John Dirks

And for that matter, what do you think is the ideal bore stroke and cubic inch?
I want to do this build-up right! :cheers:

MotorHead

434 ci would be nice, 400 block 30 over and a 4 inch stroke crank and 6 inch rods, in my dreams or you can get 427 ci out of the same combo with a uncut block :D





[Modified by MotorHead, 10:03 PM 3/12/2003]

SmokedTires

Now that's like saying what is the best flavor of ice cream :crazy: !

For myself I'm hoping to capture the quick rev & response of the old Chevy 302's & 327's with a bigger 388 displacement :yesnod: . This should give me more torque with greater rev capabilities ;) .

Clink69

Ideal for what? As an example with a 383 I recommend using 6 " rods to increase the stroke ratio. It doesn't change displacement but it does allow you to rev slightly higher.

This uses a 400 crank, 3.75 stroke and 4.030 diameter bore.

Displacement = 8 x 3.14159 x (4.030in/2)^2 x 3.75in = 382.66 CU IN

this is a less expensive setup than say a 434 or even a 406. I wouldn't mind having that 434 though...


[Modified by Clink69, 7:18 AM 3/13/2003]

75 BBC Stingray

Maybe a dumb question, but can you get pistons w/ small enough compression heights to run a 6" rod w/ a 4" stroke? The crank/rod combo would already take up 8" of deck height. That would leave only 1"?!?!? before the piston sticks out the block? (I can't quite remember what the SBC deck height is... I know the BBC is 9.8/10.25 and the SBC is fairly smaller)

gkull

With a stock block use 6 inch rods and 3.875 stroke. It's the best combo in the 4.030 bore you get a 396 and 4.125 bore you get a 415 ci

John Dirks

I will be using an aftermarket block like the little M or Motown.
I can bore it and stroke it to a variety of combinations.
What combination is best for HP/TQ and nitrous?

gkull

You have to figure out what your trying to do at what rpm range. The M block I would go with a 4 inch stroke 6 inch rod. It's a very common kit around $1500 for the internally balanced crank rods pinstons rings and bearings in nice forged parts. I would not be boring it out if it's a new block. Maybe .030 over if it needs cleaning up. The power difference in the few CI gained by over bores is minimal and it's one less time that the motor can be rebuilt.

Monty

It just depends on how big you want to go. There's nothing wrong with the Motown or Little M blocks, or even the GM bowtie blocks - they are all great foundations for a high-performance engine. Even the Bill Mitchell Hardcore 415/427 ci shortblocks are excellent choices and hard to beat for the money.
With them offering 415/427ci shortblocks for under $4000, it's alot of value for the money.

WP and Bill Mitchell like to taut the Motown blocks as having an advantage over the Dart Iron Eagle/GM Rocket blocks because you don't need a special oil pan or timing chain/cover, but they exaggerate the difference in cost. The Dart Iron Eagle/GM Rocket block feaures a couple of unique enhancements which allow it to accomodate a 4.00"+ stroke much easier and without compromising the strength of the block and the rotating assembly.

The Iron Eagle/Rocket blocks feature spread pan rails, .400" each side, which allows you to run a 4.00" stroke without any blcok machining. You can run as much as 4.250" stroke if you notch the bottom of the cylinder bores as you'd do with a standard 383 stroker using a production 350 block. The oil pan to fit these spread rails are not that expensive. Jeg's and Summit sell steel Moroso pans, including an oil pump and the appropriate pcikup for around $275. Stef's makes nice aluminum sheetmetal oil pans for $300-$600, depending on feures such as windage screen, trap doors, crank scraper, etc. also including an oil pump and pickup.

The Iron Eagle/Rocket blocks also incorporate a raised cam location, .391" compared to stock. This eliminates interference between the camshaft and the connecting rods which is problematic in stroker SBC's using production blocks. Again, the cost of the special timing chain/belt/gear over a stock component is minimal. Cloyes offers a Tru-double roller timing chain for the rased cam blocks for $100, and you still use a standard timing cover and gasket. Belt drives and gear drives are also readily available with comparible costs to the standard components.

You will also need shorted pushrods since the lifter bores are higher in the block, but any valvetrain company does custom length pushrods for not much more than off-the-shelf pushrod lengths.

