It's one tool in the tool box Johnny, that's all. It's not meant to be the all inclusive be all answer, just an understanding of how cam timing can affect the actual running compression of an engine, and how that influences octane requirement and power production. Lots of other variables to how well an engine runs for it's intended purpose. Valve size influences flow, another factor in power production. Things like prevailing atmospheric pressure, temperature, humidity all effect actual cylinder pressure, but once the engine is built, and the cam is installed, the DCR is set. I was just trying to answer Brian's latest question.
For sure shoot for 10:1 compression or even 10.5:1 with that 290 cam.... Or stick with 9:1 and use a TA212.
i just did a build of my 350 i brought the compression up to 10:1 put stage 1 valve springs in the 290 cam and alot of time i still have all the part numbers for the whole number if you are intrested. I didnt have a lot of cash so i uilt it the best bang for the buck let me know and i will email you a list of all the parts i used
Octane rating will usually be dependent on altitude--the lower altitude areas have 93 octane (east coast) and higher up like Denver will be 91. Don't know about CA's altitude but they may just limit it for emissions purposes. 10.5:1 gives the ideal compression for that cam, but if you want to play it on the safe side shoot for 10 or 10.25. Remember these figures are for sea level. 10.5:1 with 93 octane at sea level with that cam. Higher altitudes will yield less oxygen in the air so it needs less octane, and also reduces power. Compression doesn't have to be spot-on perfect, just bump it up to as close to 10:1 as you can get it and you'll be much happier with the engine's performance. A smaller cam would need less compression to achieve the optimum dynamic compression ratio. The reason that cam needs higher compression is because the intake lobe has more duration, so it will open sooner and close later. It will close after the piston is coming up for compression stroke, so the actual usable compression (dynamic compression) is significantly less than the measured compression from bottom dead center (bdc) to top dead center (tdc). In order to raise dynamic compression, you have to either increase the static (bdc-tdc) or decrease the intake lobe duration (smaller cam). If the DCR (dynamic compression ratio) is too low, the engine will still run, but it won't be as efficient or as powerful as it could be. You would, however, be able to burn regular grade pump gas in it (if DCR was about 6.5:1 or so). The engine would be pretty :sleep:below 2500-3000 RPM, so much so people might mistake it for a SBC.
How much can I shave the heads with a .040 gasket before I need adjustable pushrods? I'm thinking I'm going to end up with adjustable pushrods anyway I wanted to spend as little as possible but I like what I've heard about the ta 290 and would like to use it. I would have to mill the heads 070 to get the compression I need for the ta 290? ---------- Post added at 12:01 PM ---------- Previous post was at 11:58 AM ---------- Blah then that means I have to match the intake I just got.. don't really want to do that...
You need adjustable push rods. There is no way around that when you change cams. If you can't up the compression sufficiently, use the smaller cam. I know you want to do everything at once and get big performance, but you will be disappointed when you lose all that bottom end. Over camming is the #1 mistake made when building an engine. Bigger is not always better, and a rumpity idle is useless if the car can't get out of it's own way on the street.
I have to chime in on my setup now, I run the same cam in my SBB and I have the mildly ported heads and oversize valves and tuned q-jet. My pistons were advertised to be 10:1 but I ended up with around 6.5 dynamic and 8.9 static with a 58cc combustion chamber and .047 head gasket. While it does run well it is lacking in the low rpm 'tire shredding' range that I wish it had. The upper rpm range while passing at speed it is very responsive, and idle sounds amazing, but it lacks noticeably from a standstill. I'm currently saving for ways to bring the engine to optimum performance, to include some disassembly of my fairly fresh rebuild. I'm no expert, just trying to share that everything these guys are saying would be wrong happened to me. I'll admit its nice to run regular gas, but I really wish I would have gone about it differently.
Just buy one adjustable pushrod and use it to measure how long you need the pushrods, then get resized stock pushrod replacements from TA, who have a bunch of different sizes. You won't have to shave any off the intake, just have the intake side of the heads milled to match whatever you took off the base. It's a pain in the ass I know but it'll be worth it when it's all said and done. It's important to emphasize that getting the deck height as close to zero increases quench, which is a term used relating to the 'cooling' effect of the burn. Understanding how the fuel charge ignites and burns helps to realize the importance of quench. When the spark plug ignites the fuel/air mixture, it doesn't immediately burn all at once, it happens over time. A very short amount of time, but it still takes time. It starts out as a 'fireball' and expands as it burns the mixture. As it expands, the fuel and air that isn't burnt yet compresses due to the fireball expanding. If this unburnt fuel/air mixture reaches a pressure/heat point it will ignite under its own pressure, kind of like how a diesel burns its fuel. If this happens, it's called 'pre-ignition' and results in the spark knock you hear (like how a diesel will sound). This is harmful to a gasoline engine. The quench effect reduces the area for the unburnt mixture so there's simply not enough room to pre-ignite before the burn sequence completes. Higher octane fuel helps this because it burns slower than lower octane fuels. Too much octane and it will spit unburnt fuel out the exhaust, increasing emissions, which is probably why CA has a 91 limit on their premium. (I'm guessing) So it is important to get this combustion ideally suited with camshaft size and compression ratio to match the grade of fuel being used. To save yourself a bunch of headache, you might want to talk to TA about having a custom camshaft ground to match your combination instead of picking one of their 'off the shelf' grinds. You can have the duration matched up to the compression you end up with without too much machine work, and it can still have a lope. It will be more streetable and have better manners and vacuum at idle. A cam somewhere between the 212 and 284 maybe (custom cam is only 30 bucks more than an off the shelf cam, so why not?) For example: .455/.465 @ 1.55 lift, 220*/230* @ .050", 270*/280* advertized with 110* center line. You can tweak the numbers a bit to come up with an overlap suited to your head flow. TA can offer sound advice in this area.
