My porsche 944 S2 16 valve turbo project
09-16-2013, 11:02 PM
#61
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I'm going to throw my thoughts in here on this, as well. To answer Chris' "does it make up" question, displacement was a secondary question to me relative to valve area. A few examples of produciton engines when I was at Ford were the 4.6L and 5.4L engines. They made very, very close to the same power with the same heads, be they 2V, 3V, or 4V. The differences could be accounted for with induction and exhaust losses, for the most part.
But it all boils down to somethign called "Z-Factor" which is similar to the average port velocity during an entire intake event divded by the speed of sound. And the port doesn't care what is below it. One of the first rules of thumb I'd use is 1#/min of airflow is equal to 10 horsepower. That's rough. More clarity is ISAC - indicated specific air consumption. Again, units are pounds of airflow (per horsepower-hour).
So what that all means is that you have roughly the same horsepower potential with a 3.0L as a 2.7L with the same head. It just happens at a different RPM point. This is very rough, there are a great many other factors that come into play - cam events, intake and exhaust tuning, and internal friction.
I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.
What it boils down to in my mind is that with a smaller bore, you are going to be more robust to detonation, and can run a higher compression ratio. Yes, your friction will go up a little, but in my mind it is a worthwhile tradeoff.
So if I had my druthers, moving from a 2.5L to a 3.0L, in this specific case, I'd rather do it ALL with stroke (or a 2.7/2.8 if doing one, but not the other). You need the same valve area to do it, regardless. But in doing it with bore, you are going to run into mechanical issues trying to hit an RPM point before you run out of airflow. I'd rather run out of airflow before oiling capability of valve float.
Agree with Chris on the cylinder pressure, but countering that is the dwell. Again, when you get the piston further from TDC more quickly, you'll be less likely to detonate. You have a more favorable (i.e. smaller) surface area/volume ratio.
But it all boils down to somethign called "Z-Factor" which is similar to the average port velocity during an entire intake event divded by the speed of sound. And the port doesn't care what is below it. One of the first rules of thumb I'd use is 1#/min of airflow is equal to 10 horsepower. That's rough. More clarity is ISAC - indicated specific air consumption. Again, units are pounds of airflow (per horsepower-hour).
So what that all means is that you have roughly the same horsepower potential with a 3.0L as a 2.7L with the same head. It just happens at a different RPM point. This is very rough, there are a great many other factors that come into play - cam events, intake and exhaust tuning, and internal friction.
I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.
What it boils down to in my mind is that with a smaller bore, you are going to be more robust to detonation, and can run a higher compression ratio. Yes, your friction will go up a little, but in my mind it is a worthwhile tradeoff.
So if I had my druthers, moving from a 2.5L to a 3.0L, in this specific case, I'd rather do it ALL with stroke (or a 2.7/2.8 if doing one, but not the other). You need the same valve area to do it, regardless. But in doing it with bore, you are going to run into mechanical issues trying to hit an RPM point before you run out of airflow. I'd rather run out of airflow before oiling capability of valve float.
Agree with Chris on the cylinder pressure, but countering that is the dwell. Again, when you get the piston further from TDC more quickly, you'll be less likely to detonate. You have a more favorable (i.e. smaller) surface area/volume ratio.
09-17-2013, 06:21 AM
#62
Nordschleife Master
09-17-2013, 08:35 AM
#63
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So what that all means is that you have roughly the same horsepower potential with a 3.0L as a 2.7L with the same head. It just happens at a different RPM point. This is very rough, there are a great many other factors that come into play - cam events, intake and exhaust tuning, and internal friction.
Do you mean at the same psi?
I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.
Does going up a mm or 2 in valve size make a huge amount of difference? As from what I've seen of our heads we can't go a whole lot bigger without some incursion into the pocket of the head. Seems like you could maybe squeeze 50mm Intake in a pinch. 49mm more likely. What's stock, 46-47mm?
Do you mean at the same psi?
I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.
