Pistons determine compression. Factory blueprint was not adhered to so a 9 to 1 engine could be as low as 8.1. And with a rebuild you have to get piston measurements and with decking heads now you need the head cc. .some Replacement Pistons are even lower in compression as they have even lower compression height and could be as low as 7.7. There also several dish sizes depending on piston used . A 10 to 1 piston can be as low as 9.2. You can look up Wallace compression calculator. You have the heads off already so do the measuring. If you get the 350 setup right you may be happy with it vs all the work to change to a 455. You will need to measure piston depth at top dead center- how far down from deck it is. Overbore size. Piston dish depth/size Head gasket thickness .
This has been discussed several times already. Because it was rated at 9:1 does not mean it is. IF your pistons are at zero deck and IF you use a .020" thick gasket and IF your chambers are about 57cc then you might have 9:1. Most likely your pistons are about .060" down the hole and you will be using .045" gasket that means you would roughly need to have cut .085" off the heads to come close to 9:1. Also will need to cut the intake to make it fit the heads. You need to do the math and measure all the parts. Low compression, big cam, single plane intake is going to be a blubbering dog below 3000. Then it will want to rev out to 6000 where your 40+ year old, or $300 pistons will let go. There is no shortcut to building reliable power. You need a sound lower end or your just fooling yourself. Auto tec makes some very nice pistons and are not that much more than the $300 junk you are considering. What you save cutting the heads and intake will help to offset the cost. Also if you were to build a 455 this would be needed on that engine as well.
Well after a LOT of thought. I decided I will keep the original motor with the car. Still gonna try to hone and re-ring then redirect efforts/$$ to the heads. (We'll see how that works out). Stage 1 valves? Deck the heads? Port match? Smoothen out and polish intake runners?
Valve seats and bowl area. Work from there as needed, the idea is to maintain airspeed. I don't jump up valve sizes right away. Depends on wear or overall goals. Buicks have well engineered heads. Check out the search function for sbb head work here. Get some info from the machinist before you commit to a direction.
Good advice Steve, though I would like to point out that compression rating was indeed 'advertised' and not the same, but it wasn't considered to be zero deck when they rated it. Extra meat was added to the deck which was what really lowered it vs advertised. They considered it to be sitting somewhere below deck, plus the gasket, to get their advertised compression. Some examples: a .030 over piston sitting at .070 below deck, .045 gasket (3.9 gasket bore) , 58 cc heads, and a 24 cc dish comes out to around 8:1 true static. Shave deck down to .035, heads to 55 cc, and use the "10:1" pistons (10 cc dish) and compression comes out to a true 10:1 static. The deck doesn't have to be zero'ed, especially when considering the Buick 350's open, small combustion chamber. Zero'ing the deck will net you jack without a quench platform. You don't have to have forged pistons to rev to 6 grand either, though repeated, harsh, racing conditions with unknown detonation threshold would warrant such slugs to be on the safe side. Either way, going hypers is a huge risk when the aforementioned is considered, where normal eutectic pistons would be desired over those (even TA warns against them). Remembering that valve notches can often create hot spots and encourage detonation, particularly with an open chamber design with no quench to help offset it. There is much to be said for combustion chamber prep, polish, and hotspot removal. But yeah don't want to get into that debate again...I can't speak out against the unwarranted use of forged pistons without getting into some serious heat! Besides, I'm actually in agreement with you on the pistons for this particular application. :TU: Gary
Bowl work is where most of it is. Keep runners intact for the most part (no port match needed). Contour throat, valve guide area, and smooth over casting imperfections throughout. Leave intake runners/bowl textured, but polish the exhaust runners/bowls. Unless you plan on some major port work, leave stock valves intact. Shave heads for a trued up surface and some increase in compression. Remember the more you take off, the more that will have to be taken off the intake side too so the intake manifold will fit as the heads go closer to the block, which can lift the intake above proper runner alignment. Polishing the combustion chambers is a good idea too. Remember to work with the engineering intent, not against it, and you'll be fine. Measure how far down your pistons sit, cc the dishes and head chambers, and math out your static compression. You can shave off quite a bit from your heads to bump it up to a better ratio. This will also help you know where to put your cam's ICL for better dynamic. A little time spent here and now will save you a whole lot of headache and potential disappointment later on. Gary
Not to differ in opinion, but If you don't want to put a zillion hours into the heads don't do any polishing or smoothing. Not much to gain for time spent there (esp. for stockish engine). Some prefer the rough surfaces left by the sand casting in the chamber, most head guys prefer finish left by cutter/stone in the runner. Just remove sharp edges around the chamber only and any obvious gobs of iron that don't seem to belong. A way around the cost of milling the intake side of the head is to raise the port opening with your carbide, as long as it bolts up OK. Ignore mismatch at bottom. Most gains are near the valve seat. It will dramatically change your engine's potential. Larger valve isn't really needed until you maximize the port, and you are a long ways away.
