I'm back - after five years I've tempered my anger towards the slant six a bit (which was, admittedly, mostly due to the terrible car it came in) and I'm going to try a slow-burn build, if not to put in a car right away, at least to get all the pieces of my forged crank slant six back together and taking up less space in the garage.

First order of business is discussing what I want to expect from this engine when it does eventually run:

- Capable of 5000 RPM at least; If I'm going to be stuck with a 904 for any amount of time I want to be able to at least hit 60mph without floating valves.
- Goal of 180hp; this may be unreasonable or unstreetable for a naturally aspirated 225. Lemme know.
- Capable of boost; If I like this thing enough I may eventually want to put money into a supercharger.

So far I've got a freshly rebuilt, bone stock cylinder head that's been decked the minimum amount possible to achieve flatness - not sure of the exact measurements but it was less than ten thousandths. Turns out that, being roughly 70lbs of cast iron, it doesn't warp very easily. I've got the forged crank, cut down 40 thou on the mains and 10 thou on the rods. I have a block that absolutely needs machine work done to get rid of the gaping chasm between the original bore size and whatever three trips back to zero on the odometer did to everything below the piston rings. It might be more economical to just buy another block at this point.

I also have a set of Wiseco forged connecting rods and pistons, which will be going in. I think the pistons are only 40 over which is why I'm not sure if the block is even salvageable. No big loss if it isn't.

But for now, let's focus on the cylinder head, because it's already brand new with only minor surface rust on one of the rockers from sitting under a pile of leaves for four years. I wish I was joking. I'm willing to ditch basically everything attached to the head. I'd rather not have more machine work done to it but I will if I need to. However, I don't have much of an idea what to do here (or anywhere else) besides 'buy ARP head stud kit' but that's the obvious one. I'm planning on long tube headers and a four barrel intake but that's as far as I've gotten.

These 2 goals would tend to steer the build in opposite directions. For best results you would need different cams and different compression ratios.
These pistons probably have too high of a compression ratio to be suitable for boost.

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The slant in the 83 D150 has been chassis dynoed at 160 Hp and that motor was built for low rpm torque and regular gas and has a two bbl carb.
Cam is a something like. 212 and 208 at .050, not real big lift.
OS valves, good porting and valve seats, dual Dutra’s, HEI ignition, cold air induction, electric radiator fan. Has 8.5 static compression.
A bit more compression, carb and cam would get that to 180 hp.
Also has an a833 od and 3:73 rear gears.

The slant in the 68 Barracuda is a bit more aggressive, NA, per Desk Top Dyno is way over 200 Hp and is streetable. This one has a built 904 with a bit looser than stock TQ, 3:55 gears.

Last year 87 light weight crank & block. A lot of porting, valve and valve seat work. MPFI, long tube headers. Long rods and lightweight pistons, 10.5 static compression.
Cam duration is in the 242 range with lots of lift. The cam profile was specifically chosen for its fast ramp speeds. MSD ignition, electric fan, cold air induction.

If you choose to do one engine and to later add a power booster like a turbo or a supercharger, you can do that. Select a cam with a smaller duration so the LSA can be ran up to the 112 range and keep the static compression in the lower 8’s.
Get friendly with an on line compression ratio calculator to help your planning.
You could build one block and two cylinder heads. With one head being cut to increase the static compression for the NA motor and a second head being near stock combustion chamber cc size for the boosted engine.

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Wiesco's will be near zero deck, so normally aspirated will work fine with the right cam. Boost? Not so much I would guess.

180HP N/A should be no problem with a decent head.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Thanks for the replies, guys. Based on them I'll probably just build this engine for high compression, given that seems like the better choice for the parts I've already got. If I do want a boosted build somewhere down the line, I'll build a second engine for it and go from there. Looks like I'm getting more machine work done to the head as well if I want to see the power I'd like out of this engine. So I'm looking at porting work, oversized valves, decking the head, and I'm guessing 340 valve springs would be a good fit for this head? The rotating assembly is going to be pretty weighty on this - like I said I'd like 5k RPM and more if possible, but I'm not sure what I can safely get out of this thing.

But that kind of brings up another question; how much power can I get out of this engine and keep it enjoyable to drive? I don't mind using premium gas all the time - hell, I do that anyway even with engines that absolutely don't need it. 10.5:1 compression seems like a good starting point considering that's what my daily has, but haven't really dealt with high compression carbureted engines before so don't know what's acceptable vs. something with fuel injection before you need knock sensors to prevent it from killing itself.

Do I need anything in terms of rocker shaft/rocker arms? The stock setup seems fairly bulletproof compared to something like an SBC.

Do not deck the head (beyond truing it) if you want to run those pistons and rods and pump gas. You will end up around 10:1 static compression with that set up, with no decking. You will want 1.70/1.44 valves or you could go bigger if you like.

The trick will be finding someone who knows how to pocket/bowl port a head and will do it and not just tell you they did it. 180 HP is not hard at all with 10:1 comp.

You will want a custome ground cam in the 240 @ 0.050" duration range to be able to run 91-93 octane on 10:1 comp. We can give advice about what to order from Oregon Cams or a similar place.

A good shop can tell you if you will need a different block for only 0.040" (or really 0.044" over) using those Wiseco pistons. You might be OK, but it'll be on the border.

Happy building and keep us updated,

Lou

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Home of Slant6-powered fun machines since 1988

There are plenty of guys who have turned 5500-6000 on stock rods and pistons. With Molnar rods and Wiesco pistons I would have absolutely no worries at 6000 or more rpm. I turn 62-6300 rpm at every race in my car. The only reason I don't turn 6500 or more is the fact that I ran slower shifting at those rpm's

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Good to know! The incredibly low factory recommended RPM limit had me more than a little worried.

I do still need to find a car to put this engine in, but that could take a while - I don't really fancy buying my Duster back, and I have another project taking up space in the garage that can't be moved outside because T-Tops. And it doesn't run. So that comes first for now, and this summer is probably when I'll start buying parts for this build. I actually HAVE to get the current project out to even get to the slant six block, as it's buried behind my toolbox with every bolt that was in the slant carefully arranged into magnetic pans, at throwing speed, in the oil pan.

I do at least have a 2-barrel intake and a Carter BBD, so I won't have to shell out for much other than a Lokar cable kickdown to get it running initially.

Thanks for all your help guys! I'll either resurrect this thread or make a new one when it comes time for the block/cam/etc. I think I should be set for information regarding the head, unless anyone else has something to add.