How much do larger valves affect PTV?
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
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From: Pembroke pines FL
How much do larger valves affect PTV? so Im between AI and TEA for porting my 243s, and I think it comes down to piston to valve clearance and which head I want to send in. I have a set of heads that have been milled .030" already and would rather send these in and sell the stock ones if I can. When I checked PTV clearance I got .095" on intake and .145" on exhaust.
I know TEA uses larger valves but the diameter is increased by .040", radius increased by .020", but that extra radius is not pointing straight down, its at a 15° angle so when i do the math(.020 x SIN(15°)) I get .0052", which is what I believe would be the net decrease of PTV clearance from the 2.04" valves. the exhaust is 1.575" vs the stock 1.55 which would result .0026" on the exhaust right.
I just want to confirm that this is right. so if I send in the milled heads I should have .060" clearance on intake and .110" on exhaust if I were to go with TEA and .065" and .115" if I were to go with AI.
Just want conformation that this is correct.
I know TEA uses larger valves but the diameter is increased by .040", radius increased by .020", but that extra radius is not pointing straight down, its at a 15° angle so when i do the math(.020 x SIN(15°)) I get .0052", which is what I believe would be the net decrease of PTV clearance from the 2.04" valves. the exhaust is 1.575" vs the stock 1.55 which would result .0026" on the exhaust right.
I just want to confirm that this is right. so if I send in the milled heads I should have .060" clearance on intake and .110" on exhaust if I were to go with TEA and .065" and .115" if I were to go with AI.
Just want conformation that this is correct.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Where is the extra .025" coming from? that doesent make sense to me unless there is something else changing other than the 2.04" diameter. Is that with the stock cam?
No, that's free drop as measured with the valve pushed out til it hits on a flat surface. I have a set of TEA 243s. I measured and it was around .130" or so when I did it on my workbench with checker springs and a dial indicator on the tip of the valvestem.
Just verified my digital caliper and a straight edge. Looks like it's right around .130" with it milled to 62cc.
Just verified my digital caliper and a straight edge. Looks like it's right around .130" with it milled to 62cc.
Last edited by JakeFusion; Nov 19, 2013 at 04:11 PM.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Was that with the stock gasket or the cometic .040?
The fact that your head were milled is where the extra drop came from. That's about .018-.021 milled. Add to that the extra .005" from the larger valve I was talking about and that adds up to the .025" difference. Was this before u fly cut?
The fact that your head were milled is where the extra drop came from. That's about .018-.021 milled. Add to that the extra .005" from the larger valve I was talking about and that adds up to the .025" difference. Was this before u fly cut?
It's the bare head sitting on my desk. I measured with a straight edge across the bore of the cylinder and measured the distance to the edge of the valve.
Stock free drop is .160" so this is .030" less.
Stock free drop is .160" so this is .030" less.
Valvejob will affect this. Have a valvejob done with the existing valves and they will sink into the head farther offering more PTV BUT by the same token if you have larger valves put in and they go easy on the valvejob depth you could lose even more than you are calculating. This is why everyone chants that you have to measure.
