400 stroker questions

2485 Views 29 Replies 6 Participants Last post by lmsport, Oct 19, 2020

Seangalt

Discussion Starter · Oct 9, 2020

Ok I'm no engine expert so flame away. I ground cranks for 10 years in Tulsa at Moritz and Midwestern so I got some experience as a machinist.. and assembled many moors but just need some help on my 406.

Skip white has many kits that look promising..

Backstory
...
Can I stroke the old crank to 3.8 and find bearings and 5.7 rods and pistons to give me around a 420? I don't have a ton of money.. maybe 1800 bucks.. I'm tempted to just do the 6" internal balanced skip white 406 forged assembly with flat tops and keep it a 406...

Here's my current combo that was very strong..

1975 vette..

817 cast 400 .030 over. Sonic tested. Rehoned and new cam beaing getting notched for 6" rods.

I last ran it with stock rods. Stock crank hyper flat 6cc valve recessed tops and 220 Flotek 72cc heads and a lunati roller cam 545 lift with 1.6 rockers highly ported air gap.. pulled like a train with a huges 2500 on a th400 also have a 2 step msd and 6al.

It was 10.4/1 and ran good.. except I had debris when I broke it in with a flat tappet with too strong springs.. I ran it less than 30 minutes.. but the bearings suffered..

So I had a dirt track friend who said just clean it and put a roller kit in..

Well I did flushed it.. and cleaned.. .. and it ran great. so after a few miles I saw oil pressure low. So pulled it apart.

My skirts had scratches and the crank bearings shot.

So now I'm rebuilding..

The heads and block are all I am keeping. Possibly the roller cam and lifters .. but The new roller cam and lifters are still good but probably will use them in another 383 build as I may spray the car with 150 shot and will gap for nitrous and have been looking at a new cam with more exhaust overlap.

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Seangalt

Discussion Starter · #2 · Oct 9, 2020 (Edited)

If it matters... I want to Drive the car whenever I want. So must be pump gas and not full on race cam.

I am currently running a hp950 BG carb but jetted for street use and with power valves etc. Its a older model that really is like 830 cfm. I had no issues with it in the few miles I ran it. I have 2 afr aem gauges on each bank of my collectors of my long tube side pipes and it reads 12.5 to 13.9 most ranges. Idles at 13.1

johnsongrass1

· #3 · Oct 9, 2020

I'm so confused as to how you can grind crankshafts for a living and not understand stroke and indexing.
You cannot stroke a 3.750 crank to 3.800. Stick to the 406 for your budget is very tight to begin with.

ericnova72

· #4 · Oct 9, 2020

johnsongrass1 said:
I'm so confused as to how you can grind crankshafts for a living and not understand stroke and indexing.
You cannot stroke a 3.750 crank to 3.800. Stick to the 406 for your budget is very tight to begin with.

Sure you can offset grind a 3.75" large rod journal crank (2.100" journal) to a 3.800" stroke with 2.0" small journal rods. Speed-o-Motive and PAW used to offer it as a 415-420" kit depending on overbore. Back in the days of either stock small journal rods or Crower/Carillo as your only choices, before we had all the options we do today.
Unless you can do the crank regrinding and rod rebuilding for free you're not going to do it cheaply, not on that $1800 budget if you have to pay for the work. Don't forget the heavy metal balance job cost.

And then it is a still a cast crank with a zillion rotation cycles on it already.

The White's kit strikes me as a better move, better crank. Already configured for internal balance, won't need expensive heavy metal slugs to do the job.

The difference in power between 3.75" stroke 406 and the 3.800" stroke making 412" at the same size bore is not worth the expense....you'd have to bore it clear to .060" over just to get 418" with that 3.800" crank....and .060" is a bad place to be with a stock 400 block.

Either pony up for a 3.875" crank kit for 421" @ .030" overbore or just stick with 406" and put a better cam and intake on it.
Engine that big needs a single plane, a dual plane is restrictive.

If you were willing to regrind a stock cast crank for 3.800" stroke, then you should be fine with a SCAT cast 3.75" stroke crank kit from White's....no need for a forged crank.

I also find a forged aftermarket crank kind of a misplaced waste of resources in a stock block....why spend for a crank 3 times stronger than the block then have the crank ruined when the stock block fails? Save the forged crank expense for when you do an aftermarket block.

