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

[Ondonti]

I think 24vshadows results clearly show that throwing a 24v in your car doesnt mean your car is going to go faster. I definitly think a nasty set of DOHC heads will kill a SOHC when it comes to turbo cars that need to make 1000hp...but at the same time, I dont really know. N/A honestly doesnt seem to make a difference performance wise if you do extensive mods on both.

I believe there is a person named "AJ" (Not sure how to find more info on him) who ran an 1800hp SOHC in proRWD racing in the early 2000's. They guy also ran a DOHC motor in the 1800hp area. I dont really know any facts except that he ran 1800hp on a stock crankshaft for SMALL amounts of time. Likely it had to be replaced throughout the season because even the forged crankshaft starts cracking slowly around 900whp.
Nelson had some parts from that guys car and is likely at least pretend friends with him.


Also, valve float and lifter collapse are two different problems. DOHC 6g72's float valves when they dont upgrade valvetrain hardware (need lighter parts) and then the lifters collapse around 9500 rpms (depends on your cam profile and oil pressure and other things). Massive amounts of oil pressure have been shown to not be able to extend the rpm range much..if at all ($10,000 dry sump and external oil lines didnt help Nelson).

Nobody knows what rpm our 12v lifters collapse on a stock cam..or if the valves float first!

I am pretty sure they will collapse as I know Sunmind's built 12v collapsed and broke but we have no idea what RPM his idiot mechanics reved the car to (had no limiter on the EMS at the time).

The good news is, our rockers must be a lot stronger then some people have "guesstimated."
That means we can probably rev to high hell if we have the lifters and springs to handle it.
I used to think 7000-7500 and the rockers would be in danger but now all I have to worry about is collapse and float

I get the feeling that my cams will mean I cant rev as high as someone with a lower lift high duration cam like the Crower in Reaper's Daytona. I guess it also matters what the profile is though. My cams dont have a sharp peak, and our stockers dont either, but I seem to remember seeing quite a few cams for other cars with very peaky lobe profiles that look like they WANT to make the valves float.

My valves are 12-15% ligther then stock (way better then going with titanium retainers...which maybe we might need someday) so maybe that will offset the camshaft profile.

[Ondonti]

Ed, about grinding the valve retainer.

Do you mean to increase the install height of the valve springs, so there is less tension on the hydraulic lifter?

I seem to not have problems using stock springs on my valves which are about 1/8" taller then stock. That extra height helps make room for theoretical higher lifts without the retainer hitting the valve guide seal.

With Titanium valve retainers, you can get a totally different retainer design. A good reason to do some thinking before you get some.

I believe the DOHC guys try to get retainers with a HIGHER installation height because the DOHC springs will bind if you increase lift with a new cam. Lifting the installed height with new retainers fixes that problem and helps them rev higher

[c2xejk]

Quote:

Originally Posted by Ondonti Ed, about grinding the valve retainer. Do you mean to increase the install height of the valve springs, so there is less tension on the hydraulic lifter?

I was talking about grinding to under side to give more clearance between the spring retainer and valve guide seal.

Quote:

I seem to not have problems using stock springs on my valves which are about 1/8" taller then stock. That extra height helps make room for theoretical higher lifts without the retainer hitting the valve guide seal. With Titanium valve retainers, you can get a totally different retainer design. A good reason to do some thinking before you get some. I believe the DOHC guys try to get retainers with a HIGHER installation height because the DOHC springs will bind if you increase lift with a new cam. Lifting the installed height with new retainers fixes that problem and helps them rev higher

The T3 guys raised the install height because the valve springs were under so much pressure (setup for RPM well beyond stock...) Let me know if you go for titanium retainers. I might go for some too... I think the 12v heads have the potential to flow at higher RPMs...

I am working on a theory that 3L valve tick may becaused by installing the valve springs upside down...

[Shadow24V]

Ondonti - i still have some work to do as a driver and as a mechanic before the full potential of this motor is reached. I havent drag raced much so im still working on timing, asd traction is next. better rubber and suspension and i think i can get into the mid or low 14s. I think im still running a bit too rich in some WOT areas and a bit too lean in others, so im not making peak HP.

Hemi417 - the Chrysler 3.5 is NOT related to the mitsubishi 2.5/3.0/3.5/3.8 series motors. they are completely different and not compatible.

[irocelectric93]

Shadows engine def was still a work in progress and really didnt have any mods to speak of from what i understood. I still want to say though that the sohc 3.0 has already been proven to make numbers....Josh's 14.2? Honestly its just a matter of how much work you want to do. I think that the sohc heads can flow with the right work....i guess we're still trying to figure all that out though.

