On a production 400 block, bored to a 406

If I stuff a 3.75" stroke forged crank in it, I can run normal SBC 5.7" rods, as long as I run pistons set up for a 3.75" stroke, 4.155" bore, and 5.7" rod correct? (which happen to be around $210 / set for hypers).

I've seen some cranks that say 5.7" rod, 6.0" rod.. I don't understand why.. The rod length should only be related to the piston pin location, no ?

So to recap, I can run normal replacement I-beam 5.7" 350 rods (i.e, summit) in a 400 ?

-- Joe

 

Yes, you can run a 5.7" rod on a 3.75" crank. You will need a piston with a 1.425" compression height - this gives you 0.025" deck clearance on a standard 9.025" SBC block. Finding pistons with a 1.425" comp height should not be a problem.

I am using the same combination for my 400 build.

 

Sounds good. I have a few options open to me right now, but I'm looking at building a 412 or 406 and wanted to verify the crank thing.

Thanks!

-- Joe

 

IIRC, its not that theres an upper limit on rod length, but a minimum length... they don't want you using anything shorter than a 5.7" rod (like a stock 400 rod @ 5.565"). Probably either a balancing issue, or could have clearance problems with long piston skirts on a piston with a long pin height.

 

i would guess balance, but what do i know.

 

The minimum distance issue would be a case of skirt clearance.

 

Yes, but if the design of the counterweight was unusually.... long?... then it may not work with some pistons very well, so they recommend a longer rod so that you'll use a piston with a shorter pin height (pin closer to the piston face), and likely a shorter skirt would come with that, providing more clearance for the crank counterweights.

 

Yes. I'm talking about in the short range of the stock rod length, though. The extreme end of the spectrum, though - strange conglomeration of parts that would be.

You really don't see any "strange" counterweight designs these days, though. And 9 out of 10 times, your average guy building up a 400, will end up using either the 5.7 or 6.0" rod, for which there are ample piston designs. With either combination, and the correct parts, I've never seen part A hit part B at BDC.

 

Woah this got a lot of hits last night.


I emailed the seller of the crank I intend on using, and he said it will work fine as long as I use the correct piston, as outlined by a few of you gus.

Another member PM'd me and gave me some pretty good technical details on why I need to use the long rods, which I hadn't even thought off.

I called comp cams too, to ensure I can run the XR288HR cam on the 412, and the tech guy thought it would actually be a killer combination.

Here is the crank I bought:

http://cgi.ebay.com/ebaymotors/ws/eB...id=p2759.l1259


So, this is going to be used with some eagle SIR rods, with ARP bolts.

Pistons are TRW Lightweight 2606 forgings. (16.2cc reverse dome).


Compression should be around 10.5:1 with the right heads, which I'm thinking of using trickflow 23* again, although I'm also tempted to try summit's new "street/strip" heads.

So as long as the machine shop can balance that crank to the pistons + rods, and as long as the skirts clear the counterweights with the 5.7" rods, I think it will be a killer combo.

Thoughts?

-- Joe

 

Sounds like a good combo to me. I went with 6 inch rods in my 400. Dart block with 350 mains tho not actual production 400 block but shouldnt make too much a difference. 6" rod can be easier to balance than the 5.7 but should work either way

 

Yeah, I hear ya. It was a matter of what was available for short money. Forged lightweights, on floated SIR rods with arp hardware for $300 from a forum member. The steel crank was, as you can see in the ad, short money too.

The same forum member has the .060 over block, pretty much ready to go as well. If he can freight it out to me it will save me from having to buy and machine a local block. Do a sonic test, hone, maybe some cam bearings and call it a day.

Did you go 400 or 406 or ? EFI or Carb?

-- Joe

 

I've seen many of these ads on ebay for cranks and stuff like this. They might be just fine.

BUT, I have to wonder........ nowhere in the ad do they even mention a brand name on the crankshaft, just the name of the ebayer's store/business.
So one might assume that these are offshore pieces made by foreign slaves in a faraway land. Maybe not, but if you were trying to build up a product line brand name, and were proud of the products, I think that you would be anxious to have the name of your good product out there where people can se it.

In other words, time passes by and two guys go to the track. One guy's engine blows with a broken crank. Guy number two comes by and says "hey man, bad luck, what happened?" Guy one says "Oh, my engine blew, it's got a broken crank". Oh, says guy two, what kind was it, forged or cast, and what brand? Oh I don't know, guy one says, I got it off ebay, ah, you know, that guy that sells them thar cranks on ebay???

