Displacement / horse power increase - swappable parts

[Quimrider]

To avoid any confusion with this topic:Convert your GZ250 into a 346cc!!! (http://www.gz250bike.com/forum/viewtopic.php?f=9&t=330) THERE IS NO BIG BORE KIT FOR THE GZ250. ALSO TO ABOUT 99.999999991% OF THE POPULATION THE COST THAT WOULD BE INVOLVED IN COMING UP WITH YOUR OWN BIG BORE KIT DOES NOT MAKE SENSE. If you would like to discuss the nonexistence of a big bore kit or the fact that modifying the engine is too expensive, please do so in the thread above.

This thread is to discuss which engine parts are/are not interchangeable with the GZ250's engine and various methods one could do to increase displacement and/or horsepower. Additionally I'd like to entertain the topic of potential engine swaps as a means to get more juice out of the GZ250. For example I have read about a Honda Rebel that had a diesel engine shoe horned onto it.

Please minimize speculation/opinion and stick as close as possible to the facts.

One engine of interest is that from the DR350. It is very similar to the GZ250 engine. The DR350 has a 79mm X 71.2mm bore and stroke. The GZ250 engine is 72mm x 61.2mm bore and stroke. Aside from custom exhaust work, the main obstacle from simply swapping the top half of the engines is that the DR350 engine has a 10mm longer stroke. If I ever get my hands on a DR350 cheap enuff I will attempt to put the DR350 engine on the GZ250.

[perroloco]

It should be a big bore kit or something ,I own a Baja 300 extreme ATV made for pep boy with a 300cc head on the same eng that I have on my gz250, the head is identical to the 250 but is 296cc, when I by parts for it, I use the 250 parts catalog

[Sarris]

:jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: = Jerkin' the bananna.

[Quimrider]

LMAO

[music man]

hey Quimrider, here is an old beat up DR 350 engine, it probably wouldn't be cost effective either, but i figured I would show you anyways.


http://cgi.ebay.com/ebaymotors/SUZUKI-1 ... ccessories (http://cgi.ebay.com/ebaymotors/SUZUKI-1996-DR-350-SE-motor-electric-start_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c66Q3 a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318QQ_trksidZp3286Q 2ec0Q2em14QQhashZitem120334245113QQitemZ1203342451 13QQptZMotorcyclesQ5fPartsQ5fAccessories)

[Quimrider]

Thanks, if I can get it cheap enuff I'll have to see what it would take to make it fit. I found the DR350 service manual, we'll see if there's any useful info in there. Worse case, I'm out a few bucks and some time to learn it won't fit.

[jonathan180iq]

If you can get a running engine for a $100 or so and are able to fabricate whatever motormounts would be needed to make it fit, then I think this might be a viable option for anyone with the dough. Otherwise, it's just $h1t polishing.

[ruxpin76]

Kart racers swap and modify cylinders/head regularly for the open classes. The DR head might work IF the cylinder is the same height. (Unlikely.) To make a swap, you'd have to make sure: (1) The wrist pin on the piston is the same size as the GZ piston, (2) The cylinder was the same height, (3) the timing chain had clearance to still run the cam, (4) the studs lined up with the GZ pattern as well as gaskets. LA Sleeve makes custom sleeves, and since we're dealing with a 4 stroke, there's no custom porting IN the sleeve. It'd be pretty simple (but pricey) to have a custom billet unit made. To do so:

1. Get a piece of aluminum that's the right size.
2. Bore the cylinder stud holes with correct clearances
3. Bore the head stud holes, if head doesn't share studs with cylinder
4. Tap applicable holes.
5. Mill out timing chain hole
6. Mill out cylinder hole
7. Heat case, cool cylinder and mate the pair, including any retainer/locater, same as DR.
8. Test fit and check for any mechanical intereference
9. deburr, lube, reassable
10. Pray the extra power doesn't snap the GZ crank, which can be helped by:
11. Rebalancing the crank counterweights to match the heavier pistion by boring and adding tungsten weights
12. Start new spouse search because your old one divorced when you went bankrupt making a $3000 cylinder for a $3K bike. :)

Hope that helps....fun hobby project if you're a machinist (I am) or if you know one, but hardly cost effective.

Alternatively, you could use the DR rod on the GZ crank and use the stock DR cylinder if the lower rod bearing's the same size and all the other holes match up and the head/timing chain assy. has proper fit...

[ruxpin76]

1980's DR250 has same bore/stroke...

[Quimrider]

12. Start new spouse search because your old one divorced when you went bankrupt making a $3000 cylinder for a $3K bike. :)


:lol: how true how true.

[Water Warrior 2]

3K and 3K equals 6K. That will buy a lot of HP surrounded by a larger bike.

[blaine]

Just go all out and put on a bottle of "N.O.S."

