The Dingo

The title about says it all.

I've been shopping around for quotes for a true dual exhaust for my 90 for the last week or two. The end result being that I may not get such a sytem.

Reasons
1. Cost (most of the quotes have been far from cheap :eek:). Owning a Corvette has some downsides, one of which is you get charged more because people think you can afford to get hit a little harder :(.
2. Looking at the "big picture", if I do decide to build a 400 block based motor or something similar power-wise in the next year or two, the dual 2/1/2" pipes will likely wind up being a little too small.
3. Alot of shops get real worried about whether they can fit dual cats under the car (although not the ideal location I'd prefer them towards the back of the system rather than in the trans tunnel for heat reasons). Any comments on cat placement?

I'm going to one last place to discuss true duals tomorrow morning. If true duals are a realistic option from this shop I may still get them done. If so, I'm definitely getting twin cats (have to - although they will be flanged should I choose to use test pipes from time to time). If I do it, the system will be dual 2/1/2" mandrel bent pipes from the OEM exhaust manifold collectors through to my 2/1/2" inlet Tri-Flo mufflers. I may mod my stock collectors but would rather save the $1,500AUD minimum investment in longtube headers until after I build a motor.

Any feedback on the increase in noise volume going from single to true duals? Possible volume increase is the main reason I'm still looking at this option. I'd like more of a rumble and more noise at WOT and don't care if my car turns into a hotrod in the process. I realise the cats will tone things down a bit.

Future mod wise, I have a SR upper coming which I will install on my stock bottom end - when I do that I'll see if there is a difference with the SR on a basically stock motor.

TIA

(red90sixspeed - I remember your dyno info from before so I don't think power loss will be an issue with duals :))


[Modified by Red 90 L98 Coupe, 8:23 PM 3/25/2002]

65Z01

A guy in SW FL had a custom true dual 3" system installed on his '87 Vette 355 cid. It used a pair of Random Tech bullet cats side-by-side behind the trans and TPIS full length headers. It was tight but all fit well with ample ground clearance.

I think you need to contact a good local custom exhuast shop on this one.

NoWorries

True Duals :yesnod:

The shops, unfortunately are right, there is no room for dual exhaust with dual cats in the prop-shaft tunnel. Are you going to run mufflers? If you're not, I would put the cats up under the rear bumper where the mufflers stock location is. The noise is not any more excessive than no cats and 2-chamber Flowmasters.

Dual 2.5's is enough, in my opinion, for everything right up until 468 CID. A dual 2.5 is choking my buddies 502, but when he just had a 454, it wasn't an issue.

My exhaust is a front 2.5 inch Y-Pipe, into a 3 inch cat, out of a 2.5 inch Y-Pipe. So although I have all of this 2.5 inch piping, equating to a total of 5 inches, all of the exhaust still has to route through that 3 inch pipe. A little muffler shop misunderstanding. :mad Oh well, its a beautiful system and they gave me a great price.

I would definitely go with true duals, the next time my exhaust is redone(3+ years), it will be true duals, with the inception of a set of turbo's :yesnod:

Good luck.

The Dingo

65ZO1, I have the article at home and I know they should fit (especially since I only intend on using 2/1/2" tube.

Problem is, alot of guys over here see something that isn't a (Holden)Commodore and err on the side of caution and say - gee, I dunno if it will fit.

The one place that said no problem was $1K above anyone else and I KNOW that they can and have done better pricewise but no dice :mad . I'm not paying $2.5K AUD for two stainless pipes with some bends, flanges and two cats.

I had some work done by the shop I'm going to tomorrow a few years ago, hopefully it will be better news tomorrow. :cheers:


[Modified by Red 90 L98 Coupe, 6:52 PM 3/25/2002]

The Dingo

NoWorries, I'll be using TriFlo mufflers from an L98 system so the cats will have to go in the prop shaft tunnel or next to the gearbox.

I think my most extreme N/A motor I could build would be a 420 stroker (although that twin turbo "small displacement" motor idea is still floating around :crazy:) neither will likely happen for the next year or two though. From the exhaust diameter to engine output charts I have seen, I thought I'd need 3" duals for anything over 400 inches and 450hp. I could be wrong though, I'm just going off what I've read in that department.

If I don't get duals I was going to go with the 2.5" into 3" into 2.5" system like you describe.

We'll see tomorrow.

