smallblock chevy crank stroke

will a 4.5 in stroke crank fit in a stock early model small blcok chevy?

I believe so. But I would wait for someone with facts to be sure. The SB 400 had a long stroke length.

its going to be 427, its a 30 over 350 right now, putting the crank in it and a set of carello rods in it, from my calculations should fit and eather have a 427ci or 433ci not shure tho, one of my family members is going to the P.R.I show next weekend, if anyone will know they will be there

its going to be 427, its a 30 over 350 right now, putting the crank in it and a set of carello rods in it, from my calculations should fit and eather have a 427ci or 433ci not shure tho, one of my family members is going to the P.R.I show next weekend, if anyone will know they will be there
Hope you get your money's worth of those Carillo rods. :)

First of all, please know that this is not criticism in any way. Everyone has their reasons for their plans, but I just want to make you aware of some of the hurdles you may encounter.

Unless things have really changed, what I was told (by Car Craft) is that 3.75 is easy since that's a 400 stroke. 3.875 is usually a bolt in. 4" may require clearancing but some blocks with core shift might hit oil before you can grind enough away. Once you get to 4.125" you'll need some serious work. You'll also most likely need a higher cam centerline so the counterweights don't hit the cam. Then you're talking about custom cam, distributor, pushrods, etc. At the very least you'll need a cam with a smaller base circle which again involves different pushrods. 4.25" stroke is pretty much out of the question unless you have a special bowtie or motown block with wider oil pan rails, higher cam centerline, and still might need to grind the block. From what I've been told, 4.5" is not even in the ballpark. That's just what I was told but I have no personal experience with it.

You'll have a MUCH easier time (for several reasons) getting your cubes with bore. Even a BBC 454 only uses a 4" stroke. My Caddy 500 only uses a 4.304" stroke. Most street engines achieve a good balance with either a square or oversqaure design; meaning that the bore is bigger than the stroke if only by a little. Cad 500 = 4.3b x 4.304s. Chev 454 = 4.251b x 4.00s If anything you want to oversquare your bore like in the case of the Olds 403 = 4.351b x 3.385s or the Buick 455 = 4.313b x 3.90s

Undersquaring isn't all bad, but designs like the Olds 455 = 4.126b x 4.25s are not easy breathers. The bore size limits valve size and therefore breathing. The extent of your undersquaring with a 4.5" stroke would be so great that I don't think you could get enough air to support more than about 4000 RPMs and about 250 hp at most. You would also not be able to balance it properly further limiting your RPM potential. Another problem would be piston speed which plays huge roles in breathing, torque, quench, and detonation. Plus, the amount of bore height you have is limited. Selecting the right rod/piston combo for this means nothing if you pull the piston out the bottom of the bore :) You'll also have problems with not only the big end of the rod contacting things, but the angle of the rod will be so steep that it will most definitely hit the bore.

My suggestion is to start with a 400 block, sonic check it for core shift and wall thickness, bore it .060" over, and use a 3.875" crank. That yeilds a 4.185" bore and a 3.875" stroke totalling 426.4 ci and a good balance. If you're certain you want a longer stroke, step up to a 4" crank and clearance the block and keep the 4.125" bore for 427 ci.

yeah sorry i meant 4.25, but if thats still out of the ? i realy dont know what im goign to do, i realy dont have enought money to do much, im not old enough to get a job, right now carrelo rods is a dream for me, ive been told honda rods work well and have some of the same dimentions of the carrelo rods so ill proboboly be getting those. i cant buy anohter block and i cant buy new pistons(not enough money), im stuck with what ive got, so realy my only option for getting more ci is in the crank, the only reason why motor isnt done with a stock crank in it is becouse my dad can get deals on crankshaft speacalties cranks, so im holding out and saving money for that, i cant do much modification to the block or the oil pan, the motor is going in to a 1976 vega that im building and it reqires a speacal oil pan. i get my machining half price so the block portion is not a big deal, if i can only go to a 400 ci motor(crank and all), im putting on a 6/71 street blower, the pistons that i got are blower pistons so that would work out, my original plans where to get a blower but a guy backed out on a deal so now i have 8 to one compression blower pistons insteade of a higher compresion reg piston. but im eying another one, just a ?, does anyone know how much EFI would cost for a motor like mine? right now efi and a blower is in the distant futor, being that im building the frame right now, havent desided weather or not im going with a 4 link or ladder bar yet. ill get some answers at the pri show, hopefully i can put a 4.25 crank in it without to much modification.

