rebuilding Chrysler 400

fury1

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Alright guys I've decided to rebuild the 400 that's in my 75 Chrysler. I would like to pull some more power out of iti have a couple of grand in mind for a budget. I've heard that the biggest problem is compression. How can I bump up the compression without spending a bunch of money? I'm gonna go mostly stock. Aluminum intake and 4 barrel eddy and new ignition.I also heard that the stock heads flow OK. Gonna have them redone... Just want more compression.
 
The guy that put my engine together immediately replaced the heads on the 72 440 engine I had as a donor to a better flowing aftermarket head with smaller cc's to increase the compression to 10:1. I think if you keep the stock heads you'll have to get the block decked to increase the CR.
 
Don't have the extra cash for new heads right now... Wish I had enough to build a 451 stroker!! Just didn't know whether to laugh or cry when I found out that the 400s had 7.9:1 compression..might just have to save up a little longer.
 
Phew big ask, okay here goes,
How is the bore in the engine block? Your cheapest method for increasing CR is new pistons. I would suggest KB240's as an option. When it comes to any marked increase in CR through head milling, you must remember that anything over .40thou is going to start affecting the valve geometry including the length of the pushrods. Then you have the added need of milling the inlet manifold to suit as well. It gets expensive.
With the large array of new pistons available you can certainly pick and choose with a little research to find the right piston to markedly increase the CR for sure.
You could also use a set of 440 pistons .30 thou over and bore the 400 to match. There are a lot of different 440 pistons available.
 
You won't be able to deck enough to effectively raise the stock compression ratio. Your only practical way would be to replace the pistons. I am rebuilding a 1972 400 right now. One option, get a high torque cam. They can effectively raise the cylinder pressure. It can really make a difference. Look at RV and Truck cams. I had one in a 440 that really screamed. Only real "drawback" is that you won't get that muscle car 'rumpety-rump' sound. But who cares when you are going like hell.
 
Not sure what the bores look like...still in the car running and driving. Runs rough though. I did a compression check and they were all low... New pistons are definitely an option for me. Would I have to get the crank balanced though? I have a set of 516 heads from a 66 383 they are open chamber though?
 
The crank wont need to be balanced no, if you go 440 pistons .30 thou over, you only have to get the 400 bored .10thou. And yes a set of early close chambered heads would help too but you will need to have a set of hardened exhaust valve seats fitted.
 
That's why I figured to use stock heads... Already have hardened seats... Maybe I'll go that route with the 440 pistons... I'll try to find some closed chamber heads... We do have an old 413 block from '65 I'll check out those heads....
 
The 400 in my old Newport had freshened up 915's, along with eddy rpm intake, vodoo cam, holley 750 DP, and msd ignition. All with the stock bottom end. Was a pretty healthy engine, and moved the heavy newport well. The rest of the drivetrain was built well as well.

Planning to do the same build with the 400 in my Cordoba. Maybe some closed chamber stealth heads though... Just to stir the pot
 
I'm doing a 400 for my Challenger right now. It is a 74 engine the stock compression ratio is supposed to be 8.2:1, I am using a set of 516 heads I purchased at a swap meet years ago they cc at a shade over 73 cc's. The pistons are down in the bore approx .115 thousands, doing the math it is a 8.43:1, 8.7 or so if I use steel shim head gaskets. Realistically the only way to get compression up is to buy new pistons or stroke it to 450 cid then small chamber heads and flat top pistons will bring you right up. I am using a bunch of junk I have collected over the years and putting it to use saving my number match 383 from any more abuse. Trying to get this done and make Norwalk in Sept to see what it will run.

My can choice for you would be a 383/440 magnum resto can from Mopar performance
 
You mean a performance cam correct? 516 heads, and new pistons should help quite a bit? Then add an aftermarket can? Could I still use the stock rockers and pushrods?
 
Well that is assuming a mild warm up. Spend the money on a .030 overbore and new pistons like the Kieth Black Hyperutectic with a quench dome and just run the heads you have. You will have too much money in the 516 with bigger valves hardened seats and at the very minimum opening up the bowl area in the exhaust port to match the new 1.74 exhaust valves. I will bet $ that your pistons are down at least a .100 so any pistons you find you want the ones with the tallest compression height but the trade off is spending $800 on stock replacement pistons to not even build a engine that goes over 6000 rpm makes no sense might as well stroke it. You should be able to find some reasonable pistons for a mild build. Goggle is your friend.
 
Alright guys I've decided to rebuild the 400 that's in my 75 Chrysler. I would like to pull some more power out of iti have a couple of grand in mind for a budget. I've heard that the biggest problem is compression. How can I bump up the compression without spending a bunch of money? I'm gonna go mostly stock. Aluminum intake and 4 barrel eddy and new ignition.I also heard that the stock heads flow OK. Gonna have them redone... Just want more compression.
I have a set of KB 240 pistons brand new still in the box. looking to get rid of them. they will give you just under 9:1 with 88cc heads.
 
Don't have the extra cash for new heads right now... Wish I had enough to build a 451 stroker!! Just didn't know whether to laugh or cry when I found out that the 400s had 7.9:1 compression..might just have to save up a little longer.

Stock 1972 pistons for a 400 should raise the compression to almost 10:1.
 
You mean a performance cam correct? 516 heads, and new pistons should help quite a bit? Then add an aftermarket can? Could I still use the stock rockers and pushrods?

Do you have dual exhaust? That helps a bit too.
 
Yes it has dual exhaust... I'm just gonna put a new set of pistons and redone the heads... Won't know if I'll have to have it bored until I get it apart...it does have dual exhaust. '72 400 pistons can get me 10:1?
 
Yes it has dual exhaust... I'm just gonna put a new set of pistons and redone the heads... Won't know if I'll have to have it bored until I get it apart...it does have dual exhaust. '72 400 pistons can get me 10:1?

Real close to 10:1.
 
Just stock cast flat top pistons? I did find some 440 pistons but I'd have to bore the engine 4.350... Around $550 which isn't out of my budget but... Valve reliefs and +6.00 cc which wouldn't help compression...
 
I don't know where you get that from Bob all 400 cid engines are listed at 8.2:1 which I think is what they would have liked it to be. High sevens is a more real world figure.
 
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