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406 small block review

11K views 35 replies 8 participants last post by  lust4speed 
#1 ·
Okay guys, im new to this board but have often come here when i am in search of engine help, so i finally decided to join.

Heres the deal, im building a 406 small block that will go in a truck (yea its not a hotrod, and yes i would trade it for a 30s chevy coupe in a heartbeat)

This is my plan so far and i just wanna run it buy you guys to see if im on the right track:

400 small block that ive ran before getting bored .030"
Probe dished pistons 14cc
Scat 6" stroker rods
scat cast crank
cam: 12-246-3 - XTREME Energy

Aluminum heads with 2.02/1.6 valves and 64cc chambers
Edelbrock rpm intake
holley 800 double pumper

probably 7qt pan, high volume oil pump


Anyway so far with that setup my compression is 10.3:1 and a dynamic compression of 8.35. That will work with 93 octane if what i have been reading is correct.

My main question is how will my quench area be, stock deck height (which is about .025 if ive read correctly) and a .027" head gasket. Thats .052", and ive read that it should be around .040". How big of a deal is this? I have not purchased the rotating assembly yet so i can potentially switch it to get a bigger dished piston and therefore run a thinner gasket and still stay in the low 10's for compression, but i do like the setup i found, so basically im wondering is .052" killer, or will it not be bad? I want a solid running engine and i want it to be able to turn 8k although it will not get that high very often.
 
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#4 ·
Read through lhmurphys post about 406 build...whatdayathink.
Lots of good conversation about the tech aspect.
Your build recipie/goals are not plausible.
Cam wont support 8K rpm
Heads might...with tons of porting...if you dont ruin them
Rods will be hanging out of block at around 6500 rpm due to excess length(6.0 in) and weight Vs. velocity
Block will need decked, which means you need all parts going into to it, physically in your possesion, so you can measure the "stack" to give you a height that you need to deck the block to.
Lots more trouble here...too much to list.
Do some more reading, when you think you have read enough...read some more, then start asking some questions.
Not trying to be flip, you just need to read up and learn some more before you start dumping money into a build.
 
#5 ·
Okay forget the whole 8k thing. Moving on from that, i have read the thread and not gotten the answers i need. Block will not be getting decked as this is just a fun build, not looking to go race with it, just want about 400hp and something reliable, its a good block and until i took it apart it ran great. And its a budget build so im not gonna shell out a couple thousand or more. So what exactly is wrong that i need to fix (parts wise) to get about 400 horse and have something reliable?
 
#6 ·
Your static compression with that cam and stroke etc will be 11.4 ish to one and the dynamic will be around 9.1 to one. Way to high for any pump gas, and... that is figured with the block decked and a .045 quench height.
Without a good quench , the chamber shape on the heads you have wont do diddly for you. You wont run on pump gas without it detonating itself to death.
If you deck the block, get a good quench,run a slightly larger duration cam, keep the cooling system working very well, keeping the engine at 170 degrees F (or a bit less) you will be on the edge with 92 octane.
Here is a little chart for dynamic comp Vs. octane Vs. temperature
I stare at it for hours sometimes :D
Also last photo bump
 

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#8 ·
I just said im not decking the block, i dont think its needed. i already calculated my compression and its 10.3 static and 8.35 dynamic. My only question is if .052" quench is too high, i know its not the .040" that people claim is needed but ive seen professionals build engines with higher quench...
 
#11 ·
Just a couple tips ,try to find a 400 block from 78 or older blazer WITHOUT center freezeplug much stronger,when i build 434 small blocks from a 400 for dirt racing late model midified i vat the block in radiator vat not a hot tank then fill the block thru water jackets with epoxy 2" deep to strenthen block and better ring seal i saw you lowered expacyions of rpm & horsepower to 400 hp which is very abtainable and still be streetable.as far as cost the 2000 you mentioned,our engines have rev limiter set at 8200 rpm but they do not run at that rpm ,usually 7600 on good trackno dry slick ,as far as cost to freshen up mid year usually 20 low 30s high -fresh build from scrach 55 or better we are running bow tie block since aftermarket dart and others are not allowed hope this dont discurage your build but this is all out racibg engine never ran below 5000 Would Not stay together on street Build a good streetable 406 and enjoy it, David .
 