you will need an aftermarket block

yeah sorry i meant 4.25, but if thats still out of the ? i realy dont know what im goign to do, i realy dont have enought money to do much, im not old enough to get a job, right now carrelo rods is a dream for me, ive been told honda rods work well and have some of the same dimentions of the carrelo rods so ill proboboly be getting those. i cant buy anohter block and i cant buy new pistons(not enough money), im stuck with what ive got, so realy my only option for getting more ci is in the crank,

First of all, there is a lot of stuff here that needs to be straightened out. You can't just buy a crank and put it in. You need new rods, pistons, machine work, and careful measuring. If you just increase the stroke by a 1/4", you add 0.125" more stroke to the bottom AND top. Your pistons would smash into the heads and possibly pull the rings out the bottom of the bore. You have to have a new combination of rod length and piston pin height, as well as ring land spacing. If you just reduce the length of your rods by 1/4" you'll dramatically increase the side loads and vastly change the inertial loads and piston speeds... and that's just this small example. You're talking about going from 3.48" to 4.25"!!! That's 0.752" or over 3/4"!!! That's just unheard of. You won't be able to fit it in your block anyway without some serious grinding, a new cam and pushrods, and several other very careful parts choices.

Put is this way; you could buy an SB 427 rebuild kit with pistons, rings, all the gaskets AND crank, bearings, oil pump, and ARP hardware, AND have your block remachined for less money than you could cram a 4.25" stroke in it. Not to mention in the end you'd have a "new" engine instead of a way undersqare poor performer.

I'm also not sure where you heard that Honda rods have the same specs as a small block chevy, but that is just bull. No way, no how, nope. Even if they did, would you want to trust your 427 ci monster to rods that are designed to hold 125 hp in a 100 ci engine? I wouldn't think so.


the only reason why motor isnt done with a stock crank in it is becouse my dad can get deals on crankshaft speacalties cranks, so im holding out and saving money for that, i cant do much modification to the block or the oil pan, the motor is going in to a 1976 vega that im building and it reqires a speacal oil pan. i get my machining half price so the block portion is not a big deal, if i can only go to a 400 ci motor(crank and all), im putting on a 6/71 street blower, the pistons that i got are blower pistons so that would work out, my original plans where to get a blower but a guy backed out on a deal so now i have 8 to one compression blower pistons insteade of a higher compresion reg piston. but im eying another one, just a ?, does anyone know how much EFI would cost for a motor like mine? right now efi and a blower is in the distant futor, being that im building the frame right now, havent desided weather or not im going with a 4 link or ladder bar yet. ill get some answers at the pri show, hopefully i can put a 4.25 crank in it without to much modification.

Its kinda hard to follow you on this. If you get deals on cranks and half price machine work, you can't afford pistons, but you have new pistons, and EFI and a blower are in the plans. The blower is EXPENSIVE. The tuning is involved, the machine work to run a blower motor is intense, and EFI will probably cost you at least $2500 on a motor like this. $1100 for a good computer, several hundred for the injectors, someone to tune it, the special distributor needed to clear the blower, the coil and primaries to make enough spark for the high combustion pressures, the fuel pump, the plumbing, and the gas tank modifications will end up costing even more.

Let's put it this way. There is absolutely no such thing as cheap power. If you want a 427 small block, there is no sunny way to put it, you're looking at $6000 even if you assemble it yourself. If you want a 6-71 blown motor, you're looking at $8000. Add a bunch more for EFI. Contrast that with this scenario: give up on the extra 21 cubes, buy core SB 400 for $150, have the machine work done for $1000, assemble it yourself with a PAW rebuild kit for $280, add some good ported iron heads (another $300 for the machine work) and add a hydraulic flat tappet cam that measures out to about 236/246 at 50 with about .500" lift, some 1-3/4" headers and 2.5" dual exhaust. That should net you about 425 streetable HP for $2500. That's a really ideal situation, but I built a 450-horse 454 BB for a total investment of $2400, and THEY assembled the shortblock. If you can't do it for under $3000, you should do more shopping. If I'm on a budget, I'd be so much happier with a reliable 425 horses for $3000 than a cobbled together 600 horses for $8000

Again, no flames intended, but I strongly urge you to do some serious homework on this project. I think you've received some very wrong information and I would hate to see you lose your shirt based on it.

