anybody know if a big block crank will work in a 400 small block? or is the spacing different?

 

Absolutely not. The sizes are completely different.

 

sizes as far as mains and pins can be modified. it is 2.75 on a big block so grind it under to 2.65 but is the spacing the same?

 

Not even close.

 

worth a try. is there any small block cranks that are more than the 400 3.750 stroke? and also forged? I am thinking about doing a budget build and wanted to do more cubes instead of destroking to 377. or possibly using a 327 crank.

 

Sure! You can get 3.875, or 4". Usually you'd need an aftermarket block to fit the long stroke in there though...
Have you looked at Callies, Cola, Lunati etc?

 

If you're on a budget, you're probably best to stick to one of the more popular configurations, like a 383.

 

383 is a 350 block
I have a 400 so I was thinking about 380 +.040 with a 350 crank or maybe using a 327 crank (destroked 355)to rev higher but I don't want to lose all the torque either.
or making it a 383 by using a forged 350 crank and offset grinding pins to go from 3.48 to 3.52 and using vette aluminum heads or fast burn heads and a tpi setup all hogged out to flow more. should be over 500 ft/lbs. and around 450-500 hp.

 

None of those really fits the description of a "budget build". Destroking it won't let you "rev higher" when the limiting factor is those weenie little stock heads, and worse yet those weenie little TPI runners.

 

perfectly said. Heads and valvetrain set the RPM potential of the engine, not the stroke.

 

No.

 

who said anything about weenie stock heads. I have the room to not worry about the valves being shrouded. the vette heads are cheap and will fit a 2.05" valve. little port and polish done by yours truly and thats done. Or if I can score a set of fast burns cheap I would rather use those. also who said stock tpi runners. and it will still be budget because well pm rods are cheap and will hold up to around 550 hp or so actually a little more. and a forged 327 or 350 crank is pretty easy to come by. and I guess what I am hearing is that "ugh a 400 will rev higher than a 350 if it has lighter rocker assembly" no reciprocating weight has just as much if not more to do with rpm's has anyone ever heard of a dz302. if not highest revving sbc ever made. guess why tiny 3" crank stroke. the head assembly will increase rpm but it does not determine rpm solely by that. I have built sbc's and know what I am doing but never messed with big blocks other than stock rebuild so that was my question. but as far as a budget build I already have a 400 that has block work done but it needs honed to clear out surface rust. no big deal there. and like I explained the rest is all fairly cheap. I just want to make a fun motor than won't cost 10 grand. I am doing the expensive motor for my vert.

 

Corvette heads are weenie stock heads. You can put as big a valve you want in them, but it won't matter when the ports are still small.

Even with an aftermarket TPI runner, the design of the TPI system will restrict the top end. If you wanted to build a high revving engine, you'd need a different induction system.

When you start talking about silliness like offset grinding cranks, it's not a budget build.

The 302 was built for SCCA factory racing the Z28 in a 5 liter limited displacement class. It needed to spin fast to overcome the loss of displacement, so it was built with a valvetrain that could handle the high speeds. It doesn't spin fast because the short stroke, it needs to spin fast because of the short stroke.

The only time a short stroke engine would be preferred over a longer stroke one for high RPM operation would be if we were considering two engines with the same displacement. In that case, the lower piston speeds of the short stroke engine would provide an advantage. When people start talking about "destroking" though, the comparison is between engines of different displacements, and displacement always wins.

Power comes from burning gasoline molecules with air. More power comes from burning more gasoline molecules with more air in the same period of time. There are two ways to do that. You can burn more gas and air on each stroke (more displacement), or you can burn the same amount of gas and air more often (higher speed).

Either way, the same volume of gas and air has to be moved through the heads in the same period of time to make the same power on a slow turning large displacement engine as it does on a fast turning smaller displacement engine. This is why power is dependent on the heads. If the heads are small, they won't be able to move enough charge to make any power at any speed.

What's even more of a limiting factor to high speed operation though is the valvetrain.

 

this is going to be a street motor. so I am not as worried about hp as I am torque. and the destroked combo will provide an equal balance of both. the smaller ports help with torque. also the offset grinding is a cheap process for me because I make crankshafts for a living. we make all from 4 cylinder ford cranks to 12 cylinder cat and cummins cranks also army v8 stuff. even the the v12 cranks only have around a 4.5" stroke and they are around 1200 ft lbs. a street motor compared to a circle track motor. On the street a nice smokey burnout is more fun than revving 10k rpm's either way this is alot cheaper than you think. also the tpi setup properly setup is alot more fun than people think. I will probably do this just to show numbers on it. and cost wise it will cost me around $2k just because I already have the block. so in my opinion this is definitely budget. compared to the sb2 motor I am starting. I kinda want to do it just to see what can be accomplished with cheap and plentiful genuine chevy stuff instead of using cheap chinesse crap. not really because of savings. Callies cranks are made 5 mins from where I work (and I have known the owner since I was about 9 years old)hell their second plant used to be our old plant. I have also used Sonny Bryant quite a few times so I am not real worried about cost.

