I’m planning on getting a block zero decked for flat top pistons and use the head gaskets at .041 compressed height for quench. If memory serves with 75 cc heads I’ll be around 9.4 CR. It’s a 350 Chevy that will be .030 over. I’ll have the shop use standard pin height pistons. So should be an “average” of removing .025 off the block. I don’t have experience in this, so am turning to those who know. Thanks.
I'd consider decking the block enough to square it (figure .010-.015"? if using a fixture), then use shim gaskets....but I'm kind of lazy like that. I don't like making extra problems for myself.
Mike, it depends on the pistons. If you're using cheap "rebuilder" pistons , they are further down the hole [by approx 20 to 30 thou] I sliced 50 thou off my 283 block to get the pistons 5 thou above deck.[I was fully prepared to face the manifold] When I dropped the manifold on all the ports lined up, but I could barely get a feeler gauge under the end rails.[which is a good thing because I prefer a bead of sealer there] But I did need to slot the bolt holes, but this was only a minor amount! So I used a cordless drill to up the holes to the nearest "metric" size. El Cheapo intake gaskets have more crush which makes it easier, Also check the dizzy to see if it doesn't bottom out [I needed a spacer for my BBC] I prefer decking the block [if the engine is already apart] over specialty gaskets. This makes it easier for us in remote parts of the world to get gaskets. Decking also gets better CC gains than milling the same off the head. BUT ONE CAVEAT .........You need to dummy ***emble the short-block to get the measurements
Thanks Kerry, I did see Summit lists standard pin height flattops, that’s what I’m going to tell the shop I want. I think it was the FelPro 1010 gasket that had the .041 compressed height that would put me in the 9.3/4 CR range I want with the 75 cc heads I’m going to use. That’s ***uming standard pin location.
Deck it, so the pistons are 10 thou above. This gives the engine a 31 thou quench [and will reduce detonation] You will need to ***emble and re-measure everything. If you're paying somebody else to ***emble it [twice]......... it can be cheaper to throw some old L98 [C4 Corvette] heads on it instead. [Not HAMB friendly though]
Well....it just seems to me that whacking more than that off the block is a strange thing to do to fix a problem with how the pistons are made. Once you take it off the block, then it's gone forever. I kind of like to keep as much original metal on old parts as I can. But then I also don't try to chase that last 1% of performance out of an engine that's never going to be used for cl*** racing, and wouldn't have been compe***ive, anyways. If you want to cut that much off the block, go for it. As long as you are prepared to deal with all the stuff that needs to be done, it should work just fine.
Over 20 years ago have Zero decked a .030 over 350 with flat top pistons, used .041 compressed head gaskets and Vortec heads, have run two different intakes, a Edelbrock Super Vortec intake and now have a lower rise Summit square bore intake on it because need room for the lower hood clearance on my 64 Chevelle. Installed Fel-Pro 1/8 thick intake gaskets both times without any problems, this engine still runs strong for what it is and plan on running it down the 1/4 mile this weekend at the Ghost Rods vintage drags
Are the heads already at the 75cc’s? If you have to surface them to get to the 75cc’s you will need to take that into consideration also.
What about the .026" .028"thick composite gaskets that are available? They've been circle track racer friendly for years now, GM Performance even sells a version. Victor-Reinz , Mahle/Clevite Originals #5746. Stainless and graphite core coated composite. 4.100" bore x .026" compressed This way you only cut the deck roughly .010" to get 9.015" block height and still end up with .040" piston-to-head (quench clearance). Leaves the block deck surface a good bit stronger and resistant to warping or cracking..
I have a set of .026 Mahles, but there’s other factors here. The CR I am shooting for, and which heads to use (65 or 75 cc) to get me where I want to be.
Zero deck the block and use an .041" thick gasket or leave the piston .015" down and use a .026" thick gasket doesn't matter either way.....compression ratio is the same for either way using the same head chamber on both combinations. Maybe a pinch higher with the .015" down and .026" gasket combo because the cylinder bore is a good bit smaller than the Fel-Pro gasket bore diameter. Quick run through a calculator shows 9.25:1 with a 75cc head.
You seem to be really hung up on some numbers. 75cc, 9.3 to 9.4 cr, worried about a .015 diffence in head gasket thickness. Also wanting to cut a block down to get pistons to fit to achieve a specific static compression ratio that .015 will somehow **** up. I guess if you willing to do all the extra work and deal with the headaches.
