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Old 01-03-2005, 06:12 PM
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400 SBC project - questions...

I have some parts in my shop that are just laying around and I want to build a hot street motor out of a 400 SBC. I want to build for the maximum tolerance of the pieces that I have already, if possible. I plan to shoot for 500 HP and keep it streetable, using a solid cam and some good flowing heads I have. I already have the build pretty well figured out, I just have some questions about the limits of some of my pieces:

The block I have is a bone stock 4 bolt production 400 SBC from the early 70's. I was told it was one of the good castings, and it came from a low mileage motor and is still standard bore. I need to know what power level this block will support with reasonable reliability.

I also have a Scat cast 400 crank, never used, already balanced, that came from another engine project that never materialized. If I keep the power thrashings to under 6000 RPM, will this crank work for 500 HP or do I need to either go forged or downscale?

I also have a Mighty Demon 850 Blower carb that I was planning to use for my racing Corvette, but it turns out I will need to go bigger than that. So I'm stuck with this piece and I need to know what is involved with "de-blowerizing" it. Is this an extensive process that I should avoid and just go buy another carb, or can this be done for a reasonable cost? I'm not even sure how this can be done.

I already have the coin for this project, so if I can get these issues addressed by the good people here on this site, I can go ahead and start building it.

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Old 01-03-2005, 07:22 PM
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Quote:
I plan to shoot for 500 HP and keep it streetable
Not a problem...

Quote:
The block I have is a bone stock 4 bolt production 400 SBC from the early 70's
Problem... Have just found that the 4 bolt versions of the blocks are very weak and crack prone... A 2 bolt 2 freeze plug 400 block is a much better choice (or aftermarket of course)...

Quote:
I also have a Scat cast 400 crank, never used, already balanced
Very good crank for street and even mild strip use... A good thought here is "Fluid Dampner" to help it live and stay below 6000rpm and use forged pistons and 5.7 or longer rods (stock is fine but ARP bolts are a must)

Quote:
I also have a Mighty Demon 850 Blower carb
Sell it or save it for another project (to much work to change it)... A 750 speed demon with be a better choice or let Barry Grant`s site do the figuring...? (through email)


Just my .02 (lots more things to address... heads, cam, valve train)...
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Old 01-03-2005, 08:17 PM
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There's not much to do to make lot's of power with a 400sbc. Mine make 450hp on pump gas with a xe274 comp cam and a set of AFR heads. I run a stock crank and rods with no problems and I can turn 6500 rpms with a hydraulic cam. It floats out about 7grand. I found that out one afternoon when I got carried away in a burnout. I only run a 650dp Holley with a dual plane intake. High dollar parts are nice but putting money in the right place is more important. Spend it on good heads and a cam to match your performance level.Some say stock parts wont last but mine has lasted 2yrs and is still going.It sees the highways and backroads and has been ran hard most of the way.Even had some track time.Did I mention the hypereutectic pistons?Cheap but enough to but my 1955 chevy p/u down the 1320 at 13.02 on old street tires with crappy 60' times.
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Old 01-03-2005, 08:36 PM
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i am presently building same

Crank: cast crank is fine unless you use tranny brake.
Pistons: forged
Rods: The 5.65 400 rod has a shorter bolt than a 5.7 rod. The top of the bolt on a 5.7 rod will hit the cam lobe on a high lift. Forged cap screw rods give you the extra clearance you need.
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Old 01-03-2005, 10:31 PM
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The 4 bolt will hold up with studs. will not always take a .030 over bore. Short rods have to go, to much side thrust. Go with H beam rods. The 400 is not a high rev motor. more for torque. make sure you have the coolong holes in the head for the 400. The stock ones came with a 7 blade fan, cooling problems, crank has to be balanced with the rod and piston assembly. Forged pistons are heavy and unless you are running high compression the lighter cast will be fine but no nitrous. A 750 double pumper should be enough. Increase the ignition voltage. MSD or mallory high fire. I found a Mallory unilite to work fine with the Hyfire module. Long stroke = torque short stroke=RPM. The Z28 was a 302 with a 4 inch bore and a 3inch stroke, high RPM. You will have to watch what rear pig you use or you will run out of revs before the 1320 feet have passed. One more thing the 400 in strock form was externally balanced, not enough room in the block to balance it internally without that heavy metal add in, forget the name of it.
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Old 01-04-2005, 12:24 AM
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The best 400 block were the "509" followed by the "511" then the "817". I have seen all 3 used in hp situations. Get the block checked and since you got a 4-bolt, use main studs instead of the bolts. The Scat crank is a good piece and I had my 400 internally balanced since it was less weight. If you decide to use the stock 400 rods, definitely put good rod bolts in them as that the main cap thickness is the weak part of them. A 5.7 rod though gives more strength along with a little less sideloading along with more piston choice. Also with the 5.7 or the 6.0, watch your rod bolt to cam clearance. I had to have mine clearanced along with a small base circle cam. Whatever rod and piston combo you choose though, have it balanced as an assembly. Since you got good heads, that helps your 500hp goal immensely. That 850 will be too big in my opinion. A 750 should be all you need.
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Old 01-04-2005, 12:30 AM
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carb

i have a 400 .030 bore
flat tops
70 cc edelbrock heads
.500 lift 302 duration
10.8 to 1 comp
air gap intake
i only use a holley 650 dual pumper

also in my opinion
I would take the extra money spent on a small base circle cam and put it towards a nice set of rods. Both resolve the cam clearance problem. I just feel the money is better spent on the rods.
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Old 01-04-2005, 06:39 AM
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You block should be fine. I wish I knew where the crap about them being weak and cracking came from. I hear it all over the net and around gear heads, but noone I have ever talked to had one crack under normal conditions. The bores will usually crack before the mains, and every machinist I have talked to tend to agree.

