ApriliaForum sponsored by AF1 Racing, inc. - View Single Post

VinCBR900 · 12-17-2004, 03:53 AM

Ive had a go at summarising the differnet options I have heard for RGV engine transplants - som ehave also been performed on the RS250, but there wshouldnet be a lot fo difference. YOU can view things in two ways - performance, or cost. Many of these engines and tuning options have been discussed before on this and the RGV forum - sorry if I make any mistakes.

One of the most common is the big single, something like DR800 which is one of the biggest, but apparently they vibrate quite a lot. I think you are looking at 50bhp for a few minor tweaks, but with loads of torque, then there are race conversions which get upto 70bhp, but I understand that they dont last too long with huge 100mm pistons swinging around at 10000rpm. There are various flavours, ranging from XT600, DRz400 (which only makes 40bhp tuned) etc etc
Supposed to be relatively easy to do, possibly without frame welding, just adaptor plates, depending on how big or small your replacement engine is. You will need to fabricate an engine cradle but since this can be mild steel its not hard to do. This conversion is a different paradigm to the stroker. Could be considered a Low to medium cost conversion depending on which engine (400cc engine could be £500, but a big 800cc engine is sought after by racer and could be more) how much tuning you do to the engine, but since it is a single you only need one fancy conrod etc instead of four.
http://www.thumperpage.com/articles/XRG660.html

Then there is the RZ350/RD350YPVS conversion that Stilletoman on the RGV forum has done, which is soemthing I considered once - even had the engine in an old frame, but never got around to finishing it so sold it on ebay. Relatively easy to get a reliable 70bhp with more torque than an RGV. There are loads of spares in UK, and if you want to buy perfomance parts from US the Banshee350 quad uses the same bottom end with loads of big bore kits, complete new cylinders and powervalve, depends how much money you have. Yamaha still make new spares for the banshee gearbox and cranks which is handy when you blow a geabox and want to fit updated banshee parts (since it is tougher on the box being a quad).
The claim is 100bhp from a 500 big bore kit but I dont believe it really. From my experience, I woudl say things are a bit tight but not impossible. Needs frame welding. I would consider this a low cost conversion since 350YPVS engine are available for £200 with all the electrics in the UK.
http://www.yamaha-rd.com/forum/

There is the NS400 conversion which Anderzander first talked about on the RGV forum. YOu can eitehr use standard engine, standard engine with big bores to get 500cc, engine with CR cylinders, CR cyls with big bore cr cylinders. AParently, NSR250 carbs fit, and with a decent set of expansion chambers I dont think it would be too hard to get a genuine 100bhp from this combination - CR cylinders and big carbs should do it, definately if you big bore them, with NSR250 carbs.
Anderzander, Bloodnut and Matt Grant on the RGV forum are doing this mod. CHannel Hopper on the NS400r forum is going for a least cost NS400 engine tune but not sure which chassis he is using. Only problem is getting the engine, which is a bit scarce, and various fixes and workaround shave to be performed since Honda dont produce the crank parts anymore, but other conrods form Yamaha fit with a bit of work.
I have seriously considered this conversion for a spare VJ21 chassis but then real life comittments like job and family keep stopping (or waking me up) me from doing it.
Anderzander says it is easy to do, kickstart in right place, even one engine bolt ligning up, with minimal frame welding. MGA on this forum/gixerboy on the RGV forum will be producng a frame moutning kit in the near future I believe. I would say this is a medium cost conversion, since engines are £500 plus, but with good power to cost.
http://www.ns400r.co.uk/forum/

Anderzander is also doing the RD500 V4 engine transplant, but trying to do it properly by fitting cylinders from the RGV. I would say its a bit tight in an RS250 but it is the ultimate performance mod with over 120bhp available. Especially so if you can fit the 300cc big bore pistons making a 600cc engine. This is a perfomance at all cost conversion, since peopel want lots of money for the engine, then there are lots oc cost for the RGV cylinder conversion, then the cylinders themselves, then the cost of the pipes etc etc.
http://users.bart.nl/~bommie/YTCN/sp...00ralfkras.htm

Similar comments apply for the RG500 conversion. Big performance, big prices. Peopel have fitted TZ cylinders, loads of power. Perosnally I never liked the carbs which woudl get smashed off during a lowside. The RG500 engine does have cult status which makes the cost even higher.
http://www.suzuki-rg500.com/rgv250.htm

Things like H1, GT750 are big mans engines designed in the 1970's. They were fitted to rubber band frames when men were men and women were glad of it. Fitting one in an RS250 would be difficult, you need to do loads of work to get them to make more power since none of them had reeds originally, and I would rule them out. Try and use an engine that is the same vintage or newer than the engine you are replacing.

Boring out teh stock engine has been done and is listed in detail on this forum. In the US, the 316 engine conversion was popular, using (I think) 62mm snowmobile pistons on a 50.6mm stroke. In the UK, 60mm custom Wiseco pistons were fitted making it around 300cc. The 300 kit seems to have had better reliability but that could be because they dont seem to have been raced whareas the point in the 316 kit was that you could take on SV650s so were raced in US racing classes. The letdown is the crank, it doesnt like more than about 70bhp and it doesnt liek being revved. If you were to get JHA to design you a custom stroked crank then you might get more with the bigger pistons but fo the cost you could afford an NS400 engine transplant.
http://www.stanstephens.com/index.html?rgv.htm~contents

So thats it, cant think of anything else. You could try something new and original like fitting a twin cylinder polaris snowmbile engine - 700cc two stroke, water cooled, 100bhp, centrifugal clutch. Would be one of the fastest twist and goes in the world!

