408W or 427W

[Dana E.]

Long story short: sold the 393W so now it's time for a new motor. 393 was a 10.5 compression, factory block, with Dart Pro 1 195CC heads. Cam was a Comp XE282HR hydraulic roller 232/240 @ .050, .565./.574 lift 112* lobe separation. It was a strong runner, near as I could tell in the 173 miles that motor lasted.....and no, I did not build that motor, and yes, I won't make that mistake again.

This time around I'm going with a Dart SHP block and probably a forged Eagle rotating assembly, unless a Scat rotating assembly is better. I've read that the rod side clearance is a bit excessive with the Eagle cranks. Any truth to that? The Scat crank in the 393 looked like a decent piece. I will be reusing the Performer RPM Air Gap manifold and the Holley 750 Ultra Double Pumper from the 393.

I'm looking for an honest, streetable 500+ horsepower. A lot of people run a 408, but I'm leaning towards a big bore (4.125 bore X 4.00 stroke) 427. 10.5 to 1 compression. AFR 205 heads, or should I go bigger? Dished pistons and small combustion chambers or flat tops and bigger chambers? Any power difference between the two? What about Keith Craft Brodix heads or World Products 18* Man-O-War heads? The Comp XE282HR would probably idle like a stocker in a 427. I'm thinking maybe a Comp XR294RF-HR 242/248@ .050, .576/.600 ground on a 5.0 core (not a reduced base circle), and maybe widen the lobe separation from 110* to 112*. I'm sure I'm leaving some HP on the table reusing the manifold and carb, but hey, it should be a torque monster.

Sorry about the long-winded post, but fire away with any comments or suggestions.

[bobcowan]

That's pretty close to what I have. I'm using and Eagle rotating assembly, with SRP pistons. Rod clearances are exactly where they should be.

Still using the Dartp pro-1 heads, with some porting. My hydraulic roller cam is pretty big, with a lot of lift, and really makes cylinder pressure in the upper rpm ranges.

Dynamic compression is about 8.4. That works fine here at altitude. But at lower altitudes it's a problem. Since you live at sea level, I would shoot for about 8.4. It won't go up michy, and can easily go down.

On the chassis dyno, I'm making 510 hp.

[fordracing65]

427 if you want that magic number.

[jhv48]

With the dart block, you have plenty of metal to go 427.

[blykins]

For the amount of horsepower that you're wanting, I really see no reason to spend the extra $2000-2500 for the Dart based engine. The block is more expensive right off the bat and the forged SVO crankshafts are more expensive than what you could use on a 408.

If you do decide to go with the Dart based engine, I wouldn't stop at a 4.000" stroke, I would go with a 4.100" or 4.250" stroke for 445 or 460 cubic inches.

I prefer the Scat crankshafts over the Eagles. You will have issues with any brand if you start to use large quantities of them. I've had to mill down some rods to get the side clearance that I've needed with Scat rods/Scat cranks, but I will tell you that no engine combination is just going to fall together without touching anything. The Scat cranks have a better finish on them without a doubt. I got a batch of Eagle cranks several years ago that had journal blems, so I stopped using them altogether. I don't know what people are calling excessive side clearance on rods, but I will say that more clearance isn't always an issue.

I use AFR heads on most of my small blocks. If the customer doesn't mind some custom header work, then I'll use some Trick Flow heads as well.

The head size and camshaft specs will all depend on what cubic inches you decide on, but I would use some other lobes besides the Xtreme Energy lobes that you were referring to.

I have some big Windsor packages on my website and you can go on there and see what parts I use as an example.

My advice is skip the 500hp and go for something closer to 600. I have a lot of guys that come to me and tell me that after a year or so, they've gotten used to the car and they would like more power. Making 600 streetable horsepower is pretty easy with a lot of cubic inches and since Cobras come with a gas pedal, you only use what you need.

[Jeff Frigo]

More cubes = more torque = more fun.

[bobcowan]

Originally Posted by blykins

For the amount of horsepower that you're wanting, I really see no reason to spend the extra $2000-2500 for the Dart based engine.

I would disagree on this point. The Dart block is a lot stronger, and I kind of like the idea of additional strength. Have I needed it? IDK, maybe. But I like to overbuild things. I feel better when I beat on it, knowing it's a stronger part.

Also, I managed to do this about a year ago. Took less than a week and less than $150 to repair. If it had been a stock block, I would have been looking for another one.

[blykins]

Is a Dart block stronger? Absolutely. However, they're not indestructible. If you had broken a rod and it had windowed the block, that would have been the end of it.

With a goal of 500hp, a production 351W block would work just fine. There's a lot of them running around and before the Dart, World, and FRPP blocks came out, that's really all that we had.

BTW, I'm certainly not trying to talk Dana E. out of a Dart block if that's what he wants, but if he would be content with less, it would be nice to have the extra cash in hand.

[Jeff Frigo]

Originally Posted by bobcowan

Also, I managed to do this about a year ago. Took less than a week and less than $150 to repair.

I guess you consider your time to be free.

[Dimis]

Dana E,

Sounds like you already have made up your mind and you inherently agree with Jeff:

Originally Posted by Jeff Frigo

More cubes = more torque = more fun.

