Cherry Bomb - 87556 or 87554

[alstare84]

Hi to all,
about those mufflers (Glasspack-87556 or 87554)

http://www.cherrybomb.com/Catalog/glasspack_header_muffler/glasspack-87556.aspx and http://www.cherrybomb.com/Catalog/glasspack_header_muffler/glasspack-87554.aspx

someone of you know if fits in a standard 4in1 for a (temporary) 1200 engine? Which one could be ok?

Thanks to all  

Roberto

[Zach Gomulka]

This one:
http://www.cherrybomb.com/Catalog/glasspack_3_12_body_straight_tubes/glasspack-87507.aspx

The ones you picked aren't going to fit a standard VW header, they're meant for a V8 header flange.

[alstare84]

I forgot to say thanks 

[hotrodsurplus]

I say avoid Cherry Bomb mufflers. Every Cherry Bomb I've ever seen (and I've seen a lot) had a louvered core. A louvered core creates a ton of turbulence and, as a result, a bunch of backpressure. Despite what the internet experts say backpressure is the enemy. Also, historically speaking Cherry Bomb's marketing existed of a barrel with packs in it next to the register at Pep Boys. That's not the mark of a very high-quality product.

You want a perforated core. The inner pipe is straight yet has hundreds of holes poked into it.

Also, I know you say the 1200 is temporary but a 2 1/4" core is way too big for even many 2-plus-liter engines. The exhaust will not develop sufficient velocity and the torque will likely suffer on even very large engines. The problem is that small-diameter perforated-core mufflers are fairly hard to come by. One of the few who makes them that I know of is Walker/Thrush.

I recommend a 1 5/8-inch-diameter pipe into and out of a 1 3/4-inch-diameter core for 1600-1900 engines up to about 100-110 horsepower. It will still make your 1200 a pig--it's too big for even that application--but not as much of a pig as a 2 1/4-inch core.

http://www.summitracing.com/parts/wlk-24210/overview/

Later on if you build a big engine (like 1.9 or larger) you could probably benefit from a 1 3/4-inch-diameter pipe in and out of a 2-inch core. However, perforated packs with 2-inch cores are really uncommon in short lengths. The only one I know of who makes them is Heartthrob and only in the stainless steel flow packs (a lot of Heartthrob mufflers are louvered core so beware). You can get those in longer lengths, too. Stainless welds just fine to low-carbon steel with a MIG welder.

You can also easily cut down a longer muffler to the length you need. I've done it before--just cut the weld from the case to the core and cut what you need out of the case. You'll have to tear out the excess fiberglass packing and weld it back up at both joints but you'll get exactly what you need for really cheap--the long Thrush mufflers are like $40.

http://www.heartthrobexhaust.com/glasspacks&flowpacks.html

You can also get custom-made perf-core mufflers from boutique makers like Stainless Specialties. I have that company's mufflers under my roadster. They're not cheap but they're beautifully made.

http://www.stainless-specialties.com

If you're building from scratch you will need bends and flanges. I buy everything I need including copper flange gaskets from Columbia River Mandrel Bending. The three-bolt flanges are extra thick--like 3/8". Get the thicker 16-gauge tubing. And get raw tubing in case you want to gas or TIG weld the joints. The aluminizing will wreak havoc with those welds. In a pinch you can sand off the aluminized coating in the weld area but if you have the choice you'd rather have bare steel.

http://www.mandrel-bends.com/catalog/

hope it helps. Just don't go gigantic on the diameter. And don't use a louvered-core pack.

[bugnut68]

I say avoid Cherry Bomb mufflers. Every Cherry Bomb I've ever seen (and I've seen a lot) had a louvered core. A louvered core creates a ton of turbulence and, as a result, a bunch of backpressure. Despite what the internet experts say backpressure is the enemy. Also, historically speaking Cherry Bomb's marketing existed of a barrel with packs in it next to the register at Pep Boys. That's not the mark of a very high-quality product.