I’m not sure what you think I’m hung up on? Read my question at the top, my concern was intake alignment issues. I haven’t called the head manufacturer directly yet, but they recommend the Felpro gasket I mentioned. Hence my initial question. I never said anything about .015 thickness ****ing anything up, nor did I mention it would. I understand what @Ericnova72 said as plain as day. Of the head I want to run and the targeted CR I want, using the recommended gasket would require me to have the block zero decked. If the manufacturer says a the Mahles I have will be fine, I can adjust my request to the machine shop.
Zero decking a block is no speed secret so I wouldn't go about it that way either. As Jim said..Square the deck. Mock it up .Measure the deck on the corners..CC the heads yourself. Don't forget the valve notch c.c's are basically added to the chamber size. Then figure out what gasket to get to your sought after 9.5 c.r.. That all being said.. Any time you cut a SBC head or deck , the heads get closer together. You need to take 40% of the total removed, off the intake side or intake manifold. Also you want to take some off the China walls of the block too. Your block mill operator will know how much. Will the intake line up without doing the milling? It might. Might not. You'll find out Seems to me , you're relying too much on someone else's numbers. You could end up with , God forbid , 9.3 or 9.7 c/r
Let’s put a few things to rest, besides my initial request, I reiterated it again, yet for the life of me, a few keep thinking that I’m after a specific target in CR. Now I’ll say it for the third time, all I asked was (read above if anyone cares to) “If I have an average of .025 taken off the block, will it affect intake alignment.” Regarding the heads CC size, if they don’t come in as specified, the company will need a new piece of CNC equipment, or a better programmer, ect. I guess since I mentioned “9.3/4 range” that’s now been turned into 9.357382:1 specifically? Carry on.
Pretty sure I answered your original question above^^ Correction ..You did say 9.4 not 9.5, which is a common target for pump gas engines.
Depends on the amount of material on the heads and if the bolt holes were drill right to start with. Having the ports misaligned will kill all the power you just worked so hard to gain, and without locating pins to check with, you will never know how close they are. With it bolted together, drill a 1/16" hole down through the intake, gasket, and into the head, then use a 1/16" roll pin to align the gasket to each face once you take it back apart. You will quickly see if the ports are aligned.
Let me clarify a bit here. You never said whether the heads were new castings with all the original GM specs for the distance from the deck up to the intake bolt holes..Or whether someone redid a valve and milled them a bunch for c.c.s. If it's the former, then taking .025 off the block would mean theoretically taking about .010 off the intake sides. In that case, hardly worth doing on new , clean castings, and the intake will probably be close enough. I know that's what you wanted to hear, so there you go. ;-)
Everyone needs to remember the engine originally came with steel shim gaskets... so by installing a .041 head gasket and decking the block I dont forsee any intake issues.
You don't need to apologize for wanting whatever CR you choose to want. Given todays gas prices, if someone wants to build a vehicle that they can drive regularly, making the engine friendly to regular grade gas is a good idea. It is important to get the quench correct. I would not rely on the machine shop to order you the correct parts. I'd take an existing piston and rod and measure the distance from the top of the piston to the inside of the rod bearing. Stand the piston on its head and let the rod stick up perpendicular. Then get a reading on the bearing surface at the center of the rod. Mic the crank (might be undersize). Allow .001/.002 for bearing clearance. That gives you a piston/rod ***y that you can use as a standard. Place it in each corner cylinder and measure if it is down in the cylinder or level with the deck when at TDC. Then add your heads cc, the compressed gasket cc, and the cc of the valve reliefs if any. Use the volume of the bore + the volume of the combustion chamber as TOTAL volume. Divide Total by the combustion chamber volume you came up with. That would be your compression ratio with a ZERO DECK piston. Now calculate the volume of the cylinder with .005 depth. Add that to your combustion chamber volume and divide into TOTAL Volume. and see how much your compression ratio changes. Double the volume (.010 depth) and do it again. Then .015 and .020 till you get the CR you want. Then order pistons that give you the zero deck or below deck that you want. If you decide to deck the engine, you can also see just how much it will change with each deck change. I would get my numbers correct and check the dimensions myself before going to any shop and just trusting they know what will be correct.
Don't forget about the push rod length and rocker arm geometry, they will need to be checked pretty closely.
Well I might be thinking wrong, but let’s say all things being equal, I need a PR .025 different than stock length. Pushrods come in 1/16th increments, so I am fairly sure I’ll be okay but will check it anyways as the cam will have about .040 more lift than stock did.
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