A few comments I'd like to make about aluminum vs iron: Aluminum is easier to cast and weighs less, with other improvements over the older stock iron castings, including smaller combustion chamber (quench pad), valve placement, increased valve size provisions, improved runner placement and size/shape, and substantial weight savings (did I forget anything?) It also has the effect of increased dissipation of thermal energy over iron, which means compression ratios for use with aluminum need to be about 1/2 to 3/4 of a point over what would be needed for iron, and with quench provisions from chamber volume/shape and piston shape mated to it, would permit an even greater increase in compression vs detonation tolerance, which is a positive thing. (((Not to mention ceramic piston top coatings))) Iron is more rugged and can withstand hotter temperatures (usually, depending on how thick relating to how much material was removed in any port work done) than aluminum, and would be desirable for the purists. To touch on something Derek said, even the 2 barrel boat anchor intakes could be (not necessarily more valuable than their 4 barrel counterparts) desirable to some, for reasons I have touched on in the past, with super-wide low-mid range powerbands with specialty usage in mind, or simply for originality. (off-topic, don't want to venture too far down this path here) Always remember that even though a certain part(s) may not be the 'ideal' or 'perfect' part for one application or target goal, there are other applications to which it (they) would be suited. It just depends on what you want. Nothing wrong with any it, of course. Just be aware of the pros and cons and target usage.
Forgot production costs being significantly lowered due to much faster machine cycle times, faster feed rates and SFM, not to mention more DOC, increased chip load, reduction in tool and fixture vibration, battling uneven cutting forces with rotating tools...and tool life possibly into the tens of thousands of parts rather than the hundred maybe seen per insert corner as opposed to cutting iron. I probably forgot a few.
The myth of the that "iron heads make more power than alum heads" has been disproven over the years unfortunately people still believe it as fact. Alum heads will work great with higher compression but they do not "need" it to make the power that an iron head makes. I have read several controlled studies on this that show no Hp difference between iron and alum heads that have the same characteristics like chamber size and flow numbers. Here is one: http://www.hotrod.com/articles/ccrp-0602-iron As you said though the alum heads will have several advantages. 1. Allowing higher compression ratios which will raise HP. 2. Closed chamber design allows for a quench to be optimized. 3. The iron heads can be ported to flow very well however they are prone to cracking once fully ported. The alum will flow better than 90% of the ported irons and be more crack resistant I predict. 4. Repeatability. Instead of trying to find a Buick expert in your area to port some old iron heads we can now order up some nice flowing heads and know exactly what we can expect. I've shipped iron heads and it's not cheep! 5. CNC porting options, again this will be great as we can just order up fully ported heads from Scotty Brown once he's setup the program and we will know exactly what cfm flow we will get. 6. The valves are moved closer to the center of the cylinder so we can use larger valves, and still use our TA roller rockers. 7. Easier to remove heads. Those iron heads are a pain in the lower back to remove or instal with an engine in the car. Plus the light weight and better handling is nice too.
I'm sure you've thought of al this, but just curious. Aren't the chambers smaller on the Alum. Heads so you'd just wind up with lower SC which you'd need for Iron anyway? By milling the iron heads and running a steel gasket could you make up some of the difference without the valves hitting?
Nobody has "told" me I need that comp. ratio, I'm afraid of leaving power on the table by not having it high enough (within reason) The only "factor" in me wanting 11.5 to 1 static is in preparation for the aluminum heads, OR is that to high, even for aluminum with a closed combustion chamber VS iron with an open chamber?
Correct, I had thought of the smaller chambers on the aluminum jacking the ratio higher VS the open chamber irons. I need to find out EXACTLY what the chamber size is going to be with the aluminum's Also need to know that before ordering pistons. Guess I'm going to buy a cc'ing set up, always wanted to get one! WOW, a lot of things to factor in when having an engine machined properly
Ethan is correct.. and Mark, I didn't mean to imply that you had to be "told" how to set up your combo, sorry if that is how it came across. It's just that so many times I see things like that, and it's because the poster has taken someone else's opinion on how things should be set up and repeat it. My dyno guy will tell you that eight tenths of a point is what is required to match iron to alumium, when considering static compression. Most of us who build motors for other folks tend to be on the cautious side of that, and go about half a point, with typical street/strip cam timing. Sean, that Hot Rod article is interesting, but far from conclusive. One motor, one test. I would agree that on that particular engine with that particular combo, there was no difference, but be careful about using one test for a universal rule.. It's a test that will be difficult to do on a Buick, since the aluminum heads are almost always so much better than the iron. I do have a set of 305cfm 430 heads, that would be interesting to test against an out of the box set of Edelbrock heads, that flow similarly. Maybe we will do that test in the test car program. Hot Rod said it best, they were just looking for a page filler... If they really wanted to claim that Iron does not make more power, they needed to build several different combos with the two sets of heads, because what they found could simply be the fact that the heads, regardless of which set, were not the limiting factor in that combo. Just like headers vs iron exhaust manifolds on stock engines.. not much difference, if any, because your not flowing enough air to tax the exhaust, or in Hot Rod's case, the SBC heads they are using. At that point combustion chamber temp is not a factor. Or, as they mentioned, maybe the water jackets are so good in that design, that there is no combustion chamber temp difference in that motor, but will be on another type of engine. That test may have raised more questions than answers.
