building a stroker

[jmp]

Hi there,

I'm entertaining the idea of builder a stroker small block sometime (hopefully) soon. The common stroker is the 383, but I want to look into something different. So how about a 406?

A 406 ci stroker has a boreXstroke of 4.155 X 3.75, which is, I guess, based on a 400 block, not a 350, right?

Mathematically, you can get 406 ci by going 4.020 X 4.000, but that doesn't seem to be done. How come? Is a 4" stroke too long for a 350 block? I don't think so, since people are building 427 SBC (4.125 X 4.000), although they are using (I think) aftermarket blocks such as World Products. But I thought these blocks were only modified to support the extra big bore, not modified to support the stroke (other than changes to the oil pan rails).

So, can you take a 350 and stroke it to 406?

What about a 400 block -- I've heard that they tend to crack (which is why I want to stay away from them). Is that true? Not to mention that finding a 400 could be difficult.

If a 406 is not feasible, to what other displacement can I take a 350 (other than 383)? How about 395 ci (4.030 X 3.875)?

Thanks muchly.

 

[MaineShark]

Mathematically, you can get 406 ci by going 4.020 X 4.000, but that doesn't seem to be done. How come? Is a 4" stroke too long for a 350 block?

...

So, can you take a 350 and stroke it to 406?

It has to do with bore:stroke ratio. An engine with equal bore and stroke is called "square." An engine with longer stroke than bore is "undersquare." Reverse that for larger bore than stroke, and you have an "oversquare" engine.

Undersquare engines are rare. Even square engines are pretty uncommon. Both make excellent low-end torque, but run out of steam at higher rpm's. The logner stroke dictates a faster (linear) piston speed, which results in greater stresses. It takes more money for fancy parts to handle those stresses, and even with that, there are still finite limits as to how fast the piston can safely move within the bore.

So oversquare engines are much more common. The decision is usually how far oversquare, not whether or not to be oversquare, in the first place. While your example is oversquare, it is just barely so.

Also at issue is connecting-rod-to-piston angle. As a long-stroke crank swings, the connecting rods make harder angles, driving the piston sideways into the cylinder wall. That force is present in an engine, but the longer stroke accentuates it.

So, all-in-all, the 400 conversion is more popular than converting a 350.

What about a 400 block -- I've heard that they tend to crack (which is why I want to stay away from them). Is that true?

The 400 block needs to have two-bolt mains (the four-bolt blocks are weaker, which is the opposite of the case with the 350). It also needs steam holes drilled at the top of the water jacket, to allow steam to escape to the heads.

Joe

 

[Jack]

406 is fairly common ... it is NOT a "stroker" ... it is a stock 400 with oversize piston-bore. A stock OEM sbc 400 came with 4.125" bore and 3.75" stroke "cast iron" crank and short 5.565" connecting rods. As above, rod angles can become an issue. Those short rods are seldom used these days ... budget builders often use 5.7" (350) rods ... more common to use aftermarket rods 5.85" to 6.125". Typical 383 is a 0.030" overbore 350 block with a 3.75" stroke crank ... same rod angle issues and solutions. There are usually clearance issues with most big-inch sbc combos ... rod bolts can come too close to/hit cam lobes and oil pan rails ... rods too close to bottom of bores ... these have to be addressed via machine shop work/choice of components. If you try and throw one of these together without proper parts & prep ... you & your wallet will regret it. Best advice is to first establish a realistic budget to work from and second is get a couple books on building hipo and stroker motors ... read up on it.

BTW ... a stock OEM GM 400 crank will not drop into a 350 block ... stock 400 crank has larger main bearing journals than does a 350.
JACK:gap

 

[jmp]

Jack, you're right: a 406 based on a 400 is not a stroker. I may go that route, but what I really want is to get more cubes out of a 350, and that means stroking. So, other than a 383, what can I stroke to? Theoretically, almost anything, but realistically speaking, what can/has been done?

Right now I'm in the planning and investigation phase. This project won't start (ie. actually spending cash) until the new year at the earliest. I do plan on getting books on stroking/building 350s and on FI (since that's the other thing I want to do). However, I have, and will continue to, read articles from this forum and other sources on the Internet.

I understand some of the issues with building a stroker, including rod ratios, clearance issues, and main bearing journals. However, journals can be ground or aftermarket cranks purchased; longer rods can be used, provided pistons with an appropriate compression height can be found; and special, smaller profile rods can be used and/or blocks can be notched to help with the clearance issues.

While all these issues can be addressed to some degree, there are limits. For example, strokes can get so big that you can't find a rod length big enough and a piston CH small enough that you get a good rod ratio. Or perhaps you can find a combination that mathematically works but is not available and therefore you have to have custom made rods and pistons, which can cost a pretty penny. The biggest one I'm worried about is clearance, since while you can notch the block a bit, there is a limit, and I don't know what that limit is, and I don't want to revisit my lost math skills to find out. Hence, I'm going to be asking questions (and reading books).

Again, I'm looking into doing a stroker combination that isn't as common as a 383, but that has been done before so that I can follow an example that I know has worked.

Now, I realize that you, Jack, understand these issues (and better than I do). I just wrote this long reply to show that I have done some of my homework and that I do understand some of the issues involved.

OK, a couple of other things....

By my calculations a 350 bored and stroked to 4.020 X 4.000 will yield 406 ci (408ci with a bore of 4.030). With a 6" rod, that's a 1.5:1 rod ratio, leaving the compression height of the piston to be a maximum of 1.025 with a 9.025 deck height. These numbers are similar to the 427 SBC offered by, for example, World Products. The 427 uses a 4.125 bore but everything else is exactly the same. Oh, and the camshaft is in the standard 350 location (Dart, I believe, changes the position of the cam). The big difference would be the bottom end clearance, as the aftermarket blocks were designed with a big stroke in mind.

