Mod To Stock Mufflers

[Paddy_SP]

This is my first post for some years, so please be nice to me! Anyway - my '90 ZR1 got parked for various domestic reasons (my wife got the Big C amongst other things - she's well now though). Over the last couple of weeks I've managed to clear a space in the dedicated 'smart' garage bay, and following the fitment of a new battery, fired the Z up and moved her out of the machine-shop/car storage area (it was one of 4 cars and 2 motorcycles in there) and across the yard to the new building.

She's sitting in there looking gorgeous, and I've done various things to get her roadworthy. Although she's only done just over 31,000 from new, I discovered that at some stage the left headlight must have been broken and replaced, as there were small fragments of lens glass in the well behind. That wouldn't have been a problem except for the fact that the idiot who replaced the lamp, didn't bother to fit a new cross-pin - the remains of the sheared-off one were still in the spindle. Consequently, the headlight could be pushed back and forth with little effort. Why it didn't do this before, I don't know.

After about four hours of cursing, I finally got it all sorted out - I had to machine up a new pin partly because trying to find one over here in the UK would be a non-starter, but mainly because I live miles from anywhere and I'm used to doing such things. The biggest problem by far though was that whoever was 'responsible' for designing the headlight assembly needs a good kicking. Several of the main securing screws were obscured by other parts- all it needed was for them to have been moved to one side - there's plenty of room, and it'd have been a simple job. As it was I busted a gut and several knuckles trying to strip it all apart.

Still - all that aside, I'd now like to modify the stock mufflers a little. Partly to ensure that all four outlets actually act as exhausts (I'm an engineer, and I'm funny about such things) and partly to make it sound a bit closer to a proper sports car. I've searched high and low - both on this site and elsewhere, but haven't found any reference to anyone doing this. Possibly it's because I'm using the wrong search terms, or maybe it's because picking up replacement exhausts for a ZR is an easy thing to do in other parts of the world. Releasing extra power isn't really an issue, as I live in a place where it's not hard to have the hedges scraping both sides of the car at the same time...

It would seem to me that I have two choices - a) I use a hole saw and cut out the blanking plates in the two inner pipes, or b) I remove the mufflers, cut the tops off, do whatever I have to inside, and then TIG-weld them back on again.

I would therefore be most grateful to hear from anyone who has any constructive comment on this!

[We Gone]

First off congrats on getting the ZR-1 on the road again. and hope the wife is doing well as the C word can be devastating.

I would hesitate to open the second side as you will get a lot of un-wanted drone. You would be better off getting aftermarket muffs or a complete system. I'm sure you will get lots of great suggestions here.

[Paddy_SP]

First off congrats on getting the ZR-1 on the road again. and hope the wife is doing well as the C word can be devastating.

I would hesitate to open the second side as you will get a lot of un-wanted drone. You would be better off getting aftermarket muffs or a complete system. I'm sure you will get lots of great suggestions here.

Many thanks for your kind sentiments! As for the exhausts - if I can't modify the stocker mufflers, I'll leave it 'as is'. Right now, other things have call over my cash resources. Here in the UK we can hunt more or less as much as we want. I can, for instance, stalk deer 365 days of the year if I want to. Mostly, however, I specialise in high-tech fox hunting. I live in deepest farming country where left unchecked foxes do enormous amounts of damage to livestock. Right now, it's lambing season, and I'm out more or less every night (although NOT in the ZR1!) using high-end thermal imaging and night vision equipment. As this all costs serious money I don't have any spare to throw at a replacement exhaust!

[Racinfan83]

I know this is not related to the topic - but you talk about hunting in the UK - I thought you weren't allowed to own guns there??

[We Gone]

You can try various sizes of opening up the other side as long as you can close it back up if you don't like it. We can only Hunt wild boars and coyotes year round or deer if you farm but all other game has seasons.

[scottfab]

Many thanks for your kind sentiments! As for the exhausts - if I can't modify the stocker mufflers, I'll leave it 'as is'.
...snip...

You can in fact drill out the non-functioning side of each muffler and as mention you'll pick up a nasty resonance (drone). Of more concern is the restriction in diameter going into the front of the resonator at the front of the stock exhaust system. The welding there ends up choking the diameter to 2 1/8 in. This is a performance hit. Many of us have removed this one way or another.


I live in deepest farming country where left unchecked foxes do enormous amounts of damage to livestock. Right now, it's lambing season, and I'm out more or less every night (although NOT in the ZR1!) using high-end thermal imaging and night vision equipment. As this all costs serious money I don't have any spare to throw at a replacement exhaust!

