young olds

Just like the title says. I believe I've read a 350 block will take a 4.125 bore, what's currently available options for stroke? I'm trying to do some planning for a new engine for my 66.

cutlassefi

Been hashed and rehashed a hundred times. Do a search and you'll find plenty of info.

coppercutlass

425 pistons and stock rods for a big bore stock stroke and or chevy piston and chevy rod combo for a stroker .

young olds

I failed at searching, which I normally don't do, sorry. Is there any way to get somewhere in the 3.75-4" stroke without a custom made crank?

joe_padavano

Yeah, build a BBO...

Every single SBO every built by Olds came with a 3.385" stroke. Any other stroke is custom.

young olds

yeah i know that, but theres this thing called offset grinding, i just dont know how far you can go. and i know you can make a 425 crank fit a diesel block but idk about a gas block.

joe_padavano

The diesel block uses the same 3.0" mains as the BBO. All gas SBO blocks use 2.5" mains. Yes, you can have a 425 crank cut to 2.5 mains and 2.125 rod journals, but then you are talking about significant work on the counterweights to get it to fit in the block. Yes, it can be done, but not clear if this is economically advantageous over just buying a custom crank.

As for offset grinding the SBO crank, do the math. Stock stroke is 3.385". Rod journals are 2.125". You need to offset grind half the additional stroke, or (3.75-3.385)/2. That's 0.1825", meaning the 2.125" journals need to be cut to at least 1.9425" (and likely further to clean them up all around). This means Honda rods or something like that.

A 4" stroke requires almost 0.31" to be cut from the journals, yielding 1.8175" journals, so again you're looking at some custom Honda rods or similar parts. Once again, run ALL the numbers and see if this really is cheaper than a custom crank. FYI, H-beam Honda rods run at least $350 for FOUR. That doesn't count any custom machine work needed for this combo.

cutlassefi

[QUOTE=joe_padavano;868082]

As for offset grinding the SBO crank, do the math. Stock stroke is 3.385". Rod journals are 2.125". You need to offset grind half the additional stroke, or (3.75-3.385)/2. That's 0.1825", meaning the 2.125" journals need to be cut to at least 1.9425" (and likely further to clean them up all around). This means Honda rods or something like that.

A 4" stroke requires almost 0.31" to be cut from the journals, yielding 1.8175" journals, so again you're looking at some custom Honda rods or similar parts.[QUOTE]

With all due respect, sorry Joe it doesn't work that way.
Whatever you take off the journal in diameter is how much you can increase the stroke. Remember you're not only offsetting it but also reducing the diameter in doing so.

For a stroker small block, I'd do a welded 330 crank. Done two now, one is 3.75, the other will be 3.875. Costs about 1K and will use a sbc small journal rod, a dime a dozen. Best bang for the buck in my opinion.

oldsmobiledave

[QUOTE=cutlassefi;868087][QUOTE=joe_padavano;868082]

As for offset grinding the SBO crank, do the math. Stock stroke is 3.385". Rod journals are 2.125". You need to offset grind half the additional stroke, or (3.75-3.385)/2. That's 0.1825", meaning the 2.125" journals need to be cut to at least 1.9425" (and likely further to clean them up all around). This means Honda rods or something like that.

A 4" stroke requires almost 0.31" to be cut from the journals, yielding 1.8175" journals, so again you're looking at some custom Honda rods or similar parts.Agree. If you want to use a gas small block olds then a 330 crank is your best bet. If you want more CID you need to use the D/DX block and either a billet crank or an offset ground 425 steel crank.


Decide what your goals are @ what your budget is FIRST. This will determine which direction to go with your build.

joe_padavano

You're right, of course. Sorry about the mis-information. The centerline of the journal moves half the stroke increase, but the diameter must be reduced by the full amount of the stroke increase (or the journal welded, as you point out). In any case, that's a lot of work, so I'm back to my original point that a custom crank might not be appreciably more expensive (especially by the time you search out a forged 330 crank to start with).

wr1970

Maybe i am wrong but here goes. Why don't you use a 330 crank stroke it to a 3.5 stroke. Bore it out to enough say 4.15 then turn rod journals to small block chevy and end up with 380 ci . Well just a thought.

captjim

Been done a million times, except bore to 4.125 and use off-the-shelf SBC 400 pistons and rings.

oldsmobiledave

4.125" bore & 3.5" stroke yields a 374 cid engine for anyone wondering.

captjim

True, and if the block can take it and you want the extra cubes, bore to 4.155 which is a .030 400 SBC to get your 380 cubes.

