How long to stroke a 9.2 deck block?

Like you, I thought long and hard before rebuilding my Cleveland. I finally decided on the 408 and went with the Scat stroker. Details and build specs here:

http://www.panterapassion.com/.../Details_Engine.html

The engine was flawless. Over 520 hp with 511 ft lbs of torque. Lots of performance and yet gentle enough to putter around town in traffic.

In 16 years of hard driving it never failed to start, never overheated and never stalled!

That’s about 100,000 miles of exciting, reliable performance. During those years I regularly went on long road trips in all weather conditions - Rocky Mountains to Death Valley Deserts. Over the years I rebuilt the carb once or twice, changed the Fluidyne once and changed the plugs and fluids every year or so.

But I never touched the engine again. Not once.

longevity of a 408 will depend heavily upon the pistons themselves, where exactly they size on the skirt in relation to how far they pull out the bottom of the bore

rod length also plays into how far the piston gets pulled out the bottom of the bore. it's a very delicate balancing act as there's not much physical room to trade off between the players

longer rod shortens the ring pack and increases intrusion into the pin void (can it be avoided in a 408?)

so getting back to the where exactly they size on the skirt issue, if the piston sizes low on the skirt and that gets pulled out the bottom of the bore you'll have a terminal case of piston rock that will present itself as early onset scuffing

Stroking a stock 351-C block over about 3.75" is a swamp you may not want to enter without professional help. Those 408s all use a piston that has the wristpin hole going right through the oil control ring groove. A support rail is supposed to go under the oil control ring to keep it from sagging; sags shorten the ring which leaves a space for oil to not be removed on the downstroke and oil use skyrockets. In addition, ALL piston rings rotate in use and when the oil ring ends reach the huge wristpin access holes, they stop and the sharp ring-ends bend, then begin scoring the bores. We had one 408 that was home-built with parts sourced from all over. The builder wasn't familiar with oil ring supports so he left them out. The engine was strong but used a qt of oil every 150 miles from new. A new owner finally pulled the engine and had it pro-rebuilt after 3000 unsatisfactory miles.

A second one had a different support-ring problem. The thin flat support ring has a dimple that matches a depression machined in the oil control ring groove bottom. Some use a tiny roll pin. This is supposed to keep the split support ring from rotating. But it only works if the support ring is installed right-side-up. This one wasn't done right in all 8 bores. Again, some support rings rotated, the ring ends got stuck in the wristpin access hole and stopped, then began scoring the bores. That one is now being pro-rebuilt, too. Both were new-owner Panteras in the Reno-Tahoe chapter of POCA.

Other things sometimes happen when a con-rod is chosen. If the rod chosen isn't long enough, the crank throws will hit the BOTTOM of the pistons on the downstroke. If the rod is too long, the piston tops hit the head. And with some combinations of parts, the front crank throw will hit the Ford oil pump that overhangs it. Cutting the crank for clearance unbalances the assembly, and on and on.... And we haven't even addressed cam problems.

Buying an engineered rotating assembly for a home-assembled motor might not be a guarantee of no problems, either. 45-yr-old blocks normally need squaring up in a surfacing machine which shortens the cylinder lengths, sometimes causing interferences between pistons and the heads. And I wouldn't spend a dime on reworking a stock block without a sonic check of the cylinder walls. I suggest getting a complete assembled short-block from an experienced builder to avoid such problems. The money saved going other ways is often non-existent by the time the bugs are fixed. Good luck, anyway.

Hello Art, welcome aboard.

I would like to add three concepts to the stroker discussion:

First - most people aren't aware a factory 351C pulls its wrist pin 1/8" out of the bore at BDC. Notice in the picture below that the 408 stroker only pulls the wrist pin out of the cylinder 0.038" more than the OEM 351C dimensions. BUT the 351C has a 1.65:1 rod length to stroke ratio, whereas the 408 stroker has a dismal 1.5:1 ratio. 4V & Proud's picture provides proof as to how important the rod length to stroke ratio is. That is one of the parameters the aftermarket is juggling with their stroker kits. A short rod length to stroke ratio not only places undue wear on the piston skirts, it also places excessive thrust on the thin cylinder walls.

Although everyone understands how deck height impacts a stroker project, the height of the cylinders is seldom discussed. The 351C cylinders are about 5.5" in height. This is the second issue. To sum up my perspective on the subject, the wrist pin should never be pulled-out from the cylinders. BUT if it must be pulled out from the cylinders, the amount it is pulled-out should decrease as the rod length to stroke ratio decreases. In the case of the 408 stroker the opposite occurs, the rod length to stroke ratio decreases yet the amount the wrist pin is pulled out from the cylinder increases.

