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1973 Camaro Z/28, 434, NETO/N
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Discussion Starter · #1 ·
Hello there. I've got a complete small block Chevy top end off an engine that I threw a rod through. I am now entertaining the thought of another build. The parts I have include...

•AFR 220 Eliminators, 1110 competition ported heads, 8027 spring upgrade, titanium retainers, 65cc
•Crower stainless steel full roller rockers, 1.5 ratio
•AFR stud girdles
•Comp Cams 300BR-6 solid roller, 260/270 @.050, .630/.630, 106° lsa
•Comp Cams roller lifters
•Weiand Team G 7531 single plane manifold with 2" raised plenum, port matched
•One complete virgin Chevy 400 2-bolt engine (never disassembled)

•Rotating assembly... to be determined

I'm looking to build a high compression 406 cu in full race engine for nostalgia bracket racing.

-My first option is to have the Chevy 400 block machined for 4-bolt splayed main caps, punch it out to 4.155, and drill steam holes in the AFR heads.
-Next option is to purchase an aftermarket block and have the required machine work completed

If this was your build...
-Which option would you choose?
-Which aftermarket block would you choose?
-What are the pros and cons of each?
 

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Yeah, the factory production 400 block is not up to what you want to do. Your proposal ends up with a weak production block with 4 bolt mains. My experience here is you trade keeping the crank and main bulkheads together but the forces involved just pull the bulkheads apart. The typical failure is a fracture from pan rail to rail cause it pickup those expensive angled out side main cap bolts and the pan rail they bolt into. Then the bulkhead splits apart just under the inboard main cap bolts then through the cam bore. Sometimes one bulkhead fails and the engine runs on till one of the remaining of the center three fails then for sure the bottom end come out, but not always.

You can guess how I know so much about this failure mode! Best advice I can give is don’t use a production block this way especially when Dart, World and other name brands and some import brands are making sturdier castings.

If I was building for this application I’d run a 4340 electric melt, vacuum debased forging with 350 journals to get the surface bearing speed down to buy more RPM with less bearing drag. The massive factory main and rod journal overlap is there for the strength limits on a cast crank. Running a top end forging just eliminates the need for all of this journal overlap. However, with a medium journal exotic crank you need a super good thus super expensive damper to soak up the twists and turns highly loaded cranks are subjected to.

Bogie
 

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Agree, go to the aftermarket block. Even a BluePrint or Speedmaster block would be a better start.
You can truss the mains of the stock block up all you want, still doesn't prevent splitting a cylinder wall.

Plus, at this point you don't even know if your "never disassembled" stock 400 is any good....I once had to magnaflux check 3 blocks to find one that wasn't cracked (400 SBC).

i know of someone putting 1300-1500 hp through two of the Speedmaster blocks, for several years now(Multiple nitrous stages, and now Twin Turbos (Wuhan war whistles). 406 and 421 cubic inch.

After you get the block situation squared away...
1.6 intake rockers....the AFR heads don't need that 10° duration split and the intake side will like the increased lift and a couple degrees of effective duration @ the valve the higher rocker ratio gets you.,
A better intake than the Team G....Team G is a great intake, but for smaller motors....the runner cross section is the smallest of all the major race single plane intakes. Works best on 327-350" race engines, and street/strip 383's.

IMO, if you do decide to go forward with the stock block, don't bother with a forged crank and fancy rods, since they will all get destroyed when the block fails.
Scat cast crank and Scat Pro Comp 7/16" bolt rod or Eagle FSI 7/16" bolt rod. ($350 level)
 

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You say bracket racing: How fast are we talking?

Normally for something in the 400 or above range for sBC, i would definitely go aftermarket. However, since you already have a 400 block---which i assume is known to be in good condition, then this changes things. But still all depends on what bracket you want to be in???

i think GM has recently stopped offering the iron bowtie 400 block(baffling), but still has the aluminum which is about $6000..........


So, normally i would want an aftermarket or GM perfomnce block for a 400/400+ small block build. This is because it takes time (money) to search for a stock 400 block. And what if, after you find one, you discover it's cracked and now you can't use it. All that time (and money) wasted and you have to start over.

With an aftermarket block, say $2000? or so, not only do you know it's good to go, possibly more importantly, you know it's high quality and you can flog the crap out of it and it won't be a problem.

NOTE: This is just my opinion, and i'm not an engine person.
 

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1973 Camaro Z/28, 434, NETO/N
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Discussion Starter · #11 ·
Thanks for the informative replies. I was asking about the stock block because my old man has had that stock 400 sitting in his garage for decades. He always wanted to do a 406 track build with it and never got around to it. I was already leaning towards a Dart SHP, as I have another recently completed 11:1 434 build with the SHP.
 

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I think a street performance cruiser is fine with a 400 block, but to take serious power under competition would just lead to the investment being busted pieces spread everywhere. But to power something like a five window pickup to the A&W on Saturday night for burgers and root beer would be mighty nice.

Bogie
 

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Discussion Starter · #16 ·
no rocker shafts?
No shafts on these. Those are Crower Enduro stainless steel full roller rockers, part # 73601, with AFR 6200 stud girdles. Excellent valve train stabilization, but a little more tedious when setting lash compared to shaft rockers.
 

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i am running a .040 over 400 2 bolt main block with 12.5 compression, .600 lift solid roller, i do not race it so it is not getting beat on constantly, i had the block so that is why i used it, so far not a single problem, BUT it is always in the back of my mind that it may let go, like said in a earlier post, it will probably be fine for cruising and the once in a while go nuts but if you are gonna beat on it then go with a after market block, peace of mind rules,
Scotty
 

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Eric, out of curiosity I looked at the Speedmaster blocks, and noticed that they cost as much as (or more than) a Dart SHP.
Are there any advantages with a Speedmaster in the same price range as an SHP ?
The Speedmaster is a close copy of the Little M.....whether it is as strong as the Little M, I don't know.
I just ordered one myself, during the Black Friday sale they had...40% off.
We shall see how good it is....but I know of a couple people using them without problems.
Just got the shipper tracking info yesterday, shows it in transit.
 
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