Technical 400 SBC budget build

I hate to do it, but how about an updated post on the 400 sbc?!

400 small block bored 30 over (406)
Vortec heads (64 cc) at the machine shop now
30 over flat top pistons
steel crank at the shop now too being turned and polished

I'm trying to use what I have if possible. Yes, my question is related to rod length...
1. Use the stock rods and be fine, or too high of compression?
2. Or - Use 5.7 rods. Would this be ok or need a small base circle cam?

Please keep it simple, THANK YOU in advance for your help!

 

Stock 400 rods are only 5.565, and what octane fuel are you using?

 

The pin height in the piston has to match the rod length, so if you already have the pistons, you'll use the rods they were designed for.
Budget is budget, use the best of what you have, get the best you can with the rest of the budget money.

 

you'll need ~25cc dish for pump gas

 

You will gain a little power with the 5.7 inch rods, but as stated you need the correct pistons for them. That has nothing to do with the compression ratio.

 

I know ur on a budget but JE for one has off the self “Speed-Pro” combinations that will allow even a 6-1/8” rod but you need a 3.480 crank from a 350. We’ve built quite a few between 375-380” that could pull anything and stay cool.

 

Not sure if you have already bought your pistons. As mentioned the piston compression height is based on rod length, so they do not interchange between rod lengths. The original 400 smog heads had 76cc combustion chambers. Your vortex heads are probably 58cc. As mentioned that combination will require a dished piston. I am not a fan of vortex heads on 400s. If you already have new pistons they typically have a sheet listing different CR with different combustion chamber volume. The 5.7" rod 406 is my current favorite engine and more parts than ever are currently available. You might want to spend $14 - $16 and get a copy of Dave Vizard's " Biulding Max Performance SBCs on a Budget". It's a 20 year old book, so a lot of the newer aftermarket parts are not mentioned, but it still contains a lot of good information. May give you a better idea of what parts play nice together before spending any more money.

 

I've verified my rods are stock 400, 5.656. The flat tops were matched to these rods. My plan is to clean and check of course, then run the same rods (resized as needed) and pistons, turn the crank, and hone the block. Any issue with me using the vortec heads, other than needing to drill the steam holes? Am i going to have to use certain octane fuel? All info helps, THANKS AGAIN, keep em coming!

 

Right, I had just read where flat tops on the 5.7 rods bump the compression up quite a bit.

 

Nice, thanks!

I confirmed my heads are 64cc. My rods are 5.656, and the pistons that were attached upon teardown are a 4 valve relief flat top .030. Thoughts?

 

You could run a 3.48 stroke with 5.7 rods and your pistons. Or set your pistons up with the 400 crank and check your deck clearance. If the piston were of the cheaper variety it may surprise you how little you would need to machine off of the top of the pistons to get a 0 deck. You can get away with .005 out of the deck if you run the right head gaskets. Of coarse you will end up with at least 11.5 to 1 compression.

 

Two things.
1. Again, a piston is designed for a specific rod length by moving the wrist pin location. A flat top piston designed for the short 400 rod will stick out the top of the bore at TDC if you hung it on a 5.7 rod.
2. Yes, if you run the numbers you will find that you will have an unacceptably high CR using flat top piston and vortex heads.

 

If they are 64cc vortex heads, I will retract my unacceptably high CR statement and revise it to potentially high depending on head gasket thickness. I would run the numbers and calculate just what you will end up with. Also depends on how much you deck the block and exactly what compression height your pistons are as they vary.

 

For what it's worth; I ran a set of stock 400 rods in one of my race engines. It was a 0.030 over bore with 11:1 forged pistons running alcohol. Never had a problem with the rods, but the cast crank wore badly on the rod journals. That was under race conditions, not a lot of miles, but up and down rpm and wide open throttle.

 

400 heads have steam holes between cylinders. Your heads don't have them. I have added them to heads using a 400 head gasket as a guide. As others have mentioned your compression ratio will be over 11to1. It would be easier to just run the 400 heads.

 

If using other heads than the stock 400 heads, make sure that they have the steam holes drilled in them that
the 400 heads have. Otherwise you will have big issues down the road.

 

I'm wanting to run the stock 5.656 rods and the flat rops, with the vortec heads.

