Thread: 327 rebuild

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Originally Posted by ecreek

no, I meant vortec head casting #'s are what I don't kno what to look for.....

Lynn gave you a link for the Vortec heads from Summit back in post #5 and clarified that you'll need the Vortec intake for them to work. As for "...will they all fit?", I'll leave that to the Chevy guys that have kept up with all of the details through the years.

First off I’m not trying to get into a pi$$ing contest with this post, but I do have a couple of pointed questions.

First off have you really measured anything or are you going off information you got off various web sites to get your information from? The reason I’m asking is you reply to the question on the real chamber volume of the 76cc heads you were looking at….. “I measured 76cc on the heads +/- 2” . I’ll admit I haven’t seen everything but on all the unmilled OE Chevy heads I have CCed over the years have always been AT LEAST 2 to 6 CCs (or more) larger than the factory claimed.

Most flat top pistons also have valve reliefs cut into them and in some cases have a bevel around the outer edge…..have you measured or gotten that volume form the piston manufacture?

Have you measured how far down in the cylinder the piston actually is at TDC or are you just assuming it’s a 0 deck height? If the piston is down that volume also needs to be included in your calculations.

If you haven’t gone to the trouble of actually taking these measurements chances are your calculations for static compression you’ve figured is going to be on the high side……which is actually good news for you. Not taking the measurements reduces you to just taking a SWAG at where you will be.

Push come to shove you can get head gaskets in various thicknesses to drop the compression. We’re currently planning on .085 compressed thickness gaskets on a numbers matching DZ 302 to get compression down a streetable level.

The same would hold true for the 327 your building (assuming your real static compression ratio is what you claim). The thicker gaskets usually play hell with the quench and will drop potential power but at least the car will be drivable. Now of course you have to figure an additional $200 for the gaskets in addition to what you pay for the heads and having them rebuilt. So in the end what have you really saved by using OE heads?


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Maybe this will help:

The L31 Vortec comes in two different casting numbers, 10239906 (#906) or 12558062 (#062). Originally, the stock #906 casting head was available in two versions. One version had an Inconel exhaust seat with single angle valve grind and was available on 1 ton trucks. The other version was the traditional three angle valve grind. Other than that, the #906 is the same as the #062 head. GM Performance Parts Bowtie Vortecs are offered in “small port” (#25534351), which has 185cc intake ports/65cc exhaust ports, or the “large port” (#25534445), which features 225cc intake ports/77cc exhaust ports. (You don't want the large port heads for a 327.) Both GM factory and GM Performance Parts Vortecs come with 1.94 intake/1.50 exhaust valves. According to the engineers at GM, “Stepping them up to 2.02 valves doesn’t help them any, so it’s not recommended. The port was designed to match the 1.94 valves. With the Vortec flow velocity, you need less spark advance to make power which is a clear indication of a more efficient burn.” Maximum valve lift on Vortec cylinder heads is .460″ to .480″. This range is due to production line machining and casting variance. It is highly recommended to check for clearance on anything over .460″ lift. Vortec heads require a Vortec style 8 bolt intake.

as to Mike P's response I thot that my decision to go with vortecs rendered all ref to cast irons moot. given that, I appreciate rumrum's info on 906's n 062's. that's what I needed to start looking in the right direction. of course I am grateful for all the excellent info rendered by all rspondents. I mention again that ime not looking for a super hi perf engine, just a pump gas runner with compression that precludes detonation burning such.

“…..as to Mike P's response I thot that my decision to go with vortecs rendered all ref to cast irons moot……”

Again, I’m not trying to get into a wizzing contest about this. The main point I’m trying to make is that to really know what your static compression ratio is going to be will require that you actually measure things.

Advertised specifications for things like chamber volume, compression height etc are often on the optimistic side and this holds true on whether the parts are OE or aftermarket.

Here is a link to an article on Vortec heads that in general you might find interesting.

Vortec Cylinder Heads

One quote you might want to take away from it however is this one.

“……While they are 'advertised' with a 64 CC chamber they can vary from 64-68 CC's in production.......”


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Originally Posted by Mike P

Push come to shove you can get head gaskets in various thicknesses to drop the compression. We’re currently planning on .085 compressed thickness gaskets on a numbers matching DZ 302 to get compression down a streetable level.

The same would hold true for the 327 your building (assuming your real static compression ratio is what you claim). The thicker gaskets usually play hell with the quench and will drop potential power but at least the car will be drivable.

