More engine talk: Dart block vs. Standard

[Bren]

So, if you've been following my thought process by reading all of my questions (thanks to everyone who has helped out - these decisions are impossible without you guys), I'll tell you that I've decided to go with a 427 based on a 351W block with a standard carb setup. So, the next question is: which block? Dart 351W or the regular one?

I know everyone has their own opinions, but what I want to know is the ADVANTAGES and DISADVANTAGES of each block, not necessarily which one is best.

I have done a bit of research, but can't really confirm much. Here's what I've got so far:

Standard block advantages:
$1500 cheaper than the Dart

Dart block advantages:
improved cooling because of uniformity and increased water capacity around the cylinders
improved oiling
harder metal
thicker walls
better resale value (?)

The reason I'm even considering the Dart block is because I've heard that after a lot of use, the standard 351W blocks that are bored out to 427 can have some troubles because of the (relatively) soft metal and thin walls (by the time you've bored out to 427, there's not much left). So, my thinking is that spending an extra $1500 for a more robust engine that will keep its value better (maybe) is a good investment in the long run.

I know the Dart is necessary if I was planning on putting a blower or using NOS, but I'm not. So, I'm not worried about blowing out a standard 351W block because of too much power.

Thoughts?

[Gale K]

If you're going to the expense of building out a 351 to 427, it's not even a consideration, IMHO. Get the right block (DART) and do it right. The extra $1,500 will be "free" in the long run. Do it once. When you're thrashing on the motor, you'll be glad you went with the DART.

[Gordon Levy]

To make a 427 out of a production Windsor block you need to run a 4.030 bore but a 4.100" stroke. This in my opinion is to long. Max stroke for a production block is 4" in my opinion.. A Boss or Dart block can be bored to 4.125 and maintain the 4" stroke to give you a 427cid. The boss and dart blocks also use a cleveland main bearing size which is better for high RPM reliability.

[Bob Cowan]

You can do it with a stock block, if you can find an early model block with a little more meat in the cylinder walls. But you're pushing it right to the edge. If it overheats or you lose a little oil pressure, you'll kill it.

If you damage a Dart block, it's a lot easier to repair. A sleeve and deck job can be done in a couple of days. If you damage the stock block, you'll be looking for a new one. Been there, and done that.

The Dart block is more expensive in the beginning. But, like most things, it ends up being cheaper in the long run.

And, with the Dart, why stop at 427 cubes? There's no replacement for displacement. ;)

[Bren]

Well, then, Dart it is, I suppose!

[edwardb]

You won't go wrong with DART. They're made right here in Troy, MI. When I went to my engine builder's place to order the short block, he had stock and DART blocks in the office we could look at. It was real easy for him to upsell me to the DART block. I was considering it anyway... When you put the two side by side, there's really no comparison. Especially when he flipped it over and you could see those huge billet caps, 4-bolt mains, extended piston skirts for the stroker setup, and so on. There is a slight weight penalty for DART just because they have more metal (not a bad thing) so be aware of that. At the power levels we're normally dealing with, the DART is perhaps overkill. But it's a rock solid choice. Mine is a 302 size block set up as a 347. For the higher deck 351 size block, Gordon is absolutely right about the smaller mains on the DART. Main bearing speed can be an issue with a 351 based stock block.

Here is mine right after I received it from the builder. It's a beautiful thing:

http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/th_IMG_2108_zpsdd0e2c94.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_2108_zpsdd0e2c94.jpg.html)

http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/th_IMG_2109_zps340b2b1c.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_2109_zps340b2b1c.jpg.html)

Looks like this now:
http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/th_IMG_2250_zps6d339168.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_2250_zps6d339168.jpg.html)

http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/th_IMG_0169_zpsd253c291.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_0169_zpsd253c291.jpg.html)

[68GT500MAN]

The new BOSS 351 block is even better than the Dart in my opinion.

[EBarnes]

http://www.roushyatesparts.com/SearchResults.asp?Search=31345295
http://www.roushyatesparts.com/SearchResults.asp?Search=31344295

I now understand that the 351C main is preferable to the 302... anything else to consider other than what has been said?

[EBarnes]

Sorry, I think those were the wrong deck... 9.5" is quite a bit more money:

http://www.roushyatesparts.com/dart-engine-block-p/drt-31345235.htm

How big can one go with 9.2" anyway?

[Bob Cowan]

I think the last time I figured that out it was 454 cubes. Go to www.dartheads.com and look at the spec sheet for max bore and stroke.

[edwardb]

I now understand that the 351C main is preferable to the 302...

Why do you say that?

