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 Post subject: Exhaust diameter question
PostPosted: Tue Feb 26, 2019 10:01 am 
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Joined: Thu Nov 29, 2018 8:31 am
Posts: 6
Location: Bosnia
Hello guys, next month I planned to replace the exhaust system from the header back. In the swap from the previous owner the entire car is still on a G10A exhaust system, original cat, resonator and rear muffler, which brings me to a few questions:

1. What is actually the size of the G10A exhaust, which diameter? I doubt it's over 35mm / 1 1/3 inch?

2. Should I go 1.75" or 2" from the headers back to a muffler, a friend of mine has a GTI and he said 1.75" / 45mm to the muffler, on the other hand I read here by searching the threads that 2" is actually "better"?

Thanks in advance!

EDIT: Asking for a G13B engine, stock, only an air filter replaced and that's it.


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 Post subject: Re: Exhaust diameter question
PostPosted: Tue Feb 26, 2019 10:14 am 
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Location: Portugal
2inch is better for 5000+ rpm


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 Post subject: Re: Exhaust diameter question
PostPosted: Tue Feb 26, 2019 5:29 pm 
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Joined: Mon Oct 12, 2015 11:30 am
Posts: 396
Location: Napier
Just go 2" all the way. You will not notice any difference performance wise from 1.75-2". The only difference will be the sound.

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 Post subject: Re: Exhaust diameter question
PostPosted: Wed Feb 27, 2019 9:44 am 
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Joined: Thu Nov 29, 2018 8:31 am
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Location: Bosnia
Howsie13 wrote:
Just go 2" all the way. You will not notice any difference performance wise from 1.75-2". The only difference will be the sound.


Thanks, that was kinda what I was wondering if there would be a SIGNIFICANT amount of difference between 1.75 and 2".

I have one more question regarding the air filter that I put on in this case. The car feels really sluggish in the low end but it kicks in very hard at about 3k, sometimes earlier, where-as the stock airbox which was actually not closed and the filter was just resting in the case that's closer to the MAF had a linear acceleration through the revs. I couldn't close the stock airbox because of the power-steering reservoir that's in the way, another thing that was poorly made whilst swapping the G13B into the car.

Some people told me that actually the G13B doesn't take kindly to aftermarket airfilters with something along the line of it's getting "too much air", is this actually true? This sluggish effect is sometimes greater sometimes not noticable at all, and I didn't have such an issue before putting the filter on.


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 Post subject: Re: Exhaust diameter question
PostPosted: Wed Feb 27, 2019 12:33 pm 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 228
Location: Brisbane
50mm/2” system on stock g13b motor opened it up nicely. On the other end i found stock paper element very restrictive same for unifilter element. I used a old trumpet style filter using 60mm thick foam using no toil motorbike sticky stuff a massive improvement. When i pull the motor down i will know how well it actually works but it uses less fuel and has more grunt so i am sticking with it.


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 Post subject: Re: Exhaust diameter question
PostPosted: Wed Feb 27, 2019 1:40 pm 
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Joined: Mon Oct 12, 2015 11:30 am
Posts: 396
Location: Napier
All car engines operate on the same principle, they are an air pump. Stock paper filters usually flow quite well. ( you cannot tell just by driving the car)

Have a read of this to get your head around it...
http://www.autospeed.com/cms/article.html?&A=0629

It is usually poor airbox design that can contribute to poor down low response. Measure stuff to get the data you need to make intelligent decisions.

"Some people told me that actually the G13B doesn't take kindly to aftermarket airfilters with something along the line of it's getting "too much air", is this actually true?" - No, it is because they install a massive pod filter with no cool box or shielding from the hot exhaust next to it so it sucks hot air at low speed. Winning right there.

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 Post subject: Re: Exhaust diameter question
PostPosted: Thu Feb 28, 2019 2:34 am 
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Joined: Thu Jan 17, 2019 6:46 am
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Location: Portugal
Material makes differences? stainless steel vs iron steel


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 Post subject: Re: Exhaust diameter question
PostPosted: Thu Feb 28, 2019 5:35 am 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 228
Location: Brisbane
I got mild steel for the exhaust as i didn’t think stainless would warrant the cost and no salt on sunny Queensland roads. As for the air box the stock one does keep it quieter but sitting behind the headlight is easy to get to for the occasional service and it uses about a quarter to a third less fuel for my usual weekly driving so must be more efficent. This is in 30+ degrees for half the year as well. Pretty sure a air box not needed even though not tried it yet as just a daily driver sitting in traffic etc and weekend highway runs. But i have thought about it and read on teamswift when someone measured temps they found a air box not that much cooler. Their words not mine. Either way i think it’s too crowded in there anyway.


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 Post subject: Re: Exhaust diameter question
PostPosted: Thu Feb 28, 2019 7:22 am 
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Location: Bunya QLD 4055
And GTi did not come with power steering originally so that it was easier to work around that part of the intake. Did the motor come with upgraded cams?

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 Post subject: Re: Exhaust diameter question
PostPosted: Thu Feb 28, 2019 8:30 am 
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Joined: Thu Nov 29, 2018 8:31 am
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Location: Bosnia
pictureshowman wrote:
And GTi did not come with power steering originally so that it was easier to work around that part of the intake. Did the motor come with upgraded cams?


Exactly, afaik no GTI had power steering, this one does though because it was fitted from the G10A and with the AC compressor aswell, I'll get around to it this weekend, take the front apart and see if I could relocate the power steering reservoir and make a heatshield for the pod filter, we'll see if it makes a difference, worst comes to worst I just return the stock airbox and it's all well again.

edit: If you're asking about my engine I am sure it has stock cams.


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 Post subject: Re: Exhaust diameter question
PostPosted: Thu Feb 28, 2019 2:17 pm 
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Location: Canberra
Would recommend mandrel bends in piping to ensure you get most out of it. I have a 2 1/4" inch stainless system with mandrel bends. Got it done around 1996 and it is still in great shape. Also has stood up to me taking car from basic NA mods all the way through to current version (built turbo engine with 216fwkW on E85).

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