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GA95gsx

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Discussion starter · #1 ·
I know a 2G head will outflow a 1G head. Question is as far as extremities go, which one will become restrictive first in a high HP application?

For example. Lets take a 6 bolt engine with a 1G head that's been deburred and polished. JMF manifold, Q45 throttle body, GT42R turbo. Puts out 780HP at 30PSI on e85. Throw on a 2G head with the same cams that has the same debur and polish job on the ports and change nothing else. Which head will be able to make the most power?
 
#2 ·
The 2g head does NOT outflow a 1g head at all, and the 2g head will become a restriction first, the 1g has bigger ports, but the 2g has a smoother flow path, thats the difference, so the 2g performs well in its own way and so does the 1g it all depends on what you are looking for and what other mods you have.
 
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#3 ·
Are you trying to build a 780 hp car? Either one depending what you do to it. Consistent flow testing and lots of money. I just port the shit out of a 1g head, but I'm not going for that much power. I would say stock vs stock i like the 2g. However i think both heads stock need some serious help... and a flow bench.
 
#4 ·
Neither head is perfect, thats true. If you wanted to you could take a 1g head and make it act just like a 2g head, and the same is true for the 2g head, you could make it flow just like a 1g head if you wanted to, the 2g head flows different amounts at different valve lift and at different velocities at different valve lift, and thats the difference. Alot of guys are starting to like the 2g head becuase of this.
 
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#5 · (Edited)
My wifes GSX broke a valve (long story). I was actually calling about a turbo and must have mentioned the issue with her car because then the guy at Forced Performance told me he had a mildly ported and rebuilt 2G head from a customer that flaked on paying for the work. So, I put it on her car and was very suprised at the difference it made. It seemed to just make a little more power everywhere. I've heard many horror storys of porting gone bad but FP definately did this one right.

I should mention this was for a GSX with a T28, 3" exhaust, 650's, pushing maybe 320hp. For my setup a mildy ported 2G head was perfect. Great flow while maintaing good velocity too. On the otherhand, a 1G head is likely the better choice for setups with very high air volume. I'm not really sure how much HP a ported 2G head is good for before it becomes overly restrictive.
 
#6 ·
Kiggly is running a mildly ported 2G head and Curt Brown only recommends a 2G head. Get ahold some one of them sense they have actuality done it and can explain why they prefer that setup. AMS and Magnus has both mentioned the same thing.
 
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Discussion starter · #7 ·
dsmusmc said:
Kiggly is running a mildly ported 2G head and Curt Brown only recommends a 2G head. Get ahold some one of them sense they have actuality done it and can explain why they prefer that setup. AMS and Magnus has both mentioned the same thing.
Click to expand...
I've heard the same thing. I'm so convinced of the 2G head I'm selling my fully machined bare 1g head to start over again with a 2g head.
 
#8 ·
I agree with the 2G head > 1G head. There's a reason all the best and fastest guys say they prefer the 2G head, and there is a reason every Evo since the first one has had the small ports.
 
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#9 ·
I find the valve angle of the 2g head the main reason I like it. Honestly, the 1g ports are too big for the street it seems. But hey, anyone seen a sb350's ports? geez those fuckers are huge.
 
#11 ·
Again it just depends on your plans and where you want the power, I own a flowbench and have flowed each of them at one time or another and neither one killed in all areas, they flow DIFFERENT amounts at different valve lifts, however the 1g head does outflow the 2g head ultimately, but there is always more to the story than total flow!
 
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#12 ·
BISHILVR said:
but there is always more to the story than total flow!
Click to expand...
Absolutely!
Going too big can reduce velocity in much of the rpm range reducing the drivability of the car significantly.
Maintaining good velocity helps in several ways:
* The higher the air flow speed, the better fuel atomizes improving the combustion process.
* Higher velocity has a better inertia of the air flow which helps fill the cylinder more and improve the volumetric efficiency.
* Higher velocity improves the combustion chamber swirl and distributes the air/fuel mixture better in the combustion chamber.
 
#13 ·
Within relation to the topic, I like destroked motors. The 2g head accomadates this better. I dont really want to get into specifics, but I am sure bishilvr would know why I like the velocity more. Its not for drivability thats for sure.
 
#14 · (Edited)
4g64fiero said:
Within relation to the topic, I like destroked motors. The 2g head accomadates this better. I dont really want to get into specifics, but I am sure bishilvr would know why I like the velocity more. Its not for drivability thats for sure.
Click to expand...
Well that certainly goes against traditional thinking of "there is no replacement for displacement". This still applies to turbo cars as well. It's a fact that a turbocharged 350ci V8 engine will make A LOT more power than a similiarly prepared 2.0l turbocharged engine.
I would think in most cases you would want to match the head to larger dispacement not the other way around. The exception being a spec race class where displacement is limited. This was a common argument between the 'high reving' 327ci vs the 387ci stroker guys. When it came down to it, the stroker crowd were the ones consistantly putting down the numbers.

Now I'm curious, what would be the reason you prefer a destroked DSM motor?
 
#15 ·
I would Imagine that the destroked motor will have a higher RPM potential. With the velocity of the 2G head it's better suited. Especially if your running a fairly large turbo where you need the flow up top.


Have you guy's ever seen the intake ports on a Cadillac V8 Northstar? massive!
 
