Biggest bore you can go to right now?

[Chuck]

Total=667.  Pretty cheap if you ask me for the performance gain.

I'm with werase643.

I sold my GS for $2000.  I bought a FZR600 for $1800, and spent about $250 repairing it.

So for $50, I got an extra 40hp.  Pretty cheap if you ask me for the performance gain.

Is this really going to be truly a race bike?  Like, for racing??  In what class, that won't get absolutely spanked by a EX500?   (which puts out more than 50hp stock)

You have to really love the process of engine building to do this, because you won't be doing it for the power or cost effectiveness.

that doesnt make any sense what so ever.... unless im missing something but it doesnt make any sense to me..  this guy goes against known engine building

You are missing something. 

[coll0412]

In racing HP is not everything, I have seen a skilled rider keep up with Ducuti Monster's, and they have like 62HP I think or something in that range. Besides note everyone races to be the #1 plate.

[Chuck]

In racing HP is not everything,

We're not talking about racing, we're talking about boring and milling and cryoing, and porting, of which HP is the goal, right?  My point is the only reason do do all this stuff to a GS500 is in order to fit within the racing regulations.  If you're building a bike to have fun at the track, get a cheap 600.

Most importantly, if you enjoy engine building, and want the pride of having a really strong weak bike, that is the reason to go to all this trouble.

(And if you're racing, and you don't care about HP or winning, then go with what you have, I guess.)

[Chuck]

I should also point out that a $200 bike plus engine work and rear sets doesn't make a race bike, or even a track bike.  Plan on spending $300+ for forks (or springs + brace + emulators), $400-$800 for a shock, and you probably want to do the Katana rear wheel mod to get a decent tire on there.  Probably also want to do something about brakes (hopefully the front end came with brakes).

[werase643]

several years of building up a kewl parts casche...GR 650 engines/ GS400 8 valve engine/ cams/ CR carbs
and I figured for about $2k I'd have a fast GS....yes it would be a fast GS but a slow racebike

I sold off most of the kewl parts and bought a RS125 for 2k

GS 500   40ish HP 320-350# race ready
HONDA RS125 40ish HP 164# race ready
GSXR1000 160+HP 360-370#

translation..... PISSIN' UP A ROPE

my GS race bike was GSXR750 front end and GSXR 750 rear wheel with a GSXR shock
stock pegs are fine....learn to lean off the bike
all your mods are going to yield 3-5HP gain
not worth the $$$$
heck you can probably buy a race ready bike for 1000-1200

[darb85]

Got a resprung Katana Front fork set for the front end and the guy im building the bike with has built many bikes.

Oh and all the engine work is to stay with in a class, the EX500s are actully put in a different class at the track, and hell im doing this to learn and have fun 60% of the Bikes in the class are GS500s so im not that far out there. 

Im doing it.. so there 

[bombadillo]

wow, that is a cheapie race bike.  hope it all goes like a badger on crack.

[darb85]

heres to hoping too, but ya, im looking do have fun and hey I love building engines so at the very least, Ill have a cool street bike.

[darb85]

that doesnt make any sense what so ever.... unless im missing something but it doesnt make any sense to me..  this guy goes against known engine building

You are missing something. 

So what am i missing?  seriously, Im curious,

[Kurlon]

that doesnt make any sense what so ever.... unless im missing something but it doesnt make any sense to me..  this guy goes against known engine building

You are missing something. 

So what am i missing?  seriously, Im curious,

You're not missing anything.  There is no such thing as 'velocity porting', it's a gimmick.  ALL porting is a matter of tweaking port shape and size to achieve desired flow characteristics, with shape being far more important.  In his case while he's busy 'shrinking' the ports, his gains are coming from improved shape, not from the shrinking.  If he took the time to look at why the shape changes are working, he'd likely find there is some power being left on the table by making the ports too small to get there.  There are some motors that the stock ports are too large to achieve good velocity, but I doubt you'll find that's the case on anything resembling a modern motorcycle.

[darb85]

Thats what i was thinking... it seemed odd to me to make the ports smaller,  but your explination makes everthing make sense.  Thanks

[Chuck]

There are some motors that the stock ports are too large to achieve good velocity, but I doubt you'll find that's the case on anything resembling a modern motorcycle.

Exactly!  I'm thinking the GS500 does not resemble a modern motorcycle.  There's probably some gains to be had by better port design.  The GS valvetrain is so sketchy, you'd probably get more benefit from fixing that somehow (4 valve head, anyone?) than the extra 50cc or more compression.

[Chuck]

hell im doing this to learn and have fun

Haha, that's what I was waiting for!    Now, I approve!

[Kurlon]

There are some motors that the stock ports are too large to achieve good velocity, but I doubt you'll find that's the case on anything resembling a modern motorcycle.