Thanks for the input guys. :cheers:

cohocarl

I believe the cat needs to get hot (real hot) in order to work, and way at the back of the system may be too far away from the fire to keep the cats hot. :(

I'm planning on putting 2 1/2 true duals on my 85 soon. I need it to get a little colder down there in Holden land (warmer up here) so I can get some work done on my car. :D

Are those Holden's as nice as they look on their web site??????? I do not understand why GM doesn't slap the steering column on the left side and sell them here. They look VERY nice. :yesnod:

Take care,

Carl

Dr. Evil

I dont think 2.5" duals would be a restriction by any means, even on a 400 CI displacement motor. Especially if you get a good x or H pipe. It'd be nice if Beach Bum would chime in on this. He has I 'think' a 3" or 3.5" single exhaust on his 383 superam motor. I remember him discussing weather or not he needed a bigger exhaust dia for his application a while back(several months ago). Good stuff but I couldnt find that particular thread anywhere (I looked). As for it all fitting, are you going with a set of bullit cats? I thought they were quite a bit smaller than the oems. That might help you fit it in there. As for volume, two 2.5" pipes is 'about' the same as having a 5" single exhaust to a point.

The Dingo

Carl, I know they need to get real hot to work but my problem is if they are in the tunnel I get hot (and my motor gets hotter alot more quickly at lights and takes longer to cool down). Damned if I do and damned if I don't on that part...

It's been a little cooler lately so hopefully you should be able to commence work soon :D :jester .

Those Holdens ARE nice :yesnod:. If I wasn't into Vettes I'd probably be driving one myself. A few years back the older models didn't do anything for me but the current ones are really nice. There are getting to be more Monaros on the roads lately. I usually see green ones sitting in dealerships waiting to be sold while yellow seems pretty popular out on the road. Yellow is nice. Modded utes are nothing new, they are just getting quicker now as guys over here learn how to play with the LS1 electronics. I think that now that Mr Lutz is working at GM it is a matter of when you guys get a few Holdens rather than IF :yesnod: . All the press over here lately has been about how we might be exporting them or having them built over there for you guys.


[Modified by Red 90 L98 Coupe, 8:30 PM 3/25/2002]

The Dingo

red, I figure bullet cats would fit best, I'll have to check to see if thats what I would be getting from this place tomorrow if I go that way. The size issue does worry me because I'd really prefer not having to spend money twice in the same place doing something over again later if I build a big hp motor.

I vaguely recall Beach writing about changing exhaust size but can't recall what the outcome was. Thanks for looking though. :)

TrueBlue ChevyDude

I had dual cats with a true dual 3" exhaust setup on an 88 with Hooker Long Tubes. No fitment problems at all, you just need to stagger the cats one behind the other. I now have straight 3" pipes with custom X pipe, no fitment problems either.

You have to go with someone who knows what they're doing. I went to Mighty Muffler in Twin Oaks, PA. They do about every racer's custom exhuast around here, they have contracts with small-volume custom car builders to do the exhausts on their car. Very professional job. Every mechanic I've been to drools over the install. 3 bolt flanges at every joint, I can drop the exhaust w/o even using a lift.

I had Hooker Long Tubes, Borla stainless steel mufflers, dual 3" cats and stainless 3" pipe, all with 3-bolt flanges done for $1900. Of course a year later I had them rip out the cats and put in an X pipe.

It can be done!

1991Z07

Random bullit cats will fit in there easily. I have them shoved onto the back of my TPIS headers. The muffler shop cut about 2" off the collectors to get a smoother bend into the resonator and to position the cats right next to the heat-shields down there. I know mine don't get very hot down there unless I've been doing a hot-lap session at the track. On the street they are just fine.

With that kind of pricing for a custom system I would look at a full aftermarket LT1 style system for the car. All the work is already done for you, and all you'd need the muffler shop for would be to bend new head-pipes from the cats to the rest of the system.

I've said this in a few other posts on the Corsa system, and I'll repeat it here. You will get more torque and HP out of the 2 1/2" system than out of a 3" system (up to just over 400 cu/in). VetteDoctors did a dyno test on one of their big-inch LT5 conversions with a 3" B&B Tri-flow system and a Corsa 2 1/2" system. The Corsa got a few more ponies from the motor and no resonance inside the car.

I think I'd check pricing for Corsa, Flowmaster, B&B Tri-flow and get a complete LT1/4 system. Check the C4 parts 4 sale section. With so many going over to Corsa, you may find a complete Tri-flow system for $600-$800 US. Buy a set of exhaust hangers from GM for an LT1/4 car ('92-'96) and change them out. I think mine ran $27 from GM.

How much of a tariff do they put on equipment coming from outside Australia? To me, $1,500 AUS for a set of $650 USD headers seems a little steep.

Either way, I think I'd get the headers now along with the rest of the system. No matter what brand you go with, you'd end up paying the installation fee once. Put the headers on the car, get the cats installed on the collectors and hang the exhaust system. Take it to the shop and have them bend 2 pipes from the cats to the resonator, tighten the system up and you are out of there. When you change the motor, remove the system from the headers and set it against the wall (where mine is right now). Install the new motor, put the exhaust back together and you are ready to kick some serious booty.