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Seangalt

Discussion Starter · #5 · Oct 9, 2020

Well. For one.. I operated a machine as I said. I was a machinist. I never said I was a builder.

I did what was on the order. I ground every crank you can imagine from caterpillar to 8" oil rig cranks.. yes I also Stroked many cranks. A 383 crank is nothing more than grinding 400 mains to 350. Or a 351 Windsor offset ground to fir to Chevy rods. I never said I was a engine builder.

I understand what stroke and indexing. I have assembled many motors. I don't see why you feel the need to insult me.

Anyway... I know their are pistons and 5.7 rod and crank 4" stroke combos for 400s that with my bore will make a 434 ... that is probably a bit more than I want to push a 817 block. And I don't have the money for a dart shp.

What I am asking is that do you know of a COMBO where if I had a grinder offset the rods to 3.8 stroke that would give me a deck clearance of around .010 down or so that is cheap. Most internally balanced kits i have seen are either stock, 3.75(406 ) or 4.0 (434) if I went with the 4.0 stroke kit with 6" rods I would need about 15cc dish pistons And the notching for the added stroke. I'm ok with that option. But I want to know if anyone stroked a OEM 400 crank. LLike off set to give me 3.8 to fit the cheaper small journal 5.7 rods and what pistons would work well with those? would stock 350 pistons now sit out of the hole? I don't know I'm not a builder.

Go ahead and insult if you want . I am trying to explain it best I can.

Basically in a nutshell.. I want a bigger displacement cheap without buying a new crank and custom rod and pistons.

If it doesn't work fine. I don't know. Maybe a combo does exist. I'm asking if you know of a combo?

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Seangalt

Discussion Starter · #6 · Oct 9, 2020

ericnova72 said:
Sure you can offset grind a 3.75" large rod journal crank (2.100" journal) to a 3.800" stroke with 2.0" small journal rods. Speed-o-Motive and PAW used to offer it as a 415-420" kit depending on overbore. Back in the days of either stock small journal rods or Crower/Carillo as your only choices, before we had all the options we do today.
Unless you can do the crank regrinding and rod rebuilding for free you're not going to do it cheaply, not on that $1800 budget if you have to pay for the work. Don't forget the heavy metal balance job cost.

And then it is a still a cast crank with a zillion rotation cycles on it already.

The White's kit strikes me as a better move, better crank. Already configured for internal balance, won't need expensive heavy metal slugs to do the job.

The difference in power between 3.75" stroke 406 and the 3.800" stroke making 412" at the same size bore is not worth the expense....you'd have to bore it clear to .060" over just to get 418" with that 3.800" crank....and .060" is a bad place to be with a stock 400 block.

Either pony up for a 3.875" crank kit for 421" @ .030" overbore or just stick with 406" and put a better cam and intake on it.
Engine that big needs a single plane, a dual plane is restrictive.

If you were willing to regrind a stock cast crank for 3.800" stroke, then you should be fine with a SCAT cast 3.75" stroke crank kit from White's....no need for a forged crank.

I also find a forged aftermarket crank kind of a misplaced waste of resources in a stock block....why spend for a crank 3 times stronger than the block then have the crank ruined when the stock block fails? Save the forged crank expense for when you do an aftermarket block.

Thank. You. So the flat top forged weisco kit with the 400 mj scat crank.. stay with 406. Thats in my price point. But they only offer the 6" rods. I heard the 5.7" is better.. I'll call them and see if they could do the same kit but with the 5.7 rods and pistons for a 400. That kit will still be better than stock. As its internal balanced and also is 1.5cc smaller than my last flat tops so will push my to 10.5/1 with the 72cc 220 floteks.

Oh yes. I am also looking for a good single plane.. but my heads have .200 raised intake runners. And the vic Jr is going to need as much porting as I had to do to the air gap. So I am looking at the Dart 200 sp intake. Only it is 9" tall. And my motion cowl probably won't be able to close.. I need to find a .200 raised runner intake that is no taller than 6" or port a vic jr.. fun fun...

Thanks for the advice. I'll probably do that

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ericnova72

· #7 · Oct 9, 2020 (Edited)

Ok, not really any cheap way to do it because there is no common piston that is going to be the right height for that .050" increase in stroke.
If you've got a block that has never been deck cut, then you could get away with a standard 5.7" rod 406 spec piston since the piston ends up .025" or so down the bore at TDC in the undecked stock block, the stroke increase of .050' would put the piston .025" higher at TDC and you end up with a zero decked assembly.
I've never seen a 400 block with decks good enough to leave stock, they all need at least a clean-up cut to make them flat and square to the mains. You can offset that with a .050-.055" head gasket thickness, those are easily avaialble.

