2g combustion chamber phyics guidance.

[parker4]

I don't post much and haven't earned my 30 post credit to properly place threads.

I am currently building my 3rd engine, 2nd 4g63. I'm engineering the 7 bolt longblock with a 14b or 16g power plant. The car needs to have a power band for the track and curvy roads.

The research I've found pertaining the 2g cylinder head leaves a question dealing with the intake side. Oem the casting walls are finished rough intended for a layer of air to add a slipstream effect.
(1)Do Carburetors leave a rough finish to help with fuel atomization or for this same slipstream effect?
I read a post that Brent Rau found best results using stock head casting with only over sized valves. I couldn't find ANYTHING else but that statement and can't find any "Brent Rau 2g cylinder head" information worth while.
(2)Do I polish the head or not?
(3)Besides cleaning the burs is their anything really proven to be worth while to attempt without a flow bench, anything exhaust side? Do I knife edge the runners? TIME and tools are on my side.
I'd really love some informational thread from someone with a Brent Rau reputation... kind of like a "here's the physics and why I did it"

(4)Do I do any work to the stock 2g IM besides a 1g TB?
(5)Do I put in 1g camshafts?

-Parker

 

[e85_4g63]

I really wish rule number 1 wasn't in effect here... But since that's not the case....

(answers to your questions)..

1) Our cars don't use carburetors. So as far as the casting surface of the heads, I'm going to say that Mitsubishi cast them like that because it was the cheapest way to do it. On the other hand, fuel atomization, tumble & swirl effect, slipstream (call it what you wish), has nothing to do with the reasoning Mitsubishi casts cylinder heads and doesn't clean up the castings. They do it because it's quick, cheap, and works for there intended application.

2) Polishing: Mostly polish the exhaust side runners and combustion chamber to avoid hot spots and eliminate stress risers that lead to cracks in the casting. Doing the intake side may or may not have benefits, I don't own a flow bench, so I'm not going to state anything about it helping or hurting, other then I know that polishing reduces the chance of a crack starting from stress risers and also prevents "hot spots" and carbon build up.

3) Light bowl work and polishing are about all you need to do (it's probably 90% over kill but it does help). You could knife edge the intake runners if you wished, will you notice a gain (ehh, it's a 50/50 shot but nothing to write home about). I can 99% assure you that Brent Rau isn't going to come on here giving out secrets (and neither is Marco [Magnus]), about they're air flow research (or why would you buy there products and not just create your own?).

4) You'll def. want to port the T/B opening of the 2g manifold to match the T/B of your choice. Extrude honing is another option, as well as just replacing the part completely.

5) I don't see why you'd swap to a 1g cam honestly. An HKS (if you have the funds) 264/264 setup would be a worth while consideration.

In closing, how much power are you looking to make? What suspension mod's have you (or are you planning) to make? What diff (LSD's) are you (going) to use? And what does your budget look like for the build?

 

[parker4]

Thanks for the interest e85.
... I swore my talon came stock with a carb?! . Only trying to understand if the same aerophysics of a polished carburetor follow onto a polished head.

With the Brent Rau statement, I never expected any particular person to lay down the red carpet of the 2g head in this thread. I just always assume theirs better information out their than I'm incapable of finding. Right now the subject is casting walls.

e85, i assume you understand the theory of a rough wall for air molecules to "stick" to allowing other molecules to slip by the "stuck" layer of air, in affect making the functional port size actually SLIGHTLY smaller.
Still assuming you've looked into this and still continue to believe Mitsubishi casted the walls rough for economics, ill keep your points relevant in my mind.

As far as the polishing the bowls and sharpen the runners, I'm not expecting dollars from cents to appear. I've just got the time for it, the tools, and the desire to learn, so passing up anything that my hands can do to add power isn't optional.

Thanks for the exhaust side info.

I had looked at a jm smim but my research told me it would be overkill for even a 16g. I looked at extrude honing the 2g im and haven't come to a firm conclusion due to budget. Is their any thread you can think of that I need to read pertaining a 14b or 16g and a extrude hone or sheet metal intake manifold? Either or the tb will be 1g port matched.

The 1g cam idea came from hearing that they were slightly more aggressive. HKS or any aftermarket cam for this motor seems a little overkill on budget, but have been afraid of needed one for the power I want. Any camshaft insight?

The LSD will be quaife if I can afford it after the intial build. I'd LOVE to have it in the budget or already own one but they are expensive.

As far as the power and powerband... Not set on a number but it'll be around 22 psi, I already own 880cc injector, Ill have my fun in turns, and want controllable torque/responsiveness.

Again, thanks for the interest e85.

 

[IQ685]

I'm with you on the fact that a rough intake port will aid in air velocity because when my brother was at UNOH they flow tested 2 different heads; one original rough casting and one polished. And according to him(now this is where there may be a little area for error because it's his word, I wasn't there) the one that was still rough cast actually out flowed the polished head. And as I was typing this I remembered that on mythbusters they proved that the "golf ball effect" or the dimples on a golf ball make it more aerodynamicly efficient than a completely smooth ball of the same size

I'll add to this post that I'm not sure if it was 2 different heads or one head flowed before and after they polished it, if it were the former then I could easily see how that comment has no validity at all because no 2 heads will flow the same from stock casting

 

[parker4]

My brain yearns for guidance and information on any or all the subjects exposed.
-Parker

 

[Absit]

You need to talk to engineers.

 

[e85_4g63]

You need to talk to engineers.

Amen!

