4-bolt 400 block strong enough?

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Jun 30, 2003 | 08:50 PM

Weird Science

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From: Sacramento CA

4-bolt 400 block strong enough?

A friend is giving me a 4-bolt 400 block. I have heard the 2 bolt blocks are perfered due to added strength in webbing area. My question is, will the 4 bolt block be ok for a 475-500HP, 475-500 Ft lb engine? It will see 6000 rpm every now and then, but not often.

Thanks.

Jun 30, 2003 | 08:58 PM

GrandSportC3

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Re: 4-bolt 400 block strong enough? (Weird Science)

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475 - 500 HP isn't too high for that kind of block... You should be ok - unless the block is damaged or cracked...

Jun 30, 2003 | 08:58 PM

Xracer

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Re: 4-bolt 400 block strong enough? (Weird Science)

I would say no. The four bolt blocks tend to crack near the main to cylinder webbing. Now if it is a high nickel block then you may be ok.

Jun 30, 2003 | 09:01 PM

GrandSportC3

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Re: 4-bolt 400 block strong enough? (Xracer)

Quote:

I would say no. The four bolt blocks tend to crack near the main to cylinder webbing. Now if it is a high nickel block then you may be ok.

Are the 4-bolt 400's weaker than the 2 bolt or 4-bolt 350's??? :eek: :eek:
I've seen 465 HP engines built on 2 bolt 350's...

Jun 30, 2003 | 09:12 PM

Xracer

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From: Rochester NY

Re: 4-bolt 400 block strong enough? (GrandSportC3)

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I have found them to be. The Camaro had a 2 bolt 350 truck block that we machined to take 4 bolt splayed caps. The 3400 pound car went 9.41 at 143.5. That about 775 horse at the rear tires. If anyone wants to get serious these days they really should step up to a Dart Little M block.

Jun 30, 2003 | 10:13 PM

fauxrs

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Re: 4-bolt 400 block strong enough? (GrandSportC3)

Quote:

I dont know about comparisons to 350's but I do know the 4 bolt 400's are considered weaker than the 2 bolt variety. Considering the larger bores, I would venture to say that it isnt unreasonable to expect that the 400 block is probably a small amount weaker overall than the 350 (I say this only because of the greater material in the 350 block, smaller bore means more iron somewhere)

Jun 30, 2003 | 10:22 PM

The Money Pit

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From: Orrtanna Pa.

Re: 4-bolt 400 block strong enough? (Xracer)

I've heard both sides of this arguement,and my theory on this is for what material is lacking in the web area,the fact that the bores are siamesed,actually adds strength to the block as a whole. I've turned 6500 rpms quite a few times with the Scat 9000 crank,and not a problem yet.

I've talked to quite a few machinists on this and nobody's ever actually seen this web cracking phenomenon.(Kinda like UFO's in a smallblock!)

Jun 30, 2003 | 10:47 PM

Pete79L82

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Re: 4-bolt 400 block strong enough? (Weird Science)

Quote:

The reason 400 4 bolt blocks are considered weaker is because GM drilled the outer two bolts on some blocks into the water jacket. If your holes are not drill through into the water jacket it is just as strong as any other stock small block. If it is drill through then I recommend using studs in place of the main bolts.

At 500 HP / under 6000 RPM you wont have any problems.

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Jun 30, 2003 | 11:01 PM

fauxrs

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Re: 4-bolt 400 block strong enough? (The Money Pit)

Quote:

....and my theory on this is for what material is lacking in the web area,the fact that the bores are siamesed,actually adds strength to the block as a whole. ....snip...(Kinda like UFO's in a smallblock!)

A very good point :smash:

Jun 30, 2003 | 11:05 PM

#10

Weird Science

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Re: 4-bolt 400 block strong enough? (Pete79L82)

Pete-
If that is the issue, how would studs restore the stength in that area? I'm not doubting you, just trying to figure it out.

Looks like we have mixed opinions here on if it will work or not.. Looks like most think it will.

I've heard 400's run hot, blah bah blah. Seems to be a lot of misinformation on these so I'm just trying to get the straight scoop before I plunk down a few hundred for machine work.

[Modified by Weird Science, 8:06 PM 6/30/2003]

Jun 30, 2003 | 11:25 PM

#11

Pete79L82

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From: Shawano WI

Re: 4-bolt 400 block strong enough? (Weird Science)

Quote:

Pete-
If that is the issue, how would studs restore the stength in that area? I'm not doubting you, just trying to figure it out.

