kiggly
Supporting Vendor
- 318
- 189
- Feb 17, 2003
-
Ann Arbor,
Michigan
Over last winter I worked out a high speed data acquisition on my drag car, here are some combustion pressure and intake port pressure plots. Each channel is taken at 60,000Hz, which is fast enough to have a data point at every crank angle degree at 10,000rpm. I had a pile of questions I was looking to answer by generating this data and also a big pile of new questions have popped up since taking data at a couple dyno sessions. It has been a ton of programming and learning Octave to make some reasonable routines, but I have what I feel is a pretty good home-brew combustion system now and I can process the data quick enough to make decisions between dyno pulls. Ten seconds of data is about 25megs.
One early question I wanted to answer was what pressure do the intake valves really see during high rpm operation. My scenario is a bit unique as I'm running my own sheetmetal intake manifold and a 2g cylinder head, but it still gives a pretty good data point. The data below was gathered up at Force Engineering, Tyler and I had a blast putting this through the paces and learning a ton of new details. The pull below made approximately 740whp on a mustang dyno through the auto trans. It was on a #7 precision converter, which stalls at about 8300rpm at this power level.
Notes:
The green trace is cylinder pressure, this is a 5000psi sensor
The blue trace is intake port pressure, it is a 150psi sensor located about 50mm up the port
The red vertical lines are exhaust valve opening and closing events
The blue vertical lines are intake valve opening and closing events
This is 18psi and 6000rpm, dynamic pressure bounces around about 10psi and peaks at near 25psi at the back of the valve (40psi absolute). This rpm phases nicely with the intake cam advanced all the way and the pulse activity lines up nicely, but it is a little due to low port velocity.
This is 7500rpm and 40psi, dynamic pressure bounces around about 30psi and peaks at near 55psi at the back of the valve (70psi absolute). This RPM is about the best VE, at just over 110%. I can probably gain some by running a little more cam advance.
This is 8100rpm and 46psi, dynamic pressure bounces around about 40psi and peaks at near 70psi at the back of the valve (85psi absolute). This is peak torque and about 108% VE.
This is 9700rpm and 45psi, dynamic pressure bounces around about 50psi and peaks at near 75psi at the back of the valve (90psi absolute). It appears the header is tuned wrong for this rpm and not clearing the cylinder out well at exhaust valve close. Peak power is already past at about 8900rpm.
The point I was initially trying to get a handle on was how hard the port pulses were trying to pop the valves open. This proves it is WAY above boost pressure. Make sure you have good seat pressure as you start cranking things up. I'm going after exhaust port pressure next trip to the dyno, which I expect to be a good bit worse.
I'll post more on the dyno session after I have some of it sorted out better. I had a pile of fun stuff I was experimenting with including methanol, a new programmable version of the ARC2 ignition, etc. I'm excited to get some new parts in-hand from Fuel Inejctor Clinic so I can crank the boost up on methanol with 8 injectors. I'm also excited to get a Haltech Elite 2500 on it for my next trip back to the rollers.
Thanks,
Kevin
One early question I wanted to answer was what pressure do the intake valves really see during high rpm operation. My scenario is a bit unique as I'm running my own sheetmetal intake manifold and a 2g cylinder head, but it still gives a pretty good data point. The data below was gathered up at Force Engineering, Tyler and I had a blast putting this through the paces and learning a ton of new details. The pull below made approximately 740whp on a mustang dyno through the auto trans. It was on a #7 precision converter, which stalls at about 8300rpm at this power level.
Notes:
The green trace is cylinder pressure, this is a 5000psi sensor
The blue trace is intake port pressure, it is a 150psi sensor located about 50mm up the port
The red vertical lines are exhaust valve opening and closing events
The blue vertical lines are intake valve opening and closing events
This is 18psi and 6000rpm, dynamic pressure bounces around about 10psi and peaks at near 25psi at the back of the valve (40psi absolute). This rpm phases nicely with the intake cam advanced all the way and the pulse activity lines up nicely, but it is a little due to low port velocity.
You must be logged in to view this image or video.
This is 7500rpm and 40psi, dynamic pressure bounces around about 30psi and peaks at near 55psi at the back of the valve (70psi absolute). This RPM is about the best VE, at just over 110%. I can probably gain some by running a little more cam advance.
You must be logged in to view this image or video.
This is 8100rpm and 46psi, dynamic pressure bounces around about 40psi and peaks at near 70psi at the back of the valve (85psi absolute). This is peak torque and about 108% VE.
You must be logged in to view this image or video.
This is 9700rpm and 45psi, dynamic pressure bounces around about 50psi and peaks at near 75psi at the back of the valve (90psi absolute). It appears the header is tuned wrong for this rpm and not clearing the cylinder out well at exhaust valve close. Peak power is already past at about 8900rpm.
You must be logged in to view this image or video.
The point I was initially trying to get a handle on was how hard the port pulses were trying to pop the valves open. This proves it is WAY above boost pressure. Make sure you have good seat pressure as you start cranking things up. I'm going after exhaust port pressure next trip to the dyno, which I expect to be a good bit worse.
I'll post more on the dyno session after I have some of it sorted out better. I had a pile of fun stuff I was experimenting with including methanol, a new programmable version of the ARC2 ignition, etc. I'm excited to get some new parts in-hand from Fuel Inejctor Clinic so I can crank the boost up on methanol with 8 injectors. I'm also excited to get a Haltech Elite 2500 on it for my next trip back to the rollers.
Thanks,
Kevin
Attachments
Last edited: