Can you offset-grind the crank instead of using 198 rods for a long-rod (equivalent) conversion? If so, how much will\could it take?

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

The short answer is no. It doesn't really work like that. Stroke and Rod length are two very different (but related) aspects of engine dynamics. The other thing is, there isn't near enough meat on a 225 crank for that much offset grinding. It would probably be cheaper to buy custom rods than the crank machine work would cost.

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-MattMan
LEANED & MEAN

It depends on what you are wanting to accomplish...

Yes you can offset grind the crank...

Yes you can put in longer rods...

Sometimes you can do both, if you use pistons with a shorter distance between the piston pin and top of the piston.

D.D. does a nice job illustrating some options here: http://www.slantsix.org/articles/stroking/stroking.htm

TY Matt and Jace,

I'm looking for better pistons (lighter, less friction, better sealing) and think the 198 rods or offset-grinding to a similar benefit might be a good way to go as a longer rod seems to offer better piston options. I appreciate your opinions. My current thought process is that steel rods - while heavier - will offer greater longevity than aluminum rods. I have no plans on racing the engine but don't want to redo my work down the road because of rod fatigue. I'd love for someone to tell me that that's the old-school way of thinking and things have changed!

Matt, exactly my worry. No biggie, it's easy enough to spec with the crank out - just running some possible outcomes and options to be better prepared once I crack the block open.

Jace, I read that article a few times - both longer-rod and offset-grinding ideas are documented by DD, but I'm still not 100% sure it answers the question will offset-grinding result in the same outcome as switching to 198 rods.

Still working on it - more comments welcome.
-C

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

Offset grinding the rod journals on the crankshaft will increase the stroke of the piston, thereby increasing the displacement. There's only so much to be gained (without checking the article I think it's on the order of 0.050"), and it reduces the rod journal diameter so you'd need custom rods. This is really not worth doing for most builds. I doubt more than a handful of people have ever bothered to do this with a slant six.

Using a long (198) rod with a 225 crankshaft does not change the displacement of the engine. It increases the rod ratio, which reduces side loading of the piston against the cylinder, which reduces stresses at higher RPM. You also need a piston with a lower compression height, because your stock pistons would crash into the top of the combustion chamber with those longer rods. This is why most people with long-rod builds use some variety of metric Chrysler turbo piston. This is a stronger piston (hypereutectic aluminum, I think) than the stock cast aluminum slant six piston. This combination also increases your compression ratio without a whole bunch of milling, but you'd have to do some forum searching for more details.

Stock slant six rods (170, 198, or 225) are not aluminum. They're also pretty stout, as many race engines built by forum users here will attest.

I'll ask the "Dan" questions: What are you trying to accomplish with this build? Do you intend to rev the crap out of it or are you more interested in low-end torque? What's your budget?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Great detail Frank - thank you.

Here's the background:
Planning on a performance rebuild for street torque and power - not a racer - just a strong street performer.
Looking for 230ish HP at the wheels with as much torque as I can get without suffocating the engine on the highway. MPG is not a concern.
My travels are about 60/40 backroads (40-50MPH) and highway (65-70MPH). Warm weather weekend cruiser.

My plans so far:
> Edelbrock AVS2 500CFM carb (the new one with the annular discharge nozzles) - should give a better off-idle response than earlier carbs
> Electronic fuel pump with regulator/bypass back to the tank
> Offenhauser 527OK intake
> Lokar cable throttle & transmission controls using Lokar's bracket made for mounting to Edlebrock's carbs (sounds easy)
> Single snorkel intake with a 4" cold air intake tube from the radiator support.
> CC and port the heads for as much velocity as I can get without opening it up too much that I lose density. I don't plan on opening it up much at all - factoring about an 80-grit finish. Clean up the chamber dome.
> Bowl hog the throat and 3-angle valve job
> 1.70ish and 1.45ish valves - stainless with 7mm or 8mm stems for lighter-weight (still figuring out - part number suggestions welcome)
> Beehive valve springs & tool steel retainers (still figuring out - part number suggestions welcome - CompCams seems to have the gear)
> Standard pushrods (maybe)
> 10:0 compression (necessary machine work/milling based on actual measurements)
> 3.5 bore (or equivalent MM) matched to piston selection
> Pistons are unknown, but want to be lighter, seal tighter, and less parasitic drag (still figuring out - part number suggestions welcome)
> OCG 346 cam | Duration @ .050, 234/228; Lobe Separation, 106; Lobe Center, 102/110, Lobe Lift, 317/319, Valve Lift 476/479 (clocked at 100°)
> Ferrea LF1004 lifters (have - 66 grams each. I know it's not the heavy side of the valvetrain, but compliment other lightening and strengthening)
> Steel 225 rods with typical reconditioning and polishing (not fond of aluminum - feel steel will last longer)
> Port match intake/head & exhaust/head
> Balance reciprocating assembly/components & true lifter bores. The machine shop has CNC - so the work is precise and quick.
> NOS oil pump (running 10w30 synthetic Mobile high-mileage for the added Zinc since this is a solid lifter engine)
> Chamfered #1 crank bearing for timing oiling
> Romac harmonic balancer & timing chain
> Thermal barrier coatings: piston head, valve faces, cylinder head, exhaust ports (increase cylinder pressure and reduce detonation on pump gas - head will be done by Swain)
> Anti-friction coatings: crank & cam bearings, camshaft, lifters, oil pump gears, piston skirts, valve stems and backface, rocker shaft, rocker pad & ball (parasitic friction reduction - mostly DIY - cam will be sent to Swain because it's too large for my toaster oven :)
> Oil-shedding coatings: intake runners & ports (reduces fuel dropout, increases velocity - by Swain)
> Evans waterless fluid (reduce potential detonation at 10:1 & pump gas)
> 22" radiator & dual electric fans & fully shrouded
> 6:1 Headers (I'm running an original set of MP 6:1 headers through 2.25 pipe and Delta-50 FMs) w/white (old school) thermal coating by Swain
> HEI electronic ignition conversion - GM D1906 module & heatsink with Pertronix epoxy-filled 45111 coil at 0.600 ohms (upgrade from current MP electronic ignition & orange buzz-box)
> Decent wires and UR5/6 plugs (the ones Dan mentions a lot)
> 60 AMP alternator (don't think I need more - replacing & upgrading the engine and headlamp harness this summer)

