At what point to go aftermarket block?
 

I want to start working on a turbo build and am wondering if I should move forward with my stock block build or start looking for an aftermarket block.

I currently have the following parts that I have been collecting over the years ready to go to the machine shop: 69 400 block, ProGram splayed caps, 4" stroke RPM forged crank, Eagle 6.625 H-beam rods, lifter bore brace, and off the shelf dished Icon forged Pistons.

Was planning to just run this with some 6X heads for around 8:1 CR with an S475 or similar turbo to have a fun street/strip (67 GTO)...maybe max 700-750hp.

I just keep wondering....is it worth it to go through all the expense, etc. of installing the splayed caps, lifter bore brace etc? Or should I just sell all these parts and start over with an aftermarket block?

After market block, never have to worry about it coming apart.

At what point to go aftermarket block?
 

I’m not speaking from experience, only listing what I’m doing.

I have a 70 400 block bored .030” and installing 4-bolt billet straight caps and ARP studs. I’m filling my block to below the freeze plugs.

Running an Eagle 4.21” Forged Crank, Superod 6.800” Aluminum Rods with .927 small end. I had Kauffman order custom Ross pistons with that small end and used a HD pin. We set static at 9.5:1 so it would still have some grunt when not making boost (which will be never lol).

I have a TorqStorm with 3.10 pulley and should make around 10-12 psi and it should make an Honest 750+ hp under 6500 rpm

I have 330cfm Hi Ports and a Hydraulic Roller


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I would at least knock the sharp edges off of your piston dish with a jewelers file.

Tom V.

Sell all your stuff, get an aftermarket block and don’t look back.

You won’t regret it.

I went aftermarket but there are examples of boosted motors with factory blocks making over 1000hp, Bandit is a good example. Also, I think aftermarket blocks hold their value more than a modified factory block, unless it’s been checked.

Aftermarket blocks give you other advantages: Different deck heights, Larger bores,
stronger bottom ends, solid valley holding the two sides of the block together.
And also cast iron and aluminum block materials.

Tom V.

I'm not saying that a stock block will take the abuse but, just tore down Bandit's motor for inspection and she's mint. Thanks to Herb at Luhn performance, the head gaskets aren't even thinking about leaking and all bearings are like new. Block magged OK. This motor sees no less than 22psi on the regular. Has been on Sick Week and made PB passes at Norwalk this year. 8.42 @ 161. That was with 25 psi. Going back together for Sick Week 2024. Fingers crossed!

I would say immediately after you drive over your crankshaft might be a good time to start thinking about an aftermarket block.

I have a combo very close to what your building but with 2 bolt mains and its been alive and well for 15 years. fwiw. I would run what you have.

AGREE 70 bird.

Hope you are well and happy on the west side.

Tom V.

AGREE 70 bird.

Hope you are well and happy on the west side.

Tom V.

This 20 seconds bs is a royal pain in the butt.

Hi Tom, Im doing good. Hope all is well with you and your family!

Erik,

What prep work did you do to your block? What caps, fill the block?


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At what point to go aftermarket block?
 

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