[antirawker]

I recently picked up a SB 360 for my 54' Plymouth project and had a few concerns arise about rebuilding the motor prior to dropping it in. This will be my first V8 build and I've looked into dropping in a MP 4" cast crank to add low end torque. The car/motor will be used for daily driving duties and I plan on running aluminum heads, dual plane intake and a 750cfm'ish 4bbl carb and mild cam for low and midrange power. So with the added stroke of the 4" crank, will the rings start to crap out prematurely and need replacing after a few thousand miles? I've read up as much information as I could on the 4" crank being used in SB applications but they all seem to be weekend only or track cars, nothing really daily driver oriented. Well any information would be appreciated. Thanks.

-Ian

 

[firestone]

There is going to be more cylinder wall loading with a longer stroke. The easiest way to combat this is to run a longer rod. That will change the geometry of the rotating assembly, so that the force of the combustion is directed more down and less sideways. Either way, from what I have heard, with modern honing methods, and quality of modern rings, a longer stroke crank and shorter rod dont have as adverse of an effect as they used to.

Adam

 

[antirawker]

so with the 4" crank...6.123" rod length and KB .30 over hyperutectic piston with total seal rings, do you suspect it'd be suitable for daily usage?

 

[Max Keith]

Stroked

I hate to be the bearer of sad tidings but you cant run a 4 inch stroke crank with 6.125 rods in a small block Chevy. The block only having a deck height of 9 inches, and your rod and throw adds up to 8.125 inches, leaving you with only .875" from the center line of the wrist pin to the deck of the piston. With a .927" wrist pin, that only leaves you .4115" between the top of the wrist pin and the deck of the piston, not including the part of the rod sticking above the wrist pin.
To run a 4 inch crank will require using the 5.535" or 5.7" rods, and then you run into rod angularity causing severe side thrust on the pistons, making for abnormal wear on the cylinders, rings, and pistons. I wouldnt recommend such a combo for a street engine.
A 383 stroker would be as far as I would go with it.

Even with the best of materials, there are just certain laws of nature that cant be overridden.

 

[antirawker]

good thing im running a MOPAR setup. :thumbup: Very informative none the less Max Keith. By chance do you have any know how with the 4" crank in a 360 Dodge setup though? If so, Id really appreciate it. Thanks.

-Ian

 

[Max Keith]

stroked

Sorry but I dont know much about the internals of Mopar engines. Do you know the deck height of the 360? Is there a 4" stroker available for the 360? As far as strokers go, its a matter of mathmatics as to what will and will not work, and putting together the right combination of parts.
For instance, the Ford 347 stroker kits origionally used 5.4 Mopar rods.


My specialty is with Ford Engines.

The data needed would be the Bore size, Deck height, the diameter of the rod throw on the crank.
After that its a matter of getting the parts together. Other things to know would be compression heights on pistons, wrist pin size.

For instance, the 3.85" stroker crank for the 351W is designed to use the stock factory 5.956" rod with stock 302 pistons.

OOPS!!! I misread your thread. I read it as SB 350 intead of SB360, so I naturally went to Chevy mode.

Building a 402 Mopar would be an interesting project, and that is something I could get a few ideas on.

 

[camaroman7d]

You will be fine. Strokers are no more un-reliable or wear prone than any other. Unless you have an extreme case of a short rod there will be no issues. The difference between rod length and side loading is over rated and over blown. The truth is there is very little difference at all. I think that hype came out to sell longer rods. Don't get me wrong there is a "slight" difference but not enough for your average hot rodder to worry about. I ran a short rod 385 (Chevy) for years (7 years) and it is still together today. I beat on it at the race track and drove it on the street for many thousands of miles. It's in my friends Nova now. I would build one again in a heart beat.

I am not a Mopar guy so I am not sure how short of a rod you are talk. Also the angle of the cylinders come into play.

Drive the car and enjoy it, keep the maintenance up and you won't have any problems.

Royce

 

[Max Keith]

Stroker

So far what Ive been able to come up with is your 360 has a deck height of about 9.5 inches. IF you could find a 4 inch crank, and wanted to use the stock 6.125 rods, you would need a piston with a compression height of 1.375 inches. Your pistons have a .985 wrist pin, so that could be a problem. Knowing what diameter your rod bearings are would help in making comparisons to readily available rod and piston combinations. It would be intirely possible to run a combination of parts for other engines to accomodate an ofset ground crank to achieve your stroker. To get a 4 inch stroke would require offset grinding your stock crank .210".

Since the 360 and the 351W Ford share similar deck heights , I dont see where there would be a problem of building a 4" stroker kit with a reasonably long rod to go with it, as they are available for the Winsors.