I use to hunt pest varmints here in the US in the open country of Montana. Know what you mean. There was a bounty on some species. Take some night vision pics and post if you have the mind to.

As for the head light buckets design issue and hardware placement you mentioned before, I totally agree. I'd love to write a personal letter to the designer. I have to think he was pressured into leaving it that way for redesign cost constraints. (management)

[Paddy_SP]

I know this is not related to the topic - but you talk about hunting in the UK - I thought you weren't allowed to own guns there??

Ha, ha - I can understand why you might think that as we're not allowed handguns. But as for rifles and shotguns, so long as we have the right paperwork, we can have almost anything except semi and full-autos. I myself have .17HMR, .204R, .22-250 and .308. Other things make up for it - screw-on moderators, for example, are easy to get permits for, so I have them on everything.

You can try various sizes of opening up the other side as long as you can close it back up if you don't like it. We can only Hunt wild boars and coyotes year round or deer if you farm but all other game has seasons.

Thank you! As for the hunting - most of our deer have seasons too (not Muntjac), but the effect of the overlaps is that we can hunt them all year. We also don't need any kind of permit beyond the landowner's permission to hunt on his ground, and we can take as many deer as we like.

You can in fact drill out the non-functioning side of each muffler and as mention you'll pick up a nasty resonance (drone). Of more concern is the restriction in diameter going into the front of the resonator at the front of the stock exhaust system. The welding there ends up choking the diameter to 2 1/8 in. This is a performance hit. Many of us have removed this one way or another.

I use to hunt pest varmints here in the US in the open country of Montana. Know what you mean. There was a bounty on some species. Take some night vision pics and post if you have the mind to.

As for the head light buckets design issue and hardware placement you mentioned before, I totally agree. I'd love to write a personal letter to the designer. I have to think he was pressured into leaving it that way for redesign cost constraints. (management)

Thanks - I think I'll pull the exhaust and have a good like at the restriction you mention.

With regard to the varmints - as we don't have coyotes or anything similar here in the UK, our red foxes grow really big. I think the record is 36 lbs. but generally the mid-20's would be considered large. If you're interested, here's a link to a book I recently wrote on hunting foxes: http://www.countrybooksdirect.com/product.php/855/111/a-foxers-year I'd love to hunt in Montana!

[WARP TEN]

Those who mention a "Drone" if you open up the closed section of the mufflers are correct. Our engines produce frequency spikes that produce noticeable and annoying resonance at two primary RPM points--1,800 and 3,400, with a less noticeable one around 2,400. The closed pipes of the earlier mufflers are closed for a reason: They are behind the Helmholtz resonators which mitigate the resonance at (I think) the 1,800 RPM point, while the center resonator handles the 3,400 point. (Or vice versa; can't quite recall). Each resonator is a closed chamber with one opening and is sized for a specific frequency. The Corsa system uses a similar feature they call quarter wave tuners, as do some others. So opening up the Helmholtz resonator would result in an unpleasant exhaust sound. Later stock mufflers have only one outlet but still retain the resonator section to combat resonance.--Bob

[Paddy_SP]

Those who mention a "Drone" if you open up the closed section of the mufflers are correct. Our engines produce frequency spikes that produce noticeable and annoying resonance at two primary RPM points--1,800 and 3,400, with a less noticeable one around 2,400. The closed pipes of the earlier mufflers are closed for a reason: They are behind the Helmholtz resonators which mitigate the resonance at (I think) the 1,800 RPM point, while the center resonator handles the 3,400 point. (Or vice versa; can't quite recall). Each resonator is a closed chamber with one opening and is sized for a specific frequency. The Corsa system uses a similar feature they call quarter wave tuners, as do some others. So opening up the Helmholtz resonator would result in an unpleasant exhaust sound. Later stock mufflers have only one outlet but still retain the resonator section to combat resonance.--Bob

Thanks for your helpful post, Bob - it is most appreciated! :)

[Gunny]

Another suggestion, assuming that it will work with any government emissions requirements that you have ...

install long tube headers, no cats, and late model stock exhaust. there is no drone, almost stock quiet in the cabin, and a decent sound (subject, I know) behind the car. My current setup is SW headers, no cats, and stock exhaust from a 96 LT4 (h-pipe behind the resonator) and it works well for me.