Problem is finding a cheap forged piston for 5.7" rod 400 SBC, which is a 1.425" compression height piston, and finding it with a dish size to match your compression ratio needs. I don't know of a seperately avaialble forged piston under $500 for this application.....once you figure the crank grind cost, new rods cost, and heavy metal balance job cost on that old stock crank it doesn't sound so attractive to get just 6 more cubic inches as compared to the Skip White $1350 full kit SCAT cast crank 406 kit....which comes with good 6" rods, forged wiseco pistons, internal balance crank and everythig you need to install it....bearings, rings, balancer, flexplate.

Hard to beat that deal....i've tried to piece them together with parts sourced from other places a bit at a time, even getting good pricing i can't match a kit price that way....which is part of what you are facing here....the cost of trying to be cheap versus the actual cheaper cost of just getting an already figured out kit.

You won't find a low cost 5.7" rod internal balance kit....because they can't put big enough counterwieghts on the crank for it to be internal balanced and still have the crank counterwieghts clear the pin boss in the piston @ Bottom Dead Center with that shorter 5.7" rod.....that's why any 5.7" rod internal balance gets expensive....they have to put a bunch of heavy metal in the counterweights to get enough mass in it to internal balance. Shortest rod that will typically internal balance without mallory added is 5.850"....and then it has to be a forged crank to get enough weight in there, cast crank is just slightly lighter and they can't do it unless you use a uber light piston..

Why do you not want 6" rods?? is it that old wives tale of "it'll use oil because of that oil support ring that is needed" BS. It's been proven false

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Seangalt

Discussion Starter · #8 · Oct 9, 2020 (Edited)

ericnova72 said:
Ok, not really any cheap way to do it because there is no common piston that is going to be the right height for that .050" increase in stroke.
If you've got a block that has never been deck cut, then you could get away with a standard 5.7" rod 406 spec piston since the piston ends up .025" or so down the bore at TDC in the undecked stock block, the stroke increase of .050' would put the piston .025" higher at TDC and you end up with a zero decked assembly.
I've never seen a 400 block with decks good enough to leave stock, they all need at least a clean-up cut to make them flat and square to the mains. You can offset that with a .050-.055" head gasket thickness, those are easily avaialble.

Problem is finding a cheap forged piston for 5.7" rod 400 SBC, which is a 1.425" compression height piston, and finding it with a dish size to match your compression ratio needs. I don't know of a seperately avaialble forged piston under $500 for this application.....once you figure the crank grind cost, new rods cost, and heavy metal balance job cost on that old stock crank it doesn't sound so attractive to get just 6 more cubic inches as compared to the Skip White $1350 full kit SCAT cast crank 406 kit....which comes with good 6" rods, forged wiseco pistons, internal balance crank and everythig you need to install it....bearings, rings, balancer, flexplate.

Hard to beat that deal....i've tried to piece them together with parts sourced from other places a bit at a time, even getting good pricing i can't match a kit price that way....which is part of what you are facing here....the cost of trying to be cheap versus the actual cheaper cost of just getting an already figured out kit.

You won't find a low cost 5.7" rod internal balance kit....because they can't put big enough counterwieghts on the crank for it to be internal balanced and still have the crank counterwieghts clear the pin boss in the piston @ Bottom Dead Center with that shorter 5.7" rod.....that's why any 5.7" rod internal balance gets expensive....they have to put a bunch of heavy metal in the counterweights to get enouhg mass in it to internal balance. Shortest rod that will typically internal balance without mallory added is 5.850"....and then it has to be a forged crank to get enough weight in there, cast crank is just slightly lighter and they can't do it unless you use a uber light piston..

Why do you not want 6" rods?? is it that old wives tale of "it'll use oil because of that oil support ring that is needed" BS. It's been proven false

I got lucky on my block. I ran it up to 6k never decked with these heads and didn't leak a bit.

I guess I have just read and have been told the 6" rod length is a detriment. That the dwell time is a bunch of crap etc... it isn't worth even worrying about i guess. Like you said. It is hard to beat the cost of that kit. Even if I find cheap pistons rods etc and pay the grinder etc.... its not worth a few cubes. Ok. I'll just get the 6" kit from skip for the 406. I'll be gaining some compression and will be able to spin it higher. So its still better than what I had.

