Hi,

The goal for this motor is to run strong on the street with 87 octane.
I'm puting a set of 77 cc C heads on a 455 with 40 cc piston dishes. Compression calculates to 8:1 with a .042 gasket. The cam is .470 lift, 270 advertised duration, 216 @ .050. The intake is an Edelbrock performer.

I'm thinking it could use some more compression, so I'm planning to get the heads milled .060" or so. That should put it at about 8.75:1. Do you guys think that is about right for 87 octane?

How much do I mill the port surface and the bottom of the intake to fit?

Can I use a steel felpro valley pan/ intake gasket, or do I need a softer gasket with the aluminum intake?


Thanks, Joel

 

Don't mill the heads. Use a piston with less dish. That's the best why to get the compression on an olds engine. Several choices here.

 

Thanks for the advice Pat. But I am working on a tight budget with a junkyard shortblock. The original pistons will have to stay.

 

Stock higher compression come up quite often on e-bay. I sold a set very recently for 75 bucks with rods to another guy on site. Just a thought

 

Your best to mill the intake side of the heads. That way you can use any intake. If you mill the intake it will only work on your combo. If you take .060 off the head surface, take the same off the intake side. That is the way I do it and have never had any problems.
Gene

 

Thats an idea to consider. $75 for pistons is cheaper than milling the heads. What are the dish specs on those pistons? What would be the compression?

 

Thanks, how about the part where the intake sits on the ends of the block, do I have to cut something there? What gasket do you use?

 

With that much milled, check the intake to see if it clears the end rails of the block. It "should" clear by a little bit; seal the area with ultra RTV. You will know if you didn't mill the correct amount off the intake surface because the manifold bolts won't go into the threaded holes.

With that small a cam, you may get detonation if you succeed in getting much over 9 to 1 compression. You will probably get around 9:1 if you mill .060" and use the Corteco 55661 gasket (.028" thick).

I really think it is a waste of effort and money to do this milling for what you will get. If you want performance with low compression, step up the camshaft around 10 more degrees. Some don't like any cam with low compression but you could go 10-20 deg. and not do any worse than Olds did with the 71-2 W30s.

 

RtoR, I know we have gone back and forth on this but I was contacted by a gentleman from 442.com with the same scenerio.

He has an 8.0:1 455, had a Comp XE268 in it, ran o.k., It then wiped out 2 lobes. For some reason they sold him an XE274 as a replacement. Guess what, it ran worse, in his words "no torque". I got him a cam that will work better with his comp ratio, and yes it's smaller. I'd be happy to pm you his name for verification.

Joel, imo milling the heads .040 or so will give you around 8.5. With that compression if your cam is 216 on both intake and exhaust then you should be fine. I believe you're safer with that combo.

Jmo

 

Size of cam that is best depends on other stuff complementing it, and on rpm range you want it to run at. I shift at 6000 and sometimes run it up to 6400 and run a lot more cam than some people who think their cams still make power up there.

Small cams are fine for stock and stock-like combinations, and modest rpm. We don't have any argument there. I ran small cams like that (205-210 deg. at .050" lift) in my 360 Dodge pickup and they were more generally useful than the purple shaft from Mopar Performance (like a W31/W30 cam in size).

 

[QUOTE=Run to Rund;236024]With that much milled, check the intake to see if it clears the end rails of the block. It "should" clear by a little bit; seal the area with ultra RTV. You will know if you didn't mill the correct amount off the intake surface because the manifold bolts won't go into the threaded holes.

Hope I'm not stealing the thread but, I've got the same issue, heads milled .060 with intake and exhaust sides milled also. I set my intake on with the gaskets and those rubber seals on the block ends. My bolt holes are low, manifold holes 1/2 hole high, and I have quite a gap between head and intake manifold. I removed those rubber seals and everything seemed to fit. Can I replace the rubber seals with RTV? Thanks.

 

I have used RTV instead of end seals for 35 years. I recommend getting the rails very clean and put RTV on both the intake and the block rail, check carefully that there is no small passage to leak before putting the distributor in.

Also, you can't mill the intake side of the heads much (but I would mill them .005-.010" to get a smooth, flat surface). You would get into the valve cover sealing area and bolts, and remove too much of the dimples that the intake gasket pops into, if ou take too much off the intake sides of the heads.

 

Thanks for the info. The heads I got had all the milling done before I bought them. The intake side is milled to the point that the ridge towards the top is all but gone. Don't know how much they took off. The exhaust side is milled bringing the center divider flush. I'll have header issues also.

