GT550/ RD400 cylinders possible to do?

[Dvsrd]

I just realized that the Suzuki GT550 has 62 mm stroke, just like the RD400. The GT was in a lot more moderate state of tune than for example the H1, with 50 vs 60 hp (manufacturers numbers, of course)

Now, if one could build a GT550 based 600, using 3 x RD 400 cylinders and heads. Then it would theoretically be 64-65 hp (since Yamaha said the RD 400 had 43 hp)

This surely must have been done by someone already? From the pictures I have found, it seems the cylinder spacing on the GT 500 should allow RD400 cylinders to be fitted. Most likely the stud holes would have to be welded shut, and new holes drilled and tapped?

[m in sc]

ive seen rd350 cyls grafted onto an H1 bottom end. Im sure it could be done, but 550 cyls are narrow, im not sure the middle one could be squeezed in there.

IMHO, would be better to reed and port a set of GT550 cyls.

[85RZwade]

Gil, are you reading this?

[teazer]

I have also considered that possibility, but I was aiming way too high.  If a well tuned RD400 can make say 72hp, then surely a triple could make 106 or maybe more in a drag race motor.

First issue might be moving the cylinder studs and the second would be crankcase moth mot being close to matching RD transfer ports and of course the perennial issue of can I squeeze an RD cylinder between the two outer pots.

What would probably be easier to achieve is to fit reed boxes and bore it to 63mm.  I am assured by those that know that 63 or 64mm is the absolute maximum bore size but with a little more boring and some welding and plating, something slightly larger (say 66.5mm) might be possible.

Ian Reed in teh UK has done some interesting things with his 380 triple and of course there was a 500cc water cooled Barton version of the 380, so anything is possible.

[m in sc]

id go to 62 leave a bit of wiggle room and have at it w the 550 cyls.. but the tranfser ports are dismal. you'd have to add a boost port or 2 and machine the windows in the pistons but would prob be ok. the reeded h2 i had was around 88-89 rwhp. (and extremely rideable).

[Dvsrd]

id go to 62 leave a bit of wiggle room and have at it w the 550 cyls.. but the tranfser ports are dismal. you'd have to add a boost port or 2 and machine the windows in the pistons but would prob be ok. the reeded h2 i had was around 88-89 rwhp. (and extremely rideable).

Yes, the Suzuki 380/550/750 transfer ports were the reason for me wondering about this in the first place. I do not even have a GT550, but I somehow always thought they looked good.

[m in sc]

they can be worked to do better. it would be  fun project trying to get power out of it.

[Dvsrd]

Interesting:
https://www.oldjapanesebikes.com/mraxl_GT_Resource/GT550_files/page-9

[m in sc]

well THAT certainly changes things, had no idea that even existed.   

[Dvsrd]

well THAT certainly changes things, had no idea that even existed.   

Me neither...Suzuki sure were early with Nicasil plating, based on that info.

[Gil Gallad]

wade, yes i am. i'm about to build - when he gives me the green light - my mate a big bore gt550. using ts185 standard pistons will give you a 598cc. you'll need to fit base plates, but there's a place over here [sorry, i forgot their name] that makes several different thicknesses of 550 base plates. we were going to go the whole hog and build a 636cc engine, but decided on the 598 as that would let him have 4 rebores, just in case he needed them. plenty of meat on gt550 liners 
cheers, gil.
p.s. crown height on a 550 piston is 23mm. crown height on a ts185 piston is 24.5mm. hence the base plate. and 550 engines will stand being ported without blowing the crank to bits 
p.p.s. there's actually a web page with a 636 engine build on it - 66mm pistons, but i'm blowed if i can find it.

[teazer]

Gil,

Are you doing that with an early iron liner set of barrels or later SECAM (Nicasil) barrels?  I have never flow tested either, but the 4 port barrels appear to have a lot more transfer port area and the ability to point the ports where you want them.  In the US, only iron liner barrels were supplied with the early style crankcases that have a lot let area.

We found that single transfer ports can be opened up a long way but it's not easy to get the right port discharge angles as I am sure you already know.

[Gil Gallad]

definitely iron barrels, teazer. after talking to uncle ron at fahron this morning i asked him about squish, as obviously the 550 doesn't have squish bands. he reckoned it was an easy fix, just machine the heads out to accommodate the oversized pistons, then reprofile the combustion chambers to get the compression ratio right. mine of information that old lad is 
cheers, gil.
p.s. ron isn't doing bad, he still works 6 days a week and he was 78 last month. hope i last that long 

[Dvsrd]

definitely iron barrels, teazer. after talking to uncle ron at fahron this morning i asked him about squish, as obviously the 550 doesn't have squish bands. he reckoned it was an easy fix, just machine the heads out to accommodate the oversized pistons, then reprofile the combustion chambers to get the compression ratio right. mine of information that old lad is 
cheers, gil.
p.s. ron isn't doing bad, he still works 6 days a week and he was 78 last month. hope i last that long 

Gil, when you start that project, it would be interesting to know cylinder spacing (C-C) and cylinder stud spacing.

[Gil Gallad]

not much of a problem there me old flower, because i'm using gt550 barrels and standard ts185 pistons. the only problem being the piston crown height. the 550 pistons are 23mm and the ts pistons are 24.5mm. but that's hardly difficult to remedy. i've made alsorts of thicknesses for base plates on the gt250's i've built, including a 4mm pair for the gt350 i built. 64mm liners and ts185 pistons. easy enough to do - even by hand 
cheers, gil.
p.s. my watercooled gt250 with rd250lc top end used 3mm base plates. btw, don't try rd350 pistons in your big bore as they only use 14mm gudge pins and you need 16mm.