Gy6 ported head?

[Bob]

how much difference will a ported and polished head with more compression make with a 155cc bore kit? the head is a 57.4mm bore and the bore kit is a 59cc supposedly. i was told that i will yield anywhere between 1 to 1.5 points compression, which should be around 10-10.5:1 on a gy6 155cc. how much of a difference would that be? the guy who im going to buy the head from makes them. he will help jet it correctly and time the motor correctly. would this mod be worth spending a couple of hundred bux on? i have 14f 39 rear gears, i should be able to take full advantage of this gears i hope.
thanks guys

[90GTVert]

Who makes these heads? Is the seller local, or is he gonna provide phone/email/PM support to help you jet and time it? Jetting the 10.5:1 motor shouldn't be any differnt than jetting a 9:1 motor. If you run 93 octane you may not even have to change timing, just don't put a timing advance CDI on it. I don't know the GY6 that well though, so maybe it will need you to pull a couple degrees of timing.

Not sure what a GY6 really makes, but if you make 10HP 1-1.5 points would be good for an additional 0.3 to 0.6 HP. If you make 15HP it would be good for 0.45 to 0.9 HP.

There is a member at ScootDawg that owns a shop and swears that uncorking a stock GY6 head is one of the biggest gains you can get. It seems like the cylinder heads on lots of little 4 strokes are the bottleneck, so it wouldn't suprise me if you got good results.

[Bob]

2. STAGE II, RACE prepped, +18% hp, +11% torque and sustained 99+ mpg.

Contents: one 57.4mm GY6 professionally RACE prepped port/polished head/intake manifold combo, multiple angle race valve job (large valves), head gasket, intake gasket, exhaust gasket, intake and exhaust bolt studs, intake nuts, special intake spacer, new valve train installed (except cam) and a cam timing hardware kit. This kit has the following options:
a. Stainless steel valves, 10% valve train weight reduction
b. Heavy Duty springs, required for some race cams
c. Titanium retainers, for additional weight reduction

This kit needs a performance exhaust, performance intake and correct jetting for the full RACE performance to be fully obtained.

STAGE II+, high compression RACE head, adds additional .4 hp.

Contents: contents are the same as the Stage II kit except that the mead is milled .025" for an additional point of compresion (which in a 150cc engine that stock, puts approximently 6 hp to the ground = .4 additional horse power, incredible additional gains are also availble from dialing in the timing).

[Bob]

here is the stage II dyno sheet but not the stage II+, the plus version will be beefier. remember this is to the ground.... what is the parasitic loss of the gy6 trans? its 8.6 hp to the wheel. so the bhp would be what?

[Bob]

this is what he said to me after i inquired a few times asking about the power difference in his heads.

causticbelt,

My stock scooter top speed was 53. I will discribe my current scooter setup to best answer you question.

When I had stock tires, stock transmission and Uni, rejetted stock carb, Bando coil/wire/boot, NGK Iridium, custom tunable muffler and modified stock header with a hot CDI and the Stage II head (no timing), the rear tire would break free under way too many circumstances.

I changed my tires to: front, 110/90/13 Pirelli SL23 and the rear, 150/70/13 Pirelli Diablo. This was a much needed ride improvemet. I live in the Pacific Northwest and it is almost always wet and cold, the Perillis are a perfect compliment for this weather. That big rear tire stold a ton of power from me so I installed the Stage II+ which made back some of the lost power. I have since learned what correct timing can do for power. I am currently running the Stage II+ with spot on jetting and the absolutely correct timing, it is very impressive. The rear tire doesn't break free as it is the correct compound to hook up in this climate and, well, frankly is still monster huge and heavy but doesn't slow me down at all (this is the same size tire that comes stock on a Suzuki Bergman 400cc scoot). I have since added a windshield and my top speed has been 68 (@ 5,900 RPM). I am only ever concerned with what my scoot can do up hills not on flats (there is nothing flat where I live).

