512 Stroker Six-Pack Build

Ootb Stealths usually flow in the upper 250’s.
With fairly basic work they will flow in the 280’s.
On my bench, the CNC’d ones are about 312-315.

How much benefit you’ll get from each stage of porting with be dependent on how hot or mild the overall combo is, and how much the heads and induction are holding it back.

With the heads mildly reworked, with say 9.7:1 and a moderately sized cam, 6bbl, 1-7/8” headers...... it’s an easy 600-620-ish tq/540-550-ish hp.

That’s using a SFT that would likely be marginal for power brakes.
(You could mellow the cam out a bit for the brakes and not lose much power)

I’ve done several sets of various heads for those combos, but have only dynoed one myself.
That one had stage 1 RPM heads, and the intake had some port work done to it, along with it being around 11:1.
The SFT cam would likely have not been power brake friendly, and it was run with 2” headers.
That one made 645tq/590hp.

550-625HP and Torque from stroker 6bbl engines is common.
I decided that by the time I found someone I could trust to go through the number of factory blocks it would take to find one with acceptable cylinder wall thickness and other factors, then build it to within say 100-150 HP of its power handling limits, I might as well get a 4 bolt main aluminum aftermarket block, so I am waiting on the Bill Mitchell Products block I put a deposit on. Then seeing how it comes as a 4.49 bore (cleaned up to 4.50) AND that they accept a 4.5 stroke w/out clearancing, the madness took hold! My idea is to go "conservative" with a 4.25 stroke for a 541, which will reduce piston speed by design. Trick Flow 270s because it's a 541 after all. The sheer displacement of the engine should allow me to have a reasonable cam, solid FT lifters, a stable valve train, and no reliability concerns in the 6XX-700 HP and Torque range, but LOTS of headroom to add power, should I ever feel the need.
Since it's a V-code car, I am definitely running a 6bbl, but I'm going to be working with this old school Super Stock Weiand 6bbl intake. It will have to have the ports opened up to Max Wedge size for the TF 270s...

biomedtechguy said:

550-625HP and Torque from stroker 6bbl engines is common.
I decided that by the time I found someone I could trust to go through the number of factory blocks it would take to find one with acceptable cylinder wall thickness and other factors, then build it to within say 100-150 HP of its power handling limits, I might as well get a 4 bolt main aluminum aftermarket block, so I am waiting on the Bill Mitchell Products block I put a deposit on. Then seeing how it comes as a 4.49 bore (cleaned up to 4.50) AND that they accept a 4.5 stroke w/out clearancing, the madness took hold! My idea is to go "conservative" with a 4.25 stroke for a 541, which will reduce piston speed by design. Trick Flow 270s because it's a 541 after all. The sheer displacement of the engine should allow me to have a reasonable cam, solid FT lifters, a stable valve train, and no reliability concerns in the 6XX-700 HP and Torque range, but LOTS of headroom to add power, should I ever feel the need.
Since it's a V-code car, I am definitely running a 6bbl, but I'm going to be working with this old school Super Stock Weiand 6bbl intake. It will have to have the ports opened up to Max Wedge size for the TF 270s...
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That build sounds exciting! Seeing that intake reminds me of an article decades ago where someone was somehow modifying outboard carbs to run jets or metering blocks. I can't remember for sure though. Also, I can't remember if that was for Super Stock or street.

I have been restoring and driving Mopars for a long time, enjoying all aspects. It is easy to get caught up in the quest for power. For example, I had a stock 1970 Cuda 340 convertible and a stock Cuda AAR at one point. They were cool, but after owning stock Hemi cars including the Roadrunner and Super Bee, Hemicudas and Hemi Challengers, I just couldn't get excited about the stock small blocks. Currently, my driver muscle car is a 1970 Hemi Challenger convertible. 511 gen 2 with 625 hp. 4-speed (see photo). This car was my entrance into more-than-stock. So after getting "acquainted with" more than stock with the mild Hemi in my Challenger now I can't build a 440+6 for the 1970 Roadrunner with my son that is not respectable. I am sure that a stock 440 would be fine for him, but we want more fun than that. ;-) We don't need to get too crazy. Thanks for all the discussion! Keep it coming!

Yeh, once you’ve had a taste of stroker power....... it’s pretty hard going back to the stock-ish power levels.

jphemi70 said:

Seeing that intake reminds me of an article decades ago where someone was somehow modifying outboard carbs to run jets or metering blocks. I can't remember for sure though.

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Seeing that intake.... ah yes, "seeing that intake" would ultimately haunt me to the point where I had to get one. Long story, but the first time I saw the Weiand P3690982 6bbl intake was a F&B 3x2 TB Direct Port Injection version of it...
...and then I dove into researching it and a few months ago finally bought one.
Great car(s) you have. Stroker 6bbl with the Edelbrock/Chrysler dual plane intake are torque MONSTERS.
As far as the outboard carbs, mine have jetable plates from Promax. There are 6bbl setups where all 3 carbs have metering blocks and the center carb is 500 cfm instead of 350, and they use progressive mechanical linkage.

Hemirunner said:

Vacuum?? We don’t need no stinking vacuum... lol

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I have a 440 Source 512 with stealth heads just built it last month. Nice. Still sorting the six pack and breaking it in. I have a vacuum pump mounted under the battery tray. Invisible. Works great plenty of brakes power. On Ebay for 200 or so.

I agree the stroker will be a great combo. If you are using aa A12 style manifold, tinkering with the carbs gets you great response & power with a moderate cam, RPM combination. The Weiand tunnel would give more RPM potential. All depends on what you are looking for.

jphemi70 said:

My son and I are restoring a 1970 RR. We got a 440 to use the block to make a 440+6 for the street.

I am looking for suggestions or comments on building an engine for the car that would be fun to drive on the street and not be a slouch. Pump gas, automatic, and of course the six pack setup. I had been thinking about the 440 Source 512 rotating kit with the stealth heads, roller rockers, upgraded springs, locks, retainers, and headers. It would be a power brake/steering car so vacuum at idle would be a factor. Not sure what cam to go with or converter to work with the six pack. 6000rpm, 3:55 gear. All the parts except the block would be new.

I searched to see if someone else has done a stealth head six pack stroker build and didn't see one. I apologize if someone did and I missed it. I no longer have my engine builder I have used in the past so I don't have one set yet. I have to get my engine torn apart and the block checked and see if I have a good starting point.

In addition to wondering about the cam and converter choice, do any of you do builds like I am describing here?

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I sold a 512 440 source 400 short block. The guy who put it in a customers car said it is a BEAST!