I'm not sure bigger is always better...
For mine a revy 408 is a bit of a sweet spot, and for driving pleasure.
I'd go for that, especially in anything other than a Csx or Kirkham.
That said 427 is a romantic number, so I can understand that choice.

If you don't see sense in that logic.

Then by all means, do a Blynkins & blow in out to 460ci,
By all means even consider an LS7.

Flame suit on!!!

[vector1]

somethings to think about, the shp block will put an additional 40# on the nose. do you have the drivetrain, exhaust, bigger air breather, larger carb, brakes capable of handling the increased wt. and speeds? if not the 408 would be the choice. you can put a 454 in there but if you can't get the air in or out to make the power and keep it cool you won't enjoy the results. figure out how much cfm you can put through your air cleaner and carb and out the exhaust and tell us what you come up with.

[bobcowan]

Originally Posted by blykins

Is a Dart block stronger? Absolutely. However, they're not indestructible. If you had broken a rod and it had windowed the block, that would have been the end of it.

That is very true. Nothing survives a catastrophic failure like that, not even a Cummins block. But for anything less......

Originally Posted by Jeff Frigo

I guess you consider your time to be free.

Yeah, it is pretty much free. If I wasn't in the garage, I'd be out getting in trouble somewhere. Or being lazy on the sofa.

Originally Posted by vector1

somethings to think about, the shp block will put an additional 40# on the nose.

That is true. I think it's more like 60#, but I'm not sure. In any case, it's more than a stock block. But, that's not really much of an issue. The balance on these cars tends to be towards the rear, so you end up with more even balance.

IIRC, my car balances about 51% rear, and 49% front. In a Mustang, for instance, the car is already nose heavy.

[blykins]

Originally Posted by bobcowan

That is very true. Nothing survives a catastrophic failure like that, not even a Cummins block. But for anything less......

So what happened? Drop a valve? Valve head break off? I take it that with only $150 in the repair, there was no cylinder damage.

[Dana E.]

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For the amount of horsepower that you're wanting, I really see no reason to spend the extra $2000-2500 for the Dart based engine. The block is more expensive right off the bat and the forged SVO crankshafts are more expensive than what you could use on a 408.

Good 351 blocks are hard to find in my area. Roller block motors last about one day, when they arrive, in the wrecking yards here. The going rate is $750 for a complete motor. If you're lucky, it'll clean up with a .030 bore. By the time you add in machine work on the factory block, I can upgrade and machine a Dart block for well under a grand.

somethings to think about, the shp block will put an additional 40# on the nose.

It looks like it's about 30# heavier.

If you do decide to go with the Dart based engine, I wouldn't stop at a 4.000" stroke, I would go with a 4.100" or 4.250" stroke for 445 or 460 cubic inches.

I like your thinking. I had thought about a 438, but I don't have enough intake or exhaust for a high HP 460 cubic inch motor.

[blykins]

Like I said, it's your choice on what the budget will allow. I was just trying to give you some food for thought as I do these kinds of combinations all the time and I'm familiar with what machining needs to be done, what kind of power is expected, etc.

The difference in price that I was talking about was not only the additional cost of the block, but the fact that you have to use an SVO style crankshaft, which in turn requires H series bearings. With only a 500hp requirement, a production block and a Scat cast crankshaft will suffice with tons of room to spare. Also, keep in mind that a Dart block doesn't come fully machined. They need square decked to fit your rotating assembly, cylinders finish honed to fit the pistons, and the mains checked. I treat them like I do any other block when it comes to the machine work.

If you have an RPM Airgap, you're not necessarily working with an intake that won't flow. These can be made to flow very well and if your focus is on torque with some great mid range power, then I don't see anything against using it.

The pricing for any cubic inch displacement is pretty much the same when dealing with the forged rotating assemblies. So if a 445 or 460 is the same price as a 427, then in my opinion, it's better to get more for your money. You can always upgrade intake manifolds later. Your sidepipes are going to be a bottleneck no matter what displacement you go with, but a header that will support a 393W will not support a 427W that makes considerably more horsepower.

[Slick61]

Originally Posted by blykins

My advice is skip the 500hp and go for something closer to 600. I have a lot of guys that come to me and tell me that after a year or so, they've gotten used to the car and they would like more power. Making 600 streetable horsepower is pretty easy with a lot of cubic inches and since Cobras come with a gas pedal, you only use what you need.

This... /\ I have a KCR Dart (aluminum) blocked 427W putting out 612 hp/615 tq (at the crank). After 4 years of ownership, it still scares the crap out of me, and demands that I give it the respect it deserves.

[blykins]

I've heard a lot of customers say that they want to move up from 450-500. It seems that a lot like to fall in the 600hp range. It's all individual preference though, but if streetability isn't a concern, I'd rather have more than enough...

[vector1]

i've weighed a factory block at 163#, and i've weighed a fms 4" bore block at 205#. i'm guessing the weight difference is closer to 40#.

[bobcowan]

Originally Posted by blykins

So what happened? Drop a valve? Valve head break off? I take it that with only $150 in the repair, there was no cylinder damage.

Dropped a valve. Made a huge mess. The block had to be sleeved. In the picture you can sort of see the damage to the cylinder, towards the bottom. $150 paid for the sleeve. I think he charged me another small amount to have the block decked for a fresh surface.

I also replaced the head.

[vatdevil]

4.250 stroke makes a streetable torque motor, especially with the Air Gap.