 

Do you make pistons and rods too? because you'd need custom ones to work with the oddball stroke on an offset ground crank.

 

You're talking all over the place and not making any sense.

I suppose every build is a "budget" build if you lay out a budget for getting it done. In that case, top fuel engines are "budget" builds.

Destroking does not provide a balance of HP & torque. It provides less of each. HP is a function of torque (torque times RPMs divided by 5252 = HP), and torque is a function of force times lever arm - and force is the cylinder pressure divided by the area of the piston. Cylinder pressure is a function of how much air and fuel you get into the cylinder to burn - fewer cubic inches means less air and fuel to burn; less air and fuel to burn means less pressure; less pressure means lower torque; shorter lever arm means even less torque; less torque means less HP - so destroking reduces torque and HP in two different ways.

All other things being equal.

If you make your living making crankshafts, how come you didn't know that BBC and SBC cranks aren't even close to being able to fit one crank into the other block?

 

we mainly specialize in hd apps not sbc stuff. chevy sent all that stuff to mexico a long time ago. and as far as talking all over the place which made more torque a 427 or a 454. and I have no idea why you would need custom rods and pistons for an offset grind. off the shelf stuff works fine. it isn't hard to get small journal rods a forged 350 crank and 327 for that matter is 2.10 rod journals so you just use sj pink rods which chevy also used a sj pm rod and pistons there is no difference. and if you think $2k is not budget then I have no idea what is except buying a prebuilt which isn't much fun. cubic inches lead to more torque but chevy never made a crank with a larger stroke than 3.75 so then it would lead to aftermarket and if I am going to do that it turns out to be not so budget. also which one creates more torque the 350 based 355 or a 400 based 355 not a hard question to answer. I am just going to go ahead and try it until I get my not so budget sb2 build done. I have a lot of camaro stuff I would rather just buy another camaro and swap in this motor than leave it alone. Going by my desktop dyno it would put me around 10's with minimal cost. instead of I only got $10k in the motor and be in the same ballpark time wise. in the end it doesn't really matter if it sounds like it would work if it doesn't who cares but it will be fun. also did anyone ever tell you that the standard equation you used is not always accurate? there is many more variables to factor in in some builds. If i could find the article there was one I found a while back that the class was limited to 380 with all factory parts other than forged pistons and sbc was the only one at an advantage because of the 400. also you ever see the junk swirl port 305 heads well that same tech used to be nascar tech. it is based more on combustion chamber design hence the fast burn heads. this is actually alot easier than most of you guys make it seem. yeah it cost alot to test but if you wanna try it don't be scared just do it instead of listening to what everyone else says it should work like. also have you ever seen stock 302 heads they are far from top secret tech the vette heads flow better than they do. as long as the recip assembly is balanced you are fine.

also I am not trying to act like you guys are wrong or stupid by an means I value your opinions 5-7 I have asked you quite a few questions which the same goes with you Apeiron. (p.s. thanks for the lock up info a while back) but sometimes you can get alot better result by not going with the norm.


also th eoriginal question I figured it wouldn't work but I never tried it. the only reason it won't work is because of spacing. everyone worries about the beings being the wrong size grind them down and who cares. there is alot of oddball combo's look the 302, 307, 262 (v8 not v6)

 

If you offset grind the crank to increase the stroke, then you've reduced the diameter of the crank journal, so you need a rod with a smaller diameter to match. Also by increasing the stroke, you've moved the reciprocating assembly higher at the top of the stroke, so you need either a shorter rod, or a piston with a higher wrist pin to keep from slamming the piston into the head.

Right, not a hard question to answer, they make near enough the same torque to make no difference.

Which equation is that? HP=(torque * RPM) / 5252. It is always accurate, without exception. The units are defined that way. I could derive it for you if you like.

We're not trying to discourage you from doing some experimenting and having some fun, but you're demonstrating some fundamental gaps in your knowledge that are going to lead to disappointment.

 

the last motor I did was a big bore 358 which isn't real typical either(4.165 bore x 3.28). This was an offset ground 327 crank. This was with a set of worked over double hump heads. also compression was 11:1 so it we did run it with premium and race gas mixed because of the cast heads. this was real cheap because we had all of it there. Ran 10.31 with a 950 dbl pumper. I kinda like unusual combo's instead of just going with what works. The only difference is going to be the induction will be a hold up but I will have to improvise with it. disappointment comes and goes so no big deal, start something else. also the thing about pistons and rod length is a little misleading because the stock 400 rods are 5.565 and pm rods are 5.7 so there is a .135" difference but it becomes no big deal even with my block deced to 9" because I am also getting rid of .410" of crank stroke (maybe more this is with an offset grind from 3.25-3.34. the volumetric efficiency goes up with a long rod motor compared a long stroke motor.

 

Maybe I missed the original point, but here's my question:

Why not build up the 400? When the head and deck surfaces are flat and the rotating assembly balanced, they make great power and are very reliable.

I've known a few guys to build 400s with good aftermarket rods that were screamers. You might already have most of what you need.

Boo.