BTW, is your C4 converted over to RHD? I'd love to see some pictures of the interior. Even after driving on the wrong side of the road for 3 years in Japan and numerous visits to the U.K., I think it would be weird to get in the right side of a C4 and drive it around.


[Modified by Joe90, 10:53 AM 3/25/2002]

TPiS

A true dual exhaust is not needed. A 3-3.5 inch single exhaust works better, and no fitment issues.

Terry

cohocarl

They're calling for 2-4 inches of the white stuff here again tonight.....:(

That would be cool. I think the Commodore and the Monaro with a V-8/6-speed would be nice. I'm wondering if GM is planning on "replacing" the Camaro/Firebird with the Monaro.(?) http://www.holden.com.au/app/serve?p...&cartype=18001
I've never seen one in person, but the pics sure look nice.

Thanks,

Carl


[Modified by cohocarl, 4:51 AM 3/26/2002]

codyusa

I have an '87 383 with SR. I am running true duals, TPIS coated headers, no cats, Dr. Gas X pipe, and then out Power Effects. I installed B-Quiet under all the carpet. Still have to test the noise level. My installer really didn't have a tough time installing the system. All the connections are also welded . The headers were on , so he had to do the bending to line up with the X pipe and then out the P.E.'s. About 2 hrs. was all it took. When you get the car on a lift, the system looks as though it was from the factory, that's how good of a job this guy does. Hope this helps.

The Dingo

Joe90, I've already got the TriFlo L98 system - I bought it off a forum member here for $600. I've bid on TriFlo LT1 systems but none of the deals eventuated. I've heard nothing but good things about Corsa but I love the looks of TriFlo's and I don't think reasonance will bother me. We'll see.

I've got all the LT1 hangers, all the shop should need to do is weld tabs onto my exhaust. I'm waiting on the different LT1 lower suspension arm bolts so I can bolt up the rear brackets before I take the car in for the exhaust work. (I need an impatient smiley for this point)

Our exchange rate is such that for every AUS dollar I pay, I get 51cents American back, so prices for things I import double before shipping and duty are factored in. A Goods and Services Tax of 10% applies to all parts purchases, as well as something like 15% import duty on parts. If the part is for a car over 30 years old, duty is less ;). There are ways to minimise shipping and duty, you just need someone understanding on the
other end of the deal to help with this sometimes.

Best price for good headers made over here is about $1500 AUS. Alot of guys pay up to $2,500 AUS for this. In alot of cases it will probably be a little cheaper if I import a set off the shelf from over there.

Until I work out the specs of my motor I'll probably just run with the stock collectors. I know this probably isn't the best idea but it makes sense to me given I'm not exactly sure what motor combo I will put together when I am ready. The new front pipes aren't a major component of
the quote I got yesterday so I think I can live with that.
My car is converted to RHD. I have some pics I can post here or send you but I'm having problems uploading & sending picks. I am trying to rectify this now and will post something as soon as I am able.

Terry, I'm mainly looking at duals for sound reasons, although increased flow ability further down the track is a concern. Thanks for the info though.

P.S. - I almost overlooked saying this - the quote was about the same as the best quote I'd gotten so far. The difference was that this guy took the time to go through the quote point by point. Healso took the time to put the car on a hoist and have a good look at where things would fit with me. He gave me his working sheet instead of just giving me a card with a bottom line on it. The cats he mentioned aren't bullets - it looks as though they are smaller size normal cats, they are well priced and he says the two combined will
flow better than my current 3" single but I don't think they are anything special flow-wise. We checked the fit on the hoist and they are okay (mounting them near the motor/next to the trans). I also got to know roughly how much more the 304 stainless I've been asking for costs than the normal 419? grade. I'd like to run no cats but if I get caught without them on the road the penalty is HUGE - $20k last time I heard :eek:.

If I'm correct - random bullet cats were about $200USD each, making my total investment if I got them over $800AUS.
A little more than I am prepared to spend right now. If only the exchange rate improved (I'm sick of saying that :rolleyes:).

The local race type shop has an attitude and charges like nobodies business, so I can't really consider them.

Thanks for all the responses guys, they are all helpful. :cheers:


[Modified by Red 90 L98 Coupe, 5:08 PM 3/27/2002]

Beach Bum

I see my name mentioned above once or twice so I'll chime in on what I have discovered.... Its called "Everything Beach has discovered about C4 exhaust systems".... which isn't a whole lot, even many major engine builders are self admitted exhaust dummies.....

Anyway, the following is in a nutshell my exhaust system trial and errors over the years and my opinions based upon talks with exhaust manufacturers such as Flowmaster, Random Technologies, etc....

Started off with modified L98 with cold air box, 52mmtb, ported plenum, Accel large tube runners, ported Dart 2 heads, LPE 74211 cam, TPIS level 5 chip, Hooker headers through 2.5" front Y pipe through stock GM cat out 2.5" rear Y pipe and through two Monza style muffler resonator tips.

