6 bolt block- 1g or 2g head?

[gijoe985]

Well I've been reading all around and it seems that there is a real mixed opinion. It is obvious that a 1g head will out flow a 2g head stock. I've been hearing about many people saying that a correctly ported 2g would be better than a 1g. If you could get a 2g to flow as many cfm as a 1g would it be better? I think I read that the geometry is better, but again only if the port and polish is done well.

2nd question, kinda related- I've head that many people like the 2g head because of increased velocity. Which makes total sense tome because I am an old Ford guy, and my 4v 351c heads have "flapjacks" for valves and they flow tons, but for that exact reason many people actually fill the ports when doing head work, in order to decrease total flow, but increase velocity. The flow isn't worth it unless you are a cup car running 8k-10k rpm.

So, wouldn't the best head flow numbers be the exact amount of cfm that your engine is bringing in? Or does this not apply to forced induction? I guess I am just thinking about this because I am trying to decide whether to have a 1g or 2g head on a 6 bolt.

 

[JKL]

Maybe you'll spool a bit faster and reduce lag but i highly doubt the cost justifies the gain and that service cost could be spent for mods w/greater impact in gains. Unless you're going for a record breaking dsm or just a machine specialist who's looking to experiment. Good luck

 

[josh_GST]

My set up is 6 bolt block and 7 bolt head. If you go with a 7 bolt head you will have to get a 1g CAS and rewire it. A write up can be found on Road///Race Engineering Mitsubishi Eclipse Parts and Performance. Everything else will bolt right up.

 

[19Eclipse90]

Read up.

2g head, 1g block

 

[gijoe985]

Read up.

2g head, 1g block

Yup, already read that. It's tough just because I've heard so many people supporting each side.

Has anyone done dyno comparisons with both heads?
I know that's a lot of money to be trying both, but it seems like a tough decision. Also, will the 1g intake bolt up to a 2g head?

 

[gijoe985]

Here is a new post that discusses the velocity factor of a 2g head-

"^^velocity equals efficient flow. no other way of looking at this. there are great write ups on this already. the large ports dont mean dick which was covered. 1g head only flows more because the 1g cars came with more agressive cams and a larger throttle body. Better cams and larger throttle body on a 2g head with proper porting will outflow a 1G head with porting due to better port angle on the valve. The grosly oversized port on a 1G head only slows velocity and creates a huge angled entry around the valve. The basics of head porting state this is a poor design, much the reason why it was updated and changed on the 2G head. The whole point of using a 2g head is the angle of the air's entry into the valve is so much better. A 2g smim matches the port of a 2G manifold so a nice angled port job to straighten the path of the air down on the valve will work better. Simply having a big entry to the valve does not flow more air than a properly designed port (1g vs 2g).
I will be building my next motor soon, and its a 6 bolt and 2g head but i will spend more time properly setting up the head then i will the bottom end much due to correct porting.

I saw someone on here used a 1g intake manifold, thats a no no. Ports dont match up, but a great alternative to this and stock look is a tough find. An EVO III intake manifold is perfect fit to the 2g head, but good luck finding one. You would be better off extrude honing a 2g intake manifold or 2g SMIM."

 

[gijoe985]

I'm still not sure which route I'd like to go. If it wasn't such a time/money drain I'd love to see the 1g head,intake, and TB, (w/ 2g exhaust) bolted on, and run on the dyno. Then immediately do a dyno run with the 2g head, intake, and TB? (w/ 2g exhaust.) Have both head ports ported to match and have the 2g intake extrude honed.

Has anyone done this? This would really be an interesting read.

 

[1G90AWDTsi]

I think when it comes to rally racing, everyone for the most part goes with the 1G heads cause and "correct me if I'm wrong" but 1G heads can be opened up significantly more than 2g heads due to the difference in port designs.

 

[mountain_man]

I am doing a full motor build on my 2g right now and am using a 2g head. My father and I have both a 1g and 2g head. We debated for a long time which one we should use and so we made a basic smoke machine and blew smoke at varying velocities through both 1g: TB, Intake Manifold, and unported head; and a 2g: TB, Intake Manifold, and cylinder head.

After analyzing both heads we thought the 2g head had more of a street/performance oriented design do the swirl that was created. It had a much "looser" swirl patter.

The 1g head we felt would be ideal for a full blown racer with a SMIC and big turbo making 25+ pounds of boost. This head showed us it had a much "tighter" swirl pattern compacting the air far greater, but overall making for a very aggressive intake design.

The testing we did was not performed in a lab with controlled results but this is the best we could do. And in cast you are wondering we tested the exhaust flow too through exhaust side to and came to some of the same conclusions as those found on the intake side

We are building a performance oriented street car with a BIG 16g turbo, running 16lbs of boost. So that is why we used the 2g head. I hope this helps.

 

[mountain_man]

Here is a pic. of the porting we did on the intake.

 

[gijoe985]

Here is a pic. of the porting we did on the intake.

Ooooh... I can see my reflection...

And yes, it was also very informative.

 

[dsm-onster]

The money it takes to get a 2g head ported to perform better than a 1g head can be sunk into oversized valves for a 1g head. Its all a wash. The 1g head came from the factory better. So you're ahead of the game when you have one.

BTW, You can do particulars to greatly improve the performance of 1g head runners. . .

 

[mountain_man]

you won't have to worry about the money factor of getting it ported if you do it yourself. just clean up what you can and take out the imperfections. Get a junk head out of junk yard to fool around with. if you mess it up its no big deal cause you aren't going to use it anyway. learn by doing.

 

[97 4G63]

Ok i still don't really get this is a 2g head better than a 1g for street use for around 350hp?
whit BC 272 cams and springs??

 

[dsm-onster]

Ok i still don't really get this is a 2g head better than a 1g for street use for around 350hp?
whit BC 272 cams and springs??

There is no real answer. It seams that smaller ports would be better for a mild street setup you're wanting. but, no one has reported back that their 2g head causes their turbo to spool quicker or noted a significant change in their dyno graph.

 

[SBR Joe]

I did a lot of searching around with this when i was testing the flow results on my 6 bolt head on a flow bench. I was never able to get my hands on the 7 bolt head to do side by side testing for numbers, but i did see one. The 7 bolt head has a much better design for the air to flow into the combustion chamber, and on top of that the casting is much better. Its a more shallow floor compared to a 6 bolt head so the air has a much smoother path of travel, whereas the 6 bolt runner floors are much higher and have more of an angle for the air path to follow. The 7 bolt flows "better" but does not flow as much volume as the 6 bolt. Regardless you would see more gains with a 6 bolt head over a 7 bolt. Plus, i may be wrong in assuming this, but a turbo is a means of forced induction...forcing air into the equation. If there is a larger port for more air to be forced into, the more gains you will see. I would clean up the bowels and casting imperfections before you slap it on, if you do opt for the 6 bolt head...you'll gain almost 30 cfm per cylinder if you do. Also if you do the 7 bolt head, you will need to drill out the ead bolt holes 1mm to fit the 6 bolt's.


Joe