A local machine was recommending to stay away from Alum blocks because of "disadvantages" yet they gave no real reasons.

Is there any downsides to alum. blocks in N/A
Is there any downsides to alum. blocks under boost?

This of course excluding price.

 

Aluminum blocks are lighter, and can be fixed if they ever crack (as opposed to buying an entirely new iron block). If you're talking high compression in a N/A engine, or low compression with boost.... then aluminum is the way to go.

I believe he might be referring to the fact that cast iron 'heads' (we'll us heads in this case), are able to make more power with lower compression.... as opposed to aluminum heads.

Ask him if this is what he is referring to, regarding cylinder heads.....

 

iron blocks are simply stronger. There is a reason Ford went with an iron block in the 2003 cobra.

 

if you a boosting high psi with an aluminum block it will blow easier than an iron block. My friend drives a turbo honda (laughs) and they have aluminum blocks and if running high boost you need to sleave the block (put iron sleeves in the bores). I hear sleeving is expensive too but that would be the only down side to it i could see................... just get it sleaved if running high boost

 

on one hand alum block is weaker....

but as long as you stay under what the block can handle, it poses no problems....

25THRSS:
ford went to iron, but their blocks are STILL weak.

 

If you were to cast an alum block exactly the same as an iron block then yes the iron block will be stronger,however most aftermarket alum blocks are cast differently than iron because they are alum and are just as strong than their iron counterparts.

A good example would be the new TA Performance alum Buick V6 block as compared to the(no longer avalible)Buick Motorsports Stage 2 iron V6 block.The iron block has been known to make over 1500hp.The new alum block(I say new because 1 run of 50 have been cast so far)has already made 1200hp on a mild tune with no signs of core shift or weakness and is estimated to be able to handle over 2000hp

Another example would be the 2.2L GM Ecotec,in which the stock alum block structure and sleeves held up to around 750hp and with custom machined sleeves held together at 1000hp with no core shift.Not bad for a production 4 cyl block.

And lets not forget top fuelers run alum blocks that handle several thousand hp,of course they do pop but from my understanding it's usually not because of the block.

The biggest advantage to alum besides weight savings IMHO is they are able to(and are easier to)repair if something goes wrong and can be resleeved without much trouble should a piston let go.

For all the iron block lovers out there,I'm not trying to say that alum is better and I personally prefer iron but just saying alum has gotten a bad wrap.

HTH,
Steve

 

If you cast an aluminum block the same weight as an iron block, then the aluminum block will be much stronger.

Why do you never see a cast iron connecting rod?

 

I've heard somewhere that because the alum blocks need more metal to create the same strength, they sometimes have reduces coolant holes that actually tend to make them run hotter, despite alum. properties.

Any truth on that one?

 

depends on the design... if they made the water jackets smaller, its possible...


but ive never seen nor heard of a aftermarket block like that..... perhaps outside the chevy world.... *shrug*

 

OK… weird fact, for most normal grades of aluminum castings, steel and wood (spruce), when measured and compared by weight they have very similar strengths. The only place where aluminum (excepting more expensive, heat treated alloys) would have an advantage is where you need less strength then the smallest that the part could be easily made. Aluminum is also much easier to work then iron based alloys.

That being said, the reason that aluminum blocks have a bad rap in performance applications is that surprisingly, they have real sealing problems (at least prior to the most current generation of OEM engines). Surprisingly because you would expect an engine with an aluminum block and aluminum heads to seal better then one with an iron block and aluminum heads. The other thing is that aluminum blocks have to have harder metals inserted for almost any stress/wear point (ex, cylinders need either liners or a hard anodized coating to live without excessive wear), making working with them MUCH more expensive.

