400 budget compression HELP +++++

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Well we have decided to use the KB240 pistons and deck the block as needed for quench which as I see it equates also to compression. No stroker in the future this should be fine for what I like thinking to much again once the block is decked and heads milled (worked out to be 76CC) I know the intake will also have to be milled but how about the valley pan
 
Rob, the "stock slug" 400 in my truck has the MP .484 cam in it which is 241 @ .050". With approx. 8.1:1 CR, open chamber heads, Performer RPM intake, granny tranny 4 speed and a 3.23 rear... let's say it runs but that's about it. No low end torque at all and the truck does not spend a lot of time over 3,000 rpm. Pretty much useless cam for the combo. (not my choice, got it that way)

I will be changing it out for a Hughes hydraulic that's about 1/3 of the size.
 
Demon, that will be a good combo. IMO, ditching the heavy low compression pistons can only work in your favor, regardless of whatever else you do to the thing.
 
My math says with no decking (pistons down about .026),and 76cc heads, you might get 9.5 Scr,and zero-decked, you might get 10.1.With an open chamber head, tight-quench on this combo,is not obtainable.But I'm guessing at 76cc those heads are not open.
-So With the new numbers; 9.5Scr, that 284/484/108 cam,Installed at 70*ICA, the Dcr rolls in around 7.2, and the cylinder pressure at a tic under 140.The bottom end will be a quite soft
-If you get to zero-deck/10.1 Scr, things look a little better at 7.65Scr/150psi.Not quite so soft.
-If you advance that cam to get an ICA of 66*, then the numbers @10.1Scr are 7.9/157;and now you are getting somewhere.
- All numbers are estimates based on assumed inputs and subject to change on assembly day.The assumed numbers are 76ccheads,pistons down 6.4cc with 5cc eyebrows, and a 10.4cc gasket, so total chamber size is 97.8,unmachined, and 91.4 at zero deck. I used a swept volume of 831.5cc
-I reviewed the thread and did not see you mention anything about cam size. On that note, I would mention that the next size smaller cam would pick up the bottom end quite a bit. but then, maybe a 400 with a slightly soft bottom end, isn't really soft at all, compared to a 360. And really, even with a soft bottom, it might still be stronger than a stout 360. Sometimes a ton of torque at take off might not be the best thing,lol
Good fortune to you.
 
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Thanks Greg. And yea, that's a good bit of cam for a 3.23 gear truck, granny grant or not
 
AJ/FormS said:
I don't know anything about bigblocks.
But I can do a litle math
It seems to me,the 400 makes a real nice stroker pkg, and if stroker is in the future, Why not bring the future into today. And then bolt on the top end you already have. It seems to me, that would cover all the bases regarding compression and budget.
The cost of the crank would be offset by some/most of the machining costs.

If your current pistons really are down .125, then a 3.75 crank will raise them up by 1/2 the stroke difference or (3.75 - 3.375) x 1/2 = .193. So now the pistons would be up at (.125 - .193 =) .068 above the deck. subtracting .040 for the gasket, that puts them into the head at (.068 less .040 =) .028. Adding .035say for squish,means the open-chambers need to be (.028 + .035 =) .063 deep. Is that not pretty close? If it is, then your costs are just the crank,making it fit, and a re-balance.How much could that cost;versus some of the other solutions posted here? I guess compression would swing the other way now, and we'll get a new thread "help me reduce the compression of my 450". To answer that, I guess if you cannot machine an appropriately sized dish into your current pistons, then KB(at least) makes pistons for this application.But I get about 10.2Scr with a 90cc head, and those flat-tops.If that math is right, then it wouldn't take much of a cam to drop the Dcr down into street-friendly territory.I worked it out with a 66*ICA to 8.0Dcr/160psi. This puts you into a very mild cam; I'm going to guess something like 276/286/112, in at 108.
Oh and the math comes to 4.372bore x 3.75 = 450.3731 cubes! That is plus 12.5%
Or am I out to lunch?
Click to expand...
Actually I have a new https://www.summitracing.com/parts/cca-21-223-4/overview/make/dodge
in (three bolt instead of one)
 
dodge71demon said:
Well we have decided to use the KB240 pistons and deck the block as needed for quench which as I see it equates also to compression. No stroker in the future this should be fine for what I like thinking to much again once the block is decked and heads milled (worked out to be 76CC) I know the intake will also have to be milled but how about the valley pan
Click to expand...

