bschwarz77
I just bought some J-tubes to put in place of my filthy heater boxes for the spring/summer/fall.  This may be one to debate but will that provide better performance?  Better gas mileage?  The big question here is if I buy one of those fancy squirrelly-looking high-performance exhaust systems, I understand I'll increase a little horsepower/performance... but what exhaust option is really the best for Gas Mileage?  I'm looking to really peak the gas mileage above all else.  Horsepower would be nice but not if it's gonna turn it into a gas-guzzler.  Any other ideas on improving gas mileage on the beetle?
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MY72BUG
Did I just hear the sound of someone opening a very old can of worms?  First of all the J-tubes: they are just like the innards of your old heater boxes so you won't see any change in economy or performance unless the diameter of the pipes is radically different from the pipes in the heater boxes - which given the ones that I know - they aren't.  I run J-tubes on mine because I had no need for heat in a summer driven convertible.  Performance comes at a cost.  Just as no man works harder without using more energy you can't work an engine harder without paying a price in fuel consumption.  Moreover, you are also using up the life of your engine trying to get that higher horsepower.  The flat 4 was designed to run under stressed unlike other 4 cylinder engines of its era which were wound out at higher RPM's.  Let the old girl lope along with a stock exhaust and a clean air filtre and it will maximize your mileage.  Don't mash the pedal.  Keep all of your engine tin in place to keep her cool.  Keep your valves adjusted, your oil changed and your tire pressures at the recommended setting and you will have a happy bug.  BUT don't forget - it will give you gas mileage good for a car of its era.  Modern fuel injected four bangers have the higher horsepower AND better mileage through the miracle of modern engineering technology.  Just be happy that you aren't driving a 455 V8 from your bug's era.  I feel the pain of those who have collector cars powered by the big old iron 8 bangers!   Ouch.  Just my opinion.  Dan (MY72BUG) in Goderich
I'd rather have a partial bottle in front of me than a partial frontal lobotomy.
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olspeed
Just a note here
you guys need to look at one of the latest issues of Hot VW they have been working on a mileage project
(mileage motor) in search of a 40 mpg engine. So far I think that they have gotten to 37 to 38 mpg out of the thing, and the performance is better than stock. But please note even in the article they talk about trade offs. On my "66 Ghia" (1904cc, hyd cam & lifters, dual kadrons) I changed some of the tune up specs to those that were mentioned in one article and went from 32 to 34 mpg on the hwy. not bad for a 40yr + car with carbs!
66 Ghia 76 std Beetle
It's not a car it's a VolksWagon
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AlphaWolf
MY72BUG wrote:
Did I just hear the sound of someone opening a very old can of worms?  First of all the J-tubes: they are just like the innards of your old heater boxes so you won't see any change in economy or performance unless the diameter of the pipes is radically different from the pipes in the heater boxes - which given the ones that I know - they aren't.  I run J-tubes on mine because I had no need for heat in a summer driven convertible.  Performance comes at a cost.  Just as no man works harder without using more energy you can't work an engine harder without paying a price in fuel consumption.  Moreover, you are also using up the life of your engine trying to get that higher horsepower.  The flat 4 was designed to run under stressed unlike other 4 cylinder engines of its era which were wound out at higher RPM's.  Let the old girl lope along with a stock exhaust and a clean air filtre and it will maximize your mileage.  Don't mash the pedal.  Keep all of your engine tin in place to keep her cool.  Keep your valves adjusted, your oil changed and your tire pressures at the recommended setting and you will have a happy bug.  BUT don't forget - it will give you gas mileage good for a car of its era.  Modern fuel injected four bangers have the higher horsepower AND better mileage through the miracle of modern engineering technology.  Just be happy that you aren't driving a 455 V8 from your bug's era.  I feel the pain of those who have collector cars powered by the big old iron 8 bangers!   Ouch.  Just my opinion.  Dan (MY72BUG) in Goderich


You are wrong.  The diameter of the pipes in the heater boxes is about 1/3 what the diameter of the J tubes is .  Which is why any performance engine should not have heater boxes, it kills the flow out of the front two cylinders.

A good exhaust and j tubes will definitely help your mileage and give you more power and speed. 
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Ryan
Hardly a third, unless you're comparing 2-1/4" primaries to a heater box.  Might want to find out what size header we're talking about first.  Cross section of a heater box tube compared to a 1-3/8" header is pretty close and the difference of flow won't show up in tuning so go for it if you want.  As for larger headers,,, well you're out of luck there.  Custom built heater boxes are your only option and as far as I know, these are not a stocking item for ANYONE anymore.  I think Berg does productions runs every time Haley's comet passes, but they are on a pre-order only base, no stock.  --Ryan
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AlphaWolf

I am not talking the size of the pipe out of the heater box to the head or to the muffler.  I am talking about the pipe within the actual heater box which is choked down to not much bigger than my index finger.  Then the bends are much more severe, further restricting flow.  A huge restriction compared to the exhaust tubes on my Merged drag exhaust tubes. 