[Paddy_SP]

Another suggestion, assuming that it will work with any government emissions requirements that you have ...

install long tube headers, no cats, and late model stock exhaust. there is no drone, almost stock quiet in the cabin, and a decent sound (subject, I know) behind the car. My current setup is SW headers, no cats, and stock exhaust from a 96 LT4 (h-pipe behind the resonator) and it works well for me.

Many thanks for your thoughts! Emissions regs are generally overlooked around here, so I very much doubt that would be an issue! No - the problem would be that there are so few ZR1's in this country that I'd have to ship an exhaust in from abroad, and that would be cost-prohibitive. :(

[Bob Eyres]

A low cost approach would be to just remove the mufflers and use eliminator, (straight) pipes. Also replace the resonator with an Xpipe.
I don't know if this will give you the sound you're looking for, but at least you won't trash the expensive stock mufflers, and you can return to stock anytime.
This could be accomplished by any local muffler shop.
I'd love to drive my ZR-1,(see below), through the English countryside, loud as hell.:D

[Paddy_SP]

A low cost approach would be to just remove the mufflers and use eliminator, (straight) pipes. Also replace the resonator with an Xpipe.
I don't know if this will give you the sound you're looking for, but at least you won't trash the expensive stock mufflers, and you can return to stock anytime.
This could be accomplished by any local muffler shop.
I'd love to drive my ZR-1,(see below), through the English countryside, loud as hell.:D

Many thanks - I may well do something along these lines - I wouldn't use pipes that were completely straight-through as I live in a village where they wouldn't be appreciated, but might use some relatively 'robust' mufflers instead. Having said that, my Aprilia RSV1000SP uses a full-race titanium exhaust!

[Gunny]

Re-reading your original post and the various suggestions, it occurred to me (I'm assuming) that you have a stock 90 exhaust. Since shipping presents a problem for obtaining a complete exhaust system, it's probably best to work with what you have.

Near as I can tell (and I've checked the measurements of the 90 as well as the later years' exhaust system) the two bottlenecks of the 90 exhaust in terms of performance are the resonator and the mufflers, all of which have restrictive connectors to the exhaust pipes which should be 2.75". A couple of things you can do and still utilize your existing system is to replace the center resonator with an x-pipe (or less restrictive resonator) ... any good exhaust shop should be able to build an x-pipe to your specifications. The mufflers are also restricted (necked down) on the exhaust pipe side plus one tip is closed off ... you might want to look at the Dynomax line of mufflers to see what looks good for your situation. Dynomax muffs are not terribly expensive and should be able to be shipped easily enough.

Anyway, these are a couple of more ideas for you mull over ... good luck on finding the best solution for your needs.

[Paddy_SP]

Re-reading your original post and the various suggestions, it occurred to me (I'm assuming) that you have a stock 90 exhaust. Since shipping presents a problem for obtaining a complete exhaust system, it's probably best to work with what you have.

Near as I can tell (and I've checked the measurements of the 90 as well as the later years' exhaust system) the two bottlenecks of the 90 exhaust in terms of performance are the resonator and the mufflers, all of which have restrictive connectors to the exhaust pipes which should be 2.75". A couple of things you can do and still utilize your existing system is to replace the center resonator with an x-pipe (or less restrictive resonator) ... any good exhaust shop should be able to build an x-pipe to your specifications. The mufflers are also restricted (necked down) on the exhaust pipe side plus one tip is closed off ... you might want to look at the Dynomax line of mufflers to see what looks good for your situation. Dynomax muffs are not terribly expensive and should be able to be shipped easily enough.

Anyway, these are a couple of more ideas for you mull over ... good luck on finding the best solution for your needs.

Thanks for the constructive suggestions - I'll look into the Dynomax line and consider fabbing up a restrictor myself, as we have very few competent muffler shops in this part of the world.

[Mr Blue]

As previously stated, the stock resonator is the big restriction. The later ZR-1 and LT1 resonators are much less restrictive. Complete exhausts might be prohibitive to to ship, but you could just substitute the later resonator. I don't know the weight, so I can't speculate on the shipping. But used LT1 exhausts can be found for $100-200 USD. Cutting the resonator out and just shipping that would save some cost. Just a thought...

David

[Paddy_SP]

As previously stated, the stock resonator is the big restriction. The later ZR-1 and LT1 resonators are much less restrictive. Complete exhausts might be prohibitive to to ship, but you could just substitute the later resonator. I don't know the weight, so I can't speculate on the shipping. But used LT1 exhausts can be found for $100-200 USD. Cutting the resonator out and just shipping that would save some cost. Just a thought...

David

And a good thought it is too, David; I will certainly add it to my list of options!