TA is saying the heads will be around 54 CC once the valve job is complete. Scotty Brown has the blueprint for the TA heads showing the valve positions and therefore he can get you pistons with the valve reliefs in the correct positions for the alum heads. I will likely need to modify the valve reliefs in my pistons as they were made for the iron head valve positions, but easier now than once it is final assembled. I hear exactly what you are saying Jim regarding that article I understand completely that that ONE test is not conclusive of the opinion that the alum heads do not "need" extra compression to make the same HP as an identical iron. And like you said we will never know with the Buick conclusively because there is no identical alum vs iron head. I guess my point is that I have not seen the proof that alum heads drop the HP for an equal combo with iron heads as the only change. There are many other articles and dyno documentation that support the idea that changing the material of the heads alone does not change the HP if all the other factors are kept the same...If someone can show me proof showing testing that shows the opposite of what I am surmising from the research I have done then I am all ears and could change my mind if the evidence shows I am mistaken.
I think the material thing is a non-issue.. folks looking for performance aren't arguing to keep cast iron heads, in my experience with the 455, I can't imagine it not being the same with the 350. JW
There are high tech coating out there that the combustion chamber can be coated with to help keep the heat IN the combustion chamber, can use it on cast iron or aluminum. Would make this issue a non-issue and make aluminum come out on top because it could still be built with more squeeze. Derek
Regarding power differences in material, I would listen to Jim's dyno guy long before accepting any 'magazine type' article as valid. If interested in reading, much of Speedtalk's finest have seen the same thing. The entire aftermarket would not benefit from any such testing on equal terms, just something to think about. other than material differences, it would be sooo easy to make up for any power loss any number of ways.
By no means did I feel I was being told how to build my combo, nor did I feel you were implying anything, I look forward to your input on things such as these discussions, I respect your knowledge in these things So, generally, a half point more in compression when going to aluminum heads if its doable at the time. I honestly forget about the improved combustion chamber shape, valve positioning, and port layout/flow contributing to the improved power and tend to focus more on the material they're made of....aluminum Remember when GM came out with the "Vortec" heads for the SBC, made of iron, like the old style Chevy heads, but a drastic improvement in power, just from design. So I should rethink my comp ratio to more like 10/10.5 to 1 This is all GREAT input I'm learning!!
You should be safe at 10.5 Mark. Better safe than sorry, and it won't matter that much from 10.5 to 10.75... I once had an opportunity to drop the compression ratio, via head gasket change on the dyno. We went from 11.5 to 10.5... That 625HP 464 lost exactly 10 HP and about 12 ft bls at the peaks, and was pretty consistent in the averages.. it was a no brainer for the customer, who was present, to leave the thicker gaskets in. He ran pump premo in it back home in CA.. He reported no issues in the car, and that was years ago.
I was told the 522NP pistons that are in there are 9.25 to 1 @ .020 in the hole. I'm at .005 Plus my heads have .030 cut
Thanks Jim! I always look forward to your input and I value your advice! Now that I have a solid number to shoot for, I feel more confident. I've read dropping a point or 2 you don't loose a ton of power, but it sure is easier on the engine when using pump gas. Head gaskets, whats available for the 350 Buick that holds up to compression, and is compatible with iron/aluminum. My Fel Pro Blues were fine when I removed 'em, should I just stay with the Blues? I know Sean showed my some super duper HG's for the 350, but if I go ahead and build the engine for now with my irons, I don't wanna be spending 400 bucks on 2 sets of HG's
Everything I've read and seen on these says they are a copy of the 2nd gen LT1 design. The LT1 also came in several variations both with and without alum heads. I know they made a hot rod version of the LT1 known as the LT4 in 96 that got even higher CR of 10.8/1. It was very conservatively rated at 330hp.
