The Tale of DoctorMotorcycle's Turbocharged '77 GS400E

[DoctorMotorcycle]

Hey Folks,

It's been a long time coming. I've been meaning to get around to doing this but never did. The resources on this site helped me along the way when I was building this bike, including the GSresources.

This is the story of my '77 Suzuki GS400E that I built into a scrambler, that somehow has 16,000,000 views on YouTube! 

The bike was actually abandoned at my dads house and rotting on his side yard for who knows how many years. The previous owner said it was left of his property for multiple decades, so it at least hadn't ran since the late 1990's. The bike had 18,000 or so miles if I'm recalling correctly, other than a 2-1 header it appeared to be a stone stock original (missing a ton of parts and in terrible repair, obviously). The engine was seized, so the first order of business before deciding to do a full build was see if the engine was a runner. I unseized it with marvel mystery oil and a little heat, sprayed a bit of gas down the intakes and wired in the coils and it turned over. Instead of doing the right thing and rebuilding it, I went straight into the turbo build.

Back then, all I had was a flux core welder and a cutoff wheel, so that's what I used to make the turbo setup. Welds look pretty yucky, and I cringe to think it looked alright thinking back  .

The first setup I made, that didn't work, was an HSR42 Carb w/GT15 turbo ( I was a newb, remember?). Obviously the turbo and carb were way too big, so I tried stepping down to a smaller carb, still no dice. Then I switched to a VZ21 Turbo, which is what ended up working and is still on the bike to this day. I switched to an FCR33 carb mainly due to the accelerator pump + being worried that the slide might stick w/turbo.

In the finished build video, the bike was on regular pump gas and at the time only 5psi of boost, mainly because I was so worried about blowing it up because I had raised the compression in order to see if that would get the bigger turbo to spool ( ).

As of September 2022, I'm currently converting the bike to run on full e85, and finally found someone to convert the turbo to a carbon seal setup so that it will stop smoking like a chimney. This has the side benefit of not contaminating the intake charge with oil (which reduces the octane), which will increase the detonation resistance even further. In addition, I'm going to lower the compression to slightly lower than it was stock by running 2 base gaskets instead of not running one at all (I used anaerobic flange sealant to seal the head/block), and replace the blown headgasket from the last Glamis dune trip, in preparation for the Halloween trip we're doing.

If someone can tell me for sure that a GS500 Camshaft will be a direct swap besides swapping sprockets, I'd order up a set up cams and do the swap. I've also dug up in my research that the GR650 cams will fit in the GS500, so that might be an option as well. Supposedly the cams are .030" or .040" more lift than the GS500 cams but have less duration? If it's just a handful of degrees less then that's fine, but if it's 10+ degree's less, think I'll pass. Anyone know where to find published cam specs?

How does the bike ride?

It's a beast! It will fly up oldsmobile hill at glamis no problem. On the last dune trip, I rode the bike on 8PSI of boost in the big dunes which proved to be too much after the bike was heatsoaked. I was only running a 40% ethanol mixture back then because I was worried about E85 availability, which is now not an issue. I think going to full E85 and running a 13 tooth front sprocket is really going to be a game-changer for this bike in the dunes. It was REALLY difficult to dune the bike with stock gearing, as many times I was going too fast for 1st and too slow for 2nd, especially in the smaller dunes. On the big dunes, 2nd gear was fine, but often times I really had to ride the clutch to get the bike up on boost to make it up the really big, thick dunes. I think this is the main thing that contributed to the bike getting so hot. The gearing was so tall I was pretty much always making at least 2-3psi of boost.

https://www.youtube.com/watch?v=E95QFp2JRKI&t=532s

Thanks, Enjoy!

[SK Racing]

Welcome to GSTwins. Thanks for a really nice write-up. Congrats on a great project! 

[The Buddha]

I never went to gsresources much. But I did to the xs650 site and one of those guys popped up here. So did poodleheadmikey (KZ440 site). But yes welcome. The 400 was a 4 valve per cyl europe only wasn't it ?
Cool.
Buddha.

[DoctorMotorcycle]

Welcome to GSTwins. Thanks for a really nice write-up. Congrats on a great project! 

Thanks! 

[DoctorMotorcycle]

I never went to gsresources much. But I did to the xs650 site and one of those guys popped up here. So did poodleheadmikey (KZ440 site). But yes welcome. The 400 was a 4 valve per cyl europe only wasn't it ?
Cool.
Buddha.

No, I'm in Arizona, they sold the GS400E's in the USA. They're the 2 Valve, longer stroke parallel twin. I think '77 was actually the first year Suzuki ever made a four stroke street motorcycle. The GS400 and the GS750 are what started it all.

I stumbled on one of your posts regarding (I think) swapping cams on a GS450 to GS500 cams when I did my first ever motorcycle build circa 2016 or so. It was an '82 GS450L that I built into a brat, with a ported head, GS500 intake cam, decked head .050", TM34 Flatslides w/velocity stacks and open megaphones. That bike was so much fun! Cool to see you're still active on here. 

[The Buddha]

Cams from the 450 -> 500 - I've never done anything like that. In fact the 500 is the only GS series Twin I have even worked on let alone owned. Now I have pulled them apart in junkyards but usually I get the right side round cover cos those on the older twins were thicket and didn't have that silly hole in the middle.
Cool.
Buddha.

[Bluesmudge]

Very cool to see the grandfather of the GS500 get such a treatment! 16,000,000 views is impressive. You will get at last 5 more views by posting here 

I can't vouch for which parts of the 400 and 500 are interchangeable. I know the 450 and 500 are extremely similar. From your video, the 400 engine looks very similar but that doesn't mean very much.