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Discussion Starter #1
I have not tried cleaning the oem valves yet, but they’re quite badly caked in thick carbon. as far as I read so far, oversized valves are a little big for the standard 75mm bore, and may cause shrouding. the valves I’m looking at are oversized by +0.5mm, I will be boring the cylinders to 75.5mm with supertech 10.5:1 z6 pistons. i plan on getting a 5 angle valve job, if i were to get the oversized valves I would get the seats matched to the oversized valves heads.

I will be getting colt cam tri flow's. Will the .5mm hurt airflow and cause shrouding and would it be suggested to un-shroud the valves or should they be fine, or stick with the stock valves?

Thanks.
 

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correct me if im wrong but I believe Geoff(I think thats his name) at colt cams is very well versed with the DOHC ZC. I would discuss with him what he suggests to use with his cam. I'm sure he'll be able to guide you in the right direction.
 

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93 Legend L Coupe.
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I have only done and only recommend +.5mm OS on the intake valve and stock sized exhaust valves. The stock valves are proven for over 500WHP, and I mostly like the slight OS on the intake to open up the throat into the bowl a bit more.

5 angle valve jobs amuse me.
 

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Discussion Starter #5
is this engine NA or boosted? - compression ratio with those pistons with stock gasket and uncut head will be 8.5:1
Forgot to specify. I'm building it for boost, but will be running it n/a for a year. I'm shaving the head ~0.050in. Give or take, I plan on having ~ 9.8:1 CR. With a fel pro MLS headgasket.

I have only done and only recommend +.5mm OS on the intake valve and stock sized exhaust valves. The stock valves are proven for over 500WHP, and I mostly like the slight OS on the intake to open up the throat into the bowl a bit more.

5 angle valve jobs amuse me.
Thanks for your input Matt.

Lol, why is that? So you suggest just getting the 3 angle re done?
 

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Because most of the time the "5" angles are just marketing mumbo-dumbo. Sure, you might reach into the throat and the chamber a bit more, but overall, I highly doubt you will get any better flow from them. The only exception to this is a REAL radiused valve seat with a single, discrete sealing angle, but that requires very good machinery which most shops just don't have.

If you want to make more power at the expense of OEM longevity, you need to find a machine shop that will do the valve job with 'racing angles.'
 

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Discussion Starter #8
Because most of the time the "5" angles are just marketing mumbo-dumbo. Sure, you might reach into the throat and the chamber a bit more, but overall, I highly doubt you will get any better flow from them. The only exception to this is a REAL radiused valve seat with a single, discrete sealing angle, but that requires very good machinery which most shops just don't have.

If you want to make more power at the expense of OEM longevity, you need to find a machine shop that will do the valve job with 'racing angles.'
Thanks again, Matt.

by what do you mean "racing angles"
 
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