The third issue is the wrist pin intersecting the oil ring groove. In the past it caused oil burning, today there are solutions for the resultant oil burning, it can be lessened by second ring designs or by adding a special dimpled rail support behind the three-piece oil ring. However, from my perspective that is a Band-Aid solution for poor engineering, I would never recommend assembling an engine in which this happens but I understand perfectly the different perspective drag racers have (remember this is a sports car forum ).

10 years ago Scat's piston for their 3.85 crank did not intersect the oil ring groove, but the material between the wrist pin bore and the oil ring groove was paper thin. That combination was designed for a deck height of 9.200" , and it had a wrist pin height of 1.275". I don't know if the dimensions of Scat's 3.85 kit have changed, but the wrist pins of other 3.85 stroker kits do intersect the oil ring groove. Its safe to say that in order to avoid the intersection of the wrist pin bore with the oil ring groove requires a wrist pin height of 1.300" (of course this only applies to engines with Cleveland heads).

You haven't mentioned what type of vehicle the engine is going into, the application (racing, cruising, etc) how often the car shall be driven, or what your expectations are in regards to the engine's longevity. IF you have expectations for longevity, if you plan to drive the car frequently, or if the car shall be used in road racing my advice would be to not exceed anything more than 3.75" stroke and a 6" Chevy connecting rod.

quote:

Originally posted by Bosswrench:
Buying an engineered rotating assembly for a home-assembled motor might not be a guarantee of no problems, either.

YES, not funny but lots of guys have come up snafu when the big box arrives, the vendor never did an actual mock-up before balancing the parts and you own them. mfg'rs change specs all the time, the same crank PN that the kit vendor ordered for the last 7 years may not be the same crank tomorrow ... happens a lot

lately, counterweights & snout dimensions change back & forth on a daily basis

who you buy from makes a big difference, the kit must be guaranteed complete & compatible, no "oh you just need this & that" during attempted assembly. we recently just had an issue with a crank thrust journal that was cut as an early prototype SVO / Cleveland mains retrofit deal, that special bearing & all evidence of its' existence has dropped off the face of the earth. nice crank

We have never had an issue with our 4"/6" combinations. It is the most popular kit we have sold.
Modern technology in pistons have helped a ton with oil control.
And the new Centralign design rod is a must for the Ford guys.

Pretty neat diagram you git there George. I did some measuring, the block Tod designed has a 5.750" cylinder length. We are looking at possibly pushing that another 1/2" It would have a scalloped design at the bottom of the cylinder.

I'd like to thank everyone for their help. I posted in another Cleveland based forum and I got several posts warning me about engine longevity with 4" stroke on a 9.2" deck block. So I'm still undecided.
Application will be: very hot street use, 5:14 gears ( but my tire size is 33" tall) hydraulic roller 238-240 dur. @ .050, very re-worked factory iron heads, Strip Dominator, once a week joy rider, no daily use at all, automatic 3,000 stall.

3,000 stall speed?

I presume that you are not talking about a Pantera here?

Is Tim Meyer's 'track boss' block better for stroking? Does it lengthen that part of the bore casting?

Tim?

quote:

Originally posted by George P:
The 351C cylinders are about 5.5" in height

quote:

Originally posted by TMeyer:
the block Tod designed has a 5.750" cylinder length. We are looking at possibly pushing that another 1/2" It would have a scalloped design at the bottom of the cylinder.

quote:

Originally posted by PanteraDoug:

I presume that you are not talking about a Pantera here?

I wasn't sure if I would be overstepping boundaries by posting here since I don't own a Pantera.

You're not overstepping any boundaries, you're most welcome here, and welcome to post. We've always had non-De Tomaso owners here, some folks just aren't aware of that. A large portion of De Tomaso owners are die-hard Ford enthusiasts, and they own other Ford powered cars as well, such as Cobras, Mustangs, GT40s, etc.

The 351C powered two other De Tomaso cars, the Longchamp and the Deauville. Several other Italian sports cars were equipped with the 351C as well, the Intermecchanica Italia, 3 ISO Rivolta models (Grifo, Fidia, and Lele). And in Australia the Bolwell Nagari was a 351C powered sports car.

I drove a pair of Mach 1 Mustangs as my daily drivers for 20 years. If I had the resources I would own a Longchamp and an Italia today; they are two of my "other" favorite cars. You are amongst like minded people ... and friends.