4 Valve Head or a Big 2 Valve Head By Alleyoop (Read 1,680 times)

[Alleyoop]

A 2-big valve head has more and better air flow than the 4-valve. I haven't seen any big valves for the 4-valve head. There is not enough room to put bigger valves on a 4-valve head. You will see smaller valves not bigger valves on a 4-Valve head. Just think how a High rise manifold works on a hot rod and you will find that not all cylinders will receive the same amount of fuel and air. Same with the 4 valve head the flow of air and fuel has to split going to each intake valve.
Alleyoop

[cyborg]

I will differ in my thoughts,,,ultimately the 4 valve is better given the same diameter of a big valve and( 2 )valves of a four valve the circumference is greater with (2)four valves giving more flow,,,and also they are lighter,,so more aggressive cam profiles can be used with less chance of float,,,lighter spring pressures are also a benefit, modern super bike engines turn in excess of 14,000 rpm,,,firing over 116 times a second for hours on end,,,two valves have their place,,,respond very well to supercharging,,with high torque situations,,,also in low rpm engines I think 2 valves are better

[Alleyoop]

The only thing I agree with is the 4 valve head can produce high rpms, just as a short crank can crank out more rpms. I have yet to see a 2 valve head hit the magic rpms to cause the valves to float. One tested a 2 valve head and had it up to 14,000 rpms and no floating, I will see if I still have that Video.

[clonedrone]

Hmm.
Did not differentiate between a High Rise Duel Plane and a High rise Single Plane Manifold.
Different animal.
I run a Brock, Duel Plane High Rise RPM Air Gap on my 385 CI long Rod Stroker with a One inch open spacer.
Velocity and Cylinder Charge.
So what we have here is All Engineers for every MFG. in F-1, IRL, Moto GP, MX, SX are Wrong.
Remember the Six and Eight Valve Honda Oval Piston GP bikes?
Cost did not warrant the little Gain. true dat.
Yam, Genesis 5 Valve that was incorporated in the Mxr's up until last year went to Four Valves.
It's not what you know its what you can prove.
So show me the Flow Bench Numbers please.

[Alleyoop]

Yep and all those with all those valves where there for a reason high revving motor.
I see your not a racer running with the dual plan manifold mild motor low r's at it's best. The single plan manifold has much better flow than the dual plans and produces more r's.

I really don't want to argue with someone that thinks a dual plan is great. So have fun with that mild at best motor.

[jct842]

I would go with a 4 valve on the gy6. I also believe one of the biggest boost is making that engine breath. The head, intake and output of it.

Most of the small jap engines today make more than one hp per cubic inch and the big difference is breathing.

A stock 150cc makes about 9hp, with the same compression a majesty makes 34 for a 400cc engine with 4 valves. 6 hp per 100cc on a gy6, and a majesty makes 8.5 per 100cc.

[rapidjim]

www.forgecycle.com/FF/2v4.htm

[jct842]

There we go, now there are numbers.

Build an engine with just the 4 valve head and is going to be the biggest single power mod you can do.

If you modded with big bore and stroke and got 200cc you still have the 125/150cc breathing on it.

[dmartin95]

May 26, 2015 22:52:24 GMT -6 jct842 said:

There we go, now there are numbers.

Build an engine with just the 4 valve head and is going to be the biggest single power mod you can do.

If you modded with big bore and stroke and got 200cc you still have the 125/150cc breathing on it.

I agree 100%

I just did this.... I only boosted the cc's up to a 155, and I used a 4 valve head... The power this 4 valve makes is insane. I got on it the other day on a long stretch and was limited by gears at about 67MPH.... I was only at around 7200 RPM's.....

In addition, My SMAX is only a 155cc, but it also is a 4 valve with EFI and I've exceeded 80MPH.... 

So, as someone who's actually converted a GY6 into a 4 valve, I'm firmly in the camp of the "4 valve is the way to go"... 

I video'd the entire process
 

[dmartin95]

May 26, 2015 16:51:31 GMT -6 Alleyoop said:

 I haven't seen any big valves for the 4-valve head.
Alleyoop

Taida makes a 4-Valve Large port head. 23mm Intake, 22 exhaust.

[clonedrone]

May 26, 2015 20:24:22 GMT -6 Alleyoop said:

Yep and all those with all those valves where there for a reason high revving motor.
I see your not a racer running with the dual plan manifold mild motor low r's at it's best. The single plan manifold has much better flow than the dual plans and produces more r's.

I really don't want to argue with someone that thinks a dual plan is great. So have fun with that mild at best motor.

I made no such claim that a Duel Plane is better or equal to a Single plane Manifold. or a "Duel Plane is Great"
Agreed the Single Plane the HP picks up at A higher rpm and will surpass a Dual plane on the top end, thats a No Brainer!!
The RPM Air gap with NO spacer makes Power from 2,500 rpm to 6,500 rpm.
With the 1 inch spacer my 385 ci stroker makes power thru 7,250 rpm, Rev Limiter is set at 7,800 rpm. Low RPM??
Are you even familiar with a current Brock High Rise Dual plane manifold?
So you telling me a Gen "0" push rod motor that Pulls thru 7,250 rpm is a Low RPM Mild Motor?
This is also a Long Rod motor, Care to school us on Rod Stroke ratio's?
Running a 3:73 rear gear in a Silverado TRUCK not even getting close to my peak power RPM ran a Best 12.62 @ 108 MPH,
Its a Street Strip combo, with a 3,000 stall convertor, I drove it to the drag strip with open headers.
My Shift point are 1,000 too low,( need to change out Governr spring), with a 4;56 gear and a little weight loss will be well into the 11's, Mid motor
I don't think anyone would consider that a " Mild Motor at Best"
what do you think a current Z-28 @ 508hp, dry sump oil system with a 3:91 gear runs?? Mid 12's and its a $72,000 car.
What do you think I do for a living and who do you think my customer's are?
I didn't come her to argue with you, only to share information based on Experience, then you have to throw out your usual insults to me.
Suck up the ego and lets share information based on experience for the benefit of the members, and get off my snit
Im not here to compete with you, you no dummy.

[cyborg]

if someone would develope a 4 valve head for the Stella i'd have one within the week,,,,i probably would have real issues with the clutch,,,i'd be going thru those things like french fry's,,,

[kubi11]

May 26, 2015 21:26:09 GMT -6 jct842 said:

I would go with a 4 valve on the gy6. I also believe one of the biggest boost is making that engine breath. The head, intake and output of it.

Most of the small jap engines today make more than one hp per cubic inch and the big difference is breathing.

A stock 150cc makes about 9hp, with the same compression a majesty makes 34 for a 400cc engine with 4 valves. 6 hp per 100cc on a gy6, and a majesty makes 8.5 per 100cc.

Well i have 161qmk 171cc 12hp 2 valve scooter and im wining against yamaha aerox 155cc 4valves 15.5hp even if the driver is lighter in weight for 10kgs 🤷‍♀️
Wanted to upgrade to 4 valves but changed my mind after that even aprilia sr160 cant hold up with its 3 valves also mine is fuel injected