Does going up a mm or 2 in valve size make a huge amount of difference? As from what I've seen of our heads we can't go a whole lot bigger without some incursion into the pocket of the head. Seems like you could maybe squeeze 50mm Intake in a pinch. 49mm more likely. What's stock, 46-47mm?
09-17-2013, 08:49 AM
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09-17-2013, 08:51 AM
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Big Wallet...who has one of them anymore???
09-17-2013, 08:55 AM
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09-17-2013, 08:57 AM
#68
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09-17-2013, 09:06 AM
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Back to being serious for a moment - the interesting problem that the 'big power' motors are running in to is block flex. I believe that the block starts twisting at power levels above 500 - the 3.0 is stiffer than the 2.5. This is one of the big reasons that we see head gasket failures over time. many people with high power engines have adopted a regular head gasket replacement strategy to replace the deteriorating head gasket before it fails.
Fretting corrosion is the proper name for the problem and I have seen it in a lot of high power engine.
One other thought....its interesting that everybody likes to talk about horsepower....I like to think in torque, that really tells me how well the system is working. Big HP is just the ability to make good torque at high RPM!
Fretting corrosion is the proper name for the problem and I have seen it in a lot of high power engine.
One other thought....its interesting that everybody likes to talk about horsepower....I like to think in torque, that really tells me how well the system is working. Big HP is just the ability to make good torque at high RPM!
09-17-2013, 10:50 AM
#70
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Airflow is directly proportional to port area. In velocity. So when I lay out a framework for an engine, I look at RPM when sizing valves. If you have a poor flowing port, that'll change, but taking rough cuts, I look at RPM. So if you run out of breath at 6000 RPM, and you want to run 6500 RPM, you need 8% more port area.
Port area's relationship to valve area is dependent on the stem, seat, and taper. ON a big valve 2V production engine, you may have an 8mm stem, a 3.5mm seat, and a 10% taper. And this is area, not diameter. Valve OD - seat width*2, calculate area, then subtract area of the stem, then finally subtract the taper.
Then from there, you'd add the 8%, then add back the taper, then the stem area, and calculate the OD, then finally add the seat area back. Helps to use a spreadsheet for all of this.
And all of my comments were specific to 4V engines. I know people can make good power with 2V's, but I like 4V's. The spark plug is in the right place, which is how you can run typically 0.7-0.8 points higher CR with the same fuel. And of course, both the shape of the chamber (think "Hemi"), and the surface area/volume ratio are superior. If you'd rather go for mid range torque and give up high end horsepower, you can do that with smaller valves. That is what Nissan was doing with its 5.4L truck engine. Tiny valves for such a big bore, though I havne't looked at it in years. And of course, with 4V's, the valves are lighter, and don't have to lift as much to give peak flow, all of which enables less extreme cam events.
I think stock 2V's are about 47mm, maybe the 89 2.7 NA's were 49mm? But the 37mm 4V (S, S2) is roughly equivalent to a 52mm in terms of valve area (not port - keeping it simple), and the 39mm (968) is roughly equivalent to a 55mm. Getting a single intake valve in there that big won't happen with this bore size. Which again gets back to why I prefer 4V's.
All that said, I'm giving my opinion on things. People make GOOD power wtih 2V's, I saw Chris' thread. I just like the 4V architecture much better for reasons mentioned. That said, and I think Chris touched on this. Availability is a big factor. It isn't like one can just go down to their local parts store and order up a 4V head with 33mm intake valves, and appropriately sized ports. It would take a LOT of work to make that. Oh yeah, and the intake, and packaging, and exhaust, etc....... The higher CR you can run would make up for a lot of it, though maybe not all. If I were doing a 3.0L turbo, I'd rather run an S2 (small 4V head) than an 89 2V (big 2V head). But I'm an engineer, and we do stupid stuff because we're super Type-A.
Port area's relationship to valve area is dependent on the stem, seat, and taper. ON a big valve 2V production engine, you may have an 8mm stem, a 3.5mm seat, and a 10% taper. And this is area, not diameter. Valve OD - seat width*2, calculate area, then subtract area of the stem, then finally subtract the taper.
Then from there, you'd add the 8%, then add back the taper, then the stem area, and calculate the OD, then finally add the seat area back. Helps to use a spreadsheet for all of this.
And all of my comments were specific to 4V engines. I know people can make good power with 2V's, but I like 4V's. The spark plug is in the right place, which is how you can run typically 0.7-0.8 points higher CR with the same fuel. And of course, both the shape of the chamber (think "Hemi"), and the surface area/volume ratio are superior. If you'd rather go for mid range torque and give up high end horsepower, you can do that with smaller valves. That is what Nissan was doing with its 5.4L truck engine. Tiny valves for such a big bore, though I havne't looked at it in years. And of course, with 4V's, the valves are lighter, and don't have to lift as much to give peak flow, all of which enables less extreme cam events.
I think stock 2V's are about 47mm, maybe the 89 2.7 NA's were 49mm? But the 37mm 4V (S, S2) is roughly equivalent to a 52mm in terms of valve area (not port - keeping it simple), and the 39mm (968) is roughly equivalent to a 55mm. Getting a single intake valve in there that big won't happen with this bore size. Which again gets back to why I prefer 4V's.
All that said, I'm giving my opinion on things. People make GOOD power wtih 2V's, I saw Chris' thread. I just like the 4V architecture much better for reasons mentioned. That said, and I think Chris touched on this. Availability is a big factor. It isn't like one can just go down to their local parts store and order up a 4V head with 33mm intake valves, and appropriately sized ports. It would take a LOT of work to make that. Oh yeah, and the intake, and packaging, and exhaust, etc....... The higher CR you can run would make up for a lot of it, though maybe not all. If I were doing a 3.0L turbo, I'd rather run an S2 (small 4V head) than an 89 2V (big 2V head). But I'm an engineer, and we do stupid stuff because we're super Type-A.
09-17-2013, 11:22 AM
#71
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Airflow is directly proportional to port area. In velocity. So when I lay out a framework for an engine, I look at RPM when sizing valves. If you have a poor flowing port, that'll change, but taking rough cuts, I look at RPM. So if you run out of breath at 6000 RPM, and you want to run 6500 RPM, you need 8% more port area.
Port area's relationship to valve area is dependent on the stem, seat, and taper. ON a big valve 2V production engine, you may have an 8mm stem, a 3.5mm seat, and a 10% taper. And this is area, not diameter. Valve OD - seat width*2, calculate area, then subtract area of the stem, then finally subtract the taper.
Then from there, you'd add the 8%, then add back the taper, then the stem area, and calculate the OD, then finally add the seat area back. Helps to use a spreadsheet for all of this.
And all of my comments were specific to 4V engines. I know people can make good power with 2V's, but I like 4V's. The spark plug is in the right place, which is how you can run typically 0.7-0.8 points higher CR with the same fuel. And of course, both the shape of the chamber (think "Hemi"), and the surface area/volume ratio are superior. If you'd rather go for mid range torque and give up high end horsepower, you can do that with smaller valves. That is what Nissan was doing with its 5.4L truck engine. Tiny valves for such a big bore, though I havne't looked at it in years. And of course, with 4V's, the valves are lighter, and don't have to lift as much to give peak flow, all of which enables less extreme cam events.
I think stock 2V's are about 47mm, maybe the 89 2.7 NA's were 49mm? But the 37mm 4V (S, S2) is roughly equivalent to a 52mm in terms of valve area (not port - keeping it simple), and the 39mm (968) is roughly equivalent to a 55mm. Getting a single intake valve in there that big won't happen with this bore size. Which again gets back to why I prefer 4V's.
