Thread: 400 Small Block

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My grandmother past away leaving me a 1972 chevy Impala with a 400 small block. The car is currently a dog. Is this worth messing with to get more power from the motor as in new carb / manifold and headers or should I leave it be and just put a chrome dress up package on it?

I'm pretty sure the 1972 400 motor put out 250 HP as stock. It's a good motor to build but they did have heating problems on the earlier models. I had no problems with mine and I had it bored .030 over with new pistons, rods, turned crank,etc., It was a good running motor.

'72 Chevy 400 small block... !
>>> " read - learn- read - learn -read " <<<<<
then come back and ask....

"she must have loved you !!! "
hope you enjoy the ride " if you should choose to except it "

Thanks for the input. This car was never driven hard. I'm afraid that if I drive it hard or modify it to get some more horsepower that the motor will not hold up. Does anyone know if this is a 4 bolt main or the 2 bolt with the 3 plug? Is there anyother way to tell without pulling the oil pan? I'm told the 2 bolt is the more desirable of the 2 because it will take the higher RPM without coming apart should it be modified.

I took a 400 out of a 72 Kingwood Estate wagon. Rebuilt it with a .030 bore using dishtop replacement pistons. I found a set of 461 double hump heads with 1.94 valves, put a cam dynamics hydraulic cam with about 280 duration in it along with a torker and 780 Holley. This was a great motor and seemed to be bullet proof. It was a track only rig, but it ran on pump gas. I had a powerglide with a 10" convert and 5.13 gears with 28 inch tall tires on a 63 Nova. It ran 12.30s at 1400 ft elevation and 12.00s at sea level. If I would have changed to a 4.88 gear when I was at sea level it would have gone 11.80s because it really laid down at the top end and was running almost 7000 through the lights. Power peaked about 6750. When I sold the car the motor had over 350 runs on it and was still going strong though I held my breath on every pass as it crossed finish line. It amazes me still that the stock rods and cast crank held up that well.

Personally I think the 400 small block is one of the cheapest ways around to go fast. 406 cubic inches of torque motor will snap your neck back pretty hard.

Pat

Thanks for the input Stu Cool. This is going to be a project car for my son and I to play around with. Body is a little rough from her putting it into the side of the garage, mostly damage to the trim and a dented front fender. I think I can handle the body work with no problem but I am fishing for ideas like the ones you mentioned to get a little more out of the engine. How much time and money did you have to put in that motor to get those kind of results?

I worked on it over a period of 3 years. First year it ran middle 13s. As I could afford it and found used parts I could use I improved it. I was in the Air Force with a couple kids so did not have a lot of $ to spend. Big diffence between mine and yours is at least 1000 pounds. My Nova weighed just over 3000. If you keep your eye out for a lighter body it will make going faster a lot easier. Nice thing about the small block Chevy is it will fit in a lot of different cars. No reason not to start playing with the motor now though, and if you find a decent chassis, then you can make a swap.

Sounds like a great project for a Dad and kid.

Pat

JCT;
If you can take a look in the middle of the side of the block where a third frost block would usually be, the 400 engine had a raised area but no frost plug. Also in this same area you should see three numbers. If you can tell me those three numbers, I will probably be able to tell you if it is a four bolt main or not. Another way is to look on top of the back left of the block and get the last three numbers from there.

As for using the stock crank and rods, I wouldn’t. They are 30 plus years old and metal fatigue comes into play at some point. Right now you can buy rotating assemblies really cheap and they will have the longer rod, 5.7 inches which is more desirable then the stock length.

Thanks, I appreciate the information. I'm not in any hurry or quite sure which direction to go with this project but I like to tinker a bit and maybe my son and I can learn something together fixing this old car up. If you guy's have any suggestions then feel free to throw in your 2 cents as I'm glad that some of you have already done.

