dual exhaust

[41/53dodges]

got a few questions on dual exhausts before i embark on any big project. first of all, is it really worth the time to make it? i was debating just welding one up out of stainless, seeing as i have the resources. the other question: what does it do to the starting, run-ability, and fuel economy? thanks, josh.

[MarkAubuchon]

yes its worth it. sounds nice. My two cents, I would run a compression test, to see what you have. If you have never done it, pull and cut the head, relap the valves, dual exhaust. To really feel the differnce add dual carbs while you are at it

[hkestes41]

I think it is worth it if for no other reason than the way it sounds. Here is a link to a youtube of mine when first installed. I do also have the Stovebolts cast iron headers.

[claybill]

yep do it. easiest is to re-work an old cast iron manifold. takes a few hours and done.

in any case, watch out for the oil pump AND FUEL PUMP.

bill

[blucarsdn]

Generally speaking dual exhausts, split manifold and/or headers will do two things;

1. Separate you from a lot of your money..

2. Make a lot of noise..

On a stock street engine, the average dual exhaust will give you a lot of bragging rights via the noise, the latter of which becomes very annoying during long trips.

Headers are designed to work as an open exhaust at over 3,000 rmp's. Split manifolds can result in raw gasoline being introduced into the engine which makes the engine run rich. Headers have the same fault... No heat riser under the carb.

Tests in resent years have shown that a larger head/tail pipe with a low restriction muffler will produce better results overall.

When all the hip is separated from facts, it is very hard to beat a stock exhaust system on the average vehicle.

Do I have twice pipes on my '39 Plym ?.. Yes I do, 2-1/4" all the way to the tips, however my engine is a 330 HP V8.....Bill

[48mirage]

Anything that helps your motor breath better will make it run better. I put a second outlet on my stock exhaust manifold and left the heat riser in but took some of the tension out of the spring. Ran 2 pipes all the way to the back on the passenger side with a couple of glass packs provided my the muffler shop. The noise is not an issue with me and the muffler choices were what ever I wanted. It did wake the ol' girl up a little.

[Don Coatney]

Generally speaking dual exhausts, split manifold and/or headers will do two things;

1. Separate you from a lot of your money..

2. Make a lot of noise..

On a stock street engine, the average dual exhaust will give you a lot of bragging rights via the noise, the latter of which becomes very annoying during long trips.

Headers are designed to work as an open exhaust at over 3,000 rmp's. Split manifolds can result in raw gasoline being introduced into the engine which makes the engine run rich. Headers have the same fault... No heat riser under the carb.

Tests in resent years have shown that a larger head/tail pipe with a low restriction muffler will produce better results overall.

When all the hip is separated from facts, it is very hard to beat a stock exhaust system on the average vehicle.

Do I have twice pipes on my '39 Plym ?.. Yes I do, 2-1/4" all the way to the tips, however my engine is a 330 HP V8.....Bill

So I take it you have a lot of bragging rights with your noisy dual exhaust? How many miles have you driven your 39 Plymouth?

[Robert Horne]

Generally speaking dual exhausts, split manifold and/or headers will do two things;

1. Separate you from a lot of your money..

2. Make a lot of noise..

It does not cost much if you bend your own pipes. A pipe bender can be purchased for about $75. Sticks of pipe do not cost very much.

Dual exhausts does not make much noise if you use mufflers that are designed to cancel noise.

Raw gas sounds like a bad carb.

[hkestes41]

blucarsdn;228481]Generally speaking dual exhausts, split manifold and/or headers will do two things;

1. Separate you from a lot of your money..

I guess it depends on what you call a lot of money. Personally I do not consider the headers all that expensive at $275 and I had to get an exhaust system installed anyway. A dual exhaust is not 2X the cost of a single more like 50% or 60% more.

2. Make a lot of noise..

Not at all. If you run some decent turbo style mufflers not all that loud.

On a stock street engine, the average dual exhaust will give you a lot of bragging rights via the noise, the latter of which becomes very annoying during long trips.

Do trips of over 850 miles and 450 miles each summer and have never found it annoying.

Headers are designed to work as an open exhaust at over 3,000 rmp's.

During the exhaust stroke, an engine to loses power through back pressure. The exhaust valve opens at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted.

Once the exhaust gases exit the cylinder they end up in the exhaust manifold. With a straight 6-cylinder engine, there are 6 cylinders using the same manifold. From the manifold, the exhaust gases flow into one pipe toward the *muffler. The manifold can be an important source of back pressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold.