[trykemike]

THE FORUM IS A GZ250 SITE. THERE IS NOTHING WRONG WITH TUNING A BIKE THAT WAS DETUNED TO MEET GOV. SPECS. WHEN I WAS A KID MY BUDDY HAD A SUZUKI X6 WHICH COULD OUT RUN MOST LARGE DISPLACEMENT BRITISH AND HD BIKES. IT WAS A 250 WHICH COULD TOP 90 MPH 2-UP.

[Dupo]

Wow, that was some good weed. I just time warped back a few days.

Continue the interesting thread boys :cool:


:plus1:

[JWR]

Was that a clean-up on aisle 3???

[Dupo]

Yea, wet spill.

[Goose51683]

Seems this thread died years ago, anything ever come from this?

Sounded like an interesting topic....

[raul10141964]

i tune the carburetor and get a big imprubment on power so I thing bigger carburetor will bi beter

[Goose51683]

I would think with a bigger carb you would still hit a peak that is probably already obtained by the smaller carb.

[jonathan180iq]

Oh, goose.... Don't bark up this tree man.

[raul10141964]

2001 gz250 1981 Gn250
power 20.00 HP @ 8000 RPM 22 hp @ 8500 rpm
Torque 19.00 Nm 14.0 ft.lbs @ 7000 RPM 19 Nm @ 6500 rpm
Compression Ratio 9:1 8.9:1
Carburetor MIKUNI BS34SS 34mm MIKUNI BS32SS 32mm

Bigger carb = 2HP+

[mainlinecoffee]

If it's not too late to revive this thread,has anyone tried a adjustable cam plate or a cdi with a higher redline? Hell for 3k you could bolt on a turbo..

[Water Warrior 2]

If it's not too late to revive this thread,has anyone tried a adjustable cam plate or a cdi with a higher redline? Hell for 3k you could bolt on a turbo..

For 3K you might be able to buy an old Honda Turbo 650 that was purpose built. If you think you need a turbo you have the wrong bike. The GZ is just what it is and a bunch of cash thrown at it won't change that.
A higher red line will just make the engine explode sooner.
You might enjoy the Ninja 250 though. It has a much higher red line and more power overall.

[mainlinecoffee]

If I need a Adrenaline fix I hop on my chopped goldwing,personally I think the meager 22hp is more than enough for the job but I love wondering what if, costs too damn much to find out the hard way.

[Water Warrior 2]

If I need a Adrenaline fix I hop on my chopped goldwing,personally I think the meager 22hp is more than enough for the job but I love wondering what if, costs too damn much to find out the hard way.

I will find out the hard way with my new to me Money Pit used 1983 Honda 650. I can see an easy $1000 going into it with just repairs and maintenance to begin with. Yup, that sounds dumb but at least I will have a bike sometime this summer that is safe to ride and everything working as it should.

[mainlinecoffee]

The 83 was the first real motorcycle I have ever owned,gave a guy a shotgun and fifty bucks to drag it out of a barn, my friends laughed at me when they saw it,dead snake behind the headlight and meow mix in the airbox, everything broke rusty or covered in mouse shit...I don't think you will be disappointed, the cb650 is a wonderful machine. If you ever need any help or just a different perspective give me a shout,I know that machine better than my own body.

[Water Warrior 2]

The 83 was the first real motorcycle I have ever owned,gave a guy a shotgun and fifty bucks to drag it out of a barn, my friends laughed at me when they saw it,dead snake behind the headlight and meow mix in the airbox, everything broke rusty or covered in mouse shit...I don't think you will be disappointed, the cb650 is a wonderful machine. If you ever need any help or just a different perspective give me a shout,I know that machine better than my own body.

My bad. Should have specified GL 650. The Half Wing thing.

[mainlinecoffee]

Gl looks awesome but I have no earthly idea about what makes them tic,I am supposed to rebuild the water pump on my gl1200 next week but I burned up the clutch in my truck yesterday so it may take priority. I always thought the 650 would be beyond badass in a Amin frame with the front end raked to hell.

[JohnC]

2001 gz250 1981 Gn250
power 20.00 HP @ 8000 RPM 22 hp @ 8500 rpm

Carburetor MIKUNI BS34SS 34mm MIKUNI BS32SS 32mm

Bigger carb = 2HP+

But... It looks like the bigger carb goes on the lower hp engine...

Compression Ratio 9:1 8.9:1
Again, looks like the higher compression ratio is coupled with the lower output. Backwards?

Bottom line, if you're going to turn the engine faster you'll need a bigger carb as you're pulling in more air per second. Raising the compression ratio or increasing the RPM can both increase output.

[mainlinecoffee]

To rase compression couldn't you just shave a bit off the head?

[Water Warrior 2]

Shaving the head might work but I don't think it is a wise solution.
Will you still have room for the valves to open without hitting the piston?
Also, would there be a lot of slack in the timing chain? The auto adjuster might reach it's limits a lot sooner.

[mainlinecoffee]

Yeah it would be much easier on a 2t,I know a Lifan 110 will not crank with a 90cc head