This means roughly a 1.750" Internal Diameter of the valve seat, were as the stock npi is 1.590" and pi is 1.540".( typical over size valve is .040" more)
The pic shows an Chevy Ls 2.020" intake valve modified to 1.900".
A bigger o.d. valve seat must be installed! The valve guide must be reemed from 7mm to 8mm. The valves tulip must be ground to the 1.900" diameter(this gains a good .040" margin!), ground to length and turned for chevy keeper grooves and 7mm o.d. tips to use stock followers. The easier scenario here would play favor in weight saving by using a valve with 7mm stem. Cost savings in machine works too. Such as this replacement valve offered by Trick flow for their tfs modular heads.
http://m.summitracing.com/parts/tfs-52900211
This valve is almost a direct fit. Stock valve guide honing may be necessary to open the I.d.
Also needed is a set of offset location head dowls. You know...them things that line the head and gaskets up to the bores! These do-hickies shift the head .050". This allows for the big intake valve clearance to function. All other gasket aspects fall into place just like stock. Intake manifold may need elongated bolt holes...I have not explored this point yet. Cam sprockets can easily be align adjusted through spacers/shims....although I beleive their will be no need. .050" of an inch is less than a 16th. Front cover gasket should have enough material to compensate the .050" shift.
Now most folks will blab out about increased valve shroud. Ok I agree.....the stock valve is over 50% shrouded....25% is cylinder bore wall, 25% swirl dam.(offset head dowls heppens to be an old trick drag racers used to shift the intake valve away from the cylinder walls aiding in un-shrouding the valve) I would agree with anyone about valve shrouding on a normal high approach cylinder head(like 95% of heads available...even them chevys) where the valve angle favors the intake side of the head causing the valve tulip to become an interference. This 360° of valve un-shrouding plays favor to flow. NOT in a modular 2v head were the intake and valve tulip together are in line allowing for a straight shot charge.(no interference) This is why the valve angle favors to the exhaust side and sparkplug placement is on top! Staight shot intake ports! Create 100% in cylinder swirl motion those interference head dream of! Welcome to the nondetonating modulars! (Insert compression ratio here____)
Here is the kicker! Since the pi head has the larger exhaust valve, this topic does not play favor cause head material is missing where the headgasket needs. UNLESS!!!.....the use of fel-pro's permatex headgaskets 9792PT2. These HG allow for serious shift, but crush .050" so build accordingly!
This has been my latest R&D. Since sn95forums loves me so, I figured sharing with my family was only right! Enjoy!!
The pic shows an Chevy Ls 2.020" intake valve modified to 1.900".
A bigger o.d. valve seat must be installed! The valve guide must be reemed from 7mm to 8mm. The valves tulip must be ground to the 1.900" diameter(this gains a good .040" margin!), ground to length and turned for chevy keeper grooves and 7mm o.d. tips to use stock followers. The easier scenario here would play favor in weight saving by using a valve with 7mm stem. Cost savings in machine works too. Such as this replacement valve offered by Trick flow for their tfs modular heads.
http://m.summitracing.com/parts/tfs-52900211
This valve is almost a direct fit. Stock valve guide honing may be necessary to open the I.d.
Also needed is a set of offset location head dowls. You know...them things that line the head and gaskets up to the bores! These do-hickies shift the head .050". This allows for the big intake valve clearance to function. All other gasket aspects fall into place just like stock. Intake manifold may need elongated bolt holes...I have not explored this point yet. Cam sprockets can easily be align adjusted through spacers/shims....although I beleive their will be no need. .050" of an inch is less than a 16th. Front cover gasket should have enough material to compensate the .050" shift.
Now most folks will blab out about increased valve shroud. Ok I agree.....the stock valve is over 50% shrouded....25% is cylinder bore wall, 25% swirl dam.(offset head dowls heppens to be an old trick drag racers used to shift the intake valve away from the cylinder walls aiding in un-shrouding the valve) I would agree with anyone about valve shrouding on a normal high approach cylinder head(like 95% of heads available...even them chevys) where the valve angle favors the intake side of the head causing the valve tulip to become an interference. This 360° of valve un-shrouding plays favor to flow. NOT in a modular 2v head were the intake and valve tulip together are in line allowing for a straight shot charge.(no interference) This is why the valve angle favors to the exhaust side and sparkplug placement is on top! Staight shot intake ports! Create 100% in cylinder swirl motion those interference head dream of! Welcome to the nondetonating modulars! (Insert compression ratio here____)
Here is the kicker! Since the pi head has the larger exhaust valve, this topic does not play favor cause head material is missing where the headgasket needs. UNLESS!!!.....the use of fel-pro's permatex headgaskets 9792PT2. These HG allow for serious shift, but crush .050" so build accordingly!
This has been my latest R&D. Since sn95forums loves me so, I figured sharing with my family was only right! Enjoy!!