Header eliminate much of the manifold's back pressure. Instead of a common manifold that all of the cylinders share, each cylinder gets its own exhaust pipe. These pipes come together in a larger pipe called the collector. The individual pipes are designed so that each one is the same length as the others. By making them the same length, it guarantees that each cylinder's exhaust gases arrive in the collector spaced out equally so there is no back pressure generated by the cylinders sharing the collector.

Split manifolds can result in raw gasoline being introduced into the engine which makes the engine run rich. Headers have the same fault...

I guess in theory by reducing the back pressure in the exhaust it could lead to a rich condition which is pretty easy to adjust.

No heat riser under the carb.

My intake is plumbed for hot water heat, they can also be fairly easily plumbed for exhaust heat

Tests in resent years have shown that a larger head/tail pipe with a low restriction muffler will produce better results overall.

Yes, and if you add headers or split manifold to the larger head/tail pipe and low restriction muffler it will perform even better, to a point. You can actually have too free flowing an exhaust.

When all the hip is separated from facts, it is very hard to beat a stock exhaust system on the average vehicle.

I guess that would be the case if the car came with factory headers and low restriction dual exhaust. Or you are going for a concourse / points judged restoration. If on the other hand you are looking for improved performance and you have a factory 6 into 1 exhaust manifold not the case at all.

Do I have twice pipes on my '39 Plym ?.. Yes I do, 2-1/4" all the way to the tips, however my engine is a 330 HP V8.....Bill

And why doesn't everything you said concerning the 6 cylinder exhaust apply to your V8, when in fact your V8 has two 4 into 1 exhaust manifolds rather than a single 6 into 1. Your statements should be even more applicable to a V8.

All that said, I will agree that adding only dual exhaust and not making any other changes to the engine is not going to do much in the way of increased performance. You also have to be willing to make some changes on the intake side of things to open up the breating further and ideally go to a more suitable cam grind as well, but all in all a reduction in exhaust restriction will lead to a better performing engine.

Edited December 16, 2010 by hkestes41

[old rat 49]

Had a 74 Chevy with 250 straight six single barrel carb. Added Clifford intake with a Holley 390. Not much difference. Added Clifford headers and dual exhaust; somewhat more power. Finally went to larger valves. It came alive. If you don't do all three things you don't accomplish much because the air has to move through them all. It would have been cheaper to drop in a V8. My 2 cents worth from experience.

[claybill]

with the dual ex and the dual carbs...you wont get much performance increase...but for the 600 bucks i like it. very cool and maybe 5% increase in power, just guessing.

my coupe runs like a scared rabbit... the convertible is smooth and steady but not as peppy.. i attribute the difference to other things for sure. like a tighter motor etc..better compression..

bill

[Young Ed]

with the dual ex and the dual carbs...you wont get much performance increase...but for the 600 bucks i like it. very cool and maybe 5% increase in power, just guessing.

my coupe runs like a scared rabbit... the convertible is smooth and steady but not as peppy.. i attribute the difference to other things for sure. like a tighter motor etc..better compression..

bill

Could also be the 500 or so pounds less the coupe weighs.

[blucarsdn]

Any person that is a hard core modification guru, has a hard time digesting that the engine modifications they tout, might be flawed.

Many years ago I ran a hot rod/muffler shop... I found from practical experience that if you want more power.. don't waste time and money trying to turn a pigs ear into a silk purse, re-power the vehicle with a larger engine.

It is a fact that racing engines will preform better with improved exhaust, multiple carbs, improved cam, etc.. It is also a fact that all of these improvements generally shorten the life of the engine.

As to how annoying the sound of a muffler (s) might be... that is up to the individual... I like stealth... other people like BOOM-BOOM with lots of rap.

I have changed the mufflers on my '39 Plym twice because it was to noisy, I am about to change them again because it still emits to much sound. My Plym is built to be a driver, AOD trans, PS,PB, PW, etc., I like to slip up next to a car on the highway, then glide past them... The looks on their faces is priceless.

How much do I drive my cars?

I have a '36 Ford coupe that I bought in high school 57 years ago... It has a highly modified 59AB engine with lots of chassis improvements. A couple of years after I built the car I went to work for a company in Salt Lake City, Utah traveling the eleven western states..

In short order the Smitty's really became a drag,,, I had them removed and replaced with stock type mufflers... The silence was golden.

I drove the car almost forty thousand miles in two years. During the 57 years I have owned the car I have driven it 94,000. + miles.