You want a perforated core. The inner pipe is straight yet has hundreds of holes poked into it.

Also, I know you say the 1200 is temporary but a 2 1/4" core is way too big for even many 2-plus-liter engines. The exhaust will not develop sufficient velocity and the torque will likely suffer on even very large engines. The problem is that small-diameter perforated-core mufflers are fairly hard to come by. One of the few who makes them that I know of is Walker/Thrush.

I recommend a 1 5/8-inch-diameter pipe into and out of a 1 3/4-inch-diameter core for 1600-1900 engines up to about 100-110 horsepower. It will still make your 1200 a pig--it's too big for even that application--but not as much of a pig as a 2 1/4-inch core.

http://www.summitracing.com/parts/wlk-24210/overview/

Later on if you build a big engine (like 1.9 or larger) you could probably benefit from a 1 3/4-inch-diameter pipe in and out of a 2-inch core. However, perforated packs with 2-inch cores are really uncommon in short lengths. The only one I know of who makes them is Heartthrob and only in the stainless steel flow packs (a lot of Heartthrob mufflers are louvered core so beware). You can get those in longer lengths, too. Stainless welds just fine to low-carbon steel with a MIG welder.

You can also easily cut down a longer muffler to the length you need. I've done it before--just cut the weld from the case to the core and cut what you need out of the case. You'll have to tear out the excess fiberglass packing and weld it back up at both joints but you'll get exactly what you need for really cheap--the long Thrush mufflers are like $40.

http://www.heartthrobexhaust.com/glasspacks&flowpacks.html

You can also get custom-made perf-core mufflers from boutique makers like Stainless Specialties. I have that company's mufflers under my roadster. They're not cheap but they're beautifully made.

http://www.stainless-specialties.com

If you're building from scratch you will need bends and flanges. I buy everything I need including copper flange gaskets from Columbia River Mandrel Bending. The three-bolt flanges are extra thick--like 3/8". Get the thicker 16-gauge tubing. And get raw tubing in case you want to gas or TIG weld the joints. The aluminizing will wreak havoc with those welds. In a pinch you can sand off the aluminized coating in the weld area but if you have the choice you'd rather have bare steel.

http://www.mandrel-bends.com/catalog/

hope it helps. Just don't go gigantic on the diameter. And don't use a louvered-core pack.

Plus the fact that glasspacks sound like a wet chili-fed fart blasted into a wooden wine barrel. 

[hotrodsurplus]

Plus the fact that glasspacks sound like a wet chili-fed fart blasted into a wooden wine barrel. 

Not all do. That flabby drone is the sound of a number of things like insufficient cylinder pressure and/or poor velocity, the latter usually the result of an excessively large-diameter pipe. A tuned system with a pack fed by a properly built engine sounds tight and smooth, sort of like a slightly quieter version of a large stinger. You just never hear it because the assumption that all packs sound like the cheap Chinese garbage from mail-order retailers scares off most people who might try it out.

In light of the waning market for glass-packed mufflers it might be impossible to find the right size to build a system that performs and sounds right. It might come down to a nutcase making mufflers from scratch. It's not impossible (I have photos of handmade chambered mufflers from the late '40s) but most people won't invest themselves in that much work. Hell, I don't think I could think of more than two or three people who even invest in dished pistons to get the right deck, chamber volume, and compression ratio from an engine!

[Zach Gomulka]

The right glass pack sounds very good.

[61SNRF]

Who gives a sh*t about velocity on a 40hp?
Just get an EMPI like this and paint it red
[ Attachment: You are not allowed to view attachments ]

[hotrodsurplus]

Who gives a sh*t about velocity on a 40hp?

Ummm...I do and so does anyone else that drives an underpowered car. Forties have few beans to begin and killing the velocity with an oversized exhaust will kill what little power they DO have. Experience typing here.