wr1970

Why thank you for confirming that the 380 is possible like i was thinking. Thanks for letting the op know what pistons he can use makes his job easy when picking a combo. So with that being said looks like he would have two cheap combo to choose from and not hurt his wallet real bad. Both would make lots of power. Thanks for jumping in oldsmobile Dave.Clearing things up helps guys like me who isn't a small block guy and help others who are.Many thank to Captjim for info! I know the op can see now how to take advantage of both combo's if he decides to choose one.

young olds

I'd like to get at least 400 ci, which is 3.75 stroke x 4.125 bore if I did the math right. If I can get a 4 inch stroke then even better. In any case it's been made clear that I can reach my cid goals

captjim

a 455 is 4.125" bore x 4.250" stroke. I love small blocks, but depending on your goals, you will be way ahead going with a 455 for less money and much easier.

young olds

I don't want a big block and I'm not looking for crazy hp. A stroked small block will be plenty

cutlassefi

What is your hp goal? If it's 500 you'll need more cubes than a 380.

young olds

I want at least 400 cubes but the ultimate for me would be 4" stroke x 4.125 bore for a 427. I only want 400ish hp but I won't refuse more.

oldsmobiledave

A stroked 330 crank to 3.5" in a 0.030" over 403 block is 422 cid. With well ported early SBO heads you can make 1 hp per cid. That engine will give you all you need & is cheap to build.


Talk to the guys on here who are in the 12s with their 403s before you dismiss it as the weak sister.

Bernhard

How about a DX build?

bccan

One thing I haven't seen mentioned here is the oil holes in the journals "moving" with change in diameters. I'm not up on details or remedies but believe it has to be considered.

Compatible parts with that much stroke change seems to move into the realm of potentially very short rods or very "short" pistons as far as comp height, pin placement & skirt length. Perusal of the Mahle catalog will help.

Rod compatibiliy - lengths available, pin sizes @ styles, journal sizes & widths.

Be sure to do all that homework before pulling any triggers.

DX Build - I love mine but crank work contributes to a pricey build for mid size displacement, probably getting into same realm w/ SBO gas crank. I consider myself a small block fan but if I build another engine some day it's likely to be a 496ish BBO, bigger & cheaper if only slightly.

wr1970

You have a quality build already!You can always change your combo to make more performance and that might be less cash than doing bbo. Then again a 496 makes a very good street motor.

Bernhard

What I like about a DX build is what WR1970 said. If you build a quality engine you can keep working on the performance.
You won't find a stronger platform to build on if you go Olds power.
You might want to look into the cost difference between your build options.

oldsmobiledave

If money is not an issue then a full on D/DX is the way to go. I love the performance from my 470 cid SBO stroker. I prefer this engine to my 524 BBO stroker & I beat on both often.


His goals are 400cid & 400 hp minimums. A 403 will do this with ease with out the expense of the stroker crank. Stroked it will be even better. Yes the bottom end needs support but will handle 1 hp per cid without issues.

captjim

Hate to disagree with you, but I am going to. 403s are not good platforms for performance builds, IMHO. Ring seal is an issue, they are difficult to properly hone, not sure about piston options. Why in the world use SBO heads? If you want to use iron, use a BBO head, they are "already ported". Copper is running 12s with a very simple 355, no need for a stroked 403 to do that. Plenty of 350s running 10s, not many 403s.

To Young Olds; what EXACTLY are your goals? A certain ET? Fun street car? What exactly do you want to accomplish?

oldsmobiledave

I agree that a 403 is not a good block for an all out performance build but it will handle 1 hp per cid without issue. The OP wants a SBO with more than 400 cid & 400 hp so this seems like a viable option to me.


I suggested the sbo head because they are readily available & will yield pump gas friendly compression. The 403 does not need to go to 6000 rpm to make power so the big valves in the BBO head were less important to me. If the OP has the scratch for aluminum heads then those are a better choice than OEM heads anyways.


Personally I wont build a 403 but I see it as a good fit for the OP. Ultimately it is his decision & I am just putting some ideas out there for him.

coppercutlass

Imo strokers are a waste. Specially when half the people who build em dont race em !!!! How many stroker builds have we seen here yet no times ???? Just dyno numbers which are bs. If you want cubes build a 455. Why bother. Its nice to say i have a " stroker but imo what is the gain ????? is it worth the extra work. Im running 12's with a 355 and 67cutlassfreak and 80 rocket are running 11.teens with a 10 to 1 355 with bbo heads from what 80rocket mentioned in my other thread . now there are 2 totally diffrent extremes you got my 355 thats runs 12.60's fully streetable and 80 rockets G body that runs 11.teens in the 1/4 mile and is what i would consider a full race car . Im gonna try to squeeze another few tenths from mine with out major modifications. My views may be wrong but for most guys who wanna be street strip there is not need to build a stroker. for a race application i see it fit but thats just me.

