I understand that my compression calculation is only a ball-park estimate, but that's how Santos & Mike at TA told me to do it. According to them, that how they setup all their higher compression street engines to run on 91 octane: 145 PSI compression approximates 9.8:1. Either way I've got nothing to loose but my time. At any rate... Anyone have the dimensions off SBB woodruff key/pin or do you know if anyone makes an offset woodruff key for a SBB? Thanks,
That compression psi is NOT very high at all! I have seen 145 psi in 80,000 mile 8:1 Buick 350s that ran all day on 85 octane.... I have seen 185 psi on fresh engines that ran fine on regular as well. Can you please post your cam card info? If you can tell us what the Inlet Valve Closes ABDC number is then we can use a calculator to figuer out what your actual static compression is rather that guessing. I was going to calculate it for you but still need the Inlet Valve Closes ABDC number from your cam. 340 specs: rod: 6.387 stroke: 3.85 bore: 3.75 Calculator: http://www.wallaceracing.com/dynamic-cr.php If you have not had the block milled or heads shaved then your static compression should not be over 10.25 so i would use that in the calculator.
Retarding your cam so the intake closes later would bleed off some of that cylinder pressure. If those 4 degrees don't make much of a difference, do the calculations with a bigger cam and see how it computes. There's always water injection.....
Thanks for the link to the calculator Sean. My bore is +0.020, the block was never decked but the heads were shaved square when they were rebuilt. My altitude is about 200 feet, and I left the Boost option blank. Here is the results... Static compression ratio of 10.25:1. Effective stroke is 3.50 inches. Your dynamic compression ratio is 9.37:1 . Your dynamic cranking pressure is 194.84 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 9.37 :1. V/P (Volume to Pressure Index) is 183 I amazed at what it says my compression is 9.37:1. Then I must have a problem elsewhere. Regarding my cam card info: Lift (w/ 1.6 rockers) .475" Duration: Intake 284*, exhaust 288*. Opens: intake 32*, exhaust 74*. Closes: intake 72*, exhaust 34*. The drawing indicates: The lobe centers are both at 110* from TDC, and have an overlap of 6.5* The exhaust opens at 45* BBDC, closes at 5* ATDC with duration of 230*. The intake opens at 1.5* BTDC, closes at 41.5* ABDC with a duration of 223*. On the top of the card there is a note that says to Degree the intake to 106* for a 4* advance. I did not degree the cam, I set it up according to the timing marks on the cam and Crank gears, straight up. Based on my compression, I don't think I'm off a tooth on the crank gear because if I was I'd be 18* (360/20teeth= 18*/tooth) off either way and that would be very noticeable... I think. If I was off one tooth on the cam gear (360/40 teeth=9*/tooth) but it rotates at half the speed... so I'm not sure how to calculate the error here? At any rate... I've done timing chains before and since I did this one on an engine stand, I'm sure it is right. I installed a set of cooler spark plugs (Champion 14 RJ12YC), the plugs I had were standard AC-Delco R43S. When I removed the AC-Delcos they were white with a very light pinkish-orange hue. But I haven't had a chance to drive the car and note any changes yet. Do you think I might be too lean? As I mentioned before, I'm tuning the carb according to Edelbrocks data sheet. I'm running the orange spring, the rod has a tip diameter of 0.037", the jet is the 0.098" (their second largest) and according to Edelbrock I'm 12% rich. I do understand that this is relative. I wounder if my carb is screwed up? Or maybe it's just bad gas?
Your dynamic compression is not 9.37, it's nowhere near that. How do you know that your static compression ratio is 10.25:1? If you are reading those specs from a book, I can tell you that in most cases, the compression is less. The only way to know for sure is to measure everything. In any case, when I use my DCR calculator with a 10:1 static compression, and the cam specs you listed, the DCR comes out to 7.8, and that is fine for pump gas. Of Course DCR is only one piece of the puzzle.