 

i've never seen an aluminum sbc without sleeves. heck, the ls1 comes with them from the factory! (NOT SAYING THAT THE LS1 IS A SBC) but if your going to spend that kinda cash on an aluminum block, by g0d it better be freakin'sleeved! not to mention that the top fuel guys are all running aluminum blocks and are claiming some 7000 hp

most of my friends that run in the NSCA in the bigger classes are running aluminum blocks as well

 

in reguards to this, and the comment he was quoting, EVERY aluminum block is lined.. or like 83crossfire said it has a special coating of some sort, although as far as i know that is pretty rare, and i'd imagine doesnt work very well, but i could be wrong, i dunno, anyways every aluminum block has a cast iron liner (or coating), thats due to the wear properties... aluminum cylinder walls would wear extremely fast

as to the question about cast iron rods.. what are most stock rods? arent they cast iron? in high HP applications they use forged steel -generally heavy, and used for the higher HP levels and forged aluminum - generally lighter, and while strong not as strong as steel, also wears out faster than steel

 

Pound for pound Aluminum is stronger than steel. Unfortunately we want to save weight so we are not pound for pound. The problem comes from the blocks rigidity in the cylinder wall and deck area. no matter how hard you try to support the *liner* not *sleeve* it tends to distort and lose seal. If you were to build two identical engines, one from high nickel cast iron and one from aluminum the cast one will make more power by virtue of better ring seal. In race engines the trade off of losing some power to gaining a weight advantage, easily repairable, and the ability to cast them solid with or without water jacket (which creates hot air heat pockets) as in the top fuelers yet still weigh less than it cast counterpart. There are aluminum blocks out there without liners, they coat the wall with nikasil, it does not work real well on high horsepower though. real popular on small 1-4 cylinder motorcycle engines. Aluminum rods are used in high impact (nitrous, alcohol, nitro) race engines that have a lot of detonation control issues to help absorb the shock, so you don't pound the bearings out of the engine every pass, which most due anyway.

 

As far as I know, Chevy pioneered the process in the vega 4 cylinder, and since then it's become fairly common on the high end eurocars, like the BMWs, Mercedes… Especially their bigger, high end flagship engines.

Cast or forged steel

 

What type of aluminum blocks are your referring too, because i see a ton of guyz pushing crazy power through aluminum blocks, particularly Donovan blocks. In the past 2 issues of Popular Hot Rodding there has been a couple cars, here's the links so u can check them out :
BattleAxe
"An all-aluminum 410-inch Donovan small-block V-8 adds plenty of edge, boasting 11.5:1 squeeze, Chapman raised-port 18-degree cylinder heads, Crower H-beam rods, a Callies crank, oil control components (pan, pump, and windage tray) from Stef's, and a Dart raised-port intake manifold topped with a Demon 875 cfm carb. For most, this potent powerplant's 500+ ponies would be enough, but not Bob Johnson. A custom Nitrous Works 250-horse spray bomb was added, and a complete secondary supplemental fuel system was engineered to feed it"

And i can't seem to find the Vette, any PHR readers will probly recognize it though, its a 63? Vette, twin turbo 355ci putting out something like 1000-1200 ft.lbs out of an Aluminum Donovan block, and both these cars are daily drivers..

 

World Products has just introduced a new aluminium Motown block. It can be bored out to 4.250 and is clearanced for a 4 inch crankshaft. It only weighs 85 pounds compared to 190 for the iron Motown. Contact World Products about it and they will send you info in the mail. They even offer all of their crate engines with the new aluminium block now. Great Stuff

 

i have a hard time justifying buying anything World...heard to many horror stories.

 

I've heard nothing but good from world products blocks.

The local Green rambler runs a motown block, never had a single problem out of it.

I've never been a huge fan of their heads however.

 

i had no idea that he ran one of their blocks, of course, i really don't know him well... not to get off topic, but i didn't know if you knew i wrecked my car. my new one will be here on friday.

 

yea, I saw the thread on here, nasty wreck. Sucks to hear that. Cool your getting another one though.

 

Almost all import manufacturers use aluminum engines (blocks and heads) in their cars - even some of their base cars! The LS1/LS6 is aluminum as are a lot of the new generation GM motors.

Aluminum saves weight and is easier to machine. If you use the right alloy and make the parts right from the start, aluminum is a great material.

Titanium, which is even lighter than aluminum and many times as strong as steel is making a name for itself in connecting rods and spring retainers - just don't detonate a motor - they shatter like glass. Of course $5k for 8 connecting rods is a tad expensive, but speed costs money.

 

My spool and yoke in my race car is titainium