#12 · (Edited)
All right let's do a review on your block and parts. Let's start with the block. Suppose you were to install the crank and a piston at all four corners to calculate piston to deck height. The factory block height of a SBC is 9.025. Most likely you will end up with different measurement on each corner anywhere from .020-.025. To find the deck height you measure from the centerline of the crank to the top of the deck. To find out if the rotating assembly will fit into the block you measure (half the crank stroke - rod length - compression height) = parts stack height. Using yours for an example 1.875 + 6.0 + 1.425 = 9.300. This means the pistons will be .005 above the deck. This would take a .051 thick head gasket for a quench of .046. Your static compression would be 10.492 and the DCR 8.437. Be sure to use modeling clay to check valve to piston clearance. Using 5.7 rods, 1.875 + 5.7 + 1.425 = 9.000. This means the pistons will be below the deck .025. Say you want to use a .027 thick head gasket which cost around $100 each. For me it's easier to mill the deck to .005 and use a stock .039 thick head gasket with a bore of 4.166. You would have a static compression ratio of 10.492 and a DCR of 8.472 which will run on 93 octane gas with the correct timing. With the quench close like this there is less chance of detonation. BTW the 400 engine is not designed for high rpms. Your camshaft has an operating rpm range of 1800-6000. The crank probably has a safe rpm range of 6000-6500 rpms. Rpms is what kills engines not horsepower.
 
#13 ·
Okay im confused now, firstly if the deck height is 9.025" and with 6" rods the stack height is 9.300" then the piston would be .275" out of the block....and secondly i thought that no matter what rod you use, that doesnt change compression....
 
#15 · (Edited)
Your stactic compression did not change but your DCR did. Sorry about the math mistake. Anyway .275 above the block is something to consider real hard. Personally I wouldn't build an engine with the piston that much above the block for the street. That is some close tolerances measure carefully. I might have considered it at .005 but not at .275. What happens if your block has been milled in the past? I think the best solution would be to use the 22.5 dished pistons with 5.7 rods. This assembly would give you 9.497 static compression and a DCR of 7.689. But you will still have to deal with the quench of .053". I can suggest something but you will have to contact Cometic Gasket INC. They will make you a custom head gasket with the compressed thickness and bore size you need. I would rather check on this and try to get closer to .040 for quench. But who knows you could use the .027 compressed thickness gasket and not have any problems. I remember back in the day just using the head gaskets from the gasket kit with a .039 compressed thickness with flat top pistons and 76cc heads with a DCR of .064" and never heard any pinging.
 
#18 ·
Wage92, Is this the 406 Scat rotating assembly from Ebay (Skip White). Does it have the Probe 14cc pistons with a compression height of 1.140? If so then your parts stack height is 1.875+6.0+1.140=9.015. 9.025-9.015= .010 piston to deck height. Now to get the quench of .040 you need a Cometic MLS .030 compressed thickness head gasket. Or any other brand if you can find it. This will put you right at the edge with a static compression of 10.588 and a DCR of 8.512 so you really need a tight quench. Still should run on 91 octane so if you are using 93 octane you should be fine. This is why all information needs to be provided in the post or a part# to verify the info.
 
#26 ·
.. LOL! Nobody was considering building an engine with the piston 0.275" above deck... that was just somebody's math error...

.. With a longer rod, you use a piston with a shorter compression height... or, if budget allows, a custom piston with the perfect compression height if nothing proper close enough is available off the shelf...
 
#28 · (Edited)
.. OK, at the performance level you're talking: "400HP" from a SBC 400 for a fun road truck, everybody is OVERTHINKING this!

.. The stock SBC 400 with stock heads and crank/rods with merely flat top or domed pistons and a $50 Summit #1105 224/234 cam/lifters/Z28 valve springs added (and 4bbl. carb./intake if not so equipped already) will make 400 HP or close to it...!! And do it by 5500 - 5750 RPMs... shift at 6,000 RPMs or so... with torque peak around 4000 RPMs... pulling really hard from 2000 - 2500 RPMs or so...

.. or another combo:

.. Stock block, crank, rods, your first pistons choice but for stock 5.565" rods, your first cam choice (biggish for a fun road truck, but usable), and your first heads choice -> 375 - 500 HP depending on the exact heads used (165cc - 220cc range intake ports)... still by 6000 RPMs...

.. The 2nd cam you picked was just too big for your goals... wouldn't pull hard till 4000+ RPMs... wants to make 500+ HP... not fun truck compatible... requires other engine parts made of expensive unobtanium...

.. 6" rods make more power above 6250+ RPMs... basically, out of your needed operating range...

.. I'd suggest doing something like one of the two budget combos above... just add an ounce or two of kerosene or other octane booster to a tank of gas if you just can't tune any/all spark knock out with ignition timing/advance curve and premium gas... or can only get 91 octane premium in your area... no 93 or 94...

.. KB, TRW, or Summit hypereutectic pistons would be plenty for this build... and KB especially usually come with good compression height... and all have good price... adjust them to the gram weight of your stock pistons/pins and avoid paying for an engine re-balance job at this performance level...

