1 5/8 inch ID exhaust on 1700cc?

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FJCamper
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1 5/8 inch ID exhaust on 1700cc?

Post by FJCamper » Tue Jun 06, 2017 2:56 pm

Anyone tried a 1 5/8 inch ID exhaust on a 1700cc?

The heads are fully ported by AJ Sims, and have 40x35 valves.

The book says 1.5 inch ID is the right size. But maybe ...

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Marc
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Re: 1 5/8 inch ID exhaust on 1700cc?

Post by Marc » Tue Jun 06, 2017 3:50 pm

Our team used to campaign a mini-super with a big-valve 1775, 48IDA'd methanol motor and 1⅝" exhaust as well as three "street-stock" Beetles (stock-valve, unported heads, 8¾:1 1585cc with a Holley-Weber progressive and 1½" exhaust). Racing at a ¼-mile circletrack one of the Bugs got involved in a crash that took out the exhaust so I threw on the only spare we had with us, a 1⅝". Imagine my surprise when that car started running .2-.3 second faster lap times :o

Traffic was uncharacteristically light in that event so the RPM range used was ~4500-6000, and the "too-big" system worked well...but following the conventional wisdom I went back to 1½" after that day for fear of losing needed low-end torque in more typical crowded conditions.

Can't hurt to give it a try, especially if your gears are closer-spaced and/or you don't expect to get mired down in traffic.

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Re: 1 5/8 inch ID exhaust on 1700cc?

Post by Bruce2 » Wed Jun 07, 2017 1:41 am

FJCamper wrote:
Tue Jun 06, 2017 2:56 pm
Anyone tried a 1 5/8 inch ID exhaust ......The book says 1.5 inch ID is the right ...
Tubing is measured by the OD, not ID. If 1.5" ID is right, you buy a 1&5/8" header.

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Re: 1 5/8 inch ID exhaust on 1700cc?

Post by FJCamper » Wed Jun 07, 2017 9:18 am

Thanks, Marc, Bruce;

We run Daytona this fall and I've got to even things up with the 356's. We're swapping to Hoosier "Speedster" racing tires, and some engine tweaks, such as Weber 44's to replace our current 40's.

An actual 1600cc 356 is rare. 1720cc big bore kits are common. VW Type 4 engines are out there in the mix.

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Re: 1 5/8 inch ID exhaust on 1700cc?

Post by 66brm » Thu Jun 08, 2017 7:50 am

I run 1 5/8 on my 1600, but, and it's a big but, I spent years researching, I've read nearly every book on exhaust design I can find, and it shouldn't work "in theory" ,my combo is 69 ccwt german crank, stock reworked rods, cofap pistons, early cb044 heads hand ported and unshrouded chambers, Engle 110 cam, 1.25 rockers, 40idf carbs, 8.5:1 static cr.
What I've found is the length of the primaries to the collector is VERY important, the headers I run are an off the shelf A1 sidewinder, why? Length......I can feel each individual pulse out of the exhaust over 3ft away at idle, the engine is soggy below 2000 rpm but was expected to be considering the cam and heads.
Between 2500 and a self imposed red line on the street at 4500 it's a lot of fun given the w series cams ability to produce good cylinder pressure at reasonably low rpms. This engine with a tweaked 34pict pushed my 66 t1 to 100mph on the nullabor plain. I don't push the car that hard any more as its got over 80k miles on it and is probably due a freshen up

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