SKYCOP1

I have been looking at some here and there, what makes them so popular?
I had set on a 68 Camaro with a 350 and it was very peppy. Thinking about up grading the stock 79 when I put the new carb and intake on it, and while I am at it I had given it some thought to change out the cam too. Anyone ever had the case of "WHILE I AM AT IT".....

I like to keep price in mind too. My goal now is only 300hp or so. ANYTHING better that the sreaming 225hp that she came with..


[Modified by SKYCOP1, 9:58 PM 7/2/2004]


[Modified by SKYCOP1, 9:58 PM 7/2/2004]

Twin_Turbo

the neat thing about them was the combustion chamber design, being a closed chamber, raltivly small and with an additional quench section near the sparkplug. They however are old technology and you can get a damn nice cast iron performance head for a good price, and you'll be sure it's a fresh casting and not messed up.

wesmigletz

I agree with Twin_Turbo about the camel hump heads. Any gain would likely be from th compression boost, without port work or larger valves. If you do go with a set of camel hump heads, I would look for a set that had the accessory bolt holes. In my opinion, the Trick Flow heads from Summit are hard to beat for the price and performance. Good luck. Wes

SKYCOP1

Thanks for the info, I have seen some around for 250$-300$ ready to go w/2.02 and 1.60 valves. I am looking for a cheap head that gives some good pwr. (HAHA sounds kinds funny huh

The stock ones I have probably arent to well off from the factory.

I need something to hold me over till I build a stronger motor. I have been recearching a 400 sm blk stroked (de or overstroked). Looks like there are pros and cons to both.


Tom :flag

Lt1er

I use the 186 casting DH heads with ported and polished 2.02/1.6 Manely race flow valves.

The big gain in your application is the 1 or more point of compression gain over 76 cc.

Many of the more modern iron heads have superior chamber and port designs, so they are really not worth throwing a bunch of money into.

SKYCOP1

What would a set of them put me back???

wesmigletz

Tom, I'm currently runnig a set of 186 heads on my '59; these have the accessory holes. The heads are fully ported, and my car runs hard. The engine in my 'vette was last built over 30 years ago, by a previous owner. If I were building a modified engine today, I would go aftermarket. Chevy High Performance magazine has the flow numbers for many GM and aftermarket heads posted on their website in the tech reference section. It's a good source for comparison.

My concern with a $300 2.02/1.60 head is, who did the machine work? If the heads are fresh, short cuts were taken that will later cost you time and $$$. If you wanted to have a set of heads built by a quality shop locally, that's a differernt story. I have the same reservations about aftermarket heads sold cheaply by outfits other than the original manufacturer... the internet is full of stories from people who got burned buying an aftermarket head, that had shoddy machining and or assembly from a second party vendor. I don't think you'd go wrong with a head from AFR, Brodix (race Rite, but these really need the CNC option), or TFS. If you go with an iron head buy from the manufacturer, or source them cheaply and have them built locally. I'd also recommend buying the heads you want to run on your future engine, because buying parts twice could delay your future build, depending on your budget.

For milder engines, Vortec heads are hard to beat, but out of the box, they are limited to how much lift they can take. Also, I believe the Vortecs raise the intake a little compared to a 23* head. This could be an issue if hood clearance is tight. Good luck.

SKYCOP1

Thanks for the reply, It looks like I will have to do some researching about heads this summer. I like the idea about buying the heads that I want and using them on the real engine I build. I was thinking about (still in the planning stages) the 400 sm block, I will correct myself about stroking it, I think you can only destroke it, But there is the drilling out of steam holes?? I have heard about. Surley a machine shop would be able to fo this.

Tom

toddalin

I have double-hump heads on my '64. Originally 1.94/1.50, they were hogged to take the 2.02 and 1.60 valves, pocket ported, and port matched.

Using 9.5 CR, the Crane 327/350 hp cam, Performer RPM manifold, Comp Cams 1.52 roller-tip rockers, coated Thorley headers, 2.5" exhaust and a milled 600 cfm dp Holley, the car makes 293 ft-lb and 293 hp at the wheels on the chassis dyno.

Compare this with the reports from the ZZ engine owners doing 225 - 250 hp at the wheels, and you begin to realize that maybe Chevy knew something back then.

At the SAME CR, an iron head will outperform an aluminum of the SAME design because the iron holds the heat of combustion in the chamber better.

turtlevette

NO,

Heat is not a GOOD thing. It causes detonation. My aluminum heads will take more advance and CR and allow me to make more power.

