need info on oversized valves

[sixer3]

I have a 426 thats pretty reliable but i want to see a bit more power just b/c

i have a 426 with

p/p
10:1
stage 1 hc
450r carb
full exhaust
hd cam chain
ebc clutch


blah blah
anyways, what exactly are oversized valves going to do, and should i get intak and exhaust or just intake or just exhaust

also will it change my valve lashes
THANKS!

[deepcj7]

XR's Only just did my valves. They went with 1mm oversize intakes and left the exhaust alone. They don't like to do the exhaust side because of clearence and strength issues after the material is removed. As far as performance I don't know because I had a lot of work done at the same time.

[sixer3]

cool, thats helping, anyone else ?

[YFZ450Ridr]

oversized valves are going to flow more air. letting more air in at once and letting more air out at once. the faster you can pump air and fuel into a motor and the faster you can pump it out, the better it will run because its more effiecient.

[sixer3]

alright well i want to get them

do i need anything else with them or do i just install them and go, it seems like i would need to change my valve lashes....little help please

[GPracer2500]

I'm wondering if there is potential for a loss in torque. Big valves might allow for great breathing at high RPM but what happens to the velocity of the intake charge at lower RPM?

High RPM efficency and peak HP might be what you're after [shrug]. But adding a horse or three on the top might make for an overall slower quad if torque is adversely affected--depending on the quad's intended use.

Also, I'm wondering about putting big valves in an engine that's already been ported. Seems the ideal situation would be to start with a fresh head so the porting can be matched to the size of the valves. Maybe a head could be "re-ported" but it seems that once it's been done it's been done.

Where's wilkn250r??

[fandl450r]

From what my motor builder has said to me, it sounds like (atleast on my 450r) that a 1 to 2 mm oversized intake valve is used to creat more torque. But using an oversized exhaust valve can actually take away from this.

[sixer3]

ya, i guess that would start to make sense about the intake velocity....im actually after some top end, i have a lot of torque with the 10:1 and stage 1....my port is pretty mild....i really just want to pull a bit more in 4th and 5th, i run mainly dunes, but get to a track every once and while

[400exrules]

you might want to go witha new sleeve and get a 12:1 or higher piston with HD studs and a new rod....and a stage 2 cam

[sixer3]

i dont wanna run race gas, yes i know this is the only way to get real good power i just dont want to do it...if i did that would be an awesome idea

[wilkin250r]

I'm not an expert on every single engine configuration possible for the 400EX. But I can tell you the basic effects of certain changes.

GPracer's logic is slightly flawed. He's almost correct, as a general rule if you increase flow you decrease velocity. However, that rule applies mainly to your ports. Wider ports will flow more at less velocity, but your VALVE openings are your bottleneck. They're much smaller than your port mouths. Any increase in flow in this area will increase flow overall without adversely affecting the air velocity.

Oversized valves should give you a nice top-end boost without affecting low RPM performance. The drawback is that they are heavier, so you increase the likelyhood of floating a valve at extremely high rpms, but I don't think you're going to see those kinds of RPMs with a stage 1 cam.

For the 400EX, I'd suggest them on the intake. Increased flow just seems to be more beneficial on the intake. Look at the YFZ for example, it has 3 intake valves but only 2 exhaust.

[sixer3]

that helped a lot, and if it didnt cost 250 bucks just to get the machining done and i install them i would get em.....heh.......and they want 450 to re-port my head to match my motor....sigh....im lookin for another place that would do it right now

check out this place they are pritty cheap for the head work and stuff. http://www.lukesracing.com/luksr/440sleeve.html

[sixer3]

awesome link, thansk a lot!.....must just be expensive here in CA

no problem. some times they are a lil hard to get ahold of but it's better than paying 400 bucks.:D

[GPracer2500]

Well, hang on a second.

The extent and quality of port job X doesn't equal the extent and quality of port job Y. Notice that Lukesracing's description says "...Port and polish head-->Intake ports are smoothed and casting flaws removed, glass beaded finish to prevent fuel/air separation, combustion chamber polished, exhaust ports enlarged and polished and new valve seals installed..." The key here is what they say about the work done to the intake ports. They don't actually change the shape or size of the intake ports. Smoothing and removing casting flaws is not a FULL port job in my book. All they're doing to the inake ports is "cleaning them up".

I'm sure this is because modifying the size and shape of intake ports is hard, skill intensive, and requires the most experience when it comes to head work. That's why porting cost so much $$$. I think it's the absents of this work that allows Lukesracing to price their services as they do. I bet if you asked them for more comprehensive headwork the price will climb quickly.

AFAIK, the intake side of a port job is where much of the gains come from. Again, AFAIK, changing exhaust ports is more straight forward and the details of how it's done is somewhat less important. Many an amateur tuner has ruined a perfectly good head by botching their attempts at modifying intake ports.

Lukesracing is not being misleading--they say exactly what they do. And what they offer does sound like a good value. Just understand that what they do may not be the same thing offered by some other shop you've talked to.

Here's a recent thread on 400EX porting: http://www.exriders.com/vbb/showthread.php?s=&threadid=234485&perpage=15&pagenumber=1

[wilkin250r]

Indeed! Gpracer makes an EXCELLENT point. Cleaning up casting flaws isn't a true "port job". If you're lucky, you might see a whopping 1HP increase, and that's optimistic.

A true "port job" involves actually changing the shape and size of the ports for new flow characteristics. It requires a lot more time for the modification, as well as requiring huge amounts of R&D on a flowbench to determine the proper port dimensions. It's much more involved and in-depth, and thus obviously much more expensive.

Depending on the engine, this type of port job could easily gain you 5hp, and depending on the engine, possibly upwards of 10hp.