Okay, since curtis has provided hours of valuable, well researched advice, (all of it spot on) here is my 30 seconds of flippant advice.
Make a plan and a budget and stick to it. There is no shame in running a nearly stock motor because you cannot afford anything else. We all started out that way.
Also, put your money in the cylinder heads, instead of some fancy big cube block. It will give you lots more bang for the buck.

Finally, Vegas are traction-limited. Past a certain point, more power will not mean more speed, without chassis/suspension mods, so more power will be useless.

For all of my long-winded rhetoric, MagicRat always sums things up in far fewer words :) Your recommendation on heads is an excellent point. A very good example is a recent Car Craft (November '04 to be exact) where they tested otherwise identical 454s; one a small block and one a big block, both displacing 454 by the same bore and stroke. The small block wasted the big block in every area including peak torque, peak HP, average HP and average TQ; the whole time doing it with head ports that measured only about half the sectional area of the BB. Proving that quality of flow is more important than quantity. The BB heads flowed about 15% more quantity of air, but the engine made less overall power than the SBC.

thanks for you comments, ill keep them in mind, ill keep doing my reasearch and hopefully i can come up with something, you said i should invest in heads, i already have, i got new style aluminum lt1 heads, or head i should say, traded a guy and found out later that there was a 2 in hole in the waterjacket so my good one is being cleaned and machined right now, they are looking for a match also -about the traction limitation, im building it a frame, and im also getting a ladderbar suspention, the rear end is a dana 60 with a 4.10 gear, and the tires are mickey thompson N/50 15s, its a wide tire so i think ill be able to hook up fairly well. you had mentioned some things about the exoughst also, i think i have it covered, im getting series 40 flowmasters with a 3in pipes out the sides i know im goign to hit alot of financal road blocks, but i have 3 years to save money, i have already bought some of the major componets, tranny(muncie 4 speed), block, rear end, pistons, things of that sort, i can see i have a long road ahead of me, so as i said ill reacearch some things and see what i can do to it.

Again, curtis and rat take car of things. Just had to let you know what I did. I had an '81 monte carlo that originally came with a 229 (3.8L) V-6. Eventually that motor died and I started building a SBC. If you said you can't have a job yet I would imagine you to be 14 or 15. For a first car as well as your first motor I wouldn't spend that much money. If you mess up somehow would you feel better having a $2600 mess up or a $8000 mess up? I'm not saying that you would mess up but forced induction cars tend to be more tempermental and require more maintanance. I planned the budget in mind for my monte. I wanted a 355 just a little passed stock. I bought an 010 casting (two bolt main) 350 out of a caprice with a TH350 transmission for $250. I used the stock rods and crank (had them sonic tested and the crank cut down .010) I ordered some .030 over Hypereutectic pistons (which are generally inexpensive, I think I paid like $27 a piston?) I purchased some higher flowing stock 68cc heads (I can't remember the casting for the life of me) had them port matched. I also purchased a a wieand stealth intake, a holley 750 double pumper carb and a 283(?) crane energizer cam. Kept the stamped rockers as well. After all the machining seals/bearings/tranny/custom exhaust it was a little over $2200. Dyno'd out at 298 HP. This was PLENTY fun and reliable. After 90k miles the motor still runs but the tranny is dead. If I could do it all over, I would do the exact same thing (maybe if I could find a 400 crank and make it a 33) but I loved it. The more HP/Torque you have, the quicker things break. My 10 bolt (7 1/2") rear end with 2.73 gears is somehow still alive after 210K miles. Just do a lot of research onto your parts and you can always find a decent price. I was running 9.2:1 compression. You can always have your block decked and your heads shaved to an extent to increase your compression. Other than that, listen to curtis and rat...

im not 14, im 13, sounds like you had a decent car in your hands, i realy dont have to worry (maintnence and stuff) me and my dad work with old blowers. but also if i can get the motor to 400ci+ its not going to have a blower, anything below 400ci it will. the motor has already been decked, and as soon as i get this crank figured out ill decide weather or not im haveing the heads shaved.

i already have, i got new style aluminum lt1 heads, or head i should say, traded a guy and found out later that there was a 2 in hole in the waterjacket so my good one is being cleaned and machined right now, they are looking for a match also -.