Twin_Turbo

yes, but detonation left aside, iron heads have about the same thermodynamic heat balance as an aluminium head that raises the compression about 1 point. Iron will make more power when you are at compression levels that will not cause detonation problems that can't be avoided with the iron head and necessitate an aluminium head to "loose" some of the heat. Just saying it causes detonation is not correct. Also, compression ratio isn't evenn the determining factor, cylinder pressure is and as a guideline dynamic compression is more closely related, although still not dependant on intake/exhaust efficiency but at least it takes into account the cam profile, a BIG contributor of where peak cylinder pressures occur in the rev range.

Say you have an identical iron and aluminium head, with a chamber size yielding a static CR of say 9,5:1, then the iron head will make more power.


[Modified by Twin_Turbo, 6:27 PM 7/3/2004]

turtlevette

NO AGAIN,

Chevy high performance did a test a year or 2 ago and found no discernable difference. With the aluminum you can advance the timing more and run higher compression pistons thus getting more power.

I am sick of hearing the internal combustion engine is a "HEAT" engine. That is bullcrap. If heat is all that great why aren't we all trying to run our engines at 240 degrees? An alky engine makes power without any heat.

Twin_Turbo

Dude, if we could run the engine at those temps they would be far more efficient, heat loss is the main factor why the internal combustion engine is poor as far as efficiency goes. The hotter the engine coolant, oil (and parts) are, the less temperature difference between it and the burn temperature, meaning the driving force between energy (heat in this case) transfer is lower, so more engergy could be used for what it's supposed to do, push the piston down.

It IS all about heat and what you are saying is reasoning from back to front, the reason you can go with higher compression with aluminium is that there's more heat loss, heate lost from the combustion is not taking part in the process of moving the piston, it's wasted energy.

Before calling something bull crap make sure you know what you are talking about. What did CHP test??? did they have an identical iron and aluminium head? Or did they make more power with an aluminium head that sported a point higher compression?

If it's the latter, it's true but if you give that as a reason why my comment is BS you are talking backwards again.

Aluminium will be able to make more power for 1!!!!!!! major reason. With the hugher compression ratio you will have higher culinder pressures actoss the board and if you want you can run a longer cam and make more top end power without having as much negative results from the pumping loss at low RPM due to the long cam. Since the compression is high it doesn't matter near as much if the cylinder filling isn't as effective as with a low compression. You will still be able to make good power.
The reasoning was that CR stays the same, in that case iron makes more power simply because heat loss is less.


[Modified by Twin_Turbo, 7:12 PM 7/3/2004]

turtlevette

combustion is what pushes the piston down, not heat or expansion of air fuel due to heat. Heat is an undesireable by product of the combustion process.

The CHP test was the same head and same compression ratio. Get the issue, read it and weap.

Twin_Turbo

expansion is what drives the piston, the reaction from air with fuel resutls in gaeous compounds, this results in an expansion. The reaction is exothermic, that's just how it is and there's nothing to do about it. Can't mess with the laws of physics. Heat also has a role to play in the amount of expansion because the higher the heat the more exited the molecules and the larger the volume a gas wants to occupy, meaning the driving force is even larger.

Ideal Gas law (although nothing is ideal but the real gas law is too complicated to put down here) PV = nRT n and R are constants so if T is higher so are P & V. Volume stays the same (chamber size + swept volume) so P has to climb and there's your drivng force.

Some modern engines (GDI) have a real clever injection system and a piston with a trough and a chamber designed so that the mixture burns at the center of the chamber and not on the outside. The major reason for fuel economy and power improvement is that the burn never comes into close contact with the cylinder wall and also doesn't spread over the entire chamber and piston. Heat loss is minimized.

CHP is all about sponsoring and articles written as promotionals. Don't believe all the BS they have in there.

I suggest you do some reading before coming on here acting like you know it all.


[Modified by Twin_Turbo, 7:12 AM 7/4/2004]

turtlevette

i would argue that you are seeing most of that extra hp because of the big valves and porting work.

turtlevette

Twin_Turbo

you constantly talk about detonation but that's not a fair comparison. To compare the both you need to compare it in a situation where both work, that means a compression ratio resulting in cylinder pressures that are not prone to detonation in the iron head. If you do that, then the aluminium head is at a disadvantage.

I'm not argueing that with the aluminium head you can make much more power with the higher compression ratios available but to make a good comparison all factors must stay the same apart from the head casting material. Comparing under circumstances where the iron head will not work because of detonation is not fair.

I know the gas law is a simplification but you said heat played no part, so I posted that to prove it does.

The use of the aluminium head is because of the higher compression ratios availavle with common fuels and no detonation, meaning the engine will become more efficient due to a higher cylidner pressure available because the heat doesn't get as much of a problem.

turtlevette

thanks,

thats the main point i was trying to make. There is no disagreement then.

Twin_Turbo

yes, but the initial point was that, detonation problems left aside the iron head will make more power than the aluminium if CR and head design (flow, port size, valve size...and so on) is the same.