[Ondonti]

Quote:

Originally Posted by Shadow24V Ondonti - i still have some work to do as a driver and as a mechanic before the full potential of this motor is reached. I havent drag raced much so im still working on timing, asd traction is next. better rubber and suspension and i think i can get into the mid or low 14s. I think im still running a bit too rich in some WOT areas and a bit too lean in others, so im not making peak HP. Hemi417 - the Chrysler 3.5 is NOT related to the mitsubishi 2.5/3.0/3.5/3.8 series motors. they are completely different and not compatible.

Its good for people to know that doing what you didnt isn't like adding a 52mmtb and getting free gains.
I know with my current car I have lots of problems. My simple turbo setup and stock motor in the spirit was a lot easier to deal with. When I could ignore the motor and only think about driving, it was nice.

[Ondonti]

Quote:

Originally Posted by c2xejk I was talking about grinding to under side to give more clearance between the spring retainer and valve guide seal. The T3 guys raised the install height because the valve springs were under so much pressure (setup for RPM well beyond stock...) Let me know if you go for titanium retainers. I might go for some too... I think the 12v heads have the potential to flow at higher RPMs... I am working on a theory that 3L valve tick may be caused by installing the valve springs upside down...

Titanium lifters would have to wait until I had the ability to rev up there. I just dont have the time to sit down and read all the stuff I need to in order to take care of MS. But there are people here who could potentially help me in the future.

Since I already have a higher install height though, I dont know if we could share the same retainer design.

[c2xejk]

Let me stir the pot a little and suggest that for max performance in the 0-6200 RPM range with a stock stroke/bore 3LV6, smaller 2v/cyl would be the way to go... (yup I am implying that you could make more hp with -1 valves...) I have yet to calculate what the ideal size intake valve would be, but all the indicators are smaller.

Why? The amount of airflow needed to support the power to be generated.

Doesn't porting increase hp? Yes because improvements to _quality_ of flow, not quantity.

Isn't everybody going to bigger valves for more power. Yes and no. Some are going to bigger valves because they truely need them, some are going to them because they are following the hype. Darin Morgan (a top head porter) has mentioned that for heads that he is going all out on, he will often put in a smaller valve (than stock) and the engine will make a great deal more power. CFM is not everything.


Why does brand X have such good luck with 4v/cyl setups? Because they have a small bore, that means there is less room for valves. Thus to get enough valve curtain area, they must go to a 4v/cyl configuration. Plus, many of those engines rev very high to make their power.

Is there anyway around this? Yes, spin the engine faster and/or increase displacement. Spinning the engine faster will likely require changing the intake runner length to tune it for higher RPM.


To Shadow24v, if you want to make big power with the 24v heads, get a 3.5L or 3.8L engine...

[Shadow24V]

ed - im not looking to go all out just yet, if ever. i probably will stay sub-500hp unless i do something like AWD. For now, i just want something with balls and thats unique.

I also think that the 3.5 or 3.8 (which is drive by wire and out of the question anyways) would have too much low end torque for the weight of a P-body. now with a bit more top end power and less low end torque, a camed and supercharged 24v would probably do pretty well IMHO. The reason i think this comes down to where the powerband and useable power is. if you have gobs of low end torque like a v8 in a P-body, any decent tip-in would result in overpowering the tires. if you move the powerband up in the rpms, you still have low end power, but it would pull like a SOB on top end. With a 3.0 v6, even if you had cams and a S/C with a powerband of say 5000-7000 rpms, you'd still have enough low end torque that daily driving wouldnt be impacted.

Also, IIRC, 2v heads are better for torque whereas 4v heads are more for top end performance. I believe this is why the v8s are still 2v or 3v motors whereas the rev-happy I4, I5 and V6s all use 4v heads.

the reason ive seen that the eclipse and 3000GT (not vr4s) are going to the 3.5 is they are a lot heavier than the P-body and its a lot cheaper than turboing or supercharging the 3.0 for them. (custom turbo kit or RippMods Centrifugal S/C are all $2500+, a 3.5 with ECU etc, less than $1000). Its more cost efficient for them


as for power vs # of valves and valve size, what do you attribute the increase of 60hp and 30ft/lbs of torque between the 2v motor and the 4v? the 0.2CR increase, cams etc?

[c2xejk]

Quote:

Originally Posted by Shadow24V I also think that the 3.5 or 3.8 (which is drive by wire and out of the question anyways)

Unless they are doing more than actuating the throttle body, I don't see a problem with putting a different TB on.

