Dynamic Compression Ratio
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Registered User
Joined: Jul 2003
Posts: 38
From: Bountiful, UT
Dynamic Compression Ratio
I am planning on rebuilding my motor once I move to Salt Lake from the Charlotte, NC area.
I have a 94 Formula with 140,000 miles and have noticed a white film on the inside of the oil cap. I suspect that this indicates water in the oil and that the motor will require a rebuild. So I am planning on doing this once I get out there and begin my new job.
I plan on rebuilding to a 355 and installing a zz3 cam along with a set of Lloyd's heads (only a partial porting job - he suggested a intake flow of ~ 245). My question is ... What DCR should I set the engine up for?
According to one online Visual Basic DCR calculator, a DCR for this motor with an impala head gasket (.029) and 58 cc heads should be around 8.65. However the program does not request parameters for VE?
Please no weenie cam comments, I need a reliable daily driver and don't want any cam surge. Also, the car needs to be driveable with a stock program (please, nobody with a CC306 saying their car is daily drivable) until I purchase programming from madwolf later on.
I have a 94 Formula with 140,000 miles and have noticed a white film on the inside of the oil cap. I suspect that this indicates water in the oil and that the motor will require a rebuild. So I am planning on doing this once I get out there and begin my new job.
I plan on rebuilding to a 355 and installing a zz3 cam along with a set of Lloyd's heads (only a partial porting job - he suggested a intake flow of ~ 245). My question is ... What DCR should I set the engine up for?
According to one online Visual Basic DCR calculator, a DCR for this motor with an impala head gasket (.029) and 58 cc heads should be around 8.65. However the program does not request parameters for VE?
Please no weenie cam comments, I need a reliable daily driver and don't want any cam surge. Also, the car needs to be driveable with a stock program (please, nobody with a CC306 saying their car is daily drivable) until I purchase programming from madwolf later on.
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Joined: Aug 2001
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From: looking for a flow bench so Brook and I can race
Originally posted by utahbound
Anyone else concur with the condensation comment?
If so, great, more money for mods!
Anyone else concur with the condensation comment?
If so, great, more money for mods!
as to answer your question, do a search in advanced tech
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Joined: Oct 2000
Posts: 786
From: Charlotte, NC
Charlotte, eh? It's okay out here I suppose...
Regarding your stuff, this isnt something I'd be terribly concerned about with a really mild setup like this. Around 11:1 is plenty static/dynamic & isnt going to really hurt you in the future if you step up... of course you can always alter CR relatively easily then as well
On a side note, I think they'll end up smaller than 58cc if they've got more than a couple thou taken off of them. Generally ours are in the 54-54.5cc range with 2.00/1.56's & .010" milled off of them.
Regarding your stuff, this isnt something I'd be terribly concerned about with a really mild setup like this. Around 11:1 is plenty static/dynamic & isnt going to really hurt you in the future if you step up... of course you can always alter CR relatively easily then as well
On a side note, I think they'll end up smaller than 58cc if they've got more than a couple thou taken off of them. Generally ours are in the 54-54.5cc range with 2.00/1.56's & .010" milled off of them.
Thread Starter
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Joined: Jul 2003
Posts: 38
From: Bountiful, UT
Hey Phil,
Yeah, I'm moving to Mormonland. In talking to Lloyd, he said he generally found that LT1 heads had 57 or 58 cc chambers before they are touched. Anyway, I am going to pressure test the cooling system when I get out there and determine if there is a water leak once and for all.
I understand that I could run more compression up at around 5000 ft., but I don't want to tear the damn car down if I need to move again (This would be a distinct possibility, depending on the Sierra club lawsuits pending against the project I am going to be working on). But I'll pick up a cheap shortblock at speed automotive and build a cheap 383 bottom end while I drive the car. I know you're not the biggest fan of "truck motors", but since I will go to the track only once in a blue moon, I think I will appreciate the torque on the street more than revving it past 4500 to get any real power.
I saw Trey's post suggesting that I read over the advanced tech forums for info on DCR. I did that already and it seemed to me that different posts said different things and the mechanical engineer we have at the office sold his internal combustion engine textbook while he was in school. The one online calculator that everyone referred to (for a motorcycle?) seemed to be stuck on a chamber volume of ~74 cc's!? That would seem to be useless for figuring an LT1's DCR.
Sorry for being long ... and too bad I never got around to meeting you while I lived here.
Yeah, I'm moving to Mormonland. In talking to Lloyd, he said he generally found that LT1 heads had 57 or 58 cc chambers before they are touched. Anyway, I am going to pressure test the cooling system when I get out there and determine if there is a water leak once and for all.
I understand that I could run more compression up at around 5000 ft., but I don't want to tear the damn car down if I need to move again (This would be a distinct possibility, depending on the Sierra club lawsuits pending against the project I am going to be working on). But I'll pick up a cheap shortblock at speed automotive and build a cheap 383 bottom end while I drive the car. I know you're not the biggest fan of "truck motors", but since I will go to the track only once in a blue moon, I think I will appreciate the torque on the street more than revving it past 4500 to get any real power.
I saw Trey's post suggesting that I read over the advanced tech forums for info on DCR. I did that already and it seemed to me that different posts said different things and the mechanical engineer we have at the office sold his internal combustion engine textbook while he was in school. The one online calculator that everyone referred to (for a motorcycle?) seemed to be stuck on a chamber volume of ~74 cc's!? That would seem to be useless for figuring an LT1's DCR.
Sorry for being long ... and too bad I never got around to meeting you while I lived here.
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From: Baton Rouge, LA, USA
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That link that I posted in the old thread is very good info. It is quite correct and note that it states:
"Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine."
So, DCR has nothing to do with VE.
Rich Krause
"Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine."
So, DCR has nothing to do with VE.
Rich Krause
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