Changing the heads on standard V6

[Turbo3.0]

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BTW 220whp is a LOT more then ANY 24v 6g72 motor puts down even with lots of mods. Those 12v's really are very mild. You can go with MUCH bigger cams, custom (only ~500 bucks which is cheap) rocker arms and have ED port you up a set of heads that will make power @ 8000 rpms and you can have one insane N/A setup (maybe some spray too!)

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nobody is making 250-260whp on a dohc 24v. not even close 250-260 crank hp is more like 195whp. a LOT less then those 220+whp 12 valves. Using crank hp those motors are making 290-300hp.

Those are some pretty bold statements that I find incredibly hard to believe. For an engine of equal displacement, bore, stroke, compression ratio, and a higher stock volumetric efficiency to be the inferior of the two, that makes no sense. Do the same "mild" mods to the 24v engine and I guarantee you will be making more power. Basically what you are saying is that a two valve per cylinder design is superior over a four valve design. In that case I think I should give F1 a call and recommend that they try it out. Hell, maybe even recommend that they use pushrods and a carburetor while they're at it.

Also, a 25% power loss through a FWD transmission is a little steep.

Just my 2 cents

[c2xejk]

Quote:

Originally Posted by Turbo3.0 Those are some pretty bold statements that I find incredibly hard to believe. For an engine of equal displacement, bore, stroke, compression ratio, and a higher stock volumetric efficiency to be the inferior of the two, that makes no sense. Do the same "mild" mods to the 24v engine and I guarantee you will be making more power. Basically what you are saying is that a two valve per cylinder design is superior over a four valve design. In that case I think I should give F1 a call and recommend that they try it out. Hell, maybe even recommend that they use pushrods and a carburetor while they're at it.

F1 engines run at ~18K RPM, they are a COMPLETELY different beast than a street 3L that tops out at ~7K (or less...)

As for push-rods, pro-stock engines run push-rods and can hit peak hp at 9K RPM with 2v/cyl and a carburetor... At WOT a carburetor can perform very well, they just struggle dynamically...

Pro-stock port designs have been one of my inspirations for my 3L porting...

[phantomrt]

Does anyone have any flow numbers between the two heads? The DOHC probably flows double what the 12 valve heads can, even ported.

There's a lot of crap on 3si, as there is on any internet forum. For example, its full of people who claim 4 bolt main caps will prevent rod bearings from spinning on a stock engine.

[c2xejk]

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Originally Posted by phantomrt Does anyone have any flow numbers between the two heads? The DOHC probably flows double what the 12 valve heads can, even ported.

What would make you think that?

[Ondonti]

Quote:

Originally Posted by Turbo3.0 Those are some pretty bold statements that I find incredibly hard to believe. For an engine of equal displacement, bore, stroke, compression ratio, and a higher stock volumetric efficiency to be the inferior of the two, that makes no sense. Do the same "mild" mods to the 24v engine and I guarantee you will be making more power. Basically what you are saying is that a two valve per cylinder design is superior over a four valve design. In that case I think I should give F1 a call and recommend that they try it out. Hell, maybe even recommend that they use pushrods and a carburetor while they're at it. Also, a 25% power loss through a FWD transmission is a little steep. Just my 2 cents

I guess I will have to teach you a lesson about cars.
I am using real facts. You are using what we call magazine racing.

Factory advertised hp is just that. An advertisement.
24v dohc motors make 165-170whp. That has been proven many hundreds of damn times on the dyno.

Call up Chris @ 3sx.com and ask him!



25% power loss? this is you doing magazine benchracing because you have no idea what you are talking about.
Those motors are overated about 20 crank hp from the factory.

The actual difference between mitsubishi 12v and 24v dohc motors is 15whp. 15whp! (not talking about chryslers)
AND in case you didnt know, the stock 12v cams seem to be milder the the dohc cams.
2 valve motors require more lift because of the larger valve size and the 12v's cams have about the same lift as the dohc heads.

When you put a real cam on the 12v (a cam that should have been stock) it makes a huge difference.

Regardless of all the theoretical benchraces you can use with "what should make more power" there is this thing called reality that we are all bound by.
I can go into this in greater detail later.

------------
If you built a dohc 24v to make power @ 9000 rpms then it could make a lot of power.
I dont think anyone here is ever going to do that.
The car would run like crap between 1000-3000 rpms and not be a street car.
The 12v can in the end make about the same power as a 24v because we are not building a 10k rpm race car.
If you watch the dyno differences between the 12 and 24v the 24v only makes more power above 5k and I will also bet that the difference would mostly disapear if the sohc did not have the wrong cam lift from the factory.

[Shadow24V]

hey brent, i got a question on something you mentioned earlier - rocker arms. where did you get a quote for ~$500? and do you know when in the RPM range/cam lift that the rockers become a failure point? (kinda curious if the 24v split Y arms are prone to the same fatigue etc)

[Ondonti]

That is a quote that frank told me about. I never did the pricing.
Im not really "hooked up" when it comes to getting stuff like that.

[Shadow24V]

ahh ok. i was more curious about WHEN you needed them than where to get them at this time. just wondering if they break on you at higher RPMs or whatnot

[Tim_K]

Someone look up the specs on the 1/4 mile times and speeds for stock 24 valve cars, like Stealths and 3000GT's, and compare them to stock 12 valve cars.