.. Here's an article about adding a cam of duration similar to your first choice 230/236 duration (only expensive roller lifter type) to a mostly stock block/rods/pistons/heads SBC 383" engine and what it did:

http://www.hotrod.com/techarticles/engine/gm_ht383_crate_small_block_tune_up/viewall.html

.. Edelbrock E-Street heads would be a good pair of American-made somewhat budget Aluminum heads... although on the smallish side for a SBC 400"...
 
#29 ·
.. A 650 CFM - 750 CFM carb. or even stock Q-Jet 4 bbl. carb. is plenty...

.. Stock oil pan and oil pump is fine at this performance level... maybe add a high pressure bypass spring to stock oil pump or use a high pressure oil pump... I would avoid the power-consuming high volume pumps as unneeded ... add a windage tray if it doesn't already have some kind of one inside the oil pan...

.. What's your tranny? If it's an automatic shifting at only 3800-4000 RPMs at WOT, then it'll need governor springs to bring that up to 6000 or so for the engine to make its new power... or manually shift it when wanting that power... If a manual tranny, of course it can still simply be shifted as desired...

.. Whether you need/desire a different stall RPM torque converter will depend a lot on your current rear end ratio... and driving habits... and final cam choice... and final compression ratio...
 
#30 · (Edited)
bringing this thread back because i have another question. I have settled on the skip white rotating assembly, i wanted internal balance but for the build this is going to be its not worth it to shell out the extra money. So this is the kit SBC Chevy Scat 406 Forged Rotating Assembly ft 30 4 155 Bore | eBay

As i was thinking about i think i will use a .039" head gasket and the piston will be about .010" in the hole, and typing that all in to a static compression calc, i got about 10.37:1 which as far as i know should run on 93 octane....

Lastly, for my dynamic balance i am trying to find a cam that will be mild and not cause any issues..
This is the one i have selected thus far: 12-246-3 - XTREME Energy

That cam gives me 8.34:1 dynamic compression...

I have aluminum heads, ive heard that plays into the picture...

Any suggestions? I dont wanna have any detonation problems, am i too close to the line? And will i be able to advance it or will i have to play with the timing to get rid of spark ping?


Edit: also if someone doesnt mind could they run my numbers through a compression calc and verify im doing it right? 4.155" bore, 3.75" stroke, 64cc heads, 14cc dished pistons, .010" deck clearance, .039" gasket (unsure of bore yet so estimate), 6" rods
 
#34 ·
You are very close with your static compression ratio estimate. I came out with 10.35:1 using your supplied info. Aluminum heads require an additional point of compression over iron heads because of their ability to suck heat out of the combustion chamber so you are completely safe. An 800 DP is way too much carburetor, and no reason for a double pumper on a street vehicle. Holley backs this up on their website recommendations stating that a double pumper needs a light vehicle, loose torque converter, and lower gears. It's not sexy, but a 750cfm carb with vacuum secondaries will be much more efficient on a 406. That translates to more power and much better gas mileage. I would also come down a notch on the cam choice. The 230/236 duration @ .050" is a little rowdy for a 406 in a heavy vehicle. You should also have a higher stall converter over stock, and vacuum for your power brakes will be marginal. While the cam would work, I'd just go somewhat smaller for a heavy vehicle.
 
#35 ·
yea i get what you are saying, ive changed most of the things i said in that first post already. But yea, i will probably end up with a 750 holley. But you are saying that i should be okay because i have a aluminum heads? ive heard that but never knew why, so since its taking heat away its essentially lowering the compression in the cylinder?
 
#36 ·
Compression remains the same. A better (but not perfect) definition is that there is an ideal combustion pressure to force the piston down. Iron heads retain the heat, so say this ideal is reached at 9.3:1 compression on my theoretical example. Any less and you loose power, any more and you detonate. The aluminum heads bleed much more heat out of the chamber, so another full point of compression is required to maintain the same amount of heat in the combustion process. So the process sees the same amount of heat with 9.3 iron heads and 10.3 in aluminum heads. Over simplified, but it gets us close to what is going on.

There are also limitations in stock cast iron heads that limit the amount of porting that can be accomplished. Since the aluminum heads are designed from the beginning as a performance head, there is more meat designed in around the port area so a better port can be designed, and better flow is the result. Aluminum heads save weight, and they weigh half of an iron head. Aluminum heads are cheaper and easier to produce than iron, and are also much easier to machine and port. Because of this more companies make aluminum heads - and that competition brings a better product to the market, and keeps the prices down for us.
 
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