4-2 v 4-1 downpipes

[seth]

It's been told or years that the earlier 4-2 downpipes are smaller internal diameter than 4-1 ones fitted to the later bikes .
I know the first bikes had chrome downpipes and later had stainless ones.
And also the earlier and later pipes are interchangeable with both early and later collector boxes .
So my question has anyone actually measured and compared either the internal diameters or internal volumes of the 2 types of downpipes or is it just a myth that they are different sizes ?
Cheers 

[grog]

Seth, i dont know that answer. But as an add to your question, does aftermarket systems, Yoshi/Akra etc have bigger internal headers.

[Hooli]

I've never done so, but I've always heard the early ones are double skinned so measuring the outside won't help.

[seth]

@grog yes they aftermarket ones you mention are single skinned downpipes(why they to colour with heat) with a much larger internal bore than that's where the extra power comes from and why really a powercommander and remap is advisable after fitting .
I don't know about delvic and blackwiddow systems internal bore sizes as never even seen a set off a bike.

[seth]

@grog
Only other thing is the 4-1 collector link pipe has a restrictor pipe inside .
There was a company that did an unrestricted replacement not sure who they were and if they are still available.

[bigian14]

It's been told or years that the earlier 4-2 downpipes are smaller internal diameter than 4-1 ones fitted to the later bikes .
I know the first bikes had chrome downpipes and later had stainless ones.
And also the earlier and later pipes are interchangeable with both early and later collector boxes .
So my question has anyone actually measured and compared either the internal diameters or internal volumes of the 2 types of downpipes or is it just a myth that they are different sizes ?
Cheers 

Hi Seth,
I can't confirm the actual diameters but I replaced the standard system my K5 with a full Akrapovic 4-1 a few years back but can confirm that the standard downpipes were double skinned, for some reason i'm thinking 28mm internal diameter, compared to around 40mm on the Akra.  Only benefit of the double skin is that the outer skin doesn't turn blue from the heat.  I think the Final Edition was fitted with a full Yoshimura system with single skinned downpipes just as a final hurrah before the emissions police killed it.
This along with other small tweaks may have been to help get the emissions down as you feel the engine is being strangled around 7k rpm as it can't get rid of the exhaust gases fast enough. Replacing the system on mine (and fitting Yoshi cams) allowed it to pull hard right up to the redline, 9k rpm, and increase the rear wheel hp to 136.  Although I've since gone down the turbo route, just under 240bhp at the wheel 
Shame really as there were some cracking muscle bikes back then sadly either no longer made or watered down to keep the emissions people happy.

[gsxbarmy]

@Snapey did measure both Stainless and Chrome some years ago, I can't recall the exact outcome, but from memory, I seem that the later (stainless) ones had a slightly larger inner diameter - Snapey would have to confirm that of course.

[seth]

@bigian14
The later system is only a yoshi can and link pipe fitted by dealers.
The system still uses factory downpipes and 4-1 collector .
The yoshi can and link pipe(link pipe is restricted internally) only replaced the bazooka can Suzuki fitted .

Also I have yoshi cams in 1 of my 14's it revs out but the power stops at 136bhp @7000rpm .
Small throttle bodies stop it going higher.
Next step will be 36mm throttle bodies and hoping for over 145bhp .

[Snapey]

@Snapey did measure both Stainless and Chrome some years ago, I can't recall the exact outcome, but from memory, I seem that the later (stainless) ones had a slightly larger inner diameter - Snapey would have to confirm that of course.

The inside diameter of all inner pipes is 26mm. Just inside the opening it's a bit larger but then tapers down to 26mm about 2" in. That applies to both chrome mild steel and stainless down pipes.

In the photo you'll notice the larger diameter toward the mouth. One other interesting thing is that this is an early mild steel example outer skin but the inner is stainless and although you can't read the vernier it's 26mm ID.

[gsxbarmy]

Thanks @Snapey , - you even still had the photo as well, brilliant 

I've stickied this for future reference, just in case it gets asked again

[grog]

They sure are tiny inside.

[Notty]

They sure are tiny inside.

That's what the actress said to the bishop