Exactly!  I'm thinking the GS500 does not resemble a modern motorcycle.  There's probably some gains to be had by better port design.  The GS valvetrain is so sketchy, you'd probably get more benefit from fixing that somehow (4 valve head, anyone?) than the extra 50cc or more compression.

It can't be as bad as the 50+ year old design Honda singles I play with.  Without increasing displacement or swapping cams I've been able to take a 3.6hp 72cc motor out to 7hp just through porting and compression.  If the GS is leaving that much on the table... some quality time with a Dremel can make a world of difference.

So, how much is left on the table?

http://www.x386.net/TTR/tech/cgi-bin/motorsim.cgi?cgibore=74&cgistroke=56.6&cgirodmm=101.95&cgipinheight=19.5&cgiintakemm=27&cgiintakecount=1&cgiintakelift=8.76&cgitranseff=94

Bear in mind this sim takes forever to load (it's on my 386) and it's only looking at 1 cylinder.  I guessed the intake valve diameter based on the part number listed as a vesrah replacement for the GS500e.

What the program is showing is the theoretical output of on half of the GS500e motor, based on bore x stroke, intake valve diameter, and cam lift.  The Red portion of the chart is based on the assumption that the motor is only running at 75% VE (Volumetric efficency, ie how well it breathes), yellow is 75% to 100% VE, Green is up to 115% VE, ie DAMN FREAKING GOOD porting plus matched airbox and exhaust.  The output is adjusted to represent a rear wheel reading by tweaking the transmission efficency.  The graph caps at 19hp as thats the theoretical max usable flow through a 27mm intake valve.  Based on the valve size and lift, the mach index (speed of flow past the valve seat) shown at the top of the chart puts peak power occuring around 9k RPM, beyond that point my sim becomes wildly inaccurate.  The sim also says you don't wanna wind past 11k unless you've got good quality pistons.

The dyno at www.gstwin.com shows 25hp at 6k RPM.  So we should be seeing 12.5hp on my sim, which puts it at about 85% VE, not bad.
7k RPM shows 35hp, so a 17.5hp reading is close to 100% VE, looking good.
8k RPM, hair over 40hp, 20hp reading is a little under 100% VE, and past there the motor shouldn't gain much more 'cording to my sim.
9k RPM, peak power at 42, my sim says thats where power should peak.

So all things considered, the GS isn't doing that bad considering it's head setup.  Rather than playing with bore and stroke, try plugging in a 29mm intake valve, you'll see the prediction is you can pile on an extra 2 hp, or 4hp real world.  You'll also be moving the peak power point north just slightly.  I've been able to go from a 27mm intake to a 29mm unit without putting in new seats on my minis, seems like the same change would pay off here as well.  Without changing the valve size, the motor is going to be choked.  Putting on a higher lift cam without altering the intake valve doesn't remove the choke point, but does move peak power north, so you should get a wider powerband.

So, I don't think the stock porting is all that bad if the intake valve really is just a 27mm unit.  Anyone know the actual valve diameter, as well as the intake valve sizes on the GS400 4v head?

[coll0412]

IS this sim based on dimensionless characterization of an IC engine. It pretty interesting and I have never seen it before.

Anyways, I think I might be giving this a shot over the winter as I will be doing a tear down of the engine.

1 quick question, however, is do you need to balance the crank with the new pistons?

[Kurlon]

It's an air pump based sim.  The bore and stroke determine the displacement, and from there the CFM is computed, using valve size, cam lift, and stroke to establish flow and rpm limits.  From there, I'm using an ideal mix ratio of gas to air to reverse to HP based on CFM.  So the bore to stroke ratio influence isn't part of the equation yet, or cam duration, overlap, (or anything to do with the exhaust really), etc.  Very simplistic but fairly accurate for my smaller horizontal singles I've been working on.  As I learn new math or theory, I work it into the sim.  I'm redoing my math as we speak to account for offset wrist pins when figuring crank arm geometry.  That'll get me proper dwell info, and that along with compression ratio influence should let me start showing power curve shape instead of assuming 100% VE across the board.

[Chuck]

That's putting some serious brain cells to the problem.  Quite awesome. 

(So if a GS could rev to 16K, you'd get 80RWHP??  Now that sounds like a goal!)

[dgyver]

.... The GS valvetrain is so sketchy, you'd probably get more benefit from fixing that somehow (4 valve head, anyone?) than the extra 50cc or more compression.

When I built my first 555 with Megacycle cams & springs, it would rev to 13,5 before valve float. It still had accelerating power up to then. With lighter buckets & shims, the redline could have been increased. At what price to the reliability of the motor would be in question though.


... btw 4-valve head in the works...

[dgyver]

hell im doing this to learn and have fun

Haha, that's what I was waiting for!    Now, I approve!

Yep, that is the same reason I do it. 

[Jughead]

spend 300+ and put a 2 stroke in it.