2JZ head porting.

[Rz]

yeh hks 272 means interference , on stock pistons at least.
tested on my own motor.

[BigMuz]

How can you discuss interference without talking cam timing? And by interference the rest of the world is talking about whether an engine can survive a cam belt breking are they not? Are you saying that you may need to flycut pistons with a particular cam?

And 2iowa- can you please just type "everyone" rather than every1. Seriously, it's only two extra letters.

[CWR]

muz because cam timing is irrelevant

Think really hard about that, it's possible to have cams that can come into contact with the piston yet cam timing will prevent that in normal operation.

So yes cam timing is relevant

[Rz]

well , all engines are non interference in operation , there really should be a better term for it.

[BigMuz]

That makes no sense? The valve has plenty enough lift to hit the piston at tdc surely.

Otherwise you poofs need to harden the fuck up :D

[21OWA]

rusty is right
the way i see it, you would test interference at TDC and full lift
cam timing is irrelevant as it wont make the cam lift anymore and wont move the piston any higher

yes you will need to flycut pistons more with certain cams
or get forgies made to suit higher lift

[Rz]

ah , if you advance your intake cam , and retard your exhaust cam enough you will have problems regardless of lift.
this cant happen on a bone stock motor is all.

[BigMuz]

So what exactly are you guys talking about? The fact that if a belt breaks you are in trouble, or the fact that you need to check clearances?

[Norbie]

Non interference = no problems regardless of cam timing.

Interference = possible problems depending on cam timing, you need to check.

FWIW almost all Toyota engines with belt-driven cams are non-intereference, and almost all chain-driven engines are interference. Obviously it's done this way because a snapped belt is way more common than a snapped chain, and if the engine is interference you'll have an expensive repair as opposed to a simple belt replacement.

[BigMuz]

Soft. I'm a little ashamed of 2j's now :D

Any pushrod engine worth it's salt will eat valves if you lose cam timing.

As an example of a non intereference engine think Holden 202 VK edition :D

[CWR]

no its not, because thats not what interference means

if they dont share range of motion, ie one of them can be stationary and not hit the other when the other is rotated, then its not interference by definition

Having a lift high enough to come into contact with the top of the piston, but at the same time is prevented by cam timing is exactly what 'intereference' refers to in an engine

[Billzilla]

this came up because someone questioned whether a set of hks 272 will put a 2jzgte into an interference state (from its factory non-interference state) and the answer is that yes it will. and thats solely because of increased lift. you then asked how you can talk about that without considering cam timing, which brings us back to the definition of an interference engine. if it CAN hit.. its interference. if it CANT NO MATTER WHAT, its non interference. cam timing and whether its running the way its meant to or not, are completely irrelevant.

True.
As an example, the stock 4AGE's are all non-interference types. You can put either cam in any poisition and spin the engine around quite happily without any valve hitting anything.
That changes rapidly with bigger cam though of course.

[2JZR31]

Soft. I'm a little ashamed of 2j's now :D

Any pushrod engine worth it's salt will eat valves if you lose cam timing.

As an example of a non intereference engine think Holden 202 VK edition :D

Simplified to 202 > 2JZ

[Jay_G]

in regards to non-interference are we also talking about valves clipping each other if say the belt slips, forgetting about the piston all together at the moment. or are the valves spaced as such that this won't happen?

[Cameron_Datto]

Found these flow figures on the Kelford cams site http://www.kelford.co.nz/cylinderheads.html



Toyota 4AGE 16v

Intake Lift
.050
.100
.150
.200
.250
.300
.350
.400
.450

Exhaust Lift
.50
.100
.150
.200
.250
.300
.350
.400
.450
Intake CFM
40.6
81.5
124.5
158.1
184.2
199.2
212.2
221.5
227.4

Exhaust CFM
33.6
78.9
125.8
146.3
157.7
162.8
165.4
166.5
187.8
28"H2O Test Pressr
Ported by Kelford Cams
Intake valve size 1.26"
Exhaust valve size 1.07"







Exhaust to intake
83%
99%
101%
93%
86%
82%
78%
75%
83%
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