LT1 heads are a whole different animal. They won't work on traditional small blocks. They have different bolt patterns and completely different water passages. The only things they have in common with older SBCs are valves and chamber spacing. Rocker arms are different part numbers, but they will interchange, as will springs.

I didn't even see that curtis, thanks for pointing that out. Precisely, you would have to get an LT1 short block to run those heads. You would also need the wiring harness as well as intake and fuel rail for it as well. Those are pretty hard to find and when you do run across them expect to throw down a decent amount of money. This would probably rule your 6-71 out of the picture as well. If you're running those mikey thompsons the car probably isn't street legal right now either... you prob def want to rethink your game plan...

the tires are DOT aproved, ill have to check on the heads, maybe ill get lucky and they will fit, but from what youve said i guess they are probobly out of the picture, i was looking forward to using them, i guess im stuck with stock heads.

i know this is an old thread but oh well, ive done me reacearch and found that the lt1 heads i got will bolt on my block, i just have to get a intake, i cant do a 427 without an aftermarket block, unless i bore out the motor i have now, wich isnt an option considering i already have pistons and cant afford new ones, nor an new block. according to the books that i have read, a 4.030 bore with a stroke of 3.75, and a rod length of 6.0 should fit into a stock block without much machining,and give me a 383ci motor. and im not going to go with a blower, looked at the #s of what a motor like myne can produce and decided its more than enough for a first car, epecaly the lightwieght one like the one that im building. am i correct on these specs?

Yes, except I'm still not clear on the LT1 heads. If they are late model LT1 aluminum heads, they WILL NOT bolt on to a standard chevy small block. There are companies who make carburated manifolds to go on LT1 heads, but that should not be confused with compatibility with the rest of the small block.

I wish I could find pictures right now but I can't. The LT1 (92-97) shares many things in common with the old small block, but heads are not compatible. Its like putting a square peg in a round hole. The water passages are different, the head bolt holes are different, and the water jackets are designed with the reverse coolant flow in mind.

If you're talking about early iron LT-1 (different from the LT1 as noted by the "-" in the middle) heads, then they will work.

I've actually seen someone who grafted late model LT1 heads on an old small block. He welded shut the original coolant passages and drilled new ones, as well as drilled the proper bolt holes in the deck. In the end he had a small block that performed no better than stock. Why he did it was a mystery, especially since there are thousands of good performance stock and aftermarket heads available for the small block.

Otherwise, you have the recipe correct for a really nice 383. You've done your homework and decided to step up to 6" rods which is great. I hope it melts all the tires you can put on it :)

ive looked at the heads and they will fit, dont ask me how, but they do. and no its the new style aluminum lt-1 heads not the older ones. and if someone did what your friend did, it doesnt matter, i would have been using stock heads in the first place, if nothing else it shaved 25 pounds off the front of the car and about the manifold, im not going with a carb im doing a efi setup. will a tpi manifold fit on lt1 heads?

Friend, I'm telling you. They will NOT fit. They might bolt on, they might even look similar, but you'll leak coolant everywhere, your oil will drip right into the water jackets, and it will be a mess. They just won't fit. If you don't believe me, buy a set of head gaskets for a standard 350 and for an LT1. Lay them on top of each other and compare every hole.

A TPI won't fit on LT1 heads, either. Different bolt angles. If you're doing LT1 heads somehow, do the LT1 injection. Much more potential out of the box and 10 years newer technology.

I know it might look like they fit, but trust me, I'm talking from 15 years experience with small block chevys.

There are thousands of stock and aftermarket aluminum head choices for small blocks, so you don't need to worry about finding heads that work well.

If you want aluminum heads, look at the AFR 180 and AFR 195 for SBCs. Pricey, but worth the cash. Edelbrock aluminum heads are slightly cheaper but a slight step down in performance.