 

stroke that 400. get some great heads and a great cam. 525-575 hp not out of reach. stop making things harder than they need to be.

 

why even offer suggestions, here is someone who knows so much that they dont know anything.

 

since I was bored at work this weekend and 5-7 asked "If you make your living making crankshafts, how come you didn't know that BBC and SBC cranks aren't even close to being able to fit one crank into the other block?" here are some pics of the stuff we mainly run. this is one of the 12 lines we run most are around this size but our equipment is adaptable to work on sbc stuff. (all the old manual stuff anyway not the cnc stuff. Now maybe you see why I really didn't have a clue if a bbc crank will fit into a small block. pics are camera pics so not real high res but you get the idea.

 

i'm fairly new to most of this, but i did work in a machine shop, so here's a few cents: destroking (or stroking for that matter) a crank doesn't necessarily make the rod journals smaller. sure, it can, but you can also build up the mains side of the rod journal with welding before you grind the destroked crank. same journal size, different stroke. rod length, of course, comes into play then. but not rods with different journal sizes.

and as for stroking/destroking leading to higher/lower hp's and torque: assuming same cubes (ie: 383 attained by smaller bore/longer stroke or larger bore/shorter stroke) Hot Rod magazine did pretty intensive testing a few years back and found almost NO difference in torque, hps, or rpms. nearly the same curves and limits for each engine.

just a few cents

-Chris

 

i need a tylenol....lol

 

Hi guys. I just stumbled across this thread during my lunch break and I want to ask - who's on first? Seriously - what was the original question here? The BBC crank in a SBC is probably a bad idea (if not expensive / impossible) but a few things I've heard aside from the main discuss concern me...

1. Someone mentioned that a destroked 400 and a 350 would make almost identical torque. If the displacements are the same the 350 would have a longer stroke (given that the 400 has the larger bore) so the 350 would make more torque and I'm willing to wager it would be significant. Smokey talked at length about building an engine to the application by using different bore/stroke combinations within a certain CID limit. His main point was - for torque you want a bigger stroke.

2. Someone said destroking won't make more power OR torque. All things being equal, I could buy this. However, if the destroked motor can turn more RPM due to the shorter stroke - I would wager it has a better chance of making the SAME hp, just at higher rpm and at the cost of torque.

3. Someone said the DZ302 didn't spin high because of its short stroke but because it needed to...that fails to clarify the point. Having a shorter stroke WILL ALWAYS allow an individual to get more RPM out of a motor because it places less of a load on the crank to do so. (ie - a stock 350 cast crank is good to ~6500 rpm, a stock cast L31 (baby LT1?) crank could potentially see ~7000 rpm with the same rods / pistons. Again I make the point that one of Smokey's destroked Indy motors (209 cid) made HUGE rpm (10,000ish) because it was destroked. CID limits also have to be considered. I've heard some of the old timers argue that the 302 was particularly efficient and as such, could come closer to the 2hp/cid magic number than could any other motor (higher cid = lower hp/cid ratio).

Just thinking out loud

 

It's patently impossible.

A popular misconception says that the longer stroke will have more torque, because it applies more leverage to the crank. What it fails to take into consideration is that at the same displacement, increasing the stroke has to reduce the bore, which means that there's less piston face for the cylinder pressure to apply force to. Altering the bore/stroke ratio while keeping displacement the same has no significant impact on torque.

The destroked engine won't turn drastically more RPM by virtue of its shorter stroke alone. There's a slight decrease in reciprocating losses in a shorter-stroked engine that might allow it to turn a few more RPMs, but it's primarily the induction system that limits the high-RPM potential of an engine. The main attraction for destroking in a high RPM engine is to increase the longetivity of the engine by reducing its internal stresses.

The 209 may have turned 10,000 RPM, but similar output could have been obtained with a 418 turning at 5,000 RPM. For that matter, there's no reason why a properly-built larger engine like a small block can't turn 10,000 RPM, at the cost of longetivity.

Power comes from combining gasoline molecules with oxygen molecules in a given amount of time. To make more power, more molecules need to be burned in the same time. This can be done by increasing the displacement of the engine so that more molecules can be drawn in on each revolution, or by turning the engine faster to burn the same number of molecules per revolution more often. Either way, the same amount of fuel and air is consumed to make the same power.

This is why power is said to come from the heads, because its the airflow capacity of the heads which limits the power potential of the engine. If the heads can only move enough air to make 300 HP, then it doesn't matter if its on a 300 cubic inch engine turning 6000 RPM, a 600 inch engine turning 3000 RPM, or a 150 inch engine turning 12000 RPM, you're only going to get 300 HP.

Of course I'm not trying to say that displacement is the only thing to consider, just that its the primary one. There are reciprocating losses, rotating losses, thermodynamic losses, pumping losses, combustion propagation, and who knows how many other factors that will affect the power output of the engine, which can all vary with the bore and stroke configuration of the engine, but they're mostly overshadowed by displacement.

 

big block is not just because more cubes, it literally is a BIG BLOCK.. small block is SMALL BLOCK..