4 valve vs 2 valve By dmartin95 (Read 2,578 times)

[dmartin95]

Hi all, I've seen some 4 valve heads available for the GY6.... has anyone tried them, do you have a scoot that came from the factory with this type of cylinder head?

What are the pros/cons of a 4 valve vs 2 valve setup?

[Bashan]

Cyborg is an expert on this, I'll get him to comment. But I can tell you my SYM 300i has 4 valves and it hauls arse! The difference is notable although it does have EFI. But still I can tell a huge difference. It just stands to reason you have that much more breathing room that it's going to move more air. Setting the valves is a pain but it's worth it. I'll see if I can stir up Pedro. Rich

[cyborg]

Rich is correct the advantage of 4 valves verses 2 is in the breathing ,,,they simply Move more air,,,and the valves themselves are lighter with less chance of float at high rpm,,,i've not used a 4 valve head yet but on my next full build it'll be a 4 valver,,and a full balance and blueprint job,,,all of my latest bike builds have been 4v,,,,i've been meaning to start a thread on balancing ,,,i will soon,i've never saw it mentioned on the forum,,,it is very important,,i'm thinking 4 valve balance job lite supercharger we may be talking 20-22hp

[cyborg]

Oh i forgot to mention with the 4v breathing so well you don't need as radical of a cam profile so there is even less chance of float

[tvnacman]

Nov 16, 2014 23:08:26 GMT -6 cyborg said:

Oh i forgot to mention with the 4v breathing so well you don't need as radical of a cam profile so there is even less chance of float

May I ask where are you sourcing the valve springs and what type of spec are you aiming for . I'm not a machinist by trade but valve spring tension and valve float go side by side .

blueprinting a little GY6 interesting concept , to what rpm ?

John

[cyborg]

i'm was hoping for a 10-11,000 rpm safe zone,,,12-12.500 redline,,,,as far as spring pressure i was thinking of a reworked off the shelf 4 valve head ,,,if i need to have new valve springs made,,,Velsey engineering is where i had a bunch of springs wound,,,seat height and spring pressures will be brought in line with current 4 valve thinking and will be referenced,,,and i'll tap Valley engine services for the balancing of the rotational and reciprical parts,,,the springs will be Ti and ovate wire will be used in a beehive profile,,,which further reduces inertia mass because of the smaller retainers and keepers,,,another benefit of 4 valves is higher intake port velocities which in turn means better port filling at lower rpms,,,,i need to find a victim,,,then the fun begins

[dmartin95]

Thanks for the replies!

I appreciate the feedback!

[jct842]

Its my belief that the best single improvement for a gy6 has to be a decent head.

Four valves rather than 2 large ones, porting and the shape of the combustion chamber. Even more so than big bore and strokers. On big bore we have less strength as in thinning of the bottom of the barrel and less metal in the case. Add a cam along with carb and exhaust with the head and your good to go. Some of those balanced honda race engines yield 2 and 3 horses per cubic inch and there is no reason a gy6 could not benifit with that type of care. A big bore and stroker probably doesn't gain more than 3 or 4 horses with out a head.

[cyborg]

I agree a full balance job a decent head carb and pipe and I think I'll have a winner

[jct842]

It would be nice to come up with a quality piston too! 150cc's and just 2 hp per cube would be dyno-mite. Might need a wheelie bar!

[Alleyoop]

In reality the 2 big valve head flows better than a 4 valve head.
And who in their right mind would crank the motor up to 11-14k . At those rpms you have to then worry about the case not holding up just like a hotrods block, put to much strain on the crank and the block will give the crank will come through the case
My .02 on this unrealistic undriveable unreliable piece of work

[Bashan]

Possibly Alley, this has never been done to my knowledge on a scooter, it will be an exciting experiment. But Pete has the knowledge and experience to make this work. If anybody can do it he can even though he has never touched a GY6. But he has built so many super bikes it is dizzying. By built I mean had most of the engine parts redone or made from scratch. The man knows combustion chamber technology, valve train technology including no spring actuation, piston machining from scratch, balancing and blueprinting. He has access to a dynamometer and can actually get some hard data before and after. I told Pete I'd help him with the GY6 since he has never taken one apart but I doubt he'd have much trouble. And the supercharger? I just passed out. Rich

[dmartin95]

Nov 17, 2014 21:28:46 GMT -6 Alleyoop said:

In reality the 2 big valve head flows better than a 4 valve head.
And who in their right mind would crank the motor up to 11-14k . At those rpms you have to then worry about the case not holding up just like a hotrods block, put to much strain on the crank and the block will give the crank will come through the case
My .02 on this unrealistic undriveable unreliable piece of work

Are you talking about Cyborgs blueprint or the 4 valve in general?

[jct842]

I bought a prodigy variator from a guy on ebay, probably tiawan who claimed he had a genuine honda crank that would fit a gy6. If that is or was the case and it would work I would go that route. Maybe a lightened flywheel too.

When an engine is balanced they really can get some rpms. My old bandit I think was a 10,500rpm red line and some of the rockets do go as high as 12 and 13k.

[dmartin95]

Let me ask you guys another question about the 4-valve head.....

Do you consider the 4-valve to be worth $250~450.00 USD (price depending upon brand) in the event that you are NOT building a racing engine?

My goal is to beef my engine up, but I'm not looking to go any faster than 70 MPH. When I purchased my scoot, it went about 60MPH, by the time I got 500 miles and she was well broke in, I could (GPS verified) Get my scoot up to 62MPH, reliably too. I only weigh 150lbs. But, I've since added an XL trunk, saddlebags, carry about 20lbs tools and supplies, and have a windshield now... This brings the speed down on hill climbing, take off and even hurts top end by about 3~4MPH

Now, I would like to get back up into the 60's, maybe even 70 MAX...

At the same time, I want a reliable long distance cruiser and not a racing engine...

All the feedback I've received about the 4-valve head has been pretty encouraging so far.... Now I just need to find out about reliability,,,