Oversized valves?
- Thread starter F_T_F
- Start date
Better flow...usually in combo with a ported head. Depends on what you plan on running for a turbo (flow wise) and what HP you are trying to hit.
Cost...the valve seats have to be re-sized to fit the larger valves, plus cost of the port job. Highly recommend upgraded springs with oversized valves running a higher lift cam.
When planning all this, you have to look at what the turbo is going to flow in CFM. Your IC & piping, TB, manifold, and head need to be "matched" to support the flow.
Cost...the valve seats have to be re-sized to fit the larger valves, plus cost of the port job. Highly recommend upgraded springs with oversized valves running a higher lift cam.
When planning all this, you have to look at what the turbo is going to flow in CFM. Your IC & piping, TB, manifold, and head need to be "matched" to support the flow.
Raises the flow limit for the motor, this is why the JZA motors have a higher HP limit than the M series as they're valves are +1.5mm larger stock with room for bigger if needed whereas an M head runs into serious valve shrouding after +1mm and anything larger just won't fit as there's not enough room for larger seats (you can only bore the stock seats out so big before they lose strength and fall out while running)
2mm made for some UGLY shrouding around the CC Rich 
As it was for 1mm's we laid the chamber back a little.
As it was for 1mm's we laid the chamber back a little.
I'm going 1mm on my valves, along with all the other head work. I heard that was a good size, and I'm looking to get around 400 flywheel HP. I am looking for a good Cam, spring and valve combo if anyone has had something work really well for them.
This seems to be a common thing i keep hearing. People continue using oversized valves simply because they "hear" that its a good idea. On a stock head, oversize valves are a restriction. You can only open the stock seat so far, and even if you cut them as large as possible, the stock size valves still seat fine. The only way to make full use of oversize valves is to install bigger seats and unshroud the valves. If you drop in bigger valves in a stock head all your doing is increasing the valve shrouding. The most gain a supra owner is going to get without going nuts is to use stock size valves and cutting/cleaning up the bowls. I've flowed many heads, in various formats and the pure and simple truth is that for the amount of money spent for porting, the gain is negligable.
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The rule is - the lift should only be maximum of 25% the diameter of the valve. If you had a 40mm dia valve, you want 10mm lift tops. Dunno if thats helpful or not, just thought it was something i could throw in there
Cadman: I'm running .351"/9mm lift 280 degrees duration 226 @ 50thou with +1mm Ferrea valves/components and their dual springs.
It makes brilliant power and doesn't seem to taper off with the new IC and pipes.
I'll get to the dyno next weekend for fuel tuning then I'll have a better idea of what I have but last year it was in the low 500's at the wheels with not enough fuel or IC.
It makes brilliant power and doesn't seem to taper off with the new IC and pipes.
I'll get to the dyno next weekend for fuel tuning then I'll have a better idea of what I have but last year it was in the low 500's at the wheels with not enough fuel or IC.