Turbo Drive Pressure Question

[JMerola]

When discussing turbo's, it seems that "amateurs" like myself talk about boost pressure, and more experienced turbo/engine enthusiastasts speak of drive pressure and ratio's.



Can someone explain to me what these measurements of drive pressure and (?) ratio represents, and how they are more useful than boost when comparing and contrasting turbochargers?



Thank you in advance,



- Jason

 

[LesStallings]

When discussing turbo's, it seems that "amateurs" like myself talk about boost pressure, and more experienced turbo/engine enthusiastasts speak of drive pressure and ratio's.



Can someone explain to me what these measurements of drive pressure and (?) ratio represents, and how they are more useful than boost when comparing and contrasting turbochargers?



Thank you in advance,



- Jason

Jason, there has been a good bit of discussion on this topic on the Competition Forum here on TDR. I don't fully understand it but you are right in thinking it is important. Check out the discussions.

 

[Jeff_K]

Drive pressure is just that... . the pressure driving the exhaust wheel of the turbine section in the turbo. It is a measurement of the exhaust gas pressure.



Drive pressure ratios are merely comparing the boost pressure to the drive pressure. Ideally most people shoot for a drive pressure ratio of 1:1 when they are making maximum power/boost, but it does not always work out that way.

 

[RyanB]

Drive pressure is just that... . the pressure driving the exhaust wheel of the turbine section in the turbo. It is a measurement of the exhaust gas pressure.



Drive pressure ratios are merely comparing the boost pressure to the drive pressure. Ideally most people shoot for a drive pressure ratio of 1:1 when they are making maximum power/boost, but it does not always work out that way.

So are there any special guages for this then or will a normal boost guage work in the exaust manifold at 1500 degree's? Also, how about a boost guage between the turbo's in a twin setup?



RyanB

 

[lmills]

you would want to install a small section of coiled copper tubing coming out of the exhaust manifold. This will keep the heat from getting into the tubing going to the gauge. Also, yes the boost gauge will work for checking pressures.

 

[Jim Fulmer]

If you ever want to know if your drive pressure is worse than 1 to 1 just look into your intake, if there is black(smoke) soot then it's worse than 1 to 1. Think of it like this, the pressure is high and when the intake valve opens it blows hot air into the intake chamber for just a second... ..... heats up the air, takes away power.



Remember depending on the cam grind there is a time when both valves are open..... even for a split second.



Jim

 

[nickleinonen]

Remember depending on the cam grind there is a time when both valves are open..... even for a split second.

yep. our engines have a good bit of valve overlap. the overlap makes for good cylinder scavanging and helps cool the piston crown down.