All that said, I'm giving my opinion on things. People make GOOD power wtih 2V's, I saw Chris' thread. I just like the 4V architecture much better for reasons mentioned. That said, and I think Chris touched on this. Availability is a big factor. It isn't like one can just go down to their local parts store and order up a 4V head with 33mm intake valves, and appropriately sized ports. It would take a LOT of work to make that. Oh yeah, and the intake, and packaging, and exhaust, etc....... The higher CR you can run would make up for a lot of it, though maybe not all. If I were doing a 3.0L turbo, I'd rather run an S2 (small 4V head) than an 89 2V (big 2V head). But I'm an engineer, and we do stupid stuff because we're super Type-A.
Port area's relationship to valve area is dependent on the stem, seat, and taper. ON a big valve 2V production engine, you may have an 8mm stem, a 3.5mm seat, and a 10% taper. And this is area, not diameter. Valve OD - seat width*2, calculate area, then subtract area of the stem, then finally subtract the taper.
Then from there, you'd add the 8%, then add back the taper, then the stem area, and calculate the OD, then finally add the seat area back. Helps to use a spreadsheet for all of this.
And all of my comments were specific to 4V engines. I know people can make good power with 2V's, but I like 4V's. The spark plug is in the right place, which is how you can run typically 0.7-0.8 points higher CR with the same fuel. And of course, both the shape of the chamber (think "Hemi"), and the surface area/volume ratio are superior. If you'd rather go for mid range torque and give up high end horsepower, you can do that with smaller valves. That is what Nissan was doing with its 5.4L truck engine. Tiny valves for such a big bore, though I havne't looked at it in years. And of course, with 4V's, the valves are lighter, and don't have to lift as much to give peak flow, all of which enables less extreme cam events.
I think stock 2V's are about 47mm, maybe the 89 2.7 NA's were 49mm? But the 37mm 4V (S, S2) is roughly equivalent to a 52mm in terms of valve area (not port - keeping it simple), and the 39mm (968) is roughly equivalent to a 55mm. Getting a single intake valve in there that big won't happen with this bore size. Which again gets back to why I prefer 4V's.
All that said, I'm giving my opinion on things. People make GOOD power wtih 2V's, I saw Chris' thread. I just like the 4V architecture much better for reasons mentioned. That said, and I think Chris touched on this. Availability is a big factor. It isn't like one can just go down to their local parts store and order up a 4V head with 33mm intake valves, and appropriately sized ports. It would take a LOT of work to make that. Oh yeah, and the intake, and packaging, and exhaust, etc....... The higher CR you can run would make up for a lot of it, though maybe not all. If I were doing a 3.0L turbo, I'd rather run an S2 (small 4V head) than an 89 2V (big 2V head). But I'm an engineer, and we do stupid stuff because we're super Type-A.
09-17-2013, 11:53 AM
#73
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09-17-2013, 12:08 PM
#74
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so you have spent $6 to $7k more on hard parts...now you need to look at engine management. the 2v set up has lots of options, 4v not so much. Full stand alone can go from $2k to $5k depending on what brand and how much work you want to do your self.
looks like $10k is your ballpark answer!
09-17-2013, 12:22 PM
#75
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You can make 350-400 rwhp on an 8v with stock intake and exhaust manifolds. If you go with the SFR intake and exhaust manifolds (needed to fit the 16v on a turbo) that alone will cost you $4-5K. for a street 16v you can get away with the stock valves and springs - but for serious use you need to go with a higher temp alloy and stiffer springs...there goes another couple of $k. New pistons to get to the right compression ratio...another $1k burned.
so you have spent $6 to $7k more on hard parts...now you need to look at engine management. the 2v set up has lots of options, 4v not so much. Full stand alone can go from $2k to $5k depending on what brand and how much work you want to do your self.
looks like $10k is your ballpark answer!
so you have spent $6 to $7k more on hard parts...now you need to look at engine management. the 2v set up has lots of options, 4v not so much. Full stand alone can go from $2k to $5k depending on what brand and how much work you want to do your self.
looks like $10k is your ballpark answer!