The Iron Eagle/ Rocket blocks do not have an integral oil filter pad, so a remote oil filter mount and plumbing is reguired. Depending on which oil filter adapter you chose to use, it could cost you $50 to $300. Jeg's/Summit offer several affordable cast aluminum remote oil filter mounts for around $50 or so, or you can use nicer, billet aluminum stuff from Barnes, SCE, CV Products, etc. You'll also have to factor in the cost of the AN plumbing but it's not necessarily cost prohibative, and depending on how you set it up, it can provide alot of advantages over a block mounted oil filter.

Some additional options that you can add to the Iron Eagle/Rocket block are talled deck heights, 9.325" (offered on cast iron and aluminum blocks) and 9.500" (only offered on the aluminum version blocks), as well as a choice of BSC, BBC, and 50mm roller cam bearings. You can also chose between 350 and 400 SBC main journals. The taller deck height will allow you to run a longer rod with the longer storkes so that your rod/stroke ratio and piston compression heights do not have to be compromised. Even with a 4.0" stroke, I run a 6.125" rod and a 1.17" compression height to maintain a good rod stroke ratio. My rod/stroke ration is identical to a 454 BBC, and slightly better than the commonly used 5.7" rod 383.

If you maintain a stock deck height, the difference between using an Iron Eagle/Rocket block and using a Motown, Bowtie, or Little M is potentially less than $500 or so, depending on the components you use. But that number is reduced further if you factor in the additional machining and clearancing that must be done to the Motown, Bowtie, or Little M to accomdate the 4.0"+ stroke.

The big cost increases start to come into play when you increase the deck height, since you now need a custom intake manifold or intake manifold spacers. But to do it right, it's a good way to go if the budget allows.

It's just my opinion that if you are going to use a 4.0" stroke or greater, the Iron Eagle/Rocket Blocks are better choices because they more easily accomodate the longer stroke without interference problems.

There are several ways to make a stroker engine, and most all of these blocks can be safely bored out to 4.200". I wouldn't recommend going that far right from the start though, because you don't leave much
room for future rebuilds, etc.

Any of the above mentioned blocks can handle 600-1000hp safely, it mostly depends on the rpm range you intend and the quality of the components you fill the block with. For the average 7000rpm, 650-700hp
small block, they are more than sufficient.

Ideal or acceptable rod/stroke ratio is a somewhat controversial subject. Some people emphasize it more than others, and even the factory has used a wide range of r/s ratios successfully in production engines. 1.5 r/s ratio or greater seems to be acceptable without any negative impact on engine
durability and rpm range, while some of the high-winding racing engines from the factory had r/s ratios of 1.8 or greater.

Figuring rod stroke ratio is easy. You just need to know the deck height, the stroke, the rod length, and the compression height of the piston (the distance
from the centerline of the piston wristpin to the top of the piston crown).

Maximum rod length can be determined by subtracting half of the stroke and the compression height from the deck height.

Example:
Assume a 3.50" stroke, a 1.25" compression height and
a stock 9.025" deck height.

Max Rod Length = 9.025" - (.5(3.50) + 1.25)
= 9.025" - 3.0
= 6.025"

In this case, if you wanted to run an off the shelf 6.0" rod, you can either mill the cylinder decks down .025" which is commonly done to achieve a "Zero" deck height, or you could increase the pistons compression height by .025" to achieve "Zero" deck, or you could simply run it with the piston .025" down the hole.

Most people strive for a quench area of around .040", so if you ran the piston .025" down the hole, you'd need to use a thin .015" head gasket. Msot people would increase the piston compression height or mill the deck down, and run a .038"-.040" head gasket.

By using that formula to determine the max rod length available, you can then figure out your rod/ stroke ratio, which in this case would be 1.71 (6.0 divided by 3.5), which is pretty good.

Using the formula will allow you to juggle around all the variables, such as how a tall deck will allow you to maintain acceptable rod/stroke ratio's even with long rods and long strokes.

My block came with a 9.320" deck height, we took .005" off of it, and I run 6.125" rods with a 4.00" stroke. So when I ordered pistons, I knew I needed pistons with a 1.195" compression height to achieve a "zero" deck height.

I hope this is all clear. It really boils down to what you can fit into the deck height, given the desired stroke and rod length. I prefer to run as long of a rod as possible, and the 6.125" rod length allowed me to achieve a 1.54 rod/stroke ratio(which is identical to a 454 BBC) with a 4.0" stroke and the
taller deck. That's the reason I chose to use the tall deck. I've had my engine up to 7500rpm on ther dyno without skipping a beat. However, you do want to be careful, there is a limit to how much stroke you can run, and still expect it to safely and reliably hold together. Piston speeds of up to 4500 feet per minute seems to be about the limit where durability and longevity are concerned, and you need good parts to achieve and sustain that - i.e. forged, billet, ARP, etc. Keeping piston speed below 4000 ft/min is advisable for street engines that are expected to lead long lives inmy opinion.