Thanks

2old2fast

· #9 · Oct 9, 2020

I've been running 6" rods in my 383 for about 15 years. Had it apart about 5 years ago & saw nothing noticeably worn afa skirts or bores. I wanted internal balance , that's why the 6" rod was preferable..

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lmsport

· #10 · Oct 9, 2020

Keep the 3.75 stroke.
Use 6" rods.
Get the heads professionally ported if you want more power.

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Seangalt

Discussion Starter · #11 · Oct 9, 2020

lmsport said:
Keep the 3.75 stroke.
Use 6" rods.
Get the heads professionally ported if you want more power.

The heads are already cnc ported...2.08 intakes.. Thx. I'm going that route from all yalls advice.

Heres the heads... but the air gap I had to port them almost double the size to match...

These heads are awesome. .200 raised runners both intake and exhaust.. Only .100 thick center section in between ports.. They flow crazy over 300 cfm. Awesome deal too. Little cheaper than AFR and no runout when we checked and lapped and cut steam holes.

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Seangalt

Discussion Starter · #12 · Oct 9, 2020

301 cfm at .500

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johnsongrass1

· #13 · Oct 9, 2020

I wasn't trying to insult you. I was very confused. I assumed a crank grinder, custom crank grinding that is, would be more in a position for access to custom design/engines in general. All those that I know are real heavy into the sport and do custom engines for a living. No disrespect intended even if it read snarky.
I said you couldn't regrind to a 3.800, I should have said technically you can, but then you run to a whole bunch of work arounds that don't pay off.
Street wise, your not gonna know whether its a 406 or 420, 5.7 or 6.0 rods. The differnces are so small it ain't worth even looking at.
Youre 6" rod isn't about dwell and all that stuff, it's about the piston being light enough to internal balance easily and being slightly easier on the rods and crank all for the the same dollars.

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Seangalt

Discussion Starter · #14 · Oct 9, 2020

johnsongrass1 said:
I wasn't trying to insult you. I was very confused. I assumed a crank grinder, custom crank grinding that is, would be more in a position for access to custom design/engines in general. All those that I know are real heavy into the sport and do custom engines for a living. No disrespect intended even if it read snarky.
I said you couldn't regrind to a 3.800, I should have said technically you can, but then you run to a whole bunch of work arounds that don't pay off.
Street wise, your not gonna know whether its a 406 or 420, 5.7 or 6.0 rods. The differnces are so small it ain't worth even looking at.
Youre 6" rod isn't about dwell and all that stuff, it's about the piston being light enough to internal balance easily and being slightly easier on the rods and crank all for the the same dollars.

Its cool.. I wanted to be a builder. But I was a good grinder.. so thats where the bosses kept me. I did get to do other stuff like porting heads installing liners.. and welding and other stuff. But when it came to building I just did the basics.
Bought stock parts and whatever bearing sizes I needed etc. Or measured stuff like pushrod length and deck clearance and ptv clearance. I just recalled a small journal small block rod existed and that maybe there was a cheat to stroke the big one to it to gain a few ponies even if it meant to go to .030 bearings... Custom grinds like I used to do in the late 80s weren't that much more than any other grind so I thought maybe I could get by with what I had for maybe a hundred and 20 bucks or so... its cool i decided to go with the 1300 skip kit with the 6" rods.

Thanks.

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johnsongrass1

· #15 · Oct 9, 2020

A long time ago engine were more customized by necessity, today, most everything can be bought as is and there not much left for margins on 40 year old cranks.
It's faster, easier, and usually almost cheaper to buy whatever specs you need than custom make anything.

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Seangalt

Discussion Starter · #16 · Oct 9, 2020

johnsongrass1 said:
A long time ago engine were more customized by necessity, today, most everything can be bought as is and there not much left for margins on 40 year old cranks.
It's faster, easier, and usually almost cheaper to buy whatever specs you need than custom make anything.