302 = 2.248 mains
351C = 2.75 mains
351W = 3.00 mains

I'm not aware of anything negative for the 302 size mains in those blocks. Some performance builders get concerned with the bearing speed of the 3.00 mains in 351W's. My builder mentioned this when we were touring his shop. That's why a 351C size main is sometimes suggested. DART (and maybe others) are available this way. At our power and RPM ranges, likely not an issue. But if given the choice, I guess it's something to consider.

Wow, those DART aluminum blocks are pricey. Makes the iron SHP block in my Mk4 look like a bargain.

[tirod]

Bearing speeds are like rod angles, up to a certain point it's very theoretical and has little influence. The factory found no problem with them on the block, it was meant for truck use hauling heavy loads over long periods of time. Smaller bearings may have less bearing speeds, it goes to how many rpms the crank will see. With factory roller cams it was limited to 6200 rpm anyway, a built motor turning over 7000 is going to likely be the candidate. Then it goes to application - a 7000 rpm motor isn't "street cruiser" and will certainly cost a chunk of change more.

Horsepower costs money. The 351W is reputedly good for 700 hp, but that is short term racing use. The crank and mains still walk around a bit according to the racers. A girdle won't stop it, they say. Those running it hard who upgrade to a Dart block seem to fall into the Buy Once, Cry Once category. It was an expensive step up but worth it to them.

So, the issue is how much you want to spend vs the return on the cost. I look at it from the installed hp to weight ratio view, using a 2400 curb weight (some figures are just arbitrary.)
Factory stock motor, 10:1
300hp, 8:1
350hp, 6.8:1
400hp, 6:1
450hp, 5.3:1
500hp, 4.8:1

Note as the horsepower goes up, the rate of improvement tapers off. Typical declining return for the incremental increase.

Now, what does it cost to get to each horsepower step? Stock is baseline, call it cheap. 300hp a nice rebuild, for a 5.0 it's 1 hp per cubic inch, which is still a good standard altho the factories are making it normal now on new cars. At 350hp the 351W still has a role, no extra expense. Just go big and you don't really pay any more.

400hp and it's going to start costing money. You could do a big block, they are pricier now. Or, fit a stroker crank, about $1,200 for the lower end of the reciprocating assembly.

450hp, another step up. At this point, aluminum heads or the price of ported get added in, another $1,500. And the point is now reached where blocks need to be considered. The 5.0 stock is at the edge and not recommended. The 351W stroker with heads at the point it starts becoming peaky and loses low end torque. Not a major problem in a light car, but nonetheless it's going to take more clutch slip or a high stall converter.

There is a sweet spot in everybody's budget where they can afford at least one of the steps up, which going by the hp to weight ratio delivers a lot for the money early on. Then the improvement starts to slow down for the money spent, and IMHO, its about where the Dart block comes in. Like E said, at street hp levels it's borderline return on the dollar.

What it offers in the long run is durability, and the room to upgrade other components for major increases in power - like, supercharging. If that decision is made, about the only concern would be the pistons and compression ratio, not the block. IF it's an endurance racer, the strength of the lower end to resist a lot of up and down rpms would be good insurance to complete a race. If you don't cross the finish line, you don't even place.

In terms of money and desired goals, someone building a street kit could get into the 400's with a stock 351W and enjoy the car. Many have. But there's not much further to go - it's going to take almost the cost of a reman motor again to make the next step up.

No right or wrong in any of that, it's all about the money vs goals and how to get there. But, the fact is that the returns start quickly diminishing, and the added costs to keep the drivetrain alive with the extra horsepower start factoring in. A 500 hp kit isn't going to use a stock Tremec transmission, a used 8.8 from a Tbird might not survive extreme use. And stock brakes would be a joke. Add those costs in, too. It's not all about the engine, the car's overall handling needs a lot of consideration. Otherwise, the result is a the same as Bill Cosby tells - the car's too much to handle and you'd be better off sending it to your least favorite political representative.

If it takes $1,200 for a crank, $1,500 for heads, and another $1,800 for a block minimum to get to 450 hp, then it's likely going to need the another $4500 in transmission, rear end, and brakes to keep it from hitting every tree or guard rail in sight. And, unfortunately, youtube seems to have plenty of evidence that the driver should spend as much on training, too.

It's why you see the conscientious kit builders who want 450hp levels shell out $50k for their builds. It all adds up. Quickly. And on a budget, it takes time to accumulate the cash flow, putting the completion date years further out.

Food for thought on the build plan.

[skullandbones]

Very nice comparisons, Tirod. It shows just how critical the budget decisions affect the build: pay now or pay later.

WEK.

[galla4]

I am another supporter of the Dart block. I tried to squeeze too much out of a stock 5.0, cylinder walls wouldn't even handle 347. Went with Dart Iron Eagle 347, went to 363 and could have gone further but I have plenty of HP and grunt. Good luck with your decision.

tim