Then we can use an online dragstrip calculator to get some WHP numbers for comparison.

My '93 Shadow ES ran mid 16's at 82 mph before I started doing some light mods on it. With 3100 pounds racing weight, that equals 136 HP. I went to google, typed in 'drag racing calculator', and used the Ray Hall one for my numbers.

I've never understood why so many 4 valve per cylinder twin or 4 cam car engines have such low amounts of valve lift. It's ridiculous. They give you more valves and cams, and take away lift! And the answer "because they don't need more" isn't a good enough answer. If 0.300" lift gives you "X" power, then 0.400" or 0.450" lift should give you the ability for "X+" power, assuming everything is properly set up. Why not USE the flow capabilities of the multivalve heads if you have them?

[c2xejk]

Quote:

Originally Posted by Tim_K I've never understood why so many 4 valve per cylinder twin or 4 cam car engines have such low amounts of valve lift. It's ridiculous. They give you more valves and cams, and take away lift! And the answer "because they don't need more" isn't a good enough answer. If 0.300" lift gives you "X" power, then 0.400" or 0.450" lift should give you the ability for "X+" power, assuming everything is properly set up. Why not USE the flow capabilities of the multivalve heads if you have them?

First, at low-lift the valve and seat are the "limiting factor" for flow. As the valve lift increases port throat at some point becomes more of the limiting factor... So there are deminisioning returns on increasing valve lift.

Second issue, increasing the valve lift effects the hp/trq curve. Ideally you want the air ramming in so that you can fill the cylinder above 100%. So if the head flow EXTREMELY well, the cylinder may fill to 100% and then hold instead of having a long slow fill that gets you 101, 102, ... 130% fill of the cylinder. So if you are going for high RPM power only, yeah, lifting the valve a little further could help. But low-rpm power would suffer...

Then there are mechanical issues. How fast can you lift the valve? How fast can you drop it? Drop it too fast and it will bounce and/or pound the heck out of the valve seat... Neither of those are good for performance or durability.

Then there are valve overlap issues.... If you have a port designed for high-rpm (ie bigger ports) and you have lots of overlap, then you will likely have big reversion issues at low rpm... That would further kill low-rpm hp...

It is all a matter of trade-offs... On a street driven engine, you generally need a fairly broad power band to be "driveable"...

[Turbo3.0]

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I guess I will have to teach you a lesson about cars. I am using real facts. You are using what we call magazine racing. Factory advertised hp is just that. An advertisement. 24v dohc motors make 165-170whp. That has been proven many hundreds of damn times on the dyno. Call up Chris @ 3sx.com and ask him! 25% power loss? this is you doing magazine benchracing because you have no idea what you are talking about. Those motors are overated about 20 crank hp from the factory. The actual difference between mitsubishi 12v and 24v dohc motors is 15whp. 15whp! (not talking about chryslers) AND in case you didnt know, the stock 12v cams seem to be milder the the dohc cams. 2 valve motors require more lift because of the larger valve size and the 12v's cams have about the same lift as the dohc heads. When you put a real cam on the 12v (a cam that should have been stock) it makes a huge difference. Regardless of all the theoretical benchraces you can use with "what should make more power" there is this thing called reality that we are all bound by. I can go into this in greater detail later. ------------ If you built a dohc 24v to make power @ 9000 rpms then it could make a lot of power. I dont think anyone here is ever going to do that. The car would run like crap between 1000-3000 rpms and not be a street car. The 12v can in the end make about the same power as a 24v because we are not building a 10k rpm race car. If you watch the dyno differences between the 12 and 24v the 24v only makes more power above 5k and I will also bet that the difference would mostly disapear if the sohc did not have the wrong cam lift from the factory.

You seem to be basing everything on one source and a lot of guessing that you claim as "reality". Your original claim was that no 24v 6g72 could ever come close to making the kind of power those 12v engines were making. What I'm saying is that with two identical engines, the one with the capability of flowing more air will have the higher power potential. This assumes identical flow characteristics of the ports, cam lift/duration, and scavenging through intake runners and exhaust tuning.

Who's to say no one has built a 24v engine that revs to 8 or 9000? I dare you to go onto a Honda forum and tell them that they can't build an engine that makes power at 9000+ rpms and not be streetable.

Get some new sources and maybe some comparison data with similar mods and I might start believing your bs. You might also want to consider reading a few of those books on engine theory "that I base everything on" and stop basing everything on a couple examples.

Also, how does my drivetrain power loss statement make no sense?

[Tim_K]

While we're talking about power curves, I have another question.

With its very short 2.99" stroke, how is it that the 3.0 makes so much bottom end torque and mid range power?

My guess is the very short cam timing, keeping cylinder pressures fairly high at low-mid rpms.

[lookin]

c2xejk

I sure wish you would make intake inserts that shrink the port diamenter and increase flow velocity. That way us poo folk, who cain't 'ford no ported heads, could have somthin to hep out.

Yep, by crackie, I sho do.

[c2xejk]

I have an untested one for the exhaust port...

[phantomrt]

Quote:

Originally Posted by c2xejk What would make you think that?

Just a hunch.