Compression Ratio is not what you think...Step inside tech guys
12-20-2012, 10:17 PM
#27
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I can absolutely believe the numbers are low. Look at this from a car manufacturer's standpoint rather than our tuner point of view:
1. They want margins of safety everywhere because some bonehead is going to run 86 octane fuel in his AMG because of God knows why.
2. They want margins of safety for warranty purposes in general, and want the car to be able to go 200k miles in stock form. Reliability.
3. They like to 'parts bin' as much as they can because it keeps manufacturing costs low because they don't have to reset tooling for different applications.
Also don't forget who built these cars. As Clarkson said when driving the R8 'For instance this stalk is supposed to activate the GPS but doesn't do anything. Oh, I shouldn't have said that on national television, the German who is responsible will most likely be shot in the morning for his mistake'.
I only make this statement as Germans are some of the most highly regarded, exacting engineers on the planet and I would be more apt to trust what they say about something they built than a random engine builder(no offense he may be the Stephen Hawking of engine builders).
Just food for thought. But as WHTEVO eluded to, as a tuner on DSMs and quite a few other cars I would rather see lower static CR than higher. It gives so much more room for boost, timing and leaner AFRs with a wide safety margin.
Regards
1. They want margins of safety everywhere because some bonehead is going to run 86 octane fuel in his AMG because of God knows why.
2. They want margins of safety for warranty purposes in general, and want the car to be able to go 200k miles in stock form. Reliability.
3. They like to 'parts bin' as much as they can because it keeps manufacturing costs low because they don't have to reset tooling for different applications.
Also don't forget who built these cars. As Clarkson said when driving the R8 'For instance this stalk is supposed to activate the GPS but doesn't do anything. Oh, I shouldn't have said that on national television, the German who is responsible will most likely be shot in the morning for his mistake'.
I only make this statement as Germans are some of the most highly regarded, exacting engineers on the planet and I would be more apt to trust what they say about something they built than a random engine builder(no offense he may be the Stephen Hawking of engine builders).
Just food for thought. But as WHTEVO eluded to, as a tuner on DSMs and quite a few other cars I would rather see lower static CR than higher. It gives so much more room for boost, timing and leaner AFRs with a wide safety margin.
Regards
12-20-2012, 10:25 PM
#28
I agree on all points you made, I was simply saying there might be a variable here that we aren't looking at. They simply could using a different set of numbers to come up with their CR, who knows. Not saying anyone is at fault, just food for thought. I agree with you about the 9.5:1 CR for your specs though, should be very good. The big difference here is forged pistons. They can take alot more abuse than cast units and are much more forgiving in regards to detonation. The ring lands alone are exponentially stronger which is the ***** in our factory piston's armor. Sounds like a solid build man. I have watched your progression over the last few years and it is amazing, keep it coming!
Regards
Regards
12-21-2012, 08:32 AM
#30
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We talked about that but the area is so miniscule it wouldn't take away much if anything from the totals and would lower the totals even more. Pat from PTE just gave me his contact at Mahle so i'm going to see what the dish volume for the SLR piston is compared to the E55 style piston.
12-23-2012, 12:19 PM
#31
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amgrocket, thanks for sharing.
it'd be interesting to know how much compression would be increased by using flat face valves. On my 4cyl 2zz motor, flat face valves are worth an extra 0.3:1 over the oem domed valves.
it'd be interesting to know how much compression would be increased by using flat face valves. On my 4cyl 2zz motor, flat face valves are worth an extra 0.3:1 over the oem domed valves.
12-23-2012, 03:43 PM
#34
e55amgrocket, you can increase the compression ratio of your engine by using the n/a 55 heads with all other sc components(cams valves...).
The N/A heads have a smaller volume, look at the pics attached above the inlet valves. you have to measure the n/a heads.
The N/A heads have a smaller volume, look at the pics attached above the inlet valves. you have to measure the n/a heads.
12-23-2012, 04:01 PM
#35
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I already run N/A heads and we checked both N/A heads and S/C heads and they were both at 60cc's. That's the first thing we thought was it was due to the heads but they CC'd the same. Also the N/A motors have a smaller dish in the piston to raise the CR.
12-23-2012, 04:36 PM
#37
E55amgrocket, another thought, can you do your math using the 55 N/A pistons 2003 with 55K rods, the pistons are lower by 0.7mm and have a compression ratio advertised at 11:1, so with your new find (8.0:1 55K) maybe you will be at 9.5:1 (if 11 advertise must be at 10 plus lower by 0.7 i think you will be at 9.5:1). can you do the calculations?
