Bigger intake valves?

[RustyCaddy]

Would there be substantial gains in a 1.6D by changing out the 36mm intake valves and seats with 38mm valves (the old style valves with the 8mm stem from an AAZ) and porting the head? Would the 38mm change the flow and reduce low end power with a moderate sized turbo?  Or is it just as well to stay with stock 36mm valves with porting.  Any advice is appreciated. Thanks!

[ORCoaster]

I thought there was a reasonable gain to the porting on a standard head.  Your looking at more machine work if you go with the larger valves and you make not see a benefit there.  But I defer to those who find the time to grind on there aluminum wonder.

[theman53]

the 1.6 only has 34mm intake valves, the aaz has 36mm, 38mm is an upgrade, 40mm are ridiculous. Very well worth it if you have nothing better to do with money

[RustyCaddy]

the 1.6 only has 34mm intake valves, the aaz has 36mm, 38mm is an upgrade, 40mm are ridiculous. Very well worth it if you have nothing better to do with money

Sounds like it might be worth a try then.  The local machine shops seem skeptical of gains to be made but reading over the forum most folks who have tried it say it is a good thing to do.  From your thread it looks like you went up to 40mm (i am thinking i read over that even).  For the extra up to $300 to go over to the larger valves i could buy an AAZ head but then would have the other issues that go with that. So it is sort of a six-of-on half dozen of the other.

As far as porting  in the Lizard sticky he reported about a 10 horsepower gain porting a gasoline rabbit head; pretty good on its own.

Thanks!

[theman53]

If you haven't ported and don't have egt issues I see no reason to go up in valve size. If you have those issues and cannot get rid of it with a better turbo, porting, intercooler, etc, or if you want the efficiency bigger is the way to go. BTW, the only people that I have read that had issues with the aaz head are the ones sticking an aaz head with 200,000 miles on a 1.6 with over 200,000 miles and saying it starts hard. My 1.6 has less compression than a 1.6 with an aaz head by around 3 points and it starts fine. Jetmugg has a 1.5l with an aaz head that is race only and his starts fine.

[RabbitJockey]

yeah when i saw jetmuggs truck i don't think it smoked white at all even after it had sat... but maybe he will comment on how it is.  a good port job with a good intake manifold and nice turbo should be good,  larger valves is really for more hardcore territory, what are your goals?  alcaids freind has made over 200whp with a stock aaz head no porting, so a ported 1.6 head will flow better than that, it all depends on your goals.

[RustyCaddy]

These are good points all, Thanks.  My goals aren't for big gains but while the motor is being put back together would like to have the capability to make the most of an upgrade to a bigger turbo sometime in the future (mostly for the next owner in the family).  i believe Alcaid mentions switching out to bigger valves in a 1.6l as a benefit with a Holset. So maybe a AAZ head would be the way to go instead.  A shop in Portland suggested that changing the flow to much might yield low power at low RPMs without a big, modern turbo.  Much to consider.

[theman53]

That shop was wrong. If you increase flow it will not hurt anything. If that shop just opens holes and doesn't port for velocity then yes it will only be a high rpm help. Make it like a funnel, tune the intake runner length, and don't make it bigger make it better. Then it will drive better at all rpm. For the funnel effect the goal is to keep the flow going into the cylinder even as the valve is closing and the piston is starting up. That way you get the most air per revolution. Cutting a big hole will not do this, it will add turbulence and won't flow more air until higher rpm...I would avoid that shop personally

[jmaddocks]

  alcaids freind has made over 200whp with a stock aaz head no porting, so a ported 1.6 head will flow better than that, it all depends on your goals.

This was the basis of my decision to port my 1.6 head.  It's in shipment right now from a diesel machine shop in Illinois (http://www.hwserv.com/), who resurfaced it and machined it for the new (slightly larger) precups from Italy.  Hoping to put it back in the car this weekend.