Motor Overhaul (summer project)

[RamAir]

Hello all! :biggrin:

This is mainly to improve the preformance of the bike but I am also doing cometic upgrades as well. But for this post I will be listing all the upgrades with links that I plan on doing to make the GZ 250 more powerful and better overall to ride. I am looking for better WHP AND better MPH. I know not easy but hear me out on this! So, everyone lets begin strap your selves in boys and girls this is gonna be a hella project and a big dream until I start wrenching in summer. HERE WE GO! :cool:

First things first! Theres no replacement for displacement Soooo
BIG BORE KIT!
http://cgi.ebay.co.uk/GN300-GN250-BIG-B ... 0462854879

Need to knows for me, how sure are we that this will just bolt up and work??
Improvemnets on this I will be getting total seal piston rings for the best power and MPG!

Next, CR I would need to do far more research on this but I would like to use the piston rod outta a 1983 Honda VT500. It beeing a V-twin that means it have TWO 250cc banks. Sooo thats like two gzmotors the bore and storke are just about the same but its CR is 10.5:1 so if that rod has the same bores on both sides I can use it and see if it bumps up our CR to give use more power. The V-star 250 is 10:1 and makes more power and is faster then the GZ and uses 87 octain so I am thinking with the right tune and set-up 10.5:1 will not be that bad! Now I know that piston head and cumbuction chamber also play a BIG part in this so I will be looking into it more like I said. Here is this like.
http://cgi.ebay.co.uk/GN300-GN250-BIG-B ... 0462854879

Here is a list of the honda specs.
http://www.motorbikes.be/en/Honda_VT_50 ... _1984.aspx

And the GZ specs just compair for yourself.

http://www.mbike.com/suzuki/gz250/2009

Or even looking into piston options from 600CC bikes with the same rod to see if we could get a higher comp piston head.

Also this cought my eye. Anyone know what this is about?? The new 125GZ's are fuel injected??

http://www.bikez.com/motorcycles/suzuki ... 5_2010.php

Really? :retard:

Also I wanna do the oil cooler idea.

viewtopic.php?f=9&t=3943

And I wanna do up a ramair intake system and heat wrap the exhaust pipes and get a new exhaust system



More for looks and personally I think it would sound better once its a 300cc bike :drool:

And I will also be doing what this member did with the PP and new parts. Pretty much I will be ripping off all the work he did. And if he is still on here that would be great if he can give me some pointers or on how much better the bike was after all of his work.

Here is the link.

viewtopic.php?f=9&t=3050

And a gas tank mod and all that but thats another thread.

So to sum this up I wanna do the
Big Bore Kit.
Total seal rings.
Port and Polish.
Cold air Ram air intake system. Custom done by me.
Exhaust system. To over all help flow and help the bigger motor breath better. Same deal with the P&P.


aND i AM HOPPING THAT AFTER ALL THIS i CAN DO THE 16TOOTH MOD OR PLAY AROUND WITH THE REAR GEAR AND GET A TALLER RATIO OVER ALL AND STILL HAVE THE SAME PREFORMANCE AS BEFORE WHEN IT WAS JUST A 250CC BIKE BUT OVER ALL BETTER HIGHWAY POWER AND BETTER mpg SINCE i PLAN ON RUNNING A TALLER FINAL DRIVE RATIO GEAR!

:popcorn: :popcorn: :popcorn:

Any and all edvise and information and input will be most welcome! Sorry if there are any weird mistakes my computer screen is acting up and I cannot fully reveiw what I have typed.

Thanks again guys! :2tup:

[RamAir]

The big bore kit says our motors make,
20.78 HP at 249CC
and the kit will make,
25.47 HP at 298CC.
By my calculations it should be making
24.86 HP at the crank.

Plus all of the other mods I am hopping to be making atleast 20hp at the wheel. maybe even 25hp when fully done. Bumping up the CR will also help.

Just as I posted about the honda bike.
Our stroke 61.2mm
Honda bike 62mm.

