[Speedstang302]

so bout 300 to the flywheel..not bad for stock heads..what will those twisted wedge heads get me up to..

[1slo5.0]

Originally Posted by Speedstang302 so bout 300 to the flywheel..not bad for stock heads..what will those twisted wedge heads get me up to..

The only way to know for sure is to dyno it.

[Speedstang302]

thats what i thought..only thing theres not one around me for 100miles

[1slo5.0]

Originally Posted by Speedstang302 thats what i thought..only thing theres not one around me for 100miles

I drove over 100 miles to have my engine dynoed. That isn't a big deal. It is well worth the money too.

[ryans88gt]

Originally Posted by Darrell Please give me your definition of valve shrouding because your comment about shrouding doesn't make any sense at all.

Simply put, at low lift the air intake path is partially obstructed by "stuff" in the way. Usually the side and top of the combustion chamber, the exhaust valve, sometimes the piston and cylinder wall contribute too. Given the same combustion chamber design and valve location a 2.02 valve will always be more shrouded than a smaller 1.94 or 1.90 valve. It is going to be closer to the exhaust valve and radii of the combustion chamber. This usually has a large effect on low lift flow and swirl at low lift and thus typically hurts low end power, especially for a street engine that doesn't have a cam profile that quickly accelerates and holds the valve at a high lift region where shrouding is a non-issue. Street engines tend to have valves that spend more time in the shrouded area due to more conservative cam profiles and tend to spend more time at lower rpms where swirl is most important. So in fact a 2.02 valve does care if it is in a street engine or a race engine.

So Darrell, what are the masses of a 2.02 intake valve vs. a 1.90 intake valve? There can be as much as a 10 gram difference in mass or about 10% of the valves total mass. While you may not consider this a significant difference, being accelerated and stopped at over 100 times per second, your valve springs certainly do consider this to be a lot of added burden. You will definitely reach valve float much sooner using the same spring with a 2.02 valve as you do with a 1.90 valve. So just use a 10% heavier spring right? Then you have more valve train stress, heat, and shorter lifetime. May not be important on a race engine, but on a daily driver, I'd rather have 1.90 valves I think.

[1slo5.0]

Originally Posted by ryans88gt Simply put, at low lift the air intake path is partially obstructed by "stuff" in the way. Usually the side and top of the combustion chamber, the exhaust valve, sometimes the piston and cylinder wall contribute too. Given the same combustion chamber design and valve location a 2.02 valve will always be more shrouded than a smaller 1.94 or 1.90 valve. It is going to be closer to the exhaust valve and radii of the combustion chamber. This usually has a large effect on low lift flow and swirl at low lift and thus typically hurts low end power, especially for a street engine that doesn't have a cam profile that quickly accelerates and holds the valve at a high lift region where shrouding is a non-issue. Street engines tend to have valves that spend more time in the shrouded area due to more conservative cam profiles and tend to spend more time at lower rpms where swirl is most important. So in fact a 2.02 valve does care if it is in a street engine or a race engine. So Darrell, what are the masses of a 2.02 intake valve vs. a 1.90 intake valve? There can be as much as a 10 gram difference in mass or about 10% of the valves total mass. While you may not consider this a significant difference, being accelerated and stopped at over 100 times per second, your valve springs certainly do consider this to be a lot of added burden. You will definitely reach valve float much sooner using the same spring with a 2.02 valve as you do with a 1.90 valve. So just use a 10% heavier spring right? Then you have more valve train stress, heat, and shorter lifetime. May not be important on a race engine, but on a daily driver, I'd rather have 1.90 valves I think.

The turbulence and shrouding in low lift areas between a 1.94 valve and a 2.02 valve are minimal if any. I'll do some digging for some flow sheets on a set of Canfield heads I have so I can show you numbers. On a stock head you probably have a point but on a head with a reconfigured chamber like aftermarket heads it isn't an issue with a valve as small as a 2.02. AFR 185 heads outflow the 165s across the board and based on your theory shouldn't because the 185s have a bigger valve. Twisted wedges outflow the AFR 165s across the board and the Twisted Wedge heads use a 2.02 valve. As far as valve spring pressure goes, that is more directly related to cam design. I doubt you will find an engine builder anywhere that will tell you that you need to run a stiffer spring when switching from a 1.94 to a 2.02 valve.

[nolife]

This is just from what I read so I might be wrong but i think I understand the concept.

Bigger valves can cause shrouding if the valve is to close to the cylinder walls, this can be minimized or eliminated with changing the angle allowing the valve to open more towards the center the of the bore instead of parallel to the bore. Exactly what angle is a trade off with other things.

