Which Cylinder head?

**JET** · 03-11-2007

At 400 hp I am guessing it will be a toss up between which head to go with (on a DD dyno). The 2g is probably going to need some work at that point where the 1g still has more in it stock. Either one will work

Just start working your way up and see where you end up. I remember a time when all I wanted was 350 hp, it just keeps going up the more you get! I am to the point where I think I have enough though, it is pretty nutty on the street.

Andrew7dg · 03-11-2007

I like this, it is back to the basics of engine building

I just have a question about this

"A higher compression engine is going to have a higher pressure exhaust charge, which should facilitate earlier spool all things being equal."

Does this mean that there is more exhaust given off on a higher compression engine which would give more spool to the turbo right? Then a higher compression engine would be burning the fuel at a more efficient rate (assuming that more exhaust means better fuel burn because of expantion) then a lower compression because the same amount of fuel would be entering both engine at the correct fuel ratio. Would this be safe to assume then that a compression of 8:5 would give me better MPG then 7:8 because 8:5 would be getting more power per fire?
I am guessing then it is only when the turbo spools up adding air pressure to the 7:8 it will even out. However the higher compression wouldn't need as much air pressure when the turbo kicks in and thats why it would take off the line faster.

O wow, it just clicked in my head

Wait then this puts the theory of JETs (sorry for picking on you) invalid.

"The reason the 2g's have more HP stock is that they run more boost stock. A 1g at the same psi makes more HP, mostly because of the 2g BOV and small T25."

How would the 1g make more horse power if both cars are running the same PSI. In theory the 2g should be making more HP because of the compression ratio.

This could go into turbo efficiency

if a 1g and a 2g were equal (exept for the compression) with the same turbo, 14b the 2g should be kicking the 1g butt. This could explain why the 14b is a popular upgrade for a 2g.

This then could go into octane ratings because fuel does have a point where it starts to detonate or knock. The highest octane would be 91-94 at the pump but if I switch over to E85 with higher compression that has a 108 octane I should be able to run more boost then running on the 91-94.

**JET** · 03-11-2007

Quote:

Originally Posted by Andrew7dg

Wait then this puts the theory of JETs (sorry for picking on you) invalid.

"The reason the 2g's have more HP stock is that they run more boost stock. A 1g at the same psi makes more HP, mostly because of the 2g BOV and small T25."

How would the 1g make more horse power if both cars are running the same PSI. In theory the 2g should be making more HP because of the compression ratio.

This could go into turbo efficiency

if a 1g and a 2g were equal (exept for the compression) with the same turbo, 14b the 2g should be kicking the 1g butt. This could explain why the 14b is a popular upgrade for a 2g.

Like I said the 2g makes less power for several reasons, mainly the BOV and smaller turbo. If everything else was equal the 2g head should be making more power, lower in the RPM range. When you start getting to higher HP levels you will have to start putting some money into the 2g head sooner.

Also, "the 2g should be kicking 1g butt", I don't think you will be seeing anything that drastic. You spend most of the time in the upper RPM range while racing so the difference would be minimal.