Just get an EMPI like this and paint it red

I'm surprised that kit still exists! That's the way to go. Screw building the muffler.

[61SNRF]

Yeah sorry, but you know what I'm saying. Anyone who puts a glasspack on a VW these days is probably not looking for all out performance. I put this one on an otherwise stock 1300 just for nostalgic reasons and love it!
Funny story is that I got it for a deal used but nearly brand new from Bill and Steve's. They said a customer had bought it and put it on his car but his Wife said "No WAY!" so he took it right back and traded it in on a QP One thing I would like to change is the tip because it angles out too much, would rather have it look like an old S&S.
Not sure of their price new, but they are still shown in the current EMPI catalog.

[Zach Gomulka]

I tried that EMPI exhaust on a customer/friends speedster kit, and like all things EMPI I was very disappointed with the quality. It also sounded like crap compared to my old S&S glass pack.

[hotrodsurplus]

Yeah sorry, but you know what I'm saying. Anyone who puts a glasspack on a VW these days is probably not looking for all out performance. I put this one on an otherwise stock 1300 just for nostalgic reasons and love it!

No worries. I'm just a bit nervous that people will think that just because a part won't improve performance that it can't do any harm either. Plus there's a lot of misinformation out there. I know you weren't referencing it but the 'an engine needs some backpressure to make power' is the perfect example of a myth that won't die.

I recently experienced another transformation on an engine that had an excessively large velocity-killing exhaust. It was the S&S Thing header and tuck-up mufflers on my car. It's a 1 3/8-inch header that feeds TWO 1 5/8-inch QPs. Typically speaking for a low-speed engine the tailpipe/muffler portion doesn't need to be more than about 20 percent larger than the individual pipes in the header that feeds it (the header only works one pipe at a time after all). Well making a new single 1 5/8-inch pipe and muffler brought that engine's torque curve right to life and made the car much more enjoyable to drive.

The faceplant 40 that I worked on was in my pal's '64. It came with a Thunderbird with the big collector--it was a cut-down glasspack job from a 1300-1600 kit. The car was miserable to drive and it sounded like hell despite being a T-bird. So we slapped a used German pea shooter on it and voila, the thing woke right up. He drove it for like two years that way.

[Peter]

I am using a purple hornie,
i think its from thrush....

[richie]

I am using a purple hornie,
i think its from thrush....

I think you are on the wrong forum

[hotrodsurplus]

I am using a purple hornie,
i think its from thrush....

Purple Hornies are from Flowtech. Flowtech is a part of Holley. Thrush is part of DynoMax now.

Purple Hornies are all louver-core mufflers. The brand is so cheesy that it refers to it as a "power louver." 

The smallest pipe diameter is 2 1/4, great if you're building a 2.5-liter engine.

[Peter]

i read somewhere on a turbo engine, they turn the muffler around for better flow...
dont know how good it will work, but my   guess is that it will be louder

[hotrodsurplus]

i read somewhere on a turbo engine, they turn the muffler around for better flow...
dont know how good it will work, but my   guess is that it will be louder

That's been the rumor in the V-8 world for years. Louder? Probably. Less restriction? Highly unlikely. Those louvers disrupt air flow no matter which way they point.

Speaking of glass packs, they all get equally loud in the end. The fiberglass packing disintegrates in time. When blown out they're still quieter than an open pipe and make a deeper sound but they all wear out at one point or another.

[Peter]

I still have a part of perforated pipe of about 60 mm an 400 mm long (some leftover from my cousin),
was thinking maybe to fab a muffler with that pipe...
So you think a engine of about 2.3 l would perform better with that pipe?
I have a 1 5/8 header, and thinking about keeping it to try against a 1 3/4.
my friend who builds engines tested many, and told me a lot of engines he tested had headers that were too big...
with the smaller headers he could get more power and torque...
he does build more smaller engines and not really wild type1's, so its maybe not applicable for bigger type 1's?

