Vauxhall Owners Forum banner

1 - 20 of 31 Posts

·
Registered
Joined
·
504 Posts
Discussion Starter #1
What size are the standard inlet values?, also what is the largest size of inlet valve I can use and is it worth doing.

Thanx for the help
 

·
Registered
Joined
·
30,330 Posts
33 inlet, 29 exhaust

largest inlet is 34, largest exhaust 30. Think thats more to do with seat than actual clearance regarding the exhaust size.
 

·
Registered
Joined
·
504 Posts
Discussion Starter #4
Damn that's close, so I suppose the only way of getting more flow is to polish and port with 420-450 profile cams??
 

·
Registered
Joined
·
1,561 Posts
Increase the lift rather than the duration if you want to get more air in. That way you retain driveability.

To can pick up a bit more power if you advance the inlet cam a tad this helps with the scavenging which should increase the mid range power a bit, might over scavenge at high rpm's though.

Chris
 

·
Registered
Joined
·
11,455 Posts
increasing the lift on it's own is a surefire way to kill the lifters on the XE - the profile already has a fairly agressive acceleration and the lift already requires piston pockets - many users of wilder cams with standard pistons report excessive tappet noise afterwards.

Also, increasing inlet valve size in the XE should be one of the last things you do - and only on an engine built to take advantage of the extra flow above 6k rpm

concentrate on the head - there's plenty of potential in there - but there's no major restriction in one area that will give a large gain -it's more a case of paying attention to detail and small gains all adding up - the exhaust tract though is especially restrictive - and would show power gains if you had a well matched manifold - don't ever match the exhaust ports to the manifold though if you intend to build a well tuned NA lump - reversion is discouraged by having a good step in diameter.
 

·
Registered
Joined
·
504 Posts
Discussion Starter #7
I assume that solid lifter would solve the noise and other problems related to the 420 - 450 cams then.

Also where on the exaust port is there a restriction??
 

·
Registered
Joined
·
6,684 Posts
put your finger in and have a feel!
 

·
Registered
Joined
·
11,455 Posts
he wants to know about heads Matt, not anal polyps ;)

the exh. ports are always generally badly mismatched to the valve seat - all the heads I've seen always have a ridge on the plug side of the port, just below the seat, and another lump on the small radius of the tract.. in general though the ports can be opened out a little too, as the seat is generous and can stand a little opening out.
 

·
Registered
Joined
·
1,681 Posts
mininut said:
I assume that solid lifter would solve the noise and other problems related to the 420 - 450 cams then.

Also where on the exaust port is there a restriction??
What do you mean 420-450 cams?
It can't been duration bigger than 340-350.
The full cycle is 360 degrees.:confused:
 

·
Registered
Joined
·
30,330 Posts
can duration doesnt mean how long the lobe lasts in respect of 360 degrees in one rotation. But i agree ive never heard of a cam bigger than 310deg, so far.
 

·
Registered
Joined
·
11,455 Posts
these sound like QED cams - I'm not sure where they get their numbers, but it's not purely on duration - I think their website explains.

duration is normally quoted as the number of degrees in each cycle for which the valve is open by 0.1mm+
 

·
Registered
Joined
·
30,330 Posts
so its out of 720 then, not 360.

edit

crank turns twice to every 1 cam rotation. so technically it is 360 but geared down 2:1, or something.
 

·
Registered
Joined
·
504 Posts
Discussion Starter #14 (Edited)
420 and 450 in my simple mind are lift figures in thous and not duration. Duration is how long the valve is open for, this is lift, how far down the valve is pressed in thous.

The 420 and 450 that QED do have the same duration as the standard XE cams and just open more, based on what I'm told.
 

·
Registered
Joined
·
1,561 Posts
Cams spin at half the rate of the crank.

Duration is expressed in crank degrees. You can get 330 degree cams for drag motors and so on.

I would imagine the 420 and 450 are indeed lift figures.

Cams very intresting things, lobe seperation angles, lift, duration, base circles, ramp, flank, nose and all sorts of other terms.

The port castings usually have a step in them due to the way they are cast, bits of sand that form it fall away and leave a sharp turn at the short turn radius.

Chris
 

·
Registered
Joined
·
18,393 Posts
duration is what makes power really. having the valve open for longer gives a better power increase than having it open for the standard duration but wider. they usually go together of course, more lift and longer duration.
big lift does tend to batter lifters a bit, as well as the springs.
 

·
Registered
Joined
·
18,393 Posts
lol only mentionned it cos i am having a specific pair o cams made for mine and the emphasis is on duration as thats what showed large gains in power.
 

·
Registered
Joined
·
11,455 Posts
really, what spec you going for ? - could they be similar to '225' perchance, or wilder ?

don't forget to the uprate the valvetrain, he said condescendingly... ;)
 

·
Registered
Joined
·
18,393 Posts
not bothering with any changes other than the cams :rolleyes:
kindof similar yes to 225 so at least i have a map to start with!
 
1 - 20 of 31 Posts
Top