Ive been sitting here thinking and wondering the last few days what I could maybe do to my GS for some added fun.  I know there are various racers out there that know some key mods and how to do them I was just wondering what those specific mods were and if any of you would be willing to go into detail about those mods.  Im probley gonna end up keeping my GS for a good while so I might as well make her go fast.  The thought of completly swapping engines has crossed my mind but there are alot of issues that come into play there, I dont really want to buy an engine then not have it fit, I would really like to try an SV650 engine though if I could find one cheap enough.

Found this which seems like a good place to start.  Using this post for older threads.

http://www.gstwins.com/forum/viewtopic.php?t=14401&highlight=engine
http://www.gstwins.com/forum/viewtopic.php?t=13284&highlight=engine
http://www.gstwins.com/forum/viewtopic.php?t=12764&highlight=engine
http://www.gstwins.com/forum/viewtopic.php?t=6906&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=6510&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=6843&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=6869&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=8398&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=9072&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=9638&highlight=head+swap
http://www.gstwins.com/forum/viewtopic.php?t=14490&highlight=pistons
http://www.gstwins.com/forum/viewtopic.php?t=14401&highlight=pistons

http://gstwin.com/racers_corner.htm

Odd that you post this....just yesterday I was pondering the idea of some kind of hybrid bike/motor. Been thinking about the 4 valve head swap for awhile but have not bugged Bob about the details....yet. plus I have 2 engines that need to be put back together. One will be stock but the other will probably be total loss ignition and remove the counter balancer. Figure out how to add an oil cooler, not sure of the plumbing. I keep bugging my boss about moving another milling machine to work.....hmmm....

Yea Ive been reading through old posts for about the last 2 hours, read the racers corner deal too.   I think Im gonna bore out to the 78 mm pistons, more then likely anyhow.  Theres so many little thoughts about ideas and what not, like the 4 valve head you mentioned but theres not really any info on what parts you need or how to get it to fit, I guess you just experiment.  Dgyver, did you ever figure out what the 78 mm engine you had was making for power?

No idea about the power of the 547 (78mm). It was JamesG's motor when it split a shim and put it through the head. Someday soon I am going to put my 555 (79mm) on a dyno. It is basically the same as James' 547, same cams, ign adv, etc. But first I am going to install the CR carbs that he was running.

Bob has posted some general info here before on installing the 4 valve head. I need to pick his brain for the details.


Here is some of the info I have collected from this site since I am not sure how long posts are archived:

madman Posted: Sun Feb 08, 2004 2:14 pm    Post subject: head swap

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Well, the motor started as a stock gs motor. Then the cylinders were bored quite a bit to allow for larger sleeves. Total bore increase is 11mm per cylinder to 85mm. Then the counterbalancer was removed and the rotating assembly was rebalanced. That saved a lot of weight. Now, with my bottom end done, I am looking for a really kickass valve train setup. I could just port & polish a stock head, but I think I would get a significant gain from that by using a GSXR head. The mating surfaces of the 2 center cylinders match the GS perfectly. So, you cut the outer cylinders off of the head and camshafts. Then make a custom valve cover and adjust everything to spec. Theoretically a 4 valve per cylinder head should outflow a 2 valve by a lot. This coupled with a 156cc jump in displacement should equal close to 100hp, I think. The head will also allow the use of an oil cooler, since they came stock on the old GSXR's. So, what do ya think?  



Reknelb Posted: Sun Feb 08, 2004 5:25 pm    Post subject: Re: head swap

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Now for some useful info. The bandit 1200, the gsxr/katana 1100 and the gsxr 750 (up to 89) heads are all the same. I think they have different cams and perhaps different valve sizes (combustion chambers may be different too) but they are all oil/air cooled heads with the same construction so in theory they should all work. The cams are all interchangeable between models. The 750 cams are the best, followed by the gsxr 1100 and katana 1100, and the bandit 1200 has the mildest cams.