Man, I'm old school! Back in the day guys would be anxious to have a "Hank the Crank", "Milodon", "Callies", "Carillo" or some other well known quality crank builder's parts in the engine and decal on their fender. It meant you had some good, quality stuff in there and it got you some psyche respect and confidence before you ever fired the engine.

I'm all for saving money, and I could never afford the reaaly good stuff while rasing a family and all.
But if I was going to the cheaper/foreign made route, I think I would go with Scat brand stuff. I've heard nothing but good about them in magazines and such. And I think their higher- end cranks might be made in America.

In contrast, I've heard a few horror stories about even the higher- end Eagle pieces. Mainly end- of- the- crank snout breakage/balancer issues. But I think quite a few people have run Eagle stuff hard too with success.

 

I'm bailing on that crank. I can't take a chance of it not working with a 5.7" rod.

On another note. My machinest seems to think with the 5.7 rod, even though the cam should make power to 6000 or so, he said the rod angle will put the max HP around 5400 rpm. He said if I want more top end to put a longer rod.

How does the rod angle effect the RPM range? eh??




-- Joe

 

I went 400..actually 401 rounding up. EFI victor single plane with intakeelbows.com elbow.


As far as rod angle and rpm, i dont know how much effect it has, but different rod lengths have different effects on the cylinder walls. I believe a longer rod will push on the cylinder walls more than the shorter rod but i dont think thats gonna limit rpm at all.

Longer rod is advantageous for higher rpms anyway since you use a shorter compression height piston, meaning less weight being thrown around. Puts less stress on the rod bolts/bearings. If you want to turn some higher rpm, definately look for a 6" rod but a 5.7 with good bolts will be more than fine to 6000 rpm.

 

If I had my choice I would run a 6" rod. Seems that the 6" rod engines stay together better. I had a 406 with 6" rods, forged pistons and steel crank and it was nothing for me to turn that engine at 8400 but I tried to keep it down to about 7600 and did that regularly.

 

longer and shorter rods change the dwell time at TDC and BDC.
what i think he is getting at is that if you have more dwell at TDC, then the spark can ignite the mix more thoroughly before the piston moves too much.
this increases the pressure, aka, torque, for a given rpm, which gives you more power up top...
something like that.

 

Oddly enough, when I spoke with comp cams today he said the rod had little effect on powerband, but he did say the the longer rod would move the powerband up a hair.

He said what my machinest was probably getting at was, the powerband indicated by the cam is for a 350 block, and on a 412 I'd see the powerband go WAY lower than indicated. The 2500-6000 RPM cam he said will more likely be a 2000-5500 rpm cam in the 412. Something I hadn't considered, and oddly enough camquest and desktop dyno doesn't seem to take the engine size into account when plotting the curve..

Either way, both comp and the machinest said "over 500hp" so it's still worth it I think. May be better with 3.42 gears though. Figure a 125mph car in the 1/4.


The ebay seller tells me he's certain that crank works with 5.7 rods. Said it's from china, no manufacturer.

-- Joe

 

That cam should peak fairly high in the 412. My old cam peaked at 6300 with a 383 and its about the same as that cam. I was told that cam in my car would peak the same if not 100 rpm higher than what i have now.

A 412 with the same stroke will probly peak closer to 6000 with that cam. My 233/233 cam for my 400 turbo motor is suppose to peak in the 5800-6000 range, but turbos tend to push the rpm range a touch higher than what you'd see on a n/a motor from what i'm told.

 

If given the opportunity, I would take Scat over Eagle. I wouldn't trust any crankshaft that doesn't have a name on it. I would also take the 6.0" rod over a 5.7" rod.

If you want to split hairs over the long rod vs short rod: short rod is slower at BDC and faster at TDC. Long rod is faster at BDC and slower at TDC. Long rod actually has less cylinder side load than a short rod due to a smaller rod angle. Longer rods also slow the peak piston speeds down, and delays peak piston velocity, giving the intake valve more time to open. There's more and I could go on, and I will if someone wants me to, but that's the gist of it. On 9 out of 10 motors, the actual net gains from optimal parts isn't really worth splitting hairs over. Most people are best off by starting out finding a piston that yields optimal compression, then seeing what rod length it goes with, and going backwards that way. It's on the high RPM motors (engines that see 6k+ regularly) that you'll see people put far more attention into rod length. The 2% of piston side loading, and 1° of rod angle difference, 1/2 a mph of piston speed (between 5.7 and 6.0), doesn't really matter.

