Originally Posted by 2000SilverBullet
The aluminum heads would dissipate heat much better and you could run higher compression or more boost without detonation.
Don't forget the benefits as well as shaving off some weight.
hmmm remove weight from in front of the drive wheels...sounds like a way to remove traction....though with the alum heads you could bolt the two cast iron units behind the bumper and gain traction....
yes there are many benefits to alum heads but remember that alum castings tend to relax when seasoned and can have lowspots (look at the Chrysler castings (2.2 2.4 and 2.5, GM 2.2L heads, Ford 3.8L (which still have problems even with MLS gaskets), Chrysler 3.3L and 3.8L (ditto).
Not to mention that the clamp load of alum heads sux with only 4 bolts per cylinder, even though we have "only" 3.8 inch bores, our head bolts are located pretty far apart so under cylinder pressure spikes the head will
lift, even if we managed to fit 1/2 inch studs, now if they found a way to put an additional 2 bolts per cylinder this would be greatly reduced but I donít see anyone working an an alloy block, though TA performances alloy block casting is a possibility the casting would have to be modified a bit and drilled in the SI/SII 3800 specs.
but remember the more weight you remove from in front of the drive wheels the worse your 60'* will be without full on Pro FWD 4 link front suspensions and massive slicks. Though like i said you would be able to bolt on the ballast at the extreme front of the vehicle and be all the better for it. Though that same weight with a cast iron headed engine would be even better... at the least it would lower the vehicles center of gravity a small bit. i see this being more of a benefit to the Fiero crowd.
also realize that a thermodynamic engine gets more efficient the more heat is retained in the combustion chamber as opposed to being lost out of the cooling system (detonation causing hot spots not withstanding) alum heads are a great bandage for an inefficient cooling system and poor combustion chamber design, more could be done with the cast iron heads if a reverse flow cooling system was utilized, that and a nice direct injection setup for less chance of preignition (look at the newer designs).
All modern pro stock (and other Max effort) engines use alum heads with a thermal barrier coating to help keep the heat in the combustion chamber, which cast iron heads are good at naturally, so yes if you had the alum heads with the thermal barrier coatings, you would be on par, but the cast iron heads treated would put them above the coated alum heads again, while lowering the chance of preignition hot spots forming.
and regardles the spark plug electrode is a large part of that issue, which can be cut back to reduce this possibility.
the biggest improvement would be a better splayed/canted valve arrangement with shaft mount beam type rockers or a hemi type valve layout, also remember that most cast alum heads have smaller
water jackets for thicker alloy to maintain strength on par with cast iron.
The largest benefit i see to these is head flow rates much better than the OE cast iron units, which is as it should be for aftermarket heads, but remember that the SII engines have a very large inherent inefficiency at high rpm cylinder filling, it'* horrible rod/stroke ratio/angularity which greatly reduces cylinder filling ability at high rpm'* as well as greatly increasing internal friction exponentially at higher rpm'*.
the short rods of the SII 3800 that give it it'* excellent low rpm Tq hinder it'* ability to make power up top, where as the SI'* ability to make top end power is severely limited by it'* poor cylinder head design.
this is why i think a SI/SII hybrid is the best of both worlds, and a stroked tall deck SI shortblock with those heads (in a high port design if not a canted/splayed valve arrangement) would be the perfect setup for a max effort 3800 engine buildup, with great mid and high rpm power potential, but cylinder head clamping would have to be addressed, just look at the 6 bolt per cylinder GN 3.8L max effort engines.
I could also see a better transaxle longevity with less low rpm Tq and traction limited launches. a max power engine is looking at the whole package, desired power and operating rpm'* those high flow heads while good wont be fully utilized by the poor cylinder filling ability of a short deck short rod engine.
those are my thoughts on this anyways