[1slo5.0]

Originally Posted by nolife This is just from what I read so I might be wrong but i think I understand the concept. Bigger valves can cause shrouding if the valve is to close to the cylinder walls, this can be minimized or eliminated with changing the angle allowing the valve to open more towards the center the of the bore instead of parallel to the bore. Exactly what angle is a trade off with other things.

That is exactly it. When you run into major valve shroud issues is when you use a small bore with a large inline valve head such as a 4.030 bore with a 2.15 valve.

[ryans88gt]

Originally Posted by Darrell I'll do some digging for some flow sheets on a set of Canfield heads I have so I can show you numbers. On a stock head you probably have a point but on a head with a reconfigured chamber like aftermarket heads it isn't an issue with a valve as small as a 2.02. AFR 185 heads outflow the 165s across the board and based on your theory shouldn't because the 185s have a bigger valve. Twisted wedges outflow the AFR 165s across the board and the Twisted Wedge heads use a 2.02 valve. As far as valve spring pressure goes, that is more directly related to cam design. I doubt you will find an engine builder anywhere that will tell you that you need to run a stiffer spring when switching from a 1.94 to a 2.02 valve.

Shrouding isn't my theory, it is a result of the laws of fluid dynamics. There are very specific formulas that you can utilize to calculate how far a intake valve has to open before shrouding stops and it directly relates to the diameter of the valve. 185s out perform 165s due to 20cc larger port volume and in terms of power 165s make more low end, if they didn't AFR wouldn't make them anymore. Comparing AFR165s and trick flows is like comparing apples to potatoes. Power numbers are more important than flow numbers. A few years back an engine builder showed me dyno numbers from a small block with edlebrock performer heads with the 1.90 and 2.02 valve and low rpm power was down and didn't catch up until above 5000 rpms as I recall. The larger valve head only made a few extra hp until over 6000 rpms.
Don't fool yourself about valve mass not being an issue, valve train mass is directly proportional to the amount of spring pressure required. People spend crazy money on titanium locks and keepers just to lose 5 grams from each valve tip. Comp cams has gone to the trouble of making behive valve springs that reduce the amount of spring weight at the valve tip by reducing the diameter of the keeper and top spring coil. It has been very clearly demonstrated that this small weight savings allows for lighter spring pressures and more power as well as an additional 500 rpm cushion before valve float.
Anyway, my point is simply slapping a 2.02 valve in there doesn't necessarily make a head better for a given application. Using the smallest valve that will not adversely affect cylinder pumping is the ticket. Trick flows are pretty nice heads, but more so because the intake valve is rotated more over the bore center to provide more efficient pumping and also resulting in a shorter intake runner.

[1slo5.0]

Originally Posted by ryans88gt Shrouding isn't my theory, it is a result of the laws of fluid dynamics. There are very specific formulas that you can utilize to calculate how far a intake valve has to open before shrouding stops and it directly relates to the diameter of the valve. 185s out perform 165s due to 20cc larger port volume and in terms of power 165s make more low end, if they didn't AFR wouldn't make them anymore. Comparing AFR165s and trick flows is like comparing apples to potatoes. Power numbers are more important than flow numbers. A few years back an engine builder showed me dyno numbers from a small block with edlebrock performer heads with the 1.90 and 2.02 valve and low rpm power was down and didn't catch up until above 5000 rpms as I recall. The larger valve head only made a few extra hp until over 6000 rpms. Don't fool yourself about valve mass not being an issue, valve train mass is directly proportional to the amount of spring pressure required. People spend crazy money on titanium locks and keepers just to lose 5 grams from each valve tip. Comp cams has gone to the trouble of making behive valve springs that reduce the amount of spring weight at the valve tip by reducing the diameter of the keeper and top spring coil. It has been very clearly demonstrated that this small weight savings allows for lighter spring pressures and more power as well as an additional 500 rpm cushion before valve float. Anyway, my point is simply slapping a 2.02 valve in there doesn't necessarily make a head better for a given application. Using the smallest valve that will not adversely affect cylinder pumping is the ticket. Trick flows are pretty nice heads, but more so because the intake valve is rotated more over the bore center to provide more efficient pumping and also resulting in a shorter intake runner.

Ok, what is this specific formula? If there was such a shrouding problem at low lifts it would affect the flow numbers. More airflow equals more power, period. FYI, people don't run lightweight valve train parts so they can run less spring tension. Lighter valve train parts are used to reduce weight so the valve springs live longer and to accelerate the valve train faster. I have titainium valves, retainers and locks and I still have valve spring pressure that is 680psi open. I guess I should have skipped all of the R&D that I've done and just asked you since you have an answer for everything. The difference between me and you is I've done and worked with the things I talk about where as you are just a know it all that is spouting off things you either read in magazines or theories you invent on your own. Its real insulting to a guy that spends mass amounts of time and money on flow benches and dynos. Maybe I should try that sometime.