I would be it cam from people trying to turn alot of RPM with heavy, unbalanced parts in a long stroke engine. That will break anything.

Chris
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Old 01-04-2005, 11:30 AM
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A simple examination of the main web`s will give a little insight they are much thinner with alot less material than a 2 bolt block... Also after seeing several blocks come through several of the local machine shops with the same problems it doesnt take much to convince...? (BTW they do also tend to crack up through the lifter valley also)

I undertand their will differences of opinions and that is to expected... But time and a little real hands on will sometimes shed light...? 25 years of building SBC`s you notice things...
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Old 01-04-2005, 03:48 PM
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I have both a two and 4 bolt main 400 running in my rides, so I am not speaking from inexperience. One 509 and one 511. I dont see any difference that would cause a strenght issue. If it is an issue with the 400 it should be with the 350 as well. .02 on the main diameter does not change much. I dont see where the extra material on the main webs would go. Crank counterweights sortof limit that.

We will see how long my 4 bolt holds up in the turbo engine. I think 800HP will put it to the test. Then I will have some more insight on the topic.

Here are some pics of the block assembled and not. I would be interested to know where the difference in the two bolt is if anyone has a good pic we can look at.




Chris

Last edited by TurboS10; 01-04-2005 at 04:15 PM.
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Old 01-04-2005, 07:10 PM
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I think the only issue is that the outer bolts pass right through the weakest part of the main webbing. Technically it is weaker than the two bolt blocks with splayed 4 bolt conversions. I still agree with Chris about the cylinders cracking first.

I have an 817 4 bolt block in my Nova as well. I filled mine to the bottom of the water pump holes with hard block to give it a little help in that respect. It makes around 450hp and get beat on with a 175hp dose of juice regularly. Been rebuilt twice and showed no signs of cracking on the last build.

Larry
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Old 01-04-2005, 07:56 PM
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Think the real test would be for you to come to my "neck of the woods" and see for yourself...?

I have no doubt you most likely have a good block (for now) but in the time that I have been building SBC`s (from 337`s to 434`s) I know what I have seen and will not waste any more time on this issue...



Quote:
I undertand their will differences of opinions and that is to expected...
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Old 01-04-2005, 09:05 PM
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Coldknock,

I did a tall fill on mine to keep the cylinders in check. I have heard the same thing about the outer bolts, but I believe that the 350's are the same way and noone seems to have a problem with them. The 400 always gets blamed for over heating as well. I believe this to be total BS as well. Obviously if you have a larger cube engine making more power it will take more cooling, but aside from that I have had no issues.

Bumpstick,

I dont doubt that you have seen cracked blocks, but I am always interested to know the conditions of the failure. A local machinist here told me he built a nitrous engine a few years back that dynoed at 750HP on an oem 4 bolt block and it was still hanging together. He said it was pushing the limits, but was still hanging on.

If we were talking about building a race car that ran for money 30 weekends out of the year it would probably not live to long. For a vehicle that sees track duty 10 times a year the factory stuff when properly prepped can last a long time.

Everthing that I have read also seems to show that stresses on the mains are very dependant on the balance of the engine and the RPM with RPM being the biggest factor. It would seem that RPM is more of a factor than power output by far. The effective weight of the parts changing direction at high RPM seems to be what kills everything, not the torque output of the engine.

Chris
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Old 01-04-2005, 09:45 PM
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Holy smokes... nice to see a lot of input from a lot of people on this issue in one day

From what I'm reading, I can assume my crank will be good enough for the task, so I will certainly use it.

My 850 carb appears to be too big anyway, so I won't de-blowerize it, I'll just go buy a 750 mighty demon instead. I'm sure I will use the 850 blower in another engine, I plan on building a lot of SBC's in the future anyway.

As for the block, I'm getting mixed responses about it's strength. It is a 511 casting, and like a stated earlier it is a low mileage motor with stock bore. I will be sure to buy forged rods and have the rotating assembly meticulously balanced, and since I will not be going over 6000 RPM it sounds like it should hold up fine. How about the idea of getting billet caps and some high strength bolts to help beef it up?

Since I am planning to run this motor on high compression (over 11:1), as I always like to do, I guess I'm going to have to get forged pistons, but jeez, those can be a heck of a lot more expensive than cast hypereutectic. I currently have hypereutectic pistons in my Trans Am's 350 with about 11.5:1, should I be getting worried? I flog on this motor quite a bit and it has not had any evidence of piston damage, but I hope it is not a ticking time bomb.

Thank you for the input, everyone, it certainly does help. I know my way around an engine, but when it comes to practical experience about the quality of parts it is wise to ask others with more experience.
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Old 01-04-2005, 10:00 PM
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good thread

Unlike some threads were alot of difference of opinions arise. Everyone seems to be in total agreement with this build up of yours.
I have been told that the 4 bolt blocks are weaker but I have no expertise one way or the other.
I personally went to the forged pistons. I found SRP to be the best bang for the buck.
Good luck.
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