If I had used a standard 9.025" deck block, I would have had to use shorter rods and therefore a worse rod/stroke ratio if I wanted to use a 4.0" stroke. Using the 4.0" stroke in a 9.025" deck block would have only allowed me a maximum of 7.025" to fit in the rods and the piston compression height.

That would have meant I would have had to run a 5.850" rod, or something completely custom length and more expensive, and that would have given me an undesirable(in my opinion) 1.46 rod/stroke ratio.

Most piston company's recommend a minimum of around 1.10" compression height for street engines. If you add forced induction or nitrous, you need to increase the compression height because you want to move the piston rings away from the piston crown to protect them from the increased heat and cylinder pressure generated. Additonally, you also need to increase the
ring land thickness to provide additional support and protection for the rings.

Another factor to consider, which is also somewhat controversial, is the location of the wrist pin in relation to the oil control ring. As the compression
height gets shorter and the wrist pin moves up the piston, it's not uncommon for the wrist pin to be located under the oil control ring, or even the second
compression ring as well in tight applications.

Some people are concerned that locating the wrist pin under the oil control ring can lead to potential oil control problems and blowby, which could lead to
excessive oil burning, which leads to increased risk of detonation if oil makes it into the combustion chamber. I don't neccesarily agree with that, as you
will use additional oil support rings provided with the pistons when this is the case. There are factory production engines with this arrangement, including
some Mustangs, and they work very well without detrimental impacts on performance and reliability.

There are benefits to running shorter compression heights as well. With the wrist pin farther up the piston, it helps to stablize the piston, reducing it's
tendency to rock from side to side in the bore. The allows you to run a tighter quench which is good for power and detonation resistance at increased
compression levels, it improves ring sealing since the piston isn't rocking as much, and it allows you to run a shorter piston skirt and overall piston, which
lightens it's weight. Lightening the rotating assembly can help to increase the rpm range of the engine, as well as decrease parasitic internal engine
losses.

I hope this will help you make the most informed decision possible, based on what you want the engine to do and your budget.





[Modified by Monty, 12:46 PM 3/13/2003]

Holdon

Gidday Monty! I have just read this thread and one thing is plainly obvious....you have awesome knowledge!!! I am hopeful that you may share some of that wisdom with me? I am currently trying to source a new set of pistons & rings for my blown Motown sbc and with my combination i am having difficulty working out the best way to approach the order! Would you consider reviewing the spec's of my combination and giving me your advice??? Look forward to hopefully hearing back from you! Best regards....Holdon....Australia

jim2527

Holden, nice first post. Montes post is 14 years old. A new will get better results.

71VetteLover

The ideal stroke depends on what you intend to do with the engine. For racing you want to limit the piston speed to 4000 feet per minute.

427Hotrod

Reher/Morrison always said to use whatever would hook the piston to the crank you were using. Get lightest piston possible and go from there.

Jim.

lionelhutz

Old enough thread..

You get the rod to stroke ratio by building the engine.
- Pick the engine type and displacement you want. This sets the stroke.
- Pick the block you need which dictates the deck height.
- Pick a nice set of lightweight pistons. By default, this will put the pin as close to the piston crown as you'd want it to be.
- Pick the rod length to connect the crank and piston. Then, you have the rod:stroke ratio.

There's a constant chatter about small block builds and needing 6"+ rods to get the right rod to stroke ratio because you JUST MUST HAVE a rod:stroke ratio that is around 1.6:1. Well, this thinking is backwards because it's the lightweight pistons that put you at that ratio, not the need for that ratio in the first place.

Look at the big displacement big block combos if you want to see what ratios can still work. Around here, I know someone who had a ~640cu-in big block build and turned it >7500rpm and ran high 8's on motor. It was reliable as reliable. He'd check valve springs every so often during the season and go through it every winter. He ran the bottom end for years starting out in the 10's and working down to 8's as he did top end changes and improved how the chassis and transmission worked. The rod to stroke ratio is around 1.4:1 for that combo. He sold the car and retired from racing a year ago.