werase643 Posted: Sun Feb 08, 2004 8:47 pm

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look for a kanadian GS400 8 valve head from the early 80's..i think 81-87)
the damn thing will bolt on and all you should have to do is weld up the ex ports and bore them where a GS port is suppose to be.
just get a complete head with cams cam cover
the 400 exhaust pipes go right thru the down tubes on a 500

it is basically half of an old GS1150 head with TSCC



Bob Broussard Posted: Mon Feb 09, 2004 2:00 am
 
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The head I have is an 89 gsxr 750. There was one on ebay last week, but I decided pass on it.
Here's the deal. The 4 inner stud holes lineup perfect. The outer 4 need to be relocated outward a bit. The GS head gasket works fine. The cam chain slot on the gsxr head is longer than the cylinders. So you need to fill it in at the rear. The GS cam sprockets will fit on the gsxr cams, so you can use the GS chain and sprockets. The bolt holes need be redrilled 1mm bigger (better yet slot them for degreeing).
The cam lobes need to be relocated for a 180 degree crank (Megacycle cams can do this). Might as well get higher lift at the same time. You'll need hardened rocker arms (Megacycle again) Valve spring set.
The inner cooling chambers normally drain down the stud into the lowerend on the gsxr. The GS studs are open in front (major oily mess  ).
Fill in the drain holes and drill other holes so oil drains into cam chain area.
Then you need to make end plates to seal the the sides of the head.
These need oil passages to oil the cams and rockers through the rocker shafts. And you need to make drain lines to drain the cooling oil.
I went the extra step of installing a second oil pump in the sump, driven off the transmission. The oil goes from the pump to the oil cooler (B&M Supercooler) then to the valve cover. It fills the cooling chambers in the head and then drains back down into the motor.
The original pump does the lubrication. I tapped into the plug just below the igniton cover. It goes into the side plates and into the rocker shafts.
I'm running Carrillo rods and JE pistons. I had the pistons designed for the gsxr head. The exhaust cutouts needed to be cut forward a bit more. That's why I broke the first head  
The weak link in the crank seems to be the right side rod journal where it connects to the outer weight. The drive gear is helical. This flexes the crank and snaps it eventually.
I've milled a slot for another thrust bearing into the cases in an effort to limit the movement in this area. The bearing shows definate contact, so it's doing something (time will tell  )
I have pictures of all the mods. Was planning on putting them on my website www.gszilla.com but i've been too lazy to complete the site.
Email me for the pics and more details.
There's other things, like gsxr cylinder studs (APE). Stronger and equal length. GS studs are different lengths.
By the way how rich are you?

Hmmm, thats some good info that raises alot of questions.  How streetable do you think a 78mm engine would be?  Would there be any durability issues with the crank breaking?  Those are my two biggest concerns, with the latter of more importance.  Thanks for all your help so far dgyver, I think its cool to talk about stuff like this.  

Honestly I do not see any real issues with streetability of a large bore motor. The problem of breaking cranks seems to come from a combination of high compression and chopping the throttle at high rpms. The flywheel's mass is more than the crank can handle. Keeping the compression down (ie: not milling the head) should reduce this.

The only other issue I can think of is the extra heat with the air cooled motor. As long as it does not run too lean then it should not be a problem.

My 79mm motor actually idles better than the 74mm and the 75mm motors that I ran. A little of that I contribute to plugging one of the holes in each carb slide. No more high idle hang.

Yea those are good points that make sense.  Im still contemplating on how much modding I want to do, I contacted a guy on some turbo's but he seems to want too much for me.  Also found an 89 head on fleabay but it didnt have any cams, what do you use for cams if you mod the head, GSXR stock and then mod them?

I am not sure about the cams. I have just recieved several e-mails from Bob this morning about his work on the 4 valve head swap. Haven't had time to read through it all. 4 e-mails with plenty of pics. The cams is one question I need to ask him.

I would be happy to get any head to work with, just in case I screw up.

After reading over Bob's e-mails, looks like gsxr cams are used:

"The cam lobes need to be relocated for 180 degree crank. Megacycle knows how to do this. The stock GS cam sprockets and chain are used. You need to enlarge the sprocket bolt holes to 7mm for the cam bolts."

Send those emails my way, t_netsch@hotmail.com   Thanks.  Also you mentioned above you were going to run different carbs, what bike did they come off of?

How big is your in box? With pics the e-mails are 2.7mb, 4.8mb, 3mb, 2k

If you need a bigger one I have a few gmail invites. Just check and I have 50 invites!!!!

250 mb is the size of my box.

this is all very interesting, any chance i could get a forward of those emails?  what a collection of knowledge for future engine projects.

I don't have a problem with forwarding them but I would like to get Bob's permission first.

No problem, just let me know either way.  I actually tried to send Bob a message last night but Hotmail was being dumb so I dont know if he got it.  Ill wait to see if I can just get yours and save Bob some work.  Thanks again.    

Wow, look at this thing, amazing.  Sweet engine Bob  

wouldnt mind seeing some of those emails and pics myself, and yes. get bobs permission first.. im thinking of the earlyer GSX head from the 80-82 750 and 1000 myself, might not be quite the frankenstein, but then who knows.

Love the extended oilpan.