bnr517

Guys,
Need a little help. I want to put a 400 crank in my ZZ4 and use my existing pistons which should give me a 377. My problem is I am not sure which connecting rods I need. Does anyone know of a kit that would have exactly what I need?
Thanks!!!!

Dynra Rockets

I would think a 5.565", same as a 400. Best to measure before you order so you can account for piston pin height and block deck height. Most people believe the 5.565 is too short for optimum performance/longevity and a longer rod with different pistons is the way to go.

As stated in a previous thread about a week ago a person ordered a 3.8 crank to put his pistons at zero deck instead of having the block shaved.

Bikespace

I could have it backwards, but doesn't it go like this?

350 block plus 400 crank = 383
400 block plus 350 crank = 377

jackson

.
^ ^^^ That is correct^^^^

but a real OE 400 crank won't fit into 350 block without first machining down OE 400 crank's main journals. Suggest it'll be cheaper buy a ready-made aftermarket 383 crank. Also false economy to employ old OE SHORT 5.565" 400 rods to save $ on pistons. Short rods are not as desirable as longer. Suggest buy aftermarket 383 pistons for use with OE zz4 5.7" rods or... buy 383 pistons for use with aftermarket 6.00" rods.

jackson

Also, OE zz4, 350 and 400 pistons are PRESSED onto OE rods.
If you swap OE pistons-OE rod combos around, you have to $ pay $ the shop to both press pistons off and then back on. Some shops are kinda hard on pistons as they press pistons off. If you buy aftermarket rods you can get the bushed rod option for just a few bucks more and float the pistons onto rods yourself.

jackson

That was me with the 3.800" stroke w/ stock 350 decks

derekderek

That short 400 rod is great for low rpm torque. High rpm power, not so much. And 350 .030 over with 400 stroke is 383. And turning .2 inches off the mains puts you into really soft cast iron. The cranks are hardened. Hardness only goes down about .030 or 50. Many guys won't touch a crank cut more than .010.

jackson

I've overlooked some thing here and it's likely the very combo the OP is planning.

If someone uses a 400 or 383 crank (both are 3.750" stroke) in a 350 block with stock OE 4.000" bore it DOES make 377ci.
Only when it's bored +0.030" to 4.030" does it make 383ci

jackson

The GM / Chevy HT383 crate uses a 3.800" stroke and 4.000" bore to make 383ci.

I built similar using 3.800" stroke and 4.030" bore to make 388ci

Short rods have serious drawback: steep rod angle. The shorter the rod, the steeper the rod angle.
Steep rod angles generate more LATERAL forces on both Bores & Rings causing more wear to both; especially bores.
Shallower rod angles cause piston to dwell near TDC longer and need less cam than a short rod.

If you own the machine shop and you happened to have a free set of short rods, it might make sense to resize rods, new rod bolts etc etc... otherwise no.
I've had several sets of 400 rods as they came in every OE 400. I haven't used them, and I wouldn't unless I had No choice.

L88Plus

If you go the route of using the longer stroke crank, buy one made for the application. If you have an old 400 crank, you'll have to pay to have mains cut down .2 and you'll probably need to turn the rod pins at least .010. Machine cost will likely be close to the cost of a new Scat or Eagle cast piece.

DaveL82

Are you talking using an older 400 crank in a ZZ4? If so, the ZZ4 uses a 1 piece rear seal so I believe you can't use an older crank in the 1 piece block design.

bnr517

I was looking at an aftermarket crank that would fit without machining but was going to keep the pistons to avoid having to bore the block. Think I found a complete kit from eagle with 4.00 pistons. Might be the easiest way.

Jebbysan

Just get a balanced rotating assembly from Eagle or Scat.....don't play around with mismatched parts......you will have to balance it anyway.
$1100 will get you a balanced rotator with forged pistons and a cast steel crank with 4340 cap bolt rods......this is a tough assembly.
Have the block touch honed and set up the new assembly...checking clearance at the cam tunnel/bottom of cylinder and the pan rail (note:The last 5.700 rod 383 I assembled required zero clearancing as Scat and Eagle have fixed their rods....but you need to check it.......).
I doubt the stock pistons will work...wrong C/D and the compression would be way too high.
Get a matched kit and do it right.

Although at this price range......bolt a real set of heads on that ZZ-4 and it will pick up huge.......the factory L-98 aluminum head does not flow well......I would put a pair of Dart 180 Platinums on this with the HOT cam that everyone runs.......it will pick up about 75 horsepower total.......

Jebby

jackson

Essentially true. But several companies offer an adapter to put old 2 pc rms crank in newer 1 pc rms block. Adapter cost $100 - $200. Probably not practical for most swaps & certainly not for an OE iron 400 crank in newer block.

Jebbysan

Just FYI and continuing on the OP's question........even people who build a 400 nowadays don't use a GM 400 crank.......there is simply no reason to spend money on it and they were not that strong.
For $200 you can buy a cast steel unit that is 5x stronger than the GM piece.

Jebby

bnr517

Good stuff! I am looking at a Trick Flow top end kit that will generate 425hp with stock crank but will give me 465hp with the upgraded crank kit. Not a mechanic by all means but looked at buying a completed 383 but think I want to do this on my own and learn a thing or two along the way. One thing I have learned so far is it's cheaper to buy one already put together! LOL

Vette5311

Is this true of GM forged crank 350 or only cast ones?
thanks

Jebbysan

Depends on crank in question is nitrided.....which is a hard surface treating......if not, cranks are just as hard in the center as they are anywhere else.
Aftermarket performance cranks have to be re-treated after they are turned....big expense....and time consuming.
.030 cranks are much more common than one would think.....but for stock rebuilds. The real problem with turning the rod journals is that the oil hole gets offset

Jebby

jackson

Kit is probably a best bet for some folk / situations.

Not for me. I prefer pieces to optimize my requirements.

My local machine shop checks crank index, twist etc and does balancing.

For this, I'd do a 6" rod combo; ensuring deck height, quench and compression are top priority
For this, assuming ZZ4 decks are good & true, I'd be looking for a deal on 3.800" stroke crank.

gkull

I read through everything that was said here. They covered the obvious about crank diameter. But what they didn't bring up is the short comingsof the zz4 motor it's self. Very wimpy cam duration with small valves. 58cc chambers would raise your compression to detonation levels with flat top pistons. So your reusing internal parts like pistons and rods is not possible because of piston pin height........

The correct way to build a stroker motor is buy a internally balanced rotating kit like a 396 ci 3.875 stroke for about $2000. Then buy heads and a cam that can support the larger cubic inches and desired compression ratio