PuddleJumper

its realy depends this would be an question for the manufacturer of the crank. some need them some dont because they are never were 400 cranks.

Ryan

MotorHead

You are still in a pickle, you don't know what crank is in there. You need to find out. A 400 balancer can be modified to make it neutral, you could also have a 377 which would be a 400 block with a 350 crank, you really need to know what is inside the motor. Just putting a 400 flywheel on it I fear is not going to solve your problem.

PuddleJumper

110% with MoterHead he is right you could have an 372 in there and the vibrations could be something bad i would really pull it to cheak for the fallowing

1. what crank is realy in there
2. if the vibrations have caused damage
3. if there is something else causing the vibrations

Ryan

my75baby

How would I find out what crank is in the motor, are there numbers cast into it? Also, (why) or how often would someone put a 350 crank into a 400 motor?? Doesn't that lessen the horsepower of a 400? I think its easy enough to remove the oil pan and look, and since its a 350 crank it would be internally balanced as well, so where would the balancing weights be? How else could I tell?

larrywalk

Once again, it depends on the build of the short block. Typically if the rods are 5.565" (400 rods) or 5.7", the engine takes an external balance flywheel/flexplate, the same one used with the stock 400 sbc; if 6" rods are used with a stroker kit, often the engine is internally balanced because there is more room for larger counterweights on the crankshaft. Again, it helps to know what's in your engine.

If you want to test your unknown engine, knowing that it will be either external/external, or neutral/neutral, it would be easiest to test with a neutral balancer than change the flywheel, so therefore put a neutral balancer on it - if the vibration becomes worse (as it probably will), then replace both the balancer and flywheel to externally balanced pieces. Again, I'd bet that a 400 flywheel will solve your problem.

ARCH

Since a 400 "does'nt belong there" why don't you pull it and put in a nice mild 350? You already have the flywheel!!!!

jackson

For that matter, why would anyone put 3" stroke 283 crank in a 327 block (yields venerable 302 aka Z28) ... or a 3.25" stroke 327 crank in a thirty over 400 block (yields basic combo nascar used for years) ... it's done to meet the specific rules of race sanction bodies and/or meet powerband requirements. I have a thirty over 400 block with a 3.48" stroke 350 crank in it ... it's a 377 and it's purpose-built for circle track racing where 377ci limit is imposed ... if one were to compare it to an otherwise identically prepared motor employing a 3.75" stroke in new 4.00" bore 350 block ... the big-bore 377's horsepowerband will likely be at higher revs ... while the small-bore 377 is likely to produce more Torque at lower revs. Also, a larger bore can allow tightly-spaced valves to max flow better with less restriction from less-close cylinder wall; it can also permit larger diameter valves. Yes, reducing displacement does lessen the maximum potential horsepower. But I doubt anyone here has a vette whose motor is producing its maximum potential hp. I've never had any motor that came close & probably won't.

OMF

I'm not sure what the problem is.......in post #5 you said that you definetly have vibration.....that says to me its not internally balanced.....put on a 168 tooth 400 flywheel make sure that the flywheel is clocked to the correct position (align with the pin in the crank) and go have some fun!!

my75baby

well Arch, lets see, its about $120 for a flywheel and 1/2 day labor and probably at least $1200-2500 for a "mile 350", so which would you do?

Jackson: thanks for your insight but someone who was that into racing, would not have put an out of balance motor in my vette and would never put up with the vibration that will most definitely ruin a good motor amongst other things..

When I pull the pan, is there any way I can tell (without removing the engine) which crank I have or can someone tell me where balancing weights would be on the crank in a 350?

MotorHead

Slap a 400 externally balanced flywheel on it and if is OK you are lucky

If not the motor has to come out and you have to go through it to see what you have.

All motors internally or externally balanced should have the rotating assembly balanced at a machine shop with the parts that are going to be used so I doubt anyone that put the wrong flywheel on it had it balanced properly in the first place.

If it's a stock 400ci rebuild or someone just swapped in a used 400ci motor you might stand a chance of getting rid of the vibration with the correct flywheel.

Sorry for your misfortune and I hope you can get it sorted out

my75baby

Yes Motorhead I feel the same way, the way I figure, someone either bought the car with a blown motor, or blew it up and just put the 400 in. It is very possible that the person who put it in thought it was actually a 350 as well. Who knows.. I'm pretty sure the vibration is being caused by this. Would anyone know if the exhaust has to come out to take out the tranny? I have true duel exhuast (no H pipe), do I have enough clearance?

