BradC

I was wanting to do true duals for my car. Would that be wise? Do I need to go with a new y-pipe? Also, the collector diameter on the pacestter header is 2 1/4in. Does that mean the if I go with 2 1/2 pipe, It would not make a difference since the collector is only 2 1/4in? I was thinking of having 2 cat and 2 mufflers, one each for each header. What do ya'll think?

bigsteve7

Considering that LS1s making 300+ RWHP stock do so on a 2.75 inch single exhaust, duals are not really necessary. Itll be really expensive to fabricate and youll probably end up losing power.

If you do decide to go true duals, do small piping... you dont want to lose all of your backpressure, especially on a small displacement motor.

bbentley40

Listen to what bigsteve7 said.. also.. there is something about true duals and your question about getting a new y-pipe that is just wrong. If you have true duals you will not have a y-pipe at all... you will have to get a X or H pipe and fabricate your exhaust around it. Bottom line is that true duals work great on the LT1 and LS1 but probably is not worth the $$$ for a v6. If you want to do it then go for it, but I think you could do just as well with a set of headers, new y-pipe, and better flowing exhaust.

Bliggida

Backpressure myth rears its head again

Steve, it's not actually as bad as you think. It's like 'big gears kills top end" well yes but only minutely.

A typical V8 or in this case a worked over V6 needs about 6 lbs of backpressure at the tailpipe. 6 pounds If you were to run open headers and place your hand about an inch away from the collectors (assuming you could do so without burning yourself) that would give you all the back pressure you needed.

Having said that, you don't lose torque, either, you gain torque, but what happens is that you gain even more top end horsepower. If you plan on drag racing that's what you want. Especially if you have plans on down the road to increase flow, or forced induction.

2" dual exhaust is the same flow rate as a single 2.5" exhaust
2-1/4" dual exhaust is the same flow rate as a single 2.75 exhaust
2-1/2" dual exhaust is the same flow rate as a single 3" exhaust
etc etc.
If all you ever plan to do is just a basic air intake and exhaust system then all you would need is about a 2-1/2" single exhaust - mandrel bent. But, if you are serious about the car enough to want to go with duals then I also assume you are only starting with the exhaust and hence need to build the exhaust according to your final power plans, not immediate plans.

There is really not much of an advantage going with a dual setup, other than to say you did it. There is some horspeower to be gained through scavenging - use of an X-pipe (H-pipe is not the same thing and will not yeild a power gain, just equalize sound and pressure pulse) But the cost of doing so on a 4th generation F-body that was never meant to fit an exhaust underneath the driver side of the body is going to cost quite a bit.

A single 3" catback will flow just as much and cost half the price. Then just add your headers, Y-pipe, I-pipe and a high flow catalytic converter. Be all the flow you need.

MustangEater82

Just want ot put on my experience....


-ran my car, no i-pipe or muffler connected, jsut stock manifolds to stock y-pipe and a semi-stock clogged CAT, I ran a 15.6, in 3-4 seperate trips.

-I ran an open y-pipe when the CAT got completely clogged, never hit the 15s, I was stuck int eh 16s, 60's were slighlty slower, but no more then a 1/10th of a second.

-Put a $15 muffler form Discount Auto on my y-pipe, I ran 15.5s, eventually ran my best of a 15.4

-Put a stock z28 catback system on my car, and put a cutout jsut before the CAT, I ran with the cutout open and ran 15.9s-16 flats, then later that night I rigged something up that restricted the flow form the CAT. I ran 15.5s-15.6s consistently

-People told me backpressure was a myth and that I weaterh caused the better times since its colder later at night. So I tried this one night.

1st run no restriction open cutout 16.00@84.3
2nd run some restriction on cutou, 15.6@85.6
3rd run no restriction open cutou 15.98@84.5
4th run some restricht on cutout 15.5@86.6
5th run no restirction open cutout 16.1@84.8
6th run some restircition on cutou15.6@85.9

My expereince is the 3.4L really likes to have the exhaust opened up but eventually gets to a point where it has too much free flow.

YOu can believe me or not just sharing my expereince, geting my car form 16.8s with muffler and homemade CAI to mid 15s.

I am a pretty consistent driver, I personally do not think its a good idea, backpressure or whatever. Its a pretty expensive setup and actually I think James Montigny waaay back in the day actually setup true duals on a 3.4L and it sounded bad. I think that is maybe someone else rembers it.

Good luck with whatever you do.

Bliggida

Eric, with OBD-II systems you have to re-tune to allow the computer to make the most of the exhaust, can't just unbolt it and go like you can with a carb'ed car. I guess I should have mentioned that.

If your fuel and spark was increased and had optimum timing for running open headers you'd go faster. But you also have to bear in mind your car is nearly stock. You aren't running heads or a cam. If stock, You do need some backpressure, but not much. As I said so long as you have pipes out the back with a muffler that will be all the backpressure you need for a stock vehicle. Off the top of my head a stock V6 will need around 10 pounds of backpressure. Maybe a tad less.

bigsteve7

Just curious, not trying to discredit what youve said, but his car being a '94 would be OBD-I would it not?

Bliggida

You are correct.
I just assume - 4th gen V6 = OBD-II. Not neccesarily the case.

Same still applies though. If you don't tune the computer to what you did to the mechanics - don't expect a power gain.

MustangEater82

I have cleared all codes and driven the car for a weak with open Y-pipe, still same result.


I am giving up no one seems to give on this argument.

BradC

What if I went with headers to a flowmaster y-pipe, then 2 1/2in pipe to CC, then 2 1/2in pipe to mufflers, then 2 1/2in pipes out the back. Then I could get a custom chip burned. Could I get 20hp out of that? This would be the easiest thing since I already have the muffler.

bigsteve7

You will never get 20hp out of any kind of exhaust. I'd say youd be lucky to see 10 max. Also, computer tuning really isnt that necessary with just an exhaust upgrade on F-Bodies.

What youre talking about running is similar to what the late second gen Z28s came with and some of the third gens and late model monte carlos.

You mean a big pipe to the converter, and then split the exhaust from there right? You can do that if you want, but once again its just gonna cost you an arm and a leg for nothing but a unique set up. Stick to a single exhaust set up, 2.5 inch exhaust being plenty big for your application.

The cheapest exhaust option is to buy a complete catback from a company like Flowmaster or Dynomax. You will spend ~$300 and be done with it all at once. You can even install it yourself.

HeavyChevySS

This thread is very informative and it's a great debate back and forth! Good job .... And showing the 1/4 times after the mods was great! Can't argue there.

1 point though...when talking about proper backpressure for best hp scavenging, I think that theory goes out the window when you have an engine that is pushing over 400 hp.

Bliggida

If that were true, NASCAR wouldn't run a scavenging exhaust and they are pushing 750 horsepower!!!

Eric, you cleared all the codes, but what I meant is that "Did you retune, as in air/fuel, timing etc. once you do those you should see a gain above any closed exhaust ET you ran.

Clearing codes is not tuning, that's just turning off your SES light.