I agree that you don't need to spend a lot of time porting and polishing. Contour and reshape valve guide hump. A lot of metal there that is just wasted space.clean up port up to valve opening. Not including pulling and replacing valve you only need to spend 30-45 minutes per port. But bigger valves with some porting can easily get you up to 245 flow on intake which is 25% more flow which will absolutely show improvement in power.
^^ Agreed! In the interests of preserving his $1000 budget though, I wouldn't enlarge the valve unless replacement was needed, along with excessive seat wear. Then it's a no brainer because the machinist is starting with "fresh metal" and can easier control the seat heights, obviously important on a shafted rocker engine. It can be apples vs. oranges... Installing bigger valves doesn't always equal improvement. Not starting a sxxx-storm here, but... I see a lot of heads with bigger valves that have the seat cut to contact the middle of the valve's sealing angle, rather than towards the outside edge. (Even worse... sealing on the inside edge of the valve, lol) Putting a smaller valve in for a trip to the flowbench shows a gain, because the valve itself is in the way. It doesn't need more than a couple thou OD more than the seat (for flowing purposes). The increased curtain area from using a bigger valve assumes that the throat maintains proportion to the valve OD (gets bigger with the valve). I'm noting this because most bargain priced VJ's do not watch this real closely. They cut it much smaller for wear, and it's much easier on them. Getting 245 CFM requires experience and commitment. Not needed and possibly out of reach for a mild build effort and re-ring job. It would go like crazy though! You would have close to 500 hp worth of flow potential. Then your single plane would shine...and then forget your budget.
Polishing is probably the most forgiving activity you could perform on a head with little risk of over-doing it (and it doesn't have to be shined to a perfect sheen in order to be effective). It doesn't take THAT much more time to do the exhaust runners and combustion chambers, so this is personal preference here on my part. It depends on how much time you want to invest into it and when you can call it 'good enough'. Is it absolutely necessary? Obviously not. But it will help the exhaust move and reduce detonation potential. For the OP's purposes though, I'll agree that it wont' show as much gain vs time invested, and isn't as necessary. As I said earlier, most of it will be in the bowls/seats/contouring to smooth airflow transitions. Thanks to all for their contributions! Good stuff here. Gary
:grin: I wonder how many others simply run the tooling around places like exhaust ports and chambers to rid them of any carbon that made it past cleaning?
Took everything to my machinist and after looking at the scratches he insists that everything is fine and to not worry about the scratches. He said he is only concerned about one scratch and that one scratch wont hurt anything. But being the person that I am...I'm going to disassemble, hone and re-ring anyway. He also disassembled my heads for me...damn $7 spring compressor I bought from O'rielly's isn't worth crap. He has an air powered spring compressor and had both heads apart in less than a minute...would've taken me an hour! lol Stopped by Harbor Freight to buy a carbide burr kit...no luck. Guess I'll have to buy a porting kit from Eastwood. I don't imagine Lowes or Home Depot or Sears sells them, huh?
Harbor freight will have a polish kit with sanding rolls and arbor and the have a small grinding stone kit. Sears will have some shorter carbide bits in a kit and grinding stone kit. 2 kits one of each will get some work started. Don't worry about the runner. You can do some clean up and polish in runner but that's all you need there for starters. Maybe Sean or someone else can post or send you the Jim Burek magazine article on porting these heads.
Just read the article....so eliminate all sharp angles from valve guide and polish everything else. I'll try to take my time and do 2 ports per day. I'll post pics :TU:
