With a true 8.8:1 SCR, the Federal Mogul cam will have 6.71:1 DCR, good for 89 octane 'plus' grade pump gas. The Crower level 3 cam will have 6.98:1 DCR, so using the 89 'plus' gas is still feasible as long as the combustion chamber is polished and there's no hot spots or excessive timing advance. Otherwise, crank up the advance and pump premium in it and it'll run just fine. It's pretty much all about the grade of fuel you want to use. To get the most out of your premium, you'll have to up the SCR a bit. If you want to get away with 87 regular, drop the SCR to 8.5:1 with the combustion chambers polished and use the Federal Mogul cam. For the Crower level 3, SCR will need to be around 8.25:1 and polished chambers to be safe on 87 octane. Obviously, power will drop by doing this, but you get to use cheaper fuel. From what I've seen, premium tends to be from 30c to 45c (depending on gas station and octane (92 or 93 here in Tennessee) per gallon more than regular. Plus is around 15c-20c more. Calculate gas mileage, application of vehicle, and frequency of use to get desired results. Gary
With 7.3:1 SCR, DCR with the Crower level 3 cam will be 5.83:1. Shaving .030 off the heads will net about .75:1 SCR increase. This does not add up to 9.4:1 unless other things are done. Shaving .030 off will put SCR to just over 8:1, which will be still good for use on 87 regular pump gas, and will have way more power than the pathetic compression it has now. No wonder the engine doesn't have many miles on it. :eek2: The engine no doubt had more power from the factory with its higher CH pistons and better camshaft. Rebuilding with lower CH pistons on this sort of deck height castrated the compression ratio, and the camshaft choice only exacerbated the problem. Gary
Gary,you missed the last line. Going with Autotech pistons. they have a higher comp height (1.85) and smaller dish (14cc). Thats how I got to the 9.4. Also .030 over with .045 thick gasket with 3.9" bore ID.
That's good info Gary . but fuel isn't my concern as I want to race it. Just looking to see if engine will be strong with this combo.
It would be strong, but stronger with compression bumped up so you get the most out of your premium fuel. Gary
Gary. You say dcr will be about 6.98 for the setup I'm hoping things come out to. What would your guess be for cc of a head with .060 shaved off. I don't want to go much more . also if there a chart on dcr vs power/ torque? 7 to one is decent to make healthy power? I know 7.5 would be better.
Too many variables for a DCR to power chart, though I remember seeing a chart for a percentage of power change for SCR. I don't have it though, because it didn't look accurate. For every .020 shaved off, you get about .5 (static) compression points. I think it came to about 5 cc per .020? Someone may be able to clarify this for me. So that would be about 43cc (15 cc from 58ish on a stock head) if that's correct. Sure 7:1 DCR is ok. You'll be able to advance the timing more, as well as use freer flowing heads with more scavenging. With the Crower level 3 though, you may want to bump comp some to get more out of your premium. It'll still be fine with 7 DCR though power-wise. Just advance the timing more. The '68 350 2v with "9:1" compression was probably closer to 8:1 actual, and I could put Aamoco Ultimate in it (93 octane) and advance the ignition so far that the engine wouldn't even start, then back it down so that it would start after a few slowed turns with the fuel igniting before TDC so bad it tried to send it in the other direction...and it never detonated off this. I couldn't advance the 4v engine quite this far on 93 octane, and it had almost 9.7:1 (actual) SCR which means its DCR was well over 7:1. Closer to 7.25-7.33 or so. If you could get the comp to 9:1 (actual) or more with the Crower level 3, you'll be better off. Otherwise, you're wasting the octane. In short, you can get away with 89 octane 'plus' if you back timing down, or advance the hell out of it and pump in premium. What's the octane rating up there for premium? 91 should be plenty. Any more than that is overkill, though you could look at it as a 'safety net' for extreme conditions for your application. Performance wise, it should run good. It's hard to go wrong with the Crower level 3 cam for a noticeable increase in power over stock, though I'm not normally an advocate of larger cams for flat tappet applications if you expect to get any sort of miles out of the engine, but for a weekend toy, sure why not? Another choice for this application would be the TA 212-350. Comparing these two cams to the stock Federal Mogul cam, the Crower cam produces a little more power, with an increase of torque as well. The TA cam's torque stays about the same as stock, but puts it higher in the power band. Same with hp. TA cam gives more hp though, and for an engine with less than ideal DCR, this is an excellent cam choice (I have to side with Sean on this one), for reasons I gave earlier and on another thread concerning effective compression. This is also why the stock Federal Mogul cam is an excellent choice for engines with less than perfect DCR, and turns on even better when the DCR IS ideal. This cam goes about it in a bit of a different way though (asymmetric lobe design and wider gap between .006 and .050), but both the Federal Mogul cam and the TA 212-350 use airflow dynamics to take advantage of whatever airflow they can get their hands on. Gary