 

[antirawker]

thanks for the info...i know the combiation of parts needed to accomplish the stroker setup successfully but i was just concerned with excessive sidewall wear resulting in premature ring failure. But I figured that if I assembled it with proper clearances and what not that I'd be fine since the motor will probably never see any real RPM.

 

[Max Keith]

Stroker

Im not a genious on this stuff, but the data Ive gotten on the subject is that you do want a rod/ stroke ratio of at least 1.4:1 and its really desireable to be over 1.5:1. This is due to the side thrust of the pistons against the cylinder walls. That really gives a lot of leeway, really. With a 4 inch stroke, using rods from 5.6" - whatever will fit and still have a piston on top of it.

 

[coldknock]

You can get just about any aftermarket pistons and rods with the .927" Chevy wrist pin size. That'll fix the oil ring interference, if there is any. Be sure that the rods will clear the bottom of the cylinders the camshaft and the oil pan rails. You might have to do a small amount of grinding depending on the style of rods you use.

The engine you're planning is getting very popular with the Mopar crowd because of the torque it's capable of. Mopars have stout bottom ends from the factory so durability shouldn't be a issue unless you're planning on very high HP and revs.

Larry

 

[Max Keith]

Mopar Strokers

And you dont have to limit yourself to just Chevy pistons with the .927 wrist pin. All the small block Fords, Winsors, and Clevelands all use .912 wrist pins, and compression height does play a big part in selecting a piston as does wrist pin sizes.

Rods can be bored out if necessary, and sleeved if necessary, although those arent the most desireable circumstances. Far better to use a rod designed for that wrist pin.

The biggest problem with using pistons other than those origionally designed for your head configuration, is the valve reliefs, but those can be recut to match your head design.

 

[RCastle]

You stated that this would be a daily driven vehicle.Cool.In two differnt ways cool too.Make sure you have a cooling system capable of keeping that engine from overheating while sitting in traffic,at redlights etc.Aluminum head technology has made leaps and bounds over the last ten years,but heat is still a big enemy of any engine. With so many factory engines running an aluminum head and the aftermarket usually using more common sense in design than the car manufacturers themselves you should have a well put togather project.

 

[my350camaro84]

Just out of curiosity why do you need all that power and get up and go if it's just a daily driver that won't "see any real rpms" ? Not trying to knock ya down or anything I'm just curious.

 

[antirawker]

I figured the extra torque would help the car down the road since it will have the added weight a decent sound system setup and full air ride suspension.

 

[454C10]

Not to mention rod/stoke ratio...

Stroker engines do wear out the rings and pistons a little sooner due to more piston sweep per mile. For example, going from a 3.5 inch to a 4 inch stoke makes the piston move about 15% more per revolution. Of course, taller gears would fix that.

I like the feel of long stroke engines. Torque is king on the street!

FYI, long stroke and long rods in a short deck engine normally have short pistons which can cause a lot of piston rocking noise.

good luck with your build!

 

[antirawker]

Thanks for all of the input everyone. It's appreciated it.

 

[Max Keith]

Old age and wisdom?

There is just no replacement for displacement.

Dittos on the build up and keep us posted on how it comes out.
Inquiring minds want to know.

 

[Ratchet]

Just finished building a 383 stroker. 350 bored .030 over with a 3.75 stroke crank. (crank was from a 400 sbc )

During the build I had to clearance the Oil Pan rails about 1/4 of an inch to clear the rods/bolts. I also had to clearance the rod bolts themselves to stop them from hitting on the Cam.

I thought everything was OK Installed it in the car and started it up. Started on the first pull but had a terrible knocking sound.

A brief investigation revealed that the rods were hitting the bottom of the Oil pan. Specifically the baffle that is in the bottom of the stock 350 pan to stop oil from running forward away from the pump when you hit the brakes.

Long story short. There are three places where you could run into trouble that I know of.

1. rods could hit cam lobes
2. Rods could hit Pan Rails on Block. ( Based on what I had to cut out you will have to cut a ton out of this area. at least another 1/8 inch.)
3. You will probably need a custom Oil pan.

As for life span Im no expert but I don't see that being an issue.

Ric

 

[camaroman7d]

454C10,
I understand your point about more piston "sweep" with the longer stroke. The problem with saying there will be more wear is, it will depend on RPM's. Typically you don't have to rev a stroker (or larger engine) as high to make the same or more power as a smaller engine. Typically a smaller engine is rev'd higher to make power. Not trying to argue just pointing out a fact. When it is all said and done a stroker does not wear any more than any other performance engine. The rod/stroke ratio is a factor but, with most stroker kits the ratio is reasonable and the difference in wear is minute.

Royce