My 1st modification was too remove the very clean stock main single GM cat.... I immediately picked up a solid 2 mph and close to 3 mph in trap speeds at the dragstrip, put the stock GM cat back on, and lost the 2-3 mph I so graciouly gained. Lesson learned here.... on a modified 350 L98, the single cat design is very restrictive. It was probably costing me a real 25 hp or so. On stock motored L98's I have mixed reports.... I've heard of some gaining 15-20 hp and others have no power gain by removal. I dunno what the true gain is on a stock L98 motor, I would guess the real answer is somewhere between the two... maybe 10 ish, but just guessing.

As a further note, after a long discussion with Brad @ Random Technologies years ago, he told me his high flow catalytic converter would increase hp by 6hp versus the stock gm cat with my set-up. Which is pretty darn good, and I appreciated the guys total honesty. But it is a far cry from the 25ish I experienced. I believe the dual cat design is the best case scenario, I don't feel even with a modified 350 motor that dual cats will significantly hurt performance vs no cats... but just my opinion, don't know for fact they won't.

I switched to a 383 Motor with the Superram after this

I then felt the single 3" pipe is probably restrictive, thus recently I had fabricated a whole new true 3" exhaust with non-mandrel bent pipe, thus the exhaust at the bends is more in the area of 2.75" diameter pipe. I also got rid of the Monza style resonators and went with Holley-Flowtech-Warlock mufflers which when capped up, the exhaust takes two 180 degree turns and is really quite tame on the street noise wise, however at the dragstrip I usually uncap thus the exhaust runs straight through the muffler. Sound is obnoxious to say the least. (See some of my video's in my webpage to hear) The results ? When uncapped, I think I have roughly 1/2 mph more trap speed, thus this would indicated a 5 hp gain vs the previous exhaust set-up. However, the true dual 3" exhaust (I have a H-pipe fabricated in too) is a bit heavier than the other exhaust set-up, perhaps by as much as 20-25 lbs, thus maybe I picked up 7-8 hp.... but obviously hard to tell.

Considering my 383 is built a bit on the mild side, it makes only roughly 420-440 hp and the et improvement wasn't much, thus I think the original exhaust I was running is probably adequate up to around 450 hp before substantial gains will begin to be seen.... but once again I dunno for sure, this whole subject is kind of a mystery, and of course my results could have been skewed to perhaps another limiting factor my motor may have.(injectors are done or maybe the un-ported Superram base is out of rpm or maybe my stock ignition needs a spark boost.)

Its hard to say !! For your set-up, I think dual cats would be really nice and quiet and yes they can fit, but real tight... but others have done it. I don't think the dual cats will hurt you too much until you start boosting your cubic inches hard or rev your motor to 6500 rpm plus... but dunno, just guessing again. :crazy:

As far as cost.... Mine was done by a fellow racer and friend who happens to own his own performance exhaust shop. (How convenient:)) Thus I got an incredible deal of about $ 250 for everything bent and installed. (Minus the mufflers which I bought for $ 64 a piece through Jegs) Go to a fabricator and ask them to start bending, this shouldn't be over $ 500-600 for non-mandrel bent. If they're any good they'll bend and place right in front of your eyes and put it together in only a few hours. As a note, I think Mandrel bent is overrated and most exhaust shops don't have the capability anyway... but once again I gotta say... I dunno for sure.

Regarding what is recommended for the HP. The below is what Flowmaster says:

Up to 300 hp - True 2.0" exhaust is adequate
Up to 400 hp - True 2.5" exhaust is adequate
Up to 600 hp - True 3.0" exhaust is adequate

They're not saying a 500 HP motor won't run well with 2.5" true duals, they're simply saying it won't be optimized... in otherwords that 500 HP motor may be a 525 hp motor with true 3.0" duals.

Hope this kinda helps... even though I know it doesn't.

Cheers,
Beach Bum

jcazin

Do you need to run cats? If not, Mid-America sells a great true-dual kit- I've had mine for 7 yrs, 40,000- aluminized system to flomasters- tolerable at idle, rowdy under throttle, and a lot less heat under the hood and passenger compartment- Ive been very happy with the setup

BBA

The truth is, it's easier to put an exhaust on a C4 than almost any other car made...but shops want to rip you cause they think they can.

In the meantime, the best bet you have of a true dual system is finding a used LT1 cat back and mating it to some Hooker headers. It's a better system than most any you will have someone install anyway ( 2.75" stainless pipes with perfect bends that don't 'neck-down' ).

BBA

NW...there are a lot of people who have dual cats on L98's. They fit perfectly when offset staggered.

Besides, wouldn't putting the cats at the back of the car not let them get hot enough to work?