2 vs 4 valve/cyl heads, their capabilities and the impact on tuning

[c2xejk]

There is more we could talk about on this subject so I am starting new thread to deeper dive on this subject.

Quote:

Originally Posted by 87turbodance My understanding is that this is one of the advantages of the more modern pent roof combustion chamber? Smaller, tighter and faster burning combustion chamber allowing more power with less timing and an overall more efficient combustion. This is why I have been looking at mounting the 24V heads to our 3.0 12V block. I believe overall efficiency will improve and allow more boost and timing to be run at a higher compression ratio for better off boost efficiency and performance.

I am far from an expert on this, but the stock 12-valve head has a fairly small (modern) combustion chamber in it (and the piston.) My initial guess is that the 4v/cyl would increase the size (at least cross-sectionally where the piston and head meet.)

The main comparison is between old style V8 heads and newer modern ones. (how else is Chevy getting so much hp out of the LS2 (or whatever the latest 2v/cyl engine is.) I don't believe the valve size has changed as hp has shot up. )

4v/cyl have the advantage of more curtain area (more CFM.) However, to truely take advantage of this several other engine parameters would have to be changed (ie. max-rpm, displacement/stroke, cam lift, etc.)

I think there is a lot of potental still in the stock 2-v/cyl heads depending on the goals.

I would love to hear more about 24vshadow's tuning efforts are going.

[glhman]

Quote:

Originally Posted by c2xejk how else is Chevy getting so much hp out of the LS2 (or whatever the latest 2v/cyl engine is.

You're a few years behind. The LS2's came out in 2005 with 400 HP with 6.0L, where the 7.0L LS7 is in the new Z06 making 505 HP, and the ZR1 is powered by an 6.2L LS9 making ~620 HP (supercharged)


[/hijack]

Yes there is potential in 2 valves, but you can have an overall valve area larger with 4 valves/cylinder.

[Shadow24V]

Thanks for the interest Ed, things are going well so far got idle, cold starts, and an OK tune on the car. on a hard pull i can chirp 2nd gear right now, never got it to do that on the 12v before...

but here goes, heres a picture of the 24v compustion chamber. (not my OWN heads but the same type) total advance runs up to 32.5* and idle is around 22*



and heres my current config, you can see (i hope) the spark table on the right

[87turbodance]

Your VR table looks a bit funky. Seems like your REQ fuel is too low. VE values shouldn't go much over 100% - only to richen the mixture under boost.

Probably a good idea to start a new thread for this discussion then irritate Odonti in his thread

I think 2 valve heads have great potential but 4valve is (typically) better out of the box. Every modern hi-po car (except for a few exceptions ie Corvette) is 4 or 5 valve per cylinder now. I'm going to buy a pair of heads and an intake / exhaust off a 2.5 SOHC 24V 6G73 and start my attempt to bolt those to a 12V 6G72 and see what happens. I will likely end up using factory DOHC TT pistons. Thoughts? I am after a motor that will have N/A fuel economy and off boost performance while surviving up to 10PSI of boost likely from an HX35. Megasquirt controlled water injection will be utilized so that I wont have to pull much if any timing when under boost compared to WOT N/A.

DOHC N/A pistons are another option. I have been tempted by the idea of a water injected 10:1 compression boosted 3.0

[87turbodance]

Quote:

Originally Posted by Shadow24V and you want to run LESS timing with the 24v heads? whats the max timing on the 12v motor (modified or normal) 12-20* at most? the Hi-Po spark map i have off of a known good boosted 24v (i only got the N/A part) runs up to 32.5* advance on a 9:1 CR motor somethings not adding up in my head there lol

This is the theory that I understand to be true. I haven't been able to actually test under real world conditions. It's something I would like to discuss though.

[mopar3.0]

you never chirpped second ona 12 vlave?

my spirit used to burn most of second before i got the lsd in

[Shadow24V]

*shrug* 228K mile motor on an OEM clutch before the swap.

yeah, i have a bunch of things to iron out on the tune, been working on it lately, its running better but not perfect. it has some issues: hot idle surges etc, if you want to give me some pointers, go for it im hoping to take it to a dyno when i get home for the summer and see what i got. also going to the dragstrip in a week

back on topic -
heres an OEM high octane map for the 24v motor, a bit more conservative than the one im running

[thejoker1290]

still new at this but what do the 24v heads come off of?

[Shadow24V]

a bunch of engines, 90's 2.5 avengers, 2000+ 3.0 eclipses, 3.0/3.5 Galants diamante's (just SOHC ones, DOHCs were the 3000GT/stealth and select other cars)

[Ondonti]

The 2 valve heads have the advantage of being a crossflow semi hemi head which gives them a lot more possible potencial then a bathtub, but there area lot of good heads available for our motors.

I think Mitsubishi spent very little time on the older 6g72's figuring out what was "best"

They have the exact same 24valve sohc and dohc heads on 2.5L 3.0L 3.5L and 3.8L engines. (i believe 2.5L galant vr4's at one time had dohc 24v heads).

The only heads which truly match the engine on purpose (not accidentally) might be the Sohc Mivec heads on the 3.8L 6g75 found in the 4th generation Eclipses. These heads are made for the larger bore of the 3.8L unlike the dohc and sohc 24v heads which structurally dont have enough meat at the edges of the combustion chamber to seal the huge bore with lots of power (without modification). I believe both Sohc and DOHC 24v heads were used on the 3.8L in the montero (maybe just one) but you can see that mitsubishi wasnt very careful in the past about putting the proper heads on their motors.

They were too lazy to even change port sizes or combustion chamber sizes.

[Shadow24V]

someone said "6000rpm head on a 9000rpm bottom end" i believe the quote was, right brent?

a good set of cams would do WONDERS for the 24v motor. up the redline to 7-8000 rpms and this thing will scream. my 24v feels like it wants to rev quite a bit more but its hampered by the cams and intake/port work

[mopar3.0]

arnt the 2.s sohc24 valve cams a bit hotter then the 3.0 version,
i need to get picks of my buddies super charged 3.0 avenger soon

that timming map does that mean high octane as in rce fule or premium i might try it in on my 12 valve,i have a few maps also

[Ondonti]

anyone on here able to make sense of the 3.0 stock calibration and how much advance it gives?

The tables are a bit confusing on the 89 cal and either give way to much advance or very little, depending on how you interpret them.

[mopar3.0]

its too bad we cant mke some nice maps from the stock ones to use in ms,
speaking of ms havent seen m90daytona around in some time

[Shadow24V]

that ignition map was for use with 93/94 octane fuel.

as for the 2.5 cams, they dont have as much lift/duration as the 3.0s. swapping a 3.0 cam to a 2.5 is a gain, not vice versa