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 Post subject: Re: 351c alm blocks?
PostPosted: Tue Apr 03, 2018 9:14 am 
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Joined: Mon Nov 05, 2012 3:54 pm
Posts: 37
Thanks for posting Morgan's statement that only billet alum. blocks equal the hp of iron blocks. I had wondered for quite some time if this was true. Now I know!

DaveMcLain wrote:
blykins wrote:
From Speedtalk a few years ago....from user maxracesoftware, Larry Meaux:

"a back-to-back Dyno test on SBC
cast-iron Bowtie Block -vs- alum Block
everything exactly the same, just blocks were swapped
there was 30 HP difference at 600 rpm/sec

another back-to-back Big Block Chevy test = approx 40 HP

another back-to-back SS Hemi test on Cylinder Heads only
with cast-iron -vs- aluminum = 12 HP more w/cast-iron
same flow numbers + port vol CC's

the above were actual Dyno tests,
for theoretical HP/TQ differences between alum -vs- iron Blocks
by using FlowBench CFM Numbers -vs- what HP the different
block materials made on the Dyno =>

the results were=> for the same Flow CFM numbers,
i have yet to see an aluminum block engine make
the same HP/TQ that the cast-iron Block engine makes.

so far in all my Data,
the cast-iron Block always 100.0 % PerCent of time
makes more HP/TQ than an aluminum block

the last Dyno test was a recently as 2 months ago
with Brodix SBC and SB2.2 Heads
again the aluminum Block did not make as much HP
as the Flow Numbers suggested, about exactly the 30 HP
i found in those back-to-back Dyno test i did about 10 years ago
with another manufacturer's alum block -vs- Bowtie cast-iron.

to date, i have never seen an aluminum block make
1-the same exact power/torque as cast-iron
2-make more HP/TQ than cast-iron

it has always been LESS so far ."

There's another guy saying that the dyno showed a 40 hp bump on some engines with cast iron blocks. That's a big bump.

Darin Morgan (who works for Reher-Morrison) replied to Larry's post with:

"We see the EXACT same thing. The Billet blocks are the only aluminum block I have seen that makes the same power as a cast iron block. Aluminum blocks take longer "season" and stop moving around as well. The second or third rebuild always nets anouther twenty HP. Also, as the aluminum block engines get hotter on the dyno the crank case pressure rises dramatically and the power goes south in a hurry! They just expand and move around so much its impossible to maintain any semblance of stability."

Larry Meaux followed that up with:

"just example from ProStocker

BaseLine= 6.670 ET

6.616 ET = 100 Lbs less weight
6.709 ET = same previous weight, but 30 HP less
6.665 ET = 100 lbs Less + 30 HP Less
6.666 ET = 100 lbs. less + 40 HP less

if your alum block weight -VS- your cast iron block weight = 100 Lbs
then alum block is the way to go even though it looses 30 HP

almost dead even with 100 Lbs less + 40 less HP
at that point..no gain for aluminum block

so it would appear at that performance level,
an aluminum block has no advantage"

So, from guys who are a lot sharper than me, with some actual & factual numbers, if the hp difference is in the 30-40 hp range, you will not see any ET difference with the lighter aluminum block.


What's interesting though is that on some engines the aluminum blocks are thought to be superior for some reason. A few years ago I built a 4.6 Ford DOHC engine for a customer who ran it with two turbos. It ran 9.0's in a '98 Mustang with an easy tune up and it was built using an aluminum block. When I first got going on the project I asked him why and I was told that on those engines that the aluminum block was considered to be better than the iron versions. I don't know they look about the same to me but when I built the engine I set it up with .0015 main bearing clearance with .002 on the rods and it did just fine. He had many problems with spun rods etc in the past and I think it was strictly because the previous builders built it too loose on the mains in the aluminum block which is supposed to "grow" when it warms up. Who knows.


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