Which Cylinder head?

[Andrew7dg]

Just to warn you I love talking about engine dynamics, so please if you are going to suggest one, back it up with a reason. I know this has been talked to death but I don't think I found an answer to this question.

I am figuring out which head should I go with, the 1g or the 2g. Reading DSM tuners and vfaq, I am confused on what I should do. 1g has bigger intake ports. However there hasn't been any test done to see if that actually helps HP. It is just an assumption by people just comparing the intake ports. There are a lot of people throwing 1g heads on 2g engine blocks. There maybe some proof but it could be false proof by the difference in cams between the 1g and the 2g. However there has to be a reason why the stock 2g cars (215 hp) are making more hp and tq then the stock 1g (190hp).
The 2g head has a better angle for the air to enter onto the intake valve, which I heard is better then having the bigger intake. This has been sort of proven with the evos still having the same intake size as the 2g. And they are making good horse power yet. The 2g is also built with better metal then the 1g. My guess is the 1g does better in the higher RPM. However this car is only going to see the max RPM of 7500 so is that really considered high rpm on this car or does that mean going past redline...

what do you think I should do? I value any opinion I get.

The other question is how much will this actually matter. Will I even see much of a difference? When people run their cars on the dyno, it seems like they only look at max rpm but I am going to be looking to see what I am making in the lower rpm as well in the higher rpms.

I should probably mention what I have planned for the car so that better advice can be given. I am not building a High HP car. I am looking for good responce from the engine and the turbo from across the rpm range, not just the high rpm

I am going to go with the 1g rods with 2g pistons so I can have a compression of 8.5

I am building a MegaSquirt system to play around with (I am a DIY type person so I enjoy any chance of building stuff) The MS system is going to take over the stock ECU. I will have full tuning capabilities, also a wide band will be purchased for tuning. Going to go with MAP

255hp with a Aeromotive FPR (bigger injectors are going to be purchased soon, I don't know how big)

FMIC with hard pipes

3" exhaust system w/o cat

built my own boost controler

ACT 2600 clutch

Leaving the transmission stock (was rebuilt 10,000 miles ago)

Evo 3 exhaust manifold

Haven't figured out what turbo yet...

I want to go to E85 for the 108 octane so I won't be dealing with knock but still a little confused on what I need to do to the car to make it compatible. Where should I go to get the fuel rail treated?

Anything else I am forgetting

Spring is comming and I want to get the DSM out very soon!!!

[JET]

Your HP goals are really going to make a big difference on which head you go with. It sounds like a 2g head is going to work better for you. I would put some 272's on your list too. 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.

I would also look at going with a Wiseco/Eagle combo. Higher compression is going to get you better spoolup and more torque. You could go with the 9.0:1 pistons and a thinner headgasket or custom order some 9.5:1 or so. How much HP are you planning on and which style of dyno?

[Andrew7dg]

How much horse power... Isn't that the ultimate question....
Maybe I am kind of new to this but what do you mean by which style of dyno?

I am thinking if I got 350-450hp I will be very very happy. I kind of gave myself a limit on how much horsepower I want to give. Why, well it mainly has to do with money. I am broke! So I want to get the most out of my small budget. When I say 350-450 those are the top numbers. It is easy to get those numbers from just bolting up a turbo (well there is a little more to that then just a turbo bolt up...) but I am interested in making the engine perform well with the parts that I have added to give the car good responce. I am going to leave the transmission stock simply because it was rebuilt at the 10,000 miles ago and I don't have the money for a shep trans. I think (and hoping) that the stock trans will take the horse power. Passed the 500 hp limit, I know it won't. Plus I have to go buy a 4-bolt rear end for the car first before transmission. I also want to beef up the suspension which will be more money.

Definatly I should get the 272 cams

I went with the 8:5 compression just for better responce however I had a question about that. I have read somewhere that it does give better responce but it doesn't give better spool up time. The only reason people think so is because higher compression works better off boost before boost kicks in. Is this true and is there proof that the higher compression spools up turbos faster? I wasn't sure about this. I am more toward the idea that the only reason you get better responce is because 8:5 works better then 7:8 off boost and then when boost kicks in, you get more horse yet. And the the idea that 10 psi on a car with 7:8 compression is a lot different then 10psi on a car with 9:0 compression. I wanted to go with evo 3 pistons that had 9:0 compression but couldn't find any.

I am thinking the 2g head will work better also. I had the question then, would oversize valves help? or would that only be for higher RPM applications?

When I am out of college, I will have a much larger budget and I plan on building up an mitsu close to the 4 diget club. Then I will get the Wiseco/Eagle combo, shep transmission, and all the other good stuff that I have been dreaming about. But first I want to learn on my DSM first. I just want to play around with combos and see what works best. it is just the engine building I enjoy, and making the parts work well with eachother. Then taking information I believe I can build a kick ass Evo or something!:sasmokin:

And plus in the end which car would you have more respect for, a car that a kid just threw a lot of money in to make it run fast, or a car that someone put lots of time, custom diy parts, and actual practical engine building knowledge into the car.
I am getting sick of seeing cars that are built up and people still don't know why they are fast. All they know is if they buy this part it will give their car 20hp more. :angryfire:

Sorry got off subject a little. :rolleyes:

[Super Bleeder!!]

I too looked into this about a year ago, and ended up deciding on the 2g head. Its smaller ports promote velocity and better cylinder filling at low and mid rpms, yet it doesnt seem to fall behind the large port 1g heads on the top end either.

Turbos are driven off of hot gas entering the turbine housing and expanding due to the drop in relative pressure. The turbine wheel captures this gas expansion as work.

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

[JET]

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]

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.

[Super Bleeder!!]

Pertaining to the question "does a high compression engine generate more exhaust than a low compression version?" The short answer is no. The amount of exhaust given off is merely a function of volume (displacement). Mass going in and out of an engine is relatively constant, if you consider blowby to be minor (and it should be on a fresh engine).

As for the 1g and 2g power differences, the 14b can indeed flow far more air than the t25; its also more efficient at compressing air which simply means it heats the charge less.

E85 is actually 105 motor octane. Octane is merely a measure of how well a fuel can resist knock, so of course its going to have a higher threshold. Another benefit of that particular fuel is you can run a much more aggressive timing map.

[DBMajik]

You are correct thinking the higher static compression only seems like the turbo is spooling faster. When you think about it, it only effects the compression stroke. Sure pressure builds up before the exhaust valve opens, but the difference would be minimal. I give it only 50 rpm better spool at beest.

[Jakey]

Mass going in and out of an engine is relatively constant, if you consider blowby to be minor (and it should be on a fresh engine).
You need to be careful with this statement. The mass of air entering the intake manifold is not equal to the mass of gases leaving the exhaust manifold.

[JET]

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.