Andy, don't forget you have another block at Dave's shop that we can machine up for you to transfer the parts from that block so you can get the compression you want by having the block decked instead of milling the crap out of the heads. You even have another stroker crank over there that if you wanted to use that we could make that happen with a set of AutoTecs and your other set of take outs maybe? That way if you wanted to use those heads for something else the chambers won't be useless because after milling them they're way to small for anything but the crappy stock big dished pistons that are deep in the hole. Like how small the chambers were on the heads you brought out and they were probably only cleanup cut before. Dealers choice, but 10:1 with a quench ring would be better than 9:1 without one. Derek
I realize anything that even comes close to resembling something *gasp* stock is considered total garbage by many (then why use the Buick 350 in the first place?), but to claim that a simple quench ring (not total quench) for a small, open chambered head like the Buick 350 will make up for a whole compression point worth is just plain misleading and false. Besides, until you can get those aluminum heads (which may or may not be closed chamber), you're stuck with either an open chamber or some extra machine work to grind up into them to create a quench area for the piston to use, which will have to sit *above* deck to fully utilize...your precious forged pistons will STILL have a dish in them, just not quite so big, and with several hot spots machined into them. lol
Derek. Not in a hurry to build another engine. Carrie and my daughter need something to learn on and I'm just experimenting with a used engine and trans and spare parts. Gary,I believe your thoughts on no advantages of the quench ring may be slightly misguided. The dish is similar in size to the chamber in head. Much like how pro pistons have a partial dish to match chamber in head. If more combustion happens in dish and not against cylinder wall the force is more applied to the moving part(piston) vs non moving part(cylinder wall) . so I do believe there are gains to be had. (ie hershe built 9 to1 that produced 470 wheel standing HP). Granted this is how I perceive the internal reaction but I do believe it has merit. I believe if you take away most of the .090 piston depth and maybe some of the .043 gasket bore area it can improve combustion force to be focused directly to piston.
I never said there were no advantages. I said that to claim that it makes up for an entire compression point is false. Which is true. There's pros and cons to each. Did you know that a small, open chamber design (like the Buick 350) has advantages over a closed chamber design? Such as flame travel and exhaust evacuation, to name two. With the smaller combustion design, the Buick 350 isn't as crippled as larger chambered engines such as the big block Buicks or Chevys. There's also debates about how putting the total combustion closer to the crank as being beneficial as opposed to farther up in the head, which is what you'd have with larger dishes and smaller head chambers. You'd be able to zero the deck with larger dished pistons, so the combustion against cylinder wall argument goes bye-bye. Not saying it's 100% better, but there's pros and cons to each, like I said. The Buick 350 never came with a closed chamber design, so comparing it to SBCs is like comparing apples to oranges when considering the different combustion designs and the bore/stroke ratios. Did you know that longer barrels on guns produce better projectile velocity? The sides of the barrel doesn't seem to impede the outward force of the projectile. It does, in fact, help it gain extra velocity because the powder has more time to burn instead of getting blown out the barrel after the bullet leaves. My main point here is that cylinder walls do not hamper the downward force of the piston. If that were true, then the piston top itself would hamper it, as would the heads themselves. Everything is contained nice and neat, and the path of least resistance is taken. Gary
How do you suppose he ended up with such low compression? Quench platforms and closed chamber heads, or the stock, open chamber design and deep dishes? And look at how well it performed. Gary
The problem here is (as I've always said) that people try to apply tried and true knowledge/experience with other engines (i.e., sbc) to the Buick 350 and then wonder why it doesn't outperform a sbc with only 395 hp and 370 ft. lbs... Then someone builds one that works with (instead of against) the existing engineering and ends up with 470 hp and 450+ ft. lbs. Maybe there's something to all this 'stock' engineered junk afterall? Gary
Possible. But super stock is limited to factory style pistons and combustion chamber sizes with factory size valves. But take away piston depth on a stock type piston you get about 9 to 1. It may not be the quench that is helping but if the burn has no space other then the piston dish to burn in piston moves sooner as fuel burns since there is less space for force to apply. Just my thought
