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1g head vs 2g head

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turbo tim1

10+ Year Contributor
163
5
Sep 16, 2010
Pine lake, AB_Canada
I have read that the 2g cylinder head flows more air than the 1g head despite the larger ports of the 1g head.

If both heads were ported which one would flow more.

I have a mix of dsm parts, enough to throw an engine together so I was thinking of building a project Frankenstein, a 4g64 block with 2g pistons 1g rods and possibly a 2g ported head, depending on which head flows more.:hellyeah:
 
good point! LOL
 
Plus I don't know what you would fill the runners with that thick and precise and not be afraid of it chunking off eventually. I don't think 2g head ports can be opened up enough to be 1g-sized either, at least not safely or optimally.
 
Just that I would throw out there that I'm getting my 2g head port match on the intake side with a aftermarket intake manifold so would my head be the same as a 1g head?

It depends on how it gets ported. The 2g head leads into the valves better. The port design is much better on the 2g.

If you look at a 1g head there is a sharp turn before the valves. The 2g has a much better smooth transition into the valves.

I run a 2g head on a 6 bolt block and would never ever second guess it.
 
on second thought, filling the runner could make more power. Depending on the runner shape, filling the runner might improve the taper in the runner... 7* is usually optimum..

runners are usually filled with a 2 part epoxy.. the stuff i use is for pools, but i think moroso makes some.. basically fill it up to much, then cut it back out to the shape you want.

It depends on how it gets ported. The 2g head leads into the valves better. The port design is much better on the 2g.

If you look at a 1g head there is a sharp turn before the valves. The 2g has a much better smooth transition into the valves.

I run a 2g head on a 6 bolt block and would never ever second guess it.

The taller short side radious(smoother transition to the valve seat) doesnt mean the head will flow better eveywhere. The 2g head might flow better at .400 lift than the 1g, but the 1g might flow better at .100 of lift. Just speculation because i have know flow numbers, but its somthing to think about.
 
On a N/A motor, head is super important,but most flow figures are taken at a constant vacuum right?on these turbo motors airflow is under vacuum at low power levels but as soon as boost come on, airflow is forced into engine, I would think the larger the port opening the more air into motor under pressure the more power is fueled correctly, velocity is now a part of the boost pressure?that's why we can up our boost and produce more power thru the same port,I know port shape is important but is it as important as a N/A port where you cant change airflow without cam, carb, intake maniflod etc ,but we can with a turn of a screw or spring
 
One thing people overlook when discussing the 1g/2g heads for our cars is the fact that they are tested at a way lower pressure differential than most of us actually have in our engines. As a gas is compressed, the more it acts as a fluid. Fluids aren't very picky about velocity of flow, and angle changes, unlike a low pressure gas. For more liquid flow, a larger orifice is the best answer. Depending on the amount of boost you are running, a better designed small port(2g), or a huge hogged out port(1g) may work better. Air compressed to 30+ psi has more of the flow characteristics of a liquid, than a gas at STP.
 
On a N/A motor, head is super important,but most flow figures are taken at a constant vacuum right?on these turbo motors airflow is under vacuum at low power levels but as soon as boost come on, airflow is forced into engine, I would think the larger the port opening the more air into motor under pressure the more power is fueled correctly, velocity is now a part of the boost pressure?that's why we can up our boost and produce more power thru the same port,I know port shape is important but is it as important as a N/A port where you cant change airflow without cam, carb, intake maniflod etc ,but we can with a turn of a screw or spring

I would argue that port work is as, or more important, in a boosted application.. You shouldnt look at it as vacuum, but instead as a lower pressure in the cylinder which is what causes air to flow into it. In a boosted engine you have the same thing, But the pressure in the exhaust is also elevated, which causes the pressure in the cylinder after the exhaust valve closes to be higher as well.. for instance, In an N/A engine you have 14.7 psi (atmospheric) and a lesser pressure in the cylinder when the piston is moving down, lets say theres 10.7 psi in the cylinder. This causes air to flow into the engine, but there is also 14.7 psi on the exhaust side. This is important to remember.. Say you have the same engine only boosted at say 20 psi gauge (34.7 psi absolute) now the pressure in the cylinder is also elevated, so now theres 24.7 left in the cylinder. This is where a good turbo comes into play. on a typical setup you have 2x more exhaust pressure then intake pressure, so now your exhaust pressure is 69.4psi!! A more efficent turbo system could drop this pressure to 34.7 if it can reach a 1:1 boost to drive pressure ratio. The system works the same, the air is just more dense. so the air isnt moving faster, well not in most cases anyway. This is really hard for me to explain, so if that was more confusing then anything, i'm sorry.

One thing people overlook when discussing the 1g/2g heads for our cars is the fact that they are tested at a way lower pressure differential than most of us actually have in our engines. As a gas is compressed, the more it acts as a fluid. Fluids aren't very picky about velocity of flow, and angle changes, unlike a low pressure gas. For more liquid flow, a larger orifice is the best answer. Depending on the amount of boost you are running, a better designed small port(2g), or a huge hogged out port(1g) may work better. Air compressed to 30+ psi has more of the flow characteristics of a liquid, than a gas at STP.

