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 Post subject: Re: 351c alm blocks?
PostPosted: Fri Mar 30, 2018 6:28 pm 
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Posts: 489
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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 Post subject: Re: 351c alm blocks?
PostPosted: Fri Mar 30, 2018 10:01 pm 
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6 bolt mains on the Teksid blocks I think.

Although they went to a cast iron block on the ‘03-‘04 Cobra engines which had roots blowers.

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 Post subject: Re: 351c alm blocks?
PostPosted: Sat Mar 31, 2018 10:19 am 
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Joined: Tue Jun 02, 2015 2:28 pm
Posts: 216
the aluminum block which is supposed to "grow" when it warms up. Who knows.

Well we do know that aluminum expands at a different rate than iron.
Overcoming theses changes can be unwelcome if not understood.
Even in the alloy world itself the expansion rates can be problematic.

BMW. steel push rods valve clearance 0.012 COLD
aluminum push rods valve clearance 0.018 COLD.


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 Post subject: Re: 351c alm blocks?
PostPosted: Sun Apr 01, 2018 6:09 am 
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Posts: 2416
They grow quite a bit.

My solid cam all-aluminum engine builds require ~.014" tighter lash when you set them cold, as opposed to ~.006" with a cast iron block/aluminum head scenario.

Compression ratio also changes between cold and hot instances. You can "whistle" a hot engine and it will be less than calculated, because the blocks expand past the rods/pistons.

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 Post subject: Re: 351c alm blocks?
PostPosted: Sun Apr 01, 2018 4:33 pm 
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For non drag race applications, almost everyone that has to brake and turn wants less weight on the nose. Scott Bloomquist used to pay Don Losito 3k extra to machine the exterior of SC-1 heads to drop another 6 lb total.
Btw anyone ever used the iron big bore Ford boss 9.2 blocks?


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 Post subject: Re: 351c alm blocks?
PostPosted: Sun Apr 01, 2018 4:39 pm 
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Yes sir, I have.

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 Post subject: Re: 351c alm blocks?
PostPosted: Mon Apr 02, 2018 9:47 am 
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Posts: 276
Mpcoluv wrote:
For non drag race applications, almost everyone that has to brake and turn wants less weight on the nose. Scott Bloomquist used to pay Don Losito 3k extra to machine the exterior of SC-1 heads to drop another 6 lb total.
Btw anyone ever used the iron big bore Ford boss 9.2 blocks?


I heard that story as well. In a lot of cases, even when minimum weight is involved, you're still better off to remove weight off the engine, so you can relocate it elsewhere.

I've heard a lot of stories over the years regarding things bloomquist did that sounded just strange.


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 Post subject: Re: 351c alm blocks?
PostPosted: Mon Apr 02, 2018 11:26 am 
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Posts: 489
booyah45828 wrote:
Mpcoluv wrote:
For non drag race applications, almost everyone that has to brake and turn wants less weight on the nose. Scott Bloomquist used to pay Don Losito 3k extra to machine the exterior of SC-1 heads to drop another 6 lb total.
Btw anyone ever used the iron big bore Ford boss 9.2 blocks?


I heard that story as well. In a lot of cases, even when minimum weight is involved, you're still better off to remove weight off the engine, so you can relocate it elsewhere.

I've heard a lot of stories over the years regarding things bloomquist did that sounded just strange.


What's interesting is how certain types of racing require different percentages on the chassis in order to perform the best. On dirt the car has a tough time getting too much rear percentage. I'm sure its possible to do so but most of the time they run a lot. On pavement however things are different. One of my customers who ran a modified on asphalt had to run much closer to 50/50 front rear weight bias where as a modified on dirt would probably run 53 or 54, maybe even more rear. On the pavement car we kept the engine in the rules mandated position but we moved the driver forward about two inches and when we added lead we even had a little up on the left front about even with the motor mount on the engine.

With that said if we had an aluminum block and the rules allowed it the engine would have been set back some more in the chassis which would have been good for handling due to changes in moment of inertia even though the percentages remained the same. I would assume that's what Bloomquist was doing by further lightening the engine as much as possible.


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 Post subject: Re: 351c alm blocks?
PostPosted: Mon Apr 02, 2018 12:43 pm 
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Absolutely correct Dave. The scales can't tell the location of the weight vertically on the car. So, depending on the track we could have the same bias on the sheet, but weight locations had to be noted and followed. Not sure if sprint cars followed that so closely but with the 4 link rear suspensions roll steer played a lot into the handling characteristics.

The whole lightening scheme was getting so bad that guys were going to aluminum and even titatnium bolts in order to gain a weight advantage. Stuff was nuts.


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 Post subject: Re: 351c alm blocks?
PostPosted: Mon Apr 02, 2018 2:30 pm 
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Posts: 489
booyah45828 wrote:
Absolutely correct Dave. The scales can't tell the location of the weight vertically on the car. So, depending on the track we could have the same bias on the sheet, but weight locations had to be noted and followed. Not sure if sprint cars followed that so closely but with the 4 link rear suspensions roll steer played a lot into the handling characteristics.

The whole lightening scheme was getting so bad that guys were going to aluminum and even titatnium bolts in order to gain a weight advantage. Stuff was nuts.


About 10 years ago I was talking to Doug Wolfgang and he told me that at the time a competitive World of Outlaws sprint car weighed 1050lbs. I think they have a minimum weight rule now but it is still pretty darn light. Another time I asked Gene Hamilton if the story was true that he spent most of a winter one year making every bolt on his USAC midget exactly the right length to save weight... Yes he said.


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