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Old 06-22-2008, 10:55 PM
406cu.in. of tire smokin' fun
 

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Supercharged exhaust question

I have a question. I have a 99 K2500 truck with a whipple-charged 350 in it. I just purchased one of those desktop dyno programs and thought I'd test it out. I currently have true dual exhaust, but the program says that I'd gain 43 RWHP by changing to a high-flow single exhaust??? Does that sound right? The exhaust was on it when I bought it, so I don't even know if it came with true duals or not.

There were a couple of parameters that I guessed at, like I assumed the HP rating of the blower was 100HP, assumed 50% efficiency (already entered by the program) and left the CFM rating at 0.

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Old 06-22-2008, 11:05 PM
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Couldn't tell ya of the accuracy of that program but I can tell you that Pro-Max on South Tacoma Way has a chassis dyno. That'll give you hard numbers with no assumptions.
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Old 06-23-2008, 07:46 AM
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Ya, but to do it, I'd have to have the exhaust changed. If I was wrong, then I'd have to change it back.

Turbo Technology is where I went the last time with my other truck. They are right down the road from Pro-Max. They were nice there, but I got the feeling that I was wasting their time because I didn't have any turbos.

Last edited by Pre-Tuner; 06-23-2008 at 09:51 PM.
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Old 06-23-2008, 09:52 PM
406cu.in. of tire smokin' fun
 

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Here's another thought. What if I created a restriction at the end of the tailpipe, like covering half of it up on each side? Would this work to tell me if it was worth having my exhaust redone? Any idea of what I could do to accomplish this?
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Old 06-23-2008, 10:28 PM
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Uh, how does that help me decide to keep the dual or install single exhaust? If I do any dyno runs, it will already be too late. I can run a base line now with the dual, but then I'll have to commit to single and run it again. If it loses HP, then it would be too late.
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Old 06-23-2008, 11:35 PM
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I don't think a 43 rwhp change is realistic. You've done something fishy with the desktop dyno. I'm also highly skeptical that a single exhaust will suit you better than a good dual system. What size pipes do you have already and what kind of horsepower are we talking about? If you have a decent dual system with an H pipe, you'll be fine. If you don't already have an H pipe or X pipe, you might want to consider that.
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Old 06-24-2008, 02:10 PM
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I have dual 3" exhaust and the engine is completely stock except for the whipple and a PCM upgrade. I figure I probable have 350HP, but I haven't had it on the dyno.

F-BIRD'88, I don't want to be an a-hole, maybe you don't understand the problem. I think the dual exhaust may not be providing enough back pressure and could be hurting the scavenging. If I run open headers, that problem will only get worse, right?
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Old 06-24-2008, 09:06 PM
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I couldn't agree more with F-bird on this one.
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Old 06-24-2008, 10:47 PM
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Well that makes sense. Thanks for the detailed explanation. I guess I'll save my money and work on the other truck. Thanks.
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Old 06-25-2008, 01:32 AM
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I have seen well designed single exhaust headered cars make more power than a dual setup, particularly on turbo'ed/supercharged cars. Many dirt track cars run single exhaust setups with adjustable restriction mufflers for this reason.

The reason...exhaust pulsing is symetrical in a single exhaust and hence tuning for air fuel ratios from cylinder to cylinder is simplified.

It is correct that an engine is just an air pump...but it is an air pump with a controlled series of explosions that have to occur at the correct time individually and with the added complication of individual cyl plumbing differences. Single exhaust systems simplifies the system and allows for added tuning by changing relative lengths of cyl plumbing to be changed for specific circumstances.

Look at your firing order and you will see separated dual exhausts systems do not have symetrical exhaust pulses and one cylinder gets the short stick. Balance pipes added to dual systems improve the situation but on pressurized induction systems where mismatches on fuel air mixture can spell disaster, from cyl to cyl it is easier to tune a single exhaust engine at the edge of detonation.

