Effect of a 38mm restrictor on an LS7
Discussion
Rear diff, fairly sure the spline has stripped on a drive flange. (BMW 210mm LSD 3.91)
I was quite happy with progress on the first day considering how wet it was. Nice to be just above Peterhansel in the timesheets overnight, although he was in a different class.
I've been monitoring my phone but seemed to have missed the call from Peugeot for next year's Dakar.
I was quite happy with progress on the first day considering how wet it was. Nice to be just above Peterhansel in the timesheets overnight, although he was in a different class.
I've been monitoring my phone but seemed to have missed the call from Peugeot for next year's Dakar.
[quote=Max_Torque]Right:
1) do the regulation specify the position of the restrictor, and crucially, the geometery of the pipework upstream and downstream? if not, hurray, you can quite get a lot of air through a 38mm hole and with proper geo and get a decent pressure recovery downstream. Normally, the position is mandated to prevent people installing inlet systems that can help negate the restrictors pressure loss! (i.e in WRC, it has to be <50mm from the turbo compressor eye etc)
2) Make sure you feed the restrictor with the highest pressure air availible to you! A 38mm smooth edges restrictor will choke (the point at which the flow through it becomes just critical (supersonic) at 0.270kg/s (assuming 1bar, 15deg C upstream) and at this point the air pressure in the choke will be 52.8kPa (abs). At the critical point the downstream air (and shockwave) can no long propgate up stream (as the flow is now supersonic) so no matter how much you reduce the downstream presure you can only flow 0.270kg/s! But, increase the upstream airpressure, and the density increase will increase the mass flow. So gain say 5kPa (for 105kPa (abs) from dynamic ram in your airbox at high vehicle speed and you get 0.284kg/s ;-)
Hi, newbie here and sorry to revive such an old thread.
To Max_Torque, you very clearly know your stuff, and I was wondering if I could impose as I am trying to solve what I think is an issue with my 4g63T Evo rally car. We run similar restrictions to WRC, but with a 36mm restrictor here in New Zealand. Below is a copy of my torque curve. I am thinking there is a way to make this more of a rolling hill rather than mt Everest. My head is getting sore trying to read forums and do calculations etc and take in a wealth of info, but I am trying.
I thought I was on a winner trying to calculate choke airflow with this calculator https://www.tlv.com/global/TI/calculator/air-flow-... until I realised I am a bit lost with what primary and secondary airflow pressures are. My turbo pressure is 21psi (145kpa). Am I right to assume that that creates 21psi of pressure upstream of the restrictor by vacuum? [somehow I dont think so]. But by using 21psi as my primary, and 10psi as my secondary [have read somewhere at choke flow it could even be 7?) I come to about 470 cfm. My engine is a 4cyl 2.3 litre and I think that this is about right for a 36mm restrictor but I do not actually know the math.
I have had another guru briefly say that because my tune does not change boost for revs that I will be getting to much exhaust back pressure and this will be causing problems. He did not elaborate, but I think part of this may be that the scavenging effect would drop off due to lack of airflow, and my engine does seem to run a lot of overlap. So I am trying to solve the equation of what point I am choking in actual airflow. Then maybe I can make it more driveable by getting a better torque/power curve. Or maybe its the best it can be??
Any help greatly appreciated.
Thanks
Mark
1) do the regulation specify the position of the restrictor, and crucially, the geometery of the pipework upstream and downstream? if not, hurray, you can quite get a lot of air through a 38mm hole and with proper geo and get a decent pressure recovery downstream. Normally, the position is mandated to prevent people installing inlet systems that can help negate the restrictors pressure loss! (i.e in WRC, it has to be <50mm from the turbo compressor eye etc)
2) Make sure you feed the restrictor with the highest pressure air availible to you! A 38mm smooth edges restrictor will choke (the point at which the flow through it becomes just critical (supersonic) at 0.270kg/s (assuming 1bar, 15deg C upstream) and at this point the air pressure in the choke will be 52.8kPa (abs). At the critical point the downstream air (and shockwave) can no long propgate up stream (as the flow is now supersonic) so no matter how much you reduce the downstream presure you can only flow 0.270kg/s! But, increase the upstream airpressure, and the density increase will increase the mass flow. So gain say 5kPa (for 105kPa (abs) from dynamic ram in your airbox at high vehicle speed and you get 0.284kg/s ;-)
Hi, newbie here and sorry to revive such an old thread.
To Max_Torque, you very clearly know your stuff, and I was wondering if I could impose as I am trying to solve what I think is an issue with my 4g63T Evo rally car. We run similar restrictions to WRC, but with a 36mm restrictor here in New Zealand. Below is a copy of my torque curve. I am thinking there is a way to make this more of a rolling hill rather than mt Everest. My head is getting sore trying to read forums and do calculations etc and take in a wealth of info, but I am trying.
I thought I was on a winner trying to calculate choke airflow with this calculator https://www.tlv.com/global/TI/calculator/air-flow-... until I realised I am a bit lost with what primary and secondary airflow pressures are. My turbo pressure is 21psi (145kpa). Am I right to assume that that creates 21psi of pressure upstream of the restrictor by vacuum? [somehow I dont think so]. But by using 21psi as my primary, and 10psi as my secondary [have read somewhere at choke flow it could even be 7?) I come to about 470 cfm. My engine is a 4cyl 2.3 litre and I think that this is about right for a 36mm restrictor but I do not actually know the math.
I have had another guru briefly say that because my tune does not change boost for revs that I will be getting to much exhaust back pressure and this will be causing problems. He did not elaborate, but I think part of this may be that the scavenging effect would drop off due to lack of airflow, and my engine does seem to run a lot of overlap. So I am trying to solve the equation of what point I am choking in actual airflow. Then maybe I can make it more driveable by getting a better torque/power curve. Or maybe its the best it can be??
Any help greatly appreciated.
Thanks
Mark
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff