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true duals are 100 percent doable with out losing clearance ive got hedman lts with 2.5 inch duals to the rear axle and still have factory ground clearance i have glass pack mufflers this is just a temp set up ill post pics tomorrow
heres what i used
headman lts
headman extensions 2.5 in
18 inch exhaust pipe
cherry bomb 8 inch glass pack
and 22 inch pipe to the rear axle ( soon to be shortened )
and for a worn 305 it worked very well
and the trans crossmember is stock
Sounds like you are dumping just before the rear axle. This is not exactly the definition of "true duals". You need to get those pipes over the axle and pointing out the back for me to consider it a true dual exhaust. Of course, that's only my opinion. I consider the short, before-axle exhaust more of a race exhaust as it resonates the whole car and sounds quite different than duals that route to under the rear bumper. There is a really nice thread at the top of this forum that covers a myriad of dual exhaust system designs, and the thread dates back to 2003. *****'s true dual that is featured in there is likely the 'gold standard' of true dual exhaust systems.
Years ago, there was a speed shop out of Baton Rouge, LA called Thunder Racing that did a whole series of tests on exhaust systems that were all measured on the chassis dyno. They tested mufflers, big pipe, small pipe, single exhaust vs dual exhaust. The "magic combination" for big power seemed to be a Mufflex 4-inch cat-back, that routed into a modified Hooker Aerochamber muffler. However, it's not always as straightforward as all that. Interestingly, my best E/T I ever logged was with some Headman T.E.S. headers, and everyone seems to think that those headers were somehow restrictive.
Another more recent study of exhaust dynamics is the Engine Masters Youtube channel from David Freiburger in conjunction with Amsoil. . In it, (episode 4) they run some dyno sessions on a hot smallblock and a set of headers. They then start running back-to-back dyno sessions and start denting the header primaries to see how much it impacted performance. The interesting part is that it took some serious dimpling of all primary pipes before they lost even 10 horsepower. A nick and a tuck here and there to clearance around things like crossmember and brake lines didn't seem to faze the exhaust flow.
Check out the Engine Masters channel here - It presents some good, emperical "What if?" knowledge that answer a lot of questions with actual horsepower.
it is quiet doable with some patience and a welder and i have no issues informing you and sending you pics of how mines done but do not call me a liar this is my 2nd 3rd gen ( the first was a good practice car it was beyond saving ) ill get the pics either today or tomorrow i need to make some changes to my system anyway ill get some before and after
Sounds like you are dumping just before the rear axle. This is not exactly the definition of "true duals". You need to get those pipes over the axle and pointing out the back for me to consider it a true dual exhaust. Of course, that's only my opinion. I consider the short, before-axle exhaust more of a race exhaust as it resonates the whole car and sounds quite different than duals that route to under the rear bumper. There is a really nice thread at the top of this forum that covers a myriad of dual exhaust system designs, and the thread dates back to 2003. *****'s true dual that is featured in there is likely the 'gold standard' of true dual exhaust systems.
Years ago, there was a speed shop out of Baton Rouge, LA called Thunder Racing that did a whole series of tests on exhaust systems that were all measured on the chassis dyno. They tested mufflers, big pipe, small pipe, single exhaust vs dual exhaust. The "magic combination" for big power seemed to be a Mufflex 4-inch cat-back, that routed into a modified Hooker Aerochamber muffler. However, it's not always as straightforward as all that. Interestingly, my best E/T I ever logged was with some Headman T.E.S. headers, and everyone seems to think that those headers were somehow restrictive.
Another more recent study of exhaust dynamics is the Engine Masters Youtube channel from David Freiburger in conjunction with Amsoil. . In it, (episode 4) they run some dyno sessions on a hot smallblock and a set of headers. They then start running back-to-back dyno sessions and start denting the header primaries to see how much it impacted performance. The interesting part is that it took some serious dimpling of all primary pipes before they lost even 10 horsepower. A nick and a tuck here and there to clearance around things like crossmember and brake lines didn't seem to faze the exhaust flow.
Check out the Engine Masters channel here - It presents some good, emperical "What if?" knowledge that answer a lot of questions with actual horsepower.
i want to keep mine short for a while i like the sound once the 350 goes in then its gonna be changed again this cars my daily so i cant do to much at once
That would not true dual then. True dual as stated above would be over the axles and out the back of the car. That's the hard part of putting true dual exhaust on these cars is getting it that far and clearing the axle, gas tank and suspension.
It's. A form of true duals. Just. Not in the sense of. Over the axles true duals. Is defined. As. Each bank of cylinders on its own. Muffled exhaust just ran mine as per my preferences. After the suspension upgrades and a new rear end I may run it over the axle. But for now it works. And it's a definite power increase and not everyone wants a true dual. Set up over the axle for. Whatever reason.
Last edited by 1990rs305; Jun 10, 2016 at 09:50 AM.
Reason: More
I don't remember what the horsepower gains are. I was thinking something like 20 to 25hp more? Certainly a noticable difference. I'm still stuck with single exhaust, becuase I want to get it up over the axle and out the back. I also want to lower the car so ground clearance is a factor in mine.