And as far as being old school for having a name like HTC, Callies, or Crower - that's not really old school, people still give out the "wow, you've got some good stuff in there" treatment. You get what you pay for, and on those same 9 out of 10 builds (Joe - yours fits into this category), those Eagle and Scat assemblies work just fine. With the way things are going these days, why stick a $800 crank in the engine, when a $400 crank will hold up just fine?

 

You have it backwards... a short rod puts MORE load on the cylinder walls, the longer rod puts less.

I don't know about the rest of the answer though, so I won't comment.

 

OK thanks for clearing that up. I wasnt sure

 

Yes you can but the longer rods are better.

 

Leverage. The longer rod is better for torque and rpm in that combo. A longer rod stays straighter more up and down in the bore at the maximum deflection angle of the crank and so has more leverage to pull the piston down or push it up. Ideal is 6.125 rods but you would need to go lunati and wiseco or Ross pistons.

 

After it passes the sonic check, you might want to consider a street fill of Hard Blok.

Of course, that is supposed to be done before the final hone.

 

about the rods, i actually was curious about this exact thing a while ago and posted a vid on youtube of a test i ran in a modeling program to illustrate this exact effect.
the long rod is better in every sense.
ill post the vid if someone wants me to.
ideally, you want really long rods because at high rpms, the piston has extra time at TDC to build pressure after ignition. more pressure means more torque ect...
as for less time at BDC, thats not a problem unless your exhaust ports are terrible and dont flow very well. if you had a restricion in the exhaust, then you would want to get the air accelerating as soon as possible but in most cases, the exhaust is not a restriction enough to make much of an impact on the engine.

and as stekman said, in the scheme of things, your compression being right is much more important than the rod length.
rod length is somehting you worry about in a motor that runs the 24hrs of le mans twice without a rebuild

 

The block is junk. They didn't bore it with a torque plate.


I'm buying a set of TRW lightweight pistons from him that retail at $51 each ($408), a set of eagle SIR rods with arp bolts ($239 retail), a double roller timing set ($80 retail) and the CAST crank that was balanced to the rods + pistons. Whole thing for $300 or so plus shipping (say $350).

I would have got the block for another couple hundred bucks, but the machine work on the block was suspect. He had the rotating assembly done at a better machine shop when the first shop went out of business. Now he wants to do an LS1.


Anyway, a local guy offered me a 817 casting 2 bolt, complete short block for $190. He gave me a 30 day guarantee, meaning I bring it to my machinest, he checks it, and if its junk I get my money back.

Figure it will cost:

$50 check it
$95 hot tank, clean, etc
$225 bore it
$100 freeze plugs, install cam bearings, galley plugs, block 2 steam holes, etc.

So say around $500 in machine work, $350 rotating assembly, $200 block.

So I need to decide do I polish his cast crank, or spend wicked big money on a forged crank.. Then $130-300 on top of that to balance it.

If not, short block is around $1,100 for a wicked 412.

-- Joe

 

Happy days.

So I bought the pistons and rods, timing set, and head bolts. $350 to my door.


TRW LW-2606F60 pistons $424 new
EAGLE SIR Floating rods $259 new
Timing set $60 new
Head bolts $50 new

So I guess I guess I saved a little over $400 there.

I bought a 400 block locally for $180.


Going to the machine shop in about an hour.



Getting back on the topic of cranks.. I was looking at a nice article regarding crank strength. Cast iron being the weakest at under 100,000 psi, cast steel being a little better around 105,000 psi, 5140 at like 120,000 psi and 4340 at around 150,000 psi.

I was looking at a cast steel EAGLE 10400375057I crank. I called eagle to ask them a few questions. He said he didn't recommend a cast crank with a manual trans, he said it would probably break. He said the external balance (104003750 vs 10400375057I) is stronger due to less material in critical areas being removed, but he still recommended using a forged steel crank.

I was looking at this crank from PAW:

https://secure.pawengineparts.com/sh...431&catid=1171

With handling charges it's like $405 out the door. Not sure why it says "longer than stock stroke, block clearancing may be required". When the stroke says 3.750"..

Then we have Ohio crankshaft, who makes a 5140 for about the same price:

http://www.ohiocrank.com/chevysb_cranks.html

part # 54003750

Called and asked if it will work with 5.7" rods. Said he was going to go grab one and check it.
(though I'd think he would need to know the skirt length of the pistons, no?)

He called back. said I shouldn't have a problem with 5.7" rods.



Any thoughts?

-- Joe