How much boost do you have cruising on highway?

[smurfbus]

I fixed my MSD installation and now I have IIRC 1psi at 3000rpms = 60mph and at 80mph the turbo is really spinning as feathering the pedal the cruise is at 3psi and slight press on the pedal to keep it going gets 10PSI !!!

I don't know which hybrid it is but before the boost was much more taimed. Fixing the MSD installation feels like swapping in a much smaller AR turbine?

This is the turbo on the car
Which turbo is this 5327 101 5091 on the kompressor housing

I have 0.5 bar at 2000rpms on 4th gear now.

What do you guys boost on highway?

[Tippy]

Me, 0. That sounds weird. Granted, it makes boost nearly instantly if I floor it regardless of speed or RPM on the highway to a degree.

[torresmd]

I have slight boost around 1 psi when cruising at 80mph. I figured that was normal just the turbo spinning freely and was normal.

[RarlyL8]

Optimally you will have zero boost while cruising at any rpm and any speed on flat ground.
Many things will contribute to the turbo seeing load at speed. Gearing, timing, fuel, drag, etc. I know a car is tuned for optimal performance and fuel mileage when you can see vac at highway speeds and an instant tip-in to boost the moment the throttle is tapped.

[Ken911]

Do you have a mechanical boost gauge or are you using the electrical one in the dash?

[JFairman]

Depends on where you're taking the reading, before or after the throttle body/butterfly. There is a pressure drop across the throttle body especially when it's only open a crack during steady cruise.

Before it in the intercooler or stock recirculation blow off manifold like a stock car does for the origonal boost gauge you'll see a little pressure that just makes the needle move a hair from the spinning turbo making some pressure at steady cruise.

After the throttle body in the intake manifold like most VDO mechanical boost gauges that are plumbed into the brake booste vacuum line you will see a slight vacuum at steady cruise on level ground or zero on a boost gauge that doesn't also read vacuum.

[smurfbus]

It's taken from the kokeln IC near the blow off port. Tial is in the same line.


I have a mechanical VDO in the place of the clock.

Gearing is shorter and timing should be nicely advanced plus I run 15AFR on cruise on 93.5 oct. It's just strange that I only changed ignition system magnetic pic-up ppolarity and widened plug gap (ok, new distributor cap and rotor). Before IIRC I did not see any boost on cruise

[wwest]

Boost pressure when not needed, moderate throttle, is WRONG...!

Poor FE and early turbo demise.

Low exhaust flow/pressure along with wastegate opening should be enough to prevent that.

[Ken911]

OK i remember a while back one of the people here who has a shop mentioned something about the timing and flame propagation into the exhaust. Something about if it's retarded too much the flames from combustion blow into the exhaust system before combustion is complete. This would cause more heat and boost during cruise. My memory is pretty foggy on this and it was a couple years back. This might jog someones memory with all the details. Tried searching and couldn't find it.

[Miguel Antonett]

"0" while cruising.

[mooney265]

2/10 BAR at 75 MPH on mechanical 935 Gauge...

[smurfbus]

Mooney: Does it spool very eagerly with a little gas pedal? Mine is about 3/10 BAR but instant 0.8 BAR when I move the pedal a little at 80mph.

My timing is on the upside of the scale so it's not that it's burning in the headers IMO. I think the turbo hotside is too small for my combo of B&B headers, free flowing dual out, 964 cams (don't know the timing), tial48 w/0.8bar spring, some K2x hybrid, closer gearset, plugs at 0.04 (before they were 0.028).

[mooney265]

Originally Posted by smurfbus

Mooney: Does it spool very eagerly with a little gas pedal? Mine is about 3/10 BAR but instant 0.8 BAR when I move the pedal a little at 80mph.

My timing is on the upside of the scale so it's not that it's burning in the headers IMO. I think the turbo hotside is too small for my combo of B&B headers, free flowing dual out, 964 cams (don't know the timing), tial48 w/0.8bar spring, some K2x hybrid, closer gearset, plugs at 0.04 (before they were 0.028).

Yes on quick spool at 80 mph. And, I too have 964 cams; 1.0 BAR; B&B headers; Hooligan; K27HF; but now have stock 9:38 gearing [used to have 8:41]. My timing is stock..... and hitting 2,600 rpm at 75 mph...

[smurfbus]

I measured my backpressure before turbo and it's not bad at all. On 3rd gear WOT it's only about 1.3bar max and about the same as the boost (0.1-0.3bar) on cruise on highway?

I will try some other logs later but I thought it would be much higher? I haven't calibrated the MAP yet (used 1.6V for atmo and 5V for 2bar) so it might read wrong?

[nreed]

I'm definitely in vacuum...20-30 cm Hg. At 100MPH maybe .1 bar. You can see my setup below.

[kojo911]

same here vacuum at cruise, as soon as you tip in though....

[smurfbus]

I just checked the last log and the pressures are accurate. Same 1.2 bar on 3rd WOT at 5000rpms on my gauge and the innovate LM-2 log (1.2bar backpressure at about 0.8 bar IC boost pressure). So it seems it does not rob too much power but the hot side is just too small for continious higher speeds. It does spool fast so it's kind of nice on city limits even though it tends to light up my 315 tires on first if I'm not carefull (need to short shift) on WOT.

Or can anyone tell me why this is happening if it's not the size of the hot side.

[smurfbus]

Took the turd out and it says K27, 7200R on it so what gives?

[Tippy]

To add to this, my gauge reads anywhere from 0.4 - 0.6 on the VACUUM side.

[smurfbus]

Anyone with 7200 having these cruise boost issues?