Lot's of milling going on here. If you are using the stock 400 heads and they have been milled to 76CC that would be about .067" worth of milling. Then if you mill the deck to get zero deck height you go another, what, .026"? So now there is .093" total. You now have to mill the intake surface of the head or intake manifold .114". The combustion chamber and block milling effectively raises the block rails where the intake pan gasket bolts with the six 1/4" bolts. Then you need to mill the block rails .158" so that the pan gasket slides into place. Me, I'd figure out another plan.
 
dodge71demon said:
Actually I have a new https://www.summitracing.com/parts/cca-21-223-4/overview/make/dodge
in (three bolt instead of one)
Click to expand...

I agree with Mr. IQ52 in that you have a lot of milling going on and it will a pain to figure out how to line all that stuff up once it's done. I can see elongating intake bolt holes and trying to figure out how to seal the valley tray in your future. Make sure that head bolt holes are tapped all the way down.

A 75 CC chamber could be tough to work with on a zero deck engine that runs on pump gas. Be careful with piston-to-valve clearance etc., you will need to get the clay out and measure carefully. While not huge, that cam you linked to is still pretty big, so you will have to really be certain that you have enough room. The pistons only have a 5cc dish. You have to degree it for certain and run it through a few revolutions to make sure its right.

Not sure how much you have in the heads but it's always a tough call to put money into old, factory pig iron parts when there are shiny aluminum heads available for decent money. But, you are already into the heads now for what seems like a bunch of coin so anything 'budget' now is going to have to be made to work with your heads.

Looks like your budget will consist of pistons (pressed or floating pins?), rings (make sure the current bore finish will work with whatever rings KB specs), balancing, (may require Mallory metal since the KB pistons are lighter) deck height measurement and surfacing, head gaskets etc.

I still believe building the best short block you can will yield the best results for now and for whatever future plans you have for the engine.
 
Great people on here how about this for grin and giggles since it appears that the heads I have been milled quite a bit how about going with the 400 using 440 Source Stealth heads - stock length rod - 383 forged crank - KB184 (440) pistons with a compression distance of 1.992 without checking the true deck height just going by reference figures that would put me up around .0575 is that to much out of the hole of course head gasket thickness can be used to compensate
 
dodge71demon said:
Great people on here how about this for grin and giggles since it appears that the heads I have been milled quite a bit how about going with the 400 using 440 Source Stealth heads - stock length rod - 383 forged crank - KB184 (440) pistons with a compression distance of 1.992 without checking the true deck height just going by reference figures that would put me up around .0575 is that to much out of the hole of course head gasket thickness can be used to compensate
Click to expand...

Sounds OK if you want like 12.1:1 CR. Math is your friend.

Funny how that budget thing always goes out the window when you try and make stuff you have on hand work.
 
Well that will be a tire fryer alright' 268/280/110, and lift of .477/.480, .050 of 224/230

To run that cam, you probably don't want to go zero-deck, cuz that would put your Dcr up at 8.4/169 psi. With a ICA of 58* In a iron-headed sbm, that can be hard to tune on pumpgas.Like I said earlier, IDK about BBS, but I can't see this aspect changing much.
However at 9.5, the Dcr is down to 8.0/159psi With an ICA of 56. If you true the decks with a light cut, say .010; that would put your Scr at 9.7, and the Dcr (at 58*) of 8.1/161psi. Either way;This should be dynomite on 91gas.You will need a traction aider.
The 268 is a pretty good cam, but you are walking a very tight line as to Dcr and detonation. I wonder if the next size bigger, would let you run the zero deck with impunity.I see comp also has a 274/282/110, with 050 of 224/230, and lift of .538/.534. This would get you a Dcr of 7.9/156psi at an ICA of 61* with an Scr of 9.7. This cam has similar duration, about .061 more lift to keep the flow going a little longer, and enough advertised to keep you out of trouble with detonation.You might even be able to run a zero-deck. The numbers for that would be;
Scr of 10.1, ICA of 64*,Dcr of 8.0, pressure 160psi. The only drawback to this cam, is making the heads work to accept the extra lift, which I would make fit in a heartbeat.
The best advice I could offer is to wait to order a cam until all the numbers are in.
I can hardly wait to see this work out.
 