CHeers, Vincent

12-17-2004, 03:53 AM	#32
VinCBR900 apriliaforum expert Join Date: Jul 2003 Location: Near Loughborough, UK Posts: 616	LONG summary of engine transplants Ive had a go at summarising the differnet options I have heard for RGV engine transplants - som ehave also been performed on the RS250, but there wshouldnet be a lot fo difference. YOU can view things in two ways - performance, or cost. Many of these engines and tuning options have been discussed before on this and the RGV forum - sorry if I make any mistakes. One of the most common is the big single, something like DR800 which is one of the biggest, but apparently they vibrate quite a lot. I think you are looking at 50bhp for a few minor tweaks, but with loads of torque, then there are race conversions which get upto 70bhp, but I understand that they dont last too long with huge 100mm pistons swinging around at 10000rpm. There are various flavours, ranging from XT600, DRz400 (which only makes 40bhp tuned) etc etc Supposed to be relatively easy to do, possibly without frame welding, just adaptor plates, depending on how big or small your replacement engine is. You will need to fabricate an engine cradle but since this can be mild steel its not hard to do. This conversion is a different paradigm to the stroker. Could be considered a Low to medium cost conversion depending on which engine (400cc engine could be £500, but a big 800cc engine is sought after by racer and could be more) how much tuning you do to the engine, but since it is a single you only need one fancy conrod etc instead of four. http://www.thumperpage.com/articles/XRG660.html Then there is the RZ350/RD350YPVS conversion that Stilletoman on the RGV forum has done, which is soemthing I considered once - even had the engine in an old frame, but never got around to finishing it so sold it on ebay. Relatively easy to get a reliable 70bhp with more torque than an RGV. There are loads of spares in UK, and if you want to buy perfomance parts from US the Banshee350 quad uses the same bottom end with loads of big bore kits, complete new cylinders and powervalve, depends how much money you have. Yamaha still make new spares for the banshee gearbox and cranks which is handy when you blow a geabox and want to fit updated banshee parts (since it is tougher on the box being a quad). The claim is 100bhp from a 500 big bore kit but I dont believe it really. From my experience, I woudl say things are a bit tight but not impossible. Needs frame welding. I would consider this a low cost conversion since 350YPVS engine are available for £200 with all the electrics in the UK. http://www.yamaha-rd.com/forum/ There is the NS400 conversion which Anderzander first talked about on the RGV forum. YOu can eitehr use standard engine, standard engine with big bores to get 500cc, engine with CR cylinders, CR cyls with big bore cr cylinders. AParently, NSR250 carbs fit, and with a decent set of expansion chambers I dont think it would be too hard to get a genuine 100bhp from this combination - CR cylinders and big carbs should do it, definately if you big bore them, with NSR250 carbs. Anderzander, Bloodnut and Matt Grant on the RGV forum are doing this mod. CHannel Hopper on the NS400r forum is going for a least cost NS400 engine tune but not sure which chassis he is using. Only problem is getting the engine, which is a bit scarce, and various fixes and workaround shave to be performed since Honda dont produce the crank parts anymore, but other conrods form Yamaha fit with a bit of work. I have seriously considered this conversion for a spare VJ21 chassis but then real life comittments like job and family keep stopping (or waking me up) me from doing it. Anderzander says it is easy to do, kickstart in right place, even one engine bolt ligning up, with minimal frame welding. MGA on this forum/gixerboy on the RGV forum will be producng a frame moutning kit in the near future I believe. I would say this is a medium cost conversion, since engines are £500 plus, but with good power to cost. http://www.ns400r.co.uk/forum/ Anderzander is also doing the RD500 V4 engine transplant, but trying to do it properly by fitting cylinders from the RGV. I would say its a bit tight in an RS250 but it is the ultimate performance mod with over 120bhp available. Especially so if you can fit the 300cc big bore pistons making a 600cc engine. This is a perfomance at all cost conversion, since peopel want lots of money for the engine, then there are lots oc cost for the RGV cylinder conversion, then the cylinders themselves, then the cost of the pipes etc etc. http://users.bart.nl/~bommie/YTCN/sp...00ralfkras.htm Similar comments apply for the RG500 conversion. Big performance, big prices. Peopel have fitted TZ cylinders, loads of power. Perosnally I never liked the carbs which woudl get smashed off during a lowside. The RG500 engine does have cult status which makes the cost even higher. http://www.suzuki-rg500.com/rgv250.htm Things like H1, GT750 are big mans engines designed in the 1970's. They were fitted to rubber band frames when men were men and women were glad of it. Fitting one in an RS250 would be difficult, you need to do loads of work to get them to make more power since none of them had reeds originally, and I would rule them out. Try and use an engine that is the same vintage or newer than the engine you are replacing. Boring out teh stock engine has been done and is listed in detail on this forum. In the US, the 316 engine conversion was popular, using (I think) 62mm snowmobile pistons on a 50.6mm stroke. In the UK, 60mm custom Wiseco pistons were fitted making it around 300cc. The 300 kit seems to have had better reliability but that could be because they dont seem to have been raced whareas the point in the 316 kit was that you could take on SV650s so were raced in US racing classes. The letdown is the crank, it doesnt like more than about 70bhp and it doesnt liek being revved. If you were to get JHA to design you a custom stroked crank then you might get more with the bigger pistons but fo the cost you could afford an NS400 engine transplant. http://www.stanstephens.com/index.html?rgv.htm~contents So thats it, cant think of anything else. You could try something new and original like fitting a twin cylinder polaris snowmbile engine - 700cc two stroke, water cooled, 100bhp, centrifugal clutch. Would be one of the fastest twist and goes in the world! CHeers, Vincent __________________ Pair of Cylinders for sale - needs re-plate. PM for details Last edited by VinCBR900; 12-17-2004 at 03:59 AM.