Last week I added a Prodigy teflon variator, Prodigy pulley fan, Prodigy Clutch and bell with 17g roller weights all stock springs. Resulting a faster take off and no difference in top speed.

I could take off the fairing, empty my trunk, remove the saddle bags, test with 4 ounces of gas and tuck way down but I never do that. So my speeds will be with all the gear, the fairing installed. all my weight and the saddle bags.

I do have the GPS which I checked the stock bike with and I will check the current setup to give you the most accurate reading (I am very certain it is topping out at 68). Oh yeah, I weigh 275 pounds soaking wet , keep a full trunk of tools and spare parts and usually have the saddle bags on.

I spoke with Dave about your 155cc and we have both onceeded that you won't add a full 1.5 compression point with the II+ but it will be somewhere between over 1.0 compression point and 1.5 compression point. We are in full agreement that you will not exceed 11:0 even if you where using a 63mm cylinder. So if you want the Stage II or Stage II+ you will be safe and will love the difference. You do need to have this thing jetted/timing correct (if you go with either system I can get you very close if you are very detailed discribing your setup, I will let you know the details I need). ;D

One other note, I am using the non-option head (the options are for the people that just have to have that type of component. I test and report everything in the base setup; no options installed.

[90GTVert]

A scooter that tops out at 68MPH after a windshield that breaks the tire loose? If he means going straight, that doesn't add up to me. The fact taht he gained MPH with the windshield shows that it's not just making so much power that it runs out the gears, but yet he makes so much power that it overcomes the tire fast enough to spin instead of wheely? Get what I'm saying? It's probably a cool product, I'm not saying it isn't true, but that part sounds odd to me. Maybe he shoulda worked on his suspension before getting new tires? 5900RPM sounds low for a scoot (especially one with a big head), but maybe I'm just too familiar with 2 strokes.

[Bob]

it does sound a little fishy to me as well. i think im gonna just mill the stock head and port match and smooth it out. im sure that ought to be an experience in its own. when i come up ill call holeshotz and we will take it to him to get it milled. how's the new scoot coming along?

[90GTVert]

I'll start a thread about the new scoot in a bit. I haven't touched it yet.

[Bob]

i found a big bore head on ebay for 120 shipped, i am waiting on a reply back from the guy for port dimensions and all that good stuff.

[90GTVert]

Yeah, I got your email with a link to the auction. It just says "big port" but doesn't list any valve and port sizes that I saw. I was wondering if it was going to be like the old ct70/xr50 clone heads when we used to mess with midbikes, where we'd see people buying big valve/big port heads and they'd turn out to be the same as the E22 (I think that was the number?) head that came stock on lots of 'em. lol

[Bob]

from what the pictures look like it is a bigger head and bigger valves guess ill find out when he replies

[Bob]

here is what the original guy said........lol

caustic,

Dave and I have discussed this and we are confident that your 155cc with a stage II+ will not exceed 10.7:1, as long as you use premium gas all the time this will be great (it won't add 1.5 full points but it will add somewhere between 1.1 and 1.3 full points). I am not telling you not to buy the regular II but at 10.7:1 you are going to be making some nice power. Your timing and jetting correct will make a huge amount of change also!

So, you should do what makes you feel best, I don't need to sell you a II+ to make it through the day. You will be very happy with either, especially compared to a stock head.

Here is a reason to not purchase the stage II+; if you think you may ever change to a larger big bore or use a stroker crank, then you should definitely get the stage II only as that will further increase the compression and I know that you want a reliable scooter engine.

[Bob]

sounds to me like he is on the fence about the stage II+, i dont really know, what i want. Brent you got any ideas? if i milled down the stock head, it should be the same compression as his...is that too much? Whats your opinion?

[Bob]

well too late now i ordered a different head from scooter wolf pack and the valves are Intake Valves 30.5mm Exhaust Valves 28.5mm. the ports have been ported and polished. 80 bux for the head. cant beat it.

[90GTVert]

Sounds like good valve sizes, but I honestly have no idea what stock 150 valves are.