400 small block

[jeepin_psymon]

k, heres what is goin on. i went to break in my new engine(400 sbc punched 30 over, trw forged pistons, edelbrock cam with .442 lift, and performer intake, and 305 heads) and five minutes into the cam break in it blew a hose. i have checked and double cheacked every thing including changine radiators. but it does the same thing. now i know all about the steam holes and the guy i bought it from said that he drilled them. but i don't know what else it could be. any help?

[Chief yelling alot]

how about timing,

if your blowing hoses your overheating. witch could be porly tunded engine or and inadaquit cooling system, if everything in the cooling system is new and the rad is lage enought id look at the engine

[jeepin_psymon]

ya i have checked timing and it was using a big block radiator. what i am thinking is that the guy only drilled half the holes. anybody know if it would act this way?

[MrWillys]

Have you checked to see if you've got antifreeze in the oil? I'd pull it apart and throw the 305 in the garbage, and get a head designed to work with a larger displacement motor. Or, you could ask the guy for your money back. I get the feeling this was a problem motor when he sold it to you.

[speer13]

If I remeber correctly there are 6 steam holes per head.... the 400's are very prone to overheating especially going .030 over on them depending on how thick the cylinder walls are... double check to make sure that they drilled the 6 holes and not only 3 like a lot of places do! next get rid of those heads .... junk on a 400ci engine especially with the big bore.... not to mention you would probably need a massive dish piston ,the common chamber size on a 305 head is in the upper 50's like 58 or so even with a 22cc dish your looking at over 10 to 1 the more common 7 cc dish would be around 12 to 1 so compresion could play a major part in this if your having detonation... (unlikely but a possibility) another possibilty with the 400 is if water sat in the engine for awhile without it starting the steam holes and water jackets tend to clog up....

[mdill]

Maybe a stupid question, but have you checked your rad
cap ? If it opens when it should no hose should "blow".

You may have other problems, what is the engine temp doing ?

Mike D.

[jeep450]

I think there are 6 total. 3 per head. What you need to do is through the 305 boat anchor heads away and at the very least get some vortec heads. Those 305 heads are junk, I don't care how much you port them or modify them. You are just wasting you money.

[Greatlakeoffroad]

The 400 SBC is notrious for overheating if the steam holes are not drilled then again the rad cap is a sound idea also

[Buckshot33]

I disagree with the notorious "overheating" myth. I've ran 6 different 400's up to .040 over, from pick-up's and towing applications with around 300 hp to 10 second street cars with little iddy biddy rad's and have never had heating problems. built right and tuned correctly the 400 sbc is a very good little powerplant. In fact, I had the exact same combo in a 79 chevy 3/4 ton 4x4 but .040 over and towing up sherwin grade outside of bishop CA in 110* heat for 11 miles with my foot on the wood the whole time it would barely get to 200* which in many circles is below proper operating temperature.

*gets off soap box and puts dead horse and stick away*

[speer13]

I agree 400's are great engines..... but they do have cooling issues... I have sonic checked quite a few and found a lot to be thinner in the walls I had a standard bore 400 that had about the same material between the cylinders as a .030 over block..... I personally have only had one that had cooling issues ina personal vehicle and it was becuase the water jackets in the heads were clogged up.... before any build on a 400 a good shop will do a few checks and make sure its suitable for boring out.... especially to jump out to .030 over on the 400.... I would say 80-90% of over heating is with buildup or tune up....or lack of checking things....

[jeepin_psymon]

well the guy i bought it from was running it before the rebuild. it was already bored out and didn't overheat. but the heads were cracked so he swaped on the 305's. i havent pulled them off yet but he thinks that he only drilled 6 holes total instead of 12. so i took a pair of 400 heads i found and am getting them cleaned up today. hopefully the new heads will fix the problem. i guess good thinks dont come cheep. i only paid $250 compleat, from my instructer.

[Greatlakeoffroad]

Guys, quote unquote from John Lingenfelters book The 400 CID is a great motor although it does have the unrightful reputation for overheating. This is mainly due to the fact ignorant jerkoffs would put heads from a different small block motor on this block and not drill the steam holes in the heads. Which in turn leads to overheating. Now, if you don't know who Lingenfelter is or do not believe me do a search of his name on Google & go buy the book. Shawn

[MrWillys]

The only 400 head I would run is the 441's. I'd consider any of the good 350 castings too! Here's a link to check out on stock heads.
http://www.chevythunder.com/fuel%20i...LINDER%20HEADS

[Chevyboy51]

just to let everyone know the steam holes won't cause that problem yes you need them on a driver because at idle it will build up steam and crack the block but at 2000rpms breaking in the cam there not even an issue most race guys don't even bother drilling them unless its a driver that will sit in traffic. my truck has them drilled but my camaro doesn't and its no problem. basicly don't worry about them and find the real problem.