Mike, this is erroneous information according to John Erb, chief engineer at Keith Black pistons. He says that a motor will detonate worse with a wider squish and lower static compression ratio than it will with a tighter squish and higher static compression ratio. Squish trumps SCR.

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how and where would I order a head gasket of a specific thickness, give or take?

Originally Posted by ecreek

how and where would I order a head gasket of a specific thickness, give or take?

Summit is one place - http://www.summitracing.com/search/p...e/head-gaskets
or JEGS is another. You can also go to your local NAPA store and get some selection, but perhaps not the more exotics.

wow I dint realize head gaskets could b so expensive. but thanks for the info. summit is well organized in presenting the variety of gaskets. Rock auto wasn't as definitive and cost me a lot of time searching. Jegs was ok but summit was way betr.

ON the heads ..the 906 heads hold up better if looking for a used vtec head the stock spring pad limits the springs to what can used i cut this to a smaller seal od and open up the spring cup no deeper or bigger on spring id i do cut back second inner step on head. it could cost $700 when all said in done for machine work to a old head casting or a newer 906 used , set of RHS are about $100 more loaded and gone this way on some and iron ealges as well as the older intake will seal up fine on port runner so any intake will fit . head s i listed are a copy of Gm vtec but a much thicker head and a intake head runner of 170 cc same as gm why wast good money on Gm casting ? seen more busted then good? so you have that in the back of your mind ? well i would long with the piss poor deck finish even if new better go to the machine shop and check deck finish o have many time cut a chevy head cast past .004 just to get to the bottom of the wave finish on the deck of the Gm head and seen were the are much like a saw tooth and work on the head gasket fire ring on cc heads never taken any had for granted . many years ago i never did this build the engine if you needed you used better gas but times have changed i CC every head on evey s engine. i build i CC them on the mill to find out were there are at many times there tell tail signs to tell if a casting been heavily milled . if the cc of the pistons is listed on a fully machine piston top i may check one piston. some custom made race stuff can be much harder to check . if i have or re working a piston i use volume sleeves were i check them for cc. i start at first ring up as there is some volume here. as the top of piston to bottom oil rail is about 030 smaller then piston bore size . if piston are not fine but the only thing i can get or customer will not pay or a time deal . for customs then i may move the chamber CC or head gasket to work . if off a cc one way or another will not matter on some builds .this way works very well to is if reworking a piston is to know the gram of pistons and cc with out wrist pin or with how ever its easier for me with out pin. then cut to weight=ccs works out to be about 2.7 grams =1cc . on a fully stock or cast dome finish tops of pitons if i am getting real close to what i feel may not run good on so/so gas i check it . stock stuff i do not spend as much time as on the race stuff. well thats not to say do not know were i want the CR . i know were i want the deck on the block and what head gasket before i start any machine up to make a cut . less there some bad twisted or low spots or need a deeper valve fly cut i stay to the build plan . i am going to know what head gasket size and cc they are.i seen many gaskets out there for stock rebuild head gaskets as much as 060 thick i stay way from cheap head gaskets . the steel plate MLS or a steel fire ring plate teflon/fiber/grafoil facing will not move on the thickness much they may be lested as .041 thick you many seen after used to 002. less. ON Cams ..i would not use a flat lifter less bone shock build. even so i would have hard time buying a Gm cam . many builds i gone to retofit roller. after i go threw all the list of things they must do for a good brake in with a hyd flat lifter cam and tell them i just can not help them if they wipe it and cam company may not help them the roller cam starts sounding good to them and if i build there engine i sell the cam lifters at cost .i do not add any more time on the build if i were to put a flat lifter cam in there engine .so i do not have to hear they wiped a cam .Gm cam and lifers sound good and have a good track record .but still can fail... so then your going to ask for help ? never tired it but would think you may get the brush off at the parts counter . so if i was going to put a flat lifter cam in any thing i would buy a horwards even if it was a bone stock mild RV cam as there max 5 year certified no fault warranty is the ony way to go i did not say much about the flat soild cams as i still used them and feel that a few small steps in prep on lifter and the EDM lifter is a good way to go but hardly use much solids most guys do not want to spend the time adjusting lifters . so most all mild stuff will see a hyd roller cam the after that a go solid roller cam setup.. Well this is how i build them and just glossd over some things other may build them different so far it,s world very good for me