Gas engine turbos and leak question

[NPloysa]

Hey everyone. As some of you have read, I bought a 1993 Audi S4 recently. It is an inline 5 cylinder, turbocharged, with aftermarket boost gauge on the pillar.



First question, this is my first vehicle with an air-line gauge, my 99 Dodge had the FMS with digital readout. This one reads great and true, however I think it may have a leak. When I start to boost, it "swishes", maybe it has a leak. I don't think it's supposed to do that!? It doesn't have a relief valve does it? I will take it apart and inspect the line.



Second question, the real question, is... What is the difference in gasoline and diesel engines that makes a gas engine pull a vacuum at idle or low RPMs and low throttle? At somewhat level throttle, boost and vacuum even out.



Thanks! By the way, this little car boosts to 20 psi pretty quick just with the mild chip it has.



Nick

 

[mgoncalves]

Second question, the real question, is... What is the difference in gasoline and diesel engines that makes a gas engine pull a vacuum at idle or low RPMs and low throttle? At somewhat level throttle, boost and vacuum even out.

The throttle plate is what let's the engine pull vacuum. If you put one on a diesel (6. 4 psd rumored to have one) the intake will also go into a vacuum.



Matt

 

[MCummings]

The throttle plate is what let's the engine pull vacuum. If you put one on a diesel (6. 4 psd rumored to have one) the intake will also go into a vacuum.



Matt

The 6. 7L Cummins has one, as well as very early 6. 0's did too.



6. 7L has one to control EGT's so it can keep the particualte filter clean.



Merrick

 

[me4osu]

The only bad thing about the throttle plate is that it makes it easier for the turbo to surge when you back off the throttle real quick. The big turbocharged natural gas engines we have are bad about surge when the load backs off suddenly and the governor shuts the throttle.

 

[NPloysa]

Thanks boys, appreciate it!