great421

iTrader: (1)

Block Deck Height = 9.025” with studs on the main journals

Bore = 4.03” (0.030” overbore)

Stroke = 3.96”
(REAL Forged 3.75" Gen II SBC stroker crankshaft [i.e. - NOT Scat nor Eagle] produced for standard 2.10” rod journals, then offset ground for 1.89” rod journals)

Connecting Rods = Forged I-beam 6.00” units with 1.89" (i.e. – Honda sized) journals; (stress relieved and polished, with ARP fasteners)

Pistons = SRP 4.030 diameter units with a compression height of 1.000”

Rod to Stroke Ratio = 1.515 (JUST above the minimum suggested ratio of 1.5, and much better than the SB Chevy 400 ratio of 1.45)

ALL –

If I’ve done the math right, then half the stroke (1.98”) plus the length of the rod (6.00”) plus the compression height of the piston (1.00”) = 8.98” so even if the block has to be decked down to 9.000” (fairly standard with SB Chevy blocks), that still leaves the piston in the bore by 0.002”

Given that, my logic behind building a 404 cu in LT1/4 (or 406 if I need to go 0.040” over) is that offset grinding the crankshaft (by 0.105”) is better than partially block filling and then grinding / clearancing the block to accept a 3.875 stroke crankshaft. I’ll get more cubic inches (8 additional cubes) and I will NOT hack up and weaken the bottom portion of my block.

So, and I ask this in all seriousness, what have I overlooked?

Why should I NOT build an engine with this configuration?

What are the downsides, if any, to this layout?

Thanks in advance!

suicidal racing

iTrader: (14)

wait you say 3.96 stroke but clearancing block for 3.875 stroke..i will tell you ditch the 6" rod...you will want a 5.85 rod for a better comp height specialy if u ever even think about spraying it..with that low of a ch your pins in your ring stack..other then that build it aslong as u have the heads to support it

suicidal racing

iTrader: (14)

also you will need a small base cam

fex77k

iTrader: (2)

There wasn't really that much taken out for my 3.875, the machinist was just having fun with the end mill.

Rail side

Cam side

great421

iTrader: (1)

Yes a 3.75 stroker crank offset ground on the connecting rod journals, reducing the diameter from 2.10" down to 1.89" - by grinding away the INSIDE surface only the effective stroke is increased by 0.105" - which, when doubled = 0.210" so, the stroke becomes (3.75 + 0.21) = 3.960"

This makes the stroke longer without actually increasing the physical diamentions of the crankshaft.

Now, having said that, is a small base circle cam required when using a 383 (i.e. - 3.75" stroke) crankshaft?

great421

iTrader: (1)

No issues with breaching the water jackets / coolant passages?

Others have said that with a 3.875 crank, that could be an issue.

idformula

so how far can the normal LT1 be overbored? Is it like sbc's, about .060" over?

jaycenk

iTrader: (1)

Not all the time on true 383's (not what your doing) except when you get into Big lift then you can hit the lob with a rod, again depending on what rod and rod bolt and lift on standard base cam.

96capricemgr

iTrader: (1)

Lots of effort for no GOOD reason.

fex77k

iTrader: (2)

Sonic testing is the only way, this is just a used 95 vette block. He said he could stuff a 4" in there but it would take him awhile. As it would require a lot of rod work.

I have LT1s that are .040 and .030 you need to sonic test them if you want to go crazy. You can go .060 but you have to check that. There are some freaks out there that have been full filled and paper thin walls. My machinist basically said this about them, "yea I've done it and they have lasted longer than they should have."

suicidal racing

iTrader: (14)

you can fit a 4" crank in a lt1 an gen 1 350 block..its been done many times..u will need to do a short fill just incase u do go threw to a water jacket.

noice

I sonic tested .140" wall thickness between cylinders and .240" thickness the other way. Also this block had almost no core shift.

Some people say .100" is the min wall thickness, however if you hardblok fill it you can make the wall paper and still get some runs out of it.