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Author Topic: Performance advise  (Read 380 times)

Bounzy

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Performance advise
« on: July 11, 2018, 11:00:00 PM »

Hello  :)

I'm new here, but i'm not a noob when it comes to engines  ??? Been tuning cars, complete engine rebuilds and such since i got my license over a decade ago, however am a noob when it comes to bikes. I read a bit on your forum (a lot really) before buying a dirt cheap GT650 comet '04  ;D

So here goes; I want to start a thread about performance mods. The SV650 has some great opportunities and i se no reason we shouldn't be able to pump up our bikes as well
Current mods
Airfilter
6sigma jetkit
Performance silencer (race use only)

The bike feels great now, a lot more torque. High rpms pwer (bhp) have also increased, it now pulls very easy up on 9000 rpms. Now it sadly stop firing on one cylinder on the way home  :'(
This provides an opportunity, this is where i need your assistance:

  • Any info on (minimum) clearance we got from the valves to the pistons?
  • Does anyone have any experience with broken/worn down chain tensioner/guides?
  • Have anyone experienced any sort of bad bearings?
  • Is there oversize pistons available? (OEM 82 or 82,5mm, for repairs after ex. a faital piston ring failure, have looked!! Can't find any aftermarket)
  • Have anyone done a polish job on runners and head chamber? (still not sure this one is a good idea since i got a carby version)
  • Links to threads with well documented blown/failed/problematic engines are MUCH appreciated
  • Does anyone have any idea why our exhaust has that middle piece between the pipes?

So i am planning on a as-cheap-as-possible full tune up, mainly to keep the spirit of this bike
Rule #1 in tuning club: :o
The need to pinpoint weak points. Pushing an engine is never risk free, but same model engines often have similar weak points. These need to be assessed to ensure stability
Compression(static) is to be raised to about 12,2-12,8. An increase to 12,5 will yield about 10% performance increase, but will be borderline risky to run on a carby. Injection engines will deal with this way better and 12,8 is achievable with the right tune (from ex power commander). Before you all start slaying me for that idea remember dynamic compression is way lower and we have very long runners, my assesment is for the short runner on a car, so fear not  ;)
If we've got no aftermarket options here heads and resizing cylinders is a pro's job (about 300 here). Bare in mind a resize job will add to compresion, proper calculations and real world tests are needed before modifying the heads
Goal: Raise performance to 100+ bhp, 85+ Nm (63 ft-lb)

Damn, that was a lot  ::) I'm sorry guys i'm just excited, this little insane powerhouse has stolen my heart  8)

Kind regards
Bounzy
« Last Edit: July 11, 2018, 11:27:44 PM by Bounzy »
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Bounzy

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Re: Performance advise
« Reply #1 on: July 11, 2018, 11:19:12 PM »

Current work:

13. Jul
First up, let's see how much volume the head chamber actually is. I'll see when i get in there if a 3D model is gonna be doable or if it's better the old school way (close off with clear plastic with a small hole and a syringe to carefully measure it)
Cyl 1 need to come apart anyway, something bad happened in there. Will upload pictures later :)
« Last Edit: July 13, 2018, 01:08:52 PM by Bounzy »
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umop-ǝpisdn

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Re: Performance advise
« Reply #2 on: July 12, 2018, 12:38:27 AM »

You could add timing.

If you use an offset woodruff key, you can advance timing by 4 degrees.



If you oversize the pistons, you will always get higher compression, without reducing valve to piston clearance.

Also, if you remove the exhaust header and look inside, you will often find that the welding done to attach the tube to the flange intrudes significantly into your exhaust runner.

A pair of velocity stacks from a DL650 would increase your runner length and give you slightly more torque.



Even with all these things, I don't think you will see 100hp at the wheel. Even 75hp is unlikely.
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I used to be a sensitive, new age guy, but times have changed and now I am more of a caring, understanding, ninties type.

LX_SS

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Re: Performance advise
« Reply #3 on: July 12, 2018, 12:46:53 AM »

Here's the thing.
As fond of the engine as i am in the GT650R the amount of cost vs what gain you get is not gonna be massive.
The GT650 has roughly 80hp at the engine vs say a cbr600f4 which is about 120hp at engine.
The only one i've seen post 120hp ish + was a turbo GT650R.

Being carb you got at least some tuning options.
As umop-ǝpisdn said, the woodruff key is the biggest in the timing to get more power, you can tune the carbs to suit.

Exhaust pipes from heads to muffler could use an upgrade that would be custom made.
Heads you can give a light port and polish.

Even with the velocity stacks, woodruff key, head work, tuning, decent fuel to suit, and even bumping the comp up your still not going to gain 20+ hp.