[QUOTE=J. Chris Davis;6048376]I don't remember what the horsepower gains are. I was thinking something like 20 to 25hp more? Certainly a noticable difference. I'm still stuck with single exhaust, becuase I want to get it up over the axle and out the back. I also want to lower the car so ground clearance is a no.
the previous owner butchered mine pretty bad so I had to pull it all off and redo
I understand you there. My build came in pieces since the previous owner tore it apart 10 years ago and sat in his garage till I got it. Finding every piece I need especially hardware has been a fun task
GM did a true dual 3" exhaust (out the back totl style) on one of their 3rdgen Camaro bigblock show/test cars a long time ago.. it was in hot rod or car craft, have it at home..
GM did a true dual 3" exhaust (out the back totl style) on one of their 3rdgen Camaro bigblock show/test cars a long time ago.. it was in hot rod or car craft, have it at home..
Think I heard about that, but never seen anything.
Originally Posted by 1990rs305
its pushing 265 at the wheels an i like where its ran to it makes fuel tank and rear end work easy not to mention it sounds kick a..
I bet it has a nice tone to it now too! That is true. It seems about anything I do back there the exhaust almost has to come out of there.
That is my true dual 2.5". my transmission crossmember is my lowest point
it looks great my exhaust was pure necessity and i want to be able to change parts without dropping the exhaust so i like the way mine works my neighbors are so enthoused at 7 am when i go to work and when mines done itll dump out at my rear tires
That is my true dual 2.5". my transmission crossmember is my lowest point
It is difficult to see what you've got going on in the crossmember area and forward. Shorty headers ? Those subframe connectors look a little low, do they ever hit ? How is the ground clearance with the car on the ground ? I am also wondering if your drive shaft will hit your exhaust when your rear suspension fully decompressed/extended. Did you make the exhaust or modify the new hooked system ?
Last edited by 91ls1t56; Jun 10, 2016 at 01:08 PM.
It is difficult to see what you've got going on in the crossmember area and forward. Shorty headers ? Those subframe connectors look a little low, do they ever hit ? How is the ground clearance with the car on the ground ? I am also wondering if your drive shaft will hit your exhaust when your rear suspension fully decompressed/extended. Did you make thevery exhaust or modify the new hooked system ?
Here is the car on the ground. The clearance is fine and the subframes are where they are supposed to be. They are about 1/4" lower than the factory lower control arm mounts. I haven't checked the clearance of the driveshaft at full decompression. It hasn't hit yet. Where the exhaust is over the tranny crossmember it's at its closest point it has a lot more clearance as the exhaust goes back. The headers are headman longtubes and the exhaust is the hooker blackheart fabbed to fit the headers
Here is the car on the ground. The clearance is fine and the subframes are where they are supposed to be. They are about 1/4" lower than the factory lower control arm mounts. I haven't checked the clearance of the driveshaft at full decompression. It hasn't hit yet. Where the exhaust is over the tranny crossmember it's at its closest point it has a lot more clearance as the exhaust goes back. The headers are headman longtubes and the exhaust is the hooker blackheart fabbed to fit the headers
I remember that car/article. Reminds me of John Moss' ZL1 of later years. Amazing it took all that back then to run 12's. crazy how far technology has come. Regardless. A pony car I'd love to have in my stable
[QUOTE=86Base;6048489]Here is the car on the ground. The clearance is fine and the subframes are where they are supposed to be. They are about 1/4" lower than the factory lower control arm mounts. I haven't checked the clearance of the driveshaft at full decompression. It hasn't hit yet. Where the exhaust is over the tranny crossmember it's at its closest point it has a lot more clearance as the exhaust goes back. The headers are headman longtubes and the exhaust is the hooker blackheart fabbed to fit the headers
Way cool. It's hard to see your headers from the side view, they must not hang down as far as mine do. You've got your pipes crammed into that crossmember pretty good, I am wondering if you have them mounted to the crossmember. Also, any contact of the exhaust and anything else, any rattling or banging ? I am not trying to put you down, just curious if you are running into some of the issues that I encountered.
its pushing 265 at the wheels an i like where its ran to it makes fuel tank and rear end work easy not to mention it sounds kick a..
That's within 3 horsepower of what my 305 used to run when I tested it on a chassis dyno. I was using an Edelbrock torquer intake, Edelbrock TES header system, and a modified set of ported 305 centerbolt heads with larger valves and a HUGE amount of porting work.
Some of the details might still pop out on this forum if you search "feeble305"; a tongue in cheek nickname. The car ran a best of 14.04 @ 101MPH with that engine back in 2001. Anyway, 265 rwhp is a good achievement for the 305. That's pretty much the same power as the stock mid-90s LT1 engine.
I'm not done with it yet it's going to go from throttle body to carb and it's getting completely rebuilt with a Howard's cam Edelbrock heads Edelbrock intake Holley carburetor I'm putting more money at a 3:05 then i should be when I got a 3:50 ready to go in the car
this is my 2nd 3rd gen ( the first was a good practice car it was beyond saving ) ill get the pics either today or tomorrow i need to make some changes to my system anyway ill get some before and after 
and when mines done itll dump out at my rear tires 
