Iron block OR alloy block

Hi all. Im interested in some recommendations from your knowledge and experience.

First I'll state the essence of my query, then I'll give some background details to give you a better scope of what information might help me.

Should i use SBC Iron block OR cast aluminium block for a 1600hp CAPABLE street / strip build. (In particular it is a street master AH1 sbc block A356-T6 alloy.)

Now some details.

Vehicle is a corvette c4. I was originally planning to use a World Products sbc motown block. Twin turbo, EFI. Heads will be aluminium. I know this would work.

However, I recently came across a speed master cast alloy block for a price I'm happy with, and thought, OK, MAYBE it will work. But I am sceptical.

My intention is to mostly cruise, with seasonal strip and circuit racing. The engine management will have several power tunes with the highest output tune being 1600hp, (lowest 800 - 900hp). Only occasionally will it see 1600hp output tune.

I'm trying to get as close to OEM reliability as possible. Hence why I originally intended use of an iron block. I'm also curios to the truth of alloy blocks loosing power due to reduced ring seal with heat and high power levels?

Will the speed master block handle this as well as the motown block?

Do any of you have experience or knowledge on the speedmaster block I have mentioned?

Thanks for you replys.

Shane

Can't directly comment, but a few things you may wish to consider?

What tyres are you going to be running - if they've got sufficient grip you may have more of a problem keeping the front down that with traction, and a cast iron bloch will give you a bit more nose weight AND not only be most likely a bit cheaper but possibly more dimentionally stable.

The second question is the bore diameter, as a full 4⅛" bore will have thinner bore walls than a 4", and not only allow thicker sleeves, if used, but you have options in the sleeve material and strength.

Third thing would be the web thickness and how the mains' caps are fitted to the block, as that's a fir bit of cylinder pressure to be applying to them.

I would, probably, go for an aftermarket iron block and, if I were going to be running big tyres, maybe even iron heads (if available in the desired pattern) for a bit more nose weight and reliability.

Oh, some aftermarket blocks are also available with a raised deck - might be overboard for you, but could be something to consider if you're happy with the messing around with custom/special order intake manifolds and/or pacers and, maybe, custom exhausts if clearnces are tight?

Hi Gord, thanks for your reply.

All the reasons you mentioned are why I had originally planned to go with an iron block.

The only reason I considered this speedmaster alloy block is because it is for sale at the same cost as my purchase and import of the iron block.

As I mentioned, I was a bit sceptical of this cheap alloy block, although the supplier says it will support 1000+ hp.

And I'm really only interested in roll racing and circuit racing. Mostly however, it will be a weekend street cruiser.

I don't have experience with the block you're referring to unfortunately. I find LSX and Dart blocks most often in the 1500ish HP range, but there are likely other good options out there.

Ah, for the twisties a lighter allow block would be the way to go,

There's a big step from "1000hp" to "1600hp", so I'd pass on that option.

However, there are many other options that should be up to the mark, elbeit at a premium, such as BRODIX and DART, and there are others - but $$$s! Might be cheaper in the long run, though, as a block failure could be VERY expensive.

With those you will also have the benefit of custom features, like the larger "400" mains, and main bearing cap fastenings' options. I thought there was an extended 'skirt'option, like the LS/LT and "HEMI" engines that would allow a much stiffer bottom end with 6 bolt caps, but seems not - at least I didn't find it on a quick search - shame as with a custom dry sump pan...

Hi Gord

Yes, significant difference in hp Levels. In reality 600 hp is a whole extra engine, and a performance one at that.

I have done a bit of searching on the speedmaster block, and most comments are not favourable. Due mostly to it being a pro comp product, and for a long time now pro comp have a bad name in quality control. But, reputable retailers still offer this on their list.

I'm really not concerned about reducing weight, as my benchmark for performance of the c4... is the c4. And the Callaway Sledgehammer is my inspiration. They already handle very well with the weight of an iron block. Improvements are welcome of course.

I'll stick with my original plan of an aftermarket iron block for this build. Maybe in the future I'll do an alloy block build. Billet would be awesome.

I appreciate your input. Thank you.

Shane

Sounds great!