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Old 09-14-2007, 07:05 AM
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Why do sbc 400's run hot?

Why do sbc 400's run hot? I've heard that its because you need to have the steam holes drilled in the cylinder heads. I've also heard they just run hot. I've heard they run hot when you bore them out because the cylinder walls get to thin. What is the max you can truely bore a 400. I've heard .030 is max and I've heard .040 is max. But I do have a friend running a .060 over sbc 400 and I tell him he's insane, so who knows...

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Old 09-14-2007, 07:15 AM
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I have had several 400's with a stock bore....never had any overheating problems with them.
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Old 09-14-2007, 07:50 AM
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I had a 400 sbc in my 65 El Camino. I absolutely loved the engine. The reason they overheat easily is because of the way the block is designed w/ saimesed heads. In order to accomidate the large piston head size, chevy had to make the cylinder walls between the cylinders thinner. That is what I found in my research anyway. That being said, I installed a lower temp thermostat and that seemed to help out a lot. Using electric fans on the radiator goes a long way as well. If you are just going to use a standard fan, then as long as you aren't stuck in rush hour or downtown traffic, you won't have any problems.
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Old 09-14-2007, 09:00 AM
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I have a 400 in my camaro, alum. radiator, dual fans from a 95 F-body (they work GREAT), and I run a 180 T-stat. Harly ever see 185 with it, even in 100 deg heat.
ONly when I hammer on it does it gain any heat. Then drops quickly anyway.

I plumbed water lines (3/8" steel) from the back of the intake to the front to help get water from there to the radiator - many intakes already are drilled / taped for doing this, but I had to do mine myself. Also, have passages from the side of the block (middle) up to a port that I drilled and tapped in the side of the cylinder head (like a sprint car). You just drill and tap below the two exhaust ports that are next to each other.

i coudn't say if these two additional passages are what gives me success or not, but I thought I'd mention it anyway.
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Old 09-14-2007, 09:01 AM
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Quote:
Originally Posted by xWestonx
I had a 400 sbc in my 65 El Camino. I absolutely loved the engine. The reason they overheat easily is because of the way the block is designed w/ saimesed heads. In order to accommodate the large piston head size, chevy had to make the cylinder walls between the cylinders thinner.
I think you meant to say siamesed cylinders. The cylinders (in the block) are connected on the centerlines. There are steams holes in the block that must also be in the heads and in the gasket. You can use 350 heads on a 400 block but steam holes must be drill into the head (like a stock 400 heads) and also make sure the holes are in the gasket.

A 400 should not over heat anymore than a 350 if it is setup right. Sometimes people put on unmodified 350 heads on a 400 and it overheats and blame the overheating on the 400.

Furthermore, 400's can't handle as much ignition timing as a 350 due to the short rods, which could also cause some heating issues.
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Old 09-14-2007, 10:26 AM
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400`s were somewhat given a bad rap many years ago due to what`s been mentioned. Most of the time when a stock 400 ran hot it was from lack of coolant system maintanance. I don`t believe Chevy would have let them leave the lot if they couldn`t run cool. We`ve ran many, and we liked them the best of all the previous small blocks we had built, simply because it put them all to shame. As mentioned the 400 came with a slightly shorter rod than all the other small blocks, but many are going around this by using the basic small block 5.7 rods and in some cases 6 inch rods. How much can on be bored? well, I`ve seen a few run at .060 over, and they didn`t last long. Unless you have the block sonic checked there`s no way to know. David Vizard said in his book he`s seen 400`s with real meaty bore walls, and others that were really thin. If I had a 400 with really thick walls, sure I`d bore it to .060, if I didn`t know, I don`t think I`d go past .040.
There have been many guys on here from past and present that run a 400 under there hood, and they don`t have any issues.
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Old 09-14-2007, 10:39 AM
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My sons roller, 60 over, 400 runs cooler than my 350! So does my buddies truck. I dunno, hasn't been a problem for us.
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Old 09-14-2007, 01:14 PM
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Never had a 400 run any hotter than any 350 I ever had. If you drill the steam holes in non-400 heads and use the 400 gasket along with a well-thought-out cooling system, it won't heat any more than any other small block Chevy.

I don't know how this untruth about 400's got started, but I understand how it is perpetuated.....here's the quote:

"Tell a lie often enough, loud enough, and long enough and people will believe you."
Adolph Hitler
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