With a full merged system and a good turbo muffler your exhaust will flow much better. Engines are air pumps the more air in and out the more power/efficiency you will obtain. 

Back in 1975 when my Bug was last STOCK, its's top speed was around 80 ish mph (1970 Bug).  With just a merged exhaust added to it, the top speed went up 8 mph.  The mileage also increased

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Ryan
I know what you're talking about, I've seen the cross sections of the tubing w/in the heaters.  I also know that from a fluid dynamics standpoint 1-3/8" J-tubes vs heater boxes are pretty much a wash.
You're comparing apples to oranges saying that the addition of a 'merged header' net'd you 8 mph over stock.  The gain was from the addition of a 4-1 collector and the scavenging affect it introduces in the mid to high end.  It had nothing to do with the heater boxes.  If you were to see a difference I'm willing to bet it's in the range of 1-3 percent and you'd never be able to quantify it through road testing.  You would HAVE to do it in an environmentally controlled dyno cell for the numbers to mean anything.  --Ryan
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olspeed

I am going to have to agree with Ryan on this one,on the difference from j-tubes to heaterboxs. I used to run a 1835 with 041 heads dual 44 webers and heater boxs and header in the summer (up here in gods country). In the winter I would switch the engine out into my 74 thing but change out the boxs to j-tubes (44000 BTU multi-fuel military personel heater,can you say WARM!). You could tell no difference in engine performance with the switch. I did later purchase a system that was a complete j-tube and header setup for summer use while autocrossing and there was a noticeable improvment. I think it was 1 5/8" pipe but that was in the early 90's and it went when I sold my thing so I am not sure.   

66 Ghia 76 std Beetle
It's not a car it's a VolksWagon
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AlphaWolf
It is not apples to oranges.  The thread is about an full aftermarket exhaust not just J tubes vs. the stock exhaust.   And flow is more than just 2 tubes.  You are familiar with the term tuned exhausts?  The diameter of each tube along with their length and bends must all be correct for the engine taking into account modifications, and the rpm range it will be operated in for maximum flow.  If you make a tube smaller to 2 cylinders you effectively change their length.  If you use the wrong diameter or length of primary exhaust tubes you will change the torque output of your motor.  While this will be less in a stock 1500.  It can create dips in the torque curve and lower the rpm your engine reaches peak torque and thus affecting the horsepower it makes. 

Now if you live up in the frosty north and not in Sunny California like I do you may have very valid reasons for not wanting to use J tubes.  But as mine aged they rusted.  They began leaking exhaust into the car.  So when I was looking into replacing the heater boxes for hundreds of dollars back in the 70s or J tubes for far less it was a no brainer for me at the time.  I could get a full exhaust and J Tubes for less than the Heater boxes.  And yes it did increase the top end by the amount stated.  The stock exhaust along with the stock intake manifold are very restrictive.  Great for being quite, not for making power.

Just sticking J tubes on a stock exhaust will not do much as the muffler etc is so restrictive that the increase will be minimal.  But as I said this thread was about a full aftermarket exhaust not just j tubes.  I run a race merged system on all my engines since the mid 1980s. They do not use J tubes but have custom bent forward tubes that go into the merged collector.  This type of exhaust produces the best torque.  But they are expensive.




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Ryan
Ok, first off tubing diameter has ZERO correlation to length.  Tubing length affects the pulse harmonics and how they reinforce and cancel each other.  Diameter is a flow restriction.  Two very different things.  Bends will change the harmonics, but it's either trial and error method, or math that's probably over your head, hell I haven't had to use that stuff since my college years.  Software to do it for you is always nice though...
Torque vs rpm,,, you do know that they are related by rpm right,,, directly even.  So if you make make peak torque at a lower rpm OF COURSE you change the hp figure for that same rpm.  However it's area under the curve that matters and again in the stock application we're talking about here it's beyond the scope of 'seat of your pants' tuning.
Stock cam is the restriction, stock intake and exhaust are actually good for about 15-20 more ponies,,, if you have a big enough bag of tricks.
And in your last paragraph, you come across argumentative, yet your agreeing with me,, umm cool I guess.
You might want to leave the 'alpha' mentality at the door, this isn't the place for it.  Try The Samba if that's your game.  --Ryan

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