If your deadset on that hp gain you need to go forced induction and you'd leave the standard comp and run low boost.
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LX_SS

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Re: Performance advise
« Reply #4 on: July 12, 2018, 12:47:57 AM »

The other option to gain that sort of power is fabricating a way to fit a SV1000 donk in it.

Would probably be cheaper, but no its not a direct bolt in ( close but not direct )
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Bounzy

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Re: Performance advise
« Reply #5 on: July 12, 2018, 01:06:02 AM »

Sounds great! Thanks for the input guys!

100 bhp is surely reachable, that would be about 80 whp, given the stock dyno sheets i've found indicates about a 20% difference  ;) But i honestly just listed the bhp cause it sounds way cooler, looking for torque increase really. The stock exhaust was very restrictive and it seems the airfilter was too since a 21% increased main jet (120 to 145) still runs a tiny bit lean for trackday use, so i'm inclined to believe the 8-10 bhp increase after these mods is high but not completely unlikely (more likely is 5-8 bhp). The torque increase is very noticeable, i would say about 10%, she pulls up the nose in gear shifts now with stock vacuum springs still untouched (199cm high, 95kg dude ::) )

The velocity runners, is there still room for the top of the box? I can't run without airfilter, very windy here, lots of dust. High performance tin nets doesn't cut it

regarding costs; yes this is obviously a huge factore. This isn't gonna be a thread only about the high end stuff like resizing to 675cc, cause you're absolutely right, that stuff is for fanbois and real tuners only. However i'll try to keep costs as low as absolutely possible, this is a really cheap bike and a great starting point to build/tune up a bike engine. I got this bike for 1650, a CBR600F3 would set me back about 5250. My mate got one and after my mods i can keep up until about 170 km/t (106 mph), so i can't stop thinking, a 12,5:1 CR would give me the power to keep up with more modern SS class bikes  8)

Edit: A 82,5mm piston would yield a 2,46% increase in vol and CR, so some modding would still be required on the heads. Wait that's not 675, that's 662cc  :-[
« Last Edit: July 12, 2018, 01:23:31 AM by Bounzy »
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Bounzy

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Re: Performance advise
« Reply #6 on: July 12, 2018, 01:19:32 AM »

I read a post with a dude who had gotten some copper head gaskets cut out, 0,07mm tick. I'm a toolmaker by profession, so i got contacts to guys who can make those cuts for me on a waterjet or laser cutter. The question then remains, does that work? never tried something like that on a car. If so i wonder how much torque i would have to use with such a gasket
« Last Edit: July 12, 2018, 01:24:47 AM by Bounzy »
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Bounzy

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Re: Performance advise
« Reply #7 on: July 12, 2018, 01:40:49 AM »

Even with all these things, I don't think you will see 100hp at the wheel. Even 75hp is unlikely.

By the way i completely see your point and me having lots of time on car engine may not completely understand bike tuning  ::)

But let's play numbers:
80 bhp stock
Let's say i'm right, the stock setup was very restrictive and a decent 5 bhp more has been released
85 bhp lightly modded
a 10% CR increase (still have not idea if i got room for that) on cars that's basically a even increase in power
93,5 bhp Modded heads
Now it get's hard. I need to look at the exhaust pipping (and figure out wtf the H bridge pipe does)
Polish of chambers, rough polish of runners
the 4 degrease key is a GREAT tip here  ;D
and then idk, i'm pretty much out of ideas. I'm hopping i'll get more inputs along the way, gonna make the 100 bhp Hyosung SS class killer bike a reality  8)

BTW i do intent on buying a injection version later, to make a ethanol bike, for trackday and just general fun  ;D

PS i'm danish, sorry about the english skills  ::)
« Last Edit: July 12, 2018, 01:47:50 AM by Bounzy »
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umop-ǝpisdn

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Re: Performance advise
« Reply #8 on: July 12, 2018, 01:43:53 AM »

A set of head studs for an SV650 are a direct fit, with no machining.

The stock head studs are very weak. They are an M10 thread, but they narrow down to only 8mm. The maximum torque you can apply is very low. If you get a real set of head studs from APE, or ARP, for an SV650, they are 10mm the whole way down and fit perfectly. Obviously, they can handle a lot more torque than the standard 8mm bolts. I would need to double check what torque I used on the head studs on my bike, but I think it was about 70Nm.
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I used to be a sensitive, new age guy, but times have changed and now I am more of a caring, understanding, ninties type.

Bounzy

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Re: Performance advise
« Reply #9 on: July 12, 2018, 01:51:56 AM »

Great tip  ;D

I'm gonna be looking into what items i can get from the SV650 guys, hopefully they have a couple of interesting items that fits our biks.

Was thinking i'm gonna order a cheap SV650 headgasket to compared. Since they sell high CR gasket kits on the SV650 tuner sites (for 81,5mm too even), this would be an ridiculously easy CR increase
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