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Dumps Good Or Bad????
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Posted by: detroitmuscle

I was thinking about getting dumps on my 91 gt since you cant see the tail pipes anyways and the pipes are stock.....so i was just wondering what the good things and the bad things were....will it still have the same tone...my biggest question is it going to louder.....i have a O/R H-pipe and super 40 flows

Posted by: Mustang5L5

It will be louder, but it will drone and resonate in the interior more. If you drive the car frequently you may find it annoying. I ran dumps for a week because it took me a week to put tailpipes back on. I disliked it the first time i drove like that

Posted by: detroitmuscle

so ill gett anoyyed....i love loudness im only 16 will it be alot louder out side the car

Posted by: speedytang

Sound is louder but I notice on stock cars or ones just barely modified a loss of torque. A large loss of torque below 3000 rpm.

Posted by: Mustang5L5

Quote:

Originally Posted by detroitmuscle

so ill gett anoyyed....i love loudness im only 16 will it be alot louder out side the car

It will be louder inside and outside. The loud thing will get old quick trust me.

You do lose a little bit of low end torque, but gain top end HP. Unless you drive around at 5500 RPM all the time, keep the tails. Get 3" tips if you want it louder.

Posted by: Aussie XAXB

You guys are funny.

Yes, since the exhaust is exiting the mufflers under the body instead of outback (if by "dump" you mean a downturned shorty pipe instead of a full length tail pipe) it will be louder in the interior of the car.

A loss of torque? I don't think so. Certainly nothing you could feel. Beware the placebo affect.

Back in the day "dumps" were a Y shaped fitting that went ahead of the muffler that had a valve in them to direct the flow either through the muffler or "dump" the exhaust before it got to the muffler and the back pressure it creates. This was only effective on a radical engine and used while drag racing after driving the car to the track

Steve

Posted by: speedytang

Average dyno pull showed a loss of 27ftlbs of torque from 2200-3600 rpm and then it starts climbing back but never reaches loss of 0ftlbs till over 5400 rpm. Even being a 5speed I could feel it because I was using more throttle to move the car from idle.

Posted by: Aussie XAXB

That's very interesting. Would you happen to have the dyno charts showing this? I find it difficult to believe that there would be a 27 ft. lb. loss because there is about 5 feet less of bent pipe after the muffler. Do you know what the theory is on that?

Not calling you a liar or anything, I am just one of those people that have to see something for it to register as real. I got bit several times in my Apprenticeship by being this way with the Journeymen too.

Right now I just don't know any principle that would cause that affect.

Thanks,
Steve

Posted by: speedytang

I will find my Dyno Pulls. Plus it is 10' of pipe and you could feel it on the dyno when I was shifting at 2500 rpm to get in 4th. I installed the system and made 3 pulls with the pipes on then removed both pipes and what a dog before even looking at the graphs. I only lost like 7 rwhp and got it back on the upper rpms but could not get the torque back. I changed my tune with my PMS and still could not recover the torque. I run into this all the time on Racing Pull Tractors on the dyno so we change the length of the header pipes that are facing up that is why some look like a pipe organ. Same theory of long headers and shorties. This is no secret in the industry that is why mufflers have baffles not just for sound but to increase the length of the exhaust pulse. Flowmasters builds more power than a old Thrush muffler which has less back pressure because the flowmaster is increasing the exhaust length. You can see this yourself by removing your tailpipe and because it is louder your thinking faster till you can compare the car on a Dyno to see the drops in different rpm ranges. Head design and Cam lobe seperation is the same principle. Pulse Length

Posted by: Aussie XAXB

Thanks for all that info.

I am very familiar with long and short header issues but never thought of anything past the mufflers. Do you think using smaller diameter pipes on the shorter system would recover some or all of the torque. This would have an effect like with irrigation systems. The same volume flowing through a smaller diameter will speed up in order to flow the same amount. That could be interesting.

I have a vested interest in this since on my Mad Max project I will have zoomies that are turned up and dump the exhaust ahead of the rear wheels, right after the mufflers. If this is going to cause a loss in low and mid RPM torque then I think I would use 2" pipes instead of 2 1/4" or 2 1/2" pipes going to the mufflers from the headers, though this will be a rather short run. The engine is an Aussie 351C with the closed chambered 2V heads. I will be building the engine for mid-range torque.

Steve

Posted by: speedytang

I have 500rwhp and only use 2 1/4" pipe. I have used different pipe after the mufflers and it does have the same effect. My torque increased dumping my 2 1/2" pipe and going down to 2 1/4". I lost horspower from 5600-6800 rpm but I don't really use that power range since I don't really drag race anymore. I tried 3" pipe made by Pypes and that was like taking off the tailpipes I lost about the same torque. I would stay with the 2 1/4" pipes. Once I had the math formula to use for figuring the correct pipe length and diameter. You had to input header length, collector size, flow volume of the mufflers and muffler length and number of baffle paths then you inputed your engine specs. I think it was in the chassis engine book that Dodge(Mopar) once sold. That book had a ton of great math formulas and car designs.

Posted by: Aussie XAXB

Cool. Lots of good info. Impressive engine.

For the street, which is all I build engines for, low and mid range torque is what I am looking for. Something that plants you in the seat while accelerating to the legal speed of 70ish on the highway. Something that gets you to 35 mph real quick too. I don't want a world beater, just something respectable and very fun.

500rwhp through 2 1/4" pipes is very impressive. What is the torque like and what did you build the engine for (HP or torque, low, mid, or high RPM)?

So if Detroitmuscle is going to put on dumps after his mufflers he should reduce his extension pipe diameters to retain the most torque? This is what I am learning out of this.

Steve

Posted by: speedytang

Daily-Drag-Autocross. I have turned the car now to a Daily-Autocross and because I would need a 6-point I am done with Drag. My kids and I like cruising and the Roll Bar is just not worth it to me.
10psi 485 rwhp @ 465 ftlb 6650 rpm
14psi 535 rwhp @ 492 ftlb 6230 rpm
1/4 11.67 @ 123mph. Drag Radials with 3.08 gears and a 2.09 60ft
0-60 mph 4.2 seconds
Numbers from last year. New numbers would probably be worse because I changed to 5-lug Disc Brake rear 17" wheels and 3.73 gears. No traction at all when in boost at 2200rpm+ but it pulls like a freight train on the road course with less boost.
I would suggest if the car design allows, to put pipes exiting the sides before the rear wheels if you don't want full length pipes exiting to the rear.

Posted by: Aussie XAXB

Here is what I am replicating. I already have the zoomies.

Steve