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393w vs 408w

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I have a '74 351w block sitting in my shop that I want to build a stroker motor out of. I would reuse my current AFR Renegade 185 heads for this build. So my question is: Why would anyone build the 393 over the 408? It doesn't appear that the cost of the parts are any cheaper for the 393.
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I built a 408 out of my '69 Mexican block and absolutely love it. I never even considered anything else based on recommendation of the block machinist
 

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I used the Eagle 408 kit from Summit. No problems at all. Did not even consider the 393. There is no replacement for displacement.

edit: I should have purchased the flexplate and balancer and had Eagle balance the entire thing as I ended up buying them and then paying to have it all shipped out, balanced, and shipped back to me.
 

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I used the Eagle 408 kit from Summit. No problems at all. Did not even consider the 393. There is no replacement for displacement.

edit: I should have purchased the flexplate and balancer and had Eagle balance the entire thing as I ended up buying them and then paying to have it all shipped out, balanced, and shipped back to me.
LOL.... I did exactly the same thing with the same kit!
 

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I have a '74 351w block sitting in my shop that I want to build a stroker motor out of. I would reuse my current AFR Renegade 185 heads for this build. So my question is: Why would anyone build the 393 over the 408? It doesn't appear that the cost of the parts are any cheaper for the 393.
They are if you just buy a 3.85 inch crank, re-use your 351W rods and use 302 pistons.....
 

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Discussion Starter · #6 ·
They are if you just buy a 3.85 inch crank, re-use your 351W rods and use 302 pistons.....
That’s the kind of answer I was looking for. That definitely makes sense, although not so much in my case, since I don’t plan to reuse any internals. Thanks.
 
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It's exactly as Bart stated.

I've been considering the same thing with my 351W since it spun a bearing pulling close to 7000 RPM (I have a healthy cam). My stock 351W rods are pretty good since they're the "football rod" truck version. I've also got early CNC AFR 185 58cc heads.

My thoughts are is 15 c.i. going to make a difference at the 400 c.i. level? I already have traction problems. It is less expensive to just buy a 3.85" crankshaft & 302 pistons. Will the 393 rev faster (if the combination of part is lighter)?

I'd like to hear some pros & cons as well. I'm hoping to snag a bargain with black Friday this week.

Either way, Scat, Eagle, or something else? Where did you guys like to buy them?
 

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Will the 393 revv faster (if the combination of part is lighter)?

I'd like to hear some pros & cons as well. I'm hoping to snag a bargain with black Friday this week.

Either way, Scat, Eagle, or something else?
I built a 393 because I got a deal on a crank years ago and just had it laying around. If I had it to do all over again I would go with a 408. The 408 uses a lower compression height piston which equates to lighter pistons than a standard 302 piston. Now the rod is longer (meaning potentially heavier) on a 408, but the overall bobweight is less due to the pistons. So all else being equal, the 408 will generally spin up slightly faster than a 393.

Scat is generally recommended over Eagle for machining quality. Having said that, my Eagle crank was spot on for clearances.
 

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I built a 393 because I got a deal on a crank years ago and just had it laying around. If I had it to do all over again I would go with a 408. The 408 uses a lower compression height piston which equates to lighter pistons than a standard 302 piston. Now the rod is longer (meaning potentially heavier) on a 408, but the overall bobweight is less due to the pistons. So all else being equal, the 408 will generally spin up slightly faster than a 393.

Scat is generally recommended over Eagle for machining quality. Having said that, my Eagle crank was spot on for clearances.
Kind of the same deal here. I wound up with a 393W because that's what I got a good deal on. I too would do a 408 (maybe even a 427W) if I had to do it over again. I have a Scat forged crank and H-beam rods.



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Only reason I built a 393 was because the aftermarket didn't make a stroker crank back circa Y2K with more than a 3.85" stroke, and I didn't care to offset grind a 400 crank.

Do the 408.
 

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Only reason I built a 393 was because the aftermarket didn't make a stroker crank back circa Y2K with more than a 3.85" stroke, and I didn't care to offset grind a 400 crank.

Do the 408.
That's probably why my motor is only a 393 as it was originally built in the early 2000's by the PO.
 
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Discussion Starter · #15 ·
Any of you running AFR 185 heads with your stroker motors? I’m sure the 205’s would be ideal, but I saw the Engine Masters where they still made well over 500 HP with the 185’s on a 408w.
 

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Yes, I'm running AFR 185s on my 393w.
 

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Stroke works a lot like gears, in many regards. The longer crank throws add more leverage (along with a few extra cubic inches of air and fuel to burn) so you get more torque. But it also increases frictional losses due to higher piston speed and side loading. It also increases inertial issues because the crank's mass is usually greater, along with a larger diameter for that mass. That means that under acceleration, the crank won't gain RPMs as fast. In a lightweight vehicle with high numeric gears, that makes a big difference!

Usually, the limitation for horsepower will be what your heads can support, followed by how many RPMs the valvetrain can handle before floating the valves. In an extreme example, pitting a .030-over 289 against a 347 stroker, they have the same bore, but 2.85" stroke vs. 3.4". The 289 has a very light crankshaft, and the base circle for the counterweights and rod throws is very small. It might give up as much as 50 lb-ft of torque to the 347, and that's not inconsequential. In this fictional example, let's say that both engines are capable of making an honest 350 horsepower. The lower torque of the 289 means it has to spin to 6500 rpms to hit 350 horsepower, while the 347 can loaf along and hit the same horsepower peak at a much lower 5800 RPMs. The limiting factor for both is how much air and fuel can get into the chamber and burn. If you use the same parts (heads, cam, intake, etc.) on both, they will probably have very similar peak power. But the 347 would idle smoothly and have better manners down low, while the 289 wouldn't have much power off-idle.

You could always give the 289 more gear, restoring the torque and off-idle performance, making it comparable again to the 347.

The same engineering decisions apply to bigger strokers, too, perhaps even more. Wringing big RPMs out of a long-stroke engine means a lot of stress on the pistons, rods, crank, and bearings. When you de-stroke, you lose torque, but gain RPM capability and willingness to rev.

In a heavy vehicle with modest gearing, the longer stroke is always going to be a win, except perhaps when it comes to economy. But the lower piston speed can sometimes pay dividends, especially if you're running some kind of power adder. You can often rev quicker, and get more reliability out of a shorter stroke compared to the longer stroke, with very few downsides.
 

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I built a 393 back in ~2002. Like others have said, it was essentially the only inexpensive option back then. Today, I’d buy a 408 kit.

It was pretty cheap to build. I paid $425 for the crank and bought off the shelf hyper-pathetics for a 302, and used my rebuilt 351 rods with ARP bolts.

It’s run to 7500 and not come apart…back in 2005 I power shifted to a missed 3rd gear…floated and bent 2 exhaust valves in my GT40X heads.

Ive got chinesium 205 heads on it now. They are too big, IMO, for my cam and street usage.
 

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I've ran both strokers and if you're looking for a lightweight crankshaft, the 4" 408" crank is hands down lighter, to the tune of 6-8lbs for a typical Scat 9000 casting. The 4" crank is typically easier to balance too over the 3.85".

Also, you have to be careful when using factory stock 302 pistons as the 393 crank combo with the typical 302 piston raises the actual compression ratio higher than what typical 93 octane fuel can handle. My 393w with 3.85 stroke rods ran flat tops with an aftermarket 15cc dish piston, which gave a healthy 10.7:1 static compression ratio.

Unless you're on a strict budget and have some of the parts to build the 393w, go with the 408w hands down, especially when building from scratch as the price difference in parts is almost nil.
 
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