I am always looking for ways to do "somethime different" as far as Slant-6 engine build-ups so we have this new build plan in progress.

Some have already seen the lite weight cast crank we pulled out of an 82 SL6:

Click This Link

Looking at this light weight crank had us asking 3 questions:
- How light weight can we get the complete rotating assembly of a 225?
- Can we get this lite cast crankshaft to fit into a SL6 engine block designed to use a forged crank?
- Will the combination of lightest parts possible, survive and make good power?

The best way to find the answers is to build and test this engine combination!

We did some figuring and decided that we need to use the lightest piston we could afford and those are the 2.2 "long rod" pistons. The bad new is that the 198 con rods are, on average, about 30 grams heavier then a 225 rod, so we will be taking some serious weight off of the 198 rods.

With the exception of the cast crank, we have seen / used all these parts in past, long rod SL6 engines but this time we will work hard to get as much weight as possible, off of each component.

Before we do that, we turned our attention to fitting the cast crank into a forged crank block.
After reviewing different ways to machine the block's main bearing saddlles thinner, we decided to review a "scrapped" aluminum block we have, seeing that those blocks have upper and lower main cap inserts that are easily removed.

Come to find-out that the main caps from the alum. SL6 engine are already close to the needed width so we take measurements and pull all the saddle inserts / caps. Long story, short, only the #3 thrust bearing set needed "tricky" flycutting work on a milling machine, the rest of the "thinning work" was done with a hand grinder!

After many hours of machining, fit checking, grinding, fitting & grind some more... here is a photo of a late model cast crank, resting inside of a early aluminum SL6 block.
DD

Buster is trademarked! Nah, just joking it's a perfect name cause like you said it will either "bust" the weight limit or "bust" the engine. Did Twiggy finish strong? Two questions...
What would be the weight savings with aluminum rods?
What would be the weight savings over using the 170 set-up in the same set-up (ie stroker 170) assuming you had a block to use?

Two things that might help save weight on the rods will be the polishing I metioned earlier and the fiat owners cut the bevel at the big end so there is a perpendicular cut between the beam and the surface that contacts the side-to-side of the crank. http://www.youtube.com/watch?v=1Gf4ZB-ydS0

Is this engine going to use that aluminum block or was that just an exercise before going to town on an iron block?

I think this engine will work well if the reciprocating parts are light enough. Otherwise I can see the crank flexing and making life hard for the main bearings.

I imagine I'll have to wait some time before it's built and flogged sufficiently to know for sure.

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Joshua

I'm gonna watch this one a bit closely... since I've played with the cast crank and think I'd like to try a long rod cast crank setup and see where it 'goes'....

Thanks Doc!

-D.Idiot

I must agree this is defintely a thread I wish to follow. I contemplated talking to a cnc shop and having them turn out a billet crank. Though it would be stronger it may not be lighter, so I would love to see where you hit on reliabily vs horsepower. It seems like for most stuff in the slant six world is strong enough to survive with what we can do. What hp numbers was "buzzin half a dozen" doing on his cast crank? Have you detonated a cast crank yet? Sorry lots of question Doc you got more expirence than me.

As Josh stated, keeping the rods and pistons light will help reduce stress (flex) on that flyweight crank so we need to be serious about getting weight off those parts.

Hoping to put it all together in the "scrapped" aluminum block, now that the crank fits into it. We got nothing to loose (except time & $$$) if we blow that block into pieces because it is already .040 over and has serious corrosion and delamination around the tops of the cylinders. This block was scrapped because it will no longer hold a head gasket seal. We are going to try to fix the tops of the bores ... using some "new" approches.

Everything we do to this engine will be scary, light weight... will the crank break, or will it blow a head gasket, break a piston or bust a con rod...???
Bottomline, we are going at this build expecting to "bust-her"... hence the name.
DD

From the great dyno room in the sky, Smokey Yunick is looking on this project and smiling.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Looks like a great project, Doug. I have parts to make this happen at some point if it works well. I estimate you should be about 110 lbs under a stock late 60s iron 225 - wow.

Have you tried milling the heck out of an Al engine deck? It looks like you could take 0.100" off and just be getting into the head bolt threads, since they have deep reliefs before the threads start.

Happy sailing...

Lou

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Home of Slant6-powered fun machines since 1988

The Alm. block cuts 75 lbs and the lite crank saves another 21 so there is 96 lbs right there. A few lbs savings from the con rods and pistons and then all the standard aluminum accessories should keep the total package pretty light.

The real concern for this build is reducing the rotating /reciprocal weight and seeing if the engine responds well to that... with-out blowing-up.
As you know, grams you save out at the piston and con rod turns into pounds of forces, as the assembly spins higher and higher RPM
Alm. blocks will take big deck cuts but in practice, we don't usually take more then .030 to .050, just enough cut to clean-up the deck surface and to keep the compression in a reasonable range.

As already known, the special head gasket and open top deck design on these engines makes cylinder sealing difficult, even at 9 to 1 compression.
DD

Doug,

According to the 3 Al blocks I've weighed (76-79lbs), and a couple of late 60s - early 70s iron ones, the savings from the block alone is 84-90lbs. I guess the early blocks may be lighter. Not sure what the cast crank blocks weigh.

I have 2 170 blocks as of yesterday (thanks Chris E in MD!), so I need to weigh those too. I know my 198 crank is 68 lbs vs. 76 for a 225 crank.

OK, the weight numbers are swirling in my head - I'm obsessed!

The dream would be an Al block with cast crank and Al head. 140-150 lbs off the front of my road racer Project V would be unbelievable...

Lou

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Home of Slant6-powered fun machines since 1988

Your actual numbers are likely more accurat then my memory of weight checks I did years ago so your 110 lb weight savings estimate is pretty close.
This build-up shows that the light cast crank in the Alm block concept works and gets us 2/3 the way to that ultra-lite SL6 engine goal... the aluminum head is alway going to be the piece of the light weight SL6 "puzzle" that is hard to find.
DD

Doc if you need some track r/d work . Have Car Will Travel
Wire Possum
Dalton Ga.










It Aint Over Until I Win

From the last 'gutbuster' lifting experience putting a cast crank block in the trunk of the Hpak Duster (A-body the original SUV...), it's about the same weight as a late Forged Crank Block... but I agree, I'll lift a cast crank anyday over the forged crank....whew!


-D.Idiot

Cool project Doug.
Keeping with the lightweight theme, have you looked at the CAT ford flathead H-beam rods? 7.000", 550 grams, .866" BEW, .750 pin, 2" rod journal, $375
http://www.catpep.com/default.htm

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Franklin
'61 Valiant

I like the 550 gram weight, i will be hard pressed to get that low with factory 7 inch rods.
I don't like the .750 pin and these are a little narrow, that cast crank needs .945 to .950 in rod width.
DD