Which has more Piston to Valve clearance.. 15° or 13.5° heads?
#1
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I'm not sure that I am thinking about heads correctly. Does a decreased valve angle increase or decrease the available Piston to Valve clearance? i.e. does a 13.5° valve angle have more or less Piston to Valve clearance than a 15° valve angle? Assuming the valves are the same size.
#2
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If the chambers are the same volume, I would say the flatter valve angle would afford more clearance.
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Ok. That is what I thought. I assume that larger valves cut into that extra P2V? Since TFS is 13.5° with 2.02"/1.575" valves, the P2V is back to stock, or really close to stock? I think I read somewhere that TFS heads give you .006" more Piston to Valve, or enough to bump compression by .1.
#5
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All depends on the head. With a shallower valve angle you gain PTV clearance
But you could have a 15* head with more PTV that a 12* on the same valves depending on the valve drop
But you could have a 15* head with more PTV that a 12* on the same valves depending on the valve drop
#7
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Shrouding is in relation to how close the valve is to the cylinder wall. The angle doesn't change it's relative location to the cylinder wall, it changes the valve's angle in relation to the deck of the engine. The more straight up the valve is (lower angle number) the more the valve can go down before the edge of it will tap the piston. You're likely seeing the increase in flow because the better angle valve has a port with more of a straight shot to the valve, not because shrouding was down.
It's not just valve size. Some heads offer more valve drop alone. Then angles and valve sizes also come into play.
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The guys are correct. When TFS rolls the valves, they roll them upward to increase P to V. The 255 LS3's for instance have .040 more valve drop than standard...meaning you could cut the head .040 and still have the same clearance as a stock LS3 head.
Last edited by Summitracing; 12-22-2018 at 03:08 PM.
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Usually .030 is about the limit before requiring modifications to get an intake manifold to fit. Generally we use .060 intake and .090 exhaust as our minimums, but it would really be dependent more on what cam you're running. As an example, our Pro LS Stage 4 SUM-8709 has .061 intake and .091 exhaust clearance. This was with .045 piston to head clearance and .128 valve drop.
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Usually .030 is about the limit before requiring modifications to get an intake manifold to fit. Generally we use .060 intake and .090 exhaust as our minimums, but it would really be dependent more on what cam you're running. As an example, our Pro LS Stage 4 SUM-8709 has .061 intake and .091 exhaust clearance. This was with .045 piston to head clearance and .128 valve drop.
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So obviously the valves are not open .100 during overlap but it's just a number for easy understanding.
Valve drop is measured by having the valve all the way in the seat and seeing how far it can go down before contacting the deck. However the best way to do it is to do it with the cylinder head installed and measure the drop from the valve fully seated to how far it can go down before hitting the piston. Since LS motors have the pistons sticking up out of the hole a little you lose a little of that depth, however you also have a head gasket in there that adds to it. So you have to calculate all of that to get the true number that YOU have. But to compare heads to each other the advertised drop to the deck is fine. Gives you what you need to know to compare heads.
Also summit stated the stock LS head and the TFS have the same .157 intake drop so no you can't mill the TFS any further than the stock LS head before running into problems, since the valve drop is the same.
For several other reasons you couldn't cut the heads that far anyway
You can cut the heads on the intake plane to make them match up to the intake better, that's the more common route. But you can cut anything. The cutting makes the angle line up but as you remove material you can only go so far because if you go too far the intake wont be wide enough to reach both sides and make full contact so it's a delicate dance there.
Last edited by 00pooterSS; 12-21-2018 at 11:33 AM.
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So, unless I want to spend a lot of extra money, removing .030 from the head is the max. The price of TFS 215s over AI 226s is starting to become not worth it, since I won't be able to get more than 11.1 compression, and I won't want a cam larger than low-mid 230s duration.
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So, unless I want to spend a lot of extra money, removing .030 from the head is the max. The price of TFS 215s over AI 226s is starting to become not worth it, since I won't be able to get more than 11.1 compression, and I won't want a cam larger than low-mid 230s duration.
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There are more benefits. The TFS has a better valve angle, thicker decks, a higher ceiling/hp potential than ported OE castings if you want to compare them full out. I would think the better valve angle would show in the valve drop. I find it odd the TFS and the OE head have the same valve drop. I wonder if summit can confirm that and make sure it wasn't a typo.
I think he just means he wants to stay around 230's cause that's the size he wants
I think he just means he wants to stay around 230's cause that's the size he wants
Last edited by Summitracing; 12-21-2018 at 02:26 PM.
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It should also be said that Any factory head that’s cnc’d With bigger 2.040 valves will see a similar reduction from its original valve diameter so valve drop could go to as little as .105 with some of the smaller chambered big valve heads . Smart money is on the 220’s.