Larry, I apologize for being a neophyte about all this. This is the input info that I used for the Wallace Dynamic Compression calculator: Number of cylinders: 8 Bore: 3.77 (3.75 +0.02) Stroke: 3.85 Rod: 6.387 Static compression: 10.25:1 Intake valve closes at 41.5 ABDC Boost pressure: Altitude: 200' <FORM action=/dynamic-cr.php method=post> </FORM> <FORM action=/dynamic-cr.php method=post>And this is the results I get: Static compression ratio of 10.25:1. Effective stroke is 3.50 inches. Your dynamic compression ratio is 9.37:1 . Your dynamic cranking pressure is 194.84 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 9.37 :1. V/P (Volume to Pressure Index) is 183 I don't understand the difference between your results (7.8:1 dynamic compression) and mine 9.37:1? I have a feeling it's not as low as you think because my main issue is pinging under heavy load even after backing off the ignition timing. I also don't understand why the calculator say my cranking pressure is at 195 PSI? The rings I used are the Total-Seal conventional cast rings but have molly centers. They are suppose to be stronger then standard cast rings and seat-in just as fast as standard cast rings. I'm not sure if my rings are fully seated (after 150 miles) because I'm getting a lot of blow-by: oil leaking out the valve cover vents. </FORM>How do I know my static compression is really 10.25:1?... Because that is what I ordered from EGGE pistons, whom I always thought was reliable. I checked with a guy I know that has a Snap-on analyzer and he is going to check my A/F ratio at each tail pipe, but it may take some time before he can do it. Today I'll see if the cooler plugs make much of a difference and then I'll try re-timing it.
Drew, First, pistons do not dictate your static compression ratio. They can give you an idea, but when the motor goes together, everything should be measured. This includes how far the pistons are in the hole(this can vary quite a bit), head gasket thickness, piston dish cc's, and actual combustion chamber volume(not what is published somewhere). It is very common to use pistons that are rated for 10.2:1 compression, and end up with somewhere around 9.5:1. My point is you really don't know what your static compression is, and you really do need to know, not assume. Who did the machining, and who built the engine? They would know, and hopefully they wrote it down for you. Just the fact that your calculator predicts 195 psi cranking pressure should tell you something is not right. I use the DCR calculator that you can download at the end of this site: http://www.empirenet.com/pkelley2/DynamicCR.html. It has a SCR calculator, and it will calculate the DCR from your cams advertised duration numbers. I played with the numbers in the SCR calculator and got it to read 10:1 compression. Then I plugged in the cam specs you provided and I got 7.8:1 DCR. I think you are expecting an iron headed motor with respectable compression to run on 91 octane. That may not be possible. Before I went to Aluminum heads, my compression was 9.4:1. It would detonate on 93 octane fuel at anything over 3/4 throttle. I had to mix in a few gallons of 110 to stop it. I had .040 taken off my aluminum Stage1 SE's to make my compression 10.4:1, and it will run all day on 93 without a peep. The cam I am using is the KB 118. It has a late intake valve closing, and my DCR is 7.5:1.
Guys, It's been a while since I've updated my dilemma mainly because I'm now working again and I've spent most of July up in Portland OR. training... I'm now a Hydrogen fuel-cell service engineer. From the looks of things I'll be up here till Sept., possibly longer. Any who... I was able to measure the AFR out the tail pipe and I am running fat above 3K RPMs, as I suspected even after replacing the Carter Competition carb with an Edelbrock. Much to my disappointment the engine runs better with the Edelbrock, but she still pings. I have procured the Rollmaster double roller-timing chain setup (with the 9-way adjustable crank gear) but I just don't have the time to install it when I'm only home for the weekend every two weeks. So my next questions are... 1. Typically when a TA cam is setup with factory gears "straight up" or "Dot to dot". It's actually set up at approx +4 degrees advanced. Correct? 2. How much will my compression drop by maxing out the adjustment, another -12 degrees, to -8 degrees retarded? BTW... Just to determine where I am now, I do plan on degreeing the cam as I tear it down, it should be straight up. Thanks for the support guys,
Please post some info or a link to the show, and if it doesn't conflict with my conjugal visits home... I'll be there. Unfortunately my car will be in San Jose.
Here's the link from this site, there have been other threads too, but this is the current one. http://www.v8buick.com/showthread.php?t=185800 Here's the club's web site. This will take you right to the link for the show registration. http://www.buickclub.org/portland/ABS reg form 7-1-09.pdf I'm looking at a 50 / 50 chance of bringing my car right now. I just got the new engine in and fired today. I've got to see what's wrong with the brakes, get some seat belts, and see if it's safe to drive! I bought the car two weeks ago, got the engine home about 5:00 last sunday, pulled the old engine and got the new one in. I don't even know if the thing is going to be drivable yet since I've never taken it down the road to see how it drives yet. I will be there with or without the car though. It will be a good time either way!
