I once had an 1984 Z28 with the HO 305 that I purchased from the original owner. He changed oil every 2500 miles and had accrued 115,000 miles on the Camaro by the time I bought it. I did a compression test while doing a full tune up on the car and the readings shocked me. 180-195 psi on all cylinders. I suspected maybe a little carbon buildup on the pistons but the car never knocked or pinged. Ran fantastic for a 305.
That's interesting, wow, 180-195 psi with 115,000 miles on it, that's amazing. Never heard of that high level of compression with that amount of mileage. When I did a borescope inspection, I did see carbon build-up on top of the pistons and also experienced dieseling run-on when I cut-off the the engine. I quickly bought a carbon cleaner and no more dieseling. I also found out the car had been sitting in the garage without being driven for maybe 2 years. That's not good either. Thank you for your post. VET (Navy)
If your lifters bleed off quickly that can make your cam seem smaller than it is and close the valve much sooner. I know you have said your fighting a detention issue....and you figure out a compression ratio........and I might had missed this from other post....but are you certain 100% on that ratio.....do you know exactly how far down the piston sits, exact cc of the heads, exact gasket. These changes could easily see the same piston have any where from 10:1 all the way to 14:1
Vet, try mixing some octane booster with the gas. I used this VP octane booster with 93 octane super can increase up to eight points depending on the ratio you use. Just by idling, an a little throttle big difference. 5 gallons to a half of this can.
I have been looking at several brands of octane booster. Yours seems to be the highest I've seen so far. I will give it a try. My shop has been recommending I try an octane booster. I just don't want to live on that forever. Thank you for this recommendation. VET
Somehow, my post to you got lost. I'am not sure about anything. I had a compression check done and the psi is an adverage of 180 across all 8 pistons. Last night, I used a CR calculator with the numbers I have, it came up with a CR of 11:53 to 1. That really blew me away. I was hoping for much less. I have been told the Kenne Bell pistions sit in the hole about .045. I took all the measurements on these pistions (+23 CC's for the piston tips/dome) and the recommended head gasket as compressed and it's .041. I know the rest of the dimensions. Heads have 69cc combustion chambers and the ,455 is bored .030 over. I really don't want to pull a head to verify if i'am in the right ballpark. Maybe in the future, when I need a valve job I will pull the heads off. This is all I know, I could be off here, I've done all the homework I can. I sent all my CR calculator to a forum friend, engine builder to double check my math. VET
I'am not a mechanic, my last wrenching on a muscle car goes all the way back to 1972 when I had a 1956 Chevy Belair with a built 327 Corvette 365 HP engine that my friend and I rebuilt and added some more power adders. Of course, I could get the good Sunoco leaded gas. I have a shop doing all the engine work. The first thing we tackled was the serious dedonation issue. As of this writing we believe we have it under control. But we have only driven the Buick for a couple of test drives. The ignition system has been changed from a points to a MSD. Currently, we are in also talking a high water temperature when the A/C is engaged. Today it tomarrow, we are expecting T/A's high performance water pump to arrive, we are also installing Evan's special coolant. If all works according to plan, my Buick should be good to go. What has been done so far regarding the high water temperature. New fan clutch, new high flow 160* thermostat, new radiator. You can see, these solutions for a high temperature cure has and is expensive. What PO's me, the classic car dealership and the owner lied to me about the condition of this Buick (engine). This was supposed to be a Turn-Key drive this car away and enjoy it. That didn't work out. There were other engine issues but I will not go any further. VET
When I run the number you gave i get about 9.4 But being .045 with a .041 headmaster gives alot of quench distance which can be just as bad too
Really, can still be bad @ 9.4, wow. This is what I got on the Summit calculator. Please check my math. Did you use -.023 for Effective Dome Volume? I used + because it's a negative dish. Bore: 4.342 Stroke: 3.900 Cylinder Head Volume: 69cc Effective Dome Volume: +.023 Use (-) for Dome and (+) for Dish. Deck Clearance: .045 Compressed Gasket Thickness: .041 Number of Cylinders: Compression Ratio : 11.53 : 1 Total Displacement (in.3) : 461.98 Total Displacement cc's : 7573.44
Found my mistake. Effective Dome Volume: +.023 should Read 23 cc's Another calculation now reads - 9.39.1 You are dead-on, with head gasket .041 & in the hole .045 = .086, that is way to far down. I wonder why someone would do this??? I believe on the original rebuild the head gasket used were .028 thick Stage 1. That would get it to .073 in the hole. Still not fan good, should be more around .040 for a good Squish band. Someone, we know, changed the pistons from 2362 Sealed Powers to this Kenne Bell model. The shop has found all kinds of engine screw-ups. from the previous owner. That's all I have to say. VET
I'm glad this thread was started as I'm in the beginning stages of a 455 build right now and wasn't going to worry to much about the compression height or how to far down the top of the piston is as long as I had about 9.25 to 9.5 compression ratio I figured I'd be OK. Well I guess I'm WRONG again...lol. I definitely don't want any detonation troubles but I wonder if I would still have issues with more compression, like 10:1 and a quench of .045 to .055 instead of .080 quench? I'm already having the block line honed and squared so it's not really a big deal to machine more off the decks. We're just going to have to be careful to do it right with the pistons I'm going to use.
Jim Weise and Larry70GS are excellent sources to ask regarding your question. I would post for both these gentlemen. I would have thought a 9.0 CR would have been excellent with the junk gas we have to use. But I too was wrong. Building an engine in todays unleaded gas mixed with ethanol is a real science. VET
Austin, I'm sending you an apology for possibly making your piston sale a lot more difficult. I received a post from Max Damage, letting me know it's not good for you that I'm talking about detonation issues I'm having using the same piston design that you're trying to sale. I totally loss sight that you're trying to sale your pistons. There is nothing wrong about the pistons you're selling. The previous owner of my Buick GS didn't have a clue what he was trying to do. Because he screwed-up the engine in my Buick (lot of other issues he screwed up) I might be forced to have the engine rebuilt. Please accept my apology, I'm really sorry and stupid for letting this go this far. VET (Navy)
No problem, I don't see it doing any harm. It keeps the thread open, it doesn't die to soon. Glad this conversation has started on an important topic.
Thank you so much. I really appreciate your kind words. I'm fairly new to this forum and the last thing I don't want to do, is to alienate everyone who has been very helpful to me over the past two years. We gear heads have a couple things in common, we love our Buicks and other Classic cars and we share/help other gear heads, when it's at all possible. VET (Navy)
I have no idea. Seeing that my Pistons are way down in the hole, that makes me believe i'am way down I compression, maybe 9.to1. That's only a guess on my part. Like Larry told me, I would have to pull the heads an do some measuring. The pistions are a good design, but the previous owner of my Buick had no idea how to setup a performance build. I'am currently talking with a Buick engine builder. I may have to have the engine rebuilt to get the level of performance i'am looking for. The previous owner had these pistions installed and that's all he did. I can't find any other engine mods he did. I'am so frustrated this guy did such a poor job. I expected the day I received this car off the trailer transport something was very wrong. (1) Vacuum leaks caused no power brakes. (2) Carburator leaking gas. Had wrapped carb base. (3) Pinging at all rpm's. (4) High water temp with A/C engaged. See where I am coming from. The exterior & interior looks like a show car and the engine is junk. I'am working to get the engine in top condition. VET
