351C 2V heads - Aussie or not?

[Hack]

I see a lot of talk about Aussie 2V "closed chamber" heads and how great they are for 2V, lower rpm power.

Why bother with Aussie heads for 2V "street" power? Why not do domed pistons similar to the Boss 351 with regular 2V Cleveland heads?

I'm sure there's a reason it doesn't work, or a lot of people would be doing it. Why doesn't this work? Or is it just that the 4V heads are more streetable than people say, so it's really better to run 4V if you want real power?

 

[Route666]

2Vs give more torque, basically because they don't breathe as well as 4Vs. They allow slower air to get in well, but run out of lungs at higher rpms. 4Vs on the other hand have such fit lungs that at low rpms they have trouble producing power from slow moving air. It's like having a cam that is made for high rpm, doesn't produce torque down low. Whereas a torquey cam runs out of legs at highish rpms.

That's the gist I've gotten about it.

BTW I'd go for those Aussie aluminium "3V" heads by Cylinder Head Innovations, and get the best of both worlds, plus the benefit of aluminium. http://www.chiheads.com/main.html

 

[Hack]

Thanks for the info, those heads look really good.

I'm still curious though why you can't create "closed chamber" 2V heads using domed pistons. The 2V heads would way outflow a chivy, especially if you did a port and polish. So you should be able to make very solid usable power and torque at 1500 - 5000 rpm with heads that are dirt cheap. Cheap is my mantra, if you can't already tell.

And.. um what are the advantages of aluminum heads? They are lighter, that's an advantage. However, they are more prone to warping, problems sealing.. just less durable all around. They cost a lot more than cast iron.. you're not likely to find good aluminum heads in a junkyard.

Also, aluminum transfers heat mega fast. This might seem good, but it will reduce the output of the motor. You want to keep heat in the combustion chamber to make the best power. I suppose you could run a hotter temp thermostat to compensate, but I would be nervous to try that unless someone else had tested and proven it for me.

I'd much prefer to be able to use cast iron heads over aluminum. However, there are people here that know a lot more than me, I just have book learning.

 

[Route666]

Can't really answer your Clevo questions, haven't gotten into them.

Aluminium is only prone to warping if not heat-treated, or if machined before heat treating. This is no longer an issue, manufacturers have learnt their lessons. The CHI heads are T-6 treated. So are their manifolds btw. They weigh less as you stated. They cool the engine better, a byproduct of this is that they allow higher compression ratios, and thus more power, just from the material they are made from. Not to mention the fact that they are made well-flowing, not just modified, which can lead to holes in water jackets, etc.

As for the heat they take out reducing power output, the extra compression ratio you can run outweighs any heat loss through the tiny amount of material around the valves.

If you were keen on keeping heat in the combustion chamber, you would use a thermal barrier coating such as Jet-Hot's offering on the heads of the valves, and the crown of the pistons. To further aid the engine by utilising the combustion heat, coating headers and whole exhaust system in a thermal barrier not only makes the hot gasses work to your advantage by not slowing down in the exhaust pipe, and helping to draw air/fuel through the chamber, but the metal lasts longer, due to less extreme temperature exposure.

Also, as friction converts the mechanical work energy (the power we want out of the motor) to heat, which adds to the engine's overall temp, you would want to put a low-friction coating on the piston skirts, valve stems, and camshaft bearings and lobes. If you wanted to go crazy you'd do needle bearings, shafts and gears in the gearbox and diff gears too.

 

[D.Hearne]

As far as I've understood concerning using domed pistons with open chambered 2 bbl Cleveland heads, the reeason there is the domes don't fit the open chambers. And even with domes, they still don't produce the "quench" effect .

 

[dodgestang]

The best answer I can give you is cost/level of effort.

A shadetree motor builder looking to build up a better ride can pick up a set of Aussies, do a little work on them (studs, keepers, maybe a little porting/polishing) and bolt them on the car and get a nice bump in compression and realize an improvement in power because of it. They will also be a little more ping resistant.

Many part-time gear heads see this (and it is) as a perfect solution that lets them get more power from the motor without either the hassle of a full motor rebuild or (if they are doing it already) the added costs/time of finding/making the best pistons to meet their power/compression needs with 4v heads and can instead just order off the shelf standard rebuild type parts.

