Author Topic: Building a tuned'ish engine for the Street.  (Read 95 times)

Offline moto

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Building a tuned'ish engine for the Street.
« on: May 23, 2020, 10:46:01 AM »
Hi Guys,

Im currently in the process of building an engine for my bike.

Ive looked at all manner of options, but it always circles back to building a sweet running GS500 lump... whatever I do the bike is never going to be quick so im going to enjoy it for what it is!

So im looking at standard bore (ish) - Oversized Pistons are too expensive, GR650 parts are non existent, so im looking at a .5mm oversized bore and fresh build.

Current Anticipated General Engine Spec

  • 0.5mm oversized pistons - unless I can find some other alternative at a reasonable price.
  • Target Compression Ratio 10:1
  • Mega Cycle 384-70 Cams
  • Uprated Valve Springs
  • Port and Polish Head
  • Larger Valves - I need help on this
  • Lunchbox Filter on standard Carbs with Rejet
  • Stock bottom end
  • Modified ignition advancer


So i am a little stuck on two points, ive searched the forums but cant find anything conclusive.

VALVES


The way the head breathes seems to be the biggest issue. I have read of people putting in larger valves. Does anyone what size, where they come from, donor bike or custom?


PISTONS


The Megacycle cam requires relief cuts in pistons - is there any guidance on this?  I appreciate that it depends on the final size of the valves in the head, cam valve lift, and how much i shave off the mating face of the head in my quest for compression. Is there a way of calculating this, its new territory for me, any help or guidance would be very much appreciated.






« Last Edit: May 23, 2020, 12:46:31 PM by moto »

Offline SK Racing

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Re: Building a tuned'ish engine for the Street.
« Reply #1 on: May 23, 2020, 11:53:42 AM »
Sorry, can't help on those two points, but I'm wondering why you want to go to 0.5mm oversized bore and new pistons. The horsepower gain from such a small increase in the total displacement is going to be negligible and probably not worth the expense and work.

You probably know this already, but I want to emphasize; To get the GS500 to perform better, you have to improve the breathing. The stock headers should be fine, but replace the muffler with a performance unit. A higher compression ratio may require higher octane fuel to prevent knocking (detonation). If you don't have a ready supply, then this might be a deciding factor.

If you're not going to race, then why not do a pseudo power improvement, like changing the gearing? A 14T front sprocket will make the bike feel much more lively without increasing the actual horsepower. A 15T front and 42T rear sprocket will give the same gearing, but will be gentler on your chain.

If you haven't read Racing the Suzuki GS 500E in the Racers Corner yet, you should do so. It contains a lot of tips on improving the performance of the GS500: http://www.gstwin.com/racers_corner.htm

Lastly, you may want to add an oil cooler if your bike doesn't have one. Making more power, generates more heat.

You donít stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda 750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

Offline moto

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Re: Building a tuned'ish engine for the Street.
« Reply #2 on: May 23, 2020, 12:45:08 PM »
thanks for your notes, ive read racers corner back to back more times than i can count, great for the basics - this is a little beyond that.

This is my build so far:

http://gstwins.com/gsboard/index.php?topic=71441.msg858881#msg858881

Im already running a full stainless system, k&N lunchbox, its always run on 98ron fuel (UK) 94 us?

The reason for the head work is to make it breath, ive done all I can with bolt on bits.

The 0.5mm Overbore has nothing to do with chasing capacity what a pointless effort that would be :laugh:. it is just to give me a clean slate with a fresh hone - my current engines compression isnt great. So i need to have the liners bored an honed to tolerance with larger pistons.

This is more about building a nice sweet running streetable engine - Its having a complete tear down anyway, i may as well make it a little hotter in the process.



Offline SK Racing

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Re: Building a tuned'ish engine for the Street.
« Reply #3 on: May 23, 2020, 01:57:03 PM »
Ok, noted. Well, just the porting job alone would make a nice difference then. And while you've got the engine open, why not have it balanced? ... and remove the balance shaft as is suggested in the Racers Corner.

Another way to regain some usable power is to go for a total loss system. Only works if you don't have to do long trips, though.
« Last Edit: May 23, 2020, 05:33:53 PM by SK Racing »
You donít stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda 750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

Offline cbrfxr67

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Re: Building a tuned'ish engine for the Street.
« Reply #4 on: May 26, 2020, 02:28:40 PM »
I understand your point and have been there myself in wanting to make a bike quicker, but having a decent gs and loving it, even if I made it a bit faster,....it can't compare to a bigger bike. 

Again, not shooting your plans down at all, but a couple weeks ago I rode my neighbor's gsxr 1000 to work and I mean, personally I'll take my gs for what it is and keep trying to fix my r1 to go fast on. 

Sure I wouldn't listen to anybody telling me to get a bigger bike either back when.  hahah Good luck with whatever you decide to do.
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Offline The Buddha

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Re: Building a tuned'ish engine for the Street.
« Reply #5 on: May 26, 2020, 05:46:47 PM »
Most attempts to boost compression results in lower end torque and mainly lower rpm power. IMHO on a GS that is relatively pointless.
If you want high rpm power, you need to increase the max rpm it will rev to. Obviously.
That means flow. If you port and polish etc etc you'd get it to rev higher easier. Larger valves would be needed here.

Then you run into the brick wall called the counter balancer. If you get rid of that, you're motor will rev but feel like it will shake itself to bits. However if you balance it right - and Bob Broussard has done and posted about it, between 8 and 11K I think he got a motor that was almost as smooth as the stock.

The limiting condition after is valve float. Lighter valves and stiffer springs.
Then come rod stretch - and that needs lighter pistons. With that said - you need to balance the crank and piston assy at the same time as the counterbalance removal. So essentially you're better off doing all of this in 1 swoop cos step 1 and step 4 are tied in together.
If you did just the head part - you may get most of the gains without going out too much $$$.

Cool.
Buddha.

You're looking at serious $$$ - the instant you open the cases you're over a $1000 in and that's just labor.
See if you can buy a motor out of Bob Broussard or Dgyver.
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