imjoesnuffy
I just break stuff!
- Joined
- Sep 13, 2005
- Messages
- 1,541
May not get much interest in this thread and I did do a search but there are so many extremes in opinions.
I understand that some may not want to share the benefits of their experience, as it has come from years of experience in building engines and is their way of making a living.
Preface:
The reason for me thinking about the things I am asking about, is because I think my engine will probably need a rebuild within the next year. My current engine has been in the car for the past 6 years now, with almost 40K miles on it. To be honest, I flog the everliving pi$$ out of it every time I drive it, usually a lot more than once. On 93 Octane and Alky and at a minimum of 23 psi. I have even had the boost as high as 32 psi on 93 octane and alky. The car still runs like a raped ape, despite popping head gaskets at least three times over the years. The oil pressure is getting lower when hot, dropping as low as 18 psi at idle in 100 degree heat, where it used to be 35 hot. Still 50-60 while cruising. Slowly but surely getting a little more blowby out of the breathers. In other words the engine is starting to get tired. If it split in two tomorrow I could not be dissapointed as it has surely exceeded any and all expectations I have had.
Question #1 For a mostly street driven engine with 7-8 trips to the track a year, how much compression ratio is too much? I realize that many factors have to be considered when making this decision. The desired boost range, cam duration and timing all play a big role in this. I think 9:1 would be safe for an engine that could see as much as 30 psi with a good tune. Or am I being overly optimistic here? Is anything above 9:1 worth the risk or even considering?
Question #2 Timings affect on detonation in regards to CR. The higher the compression ratio, the less timing an engine can take, and the more likely it is to detonate. I know it is all in the tune, but the average guy like me doesn't have the time or money to play with advancing/retarding the cam over and over to find the sweet spot. Is this even something worth considering, and would anyone consider sharing what has worked for them?
Question #3 Cam duration and lift also are a key element in making power in a turbo charged application. These specs determine where the engine makes power at and therefore changes shift points. You just dont see the fastest Turbo Buicks shifting at stock rpm levels. I am thinking in my next build I am going to look for a cam in the 224 range. I already have a roller cam, so for parts its just a matter of choosing the right bumpstick. At what point in duration do you get to a point in diminshing returns for an engine that will not see above 6200 rpm?
Question #4 So basically I am thinking 234ish cubes, 9-9.5:1 CR, somewhere around 224 HR cam (shifting around 6000 rpm), timing: 25 in first, 24 in 2nd and 22 in 3rd gear and 30 psi (My current Alky tune with lower CR for now). Is this doable or do I need to read alot more?
I understand that some may not want to share the benefits of their experience, as it has come from years of experience in building engines and is their way of making a living.
Preface:
The reason for me thinking about the things I am asking about, is because I think my engine will probably need a rebuild within the next year. My current engine has been in the car for the past 6 years now, with almost 40K miles on it. To be honest, I flog the everliving pi$$ out of it every time I drive it, usually a lot more than once. On 93 Octane and Alky and at a minimum of 23 psi. I have even had the boost as high as 32 psi on 93 octane and alky. The car still runs like a raped ape, despite popping head gaskets at least three times over the years. The oil pressure is getting lower when hot, dropping as low as 18 psi at idle in 100 degree heat, where it used to be 35 hot. Still 50-60 while cruising. Slowly but surely getting a little more blowby out of the breathers. In other words the engine is starting to get tired. If it split in two tomorrow I could not be dissapointed as it has surely exceeded any and all expectations I have had.
Question #1 For a mostly street driven engine with 7-8 trips to the track a year, how much compression ratio is too much? I realize that many factors have to be considered when making this decision. The desired boost range, cam duration and timing all play a big role in this. I think 9:1 would be safe for an engine that could see as much as 30 psi with a good tune. Or am I being overly optimistic here? Is anything above 9:1 worth the risk or even considering?
Question #2 Timings affect on detonation in regards to CR. The higher the compression ratio, the less timing an engine can take, and the more likely it is to detonate. I know it is all in the tune, but the average guy like me doesn't have the time or money to play with advancing/retarding the cam over and over to find the sweet spot. Is this even something worth considering, and would anyone consider sharing what has worked for them?
Question #3 Cam duration and lift also are a key element in making power in a turbo charged application. These specs determine where the engine makes power at and therefore changes shift points. You just dont see the fastest Turbo Buicks shifting at stock rpm levels. I am thinking in my next build I am going to look for a cam in the 224 range. I already have a roller cam, so for parts its just a matter of choosing the right bumpstick. At what point in duration do you get to a point in diminshing returns for an engine that will not see above 6200 rpm?
Question #4 So basically I am thinking 234ish cubes, 9-9.5:1 CR, somewhere around 224 HR cam (shifting around 6000 rpm), timing: 25 in first, 24 in 2nd and 22 in 3rd gear and 30 psi (My current Alky tune with lower CR for now). Is this doable or do I need to read alot more?