Quote:

Also, IIRC, 2v heads are better for torque whereas 4v heads are more for top end performance. I believe this is why the v8s are still 2v or 3v motors whereas the rev-happy I4, I5 and V6s all use 4v heads.

Sort of but not really... The current trend is to go with small bore engines, that gives a 4v/cyl setup an advantage. On a big bore engine like the 3L, 2v/cyl setup does very well. And there is room for bigger valves.

Remember, I said for "max" performance. There is much that can be done to improve the performance of the stock 2v/cyl setup...

Quote:

the reason ive seen that the eclipse and 3000GT (not vr4s) are going to the 3.5 is they are a lot heavier than the P-body and its a lot cheaper than turboing or supercharging the 3.0 for them. (custom turbo kit or RippMods Centrifugal S/C are all $2500+, a 3.5 with ECU etc, less than $1000). Its more cost efficient for them as for power vs # of valves and valve size, what do you attribute the increase of 60hp and 30ft/lbs of torque between the 2v motor and the 4v? the 0.2CR increase, cams etc?

So you are telling me that the difference between the 2v and 4v motors is only .2CR increase and cams? The intakes are the same, the exhaust is the same, the machining is the same, port design, the electronics are all the same? Obviously the answer is none of those things are the same... There are many parameter that can be tuned for max performance.

[Shadow24V]

Quote:

Originally Posted by c2xejk Unless they are doing more than actuating the throttle body, I don't see a problem with putting a different TB on.

Good point, didnt think about that, The 3.8 also has a returnless fuel system so im not sure how that would play into things

Quote:

Originally Posted by c2xejk Sort of but not really... The current trend is to go with small bore engines, that gives a 4v/cyl setup an advantage. On a big bore engine like the 3L, 2v/cyl setup does very well. And there is room for bigger valves.

makes sense, didnt know about the trending for smaller bore etc

Quote:

Originally Posted by c2xejk Remember, I said for "max" performance. There is much that can be done to improve the performance of the stock 2v/cyl setup...

not disputing this, Ondonti kinda proved that one i think. I dont think that the 4v heads have been fully explored for improvement yet. Seems like many people go with a S/C or turbo and leave cams and P&P for later. Im still trying to get a junk head so you can take a look at its characteristics etc.

Quote:

Originally Posted by c2xejk So you are telling me that the difference between the 2v and 4v motors is only .2CR increase and cams? The intakes are the same, the exhaust is the same, the machining is the same, port design, the electronics are all the same? Obviously the answer is none of those things are the same... There are many parameter that can be tuned for max performance.

I was just trying to say they are essentially the same motor at heart with minor tweaks. The biggest difference i can see is the 4v heads and possibly the intake, with the heads allowing different tune parameters in conjunction with a slight CR bump and cams. But i only speculate

Yes, there are many aspects that cat be tweaked for MAX performance, so its hard to pinpoint what exactly gave what gains.



Edit: btw, the 4v heads are identical for the 2.5, 3.0 and 3.5L motors save for cams. not sure about the 3.8 due to MIVEC etc. Same valve sizes and location. Are you saying that a 3.5 would be better apt to make use of a 4v setup than the 3.0? bore increase is only 1.9mm. (6g72 91.1mm bore by 76mm stroke, 6g74 93mm bore by 85mm stroke)

[Ondonti]

Quote:

Originally Posted by Shadow24V as for power vs # of valves and valve size, what do you attribute the increase of 60hp and 30ft/lbs of torque between the 2v motor and the 4v? the 0.2CR increase, cams etc?

But there is no 60hp 30 ft/lb difference in reality. The dyno is very humbling.
Compare a healthy 3000gt 12v and 24v n/a and its about 25hp different.

And I will again say, the camshafts for the 12v are about the same size as the 24v's even though camshaft lift requirements are VERY different for 2 valves vs 4 valves because of valve diameters.
Put equal cams on the 2 valve (same lift compared to valve diameter) and I think the power difference will disappear.

[Shadow24V]

i can see what your saying Ondonti. I think for what i would like to do (higher RPMs) the 4v will serve me well.
heres some specs on the valve setup on the 24v
Inlet Valve Diameter 34.30mm
Exhaust Valve Diameter 31.8mm
Valve Face Angle 45 º
Valve Clearance Maintained by hydraulic lash adjusters
Inlet Opens 9º BTDC
Inlet Closes 59º ABDC
Inlet Duration 248º
Exhaust Opens 47º BBDC
Exhaust Closes 21º ATDC
Exhaust Duration 248º
Overlap 30º
Inlet Cam Lobe Height 37.58mm
Exhaust Cam Lobe Height 36.95mm