#16 · (Edited)
90BLACKAWDTSI said:
I would Imagine that the destroked motor will have a higher RPM potential.
Click to expand...
Ok, if you can make enough HP using rpm to make up for the loss of torque than that 'might' make some sense.
Ultimately, (Torque x Engine speed) / 5,252 = Horsepower
Getting a motor to spin that fast = $$$$ Can it be done? sure look at Formula 1 cars. But you can be sure if one team was allowed to increase displacement beyond the rules the other teams would be screaming fowl. Nascar engines make about the same power. Which do you think costs more?
You could argue that the F1 engine is lighter and you would be correct however, destroking a 4G63 motor to say 1.8l will not make it lighter than a 2.3l one so that would not apply here.

I stand by my statement that it makes more sense to increase the port size to the displacement of the motor. I mean if you are destroking something you are obviously changing the bottom end anyways. Why not make it a stout 2.0 or 2.3 that you can spin?

I have seen this agrument so many times over the years so to the smaller displacement, higher rpm crowd I say, let's just agree to disagree.
 
#17 · (Edited)
gprix1 said:
Ok, if you can make enough HP using rpm to make up for the loss of torque than that 'might' make some sense.
Ultimately, (Torque x Engine speed) / 5,252 = Horsepower
Getting a motor to spin that fast = $$$$ Can it be done? sure look at Formula 1 cars. But you can be sure if one team was allowed to increase displacement beyond the rules the other teams would be screaming fowl. Nascar engines make about the same power. Which do you think costs more?
You could argue that the F1 engine is lighter and you would be correct however, destroking a 4G63 motor to say 1.8l will not make it lighter than a 2.3l one so that would not apply here.

I stand by my statement that it makes more sense to increase the port size to the displacement of the motor. I mean if you are destroking something you are obviously changing the bottom end anyways. Why not make it a stout 2.0 or 2.3 that you can spin?

I have seen this agrument so many times over the years so to the smaller displacement, higher rpm crowd I say, let's just agree to disagree.
Click to expand...
If you can figure out how to keep the stroker bottom end together at 10K RPM let us know!

Bigger Turbo's flow better up top.
Stroker motor's are RPM limited up top due to excessive piston speed.
So it only make's sense that if you run a extremely large turbo that you want a engine that will be able to fully utilize the flow up top.

Personally if I were building a all out drag car that I would want a Engine that will be able to achieve a higher RPM potential than one that will have a better low end torque. Once i am off the line I could care less about torque because now I am at the point that torque has done everything it's going to do and the horsepower is now taking over.

If the turbo has the capability to flow enough air at 10,000 RPM then naturally I would want to match that with a Engine that can turn said 10,000RPM and beyond. A stroker motor would be useless with said turbo.

Remember, Torque get's you off the line. Horsepower keep's you going.
 
#18 ·
A turbo could give a rat’s ass what rpm a motor is spinning. It is flowing x amount of air and the big air pump we call an engine is the resistance it comes up against creating back pressure or “boost”. It doesn’t matter if a 1.0L engine has to pump two times vs. one pump for a 2L for the same amount of air. If the wastegate is having to open to control the boost what more does that turbo want?
And HP is not independent of torque, it is the result of torque x rpm’s (divided by the constant 5252 to bring the result back to a reasonable number). You don’t just need torque to take off, you need it in the upper rpm’s too or you are not making any HP.
The faster a motor spins the more it is affected by pumping losses as well.
From Wikipedia:
“This pumping loss is minimal at low speed, but increases approximately as the square of the speed, until at rated power an engine is using about 20% of total power production to overcome friction and pumping losses.”
Tell you what, you get yourself a 1.5L motor, put a huge turbo on it, and spin it 10,000 rpm’s. Then run it up against a 3L motor running the same exact turbo and only spinning 7,800 rpm’s and see who is making more power. I know where I'm betting my money!
 
#19 ·
I don't think you quite understand the concept of it.
If X turbo has enough flow characteristics to flow on a motor up to 10,000 RPM and you put it on a stroker motor that can only rev at most to maybe 8500 then you are missing out on 1500 or so RPM. Now that may not seem like that much more but when your in a higher gear ie 4th gear 1500RPM is quite a bit of difference.
You have "more" power band.

Why would I want a 1.5L? you do know with the proper head work, springs and retainer's you can spin the stock 4g63 bottom end to right around 10,000.
 
#20 · (Edited)
90BLACKAWDTSI said:
I don't think you quite understand the concept of it.
If X turbo has enough flow characteristics to flow on a motor up to 10,000 RPM and you put it on a stroker motor that can only rev at most to maybe 8500 then you are missing out on 1500 or so RPM. Now that may not seem like that much more but when your in a higher gear ie 4th gear 1500RPM is quite a bit of difference.
You have "more" power band.

Why would I want a 1.5L? you do know with the proper head work, springs and retainer's you can spin the stock 4g63 bottom end to right around 10,000.
Click to expand...
It's not about rpms, the turbo has doesn't care what rpm you are running. It comes down to how much air is being moved through the engine. Now using your own example, and thinking of it in terms of the engine as purely an air pump let's look at the numbers:

10,000 rpms vs 8,500 rpms = 17.6% difference
2.4L vs 2.0L = 20% difference

That is a 3.4% difference in air volume being moved and that's not taking into account the pumping losses at higher rpms.
The powerband will start pulling stronger at a lower rpm on the 2.4L motor so you haven't really changed the width of the "powerband" all that much either.

Let's not even get into engine longevity for a motor spinning 10,000 rpms :eek:
 
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