 

theres a used set of trw's with rods on ebay right now i think there only at $60 with 2 or 3 days left, good luck

 

How far can you mill heads before having to mill the intake side to keep from getting into fitment issues with the intake?

 

Im in the same boat as the op, low comp pistons, and I want the most compression I can get without getting into to much work.

 

If you mill your heads .060 you will only reduce the ccs by 12ccs you then have to mill your intake the formula is .060x1.3=.078 Also consider running a thinner head gasket they work fine when sprayed with Permatex high tack sealer on both sides. Just a suggestion.

 

Young Olds I didnt see your question until after writing the post but usually max .030 if you use the thicker head gasket it will hardly make a difference compared to the factory head gasket. If you shave .040 off the heads and deck the block I would use the formula .040x1.3= .052 just keep it even and take off .050

 

I figured I would take .072 off to get 70cc, by .006=1cc. with your formula for the intake side, is that individual or do you split it across both heads?

 

"I would use the formula .040x1.3= .052"

Where did that formula come from, a Chevy?

There's only 2 things to worry about on the >90 degree surfaces< Olds head.

Lowering the intake to match the lower head, and
Clearing the end rails.

Lowering the intake to match the head is a 1:1 ratio, disregarding head gasket differences. This can be seen easily if you tilt your engine 45 degrees, in your head or on your paper. Now you have one head's intake surface horizontal and one vertical.

Now move the bottom head, the one with a horizontal intake surface, towards the block. Pretend the intake is secured to it. In order to move that head horizontally towards the block, the other end of the intake will move the EXACT SAME AMOUNT. 1:1 ratio. No funny Chevy angle shyt.

There is one triangle to worry about here... the rails clearance.
45 degree triangle, 1:1:sqrt(2) = 1.414...

[EDITED the below text 3pm 6/8/13- I had the triangle drawn wrong and had asserted the rails cut was smaller by a factor of sqrt(2)- in fact, it is larger by that factor.]

If the intake rail surface or the block rail is cut by
Sqrt(2) * the amount that each head/intake interface was moved, then the end rail gaps will be unchanged


Sqrt(2) = 1.414

So, to maintain the same end rails gap, cut the rail surface (of the block and/or intake) by a total of 1.41x as much as you have moved the HEAD. E.g.,

Head is 0.010" closer to crank ==> rails cut 0.014"
Head is 0.040" closer to crank ==> rails cut is 0.057"
etc.

That said, if you are using a 0.040 gasket and a head/intake surface cut of 0.060 then the head has actually MOVED only about 0.040" from the stock location which used approximately 0.020" thick gaskets.

Remember to account for block decking if that was also done.

 

I don't have the definitive answer to that question, but i recently had mine milled an additional .060 (cleanup cuts done prior). I did NOTHING to the intake manifold or intake side of the heads, used the valley pan gasket (never did like saying turkey tray ), and the intake bolts and holes still lined up perfectly. I'm not sure if using The Right Stuff instead of the rubber end rail gaskets made a slight difference with where the intake ended up vertically, but anyway there you have it. By the way, CC's are now between 70 and 71.

 

The formula came from Terry Schaefer who built over 69 national and world champion Oldsmobile race cars its proven and it works not a Cheby!! ON the formula you mill both sides of the intake the same so if you milled the heads .060 x1.3= .078 BUT!! check your intake fit first after you get the heads back! on some intakes especially aftermarket you dont have to mill them and if you dont use the gaskets "I dont" I use the grey right stuff, remember Mr.Gasket and edelbrock intake gaskets are thick depending on what you use like the valley pan tray is thin, you have to check it with what your using as far as gaskets are concerned, a perfect fit is important. If it doesnt line up the mill them according to the formula. NO CHEBBY STUFF HERE!!!

 

Let me clarify the part I dont use gaskets, I dont use the end gaskets I use the lifter valley pan, cut off except for the tangs and I use Edelbrock intake gaskets with the grey right stuff on the ends.

 

EDIT: Ignore this incorrect info and see the correct drawing below. Sorry about that.

Sorry, but this is high school trig, not rocket science. ASSuming everything else stays the same (same compressed height on head gaskets, intake gaskets, etc) then each side of the intake needs to be milled by exactly one half of the cut on the heads. Mill the heads 0.060 and you need to cut the intake by 0.030 per side. This puts the intake manifold bolt hole centerlines (and presumably the port centerlines) back in the same orientation as they were before the milling. ANY different amount changes that. I got my information from Pythagoras, who I trust with trig a lot more than any engine builder.

