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j10nbom
Samba Member
Joined: February 14, 2007
Posts: 262
Location: Philly
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 Posted: Tue Aug 03, 2021 5:32 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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| Koeppler wrote: |
| j10nbom wrote: |
| I bought the Empi 3312 single quiet pack (1-1/2") for my '71 with a 2110. It hasn't actually gone into the bus yet, but allegedly it fits '63 - '71 T2s. |
I checked this EMPI 3312 out. On cip1 it says “Fits: 13-1600CC BEETLE/GHIA/BUS (Pre '67 Buses without Mustache bar)”.
I’m not saying it won’t fit a 71. I’m just saying that not every retailer agrees about what headers fit what models. It sucks. |
That's fair, I just emailed Empi to find out so I'll keep everyone posted. I'm 90% sure I have the Empi 3655 on there now which is the 1-3/8" one. |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Tue Aug 03, 2021 9:13 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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| aeromech wrote: |
Steve,
Please explain the concept of “back pressure” in this discussion because from what I’ve become to understand, an engine needs a certain amount of back pressure. Otherwise we’d all just install huge pipes to flow more than enough air. |
Gary - there are two aspects to the exhaust. The first is its ability to flow the gases that are in the cylinder after it burns. The second is the ability of the exhaust to scavenge the gases left over after the stuff under pressure flows out the exhaust port. Imagine a child on a swing. You have to push at the right time to keep the child swinging or you are fighting the child swinging. We learned that early in life. What one is looking for is a fast enough exit of the gases out of the exhaust, and a back pressure pulse that arrives at the right time from the tailpipe / muffler / resonator to scavenge extra gases from the cylinders as it hits the back of the exhaust valve and creates momentum moving away from it. That timing includes length and diameter of the pipe. Think of it this way, it may be easier to blow into a 4" pipe than a 1" pipe but if you measure the speed at which air comes out the 1" pipe vs 4" pipe there will be little air momentum out of the 4" pipe because you have to get all that air moving. Likewise the air in the small pipe has less mass so it takes less energy to get it moving. An exhaust is really like tuning a clarinet, oboe or flute - like a pop bottle. It has its own frequency. If that frequency is matched closer to the resonance of the engine then more exhaust gases will flow thru it. That chart appears to reflect that. Meaning that there is an optimal RPM range for each engine and pipe size. If you will run the engine at 6000 RPM all the time then choose a pipe size that supports that. If you will run the engine at 4000 RPM all the time then choose a pipe size that will support that. To be really frank, header building is sort of like a voodoo science, Ive seen master header builders fail miserably on getting more power out of an engine. Unless one has an engine dyno to test different arrangements, it is pissing upwind to sit around drinking beers and stroking each other by pretending to know about it. Most of the conversations around here are at that level. Remember when you were a child and you had a .049 airplane or such and you would find that sweet spot where the engine just purred and the RPM went up as you adjusted the needle? Exhausts are like that but without an engine dyno and multiple exhausts, one will never experience it. I have to trust that the existing designs are as good as it gets for the layman. Generally, like any musical instrument, the shorter the pipe length the higher the RPM it supports. Since we can't really play with pipe length on a daily driver, we can only play with pipe size. Use the chart or piss upwind is what I would say. Your dual pipe stock system is great for a bus. I drove a 1600 for many years that had a header system and had no issue maintaining 6000 RPM for hours on the way out to the River from the LA area, or driving up 5 between LA and Sacramento once it got fairly flat. I doubt many people drive their buses like that but this was the early 80's when low mile AE cases and other factory parts were really easy to come by. I worked in a machine shop that did racing work for Indy cars, F1 Cosworth engines etc and it cost me nothing for the labor to machine something getting it ready for something I broke driving the engines so hard. I would not do it again however because quality parts are too hard to come by.
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aeromech
Samba Member
Joined: January 24, 2006
Posts: 16958
Location: San Diego, California
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| Posted: Tue Aug 03, 2021 10:39 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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Thanks Steve
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j10nbom
Samba Member
Joined: February 14, 2007
Posts: 262
Location: Philly
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| Posted: Wed Aug 04, 2021 8:34 am Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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This is the response I got from Empi...
"Thank you for your interest in our products. The exhaust system #00-3312-0 will fit the 71 bus with some modifications. You will need to clear the rear motor brace and the bumper. The 00-3655-0 is designed for the bay window buses and this system clears the brace and the tip is extended to clear the bumper." |
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Koeppler
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Joined: April 21, 2011
Posts: 481
Location: Aging gracefully
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| Posted: Wed Aug 04, 2021 3:41 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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| j10nbom wrote: |
This is the response I got from Empi...
"Thank you for your interest in our products. The exhaust system #00-3312-0 will fit the 71 bus with some modifications. You will need to clear the rear motor brace and the bumper. The 00-3655-0 is designed for the bay window buses and this system clears the brace and the tip is extended to clear the bumper." |
Now that’s a pain in the butt. Are you going to return it? If the place you bought it from sold it to you as ready to go for your bus then they should do the right thing and even pay return shipping. |
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richparker
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Joined: November 24, 2011
Posts: 6980
Location: Durango, CO
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| Posted: Wed Aug 04, 2021 4:24 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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| D/A/N wrote: |
Well, to this eye the ramps/lobes look not entirely unlike a 110, which is what I meant though I know it behaves differently than a 110.
But if you’re here and actually feeling helpful maybe you can help with a question this thread is giving rise to for me: Does a Web 218 with 37x32 heads and 40 Dellortos in a heavy camper with an early 3 rib trans call for a 1 1/2” or a 1 3/8” header? Consider that my max speed is probably 70 mph given a young’un on the rear bench and that I’ll see 4500 rpm only very rarely. |
I run CNC ported CB super mag heads with 35.5x40 valve ports and an Engle 110 cam.
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j10nbom
Samba Member
Joined: February 14, 2007
Posts: 262
Location: Philly
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| Posted: Wed Aug 04, 2021 6:40 pm Post subject: Re: Need some schooling about 1 1/2” headers and early bays |
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| Koeppler wrote: |
| Now that’s a pain in the butt. Are you going to return it? If the place you bought it from sold it to you as ready to go for your bus then they should do the right thing and even pay return shipping. |
Nah probably not. Knowing myself it will probably sit on a shelf for another decade and then eventually I'll find it again and think to myself sweet I got a free exhaust. |
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