young olds

im not in it for a "stroker" i just want the cubes and this car will always be a small block car, thats what i want in it. and it will see the track often, free time permitting. its already got a decently healthy 355 in it now but im planning on more. i just wanted to know if i could get the cid im after cause if not id be staying with the engine thats in it. im kinda like copper, i want a mild mannered car for when im on the street.

coppercutlass

I would build a 403 then and keep the revs down and do a halo for support and what not. J&S claims their halo makes them live. Why build a gas stroker that will only hit 380 cubes when the 403 has 23 more in stock form. The only stroker I would build would be for a big cube sbo so dx would be the way to go but not cheap and imo not worth my time or effort. I know the 403 has its weaknesses but there is bottom end support for them out there. I'm not trying to dump on your cupcakes but is the effort worth the pay out ???? I mean what does your car run now. Will the extra cubes translate to only a few tenths ????? I would get your set up now to the track build a stroker and see what its worth on the track . the 403 would be a much cheaper route even with the bottom end support stuff. Is there anyone out there with a 380 build with e/t times ?????? That's the stuff I look at.

Mr Nick

Not everybody builds cars for the 1/4 mile. Mine is a street car, with a stiff lowered street suspension, 5-speed, low profile tires etc... Only been to the 1/4 mile with it once, ran a 13.8 @ 101.9 mph with a terrible 2.20 60ft time. I'm considering a stroker as an update, and I don't give a **** how much my ET may drop. I want more power on the street, and a light small block to match the 5-speed, and I don't want the weight of a BBO as I plan on getting into auto-crossing.

My point, different strokes (har har) for different folks.

coppercutlass

I have a street car when we go to the track I swap the tires, take the mufflers off , take the sway bar off and then put it back on when we head home. I cruised all summer then august hit and the last 400 miles where put driving to the track and back and racing ., One summer night we put 120 miles hitting up 3 diffrent cruise nights. Drove the hell out of my car . Its truly is dual purpose. 12.60's 1.80 60 ft @ 105 drove 60 miles to the track and 60 miles back on 3 occasions with an extended drive in between to pops shop . I didn't have to stroke it and it has plenty of power on tap on the street. I don't know what gear you have but with a 5 speed I would do a 4.10 and there you go instant tq. On the street for a real seat of the pants power feel. How fast do plan to corner is will a 4.10 hamper the top mph with your combo on the straight aways ???? I think you have more engine than I do component wise. Either way I got way off topic youngolds for your goals I think a 355 will do or even a 403 properly built. if you want 400 hp it can be done with a 355 and its been done.

captjim

Because you sacrifice a LOT to get those extra few cubes, IMO. The cylinder walls are very thin, coupled withe the large bore makes it difficult to hone and ring seal is an issue. There is also the heat transfer issue with the Siamesed cylinders causing over heating and detonation problems.

captjim

I disagree with that statement. If you do the numbers both ways, stock stroke vs stroker, with the stroker you end up with new rods, better pistons and rings for just a few $ more, it is like a 5% increase. The extra inches are just an added benefit. IMHO.

bccan

Brownbomber has a set of fresh heads that would probably fit whatever bottom end you decide on @ a nice price. Check em out in "For Sale."

coppercutlass

A lot of guys have built 403's J&S machine built a buisness around it . I doubt they are that bad. I have never built one but would not hesitate to do so.

wr1970

I have to agree with you captjim.The stroker will have more power on tap at the hit of the throttle than the stock stroke. Twenty five cubes makes a lot of difference. I think Rallye Bob used a gas block was in the tens with it. Then he changed to the motor he has now i maybe wrong hope he see this and chimes in.I know Cutlassefi will disagree with me but that is okay we talked about this on a different thread.

coppercutlass

For a race car yeah I agree its great and at that point its apple to oranges. I'm very minimalistic. My build is bare bones and makes great power compared to other builds. And looking around I have not been able to find a combo like mine engine and running gear wise.

83hurstguy

It's pretty simple... if you have an engine with 1 hp/ci, and you add 30 cubes, you have an easy 30 hp or lb-ft on tap, likely without having to spin the engine to a higher rpm.

On a relatively heavy street car with moderate gear and converter, cubes win. Just my .02... when talking race car, you want RPM and horsepower and the cost of streetability. All depends what someone is looking for in their car.