2v heads historically have the reputation of being better for the street because they produce more torque....but that isn't entirely correct. A better way to say it would be that 2v heads produce more low RPM torque as a % of total power than their larger 4v brothers do. Anyone who has had a 4v motor knows that they have gobs of power period. Simply because as a % more power is available higher in the RPM band people started boiling it down to concise yet unclear statements like "4v heads have no low end"

 

[Route666]

That's what I was thinking about the subject dodgestang, that 4V heads produce so much power, the chart LOOKS like the low end is poor, when in fact the low end is not bad, but top end is supreme. I've always heard the argument that it IS actually poor in low end though. You can't really run a 5.8L motor and have gobs of power up top and have nothing down low, it is after all, still a 5.8L motor.

 

[D.Hearne]

As one who has acytually driven a 71 351C 4 bbl Torino GT back in the 80's, I can honestly say that the 4 bbl headed motor had plenty of bottom end. Even in a heavy car like the 71 Torino, with a stock FMX and 3.00 gears out back.

 

[Hack]

Thank you for the information, gentlemen.

 

[ratio411]

Some comments:
Heat is not power once it is soaked into the engine. It is a by-product of the power created by combustion and must be dealt with for the integrity of the parts themselves. Parts melt, break, bend, warp, etc with the heat and detonation it causes if you were not to expell it.
That is why aluminum heads, headers, and forged pistons make power. They can dissipate heat and tolerate heat faster and better than heavy cast iron and, in the case of the pistons, cast aluminum.
Another note: I did some reading the other day that involved a comparison between Aus 2Vs and US 2Vs. As it turns out, the Aussie parts are a completely different casting in the area of ports as well as chamber. They were on 302 cid engines and have smaller ports than the 351 cid 2V heads.
I never knew this, I thought they were identical except for the chamber.
The flow numbers, although I do not remember specifics, were skewed heavily in favor of the US heads. The Aussie part was markedly less efficient in flow on both sides of the head.
They also have less room for porting to improve the problem.
Now that I know this, I think that I would opt for US heads in favor of flow on a 351, instead of the 1 point of compression that the closed chambers would tolerate.
It does make sense though, if you think about it, the only reason Aussie heads started coming here was the 'street-boss' craze of the late 80s-early 90s. This was 302 cid stuff, perfect for the 302C heads.
Some food for thought.
Dave

 

[Hack]

Some comments:
Heat is not power once it is soaked into the engine. It is a by-product of the power created by combustion and must be dealt with for the integrity of the parts themselves. Parts melt, break, bend, warp, etc with the heat and detonation it causes if you were not to expell it.
That is why aluminum heads, headers, and forged pistons make power. They can dissipate heat and tolerate heat faster and better than heavy cast iron and, in the case of the pistons, cast aluminum.
Dave

I don't have a lot of experience with motors, but these statements seem contradictory to my logic. Perhaps I'm missing something?

You say that heat is not power when soaked up by the engine. Since aluminum conducts better, that's an argument against aluminum. The aluminum will soak up more heat than cast iron. That means the cooling system will have to work harder. It also means the greater thermal conduction of aluminum will reduce power.

Aluminum can't tolerate more heat than cast iron. Aluminum melts at 1220F, while cast iron melts at 2400F. Cast iron has a lot more tolerance for heat.

 

[Hack]

Some comments:
Another note: I did some reading the other day that involved a comparison between Aus 2Vs and US 2Vs. As it turns out, the Aussie parts are a completely different casting in the area of ports as well as chamber. They were on 302 cid engines and have smaller ports than the 351 cid 2V heads.
I never knew this, I thought they were identical except for the chamber.
The flow numbers, although I do not remember specifics, were skewed heavily in favor of the US heads. The Aussie part was markedly less efficient in flow on both sides of the head.
They also have less room for porting to improve the problem.
Now that I know this, I think that I would opt for US heads in favor of flow on a 351, instead of the 1 point of compression that the closed chambers would tolerate.
It does make sense though, if you think about it, the only reason Aussie heads started coming here was the 'street-boss' craze of the late 80s-early 90s. This was 302 cid stuff, perfect for the 302C heads.
Some food for thought.
Dave

http://www.jason.fletcher.net/tech/flowdata/cleveland.htm

The information I've seen comparing Aussie and US 2V heads say that the flow is quite similar between the two. Check out the link above. Do you have a link to the information saying that the Aussie heads flow less?

edit: I don't know this Jason Fletcher guy from Adam so I don't know if his site is accurate or not. I just did a quick search and that's the first site I found. I always try to take info on the internet with a grain of salt.

