Safe to mill a bit off 73 stock heads to raise compression?
#2088864
06/09/16 03:44 AM
06/09/16 03:44 AM
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xyxxjx
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I'm getting my stock heads rebuilt, valve job and valve guides. This head is a stock 73 charger head. As far as I understand the compression on these things suck, 8.2:1 http://www.automobile-catalog.com/auta_details1.phpWould it be safe to mill a little off the heads to raise the compression and gain a bit of power on the cheap?
1973 Dodge Charger SE 400 automatic transmission. Curb weight: 3800 lbs. All stock so far.
Goal: Reliable everday driveable warmed up 400 as close to 400hp as possible, then a 470 stroker if need be.
Don't protect a feminist when the collapse comes!
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2088881
06/09/16 08:53 AM
06/09/16 08:53 AM
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69L78Nova
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To get any kind of a noticeable result, you'd need to take quite a bit off. Which would mean custom length pushrods, and possible intake manifold fitment issues. It's not worth doing. Just live with what you have for now until you can go through it and change the pistons. The pistons in my 69 440HP were sitting .110" down in the hole at TDC. My 2355s are at .005". See what I mean?
1969 Nova 454/M21/3.31 Mild mid-11 second weekend cruiser
1994 F150 XLT Super Cab 2WD 5.0/4R70W/3.55 (Daily driver)
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2088900
06/09/16 09:50 AM
06/09/16 09:50 AM
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DAYCLONA
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I'm getting my stock heads rebuilt, valve job and valve guides. This head is a stock 73 charger head. As far as I understand the compression on these things suck, 8.2:1 http://www.automobile-catalog.com/auta_details1.phpWould it be safe to mill a little off the heads to raise the compression and gain a bit of power on the cheap? Assuming your talking B/RB, and assuming the heads have never been cut, you can take up to .060 off the heads, depends on how much is getting/has been decked off the block, or just head work? example: standard block decking is .010, then you can take .050 off the head = total .060, IF your going to be using factory steel type head gaskets that are .020 compressed, you need to know what head gasket your using as far as compressed/installed height, but the above mentioned .060 cut, with a steel head gasket should put you in the 9.5 range, your cam choice will be important, with a .060 cut I wouldn't go over .490 lift, cam duration will have an effect as well, long duration cams will kill your compression with valve overlap, if your going with a factory style lift/duration you should be fine, you still want to check piston to valve clearance regardless during the build, if your running stock valve train components, there's enough slop in the factory stuff to allow for a .060 compression cut, same for the manifold install as long as your using the factory style "turkey" 1 pc metal gasket, if your using aftermarket manifolds/gaskets along with the valley cover you may have to have the manifold milled for port/bolt alignment Mike
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2089033
06/09/16 01:13 PM
06/09/16 01:13 PM
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RapidRobert
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I'm getting my stock heads rebuilt, valve job and valve guides. This head is a stock 73 charger head. Would it be safe to mill a little off the heads to raise the compression and gain a bit of power on the cheap? Yes I have em cut 60 thou. ideally you'd want to mockup the heads back on the block & see how much if any the intake faces of the heads need to be milled to get bolt hole alignment in the ballpark (your port alignment is what you are really after) & that means another trip to & from the machinist or you can have the intake milled which is another trip also which might make the intake only fit your eng with the milling but if it'll be together for years then no big deal. there may be a preload (pushrod length) issue to be dealt with, maybe not, you'll see when you mockup. I milled some 906's 60 thou and advanced the 509 cam 4 deg & it woke it up. agreed SCR is the issue but if the short block is in the car & you dont want to pull it & go thru it (I totally understand that) then yes go to town on the heads & dial in the cam then dial in the ign curve
live every 24 hour block of time like it's your last day on earth
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: dogdays]
#2089170
06/09/16 04:46 PM
06/09/16 04:46 PM
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Joined: Dec 2007
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DAYCLONA
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Milling heads 0.060 will certainly require the intake faces to be milled. Check prices before you do this, it won't be cheap unless you live in a parallel universe. Two heads and two intake faces equal 4 setups and 60 is a lot to take off, will require several passes. I was quoted $200 years ago for flattening out the heads, meaning not milling that much. Anyone got current prices for the work?
