that's very good to do?

You shouldn't ever have to touch that idle control screw. if you are you are just masking another issue(s). When Merc received those, they did not adjust them, they were bolted on and left at the predtermined point. The IAC does more to control the idle.

I've played witha few TB's and have seen the primary bore hang open when slowly being closed. When snapped shut it closes. I hate to see you spend money on a 63mm when you shouldn't have to.

[Patton]

WOW,... I thought ZR-1 mods are pricey until I got curious about other exotics and went lookin. A Lamborghini Diablo (early 90's) muffler,... 3000 dollars.... A whole cat back system is 9,000 and the headers are 4000. Thats not taking into consideration that its gonna require you to pull the goddamn engine to do it.

Ya,... I take it allllll back! Thank God for GM

[tomtom72]

You got that right Patton! What was it some one said? "If you have to ask how much, you can't afford it!" Well , that's me!

Aurora, Yes you & I are a similar with our buying experience. I shrug & just chaulk it up to buying a used car. I am in no way less jazzed about the car, it's too amazing to me that I actually own a ZR-1! That I get to drive it whenever I want is like a drug. I'm addicted to this car. My previous owner was a book maintenence type guy, except for the coolant & oil. The rest he let the dealer take care of & it wasn't much except for recalls. Heck, he didn't even complain about the old chip & the idle problems. I'm down with you on the price but I consider the well kept cars will always carry a bit of a mark-up over the norm. I was well pleased with what I got for my 24,900.00. But that is in the eye of the buyer & it's subjective.

What has me stumped with this header thing is that I read that you want bigger dia. exhaust after the headers & cats. It seems to me that the ticket is 3" stuff but I only found 2.5" to 2.75" stuff. I have not looked at the designer stuff, only the standard packaged cat back sys from like Flowmaster. It looks like you need to know how to weld or know a shop that's willing to do some fab work. I got stuck on that write up by Hib about his exhaust sys. That seemed like the way to go. I gotta hang out with the local gear heads so I can find out which shops do that stuff in my area. I've been gone too long for me to know. Oh well once more into the breech! Gotta go drum up some side work to fund the ZR-1 project. Mod proof...ha! Now I'm gettin the bug.

If I knew enough to offer info on your problem I sing out...trouble is I don't. Can't wait for you to tell about the stuff when it comes back from Marc! Good luck!


Tom

[Aurora40]

Originally Posted by tomtom72

What has me stumped with this header thing is that I read that you want bigger dia. exhaust after the headers & cats. It seems to me that the ticket is 3" stuff but I only found 2.5" to 2.75" stuff. I have not looked at the designer stuff, only the standard packaged cat back sys from like Flowmaster. It looks like you need to know how to weld or know a shop that's willing to do some fab work. I got stuck on that write up by Hib about his exhaust sys. That seemed like the way to go. I gotta hang out with the local gear heads so I can find out which shops do that stuff in my area. I've been gone too long for me to know. Oh well once more into the breech! Gotta go drum up some side work to fund the ZR-1 project. Mod proof...ha! Now I'm gettin the bug.

Well, B&B has a 3" system. Callaway has a 2.75". And Corsa and Flowmaster have a 2.5". The stock system seems to be ~2.75" at the cats, 3" back by the mufflers, and neck down to less than 2" into the resonator and back out.

In my opinion, the design matters as much as the size. For example, say you have a 3" system that has two 180-degree bends in the mufflers. Or has a bunch of chambers with offset entry/exits. Or it has baffles in the airflow path. Will that flow better than a 2.5" pipe that has no bends or chambers?

In general, OEM mufflers tend to use bends, though I don't know about the Corvette. Mufflers like Dynomax also use bends. Sometimes the bends are in conjunction with chambers. Flowmaster uses chambers and baffling. Companies like Borla and Magnaflow use perforated straight pipe with glass matting around the pipe. I suspect this is what B&B uses, but I've no real basis and never asked them. Corsa uses resonance chambers around a straight pipe. So the pipe only has one small ring cutout, not perforation.

In general, a given diameter of pipe will flow less when it is heavily perforated than it will when it is solid. And certainly chambers and bends will flow less than straight. So then the question is how much does size matter when you have different constructions? Does a custom 3" Flowmaster system with chambering and baffling flow better than a 2.5" non-perforated straight pipe? I dunno, maybe, maybe not. Flowmaster also has different degrees of baffling/chambering depending on the muffler. The loudness goes up with the less baffling.

As to how much is enough, I imagine that depends too. On a 350ci motor at 7,000 rpm, how much flow is needed? Dual 2.5" pipes have the same cross-sectional area as a single 3.5" pipe. To put it in old-school Corvette perspective, a 350ci motor at 7,000 rpm is displacing as much volume per second (i.e. flow) as a 427ci motor at 5,700 rpm, or a 454ci motor at 5,400 rpm.

I think Corsas in general are neat. I have them on my Aurora and was impressed with the quality, the light weight of the mufflers, and the sound. I just think the tips are too flashy for the '84-90 style of 'vette. But they'd be strong on my list of replacements. I would like a bit deeper/rougher sound, though. The Corsas in Jeff's clips sound like my Aurora on steroids, sort of a refined crips burble, very exotic, though Jeff's car sounds a lot more rough and tumble than the Aurora, as you'd expect from an extra 1.7L of motor. I'm not sure if that's the sound I want or not from the ZR-1. I'll have to think about it. But I definitely like the design of the system. A 2.75" system would appeal even more, though. 3" seems a bit big for a stock motor, but what the heck do I know...

Only mildly related, the Aurora had a stock single pipe of about 2.25" that Y-d into 1 7/8" to the mufflers. The Corsa is 2.5" all the way, and bumped the power very noticeably. VERY noticeably. This is a 4.0L motor that revs to 6,500 rpm, so it is trying to push about 35% less volume out per period of time. Yet it gets by with a single 2.5" pipe quite well. Though, maybe there's even more power left on the table, who knows. I'm sure there is in the manifolds, as it's a big transverse motor with a big tranny, and there isn't much room for the manifolds at all.

Jeff, I'll PM you about the TB. Thanks.

Originally Posted by Aurora40

The Corsas in Jeff's clips sound like my Aurora on steroids, sort of a refined crips burble, very exotic, though Jeff's car sounds a lot more rough and tumble than the Aurora, as you'd expect from an extra 1.7L of motor. I'm not sure if that's the sound I want or not from the ZR-1. I'll have to think about it. But I definitely like the design of the system. A 2.75" system would appeal even more, though. 3" seems a bit big for a stock motor, but what the heck do I know...

Jeff, I'll PM you about the TB. Thanks.

On the engine size, the Aurora is lacking 2.0 litres. I'm running a 368.

As far as exhaust, the Corsa with the 2.5" pipe does just fine for a 350, and even up to the 368, although I know I'm probably missing some ponies. Going to a 3" system doesn't hurt either. Most people claim back pressure helps, but after seeing a car with supertraps adding removing discs didn't affect the hp/tq output. The LT5 just wants to move air and it seems to do it no matter what.

Reponded to your PM.

[tomtom72]

Aurora, thanks for the results of your research. I started to remember some of the HVAC stuff I was taught. Yes bends generally are bad but they can be overcome...that's where the R & D $ goes. I guess it's time to save up for the headers.

Jeff thank you also for the sharing of your experience. I will worry less about what size pipe & more about coming up with the cash for headers and an exhaust system to mate to the headers. I gotta do cats due to DMV regs.

I think I will lean more toward getting space to pull the plenum & I/H to get port work & finish work done by the friendly local west coast duo. I also like stealth! I know how to pull that stuff off, I'm not so sure I'm ready to do headers & an exh. system with my short experience.

Good luck with the T/B and thanks again for sharing info Aurora!


Tom

[Locobob]

For those who wanted to see my porting work I put up a new thread with some pics for you.

[Locobob]

Originally Posted by Jeffvette

On the engine size, the Aurora is lacking 2.0 litres. I'm running a 368.

As far as exhaust, the Corsa with the 2.5" pipe does just fine for a 350, and even up to the 368, although I know I'm probably missing some ponies. Going to a 3" system doesn't hurt either. Most people claim back pressure helps, but after seeing a car with supertraps adding removing discs didn't affect the hp/tq output. The LT5 just wants to move air and it seems to do it no matter what.

Actually thats not quite accurate Jeff. When we played with my Supertrapp mufflers on the dyno the car lost about 10hp up top when we added backpressure. I expected the added backpressure to add low and mid range torque but it did not. The car made best power at all rpm levels with the exhaust wide open.
Lesson = LT-5's like to breath.