If your grandmother didn't beat on it too hard the 400 is probably still in good shape.I'll try to put things in sequence to give you a direction. If I left something out or have the priorities wrong someone will correct me or offer an alternative approach. There are a few more knowledgeable members on CHR.

The first thing to do would be a compression test on each cylinder. If it flunks the test then it'll need a rebuild or maybe a valve job.

If compression is good then you should really pull the oil pan to see what you're working with. Check the bearings and the crank for wear. The bearings should show some wear. The crank shouldn't. If the crank looks good I would replace the bearings even if they look good. They don't cost that much and if you have it apart you might as well freshen it up. With good compression and new bearings the engine can handle a little more horsepower. You could just assume all is well in there but it will cost a lot more to fix later if it's not. When you eliminate the doggyness it's going to put more stress on the bearings.

Next would be a new cam and timing set. After that (or at the same time if you can afford it) you'll need a new intake and carb. I like the "Edelbrock Performer" manifold, carb and cam as they are dyno tuned to work together and you can buy the parts seperatley. It makes it easier for us amateurs.

Other things to upgrade when time and money allow are the ignition system and the exhaust and chrome stuff. And sooner or later a valve job might be needed.

Thanks AL Show. I think the motor is in pretty decent shape as it is actually newer than the car. I was told the original motor had a problem at about 20,000 miles and was replaced by the dealership under warrenty. I believe the car has about 60 sum thousand miles on it so the motor has to have about 40 sum thousand miles on it. I have been looking for the paper work but have yet to come across it. The car is currently setting garaged until probate is finished. I was more concerned with what TyphoonZR mentioned with the metal fatigue as the motor is still 30 years old.

Originally posted by JCT400SB
I was more concerned with what TyphoonZR mentioned with the metal fatigue as the motor is still 30 years old.

If the car is stock and you plan on keeping it stock, you won't have any problems. However the current after market cranks are superior in strength to 30 year old stock cranks. I would not use a 30 year old crank to make over 300 hp. Whereas the current after market cranks I would trust up to 450 hp and of course the fordged cranks, up to 700.

First decide honestly what your going to do with the car....If you and your son are going to just fix it up with minor mods and enjoy. I would just throw an intake and carb combo on,then a set of headers and flowmasters....Evaluate the performance then,If not satisfactory tear in to the engine then......That will help the budget build.

Thanks Chap, I'm going to try to pick the car up this weekend or next before the Estate sale. I need to get it home and cleaned up. The body is a little more dinged up than what I originally thought. I'm not sure how much this car is worth but I would hate to let it get away without taking a good look at it to see what the possibilties may be. My first vehical was a 1968 Chevy 3/4 ton pickup 327 motor with a granny gear bought by my parents the same year I was born. I did some body work on it before I turned 16 and had my neighbor at that time paint it in his driveway. Truck came out great for the money I had in it and got compliments everywhere I went. This car is not in as good as shape as that truck, that's why I'm having some 2nd thoughts as of what to do with it. Pulling the motor and dropping it into something lighter is starting to look like a better way to go but I may be getting in over my head?

Sounds like your a very lucky fellow JCT400sb, nice car but a bad way to get it.

I do have a question for you guys about the 400, especially Stu Cool. I am wanting to get to around the 400-450 hp range which I think the 250hp 400 is a great place to start. I have put money down on a (I was told) 1980 motor that the heads have already been worked to 194 valve's. I have pretty much chosen an edlebrock 280 cam. I have a 780 double pumper duel feed holley from an old project, but no manifold yet.

Ok, having said that, what was the compression ratio of the piston's you where running? Where you running a stock electronic ignition? Would you use the torker again if you had the chance? How many HP do you think you where running? Unless I am mistaken, you can run a 280 cam without a stall right? My '48 chev sedan is a heavy car and I think the 400 will be a great engine for it. Any suggestions will be greatly appreciated from all of you. I may even put it on the bottle, who knows, this car is strickly for "Daddy's" fun!! It's about time!!