Now, as Chris showed above, if you change ANYTHING else (say, using a thick composition intake gasket instead of the steel shim turkey tray), then all bets are off. Similarly, if the intake port centerlines were mismatched originally and you are trying to correct that, again all bets are off.

 

Thanks for the replies, though joe's is the easiest i appreciate everyones input. On my first olds I had the heads milled .028 to try to keep the comp close to stock. Assuming my factory shims were .017 and the new felpros were .045, and the intake fit perfect with a stock turkey tray gasket. so If I mill the heads .072 I should do .036 on the intake side to keep the intake fitting like it did before I took it off?

 

No, Joe is having a rare moment of incoherence. Along with "according to the formula. NO CHEBBY STUFF HERE!!!" man. The "formula" for Olds is 1:1.

IT IS simple math.

Viewing the engine in the normal position confuses me, but when your x and Y axes are in line with the surfaces of interest, it becomes simple.

Stand by for visuals using the base case of no changes other than milling the heads.

 

DOH! Yes, I'm an idiot. Sorry for the misinformation. This proves yet again why I shouldn't post from work.

Here's the correct visual, and yes, it's 1:1. When I drew this CAD model the first time, I didn't zoom in close enough and accidentally picked the wrong point.

 

After seeing your diagram I agree to that but I am just going by what they use to use as the formula Terry Schaefer used, I guess his formula worked ok and on my engines and all those Olds race cars but this diagram is correct. Thanks Joe and Ocatania.

 

Ok so mill .072 off each surface? After all this im thinking, should the machinist know this and not have to have me tell him I want the intake side milled too? Im only 19 and am building my first engine, on a budget, so i have a lot of questions and only hope it all comes out right in the end. Thanks again for the replies.

 

Asking questions is how you learn, so fire away.

Unfortunately, most "machinists" only know how to machine Chevy motors. I'm more of a "trust but verify" kinda guy. (Perhaps you read about Ronald Reagan in history class. )

To refresh my memory on your motor, is this an all-original motor that you're now machining? What head gaskets will you be using? As Chris pointed out above, if you are going from original steel shim gaskets to thicker FelPros, this negates some of the milling (and negates some of the CR increase also). You need to figure out your actual change in the intake bolt centerlines (total head machining from stock, less any increase in thickness from a head gasket change) and that's how much to cut the manifold.

Actually, you might want to consider not cutting the manifold, but having the machine shop cut the intake side of the heads instead. Doesn't matter which side of the interface you cut, and by cutting the heads, you preserve the geometry of intake manifold interface, so you can use any intake with stock dimensions instead of a custom-machined one. You will need to verify that the end rails on the intake don't touch the block, but if you throw away the rubber end rail gaskets and just use RTV instead, you'll probably be fine.

 

The engine is out of a 69 toronado. When I tore it apart I found it had been rebuilt already, still has cross hatches in bores and bearings are barely broke in. That, and wanting to get my cutlass running soon, is why im not rebuilding it with high comp pistons and other goodies I really want. I bought a felpro gasket set, so im using whatever head gasket comes with that, i believe a .045 or .042 compressed thickness. I looked for some thin head gaskets but they all cost as much or more than my whole gasket set. I always planned on only having the heads milled, by intake surface I meant on the head. If you click the link to my build thread i have a question about water pumps \/ \/

 

Head gaskets of the correct thickness probably cost about the same as the milling and fiddling. Which will surely bring other headaches.

I have seen factory original engines, especially Toronado engines, that look as you describe. Are the bores larger than stock? If the bearings say GMM400 on them they are probably original. Usually a date code on there also. But, that's a moot point I guess, to your task of re-assembling and maintaining the compression you want. Did you measure the pistons' dish to calculate the cc's? Are the pistons marked with an oversize stamp maybe? Maybe all you really need is that pricey gasket set. Too much compression and you will need a cam to match, pricey fuel, and you mitaswell your way into headers, higher stall converter, gearing, OAI, etc. etc. etc.

Anyhow, here's Riverbottom Motors' Milling 101 for the Olds V8 '64-'90:

We don't have AutoCAD - maybe Sketchup. Hand cut pcs of paper and drawn lines seemed to be easier and faster though. Here is the engine, tilted 45 degrees CW so that our surfaces of interest are vertical and horizontal.