So I did find skip white does offer a internal balanced 3.875 stroker kit with dish pistons... but the cost is 700 more than the 406 kit... so I'll probably get this one.. (only the 030 one not the 040 one)

"sbc-chevy-406-assembly-scat-crank-6-rods-wiseco-flat-top-4165-pistons-400-mj" | Skip White Performance - We have the best prices you will ever find for aluminum heads, rotating assemblies and strokers

Skip White Performance provides many high performance racing and engine products such as, stroker engines, turn-key engines, cylinder heads and pistons

www.skipwhiteperformance.com

here's their 421 kit both 4.155..

lmsport

· #17 · Oct 9, 2020

Pump 93 octane with aluminum heads and big cam will only tolerate about 10.5 compression---check it closely

ericnova72

· #18 · Oct 9, 2020

I know you commented and mentioned you had to really grind on the port outlet of the Air Gap to make it fit the heads....but the intake port outlet isn't the restriction problem.....the entire manifold port from head to carb pad that you can't access with a grinder has the too small problem also....the only way you can get to them is like the undercover circle track modification is done - a 1-1/2" or 2" hole saw is used to cut acces holes in each runner, the runner gets ported using that access hole, and then the piece cut out by the hole saw is welded back in place and ground back smooth to be undetectable.

If you've got another 1" of height space, the Holley Strip Dominator or Professional Products Hurricane would be good single plane starting points. Vic Jr or Weiand Team G if you don't have the space. at least with a single plane you'll be able to get the entire port length to a big enough cross section to not ba a restriction to a 300cfm port.....Numbers I've seen posted for the Ari Gap is about 270 cfm on the best port and about 250 on a few of the least flowing ports. Porting the manifold outlet doesn't change that very much.

Reason you can't find a lower cost 3.875" stroke kit is because no one makes a cast 3.875" stroke crank....all the 3.875" stuff is forged crank only.
The added crank cost and the fact the 3.875" kits come with the premium 7/16" bolt SCAT I-beam rods is the price difference.

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Seangalt

Discussion Starter · #19 · Oct 9, 2020 (Edited)

ericnova72 said:
I know you commented and mentioned you had to really grind on the port outlet of the Air Gap to make it fit the heads....but the intake port outlet isn't the restriction problem.....the entire manifold port from head to carb pad that you can't access with a grinder has the too small problem also....the only way you can get to them is like the undercover circle track modification is done - a 1-1/2" or 2" hole saw is used to cut acces holes in each runner, the runner gets ported using that access hole, and then the piece cut out by the hole saw is welded back in place and ground back smooth to be undetectable.

If you've got another 1" of height space, the Holley Strip Dominator or Professional Products Hurricane would be good single plane starting points. Vic Jr or Weiand Team G if you don't have the space. at least with a single plane you'll be able to get the entire port length to a big enough cross section to not ba a restriction to a 300cfm port.....Numbers I've seen posted for the Ari Gap is about 270 cfm on the best port and about 250 on a few of the least flowing ports. Porting the manifold outlet doesn't change that very much.

Reason you can't find a lower cost 3.875" stroke kit is because no one makes a cast 3.875" stroke crank....all the 3.875" stuff is forged crank only.
The added crank cost and the fact the 3.875" kits come with the premium 7/16" bolt SCAT I-beam rods is the price difference.

Makes sense.. you think the cast scat 500hp is good enough for this build? My last desktop dyno had me kinda close to that number even externally balanced at 450 hp ish.. I could save a few weeks and go with the 406 kit with the $570 forged crank upgrade.. but then its only 1800 more for a dart SHP.. lol... maybe I'll run this to 6500 this season.. then later get a shp... idk. Wife would kill me if I did both this close to Christmas..

but Yes. I'm going with a single plane. Probably the vic Jr. I agree the air gap is hurting and not ideal. At the time I built it I thought I didn't have room. But after I closed the hood I had more room than I thought. So I tested.. I was using a 1" spacer on the air gap as I found the hp950/motor seemed to like it better. I could really feel the power difference in the few days I ran it before tearing down last weekend.. Luckily I do have that inch higher I can go. So any intake 6.5" or 7" tall or less should fit under the cowel. The dart 200 9" may work with a 2" filter and is already provisioned for the .200 raised runners.. but not sure if I want it that tall. I do have another hood. I could suck it up and get a scoop or smomething.. its just my hood is a collector Motion Cowl and I like it.

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Seangalt

Discussion Starter · #20 · Oct 9, 2020

lmsport said:
Pump 93 octane with aluminum heads and big cam will only tolerate about 10.5 compression---check it closely

I agree. I ran it with flattops and 10.4/1 with no pinging. But yes I know I'm on the edge. Thx.

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