Up until three years ago when I semi retired, I averaged over a hundred thousand miles in three years on my primary car plus another 15,000 + miles on my RV.. My current RV has 95,000. on it in eight years, the SUV I just traded in had 97,000 on it in eight years.. Neither of these vehicles were my work vehicle.

I guess it could be said, I drive a lot of miles...Bill

[BrianInPa]

I really don't have any experience yet making modifications to Plymouth / Dodge flatheads, so I can't make any claims as to the performance increase on those specific motors. I do have some experience playing with GM V8's.

On those motors, I've seen a noticeable difference in modifying the exhaust systems.

Just placing something on a motor that is referred to as a "header" is not necessarily going to make it perform better. There are all types of variables that come into play.

One of the biggest issues I noticed in V8 exhaust systems that I've played with was the header length. I've run full length headers on some motors (primary tubes approx 36" long) and the short "block hugger" type headers on other motors.

In fact, one time, I swapped from full length headers on my 65 chevy truck (350 small block) to block huggers and instantly noticed a difference.

First of all, the sound from the block huggers was awful. It actually sounded somewhat muffled, like the exhaust was a little restricted. The full length headers had a much better tone. The power from the full length headers seemed better as well. However, it wasn't a huge difference, as this motor was otherwise stock with the exception of a better carb and alum intake.

Other issues that will affect how your exhaust performs is the manner in which the exhaust tubing is bent and routed, the mufflers, crossover pipes, etc.

As far as the cast iron headers that are available for the flathead 6's, I doubt that there is a big difference in power or economy, but I don't know for sure, because I've never used them. However, they definetely look nice.

My only point in my ramblings here is that there are a number of issues that will affect how well your exhaust works.

[Don Coatney]

With my modified flathead 6 I have no problem passing cars at 70 MPH. After the pass is complete I then shift into overdrive. I cruse at 70+ MPH and my engine is spinning around 2200 RPM's. I have driven my car over 40,000 miles and it is as dependable as the day is long having never been on the hook. Not bad for a "shadetree" home built car. I have nothing against a V-8 engine swap but I like the fact that my flathead six can run with the V-8 powered cars.

Edited December 18, 2010 by Don Coatney

[greg g]

Some other side of the coin options. I have a slightly modified 56 230 engine in my car. 30 over, head and deck shaved to equal .050, dual carbs on a fenton intake. Single exhaust, with Dynimax turbo flow muffler. Results, very good drivability, adequat power for climbing hills and keeping up with traffic, much better seat of the pants feel over the stock 218, and 2 mpg better economy on the road. I usually get 19+ when travelling, I have driven several long distance trips with the car over the years, and it still runs the stock trans and the 4.1 to 1 rear end. Calculators suggest I am running around 3200 rpm at an indicated 65mph (63 actual by gps)

The most noticeable modification is the increase in compression ratio. I believe the 218 was 6.7 to one. My machinist figured the set up to be just over 8 to 1.

I made the choice to not deal with the extra plumbing under the car. The single turbo flow speaks when the engine is used and is silent for cruising and travelling. I did use 2 inch id tubing throughout the system.

My experience with several other modified Flatheads, is that the only thing I may be giving away is the relaxed rpm cruising that the OD or rear end ratio change might yield.

Your car, your money, your ideas. Do what you wanna do and enjoy.

[BeBop138]

With my modified flathead 6 I have no problem passing cars at 70 MPH. After the pass is complete I then shift into overdrive. I cruse at 70+ MPH and my engine is spinning around 2200 RPM's. I have drivin my car over 40,000 miles and it is as dependable as the day is long having never been on the hook. Not bad for a "shadetree" home built car. I have nothing against a V-8 engine swap but I like the fact that my flathead six can run with the V-8 powered cars.

I go with Don, it is just fun to run with the big dogs with a flattie six. We pretty much have the same engine and modifications, it is yet to be determined who is faster:D......Lee

[1941Rick]

One has to remember you are only working with an engine that has no more then 100HP.

A 10 to 15% increase in power would not really be noticed. My 218 has .040 pistons, .040 shaved off the head, twin B&B's on an Offy manifold and is nice and tight. (fresh rebuild) I still have single exhaust and most likely will remain so. I run with a bunch of V8's in all sorts of rods. Have no problem legally keeping up with them.

Don....how fast is your engine running at 70mph before you shift to overdrive?

I get nervous at 55mph...I am in O/D at 40....have been told RPM is the killer of these engines.