Good reading right here.. http://www.v8buick.com/showthread.p...erence-between-these-two-cams-I-want-to-learn
i dont have the option of doing everything at once which i guess is a good thing. It makes me really think out my build!`so i guess its a blessing in disguise. To match my intake to the heads do i ask them to mill them the same amount? is .070 off what im going to need with 040 gaskets to get the compression i need?
I think you may be getting ahead of yourself here, lets step back. What pistons are you using? Have you purchased a camshaft yet? Either build the compression to match the cam you want to run or pick a camshaft that works with your compression. If you want to simplify the machine work and just use a TA212 cam then just mill 20 thou to make up for the thicker gasket and call it good. If you want to maximize the power then mock up the engine, measure deck height to piston depth on all 4 corners, have the block deck squared, zero decked, mill the heads 50 thou as well, and use the 294 cam. Any machine shop should be able to mill the heads and correct the intake angle so that you can use a non modified intake manifold. If a shop can not do that then take it somewhere else.
Actually you can buy of the shelf pushrods in different lengths that are right at the length you need or close enough. A lot cheaper.
the pistons im using are the stock 9:1 pistons that came in the motor, i have not purchased a cam shaft yet for this reason. the block is still at the machine shop, im having them do all of the machining and build the short block. After that im going to peice together my build as funds become available. Next thing i was going to purchase was the cam, lifters, timing set, ect. install them and then get to work on the heads. Im not getting ahead of myself my pockets wont let me! I understand that the engine is pretty much built around the cam if i can get the heads and intake in order will everything else work out for this cam? or should i really consider a different cam? ---------- Post added at 10:57 PM ---------- Previous post was at 10:15 PM ---------- Is zeroing the block a must for raising compression? if i have the heads and intake milled and matched do i have to take the block in also? The block is supposed to be finished this week so it might be a little late to zero the block now...
did you have to bore motor oversized? I have a set of standard SP pistons still on rods just clean up and put on new rings 100 shipped then you wont have to deck or mill anything and with thicker head gaskets it will bring comp down slightly for pump gas should be cheaper then all that measureing and milling
1. Zero deck the block for the reasons listed in post #28 2. DO NOT (TOUCH/ MILL) the intake it self. U will(for the lack of a better word) fubar it... 3. Only mill the heads. The intake side and the side that sits on the block. If you mill the block side have the machinist mill the intake side to match what was taken off the block side so the intake manifold fits. If you don't want to go through all the milling just get a 212 cam... Food for thought search for threads in the small block section on cams and see how many users didn't take the advise given and are disappointed with their setup. Side note...Anyone remember that guy who wanted a Thumper cam bcause his Chevy guys recommended it? :-(
wish i could have had the chance of buying those before the engine was being built.. maybe ill give them a call and see how far along they are.. is there any other cam recommendations other then the 212 i should consider? i want something a little bit more.. hows the comp cam 268?
I liked the comp 268 when I ran it in my 350 I would expect you to get in the mid-high 14s with that cam in a hi comp engine and with a well matched setup
The comp cam 268 is a 'straight pattern' cam and would work ok, but you're better off with a 'split pattern' camshaft unless you can get your int/exh flow ratio closer to 75%. For simplicity purposes, the TA 212 would probably be your best option if nothing else is done to the engine. It's similar to the comp cam 268 but is better suited for 'stockish' engines. You won't have the window rattling lope that you want, but the engine will perform better. If you insist on having a massive lope, find a cam that lopes and pray the cam doesn't wear out in 20,000 miles. It'll sound 'bad' at stoplights, but don't expect to impress anyone when you hit the gas. Heck, you won't even need to tune it properly. You'd not tell much difference in idle quality or performance below 3,000 RPM, so that's a bonus... Listen to the other guys here. I don't think I'm much use here. Best of luck to you.
alright but the only cam being recomended is the 212 for my set up? im thinking ill go ahead and raise the compression im sure that im going to want more then the ta 212, im not looking to build the engine quickly or anything so im trying to gather as much info as i can to see what i need to do.