Plans after that call for power front disk-brakes, 8.25 rear w/3:23 gears (anti-friction coated ring/pinion w/synthetic oil) & TransGo TF2 904 transmission kit, custom torque converter (2300 stall?) w/ synthetic Dexron-6 fluid - then lastly I'll tighten the suspension with matched 150# torsions and springs with select use of rubber & select use of poly bushings, and a front swaybar (if needed). Hotchkis adjustable shocks are already at all four corners.

Budget - don't have one, but I'm patient.

Comments - critique - experiences to share - all welcome (I'm hoping for a lot of it!)

This is an awesome group, I've learned so much about the /6 since joining (former Ford small-block V8 guy) and hope I'm on the right track here - thanks all!
-Chris

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

You might want to see this thread for kickdown options other than the Lokar, which some installers find problematic.

Spend time and effort on this (port/polish, etc—Doc has published info on how to do this)

That is an unnecessarily high viscosity—we don't live in 1955; higher viscosity does not mean better lubrication, better protection, or better anything else, and on a new engine where everything's tight a lower viscosity does a better job by getting into the tight clearances faster. 5W30 will reduce parasitic drag and reduce stress and strain on the oil pump drive. As for Zinc: We don't live in 1985, either. See here and here.

In my experience this stuff works as claimed.

With altered piston deck height and head milling, the projected-nose plugs may no longer be a good fit, and you may need a colder heat range of plug anyhow (something like an NGK № 6 in whatever variety)

60A is plenty, but since you'll need to upgrade the charging circuit anyhow, you might consider an upgrade to a later-model alternator such as a Nippondenso 40/90 item. Smaller, lighter, more efficient, better charging at idle, etc.

All Dexron-6 fluid is synthetic, so pick a reliable brand rather than wasting money on whoever is charging extra by trumpetting "SYNTHETIC!!!" on the label. (No Dexron fluid has a "t" in the name )

I'd plan on it if I were you.

Also see this post for ideas on other upgrades that go from being a good idea to being a really good idea with a stronger motor. Better seatbelts, better lights, etc.

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

Check the Engine Build Matrix.

I have a couple stroker cranks. The one in my Valiant swings 4.475" of stroke on standard slant bearings. I had it built in 2007, at a cost of $750ish. Can't remember exactly. Weld up and cut, straightened, no nitride. It flexes too much for that.

The other is a 4.440 stroker that swings Chevy Journal sizes. That gives a bunch more space to offset. I have a set of R&R Aluminum bottom loading rods that work on it. I ought to go measure my titanium rods. I think I had them built on a Chevy journal.

This kind of thing can be done, to good effect, just remember that a long stroke engine won't be spinning up to high rpm.

The Hooptie engine displaces 250 CI with 0.45" over pistons. The compression height is pretty small. I can't remember at this stage of the game what it was. Not the most important numbers floating around in my head these days. I'm pretty sure it's in the matrix.

It was an interesting experiment, and it makes gobs of mid-range torque. It will never post high HP numbers, because it doesn't like life above 5000 rpm. It still was able to put my four door Valiant down into the mid 14's. If you want an engine that pulls hard from 2500 to 5k or so on a four barrel, then go for it. It'll take more cam than you might expect.

CJ

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Part of Tyrde-Browne Racing

Molner rods are steel, as are K-1, not aluminum. They are 198 length 7.005 inches.

If you want stock 225 rods, I have several sets of new. PM me.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

> Good stuff.

TY Dan - as always.

BTW, will likely use the Stromberg WW3 initially - thanks again for the carb.

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

Somehow I missed that all this time! That opens options. Thanks Charrlie.
-C

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

I have - good stuff, I picked up a lot of tips there. Thank you for all your build info, much appreciated.

TY,
-C

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'68 Barracuda - taking advice on increasing street torque, power, & road handling. Click To See It

csheehy, you look to have crossed up your {quote} {/quote} levels in your reply to my reply—might want to hit {edit} and see if you can fix it. I'll untie the knot here in this re-re-reply:

There's good stuff there, yup, and bad stuff there, too. Everyone's an expert on the internet, just ask us/them/me/you/him/her!

I think you could make a much wiser choice. Lubegard aren't quite as slimy as some of the other snake oil people (Lucas, Slick-50, etc) but they don't back up their stuff with science (compare Evans coolant) and they tell enough whoppers and make enough bogus claims that they're best avoided. Also, they're not a legitimate brand of Dexron-VI. The list of legitimate, licenced Dex-6 fluids is here. You probably won't kill your trans using the Lubegard stuff; these transmissions are sturdy enough to withstand even seriously deficient fluid (Type F of any brand), but why not use the best you reasonably can?

Also, ATF is specified in some GM and Ford power steering systems. It is bold-typeface UNspecified in Chrysler systems, and is notorious for causing leaks and problems if misused that way. Use the correct Chrysler-spec power steering fluid.

Fer sher, fer sher!

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

Don't waste your time with the Offy, that manifold is not much better then a cast iron super six. Go straight to a Clifford. Perferably the water heated version. The 500avs was a good carb, It has problems with the floats. Maybe the 500avs2 will be better.