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Building a 512 - some advice needed

Performance Upgrades

  1. JurgenS

    JurgenS Member

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    Dec 7, 2018
    Since a few months I own a Plymouth Barracuda. Currently with a 318 but am working on collecting parts to build a 512 stroker. I have a 400 B block, stroker kit, Trickflow 240 heads and some smaller things. Do not have intake, rockers, lifters or camshafts. The intention is to build a multi point injection system with a free programmable ECU. There are not really many intakes to be found ready for a multi point injection so the idea was to fab one but wondered what the best base would be, a single plane or a dual plane. I have read a lot and I am not sure, both have advantages and disadvantages and apparently it is not as black and white as dual is for the street and single for racing.

    Not trying to squeeze every last bit of power out of it and would therefore think of a dual plane but on the other hand I read that a stroker can also get along with a single plane. Car will be used for cruising, but occasionally a stoplight sprint will certainly be there.

    Who has experience with this and can give advice, in combination with a suitable camshaft.

    Other question, also my automatic transmission will no longer fit on the B block. What options are possible here, both manually and automatically? The 10k I was quoted for an SST Tremec magnum is not a valid option for my budget.

  2. Adam

    Adam Well-Known Member

    Likes Received:
    Dec 25, 2012
    Nice project. Given the intended use of the car (cruising) I think a dual plane would be more suitable; however, with multipoint fuel injection adding gas right at the head it may not matter much. A single plane vs dual plane is about breathing and fuel distribution, so either should work if it is a good manifold... I think even with fuel injection you will be lucky to get 10 mpg...

    Camshaft choice changes a little depending on what rear end gears you have and which transmission you choose. A stroker motor makes huge torque because the rod journal is further away from the crank centerline, this gives it greater leverage (like a longer wrench vs a stubby wrench) but the mass has further to travel all the way around, not as rpm friendly as a short stroke.

    A big block 727 automatic would be the easiest and least expensive way to go because your car doesn’t have a clutch pedal, and if you have a console shifter it will still work. A 727 auto does not have an overdrive so the rpms will be up a little on the hwy. So hypothetically, with a 512 stroker torque monster, I would go for gears like the 3.23s... to keep the rpms down; there is enough engine to move that heavy car very fast... in fact getting traction will be another problem (burn outs). With this scenario I would look at cams with around around 225 to 230 duration...

    If you did a pedal conversion and went with an overdrive 5 spd I would actually go with lower rear end gears like 3.73s and drop the cam duration a few degrees like 220 to 225 duration.

    This is because in top gear (overdrive) even with 3.73s you will only be pushing about 3000 rpm at 75 mph, depending on tire size. No sense having a cam that makes all its power way up in the power band if you are not racing it.

    To illustrate, I have a very strong 440 with a Tremec 5 spd and 3.55 gears. The Tremec first gear is really low, 3.55s are equal to 4.11s according to Tremec’s online calculator. This is sufficiently low enough to launch the car quickly, although it will light up the tires quite easily. When on the fwy my car is only turning 2200 to 2500 rpm at 75, or so...

    I chose a cam that had it’s power band a bit lower in the rpm range because I wanted huge torque down low and my engine would rarely see anything over 5000 rpm.. I am very happy with the results, and it will light up the tires going into every gear, even 5th if I am getting on it hard..

    You should decide on a trans and gears first, look at some rpm/tire calculators online, and given your intended use I would call Hughes Engines and talk to them about a cam...

    Good luck, keep us posted.
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