compression ratio
 

so i recently aquired a L98 block and im porting 601 heads. now if i use these together and get a .040 headgasket what compression ratio would i be at. block is stock never been redone but the heads have been milled flat so i dont exactly know what cc theyre at. also ill be using a zz4 cam in this motor. now im wondering if the compression will be too high on this motor? if so how can i get it down without cutting into the combustion chambers and changing pistons.

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need more specs like flat top or domed pistons, bore size, stroke , how much the piston sits down in the hole at tdc

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well this is all on a stoke L98 block. all internals except for the cam are stock. if it was 9.5 cc stock with the 083 heads which are 67 or 64cc then i drop to 53cc's would it be too high?

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I come up with 10.9 assuming flattops with 5cc relief and a standard fel-pro gasket.

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Lower it by grinding the combustion chamber. F-bird has made nice mspaint diagrams lots on this topic. You want to enlarge the chambers and increase flow near the intake valve towards the spark plug.
I did that on my 416's to get down to 10:1.

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ok cool thats great how much grinding from each chamber would i have to take off to get the compression down to 10:1ish?

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A bit. A smidge.
This much.

How can I quantify this over the internet?

Get some plexi and a 100ml syringe from your local vet and find out.

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thats a little strange going to my vet for a needle plus theyll probably think im some kind of drug addict. but roughly how much grinding would i have to do, just a little deshrouding and polishing will do the trick maybe? and how many cc's will i want to end up with in each chamber?

Re: compression ratio
 

No, you're not asking for a needle, otherwise they will think you're a drug addict. A "syringe". It's a needle, but without the sharp metal point. It's like what you'd use to squirt liquid into your ear if you've ever had an ear infection. Or, at a vet, what you'd get to squirt medicine in your dog/cat/horses mouth. A big 100cc one would probably be for your horse. They sold me a 50cc one for $5 without even batting an eye. I told them what I was using it for and they didn't quite understand but "an easy way to measure liquid in the 50-100cc range for some car work", kinda seemed to click for them.

It's quick and easy to use, and gives you the peace of mind that your chambers are all pretty close to each other.

Yea, just a quick deshroud and polish job gave me 58-64cc's on my 416 heads. But I never cc'ed them before, so I don't know if I was actually starting at 58cc's....

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Your 601 heads are going to need bigger valves than stock. The fact that you will have to hand clearance the combustion chamber for the larger valves to fit, will make the chamber larger than it is now.
The actual cc size of the stock chamber on 601 castings varies a bit.
The only way to know the cc volume of your heads is to cc them yourself.
You want to install large 1.94x 1.60" valves in your heads for a high performance 350ci motor.
By the time you have reworked the chamber for the larger valves the volume
will be in the 60-65cc range. CC after you're done and mill accordingly to get the finished cr you want. The radius of the new larger valve is .050" larger than the old stock valve. So the chamber wall will need .050" of grinding around the valve to restore the chamber wall clearance with the new larger valve.
Not that hard. Do not use the head gasket as a grinding guide. it is much larger than the cylinder bore.
use old valves to protect the valve seats while you're working the chamber.

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Do you have the ZZ4 camshaft specs? I tried a quick look on the internet and couldn't find the right info. (Sallee/ Gilbert)

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Found the cam specs online and did a little math.
With the following: 56cc chamber,
flat top piston and assuming 5cc dish volume,
.025 piston below deck
.040 gasket w/4.060 gasket bore
ZZ4 cam installed straight up on 112 ICA
Static compression ratio works out to 10.6:1.
Dynamic compression ratio is 8.1:1
Conventional thinking says you should be OK with that kind of DCR. That's getting near the top for street engine.
I would double check the chamber volume and piston deck to be sure.

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Skinny; this should be on a stock L98, do those have 5cc flat tops? I assumed larger?
I also think most 350 gaskets are 4.1 or 4.150" bore, 4.060" is a typical 305 gasket.

Either way, 10.6:1 with .065" quench on iron heads will NOT work IMHO. It'll knock when you load the engine. I'd use a shim gasket to get better quench, and open up the chambers to deshroud the valve, and/or to get down to 10.3:1 or so.