[Peter]

Cool,
no need for glasswool and a deeper sound!
double win

[hotrodsurplus]

I still have a part of perforated pipe of about 60 mm an 400 mm long (some leftover from my cousin), was thinking maybe to fab a muffler with that pipe...
So you think a engine of about 2.3 l would perform better with that pipe?

Okay, here's a comparison. 60mm is about 2 3/8". I use two 2 1/4" pipes on my 327. That's 5.4 liters. The engine makes 354hp. Half of that would be 2.7 liters/177hp. And I do that with 2 1/4" pipes.

The displacement is almost irrelevant; it takes a given amount of air and fuel to achieve a specific horsepower. Do you think you're going to move enough air/fuel to make 177hp? If so, a single 2 3/8" muffler might work.

I have a 1 5/8 header, and thinking about keeping it to try against a 1 3/4.

Against a 1 3/4 what? Header? exhaust pipe?

my friend who builds engines tested many, and told me a lot of engines he tested had headers that were too big...with the smaller headers he could get more power and torque...

He sounds like a pretty observant guy. I think most people in the VW world use headers with pipes that are too large for the application. My 327 makes 354hp with 1 5/8-inch headers. I see a lot of guys running 1 5/8-inch headers on 2-liter engines. That would be like running a 4-liter V-8 with 1 5/8-inch headers. The most common Ford Flathead is 4 liters (239ci). A 1 5/8-inch header turns a stock-size Flathead into a weak dog. A 1 5/8-inch header might make sense on a 2 liter if you were buzzing it to 8,500rpm but the cam timing, port configuration, and carburetor setup would make it pretty weak at very low speeds like we use on the street.

The VW world seems to be still obsessed with peak power. It's true that an excessively large header and/or pipe may make a given engine produce more peak power but peak power doesn't translate to performance. What matters more than peak power is power output over the entire operating-speed range. A car with an engine that makes 150hp yet starts making lots of power at 2,500 rpm will blow the doors off of a car that makes 180hp yet doesn't start making power until 5,000rpm. The power curve on the 150hp engine will look flat like Kansas whereas the 180hp torque curve will look like the Matterhorn.

The only time those real peaky curves help is when you're trying to extract every last bit of power from a given displacement (like spinning it at really fast speeds). That requires gearboxes with many closely-spaced gears. That's how Formula 1 engines do so well--you constantly have to keep them in a very narrow engine-speed range. 

he does build more smaller engines and not really wild type1's, so its maybe not applicable for bigger type 1's?

Naturally-aspirated gasoline-engine dynamics are consistent regardless of brand, configuration, cylinder count, and displacement. An engine is just a pump and all of the components must work within the same parameters to make the most power.

And for reference, a 'wild' type I is basically a standard-performance '90s H0nda engine as far as power-to-displacement is concerned. A stock B20B makes 143hp @ 6,200rpm and 133lb-ft torque @ 5,600 with less than 2 liters. A 2276cc type I would have to make 164hp to match that. That's not impossible but it takes some homework to get there and the engine might not be totally daily-driver friendly.

FWIW, those B20B H0ndas make that power with manifolds that have passages smaller than a 1 5/8-inch header.

[Matt Tobias]

This is a great thread with a lot of good info, thanks!

[Peter]

Me personally, I like a peaky engine...
not for my daily driver, but for my weekend car..
i know its maybe not the fastest in regards of torque, but i like the feeling of the kick in the butt that a long duration cam gives...
i had a webcam 86C in the past, but the lobes went flat...really liked that cam,
now an fk8 is installed, and like you say, it has more torque down low, but the fun stops at about 6500,
and i like the scream in higher revs,it feels more mild mannered now.
In an ideal world, i d like to have both kind of engines, but for now i have to choose

[hotrodsurplus]

Me personally, I like a peaky engine...
i know its maybe not the fastest in regards of torque, but i like the feeling of the kick in the butt that a long duration cam gives...