[A-DOG]

Check your jetting on your carb if you increased displacement without rejetting. It could be running very lean causing overheating. Steam holes are for preventing air pockets in the block around the tops of the siamesed cylinders at idle and low rpm. At medium or high rpm they do nothing as water pump output is sufficient to prevent air pockets in the block. As far as your hose blowing off your radiator cap should vent first. If you are running a chrome thermostat housing they are slippery and cheap ones will not have a lip on the end to retain the hose behind it when the clamp is tightnened. Throw that sh*t away. I got badly burned one time working on some other guy's truck. Breaking the cam in I was reaching across the left fender to turn the idle up and the hose blew off the t-stat straight onto my chest @200 degrees. Lots of fun. Just some suggestions.

[mdill]

Yeap, Check the basics first, timing, mixture, pull a plug or two to take a
read, vaccum leaks ..., only after checking and knowing all the easy external
stuff is dead on, is it time to start tearing in to it and checking for internal
problems.

Mike D.

[positrack@earthlink.]

I too think that the 400 overheating problems are greatly exaggerated. I've got one in my '76 3/4-ton and haven't had it past the 160 degree thermostat once. I took it out west on vacation one summer to go wheeling and camping (from IL, yeah, us flat-landers are that desperate!), and drove through plenty of 110-115 degree desert heat and the needle never even twitched. Idling in traffic or holding 100 MPH w/ 4.10s for several hours at a time with the air on, it didn't care. It is stock bore, I keep it in good tune, and it's got a BB rad, but still... That's a test for anything. Not a scientific study, just my personal experience. To this day, it has never overheated or even gone past the thermostat to any significant degree, and it's been my driver/trail rig/sports car for about 4 years now.

As to the problem with hoses, like the other guy said, the rad. cap should have vented long before a hose popped. Something's wrong there... Which hose was it?

Also, it sounds like the engine was built with different heads than the 305 heads that you are currently running (or did I miss something)? If that's the case, you are probably running ridiculous compression w/ 305 heads on a bored 400. You'd be WAY out of pump gas range if you have flattops and 50-something cc chambers. That will cause overheating to say the least.

Like everybody else said, the 305 heads are junk anyway. They probably have thin-ass decks and they won't flow worth shit no matter what you do to 'em. They would choke a healthy 350 so building a runnin' 400 around 'em is the very essence of polishing a turd.

Hopefully I'm wrong but if you had to shut the motor down only 5 min. into a new cam break-in, you'll probably be doing that again real soon...

Jetting is a good suggestion too. If you run it real lean, even with no load (like during cam break-in), it will get hot. ESPECIALLY if you are running un-Godly compression w/ the small chamber heads. It's a perfect recipe for overheating.

One more simple thing, you are running a fan shroud aren't you? A lot of guys get away w/o running one but they do make a real difference at low/no speed, especially if the fan is quite a ways from the rad. It could certainly make the difference in a heavily taxed cooling system.

EDIT: Just for the record, I would agree that it is probably a good idea to have a 400 block sonic tested prior to boring due to the large bore and likely thinner walls. I would have this done for most any serious big inch motor, but most sources seem to agree (including my machinist) that it is particularly important with the 400 blocks.

[read306]

I agree the 305 heads are pure junk. Try a set of vortecs or buy a new set of Darts and I think your problem will be alot closer to solved.

[jeepin_psymon]

k here is what i got so far. ya the compression was way the f#@k up there some were around 11 to 1. which the builder of the engine told me that it would have high compression but not that god damn high .so i pulled the heads and am getting a set of stock 400 heads done up. already had them magnufluxed so i know that they are crak free. this should drop my comp. down to about 9 to 1. i talked to my machinging guy and he said that it is most likly the high copression and pinging that was causing the heating problem. i also checked the compression rings and they seem to all still be intact.(finally something goes my way) as far as getting vortechs, i wish. i am a broke as college student, this thing is already past budget. thanks for all the help guys. let me know if you have any other ideas.

[racin69z]

Not to overlook the obvbious, but did you fill the radiator with the thermostat in? I have had air pockets develop in the heads and when the motor gets hot the air expands shoving the rest of the water out.

Chevyboy51 was right, steam holes are only necessary on a everyday driver. I ran a 12.5:1 377 around on the street for about 5000 miles without steam holes in my camaro and it never gave me any trouble. The most important thing I found was getting enough air flow through the radiator. When I first had the car running it would overheat on a 20 mile trip. That was with 1 aftermarket elec. fan. I bought a used cavalier fan and switched the aftermarket fan to a pusher and it never got over 180 even in 100 degree hit idling in traffic.