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Raising compression in a 400? #303068
04/29/09 03:49 PM
04/29/09 03:49 PM
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polkat Offline OP
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It is my understanding from earlier posts that I cannot mill the heads (213's) on a 400 enough to get any noticable compression raise. I live in a rural area without a running vehicle (yet) and don't have an engine lift. I can get the heads to a shop, but not the block, so I can't get the block decked.

So what pistons can I install, without boring, that will raise the comp maybe a point?

Re: Raising compression in a 400? [Re: polkat] #303069
04/29/09 04:07 PM
04/29/09 04:07 PM
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Unless you have a low mileage cherry block with no taper or other wear I sure wouldn't put in new high performance pistons. No sense putting new pistons in a marginal bore. Heck mill .060 off the heads and .074 off the intake side. There will be a performance gain. There again make sure that you are starting with a good set of heads that have had the seats, valve faces and guides checked and surfaced.

Re: Raising compression in a 400? [Re: MoparforLife] #303070
04/29/09 04:11 PM
04/29/09 04:11 PM
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polkat Offline OP
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Okay, I'll consider that. What increase in compression will that get me?

Re: Raising compression in a 400? [Re: MoparforLife] #303071
04/29/09 04:14 PM
04/29/09 04:14 PM
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2boltmain Online content
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Something to ponder- the costs to machine the block and heads are not cheap. With my smogger 360 the cost of new KB107s at under $200 a set is cheaper than all the machining of a block and 2 head surfaces. I dont know what a set of 400 B pistons costs but a psiton change is better than milling to get comp.


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Re: Raising compression in a 400? [Re: 2boltmain] #303072
04/29/09 04:25 PM
04/29/09 04:25 PM
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I agree w/ 2bolt, for the money you spend on milling it does not make sense. I would just bolt it together as-is. A .060 mill will probably gain you around .5-.6:1 compression. Hardly worth it for the $$$ it'll cost IMO.

Re: Raising compression in a 400? [Re: 2boltmain] #303073
04/29/09 04:28 PM
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Quote:

Something to ponder- the costs to machine the block and heads are not cheap. With my smogger 360 the cost of new KB107s at under $200 a set is cheaper than all the machining of a block and 2 head surfaces. I dont know what a set of 400 B pistons costs but a psiton change is better than milling to get comp.



Granted it is better but not less $$$. Would you put a set of new pistons in a marginal bore??? Plus rings and bearings, + machine work to press the old pistons on and either press the new pistons on or float the rods. Not cheap or right either way but----

Re: Raising compression in a 400? [Re: MoparforLife] #303074
04/29/09 05:24 PM
04/29/09 05:24 PM
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Milling the block and the heads to raise compression in this particular case is just silly. it's going to cost more to do all that machining and in the end you end up with parts that will fit nothing else .

Just throw it together and run it till you have the money and equipment to do it RIGHT ...

Re: Raising compression in a 400? [Re: JohnRR] #303075
04/29/09 05:37 PM
04/29/09 05:37 PM
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its aaaaaaall in the pistons.

We got 9.5 to 10 compresion Rate with same heads volume on earlier years BB and RBs

Pistons and you are done... $400-500 rate.

then mill and porting heads for extra, but main win is on the pistons.


With a Charger born in Chrysler assembly plant in Valencia, Venezuela
Re: Raising compression in a 400? [Re: JohnRR] #303076
04/29/09 06:35 PM
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Quote:

Milling the block and the heads to raise compression in this particular case is just silly. it's going to cost more to do all that machining and in the end you end up with parts that will fit nothing else .

Just throw it together and run it till you have the money and equipment to do it RIGHT ...


Machining the heads the right way does not make them parts that will fit nothing else. Done right they are interchangable between engines. I agree that the gain will be minimal and that pistons is the right way to go but as I stated but would you put pistons in a marginal or high mileage block without boring & fitting?? I wouldn't. Nor would I put new pistons and a bore job into the engine without having the heads reconditioned and the crankshaft checked out and trued if needed. But what do I know I am just a shadetree mechanic. Right Johnahah??

Re: Raising compression in a 400? [Re: MoparforLife] #303077
04/29/09 06:46 PM
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polkat Offline OP
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If one mills the heads .060", must something be done about the pushrods? I remember in the old days people talking about shimming the rocker shafts to make up for milling. I believe some companies made these shims. Seems to me they could be homemade from .060" stock. Right?

By the way, is there a way to tell if big block heads have already been milled?

Re: Raising compression in a 400? [Re: MoparforLife] #303078
04/29/09 07:46 PM
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Quote:

Quote:

Milling the block and the heads to raise compression in this particular case is just silly. it's going to cost more to do all that machining and in the end you end up with parts that will fit nothing else .

Just throw it together and run it till you have the money and equipment to do it RIGHT ...


Machining the heads the right way does not make them parts that will fit nothing else. Done right they are interchangable between engines. I agree that the gain will be minimal and that pistons is the right way to go but as I stated but would you put pistons in a marginal or high mileage block without boring & fitting?? I wouldn't. Nor would I put new pistons and a bore job into the engine without having the heads reconditioned and the crankshaft checked out and trued if needed. But what do I know I am just a shadetree mechanic. Right Johnahah??