 

Yes, and before you assemble it you need to take the crank stroke, the block deck height, the bore diameter, the rod length, the piston compression height, the piston valve relief volume, the head gasket volume based on the thickness, and the cylinder head combustion chamber volume and compute the compression ratio before being comfortable with the vortex heads. And as mentioned, they will need steam holes.

 

Keep the quench tight and you should be good for good pump gas if this is a street car.
Think I have pictures for the drilling the steam holes.

 

Yes, my reputable head builder is adding the steam holes. I am most concerned with too high of a compression ratio. I'm sure I'm over-thinking it, but better to ask a lot of questions on the front end! Yes, street car.

 

Wow!

 

A thick head gasket is not the way to drop compression. You want a tight quench, that helps combat detonation.

 

Use to calculate by hand. Once you have your data, many online apps chug out the math.

 

@57bentley What's the casting number? 906 and 062 are 64cc (350) heads and the 58cc heads are 305 heads which will increase you CR.

 

If you have the good replacement flat tops with the factory 1.560" compression height(distance from center of wrist pin to top of piston), stock undecked block which puts piston .025" down the bore at TDC, the 64cc head and the typical .041" thick x 4.190" bore head gasket the resulting compression ratio is 10.94:1 with a rather poor quench(total piston to head clearance as assembled) of .066"(ideal for detonation resistance is .035-.045" total).

If you've got a cheap "rebuilder's" type reduced height piston at the common 1.540" height these things come in at, with the rest of the specs remaining as in the above lay-out, then compression drops to 10.44:1 but quench gets really bad at .086"(closer you get to .100" the more detonation prone the engine becomes even with lower compression).

To do it right you really need a dished piston with a 64cc head on a 406" SBC engine.

You're just asking for trouble to try to run what you have on pump gas due to poor quench combined with compression ratio pushng at or above the limit for pump 93 octane.

Basic compression ratio calculator, learn it, know it, use it...
http://wallaceracing.com/cr_test2.php

If your flat top is thick enough, you might get this to work by having a 3" diameter x .060" deep dish cut in the top of the piston you have, that would remove 7cc and drop compression by 0.75:1 in the above examples.
Cast or hypereutectic piston needs to maintain about .230-.240" thickness in the top after the cut if you want to look into this.
3.5" x .045" dish would do it too.
I've done it a handful of times in the old days before there were very many 400 piston choices for either the 5.565" or 5.7" rod lengths.
I've also cut the TRW forged dish 5.565" rod piston into a flat top for a 5.7" rod, back before a 5.7" rod forged flat top was even available for the 400.

Stock or stock style bolt and nut 5.7" rods will typically need a either ARP bolts and a little clearance grinding on the rod and edge of the rod bolt head to clear the cam...or use a reduced base circle cam.
Most of the aftermarket capscrew style rods available now either clear a stock base circle or need a very minor clearance grind on the rod shoulder...but you don't have to worry about the bolt head like a stock rod.

 

You COULD........ try smoothing out your chambers and remove material in the process. IF enough material is removed it could lower your CR enough to try it with hi test fuel and pull some timing out of it.
(A real crutch-job though!)
6sally6

 

Yeah, it's another tool in the arsenal....hard to get 7+cc's out of a chamber though.
3cc, maybe 4cc is about the max you'll find easily in a Vortec chamber, and it won't be enough to do the job all by itself.

 

So after asking similar questions before, you need to verify the pistons you have
i/e stock they should be around .025 in the holes. If you did not deck the block .025 AND you have rebuilder pistons, you start at a min. .050 in the hole. So make sure the pistons you have are set for the machine work on your block.

Assume nothing, my buddy has a fully rebuilt machined, .030 327. I checked and his flat tops are .053 in the hole...the shop just ordered rebuilder pistons-or whatever you call them, and didn't deck the block to match.

Edit:

@Ericnova72 clued me to this a bit ago

 

My 400 is 0.040 over. The damn thing was overheating from day one until I drilled the extra water holes in the block, yes the block. Problem solved. Use the correct 400 head gaskets as templates.
Oh yeah, steam holes in the heads are mandatory, too. Other than that, enjoy the torque. Feels like a nailhead, ha.
110 degrees Texas heat, no problem anymore.

 

The extra water hole in the block deck was a running change, so depending what year the block is it may, or may not, be there. Fel Pro has a bulletin on it. The hole existed in all heads, but initially not all blocks. Some benefit can be had by restricting the three big water holes at the top of the deck on both sides.