R Agreed there's a machinist formula for milling X amount off the intake side mating surface for every .010 removed from the head any competent machine shop is going to perform this operation unless you decline it, some shops charge per "pass", a pass being .010, most shops doing a complete R&R on a set of heads (valve job/etc) price the time/labor to perform the task, rather than tooling degradation cost for just a head cut...prices are going to vary depending on your location and the type of machine shop
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: NANKET]
#2089184
06/09/16 05:13 PM
06/09/16 05:13 PM
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JohnRR
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.010 off the head gasket surface = .0123 off the intake manifold surface.
This is according to direct connection BB engine book. In case an argument starts. That is the correct amount .
Mainstream Media is the new Pravda
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2089611
06/10/16 01:04 PM
06/10/16 01:04 PM
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Joined: Jan 2003
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JohnRR
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I would look into sidewinder heads , do a search using the google search box at the top of the page , they were/are cheaper than the head you link and better performing out of the box. moparts sponsor Marsh Performance . http://www.mopartsracing.com/parts/Sidewinder.html
Mainstream Media is the new Pravda
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2089656
06/10/16 02:44 PM
06/10/16 02:44 PM
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451Mopar
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On my 383, I had 906 heads milled 0.060" (plus the intake side milled os the manifold would fit), and it makes fitting the valley tray a bit difficult, plus need shorter pushrods. The aftermarket heads are a good value upgrade. More compression, better flow, better combustion chamber design, hardened valve seats, larger valves, usually stainless valves with single grove locks. The one extra expense of these aftermarket heads is usually the need to use a head bolt kit.
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2089674
06/10/16 03:20 PM
06/10/16 03:20 PM
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Posts: 21,318 Manitoba, Canada
DaytonaTurbo
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Compression ratio is even lower in real life than the factory advertised 8.2. More like 7.8 to 8.0. I wouldn't waste time on the stock heads at this point. I bought the 440 source heads many years ago, but the chambers aren't small enough to raise compression up all that much. They'll bring you to around 8.5 unless you have them milled as well. I'm not up to speed on the trick flow, sidewinder, pro comp offerings these days, but IIRC at least one of them offers a smaller chamber. FWIW, your stock chamber is like 90cc, a 440 source around 85. You would need to find something with like a 70 or 75cc chamber to really help boost CR.
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: JohnRR]
#2089847
06/10/16 10:37 PM
06/10/16 10:37 PM
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xyxxjx
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I would look into sidewinder heads , do a search using the google search box at the top of the page , they were/are cheaper than the head you link and better performing out of the box. moparts sponsor Marsh Performance . http://www.mopartsracing.com/parts/Sidewinder.html Are those steel heads? Wouldn't they weigh considerably more. You also have to buy springs.
1973 Dodge Charger SE 400 automatic transmission. Curb weight: 3800 lbs. All stock so far.
Goal: Reliable everday driveable warmed up 400 as close to 400hp as possible, then a 470 stroker if need be.
Don't protect a feminist when the collapse comes!
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2089850
06/10/16 10:42 PM
06/10/16 10:42 PM
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Joined: Nov 2011
Posts: 2,154 Its a TRAP!
DARTH V8Я
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Aluminum. yah you'll need springs/valves/retainers/keepers. IMO go with the source heads.
When it takes more than a sweet mullet to prove you rule at the trailer park..
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Re: Safe to mill a bit off 73 stock heads to raise compression?
[Re: xyxxjx]
#2090379
06/12/16 12:19 AM
06/12/16 12:19 AM
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Joined: Jan 2003
Posts: 75,274 A gulag near you.
JohnRR
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I would look into sidewinder heads , do a search using the google search box at the top of the page , they were/are cheaper than the head you link and better performing out of the box. moparts sponsor Marsh Performance . http://www.mopartsracing.com/parts/Sidewinder.html Are those steel heads? Wouldn't they weigh considerably more. You also have to buy springs. No they are alum. ... your stock heads are cast iron ... and depending on your cam choice you may need springs anyway ... which aren't that expensive .... Call Todd and talk to him about what you need, the springs aren't that expensive. Edlebrock also has the E street head which has a 75cc chamber , that would bump the compression ... but you don't want to go higher than 9.5 with those stock piston deep in the hole ...
Mainstream Media is the new Pravda
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