 

[D.Hearne]

One more thing to ponder as to iron vs aluminum in heads--- true aluminum transfers heat faster than iron, but the engine is constantly producing heat thru combustion, that heat HAS to go somewhere, otherwise you'd have a melt-down. While I had the Canfield heads on my Ranger, I didn't see a difference in engine temps over the factory E7 iron heads. The engine DID make far more power with the Canfields over the ported E7's that they replaced. So in my opinion, the whole debate over iron vs aluminum is a waste of time. The ONE advantage I have seen in my limited experience with aluminum heads vs iron, is the iron head's ability to deal with over heating. I've had motors overheat with aluminum heads twice and both times, they blew the head gaskets. I've had iron heads do the same many times over the years and only once have I seen them blow a gasket. The gasket in question then was on my 68 Merc's 390 with it's original 34 year old steel shim gaskets , if they had been composite ones, they probably would have held

 

[ratio411]

Okay, I didn't want to get too long on post...
Aluminum heads conduct heat better.
Therefore they dissipate it faster.
This allows for higher compression without detonation.
Cast iron holds the heat and creates hot spots that ignite fuel before the spark plug can. Aluminum heads can run 1 point more compression than cast iron on the same gas.
That is what I meant by handling the heat better. Poor choice of words trying to keep it brief.
Forged aluminum pistons don't melt/break as easy as cast. Therefore more compression, heat, and detonation can be tolerated.
Headers dissapate heat faster than iron manifolds.
The idea is that once the power is made, the heat needs to go because all the parts have their limits and the fuel used is by far the most limiting factor. Gasoline is volatile and heat byproducts must be controlled or the whole order of the internal combustion process is out the window. If heat detonates the air/fuel mix before the sparkplug can, the engine will not produce work, it will just melt itself into a heap.
That is why potential heat is power, but by product heat is something to dissipate quickly. The cooling system does it's job no matter if cast is conducting heat slowly or aluminum quickly.
I hope this made sense, I am still trying to be brief...
Dave

 

[ratio411]

http://www.jason.fletcher.net/tech/flowdata/cleveland.htm

I have seen that site before, I have trouble making heads or tails of it.
The aussie heads have non-stock valve sizes is the first thing to notice. The 2v heads for the most part have stock valves in much smaller sizes. The unported 2v head flows better than the ported stuff?
Then the ported 2v head has more volume than the 4v stuff?
It all seems to be very contradictory, or at least full of typos or technical errors.
It would be great if that table was worked out correctly, but I would bet good money that there are typos and apples/oranges comparisons all over that page.
No links to what I read, but I will seek it out and post mag title, date, and page if I run across it.
Dave

 

[nosaj122081]

I've had a set of cc 4Vs, Aussie 302C's, and 2V's, and the Aussie port was definitely slightly smaller than the 2V port.

The chamber was also smaller on the Aussie than the 4V, so to run mega-compression, dome pistons wouldn't be interchangable between 4Vs and Aussies without work being done.

The quench effect created with the closed chamber heads allows more compression than the open chambers, open chamber max is in the mid 10's for pump gas with the right cam, whereas the 11's are possible with closed chambers and a properly setup quench clearance.

On the 393 I'm building the only way I could get reasonable compression was with open chambers and flat tops, so I'll be using a set of US 2V's (even on the bigger motor I've decided that they'll give the most area under the curve in my power range).

 

[Hack]

One more thing to ponder as to iron vs aluminum in heads--- true aluminum transfers heat faster than iron, but the engine is constantly producing heat thru combustion, that heat HAS to go somewhere, otherwise you'd have a melt-down. While I had the Canfield heads on my Ranger, I didn't see a difference in engine temps over the factory E7 iron heads. The engine DID make far more power with the Canfields over the ported E7's that they replaced. So in my opinion, the whole debate over iron vs aluminum is a waste of time. The ONE advantage I have seen in my limited experience with aluminum heads vs iron, is the iron head's ability to deal with over heating. I've had motors overheat with aluminum heads twice and both times, they blew the head gaskets. I've had iron heads do the same many times over the years and only once have I seen them blow a gasket. The gasket in question then was on my 68 Merc's 390 with it's original 34 year old steel shim gaskets , if they had been composite ones, they probably would have held

You're right about the debate being somewhat of a waste. It's not like you can buy cast iron AFRs and run a comparison. I think sometimes I just like to be contrary. Maybe I got out of bed on the wrong side.

It does bring out more people to comment and more learning though. I appreciate the comments from all.