[hkestes41]

Any person that is a hard core modification guru, has a hard time digesting that the engine modifications they tout, might be flawed.

Many years ago I ran a hot rod/muffler shop... I found from practical experience that if you want more power.. don't waste time and money trying to turn a pigs ear into a silk purse, re-power the vehicle with a larger engine.

Not a guru by any stretch, but I have had a couple of pretty healthy engines including a low 12 second on street tires big block Cuda, but you are correct I could have had a V8 for what I have spent on my flathead. The thing is I didn't want a V8, didn't want to get lost in the sea of V8's. My flathead gets much more attention than another V8 at a show.

Edited December 18, 2010 by hkestes41

[Don Coatney]

Don....how fast is your engine running at 70mph before you shift to overdrive?

I get nervous at 55mph...I am in O/D at 40....have been told RPM is the killer of these engines.

I have a 3.55/1 differential and my tires measure around 27". At 70 MPH without overdrive I am turning around 3100 RPM's. This is well below the maximum RPM's I am willing to spin my engine. I have ran my engine up to around 4200 RPM's for short periods of time.

[greg g]

Coventional wisdom used to say that a cruising rpm that was 80 to 85% of peak HP rpm was reasonable for egine life, and fuel economy. given that the hp rating was taken at 3600 rpm, and that the factory test was to pull engines from the line, and run them on a test stand for 50 hours at 3600 rpm. The 20 /25% cushion should serve you well.

I believe the flywheel HP for the 230 was 125 beginning in 54. The 59 Dodge 230 was rated at 130 HP with a cr of 8 to 1, as opposed to 103 in 50 with 7 to 1.

So any cruising speed in the 3000 to 3250 RPM range shold be healthy for the engine, assuming proper oil pressure and good condition.

Edited December 18, 2010 by greg g

[Andydodge]

The biggest problem these mopar 6's have is high rpm's and Don's 3.55:1 diff would certainly offset the rpm issue, as would his car using a T5 overdrive......my still stock driveline 1941 Plymouth Coupe has a 4:1 diff and even with a tailwind & me leaning forward gently beating the outside of the door with a light whip, at 3000rpm I can hear every piston as it hits TDC ....."once more buddy, once more!!.......and we'll all stick our heads out the side of the block!!" ..............they don't like revs...........at all......lol.........andyd

[Dodgeb4ya]

I don't want to show anybody I can keep up with them on the road. I just let them all pass on by........I like to keep my cars/ trucks drivetrains all stock. They sure last forever that way too. Also helps keep my maintence $$$ down too.

Edited December 20, 2010 by Dodgeb4ya

[41/53dodges]

i am actually looking into this for the 53' 1/2 tonner, engine questions get more answers over here, especially mods. the only reason i look into this is the fact that there are a LOT of people that dont know how to drive around here, and it would be a hell of a lot easier to get things done with just a little more power.

[blucarsdn]

In all of my earlier comments to this topic it should be noted that I never said that a six cylinder could not be modified to run very well...

In the mid to late 1950's, the GMC 270/302 CID engines were modified to the point that they would run off and hid from the average V8. Vehicles equipped with the Jimmy's set records that stood for many years. In 1951 I modified a 270 Jimmy, installing it in a '38 Chevy... There was nothing in Eastern Idaho that could beat that car... that is until a kid from Pocatello got tired of me blowing him off the road... His father owned the Ford dealership... The dealership installed a new Olds Rocket V8 in the '36.. The '36 Ford ran off and hid from me. I sold the Chevy to a guy that just had to have it.

Clifford, (6=8) proved in the '60's-70's that he could modify Ford, Chev and Mopar six cylinder engines that would beat the V8's on the drag strip on a regular basis.

The original question posed in this topic was about dual exhausts, how much they can be expected to improve performance on the average car?

I still stand by earlier position that the improvement is minor, especially when compared to the cost. Of course the bragging rights are priceless.

Many years ago a friend of mine changed the transmission in his truck from a TH350 to a 700R4 OD,,, The purpose being to improve the fuel mileage..

The cost of the conversion was $2,800. with an expected mileage improvement of 3 mpg. My friend told everybody that would listen about how great his truck performed.

I considered the conversion to my pickup... I ran the $2,800. cost through my calculator.. At the then current price of fuel, and at 3 mpg, I would have to drive the truck 60.k miles to break even.. I did not go forward with the conversion. When I told my friend about my findings he looked at me, saying "I guess I blew it on that one".. A year later he sold the pickup....Bill