You do realize that in a roundabout sort of way you're admitting that you like cars that are slow most of the time and surprise you with a brief psychological kick, don't you? 

Long duration camshafts aren't synonymous with peaky horsepower curves, either. Look at the engines built for Popular Hot Rodding's Engine Masters contests. They produce peak power at a pretty fast speed--6,500 on a big-block anything is turning pretty hard and even though the contest doesn't measure horsepower at 7,000rpm many of those engines are still building power at those speeds. But the difference is in the combination. Everything is suited to build power over a broad range so they develop insane torque at really low speeds--like 450lbs-ft from a 400ci engine at 2,500rpm.

Cars built around those engines get that kick-in-the-pants feeling the moment the pedal hits the floor. And when you're starting to feel your kick in the pants those cars' occupants are feeling nothing under their pants because the constant and impressive acceleration has pinned them to the seat backs. Trust me, cars with big, flat torque curves that produce a ton of power across a really broad range are WAY more fun to drive and ride in than cars with peaky output. I know because I'm super lucky to have a career that gives me access to such vehicles. Hard launches, burnouts, and donuts happen as fast as you want them. And you can do it in a VW too.

[Jim Ratto]

I think preference of type of powerband kind of sometimes goes hand in hand with what a guy has built in the past, and his "threshold" for pain. When I built my first few VW motors in the late 1980's/early 90's, it was all about getting the rush of an "overcammed" (again, how do you qulaify that term?) VW motor. Like 256' @ .050 in a 1641cc... overcammed by most sensible standards. But because I was used to the asthmatic wheeze of stock dual ports, stock cam, etc... the glaring and quite shocking contrast of the Jekyll and Hyde effect @ 4000rpm was better than any illegal substance effect at the time.
But as you get older and find the pleasures of refinement and the displeasures of trying to make a silky street motor out of a sow pig race motor (jetting/venturies/gear ratios/life with race fuel, etc, you know all the stuff your significant other sees @ The Enemy) you learn to come down a few notches and find a sense of balance.
i.e. cam profiles that are better married to displacement/ring and pinion ratios/port volume, etc. Cylinder pressure and air speed are the things you want to focus on, man.
Amazing what a simple thread about old glasspack mufflers can turn into.

[hotrodsurplus]

But as you get older and find the pleasures of refinement and the displeasures of trying to make a silky street motor out of a sow pig race motor (jetting/venturies/gear ratios/life with race fuel, etc, you know all the stuff your significant other sees @ The Enemy) you learn to come down a few notches and find a sense of balance.

In other words, we got older and wiser. That's a good point and it applies to everything. I can't stand rattles or the occasional whiff of burning oil but when I was a kid I was almost blissfully ignorant to it.

Actually the whole industry has gotten older and, in some cases, considerably wiser. Once upon a time only gurus like Yunick and Navarro and Gene Adams understood the interrelationships among cam timing, compression, port flow and velocity, header design, and intake tuning. But I remember in the 1990s when Edelbrock started releasing its 'packages.' Someone who knew all of that stuff coordinated a series of parts that, if you bought all of those parts, you could build an engine that would make as much or more than Edelbrock's advertisements. They did all of the homework and the combinations worked. Case in point, my dad built the 400-something horsepower package for the 350 and it made even more power than Edelbrock claimed at 2,000 feet above sea level with a really conservative conversion factor. And I can tell you firsthand that it made his roadster absolutely terrifying to drive.

What set these packages apart was that they dispensed with the troublesome low-speed and tuning issues. Wanna drive like grandma? Go ahead. You could short shift into second and if you rolled into the throttle the rear tires would go up in smoke. The torque curve made it feel almost as if it were Roots blown.

The V-8 titles really ran with this and hired guys like Vizard to interpret these once-obscure dynamics so peons like us can understand it. And say what you will about it but the tuner crowd took it even further with pretty sophisticated forced-induction systems.