There is a lot of good info out there. Just nothing super specific to the 4g63 2G cylinder head. Honestly, your splitting hairs with anything more then bowl work, removing stress risers, and polishing the exhaust runners (and gasket matching). Unless you have a bench (superflow 600 or what have you), it's simply a shot in the dark. Remember KISS (Keep It Simple Stupid), and you'll do fine!

As for cams: 16g's (EVO III specifically) has made almost 500AWHP

http://www.dsmtuners.com/forums/bolt-tech/281031-new-16g-dyno-numbers-c16.html

so cam choice is pretty important, as is the intake manifold. Of course, it's "all in the tune"...

Sorry I cannot help with the actual engineering part of the question, as I just have a normal boring job like the rest of the world.

 

[tkelly27]

I have a piece of paper that says I'm an engineer, and all I can tell you is this kind of itch is one you're just going to have to scratch yourself to get a satisfactory answer. I've seen some crazy stuff on the flow bench, and I've only used one 3 or 4 times. Trying to explain why what happens happens is better left to phd's. I can give you some examples if you'd like.

Before you go too far into this and spend all day at your flow bench and porting station like a meth head, my advice is that you should just be thankful that you have 4 valves per cylinder and leave it at that. At your power level and for your goals, if you spent a day finding where you could remove weight that you wouldn't miss, you would probably be going a lot faster than two weeks at a flow bench.

http://www.dtec.net.au/Tech Articles/DIY Flowbench Design.pdf
Flow Bench

this guy has some really good info on porting dohc heads
The Old One - Energy Dynamics
The Old One - Energy Dynamics

With a 16g I don't think the head is going to be where things are choking off.

 

[neoviper]

As for cams: 16g's (EVO III specifically) has made almost 500AWHP


100% true, BUT the OP said his goal is to create a car to handle a road coarse. If you pushed an evo lll to achieve those numbers, the amount of heat it would generate would send your IT's through the roof. Thats a nightmare waiting to happen out on the road course.

As far as head flow rates goes, I'm someone who LOVES digging into the sciences behind racing. Unfortunately, withought being able to test a heads flow rate on a bench, I can only speculate what head design would work best. So for me personally, when it comes to parts of a motor that involve flow, I leave it to the people who have years and years developing and racing our engines. It takes a great deal of pride swallowing for me to come to that conclusion but if it means me getting the results I want, I'll do it

 

[parker4]

There is a lot of good info out there. Just nothing super specific to the 4g63 2G cylinder head. Honestly, your splitting hairs with anything more then bowl work, removing stress risers, and polishing the exhaust runners (and gasket matching). Unless you have a bench (superflow 600 or what have you), it's simply a shot in the dark. Remember KISS (Keep It Simple Stupid), and you'll do fine!

As for cams: 16g's (EVO III specifically) has made almost 500AWHP

http://www.dsmtuners.com/forums/bolt-tech/281031-new-16g-dyno-numbers-c16.html

so cam choice is pretty important, as is the intake manifold. Of course, it's "all in the tune"...

I agree with you're first comment in this post and I really didn't think when I made the OP that their would be much more inside the head for me to do. I will do some research and see what I can find about polishing the exhaust side runners. I've just done a limited search pertaining the exhaust side. Unless you or someone want to post a thread/prove here.

c16 and 500hp is WAY to serious for this particular engine, It may not even have an LSD at birth. This engine (and suspension) really only needs to be a damn good excuse to get to the track. The competitive motor with a scm6152e turbo (from first motor build) will be the c16 RACE car only after track skills are built and toned. I merely want to hone my skills with motor work on this engine for future knowledge. Wither it be my dd 65hp Suzuki samurai or a 600hp race motor I'd like it to have some quality in my engines. Hp isn't really what I'm after, its performance.

Ill start some troll research on cam choice without budget in mind and really ask myself some questions when I feel much more confident with the lob and power band relationship.

http://www.dtec.net.au/Tech Articles/DIY Flowbench Design.pdf
Flow Bench

this guy has some really good info on porting dohc heads
The Old One - Energy Dynamics
The Old One - Energy Dynamics

With a 16g I don't think the head is going to be where things are choking off.

Perfect! thanks for the information, ill get to it soon.

With your 16g statment... What do you think would be choking potential power inside the complete long block pertaining AIR delivery besides the 16g itself? Reminder, I'm using the 1g TB. Assume I'm master tuner. The rotating assembly will be balanced eliminating the harmonic pulley; the balance shafts will be eliminated as well. Thinking of using the stock IC and will use steel pipe. Do I really notice a difference with at most a 16g turbo and a SMIM vs an extruded stock IM?

As far as head flow rates goes, I'm someone who LOVES digging into the sciences behind racing. Unfortunately, withought being able to test a heads flow rate on a bench, I can only speculate what head design would work best. So for me personally, when it comes to parts of a motor that involve flow, I leave it to the people who have years and years developing and racing our engines. It takes a great deal of pride swallowing for me to come to that conclusion but if it means me getting the results I want, I'll do it

I respect your decision. And you're right when you want known results go with the known vendor. But between my salary (lacking) and owning the passage way to my passion confidently (adrenalin). Accepting engine air flow as something outsourced is unacceptable. I've learned so much in the past 2 years with the garage, tools, and gray hair I have access to I cant stop here. Not saying you're clueless to head work, more than likely you have more experience than I, but book smarts and experience are two different things unless your a proven winning professional.
Just the difference between two people.

Thanks for the replies and any future interest.
-Parker