ARCH

Exhaust pipes are always in the way, and we remove them to take trans out. Not a big deal on my 68.

And I am only saying if it is so idiotic to have a 400 in the car maybe you should remove it. Seems strange to me if you are on a corvette forum asking for help about a 400 engine, you may offend people who happen to have a 400 wrapped around a corvette saying its an idiotic combination.

my75baby

I trully doubt that I would offend people when I said a sbc 400 does not belong in a corvette. Simply b/c it doesn't, no where in corvette's history did the factory EVER put a 400 into a corvette. Anyone can put any engine they want in any car, it doesn't mean that it was supposed to be there. In fact in my case, it is tearing my car apart b/c someone decided to match up parts that belong in the car with ones that do not. If someone decides to place an engine in a car that it was not designed for, more research would have to be done to make sure that the car is modified accordingly. I am sure I am not alone when I say that I would rather have a correct engine in the car even if the numbers do not match. (in my case, if someone would have done that I would not have to spend time and money trying to correct someone else's mistakes). And since someone didn't know what they are doing, my great 400 has a bearing knock in it b/c it has been run unbalanced for god knows how long, before I throw it away, I would rather see how bad it is and try to salvage it. I appreciate your help, and in my case I cannot agree to the engine swap.

ARCH

Saying a 400 does not belong in a vette is an opinion. Saying only an idiot would put one in is an insult to those of us who have them.

If an engine is not original numbers matching what difference would it make what someone replaced it with. My original 327 is sitting in the basement, should I have replaced it with another 327 so it looks correct? I would venture to guess that most people replace their wore, broken engines with 350s becuase they are so common. I assure you nobody knows my car has a 400 in it unless I tell them.

Its unfortunate that you are having the problems that you are do to a bad build. I imagine though if you are able to get it worked out you will be happy with a 400.

Just a thought on the 400, if we are specualting that the builder did'nt know what he had or what he was doing, wonder if your heads have steam holes?

ED69ray

You never know what you are gonna find on a NOM engine in any 30yr old car. In my case the previous owner used an engine exchange shop to replace the 350/350 L-46 in my '69 model and got a '73 350/165 L-65 in exchange - boy that was a heck of a deal

Not only that - it came with a 1955 265ci flywheel, 10.5 in clutch, and 12 in truck bellhousing to name a few of the mismatched parts. Most of these exchange shops are hacks who will throw anything together to get you out of sight and out of their warranty. Sad but true.

In your case I would try a 400 flywheel on it and see what happens. If that does not cure the problem or you simply just don't want a 400 period - don't waste the money on a flywheel - just buy or build a 350.

Good Luck, Ed

my75baby

Well I hope the heads are drilled, just another little problem with the 400, seems like alot to worry about with the 400, some of the people on here really like them, but for my purposes, this motor has been nothing more than a problem and a potentially expensive one at that. If nothing else on the vette, i was hoping the drivetrain would be strong and dependable, but not on mine. So i have to bite the bullet and get rid of the 400 ($$), rebuild it b/c of the knock ($$), or try to put a set of bearings in it and change the flywheel and maybe make out ok ($). I am not a road racer, I don't plan on beating the crap out of the car, I just wanted to fix it up, paint it and tool around on the weekends, so even the stock 350 L-48 motor would have been fine. So it will just take me longer, but I will fix this problem, just not too much fun right now. Again I appreciate everyone's input.

jackson

Suggest you fill in your profile with an APPROXIMATE geographic location ... we do not need your address; same goes for others w/ no location

If ... IF you are nearby ... and a good 350 will satisfy ... perhaps, perhaps we could work out a fair exchange ... or simply another pair of eyes. If you're nearby.

Bill colombo

. Is the center hole and bolt pattern bigger than the stock flywheel?

76Rat

I think you are a few years late with a response. This thread ended early 2009

Krystal

I guess that makes me an idiot.

Absolutely effortless destruction of tires and gobs of torque.......nothing like that belongs in a late model C3 right?

The idea of a 383 that makes no less than 425ft pds of torque anywhre between 2500RPM to 6000RPM.....peaks out at 468ft pds and ultimately makes 456HP......that's not for you?

Are you telling me that the 195HP L48 or the equally weak L82 PERFORMANCE version that actually got a CODE printed on the hood that today only signals less power under the hood than typical economy cars have today is enough for your Corvette?

If so........it may be time to reconsider why you bought this car in the first place.......there are more economical and comfortable ways to go that slow on the street.