Now you know why the guys with dual turbos have trouble getting a good balance from side to side in fuel/air mixtures and typically have to tune for the lean side. Usually adding a single exhaust outlet evens out the problem and allows the tuner to fine adjust the system to the ragged edge of detonation better than a dual exhaust setup.

Mainly dual exhaust systems just look cooler from a rodding standpoint, they don't necessarily add more power than a well designed single exhaust system.

BTW backpressure is something that cannot be dismissed as not necessary or desirable, some back pressure is needed to build low end torque at low speeds where cam overlap will bleed cylinder pressure. If all your looking for is a peak figure then a open exhaust will always outperform a closed exhaust system, however as most experienced rodders know its the area under the curve that counts and that means from idle to peak rpm. If adding a little restriction to the exhaust adds low rpm power with little loss up top then you have a net gain which adds up on the chronometer at the end of the strip.

Just something to think about.
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Old 06-25-2008, 02:03 AM
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Great Thread. (loud Applause In Background). :d
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Old 06-25-2008, 08:07 AM
406cu.in. of tire smokin' fun
 

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Damn, back to square one.
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Old 06-25-2008, 07:20 PM
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Quote:
Originally Posted by 4 Jaw Chuck
I have seen well designed single exhaust headered cars make more power than a dual setup, particularly on turbo'ed/supercharged cars. Many dirt track cars run single exhaust setups with adjustable restriction mufflers for this reason.

The reason...exhaust pulsing is symetrical in a single exhaust and hence tuning for air fuel ratios from cylinder to cylinder is simplified.

It is correct that an engine is just an air pump...but it is an air pump with a controlled series of explosions that have to occur at the correct time individually and with the added complication of individual cyl plumbing differences. Single exhaust systems simplifies the system and allows for added tuning by changing relative lengths of cyl plumbing to be changed for specific circumstances.

Look at your firing order and you will see separated dual exhausts systems do not have symetrical exhaust pulses and one cylinder gets the short stick. Balance pipes added to dual systems improve the situation but on pressurized induction systems where mismatches on fuel air mixture can spell disaster, from cyl to cyl it is easier to tune a single exhaust engine at the edge of detonation.

Now you know why the guys with dual turbos have trouble getting a good balance from side to side in fuel/air mixtures and typically have to tune for the lean side. Usually adding a single exhaust outlet evens out the problem and allows the tuner to fine adjust the system to the ragged edge of detonation better than a dual exhaust setup.

Mainly dual exhaust systems just look cooler from a rodding standpoint, they don't necessarily add more power than a well designed single exhaust system.

BTW backpressure is something that cannot be dismissed as not necessary or desirable, some back pressure is needed to build low end torque at low speeds where cam overlap will bleed cylinder pressure. If all your looking for is a peak figure then a open exhaust will always outperform a closed exhaust system, however as most experienced rodders know its the area under the curve that counts and that means from idle to peak rpm. If adding a little restriction to the exhaust adds low rpm power with little loss up top then you have a net gain which adds up on the chronometer at the end of the strip.

Just something to think about.
Thus the advent of H or X-pipes, do not mean to step on toes but, a well designed dual with a balancing pipe will offer a good scavenging effects from the use of dual smaller pipes and balance pipe, and still have more volume to flow more at higher rpm.

You don't see many cars running 7's or 8's through a single exhaust system, or a dual without a balance pipe.
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Old 06-26-2008, 01:24 AM
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Well technically a H or X piped car is a 2 into 1 into 2 exhaust system...would a single exhaust of the same flow rating as the two pipes after the X or H change the HP output?

Think about it.
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Old 06-26-2008, 07:41 PM
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It might not change the horsepower output at all, but any dork knows that the exhaust velocity will be higher in the dual exhaust, making for a torque curve that comes on sooner.

The same reason multi-valve heads are common place in modern engines, 2 small valves flow the exact same amount of air as compared to one large one, only the two valves flow that volume at a higher velocity.

Last edited by stroker_SS; 06-26-2008 at 07:47 PM.
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