Sorry Gary, I should of wrote with the Crower level 3 cam that 10:1 with a quench ring would be better than 9:1 without one(that's what I meant). It is still better to deck the block than it is to mill the heads, unless the piston is already zero decked and more compression is still wanted. And I respectfully disagree with you, even though the sbb 350 heads are open chamber heads the chambers are still quite small and the .400" wide or so of piston top that's left before the dish goes down to its dish depth, that ring at the top of the piston can act as the quench area if its in the quench zone thickness of .035" to .045". Its not an ideal quench area but its not nothing and when building for that every little bit extra that every little bit counts. Even when using stock pistons blueprinting the engine block to the original factory specs will net more HP and torque closer to the factory ratings. The block at the shop deck is about .030" higher than the factory spec, just by correcting that would net over .5 of an compression point. But while its set up why not take it down a bit more and put the top of the piston exactly where you want it to maximize VE with the cam choice with the compression ratio with the grade of fuel that one wants to run, in other words why compromise while its there anyway. And as for the "precious forged pistons", better rings with a whole lot less drag can be used with those that unlocks even more HP and torque, plus they're lighter than the factory pistons. Plus using those pistons the compression distance is customizable for less machining of the deck and so is the dish volume. Not at all worried about any "hot spots" with those pistons they are very well designed and machined, they are forged so they're more durable if the engine isn't tuned properly or a bad tank of fuel gets in there that causes detonation. One of the choices I gave him was honing the block without boring it so he could transfer the factory pistons and crank from the other engine block if that's what he wants to do. That way the block can be decked to get better compression instead of shaving the crap out of the heads and still having crappy compression. And the oil mods can also be done to the block as well if he's going to race it a lot those are good mods to have done. The worst part about that is cleaning all the pieces to go in the freshly cleaned block. The good thing is that the oil mods are there and it gets new rings and main bearings, cam bearings, new gaskets and maybe some nice new shiny bolts with a nice new paint job. "060" off of the block would net more compression than .060" off of the heads, just sayin.(probably up to about .3 more) And if the piston isn't zero decked after .060" taken off then more can be removed up to .090" if the starting point is plus .030" of the factory spec. New pushrod length you say, well with the heads shaved and a valve job he would need those anyway. FYI I NEVER said a stock sbb 350 was garbage, I simply offered some advice while he was taking it apart and making it not stock anymore anyway. Just gave him some choices with the extra parts he has over here is all in case he forgot he had them. Derek
Fair enough. Keep in mind though, there's a whole lot more done to it than simply zero'ing the deck to eliminate cylinder wall exposure. That may have little if any effect on its overall performance when compared to the rest of what's been done, which is essentially keeping the combustion chamber stock. The original engineering is retained. No quench. No huge valves. No closed chamber head design...but hey just think how much better it could have been if he'd only have butchered it up and milked a pinch of quench out of it and added some oblong, hot-spot-laden chunks of forged aluminum to get 10:1, right? I mean, chevy does it so it must be good, right? I read all over the place how people complain about chevy's combustion chamber design, and that quench is the only saving grace that makes it even halfways worthwhile. Chevy NEEDS quench to even compete, as does all larger chamber designs. Then comes this little open chamber head design of the Buick 350 and people scratch their heads as to why it does so well. Figure it out folks. It's the stock design that did so well from the factory (even in its thrown-together, non-blueprinted, assembly line state) that made people want to put larger components inside it to see how well it would do with more stuff done to it, only there was nothing to go on other than knowledge from other engines. Now there's more and more information and experience coming in from people who took a different path, and the results are truly impressive. Gary
Yes yes, we know. You're not disagreeing with me, whether you realize it or not. That tiny quench ring amounts to very little in the way of reducing detonation when the combustion chamber design is pretty much already doing the work for you, providing you remove hot spots instead of adding them. Nothing is gained when you add a quench ring and then add hot spots; quite the contrary in fact. You WILL end up with hot spots (or at least 'warm' spots) with thinner metal resulting from valve reliefs...there's no way around it. It's thermodynamics. Letting the piston sit lower in the hole will eliminate the need for reliefs, which will offset the 'quench' gained from the ring around the dish by allowing the compression to remain about the same, if not higher, than bringing things closer and then putting hotspots in it. You can disagree with that though if you like :grin: Gary
Ok I disagree then because if the cam lift isn't that high and the block is decked to bring a stock piston higher in the bore then you're basically saying I'm right. Well as good as it gets from you anyway. LOL Derek
Yes Gary hershe got some really good"tricks" on his engine builds. I do feel the if there is less volume for combustion the piston moves sooner and faster movement as you don't loose force in that .090 of piston depth. Its got to have an advantage in theory. Would like to know what else they do to get that kind of power.
