so i was just having fun looking for stuff i cant afford on summit and came across rotating assemblies for a 350 with various strokes from 3.5 to 4 inches did some research and found this http://www.cprparts.com/products/cranks_5140.html so whats the deal? i thought 3.75 was the biggest you could do

4" will fit but you start running the rods into the cam etc . 4.155(400 .030 over ) x 4 is 427 I think . Motown or some other aftermarket company makes a tall deck small block with the cam moved up so I think I remember 454 -460 cid small blocks . Search Bill Mitchell Hardcore . They sell turnkey 427's

A 4" stroke in a 0.030" over 400 is 433.8 ci. 427 is a 4" stroke couple with a standard bore 400.

Eagle and others sell 6" rods just for putting a 4" stroke in a SBC, but you still have to use a cam ground with a reduced base circle. Also, a 4" stroke is nearly impossible to internally balance, even with the 6" rods required. No other rod length works. Any shorter, you pull the piston into the crank counterweights, any longer and you have piston failures.

what about like the 3.875 and other lengths?
basically, its not going to happen on a stock gen1 block though correct?

Why stop at 3.875" when it costs just as much as the 4"? The 4" can be done to any SBC from the '57 283, if you bore it to 4", up to today. The 4" bore is required to clear the angularity of the 6" rods.

At one shop I worked at, we did this to a late 350, and while clearancing, we hit water. So we duct-taped the spot, then poured in a half inch depth of rockblok and let it harden overnight. Then I finished all the machining, and here 5 years later the guy is still street-driving it every day it's nice weather.

One guy on this forum has a 350 with a 4" stroke. A 408. I forget his name, but he bought it as a crate motor. You can build them yourself, it's not a crazy mod.
- small base circle cam
- 6" rods
- and lots of clearancing.

by clearancing, you mean basically get rid of anything that gets in the way of the crank?

The cranks fit fine, depending on who made it. Clearancing is mostly at the bottoms of the cylinders, and the pan rails, whatever's too close to the heads of the capscrews. You can't use rods that take the older through-bolts with nuts, even with a small-base cam. And forget H-beam rods, stick with the traditional I-beam style.

the kits summit sells (eagle i think) use H beam rods and screws.
the website i posted seems pretty legit to me but i have no clue.
the interesting thing is that the 4" crank is pretty much the same price as a 3.48" and 3.75" crank, so if i ever do end up doing a rebuild, i will go with the 4" crank.
6" rods are necessary, and a new cam as well, but do i need specific pistons?
2" + 6" = 8".
not knowing the distance from the deck to the crank bearings, what pistons would i need for this to work?

keep in mind its not going to happen for a good while, if at all, but just for knowledge's sake i guess.
i like learning things.


oh, and i would assume that TPI would be completely useless at those displacements?
thats about 75% more engine than GM intended (for a 305)

crank bearings to deck is 9" on a small block chevy. +/- a bit eh?
Yes, the specific pistons are what make this very expensive.
The rods are straightforward 6" I beams, or something plain-jane like that eh? The crank is a 4" stroke, but still nothing NASA-approved. As you say, roughly the same price.

However now you need weird/strange/custom pin height pistons. And THOSE are pricey, and rare.

Please remember - stroke increases displacement, but it also skyrockets your compression ratio. Do the math on this first, as most likely you'll need huge chamber heads and big dish pistons.

thats odd because most of the kits have dome pistons.
they must not be zero decked...
i guess thats what makes the pistons so expensive.

how huge are we talking?
head wise?

and i have no problem running premium... i have been for the past few years so thats no concern lol.
as long as i dont have to mix race gas...
my uncle has a GTO judge that needs race gas.
every time i ride with him he says something along the lines of:
"you know, i really hate having to mix race gas for this thing, and i could just retard the timing and get new pistons, but damnit, its just so much fun this way..."

JE and Mahle stock pistons for this. The compression height, from center of wrist pin to combustion face, is exactly 1.0000" Stock SBCs spec at 9.025" from crank centerline to deck, and it usually is between 9.024"-9.026", but most performance builds include decking to exactly 9" after the line-hone.
A flat-top piston, with 4cc of valve reliefs, a 4.060" x 0.038" gasket, a zero deck, and an AFR 75cc head gets you 10.6050:1 compression.

Rock on Atilla, thanks for the legwork!

My point is that, you don't have much selection in pistons. You now have the biggest chambered SBC heads (rare exceptions perhaps?) and you've got 10.6:1 CR, which is just barely ok for pump gas. ie. you can't re-use your old 64cc heads. You can't really use this as a blower/turbo motor, 'cuz it's nearly impossible to lower the compression. Where would you put the dish? Pistons are already very short in this application.

Also, forged pistons for a 350 are about $200 a set, for entry level speed-pros or something. 383 pistons are only slightly more. But with a 4" stroke you have to buy expensive ones. You don't have the option of buying the entry level stuff. So you are forced to buy the "good" (expensive) pistons. What is the going rate on those pistons Atilla?

Don't get me wrong, i'd do it in a heartbeat, the only problem (in my eyes) is it closes the doors to doing forced induction later. It'd be an AMAZING low RPM street engine. A great high perf NA motor as well...

The pistons are running at least $550 plus rings. within the last 2 years Popular Hot Rodding did this 408, build by David Vizard, with AFR heads, made like 540 horses at 6500 rpm. No, it peaked at 6000, but it pulled 6500. I have that article filed away, would you like me to look it up?

wow...
please, if you dont mind.

i see what you mean about not being able to do forced induction as a minus, but honestly, i really cant see myself ever owning a DD car with any kind of forced induction, and bear in mind, that my camaro IS my DD.
thats great though.
how much fun would it be to pop the hood and have it look like a stock 305, but be over 100 ci bigger...
that just makes me laugh.

although like i said, TPI would be out for sure.
heads would also be a problem as you pointed out.

I'll dig it out tonight, no trouble.

Popular Hot Rodding, May '08. It says, basically, flattop 2vr pistons, AFR 1036 heads, custom COMP street roller, with 286XSR lobe for the intake, 292XSR exhaust, lobe separation angle not told. They used 1.65:1 rockers intake and 1.50:1 exhaust. With an RPM AirGap, and 1.75" long tubes, (which for us would be Hooker SuperCompetition) they found 548.6 HP at 6200 rpm, 510 ft-lbs at 5300rpm, over 500 ft-lbs from 4700 to 5700 rpm, over 475 ft-lbs from 3700 to 6100 rpm, over 450 ft-lbs from 3300 to 6300 rpm, and over 425 ft-lbs from 2900 to 6500 rpm. Switching to a Holley StreetDominator single plane, they found 595 hp at 6600 rpm, but massive loss of torque below 4600 rpm. Like 50 ft-lbs at 4200 rpm. Like 55 ft-lbs at 3000 rpm.

thats weird.
you would think that with such a long stroke (and a perfectly square engine combo) there would be gobs of low end torque not power high up

Look how big the cam is! and 425 ft-lbs at 3000 rpm will shred any street radials. With a more reasonable cam, 500 ft-lbs at 3000 rpm is possible, but how would you use it? It'd seem like a good diesel, except it would turn 5500 rpm. Diesels aren't happy reaching for 5500.

true, i guess the numbers got away from me, but thats true that 425 is plenty for the street lol.
for me, a big cube engine like that would be expected to make peak torque at 2500 or so where you spend most of your street time, and just above where you would cruise on the highway...
then again, i dont race much (at all) so i have different goals than your average joe hot rodder...

500 ftlbs...
wow.
thats great
i NEED this stroker kit...
how about each member sends me a dollar and in return i will post a video of me shredding 3 sets of tires...
sound good?

It might peak at 2500 with stock heads which would be out of flow by then, but that puts you back to feeling like a diesel.