Re: compression ratio
 

I can't recall if my L98 had dished pitons. I think that the dish is more than 5cc too however I used that number as a reference.
Head gaskets do come with 4.150 bores. Again I used 4.060 as a reference mostly because that's what I'm using.
Changing either if those values will produce a LOWER SCR which makes things a little more pump gas friendly.
I agree on your quench analysis. .065 is about .025 too much and that can result in some problems with detonation however he is limited to the stock deck height (which should measured) and a thicker gasket to try and keep the compression down.
As far a 10.6 being too much SCR. I'd have to disagree solely because it's the DCR that determines how the engine will behave. The ZZ4 cam, although not large, will bleed off some of the static compression and allow the engine to run on premium fuel.
As for the heads, I'm no expert on the 601's. There's a lot of work to do to bring them up to what you can get in the aftermarket or GMPP. If he goes so far as to install larger valves and have the chambers fly cut to unshroud them, he's well on his way to buying something better. However, we all have a budget to work with and working with what you have is the cheapest way to start.
I like your idea about about a thinner gasket (with larger combustion chambers) however I'm in favour of composition over shim unless your shim gaskets don't require retorquing.

Re: compression ratio
 

I think most shim gaskets (ie factory style steel) never require retorquing.
I'm not thinking so much about a larger bore&shorter height gasket, just the shorter height. I'd rather have better quench and .2 or so more SCR than terribly quench and slightly lower CR. It tends to be better as far as detonation goes this way.

You're right WRT to DCR, but DCR is so hazy that it's kinda hard to put much faith into it. Cylinder head material, quench, ambient temperature (CAI or hot air intake) and altitude tend to do more for me than DCR. Just a few :2cents: right there.

Fly cut just refers to surface milling. You can't use a fly cutter to plunge cut, ie deshroud valves. :)

In other words, I think we all agree using his 601 heads, 'as cast' isn't too wise. Bigger valves, porting, bowl work, and some chamber deshrouding will basically finish up the job. CC a few chambers when you're done deshrouding to get a ballpark.

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The shim gaskets I'm familiar with require retorquing however my experience is a little dated.
I used the 4.060 gasket bore because I have the data handy. The difference between 4.060 and 4.166 is about a 1/2 a point. I agree with you on the quench issue. I went out of my way to get my quench to around 40 thou.
I put a lot of stock in DCR. I have personally witnessed 14:1 SCR engines run on pump gas. The massive camshafts allow (and require) high SCR. However, like you state, things like temperature (intake air, coolant and oil) have to be carefully monitored. Keep in mind that these are drag race engines but the same principles can (and should) be used for a streetable engine. 10.6:1 and a ZZ4 cam will work.
601 heads? After the new valves and valve job (pay a machine shop) and the time spent with a die grinder (although the labour is free) you've almost paid for set of heads that ready to go with better specs. There must be a few Vortec heads out there that are economicaly priced.
Incidentaly, I've seen chamber work done with a mill that unshrouded the valves along the chamber wall and I thought it was referred to as fly cutting.

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Fly cutting is a big disc with many indexable cutters on it. Typically they can only cut from the sides, not on the bottom of the cutters. So you can't plunge cut.

Yea, I guess with a wild enough cam you could get away with 14:1, but it gets so dicey up there. Mainly in that they aren't/can't load the engine at low RPM so detonation is avoided.

If you are putting a decent amount of coin into the 305 heads, it gets harder to justify. I only paid $300 for the work done to mine I think, and at the time I couldn't find Vortec heads for that price.

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It was the cutting at the sides that I was checking out. Carved the bowl out to a scribed gasket matching line. No plunge cutting.
David Vizard has spent a lot a time reworking cylinder heads so although I'd rather buy ready to go heads, there is certainly value in making what you need.
It will be interesting to see what vipershark comes up with.

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L98's had either 7cc flat top or 12 cc dished. 90+ L98s or corvette L98s were the 7cc flats

my 89 has 12cc dish so with a 64cc head, pistons .025 in the hole, with .015 factory shim gasket, i get 9.3 to 1 compression


i dont know anything on 601 heads. You'll need to know how far milled they are. if they are 56cc-58 cc and your using a 12cc dish, you will be looking at 10.1-10.3 to 1, which is doable. ZZ4 is mild tho. i dont know the valve events on that cam to get what the DCR will be but i think it will be in the low mid 8 region which is pump gas friendly with a good tune

so you really need to know what your heads CC at to figure out what your gonna beable to do with this motor. too high compression with that small cam wont work well with iron heads.

Re: compression ratio
 

This hydraulic roller tappet is used on the 5.7-liter H.O. 350 ZZ3 & 4 engines. The duration at lash point in degrees (intake/exhaust) is 275/280; duration at .050" tappet lift (intake/exhaust) is 208/221; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 474/501. Valve lash is zero/zero and lobe centerline is 112 degrees. ( Courtesy of General Motors Corporation )
http://www.gmpartsdirect.com

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sweet i always wanted to know the advertised specs on that cam for my DD2003

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Hey Viper

Just curious to see what you've worked out. We sort of jacked your thread for a bit. Hope the info was somewhat useful.

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o sorry i have been having troubles with my internet lately so i havent been here. but anyways i havent put anything together yet im just sitting on it for now because im lazy.