I would say your correct that the air in a boosted engine is more dense, but i would argue that a more dense fluid takes more effort to travel over inperfection, and poor designs, than a less dense fluid would. like to get 30 cfm of water thourgh a 1" pipe would take more effort than 30 cfm of air.. As far as a larger orfice being better, i agree, but the restriction isnt the runner, its the valve. The smaller runner could "channel" the fluid around the valve better than the larger runner... Theres also the arguement Paul brought up, about the inertia of the pulse. The faster moving fluid takes more energy to stop it than the slower moving fluid, so as the port reaches peak velocity and the valve begins to close, the airs inertia can help it "flow" around the valve.
 
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I would argue that port work is as, or more important, in a boosted application.. You shouldnt look at it as vacuum, but instead as a lower pressure in the cylinder which is what causes air to flow into it. In a boosted engine you have the same thing, But the pressure in the exhaust is also elevated, which causes the pressure in the cylinder after the exhaust valve closes to be higher as well.. for instance, In an N/A engine you have 14.7 psi (atmospheric) and a lesser pressure in the cylinder when the piston is moving down, lets say theres 10.7 psi in the cylinder. This causes air to flow into the engine, but there is also 14.7 psi on the exhaust side. This is important to remember.. Say you have the same engine only boosted at say 20 psi gauge (34.7 psi absolute) now the pressure in the cylinder is also elevated, so now theres 24.7 left in the cylinder. This is where a good turbo comes into play. on a typical setup you have 2x more exhaust pressure then intake pressure, so now your exhaust pressure is 69.4psi!! A more efficent turbo system could drop this pressure to 34.7 if it can reach a 1:1 boost to drive pressure ratio. The system works the same, the air is just more dense. so the air isnt moving faster, well not in most cases anyway. This is really hard for me to explain, so if that was more confusing then anything, i'm sorry.



I would say your correct that the air in a boosted engine is more dense, but i would argue that a more dense fluid takes more effort to travel over inperfection, and poor designs, than a less dense fluid would. like to get 30 cfm of water thourgh a 1" pipe would take more effort than 30 cfm of air.. As far as a larger orfice being better, i agree, but the restriction isnt the runner, its the valve. The smaller runner could "channel" the fluid around the valve better than the larger runner... Theres also the arguement Paul brought up, about the inertia of the pulse. The faster moving fluid takes more energy to stop it than the slower moving fluid, so as the port reaches peak velocity and the valve begins to close, the airs inertia can help it "flow" around the valve.

Fluids don't pulse with compression waves as a low pressure gas does. Fluids also don't "channel", or create pressure eddys around an obstruction. Fluids are incompressible. The more a gas is compressed, the more it acts as an incompressible fluid, hence, any of the compression related anomalies of a low pressure gas are greatly reduced as the pressure of the gas increases.
 
A gas is a fluid, so is a liquid. Compressed air is far away from becoming anywhere near a liquid or acting like it. I would say that designing anything that flows a fluid matters more when the fluid is more dense, no matter if it's being drawn through (n/a) or being forced through (boost.) Velocity aids in flow, and I don't think the limits of the 2g head will ever be seen.
 
Liquid doesn't eddy like a gas does? Just because liquid cannot be compressed doesn't mean it doesn't have pressure to it or doesn't create eddys around obstructions. Gas and liquids are both fluids, they have similar dynamics, with the biggest difference being liquids cannot be compressed. Any moving fluid is done so by pressure.
 
Liquid doesn't eddy like a gas does? Just because liquid cannot be compressed doesn't mean it doesn't have pressure to it or doesn't create eddys around obstructions. Gas and liquids are both fluids, they have similar dynamics, with the biggest difference being liquids cannot be compressed. Any moving fluid is done so by pressure.

A liquid does eddy, it doesn't form compression waves as a result. Have you ever taken an actual fluid dynamics class?
 
Liquids are essentially incompressible, but it's not impossible, in small amounts. We have yet to come close to breaking the speed of sound or even come close to have objects moving that fast through liquid. So the guess to how liquids operate compared to gases are just a guess to you or me. And taking a class doesn't make one an expert. One doesn't need to go to school to learn things, reading accomplishes the same thing...
 
I'm not sure the differences, and I'm sure there is something to be learned by studying how the air acts under pressure as opposed to less dense air. I think that comparing compressed air to a liquid, in this situation, isn't a valid argument.
 
I know the pros and cons of both heads, but everyone seems to have their personal opinion, but I have yet to see someone really compare both heads with real evidence like dyno graphs... Since I have both the 1g head and the 2g head with all their other components like manifold, coolant thermostat, water pipe, ignition coil, etc... when I finish my project, I'm going to dyno both the 1g head and the 2g head on my 2g gst...
 
Not trying to resurrect an old thread, but there was never an answer to the flow bench test on head comparison.z I'm cuerious to how the flow bench results came out.. Did anyone ever get the results?
 
Yeah no evidence to support any claims, I see that they are both good, depending on what you use them for, but i haven't seen any comparisons like for Example: 1g head does ______ and is good for ______. While the 2g head is better for _____ and can do ______?

I read the whole thread and didn't really see comparisons in real world applications.
I too have both heads, and currently run a straight 6bolt long block, so i am curious.
 
There are no numbers because the power an engine makes is based on a total package. For example, if we only swapped the head we may gain power, but a different intake manifold may lose the power gained from the head. If I was starting from scratch I would use the 2g head based on my S/S experience. Too many people focus on peak numbers and not the total power curve.
 
Curt brown says...", I highly recommend the 2G head for 90% of#us who want#a better usable powerband.For goals of over 800whp and 160mph in the 1/4 mile stick with the 1G head."
 
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