A 350 bored and stroked to 4.030 X 3.875 yields 395ci. With a 6" rod thats a 1.54:1 rod ratio leaving the CH to a max of 1.088. Is this a more feasible combination? A 3.875 crank seems to be meant for the 400 block, but the main bearing journals can be modified to make that work, so the issues would be availability/cost of pistons, and bottom end clearance. Even the bore to stroke ratio is better (smaller than a 383, but bigger than a 427).

Finally, my goals in the project:
1. Experience building up a 350.
2. min 400hp/400tq
3. NOT to break the bank

I'd love a 427 SBC but I thought that would be a little too much. A 383 seems to be significantly cheaper to build (for starters I don't need a special block), but I'm looking at options. The more expensive the project, the longer it'll take me to do, so in some sense expense doesn't matter. But that might mean I'd be finished in 50 years! =) Basically I want to keeps costs down, so I won't be buying parts that aren't necessary, and I won't be building "the fastest car out there". If it turns out a non-383 stroker isn't feasible without lotsa cash, I won't do it.

Well, I hope this clarifies some things, both with what I do and do not know, and with what I want to do.

Keep the replies coming!

 

[Jack]

Dunno if you can stroke a 350 block to 406 … but it seems it would be popular if it were both possible & practical.
The shorter the piston’s compression height, the greater the difficulty placing a durable ring pack in the small space.
OE sbc deck typically 9.025”, often takes a 0.010”-0.025” cut to clean & straighten, so don’t count of keeping 9.025.
Many of the big inch sbc motors run a tall deck block (i.e. 9.500); providing room for longer rod lengths and taller compression height pistons.
Rod Length to Stroke ratio is important; IMHO, bore to stroke is less so.
OE sbc 400 RL/S ratio = 1.48
5.7” rod/3.75” stroke = 1.52
6.25" rod/4" stroke = 1.56
6” rod/3.75” stroke = 1.60
OE sbc 350 RL/S ratio = 1.64
6” rod/3.48” stroke = 1.72

Just a guideline for RL/S ratios
Short Rod
Min Rod/Stroke Ratio ~ 1.60
Max Rod/Stroke Ratio ~ 1.80
Long Rod
Min Rod/Stroke Ratio ~ 1.81
Max Rod/Stroke Ratio ~ 2.00

 

[jmp]

OE sbc deck typically 9.025”, often takes a 0.010”-0.025” cut to clean & straighten, so don’t count of keeping 9.025.
Many of the big inch sbc motors run a tall deck block (i.e. 9.500); providing room for longer rod lengths and taller compression height pistons.

True, but the World Products 427 SB has the standard deck height of 9.025, so they are either using pistons with a CH of 1.0" or 1.025". So, it can be done.

Just a guideline for RL/S ratios
Short Rod
Min Rod/Stroke Ratio ~ 1.60
Max Rod/Stroke Ratio ~ 1.80
Long Rod
Min Rod/Stroke Ratio ~ 1.81
Max Rod/Stroke Ratio ~ 2.00

The numbers I've read (I haven't seen a differentiation between short and long rods) has been 1.5 to 1.8. But there seems to be a lot of differing opinions out there, so....

Thanks for the reply!

 

[grumpyvette]

I think you might want to look this over

go to
http://www.airflowresearch.com/
click (ARTICLES)

then (401 stroker)

 

[jmp]

I think you might want to look this over

go to
http://www.airflowresearch.com/
click (ARTICLES)

then (401 stroker)

Thanks Grumpy,

I saw the same article in Car Craft, but I kinda skimmed over it thinking it was more to do with a crate engine and/or a GM Goodwrench block. It is, but when I re-read it, I realized it contained a lot of good stuff.

I think going to a 406 might be too risky, but given this article, stroking a 350 to 395 (4.030 X 3.875) looks perfectly feasible. It'd be the same as the 401 in this article, except the 401 has a 4.060 bore, which is probably too big for an original vette block.

I've even found some pistons with a small enough compression height!

Well, the research continues.... Thx!

 

[grumpyvette]

I think one of the more important points you might want to think over is the way the cam and heads are matched to the compression /displacement in the article, notice the cam is NOT some wild high duration part meant for only peak power (with its 236/242 duration)and that the compression and head flow are responsible for much of the results.
notice also that they use a dual plane intake and a reasonable carb size to make max high mid range torque rather than only high peak hp at the expence of mid range pulling power
BTW the CROWER 00471 cam works very well in similar combos
or if your looking for slightly better mid range torque and are willing to give up just a bit of peak hp the CRANE #119661 like IM useing in my 383 with its 230/238 dur.
http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=119661&lvl=2&prt=5

http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=00471&x=27&y=6

keep in mind you wanT THE MAX COMPRESSION and the lowest DURRATION that matches the intended rpm range, that still allows good breathing and no detonation to get the best torque curve, over caming and under gearing an engine KILLS USABLE POWER FAST and is a very common mistake, if your engines built for max power in the 6500rpm range with a cam that does not pull well below 3500rpm but the trans shifts at 5600rpm youll be driving a far less responsive combo tha a smaller durration cam that pulls hard from 3000rpm and peaks at 6000rpm,could have given you in most cases, the differance does not seem to be much on paper in the cam choice but its CRITICAL to the results