Not sure what .8 of a mm will do but until I get more specs and an online CR calculator I willnot be sure of anything.
Also a side not the V-star 250 that has a CR of 10:1 has an HP rating of 21HP over our 20HP. So I could see anywere from .5 to 1 hp with a CR of 10:1/10.5:1. However the V-star have a longer stroke and is more set up more trq then our bikes and more factors should be takin into consideration but 4.5 to 5 hp jump for the big bore kit, .5 to 1 hp jump for higher CR and 5% to 10% increase for the P&P And 5% to 10% for the total seal rings (keep inmind that the (&) will go up with the motor so its 10% power for a 300CC motor once the big bore is done) about 8 hp hopefully and 5hp realistically! Not much, not much at all but lets wait and see!

[Water Warrior 2]

Wow, that is quite an ambitious plan. I would really like to see it happen but I'm afraid you might be setting yourself up for an engine meltdown or grenade. The big bore kit sounds great and is more than likely a plain simple R+R kind if job. However I would be leary of trying to raise the compression. A bigger bore, a little more intake and exhaust flow will probably make a noticeable difference without stressing the various parts overly much. That and an extra tooth on the front sprocket will make the bike seem a lot bigger and better.
You mentioned the Yamaha 250. Don't be mislead by it's numbers, it is a V-twin to begin with and has it's own set of rules to play by. I'm not trying to rain on your parade in the least, just me and my err on the side of caution attitude after a few experiments years ago that didn't work out well.

[RamAir]

WW This is what I am talking about man You speaking from been there done that will really help me!

Also This is a two or more maybe year plan. This summer when I pull the motor apart and see if I can save the bottom end then I will be going BB kit. And if I can P & P I will but the CR bump up and the exhaust and all the other stuff will ahve to wait till I can get my hands on a connecting rod or atleast the specs of one.

I head what your saying about the drive train and putting almost 50% more stress on all the parts then they where built to take. But when I am cruzing down the road or highway at half throttle I am putting what about 10hp on all the parts, they were ment to take that stress daily! Now every now and again when I really push it thats when they will have all that power and pressure on them but if its every once in a while it should hold up fine. Thats why the BB kit first and PP and see how reliable it is then I will be moving on! Also that is why I want the oil cooler. So that it helps keep everything living longer and keeps it all healther!

[RamAir]

ONE MORE IDEA

I was planning on Frankensteining a motor. I posted about this viewtopic.php?f=9&t=2777 and a lot of members really helped me out BUT if it is true that the newer heads do have a bit better flow AND get 1 more MPG man then I say do it!! Since my top end spun I am looking for an almost new to new one! And if I was to keep my bottum end, newer cylinder head this would mean.
Better flow.
More MPG.
BB Kit.
P&P < (The added flow of this would complement the newer heads)

And since it will have an oil cooler (I will look for oil coolers for 300CC bikes since the BB kit is what I am after) it will keep it cool. And since they did not report any power losses with the newer head desings I am figureing all my numbers SHOULD still be pretty much the same!

There is more to this project but if I tell all most here would strat to hate me :neener:

[Water Warrior 2]

I was going to suggest using a 2 valve head for a cooler engine but then my memory kicked in. The big bore pic shows a piston with cut outs in the top for 4 valves.

[RamAir]

Our motors have a 2valve set-up?

If I can amek the oil cooler work I dont mind running at normal temp sence that means its working.
What head has 2 valves?? Plus I want the 4v for better flow!

[Water Warrior 2]

Older GZ engines had a 2 valve head. I think you might be hard pressed to find one though. Let's just forget I brought it up.

[RamAir]

Forget what? Still the more info the better! You can never know to much!

Any what edvise would you give WW since you are speaking from past expariance. And also what have you tried in the past?? Any posts of it on here?

[Water Warrior 2]

Past experience and advice ? You can spend a pile of money to achieve nothing noteworthy. For every small achievement that works rather well you have created at least 2 disadvantages that will haunt you later.
Rather than trying for more power, performance or pizzaz I learned to concentrate on reliability and ease of serviceing. I learned the designers of cars, trucks and bikes are better equiped than I am to make things that don't break. I gave up on aftermarket performance parts and stuff because you are at their mercy when things go south. OEM parts are more readily available and they have a better overall quality to them.
I haven't tried modding an engine for a long time and have never had a stocker go bad or die to soon. But don't let me dissuade your plans. I want to see the results with younger enthusiasm and more resources thanks to the internet.