But for some reason the VW industry really trails. Right now there are guys who can make real big power across a broad speed range in an engine that will behave nicely and live a normal lifespan but they're pretty few and far between. But to the best of my knowledge nobody has assembled a comprehensive package to achieve a confirmed goal, a real shame because IR-fed engines are really capable of good manners and big power.

For some reason the VW world is mortified by compression ratio, no surprise considering that so few people in the community understand the benefits that a custom-tailored advance curve offers. While the rest of the world has embraced super-tight deck clearances and tiny chambers the VW world is still carving chambers into big arbitrary shapes and using deck height to set static CR. Stand behind a running 'hot' car in the VW world and you'll choke on hydrocarbons. People make a huge deal out of running exhaust diameters that would do a big-block anything justice (admit it--you've seen 3-inch pipes hanging off the back of VWs before). And if you ask people why that is, they'll just fall on that tired old refrain, "Because VWs are different."

i.e. cam profiles that are better married to displacement/ring and pinion ratios/port volume, etc. Cylinder pressure and air speed are the things you want to focus on, man.

Exactly. And the irony is that Harry Ricardo revealed these principles in the 1920s! It incenses me when people defend poor practice by saying that it was relevant in the '70s and '80s. Man, the rest of the performance world knew that some of the things the VW world did wasn't even relevant then! 

Amazing what a simple thread about old glasspack mufflers can turn into.

I bet most of the people who'd turn it into a spiraling flame war didn't read it because they read glasspack and wrote it off. I wish more people who had proven comparative experience could chime in.

[Jim Ratto]

we need our own thread. Or forum. 

[modnrod]

. I wish more people who had proven comparative experience could chime in.

OK.

1641 I had in the early '90s (in my avatar pic, still miss it!  ). I went through 3 sets of heads, 4 cams, 4 different single carb options, etc, etc, etc, and tried to optimise the exhaust for each combination, because at the time it was easy and fun to build my own or modify what was available.
The results surprised me at the time, but now I know a bit more about engines in general, not so much.

The motor made everywhere from 60rwhp up to 90rwhp, with varying degrees of finesse! But my favourite, one I'm getting similar parts together for now as an "older & wiser & smarter" assembly, made 80rwhp. It had 8.5:1 comp, W100 but on 112LC, custom centrebranch with Stromberg 1BBL, and ported 355A stock heads with 35.5/32 valves. With the stock exhaust but with 1.1/2" peashooters, it looked absolutely bone-stock, except for a slightly different air filter assembly, it even fooled VW guys. In that little blue slammed Baja with a 1300 box and 185/60R14 tyres it ripped out mid-15s all day long.

When I went to optimise the exhaust to suit this package with a 4-1, I tried cheap crappy 2nd hand sets, then an expensive merged set up, and everything from a 1.3/4" hotdog (glasspack) up to a 2.1/2" Hooker chambered deal. The difference over and above my tweaked stocker with big pipes and ALL the different set ups?

4rwhp.

That's it. A paltry 4rwhp, or about 2 tenths. I left the stock muffler on coz it made me more money.............

If the OP wants to put a really restrictive glasspack on his street motor coz he likes the "good old days" feel and looks and sound, then I reckon go right ahead mate.
Have fun. 

(PS: hence my saying in an earlier thread about way too big exhaust PORTS, not pipes, but just exhaust ports being worth ONLY 2 or 3%).

[hotrodsurplus]

80rwhp. It had 8.5:1 comp, W100 but on 112LC, custom centrebranch with Stromberg 1BBL, and ported 355A stock heads with 35.5/32 valves.

Eighty wheel horse? Damn. I would've deemed that 80 flywheel. That's healthy. And you could run that on US 87-octane fuel!

Baja with a 1300 box and 185/60R14 tyres it ripped out mid-15s all day long.

Damn!

4rwhp.