If you use a stud and trim it so it goes into the block only as far as the last full thread, use stud & bearing mount to lock it in place then the stress is placed evenly on the entire thread surface. If you use a bolt you will have to use a flexable sealer which will not "tie" the bolt to the block like a stud will. With a bolt the threads on the bolt do not touch all the threads on the block evenly which can cause stress riser which can lead to cracking. With blind bolt holes this is not as much of a problem as with drilled through holes.

Before you "plunk down" any money for machine work be sure to have the block sonic checked to be sure there is minimal core shift.

Pete

[Modified by Pete79L82, 10:27 PM 6/30/2003]

Jul 1, 2003 | 01:13 AM

#12

Schmucker

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Re: 4-bolt 400 block strong enough? (Weird Science)

If it worries you, get some ARP fasteners and no longer worry. I don't think you'll have a problem.

Jul 1, 2003 | 01:17 AM

#13

BSeery

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Re: 4-bolt 400 block strong enough? (Schmucker)

Quote:

If it worries you, get some ARP fasteners and no longer worry. I don't think you'll have a problem.

Won't help much if the block has a thin spot or a stress riser. The bolts will be on the highway with the block material around them.

Jul 1, 2003 | 11:10 AM

#14

Weird Science

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From: Sacramento CA

Re: 4-bolt 400 block strong enough? (Pete79L82)

I see. So it sounds like if I stud it, it doesn't really matter if it's 2 or 4 bolt block.

Doesn anyone have a different opinion? Has anyone actually seen one of these blocks cracked?

Jul 1, 2003 | 11:23 AM

#15

Let 'er eat!

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Re: 4-bolt 400 block strong enough? (Weird Science)

Mine is a 4 bolt - casting number 3951509. I'm running at least 500 hp and haven't blown it up - Although the blower has only been on for the last 1000 miles, but the engine did have almost 30K before I put it on.

Jul 1, 2003 | 11:44 AM

#16

GrandSportC3

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Re: 4-bolt 400 block strong enough? (fauxrs)

Quote:

I would say no. The four bolt blocks tend to crack near the main to cylinder webbing. Now if it is a high nickel block then you may be ok.

Are the 4-bolt 400's weaker than the 2 bolt or 4-bolt 350's??? :eek: :eek:
I've seen 465 HP engines built on 2 bolt 350's...

I dont know about comparisons to 350's but I do know the 4 bolt 400's are considered weaker than the 2 bolt variety. Considering the larger bores, I would venture to say that it isnt unreasonable to expect that the 400 block is probably a small amount weaker overall than the 350 (I say this only because of the greater material in the 350 block, smaller bore means more iron somewhere)

I learn something new every day!! :thumbs: :thumbs:

Jul 1, 2003 | 12:59 PM

#17

Twin_Turbo

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Re: 4-bolt 400 block strong enough? (GrandSportC3)

smaller bore doesn't necessary mean more iron, the 350 has non siamesed cylinder walls, whereas the 400 has siamesed ones in the center.

As for the 4 bolt being weaker, yes that's because the outer bolt is drilled in an already thin section of the main webbing. A splayed 4 bolt from a 2 bolt would be the best option.

Jul 1, 2003 | 01:40 PM

#18

Tominator

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Re: 4-bolt 400 block strong enough? (Twin_Turbo)

Quote:

I see the term "splayed 4 bolt from a 2 bolt" advertised, but don't fully under stand it, can any one give a more indepth descriptions?

Jul 1, 2003 | 02:59 PM

#19

Weird Science

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Re: 4-bolt 400 block strong enough? (Tominator)

Quote:

I see the term "splayed 4 bolt from a 2 bolt" advertised, but don't fully under stand it, can any one give a more indepth descriptions?

A 2 bolt block is drilled out to 4 bolts. The outer two bolts are at an angle, and not straight up and down. Supposed to be much stronger. In a 400- that would give you the stronger block, and the benefits of a 4-bolt main.

Jul 1, 2003 | 10:03 PM

#20

Racer16k

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Re: 4-bolt 400 block strong enough? (Weird Science)

Quote:

I see. So it sounds like if I stud it, it doesn't really matter if it's 2 or 4 bolt block.

Doesn anyone have a different opinion? Has anyone actually seen one of these blocks cracked?

I've had one crack! At three center caps. From the cap bolts up through the block into the cylinders and cam bearings. This was a dirt track engine with 15:1 compression and 28 nights of racing. It ran fine at the time it was torn down, but I can't imagine it would have lasted much longer. This engine also had ARP bolts. You could see on the threads where the block had been cracked for awhile and was flexing. It actually had worn some of the threads away. Where the crack started was where the block is machined above the main cap bolts. I think a 4 bolt 400 block would be fine for street use. It wouldn't hurt to use a die grinder around that area to radius the sharp machining.

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