GPR Camp: Replica Racers

This is the last open question / part that I need to find. So, looking for some thoughts, and recommendations.

2002 GRP 50 with an Airsal Extreme 80cc top end. And a Dellorto PHBG 21mm carb.

Bike is being built for torturing the neighbors, and track days.

Any thoughts? Anyone have anything they want to sell?

I have an Arrow pipe on my 75cc GPR, and it seems decent.

I repacked the silencer, which quieted it down a bit. The pipe probably shifted the power up higher, but mine has a 24mm Mikuni Flatslide on it, so it's going to be pretty flat down low anyway. The 24mm is too much IMO, but it was on there when I got it.

You will have to see what's available at this point, and may not have a ton of options.

There are probably very few exhausts on sale today (if any) that 'officially' fit to old version (pre-2004) GPR. I suggest that you search an exhaust for AM6 bikes like Yam TZR 50 or Rieju RS2/RS3, for example Yasuni R4 or Bidalot RF-WR 80. Many AM6 exhausts come with brackets for new version of Derbi GPR/Aprilia RS too, which you should, if necessary, modify or make new ones to fit old version of GPR.

Yea, not a lot of options at this point. Anyone have something sitting on a shelf gathering dust?

Looks like Dos Cycles has a couple of SCR Corse exhausts, so that's an option. And they say they can still get Metrakits, as well as Giannelli.

Any thoughts on the SCRs?

Puled the pin on the SCR CORSE Racing pipe from DOS. A combination of availability, and free shipping made all the difference. And it looks like I may have gotten the last one, because I cant see it on the site anymore. But they do have other SCR options, just not one tuned for the 80cc cylinder.

I will say the quality welled, and fitment is very good.








I assume this is the original pipe. So you can get an idea of the different shapes.



And fits perfectly with the new fairings

I've heard of SCR Corse pipes before, but don't have any experience with them. By build quality it certanly looks nice. I'm courious, can you measure header pipe internal diameter? Thanks.

Hey Jaxx, the internal diameter of the header is 28 mm.

All other dimensions are external circumference. Or outer distance weld to weld.

The image below has the rest of the measurements, incase anyone in curious. I tried to snake a wire down the stinger to see how far into the chamber it goes. I put a hook on the end hoping to find the end but I couldn't. Lots of information about two stroke chamber tuning relating to how big, and how far into the chamber the stinger goes. It's at this point I want to order a boar scope to find out. Stay tuned.

Hey Jaxx, the internal diameter of the header is 28 mm.

That appears to be standard for 70-80cc big bore kits, but for 80cc I think it wouldn't hurt having 30-32 mm. About stinger, are you sure that stinger protrudes into chamber? Most pipe designs I've seen have stinger pipe just welded on the baffle cone smaller end...

Jaxx wrote: ↑

Sun Oct 16, 2022 1:24 am

Most pipe designs I've seen have stinger pipe just welded on the baffle cone smaller end...

For some reason I thought I read something in Gorden JenningsTuners Handbook about it. But as I try to find a reference, I cant. I will stand corrected.