That doesn't really surprise me. And I bet you that 4hp cost you a noticeable amount of low-speed torque and throttle response.

A lot of people have it out for that stock peashooter exhaust but damned if it doesn't work well. My learning experience was on a girlfriend's '70. It needed an exhaust and I had a boner for those tuck-up systems that had recently come out (1992 or so). It made a difference: the car got SLOWER. Seriously, it took more throttle to maintain freeway speeds. Off idle it wouldn't quite stumble but it felt lazy. This after jet and timing changes. It did pick up a bit more at the top of the scale but it was so much slower at low speeds that it wasn't worth it. And here's the thing: even SHE noticed it. In fact she told me to put a stock muffler back on even if it meant using the rusty old one.

I ended up getting her a new one and owning the tuck up for myself. The power came back and because she was happy I was happy. The learning experience was worth more than the money that the exhaust cost.

FWIW, a pack isn't necessarily more restrictive. A straight-through perf-core pack poses no more restriction (and offers hardly more sound reduction) than an open pipe. The louvered-core ones, on the other hand, impose a lot of backpressure. And as mentioned earlier the excessively large ones kill velocity. The worst of both worlds would be an oversized louvered-core pack. That would truly kill all performance.

[Jon]

With regards to exhaust tuning, a open-chamber type muffler makes it easier to calculate lengths. As pr David Vizards article "Designing a zero loss exhaust". http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/viewall.html
Maybe the article is irrelevant, since VWs are different? To my knowledge there's not a exhaust system on the market following his logic.

Don't ever go away hotrodsurplus! 

[hotrodsurplus]

With regards to exhaust tuning, a open-chamber type muffler makes it easier to calculate lengths. As pr David Vizards article "Designing a zero loss exhaust". http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/viewall.html
Maybe the article is irrelevant, since VWs are different? To my knowledge there's not a exhaust system on the market following his logic.

Typical for a Vizard entry, there's a considerable amount of very good information in there. The only potential problem that I see is how well people comprehend it. He gets pretty lofty which is inevitable but that is often difficult for people to grasp. The research feedback we would get indicated that almost everybody looked at every picture in a magazine, quite a few people read the captions, and not all that many read more than two or three whole stories in a 200-page publication. And almost nobody read a story twice. I can't speak for the rest of the world but Americans are notorious skimmers. I'm no different: I can't justify reading the whole thing right now. I'll have to read it more thoroughly later on.

Regarding relevance, as noted earlier a VW is no different than a V8 from a dynamics standpoint. Both engines are just pumps. There are a few packaging differences like the one he reveals in the passage about equal-length headers. The typical V8 engine splits into two inline-four engines each with a woefully uneven firing order. Luckily we don't have to worry about that (although some people seem determined to create that problem for us--for example those G Down headers create the same problem that V8 headers do). There may be some other things in that article that pertain specifically to race practice. The 1:1.75 primary:collector formula is quite excessive, at least for a street-driven engine. By that logic a 1 3/8-inch header would justify a 2.4-inch collector.

I do know one thing from experience that I don't think he addresses fully in the article: total exhaust length. I know from my experience in 'real' cars that cutting off the exhaust pipe before the axle usually results in a measurable torque loss at slower speeds. I know this because I temporarily had to do that to one of my pickups and it got slower (and louder). That's one thing that presents an issue to the ACVW: the exhaust systems we use are less than a meter long at best. I know we're leaving drive quality and probably even mid-range performance on the table but how do we run a long exhaust without snaking it around the car? Guys tried that in the late '80s and early '90s by dumping the exhaust ahead of the rear wheel and it wasn't pretty. Racecars can benefit from short pipes because their exhaust systems operate at such a high resonant frequency but street cars benefit from a lower frequency tuning.

 

Don't ever go away hotrodsurplus! 

Now you're making me blush. Well no angry mob has run me off with pitchforks and torches yet but give them time.