Lighten up Francis , Don my post was not directed at anything you said, the OP has been asking this question 30 different ways and is not getting the answer he WANTS to hear.

Re: Raising compression in a 400? [Re: polkat] #303079
04/29/09 07:50 PM
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Quote:

If one mills the heads .060", must something be done about the pushrods? I remember in the old days people talking about shimming the rocker shafts to make up for milling. I believe some companies made these shims. Seems to me they could be homemade from .060" stock. Right?

By the way, is there a way to tell if big block heads have already been milled?




Shimming the rocker shaft is the HACK way to make up for aggressive head and/or block milling , shims are to CORRECT for INCORRECT rocker to valve geometry.

Measure the outer row of head bolts , under the exhaust flange , stock heads would be 1.000 plus or minus a couple of thou.

Re: Raising compression in a 400? [Re: JohnRR] #303080
04/29/09 08:52 PM
04/29/09 08:52 PM
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shims:
http://store.summitracing.com/partdetail.asp?part=CRN-99170-1&autoview=sku

mancini racing carries too on 010, 015 and 030, and a complete kit in all those measures.


With a Charger born in Chrysler assembly plant in Valencia, Venezuela
Re: Raising compression in a 400? [Re: NachoRT74] #303081
04/30/09 12:17 AM
04/30/09 12:17 AM
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polkat Offline OP
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Well...heh...as the OP there was nothing I really WANTED to hear. My first post asked about pistons. Then I was told that my engine is probably too worn for performance pistons. I have miked the bores and they seem fine, and I was only looking for a piston to bump the compression a bit. Then the fun started. So I'll ask again; what pistons can I use to bump my compression maybe one point? Someone told me that .030" over 440 pistons would work. That sound right?

Re: Raising compression in a 400? [Re: polkat] #303082
04/30/09 12:37 AM
04/30/09 12:37 AM

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You use the "Lighten up Francis" ALMOST as much as you use the "Outside the box thing" Think up some new ones or crawl back under your rock PLEASE!!!!!!!

Re: Raising compression in a 400? [Re: polkat] #303083
04/30/09 12:38 AM
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Doesn't your bore have a ridge at the top where the end of the piston ring travel was? Usually old worn motors will have it.

Re: Raising compression in a 400? #303084
04/30/09 12:52 AM
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as I told... PISTONS is all you need to get the old good numbers from BBs. EVERYBODY will say you diff opinions mostly of them are not on budget just on performance, but PISTONS is the only real difference between a 330 HP from 383 and 260 HP from 400.

THEN you can get some more points extra with some milling, porting and cam... or simply headers and intake, you choose.

I bet you can get same 330-350 HP from a 400 than a 383 with JUST THE PISTONS and the basic resto MP HP camshaft, because IS ALL THAT 383 GOT !.

CRANKSHAFT was different to, because 383 HP were mostly forged and 400 are casted, BUT a casted crank can handle it without problem.

we have a "cheap" solution using KB240 pistons what are same kind of stock pistons ( casted, not forged ) but hypereutic technology/design. I woudl say is the only "cheap" solution for 400s we have out of the shelf

KB can get you some forged pistons too, but a little bit more expensive than the KB240.

Then you have Ross, Diamond what gives you teh option for custom built

But PISTONS and yu are done. I can't think somebody wouldn't be agreed on this, being the DIRECT relation with CR, being THE REST of engine is the same than earliers.

2 advantages of 400 beside a 383... stock manifold is already SPREADBORE design, and more displacement... so who can say you can't get 330-350 HP from a 400 with just that piston change ?

anyway I dunno if a KB240 could give you those 330-350 HP rate, because even they are higher than stock 400s, don't know how much they really are againts 383 ones with OEM/Stock 9.5 CR.

I'm not an expert on this, just being LOGICAL.


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Re: Raising compression in a 400? [Re: polkat] #303085
04/30/09 01:01 AM
04/30/09 01:01 AM
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Snce the block CANNOT come out I'd get some (std bore I'm assuming) KB quench dome pistons of the correct CR & mill them(& the open chambered recess's) to get quench & pull your old pistons & weigh them & hope that they are close to the KB's(if heavier lighten them) & put it together w the block in place! Your piston/bore clearance might be not perfect but this will satisfy your parameters. I'd do it in a second.


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Re: Raising compression in a 400? [Re: polkat] #303086
04/30/09 01:11 AM
04/30/09 01:11 AM
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leave the short block alone, ive got a set of good running closed chamber heads 1964 big block 516s 74 cc, your 400 open heads spec out @ 84-88ccs. this would take your 8.5 to 1 400 up in comp to 9.25-10 to1 you can mill 74 cc heads 40 thou with no issues with valvetrain or intake fitment.


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Re: Raising compression in a 400? [Re: hemigod426] #303087
04/30/09 02:06 AM
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Well, I suppose if there was something I WANTED to hear, what hemigod426 just added would be it! So if I mount a set of 516 heads (say with the steel shim gaskets-I have some) on the 400, milling them .040" if necessary, I would get something near 9.2 to 1 compression? That's what I was after. Does anyone else agree?

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