Going to lighter parts almost never requires adding heavy metal unless the assembly balance was garbage in the first place, which is fairly common with stock parts being balanced using actual parts instead of a nominal assembly. S/F....Ken M
 
EchoSixMike said:
Going to lighter parts almost never requires adding heavy metal unless the assembly balance was garbage in the first place, which is fairly common with stock parts being balanced using actual parts instead of a nominal assembly. S/F....Ken M
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Well, true, just thinking that balancing in general always seems to wind up costing more for various reasons, especially with non-stock parts.

My local 'speed' machine shop charges $275 for internal balancing while they charge $375 for 'dependent' balancing which I take to mean external balance such as a cast crank 400. Adding Mallory plugs is $75 each. There are various charges for whatever other operations are required.

To measure deck height, they charge $195. To deck the block, they charge $125 + $20 for anything over .020".

So like I was saying, if our OP here buys pistons, gets them balanced and cleans up the block for zero deck, he will still be a few bucks ahead over getting heads. But that does not factor in any other work that needs to be done including getting his components to line up and seal.

And again, trying to 'make it work' with whatever you have on hand always seems to add up the same as if you start fresh and do things they way you want the first time. No such thing as a budget build unless you don't care about any sort of real performance and/or own a machine shop.
 
Thanks for everyone's feedback so with that in mind this is what I'm hoping for depending how things come out at the machine shop - 383 forged crank -KB240 pistons with eagle rods - ditch the heads I have and use the 440 Source Stealth heads - deck the block as needed for proper quench ( I figure using blue print specs the pistons will be down in the hole .027) balance the rotating assemble figure rest from there
 
Sounds like a decent street combo. Like stated already, don't over cam it and it will be fun to drive.

Just one point though is that stroker 'kits' are generally not too much more than standard rotating assembly parts. If you have the crank already, then OK but if you have to buy it and it needs any work, you might want to consider that stroker after all.
 
rmchrgr said:
Sounds like a decent street combo. Like stated already, don't over cam it and it will be fun to drive.

Just one point though is that stroker 'kits' are generally not too much more than standard rotating assembly parts. If you have the crank already, then OK but if you have to buy it and it needs any work, you might want to consider that stroker after all.
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Right now it boils down to the heads do I trust what I have or buy new ones if these would work I may consider the stroker I don't know how to check them or anybody that can for how much have been milled plus may be tossing away $$ to find out Believe me I know this but when do you stop not too much more or while I'm at it might as well been there done that more times than I care to think about -- thanks for all your input
 
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dodge71demon said:
Thanks for everyone's feedback so with that in mind this is what I'm hoping for depending how things come out at the machine shop - 383 forged crank -KB240 pistons with eagle rods - ditch the heads I have and use the 440 Source Stealth heads - deck the block as needed for proper quench ( I figure using blue print specs the pistons will be down in the hole .027) balance the rotating assemble figure rest from there
Click to expand...
Congrats on the plan, I like it.
 
Decision made block and crank (forged from a 383) are at the machine shop now the plan is Eagle rods - KB240 pistons - decking the block to zero deck with pistons of course balance the rotating assembly- Sidewinder heads - .040 head gaskets (should put compression in the mid to upper 9's)- Edelbrock dual plane manifold - 750 Street Demon Carb (because I have a new one) - adjustable Mopar rockers (again because I have them) - mid range flat tappet cam unknown at this time - Schumaker headers (again I have those) - possible some sort of HEI dizzy - 727 tranny with manual reverse valve body (column shift should be interesting) torque converter to be decided when cam is picked out probably somewhere in the mid to upper 2's any suggestions on a mid range cam would be great -- Thanks again for all your suggestions
 
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