13159_Milling_100_zpsf4936750.jpg

13159_Milling_102_zpsa4519336.jpg

Looking at the front of the engine, we have the intake secured to the engine's LH head- the one on YOUR right as you view the illustration. Thus, the original intake to head bolt alignment is preserved- the underlying assumption and goal here. If the intake is not in the same position with respect to each mating head, then you may have difficulty getting the intake to head bolts installed, and obviously you can get into some slight port alignment mismatch problems.

I called the amount that the heads were [M]oved "M" with subscript L for Left and R for Right (not shown). The Gap between block and intake at the end rails is labelled "R" here, for Rail gap. Should have gone with "G" like the later drawing, but oh well.

Let’s examine ONE cut at first. In order to move that LH head horizontally (in the illustration) towards the crank, the other [RH] head (and/or its mating intake surface) must be cut a total of the EXACT SAME AMOUNT- “ML” in the illustration. Not 1.3 or 1.567 times as much; 1.0 times as much, exactly. This part is a 1:1 ratio.

For the other head, the same applies, but the motion is vertical instead of horizontal. Another way to look at that is: when you drop the RH head [the one at the top in the illustration] down by amount "M" then the intake MUST move along with it [to maintain the bolt and port alignment]- therefore you will remove material from the LH head-intake interface [head and/or intake as you wish] in order to allow that movement.

So, we see that ML = MR; the left bank and right bank cuts are identical. Since L & R bank M’s are identical, we can just call it “M” - the net total amount of Movement [head with respect to crank centerline] attained by cutting the block deck, cutting the head gasket surface, and changing gasket thickness. This will likely be significantly different from just the amount milled from the head’s head gasket surface.

Now, about that end rail to block gap. I picked a point on the intake to illustrate- any point will do. Imagine a point “P” near the "R" shown in the block & heads depiction; Po for Original location, and Pm for location after Moving the head. The "G" is to show the block to intake Gap, with Go being the Original gap, and GM being the Gap after Moving the intake. Having moved the head-to-intake mating surfaces, the intake now resides closer to the block. The point “P” has moved horizontally by the amount ML, and also vertically by the [equal] amount MR. The result of these two, in a direction directly towards the block, is the amount by which the rail gap has been shortened- “X” in the illustration.

This is the well known 45 degree right triangle, easily rendering the result that the rail cut required IF you want to maintain the exact same end rails gap is:

X = M * 1.414


Here's a close shot of the intake to block end rail's gap- the dashed line represents the position of the intake bottom rail after the head cuts:

13159_Milling_200_zpscc1eb4e9.jpg

13159_Milling_205_zps0c2f2807.jpg

13159_Milling_210_zps5f24c4d7.jpg

To maintain the original gap on the end rails for some reason, then the block and/or intake rails must be cut by 1.4x as much as the heads were *moved*.

Note that with modern RTV [Room Temperature Vulcanizing] silicone sealants, we do NOT need to maintain this gap exactly as it originally was- as long as there is SOME gap, the sealer will take care of it.

And, yes, many folks have trimmed more or less than the 1:1 ratio from the intake-to-head surface and gotten by ok. Clearances [“slop”] in the holes, which are intended to allow for manufacturing tolerances, can often accommodate such errors. As long as it works out for you, intake bolts go in, and port alignment is acceptable…. all is well. But, the above is the mathematically correct assessment of the Olds V8 fitment modifications. Again, among the assumptions: the fit was perfect initially, and the main goal is to maintain the initial alignment or relationship between the intake and the head, so that bolts still work as intended, and ports have good alignment.

Oops... In that final math illustration- that's not "X minus rail cut"
it was supposed to be pointing out that the figure calculated IS the rail cut.

 

The engine im working on currently is definatly rebuilt. It has .030 over silvolite pistons, part number is how I know the dish, and bearings still show signs of of that first brake in layer as well as having an aftermarket oil pump and new looking rocker arms. With .030 in the hole 38cc pistons 80cc heads and a .045 head gasket is about 8:1 comp. this is how the engine was in the toro when i got it, i drove for about two months before taking it out to tare down to build up for the cutlass. I was going to go with high comp pistons and other goodies but I want and almost need to get it running asap so im going with what i have to get the engine running again. The toro was no slouch for the weight but i would like as much comp as possible working with the pistons I have. I was looking towards 9:1 but honestly the engine ran decently strong before i tore it apart so ill be happy with whatever I can get. Thanks again for all input, it is appreciated, and I will let you know how it all turns out in my build thread.

 

if I mill .060 for heads and intake on a 73-76 455 how much will it raise my compression to