Stroked 402 BBC

[KWIKND]

I have a spare 402 BBC using up space in the corner that I was considering stroking to ??? cu. in. Anyone up on what components are needed to do this? And what clearances are effected? I would prefer to build and install this motor in my 69 A body and save the numbers matching 396 for future use. Drop a valve in an original motor how bad would that suck!

Dan

[Lowend]

We did this on Tony Huntimer's car and it worked great... We had to have Wiesco make up the pistons, but I think a standard 454 crank drops in to make a 432
Ask Tony for more info, its been 5 years

[yody]

isnt a 454 crank in a 396 a 427? or is the other way around? 396 crank in a 454 block? actually i think it is the later.

[KWIKND]

So we are looking at crank and pistons, what about rods? or does that go w/o saying.

http://www.strangemotion.com/html/whats_happenin.html

[strokerengine]

To stroke any engine you need the parts to pull it off. The main thing is the pistons. You need the correct compression height. To install a 454 crank in a 396/402 block with stock length rods will require having someone like Ross or JE etc make you up a custom set of pistons. The cost of having pistons made is typically around $700 plus. For this reason alone most hot roddders choose to look for a 454 block.

You will make more power with a bigger bore shorter stroke than small bore, long stroke combination every time. Increasing the stroke requires the piston and rings to be drag further up and down the cylinder, increasing friction loss, also the piston has to accelerate to a higher speed then decelerated to a stop again in the same amount of time, ie. one crankshaft revolution, this further consumes energy.

So why is stroking popular? Because stroking can dramatically increase the cubic capacity, which increases torque output, where as boring a cylinder .060 over makes very little difference in size.

4.00" + .060" with a 3.48" stroke becomes 360cid
4.00" + .000" with a 3.75" stroke becomes 376cid
4.00" + .030" with a 3.75" stroke becomes 383cid

To increase a 350 Chevy bore you either use a 400 block (4.125")
or buy an aftermarket block.

While it may seem like a good idea to stroke your 396 block, the cost of the custom pistons will undermine your desire to get more power for less money. It is typically less expensive to find a 454 short block and rebuild it with off the shelf 454 pistons, and make more power.

However, some 396/402 blocks can be bore to 4.250, allowing you to use less expensive 454 pistons. Boring the cylinder this far over always comes with risk. Core shift and porosity in the block can lead to problems. You really need to sonic test the wall thickness.
Some 396 blocks have thicker walls than others. Most 402 are thinner. One way to check is the gap between the cylinders. With the freeze plug remove, see if a No2 pencil will slip between the cylinder in the water jacket. If it goes through the wall thickness isn't great enough.

While bigger bores are better than longer strokes, having a bigger bore only leads back to the same question, "what if I increase the stroke with the bigger bore?"
A 454, with a 1/4" stroke leads to a 489. 4-3/8" 4-1/2" and 4-3/4" are also available.

More stroke makes more torque, because of the increased displacement.
Doing it with stroke rather than bore, lowers to peek RPM where both torque and horsepower are achieve.
The following are numbers lifted from my web site as calculated in a desktop dyno.
http://www.strokerengine.com/strokerengines.html

4.00" X 3.48" = 350 382TQ/4500rpm 370HP/6000rpm + 0TQ + 0HP
4.03" X 3.48" = 355 386TQ/4500rpm 373HP/6000rpm + 4TQ + 3HP
4.03" X 3.75" = 383 406TQ/4000rpm 374HP/5500rpm +24TQ + 4HP
4.15" X 3.48" = 377 404TQ/4000rpm 378HP/5500rpm +22TQ +8HP
4.15" X 3.75" = 407 426TQ/4000rpm 379HP/5000rpm +44TQ +9HP

5.00" X 2.44" = 383 408TQ/4500rpm 389HP/6000rpm +31TQ + 21HP
3.00" X 6.78" = 383 363TQ/4000rpm 311HP/5000rpm + 9TQ - 57HP

There is a lot you can learn from these figures, but the main point is stroking is the second best way to increase power, but becomes first again once you have the larger bore.

The bottom line is you can stroke a 396/402 to 427, and 454, or you can increase to bore to these same sizes, and then stroking will lead to 489 and 517.

I build stroker engine everyday and can help find the best solutions.

John Nijssen
The Stroker Engine Company

[KWIKND]

John
Wow!! Thanks for all the info. This may be an "inside baseball" question but - There is'nt enough of a market for stroking big blocks to produce the pistons in production batches? Or am I over simplifying how many different sizes would be required for each bore size
(.010 over .030, .060 etc.). Is this more common in the small block arena due to lack of big bore options and shortage of low end torque? Do stroked small blocks also require custom one off pistons? A buddy of mine does late model clay oval and he made it sound like everyone is using stroked small blocks with 350 cfm carbs!!
Beyond that a little more low end torque sounds very appealing to me.
What would be the minimum wall thickness allowable/advisable if all else looks good? Why can't the differance be made up in the rod length instead of custom pistons? Alright I'll take a breath. Mind is racing. (for lack of anything else racing)

http://www.strangemotion.com/html/whats_happenin.html


Dan